Input: Lin reported a graded microstructure along the build direction and identified the martensite structure, Widmanststructure and basket-wave structure from the bottom to the top region of the fabricated component, as shown in 3.

graded microstructure

build direction

martensite

as

structure

fabricated

component


Input: An epitaxial growth of grains with discrete direction is also observed along the build direction owing to thermal gradient, commonly seen in additively manufactured titanium alloy components.

epitaxial

grains

build direction

thermal gradient

additively manufactured

alloy


Input: 3 summarizes the microstructure and mechanical property data of Ti6Al4V samples fabricated using various WAAM technologies.

microstructure

mechanical property

data

samples fabricated

technologies

WAAM


Input: The as-forged and as-cast minimum specifications from ASTM standards are also listed for comparison.

specifications

standards


Input: As shown in 4, the tensile property of as-fabricated Ti6Al4V samples is close to that of wrought Ti6Al4V and exceeds that of cast Ti6Al4V as specified by ASTM standards.

As

as

tensile property

samples

wrought

standards

cast


Input: In addition, WAAM fabricated Ti6Al4V samples show anisotropic properties with lower strength and higher elongation values in the build direction compared to deposition direction, which is mainly attributed to the grain size of lamellae and the orientation of the elongated prior grains.

WAAM

fabricated

samples

orientation

grains

anisotropic

strength

elongation values

grain size

build direction

deposition direction

lamellae


Input: 3.2 Aluminum alloys and steel Although fabrication trials for many different series of aluminum alloys, including Al-Cu, Al-Si and Al-Mg have been successfully carried out, the commercial value of WAAM is mainly justifiable for large and complex thin-walled structures, since cost of manufacturing small and simple aluminum alloy components using conventional machining processes is low.

Aluminum alloys

steel

aluminum alloys

Al-Cu

Al-Si

Al-Mg

aluminum alloy

fabrication

WAAM

simple

conventional machining

complex thin-walled structures

cost of manufacturing


Input: Using WAAM to fabricate steel is unpopular for the same reason although it is the most commonly used engineering material.

WAAM

fabricate

engineering material


Input: Another reason for the poor commercial application of WAAM in aluminum is that some series of aluminum alloys, such as Al 7xxx and 6xxx, are challenging to weld due to turbulent melt pool and weld defects, which frequently occur during the deposition process.

WAAM

deposition process

aluminum

aluminum alloys

as

Al

melt pool

weld

weld

defects


Input: In general, as-deposited additively manufactured aluminum alloy parts have inferior mechanical properties compared to those machined from billet material.

additively manufactured

machined

alloy

billet

mechanical properties


Input: In order to achieve higher tensile strength, most of the as-deposited aluminum parts undergo post-process heat treatment to refine the microstructure.

tensile strength

aluminum

post-process heat

microstructure


Input: 4 lists the yield strength, ultimate tensile strength, and elongation of WAAM-fabricated 2219aluminium alloy samples.

yield strength

ultimate tensile strength

elongation

alloy


Input: Due to the uniform distribution of large diamond particles within the microstructure, the sample exhibits lower UTS and YS than that of the wrought part specified by ASTM standard.

distribution

microstructure

sample

wrought

standard

diamond

UTS


Input: However, after heat treatment, significant improvement beyond ASTM standard can be observed in both strength and elongation as a consequence of the grain refinement.

heat treatment

standard

be

as

strength

elongation

grain refinement


Input: 3.3 Nickel-based superalloys Nickel-based superalloys are the second most popular material studied by the additive manufacturing research community after titanium alloys, mainly due to their high strengths at elevated temperatures and high fabrication cost using traditional methods.

Nickel-based superalloys

superalloys

material

titanium alloys

additive manufacturing

fabrication

strengths

temperatures


Input: Nickel-based superalloys are widely applied in aerospace, aeronautical, petrochemical, chemical and marine industries due to their outstanding strength and oxidation resistance at temperatures above 550 To date, various Nickel-based superalloys, including Inconel 718 and Inconel 625 alloy have been studied after WAAM processing.

Nickel-based superalloys

Nickel-based superalloys

Inconel 718

Inconel 625 alloy

aerospace

aeronautical

marine industries

strength

oxidation resistance

temperatures

WAAM


Input: The microstructure of WAAM fabricated Inconel 718 parts generally consists of large columnar grains with interdendritic boundaries delineated by small Laves phase precipitates and MC carbides.

microstructure

fabricated

Laves phase

WAAM

columnar grains

boundaries

MC

carbides


Input: Xu reported that columnar dendrite structures decorated with a large amount of Laves phase, MC carbides and Ni3Nb are also present in WAAM-fabricated Inconel 625 parts, as shown in 5.

columnar dendrite structures

Laves phase

MC

carbides

Inconel 625

as


Input: It is worth noting that the microstructure can be refined to smaller dendritic arm spacing, less niobium segregation and discontinuous Laves phase in the interdendritic regions using post-process heat treatments, which are beneficial to the mechanical properties.

microstructure

niobium segregation

Laves phase

post-process heat

mechanical properties

be

dendritic arm spacing


Input: 5 lists the mechanical properties of several Nickel-based superalloys fabricated using the WAAM process.

mechanical properties

fabricated

process

Nickel-based superalloys

WAAM


Input: For GMAW-based WAAM-fabricated Inconel 718 alloy, the yield and ultimate tensile strength is 473 6 MPa and 828 8 MPa respectively.

Inconel 718 alloy

ultimate tensile strength

MPa

MPa


Input: These values lie between the minimum values specified by ASTM for wrought and cast materials, whereas the elongation is much lower than the standards for both wrought and cast conditions.

wrought

standards

wrought

cast

cast

elongation


Input: As for WAAM-fabricated Inconel 625 alloy, the YS, UTS and elongation all meet the requirement set by ASTM for cast materials, and are slightly lower than those for wrought material.

As

Inconel 625 alloy

wrought material

UTS

elongation

set

cast


Input: 3.4 Other metals Other metals have also been investigated for potential fabrication using WAAM, such as magnesium alloy AZ31 for automotive applications, Fe/Al intermetallic compounds and Al/Ti compounds, as well as bimetallic steel/nickel and steel/bronze parts for the aeronautic industry.

metals

metals

as

alloy

intermetallic compounds

Al/Ti

as

as

fabrication

WAAM

automotive

aeronautic industry


Input: The detailed mechanical properties of these materials fabricated using WAAM are listed in 6.

mechanical properties

materials fabricated

WAAM


Input: Most of this research has focused on determining the microstructural and mechanical properties of samples taken from simple straight-walled structures, rather than developing a process to fabricate functional parts.

research

microstructural

mechanical properties

samples

process

simple

fabricate


Input: Manufacturing intermetallic parts with accurate pre-designed composition still poses major challenges for the WAAM process.

Manufacturing

WAAM

intermetallic

accurate

composition

process


Input: 4 Common defects in WAAM-fabricated component Although the mechanical properties of components fabricated by WAAM are in many cases comparable to those of their conventionally processed counterparts, there are however some AM processing defects that must be addressed for critical applications.

defects

mechanical properties

processed

defects

component

components

WAAM

AM

be


Input: Porosity, high residual stress levels, and cracking, must be avoided, particularly for parts exposed to extreme environments where these defects lead to failure modes such as high temperature fatigue.

Porosity

residual stress

failure modes

temperature fatigue

cracking

defects

be

as


Input: Defects in WAAM can occur for various reasons, such as poor programming strategy, unstable weld pool dynamics due to poor parameter setup, thermal deformation associated with heat accumulation, environmental influence and other machine malfunctions.

Defects

weld pool

parameter

WAAM

as

thermal deformation

heat accumulation

machine


Input: As shown in 6, certain materials tend to be vulnerable to specific defects.

As

be

materials

defects


Input: For example, severe oxidization for titanium alloys, porosity for aluminum alloys, poor surface roughness in steel as well as severe deformation and cracks in bimetal components have been found to typically occur.

titanium alloys

aluminum alloys

steel

as

as

porosity

surface roughness

deformation

bimetal components


Input: 7 lists the major defects that are commonly present in components fabricated using current WAAM techniques.

defects

components

WAAM


Input: The details of these common defects and their relationship to the materials will be discussed this section.

defects

materials

be


Input: 4.1 Deformation and residual stress Like other additive manufacturing process, distortion and residual stress are inherent to the WAAM process and it is impossible to completely avoid its generation.

Deformation

distortion

process

residual stress

residual stress

additive manufacturing process

WAAM


Input: The residual stress can lead to distortion of the part, loss of geometric tolerance, delamination of layers during deposition, as well as deterioration of fatigue performance and fracture resistance of the additively manufactured components.

residual stress

fatigue

fracture resistance

lead

as

as

distortion

deposition

geometric tolerance

delamination of layers

additively manufactured


Input: Therefore, control and minimization of deformation and residual stress is a key area if research.

deformation

research

residual stress

area


Input: Various types of deformation appear in WAAM fabricated parts, including longitudinal and transvers shrinkage, bending distortion, angular distortion and rotational distortion.

deformation

fabricated

shrinkage

distortion

distortion

WAAM

bending


Input: The distortions are caused by thermal expansion and shrinkage of the part during repeated melting and cooling processes, which is particularly an issue for large thin walled structures.

thermal expansion

shrinkage

thin walled structures

melting

cooling


Input: Residual stress is the stress that remains in the material when all external loading forces are removed.

Residual stress

stress

material

forces


Input: If the residual stress is sufficiently high, it can be a critical influential factor in the mechanical properties and fatigue performance of the fabricated component.

residual stress

fatigue

be

mechanical properties

fabricated

component


Input: If the residual stress exceeds the local UTS of the material, cracking will take place, while if it is higher than the local YS but lower than UTS, warping or plastic deformation will occur.

residual stress

UTS

UTS

plastic deformation

material

cracking

warping


Input: Ding found that the residual stress uniformly distributes across the WAAM deposited wall, and the residual stress in the preceding layer has little effect on the future layers.

residual stress

residual stress

WAAM

layer


Input: After release of clamping, however, the internal stress is redistributed with a much lower value at the top of integral part than at the interface to the substrate, resulting in bending distortion of the component.

internal stress

interface

substrate

bending

component


Input: Path planning also involves the distortion and residual stress evolution in WAAM process.

Path planning

distortion

evolution

process

residual stress

WAAM


Input: If appropriate deposition path designs, it will help in the significant improvement in these defects, especially in large metal fabrication.

deposition path

defects

metal

fabrication


Input: A detailed overview of the residual stress origin would exceed the scope of this article.

residual stress


Input: Among all WAAM engineering materials, bimetal components exhibit high levels of residual stress and deformation due to the material thermal expansion difference.

WAAM

engineering materials

material

bimetal components

residual stress

deformation


Input: Hence, accurate interpass temperature control is needed when bimetal materials are used.

accurate

temperature

bimetal materials


Input: WAAM-fabricated Inconel alloy has comparatively lower residual stresses levels, but it is more susceptible to process defects such as delamination, buckling and warping, since its residual stress is usually higher than the yield stress.

Inconel alloy

as

residual stresses

buckling

residual stress

yield stress

process defects

warping


Input: Other comparatively softer materials, such as aluminum alloys, easily respond to deformation defects due to their high thermal expansion coefficients.

materials

as

aluminum alloys

deformation defects

thermal expansion coefficients


Input: A better understanding pf the effect of material characteristics in WAAM processing is needed for controlling residual stress and deformation during deposition.

material

WAAM

residual stress

deformation

deposition


Input: Deformation and residual stress are associated with many process parameters, such as welding current, welding voltage, feeding speed, ambient temperature, shielding gas flow rate, etc.

Deformation

process parameters

residual stress

as

welding

temperature

gas flow rate


Input: Fortunately, several post-process treatments that have been proven to effectively mitigate residual stress and deformation, and these will be discussed 5.

post-process

deformation

residual stress

be


Input: 4.2 Porosity Porosity is another common defect in WAAM processing that needs to be minimized due to adverse effects on mechanical properties.

Porosity

defect

mechanical properties

WAAM

be


Input: Firstly, porosity will lead to a component with low mechanical strength by damage from micro-cracks, and secondly, it usually brings low fatigue property to deposition via spatially with different size and shape distribution.

porosity

mechanical strength

damage

fatigue

lead

component

micro-cracks

deposition

distribution


Input: In general, this type of defects are mainly classified as either raw material-induced or process-induced.

defects

as


Input: The WAAM raw material, including as-received wire and substrate, often has a degree of surface contamination, such as moisture, grease and other hydrocarbon compounds that may be difficult to completely remove.

WAAM

raw material

substrate

as

be

surface contamination


Input: These contaminants can be easily absorbed into the molten pool and subsequently generate porosity after solidification.

be

molten pool

solidification

porosity


Input: Among common engineering materials, aluminum alloy is the most susceptible to this defect as the solubility of hydrogen in solid and liquid is significantly different.

engineering materials

aluminum alloy

as

defect

solubility


Input: Even small amounts of dissolved hydrogen in the liquid state may exceed the limit of solubility after solidification, resulting in porosity.

liquid state

limit

solidification

solubility

porosity


Input: Therefore, the cleanliness of raw materials is critical, especially for aluminum alloys.

raw materials

aluminum alloys


Input: Process-induced porosity is usually non-spherical, and mainly caused by poor path planning or an unstable deposition process.

porosity

non-spherical

path planning

deposition process


Input: When the deposition path is complex or the manufacturing process is changeable, insufficient fusion or spatter ejection is easily produced, creating gaps or voids in these influenced regions.

deposition path

manufacturing process

insufficient fusion

spatter

ejection

voids


Input: To control porosity, the following methods can be adopted: an AC GMAW-based process or CMT-PADV based process is preferred, especially for aluminum; the highest quality shielding gas, tight gas seals, non-organic piping and short pipe lengths are highly recommended; the wire and substrate surfaces are as clean as possible before fabrication; high quality feedstock should be used; the deposited bead shape needs to be optimized; the thermal profile during processing should be monitored and controlled; post-deposition treatment, such as interpass rolling can be applied.

porosity

be

aluminum

substrate

as

as

feedstock

be

be

be

as

be

process

process

quality

gas

gas

quality

thermal profile

fabrication

rolling

deposited bead shape


Input: 4.3 Crack and delamination Similar to residual stress and deformation, cracking and delamination not only involves the thermal signature of the manufacturing process, but also relates to the material characteristics of the deposit.

delamination

deformation

cracking

delamination

residual stress

manufacturing process

material


Input: Ordinarily, the crack is categorised as either a solidification crack or grain boundary crack within the WAAM component.

as

solidification crack

grain boundary crack

WAAM

component


Input: The former type of crack depends mainly on the solidification nature of the material and is usually caused by the obstruction of solidified grain flow or high strain in the melt pool.

solidification

grain

material

melt pool

strain


Input: Grain boundary cracking often generates along the grain boundaries due to the differences between boundary morphology and potential precipitate formation or dissolution.

Grain boundary

cracking

grain boundaries

boundary morphology

precipitate


Input: Generally, this deficiency is visible and can not be repaired by post-process treatment.

be

post-process


Input: In order to prevent this defect, pre-process treatment such as preheating of the substrate needs to be considered.

defect

as

substrate

be


Input: Bimetal material combinations, such as Al/Cu, Al/Ti and Al/Fe, are quite susceptible to cracking and delamination when fabricated with the WAAM process.

Bimetal material combinations

as

Al/Cu

Al/Ti

Al/Fe

cracking

delamination

fabricated

process

WAAM


Input: The dissimilar metals have large differences in their mutual solubility and chemical reactivity so that the intermetallic phase-equilibrium is freely broken, thus inducing crack growth along grain boundaries.

metals

intermetallic

mutual solubility

crack growth

grain boundaries


Input: Also, Inconel alloy readily generates solidification cracking issues due to the existence of liquid film at terminal solidification.

Inconel alloy

solidification cracking

solidification


Input: Both of these material types should receive particular attention to avoid cracking and delamination.

material

cracking

delamination


Input: To control crack defects, corresponding measures can be taken as follows: Mixed wires and optimization of their compositions; Decrease the cooling rate during the deposition process Other measures to improve strength rather than solution treatment.

crack defects

strength

be

as

optimization

cooling rate

deposition process

solution treatment


Input: 5 Current methods for quality improvement in the WAAM process Generally, WAAM parts require post-process treatment to improve material properties, reduce surface roughness and porosity, and remove residual stress and distortions.

quality

process

post-process

material properties

WAAM

WAAM

surface roughness

porosity

residual stress


Input: By appropriate application of post process, the majority of issues that influence deposition quality can be mitigated or eliminated.

process

deposition quality

be


Input: Presently, several post-process treatment technologies have been reported to improve part quality in the WAAM process.

post-process

technologies

quality

process

WAAM


Input: 5.1 Post-process heat treatment Post-process heat treatment is widely used in WAAM to reduce residual stress, enhance material strength and as a method of hardness control.

Post-process heat

Post-process heat

WAAM

residual stress

material strength

hardness

as


Input: The selection of a suitable heat treatment process depends on the target material, additive manufacturing methods, working temperature and heat treatment conditions.

heat treatment

additive manufacturing

heat treatment

material

temperature


Input: If the heat treatment state is set incorrectly, the probability of cracking will increase under mechanical loading, as the combination of existing residual stress with load stress exceeds the materialdesign limitation.

heat treatment

set

probability

cracking

mechanical loading

as

residual stress

stress


Input: As summarized s 3after heat treatment, the mechanical strength of WAAM-fabricated parts improved significantly, with increase of 4%, 78%, 5% and 17% being reported for titanium alloy, aluminum alloy, Nickel-based superalloys and intermetallic Ti/Al alloy, respectively.

As

s

titanium alloy

aluminum alloy

Nickel-based superalloys

intermetallic

alloy

heat treatment

mechanical strength


Input: In addition, post-process heat treatment plays an important role in grain refinement, especially for WAAM-fabricated aluminum and Inconel alloy.

post-process heat

grain refinement

aluminum

Inconel alloy


Input: The decision to use post-process heat treatment depends on the material alloying system and also the pre-heat treatment state.

post-process heat

material

alloying

pre-heat treatment


Input: Generally, high carbon content materials must be heat treated, while a few materials can be damaged by this technique.

carbon content

be

be

materials


Input: Therefore, the utilization of post heat treatment process to WAAM component needs to consider the specific material and its application.

heat treatment

WAAM

component

specific material


Input: 5.2 Interpass cold rolling Rolling of the weld bead between each deposited layer has been shown to reduce residual stresses and distortion.Interpass cold rolling not only lowers residual stress, but also brings more homogeneous material properties.

Interpass cold rolling

cold rolling

weld bead

deposited layer

residual stresses

residual stress

homogeneous material


Input: In the WAAM process, the thermal gradient with deposition layers and alternate re-heating and re-cooling process result in the target part having anisotropic microstructural evolution and mechanical properties.

WAAM

process

process

anisotropic microstructural evolution

mechanical properties

thermal gradient

deposition layers


Input: The cold rolling technique significantly reduces microstructural anisotropy through plastically deforming the deposition.

cold rolling

microstructural

deposition

anisotropy


Input: 7 shows the schematic diagram of an interpass cold rolling system developed at Cranfield University.

interpass cold rolling


Input: A slotted roller is used to refine the microstructure and enhance tensile strength in the longitudinal direction by supporting external force.

slotted roller

microstructure

force

tensile strength


Input: As shown in 8, both ultimate tensile strength and yield strength in the build direction were improved through interpass cold rolling, which contributes to more homogeneous material properties in the target component.

As

homogeneous material

ultimate tensile strength

yield strength

build direction

interpass cold rolling

component


Input: Interpass cold rolling also can play a critical role in the healing of hydrogen porosity in WAAM-fabricated aluminum parts.

Interpass cold rolling

hydrogen porosity

aluminum


Input: Generally, high dislocation density is produced by the rolling process.

dislocation density

rolling process


Input: These dislocation can act as preferential sites for atomic hydrogen absorption and as well as for the hydrogen, allowing to diffuse to the surface.

dislocation

atomic hydrogen absorption

surface

as

as

as


Input: 9 summarizes the outcomes documented in the literature, in terms of the pore incidence and size distribution in aluminum components fabricated using WAAM with interpass cold rolling.

pore

distribution

fabricated

aluminum

WAAM

interpass cold rolling


Input: The porosities existing in as-fabricated component can be reduced or even eliminated when interpass cold rolling is applied.

porosities

component

be

interpass cold rolling


Input: This technique is only feasible for simple deposited parts, such as straight walls, due to the geometrical limitation of the rolling process.

simple

rolling process

as


Input: For more complex components with curves and corners, special flexible tooling need to be developed to achieve an effective rolling process, thus limiting the range of industrial application.

components

flexible tooling

be

rolling process

range

industrial


Input: Cold rolling technique will also reduce residual stress, but the ability to reduce overall part distortion is yet to be proven.

Cold rolling

residual stress

distortion

be


Input: 5.3 Interpass cooling Recently, interpass cooling has been developed and evaluated at the University of Wollongong.

Interpass

interpass

cooling

cooling


Input: 8 presents the schematic diagram of a WAAM system with interpass cooling.

WAAM system

interpass

cooling


Input: The moveable gas nozzle, which supplies argon, nitrogen or CO2 gas, is used to provide active, or forced, cooling on the fabricated part during and/or after deposition of each layer.

gas

fabricated

deposition

argon

nitrogen

cooling

layer


Input: Using such rapid cooling, the in-situ layer temperature and heat cycle can be controlled within a range to obtain the desired microstructure and mechanical properties.

cooling

in-situ

microstructure

mechanical properties

temperature

range

heat cycle

be


Input: This process may also potentially reduce residual stress and distortion, although this aspect has not been investigated.

process

distortion

residual stress


Input: An initial feasibility study shows promising results when using forced interpass cooling with compressed CO2 to fabricate Ti6Al4V thin-walled structures, as shown in 9.

feasibility

interpass

cooling

fabricate

as


Input: It was found that interpass cooling produces less surface oxidation, refined microstructure, improved hardness and enhanced strength.

interpass

cooling

surface oxidation

microstructure

hardness

strength


Input: In addition, manufacturing efficiency is significantly improved due to the reduction of dwell time between deposited layers.

manufacturing

reduction

dwell time

deposited layers


Input: More detailed research findings will be presented in future.

research

be


Input: 5.4 Peening and ultrasonic impact treatment Peening and ultrasonic impact treatments have been used in welding applications to reduce local residual stress and improve weld mechanical properties.

Peening

Peening

welding

ultrasonic impact treatment

ultrasonic impact treatments

local residual stress

mechanical properties

weld


Input: Both techniques are cold mechanical treatments that impact the weld surface using high energy media to release tensile stress by imposing compressive stress at the treatment surface.

cold mechanical treatments

impact

surface

weld surface

tensile stress

compressive stress


Input: Usually, the mechanical peening process produces compressive stresses at a limited depth below the component surface, such as around 1mm in carbon steels.

mechanical peening

compressive stresses

component

as

carbon steels


Input: Ultrasonic impact treatment produces grain refinement and randomizes orientation, thus contributing to mechanical strength improvement.

Ultrasonic impact treatment

grain refinement

orientation

mechanical strength


Input: It is reported that after ultrasonic impact treatment, the surface residual stress of WAAM-fabricated Ti6Al4V part can be reduced to 58% and the microhardness can be increased by 28% compared to the as-fabricated sample.

ultrasonic impact treatment

surface

microhardness

sample

residual stress

be

be


Input: Also, the surface-modified layers undergo plastic deformation with significant grain refinement and dense dislocations.

plastic deformation

grain refinement

dense dislocations


Input: The ultrasonic impact treatment is limited by penetration depth, which is up to 60 below surface.

ultrasonic impact treatment

penetration depth

surface


Input: Therefore, although both techniques are good post-process treatments, they have negligible effect on internal residual stresses of large metal part fabricated using WAAM.

post-process

fabricated

internal residual stresses

metal

WAAM


Input: 6 Discussion Improving process stability, eliminating or decreasing deposition defects and producing components with high quality and mechanical performance have become major research focuses in making the WAAM process more competitive against other additive manufacturing methods.

process

quality

research

process

deposition defects

components

mechanical

WAAM

additive manufacturing


Input: An in-depth understanding of various materials, ideal process setup, in-process parameter control and post processing is essential for achieving such a goal.

various materials

process

parameter

post processing


Input: After a systematic review and analysis, a quality-based framework aiming to achieve high-quality and defects-free WAAM process is proposed, as shown in 10.

framework

process

WAAM

as


Input: Three main aspects are considered: feedstock optimization, manufacturing process, and post-process treatment.

feedstock optimization

manufacturing process

post-process


Input: Selection of the most suitable welding WAAM process for the deposition material can ensure manufacturing process stability and contribute to reduction of defects.

welding WAAM

manufacturing process

process

reduction

defects

deposition material


Input: For example, if the CMT-PADV process is used for producing aluminum parts, porosity defects can be dramatically reduced when compared to other GMAW modes.

CMT-PADV process

GMAW

aluminum

be

porosity

defects


Input: Moreover, integrated and reliable process monitoring and control systems are needed to maintain the stability of the process and ensure the quality of production.

process monitoring

process

quality

control systems

stability

production


Input: Usually, the bead geometry, interpass temperature, arc characteristics and metal transfer behaviour are included in process monitoring and control.

bead geometry

interpass temperature

arc

process monitoring

metal


Input: Controlling the interpass temperature within a reasonable range is beneficial to microstructural evolution and the resulting mechanical properties.

interpass temperature

range

microstructural evolution

mechanical properties


Input: Further, regulating the arc characteristics and metal transfer behaviour in real time is helpful to process stability and avoidance of defects.

arc

process

defects

metal


Input: Based on the process monitoring data that has been collected during deposition, one of several post-process treatments can be selected to mitigate defects and improve mechanical performance.

process monitoring

data

deposition

post-process

defects

be

mechanical


Input: Considering the material characteristics, microstructural evolution and mechanical properties can also be optimized through new feedstock composition design.

material

be

feedstock

microstructural evolution

mechanical properties

composition


Input: It is well known that different alloying elements have specific effects on material properties.

alloying elements

specific effects

material properties


Input: By referring to the phase diagram, the desired deposition microstructures can be obtained via adding specific alloying elements in the feedstock and subsequent mechanical properties improved.

phase diagram

deposition

mechanical properties

be

alloying elements

feedstock


Input: For example, twin-wire GTAW-based WAAM has been successfully developed to produce intermetallic graded materials.

WAAM

intermetallic

materials


Input: The development of new powder cored wires, will offer exciting opportunities for fabricating target components with accurate metal composition.

powder

fabricating

components

accurate

composition


Input: In summary, using new welding consumables brings a cost effective solution, which supports high deposition quality through obtaining the desired microstructures, lowering manufacturing costs by reducing or eliminating pre-weld cleaning and re-work, and providing safer working environments by reducing weld fumes.

welding consumables

solution

manufacturing costs

supports

deposition quality

weld fumes

microstructures

pre-weld cleaning


Input: Another essential part of WAAM processing for most materials is post-process treatment, which is used to reduce residual stresses and distortion, refine microstructures, improve microhardness and enhance material strength.

WAAM

materials

post-process

distortion

microhardness

residual stresses

material strength

microstructures


Input: However, post-process technologies have their own limitations, for instance, peening and ultrasonic impact treatment only improve material property and reduce defects near the part surface, while extended heat treatment of certain materials promotes grain growth rather than grain refinement.

post-process

material property

defects

surface

materials

grain growth

peening

heat treatment

ultrasonic impact treatment

grain refinement


Input: Currently, most WAAM fabricated parts need to be post-process treated with a selective combination of technologies to reduce the defects and improve the product quality to the greatest extent possible.

WAAM

fabricated

technologies

defects

product quality

be


Input: 7 Conclusions A detailed review of recent technological developments in WAAM process has been presented, with a focus on microstructure, mechanical properties, process defects and post-process treatment.

WAAM

process

microstructure

mechanical properties

process defects

post-process


Input: Through matching a knowledge of material characteristics with the performance features of particular WAAM techniques, a quality-based framework is proposed, for producing high-quality and defect-free components.

material

performance

framework

WAAM

components


Input: In WAAM of metallic materials, the fundamental interrelationships between material composition and microstructure govern the material properties and fabrication quality.

WAAM

fabrication

metallic materials

material

composition

microstructure

material properties


Input: Since the WAAM process is an inherently non-equilibrium thermal process, it is challenging to predicate and control the microstructural evolution, which is responsible for the variation of mechanical properties in the deposited part.

WAAM

process

process

microstructural evolution

variation

mechanical properties


Input: Further research attention should be paid on the study of underlying physical and chemical metallurgical mechanisms in WAAM process to provide a guidance for the process optimization, improvement and control.

research

process

process optimization

be

metallurgical

WAAM


Input: The defects generated in WAAM-produced part are closely related to the target material characteristics and process parameters.

defects

process parameters

material


Input: The development of strategies or ancillary process to overcome defects generation are of prime importance.

ancillary process

defects


Input: As WAAM matures as a commercial manufacturing process, development of a commercially available WAAM system for metal components is an interdisciplinary challenge, which integrates physical welding process development, materials science and thermo-mechanical engineering, and mechatronic and control system design This study presents a review on powder bed laser additive manufacturing of stainless steel.

As

as

metal

stainless steel

manufacturing process

welding

powder bed laser additive manufacturing

WAAM system

components

control system

process

materials

thermo-mechanical

engineering


Input: The powder bed laser additive manufacturing processes that are presented in this paper are the selective laser sintering and selective laser melting.

powder bed laser additive manufacturing

selective laser sintering

selective laser melting


Input: The powder bed laser additive manufacturing process of stainless steel are reviewed in this paper.

powder bed laser additive manufacturing

stainless steel


Input: The process parameters was found to plat an important role in the evolving properties of the powder bed based laser additive manufacturing process.

process parameters

properties

powder bed

laser additive manufacturing


Input: Selection and/or Peer-review under responsibility of Materials Processing and characterization.

Materials Processing


Input: Steels are important engineering material invented by mankind because of their extreme multiplicity in operties.

Steels

engineering material


Input: Stainless steel originated from steel as a result of the addition of chromium.

Stainless steel

steel

as

chromium


Input: The percentage composition the chromium is sufficient enough to prevent rusting in corrosive environment.

composition

chromium

corrosive


Input: Different grades of stainless stee ludes, Martensitic stainless steel, Ferritic stainless steel, Austenitic stainless steel, superferritic stainless steel plex stainless steel, precipitation hardening stainless steel and super austenitic stainless steel.

Martensitic stainless steel

Ferritic stainless steel

Austenitic stainless steel

superferritic stainless steel

stainless steel

steel

austenitic stainless steel

precipitation hardening


Input: ection and/or Peer-review under responsibility of Materials Processing and characterization.

Materials Processing


Input: Asides from its high corrosion resistance property, stainless steel are malleable enough to be bent, folded, welded, machined and deep drawn, they also have a high heat conductivity and high strength.

corrosion resistance

stainless steel

be

welded

machined

heat conductivity

strength


Input: Stainless steels find extensive applications that include: chemical equipments, food processing equipments, cryogenic vessels, X-ray tube bases, heat exchangers, cutleries, jet-engine parts, automotive fasteners, valves, brewing equipments, and aircraft fittings.

Stainless steels

cryogenic vessels

X-ray tube

heat exchangers

brewing equipments

automotive


Input: Methods of fabrication of stainless steel include hot forming processes and cold forming processes.

fabrication

hot forming processes

cold forming processes

stainless steel


Input: Complex parts are broken down into smaller parts when these conventional manufacturing processes are used.

conventional manufacturing


Input: These does not only make the process to be cumbersome but also heavier because of extra materials that are used in joining the several parts together.

process

materials

be

joining


Input: Additive manufacturing processes is an advanced manufacturing process that can produce complex parts no matter the complexity as a single unit part.

Additive manufacturing processes

manufacturing process

complexity

as


Input: Additive manufacturing is a modern method of fabrication process which is used in producing a functional engineering metallic components one layer at a time from computer aided design model data.

Additive manufacturing

fabrication

engineering

components

layer

computer aided design

data


Input: There are various types of additive manufacturing technology, which include: vat photopolymerization, fused deposition modelling, selective laser sintering/melting, laminated object manufacturing and Laser metal deposition that is also referred to as.

additive manufacturing

vat photopolymerization

selective laser

laminated object manufacturing

Laser metal deposition

fused deposition

as


Input: Vat photopolymerization is the first commercial additive manufacturing method that is used to create a layer of solidified material using ultraviolet radiation to selectively polymerize a curable resin until a complete part is formed.

Vat photopolymerization

additive manufacturing

layer

material

curable resin

ultraviolet radiation


Input: Its advantages includes high building speed and flexibility.

flexibility


Input: Major disadvantages are high cost of materials and process errors due to over curing.

materials

process errors

curing


Input: Fused deposition modelling additive manufacturing is also referred to as material extrusion process, this process is used for fabricating 3D parts by deposition of laser heated thermoplastic filaments in a layer wise manner.

Fused deposition

process

deposition

additive manufacturing

extrusion process

fabricating

as

thermoplastic filaments

3D parts

laser

layer


Input: With this method, complex durable parts can be easily manufactured with high accuracy.

be

manufactured

accuracy


Input: Draw-backs of this additive manufacturing technology include poor surface finish, time consumption and high porosity of manufactured parts.

additive manufacturing

surface finish

porosity of manufactured parts


Input: This method has been applied in automotive, aerospace, medical and plastic industries.

automotive

aerospace

medical

plastic industries


Input: Selective laser sintering/malting is a powder bed additive manufacturing method that involves atomic fusion/melting of metallic powder deposited in form of layers.

Selective laser

powder bed additive manufacturing

metallic powder


Input: Parts can be easily processed within a short time frame, it is flexible and accurate.

be

processed

accurate


Input: This additive manufacturing method has been mostly used with metals such as stainless steel 316L austenitic grade, precipitated hardened stainless steel.

additive manufacturing

metals

as

steel

austenitic

steel

precipitated hardened


Input: Selective laser sintering has an extensive application in the field of aerospace, medical and automotive engineering due to the ability to control the stiffness of components in a desired model.

Selective laser sintering

aerospace

medical

automotive

stiffness

components

model


Input: Selective laser melting is a powder based bed fusion that is used to produce metallic components by deposition of a thin metallic powder on a substrate and using a high intensity laser beam to melt and fuse selective region of metallic powder according to the computer aided design data in a layer-wise fashion.

Selective laser melting

bed fusion

fuse

powder

metallic

thin metallic powder

substrate

metallic powder

components

intensity laser beam

deposition

melt

fashion

computer aided design


Input: This method has an advantage of less porosity of built parts with better mechanical property, manufacturability of complex shapes and excellent scanning efficiency.

porosity

complex shapes

mechanical property

manufacturability

scanning efficiency


Input: The disadvantage is similar to that of the process discuss earlier in terms of process control challenge due to too many parameters and also there is a material wastage.

process

process control

parameters

material


Input: Selective laser melting has been extensively used with the employment of stainless steel.

Selective laser melting

stainless steel


Input: Selective laser melting has an extensive application in the field of aerospace, medical, automotive engineering and medical health care sectors.

Selective laser melting

aerospace

medical

automotive

medical


Input: Benefits of this methods include good efficiency of material usage, parts with complicated shapes can be built, high strength material can be achieved, materials can be customized, it takes less time and it eliminated oxide impurities due to vacuum environment.

material

be

material

be

be

strength

oxide impurities

materials


Input: Disadvantages of this methods are high price of set-up due to integration of vacuum with the machine for good thermal and impurity free environment, X-rays are formed during the process which is detrimental to human health.

machine

impurity

X-rays

process


Input: Laminated object additive manufacturing is an additive-subtractive rapid prototyping manufacturing process where 3D objects are manufactured by metal sheet material that are bonded together by thermally activated adhesive coating layer by layer.

Laminated object additive manufacturing

manufacturing process

thermally activated

rapid prototyping

3D objects

manufactured

layer by layer

metal

material

adhesive


Input: Each layer is formed from a sheet of paper coated with a thermoplastic adhesive and sheet is bonded together by using a heated stainless steel roller after which a CO2 laser cuts cross-section into a layer of paper according to the information from the CAD model repeatedly until the required object is formed and lamination is actualized.

layer

layer

sheet

thermoplastic adhesive

sheet

stainless steel

coated

roller

CAD model


Input: The process is simple and faster since the laser doesnhave to scan the entire area of the cross section.

process

cross section

simple

laser

area


Input: Merits of this method includes that fact that large size parts can be built, it is cheap, no microstructural alteration during the process, and it is flexible in the sense that component does not need support structures.

be

microstructural

process

component

support structures


Input: Setbacks of this methods includes wastage of material during the subtractive process, complex internal cavities and hollow parts are difficult to build, and it has poor surface finishing.

material

subtractive process

surface finishing

build


Input: Laminated object manufacturing has been demonstrated in aerospace and tool design industries.

Laminated object manufacturing

aerospace

tool design industries


Input: Laser Metal Deposition, an additive manufacturing process, is used in building parts by melting a metal powder that is injected into a specific location by mean of a high power laser beam.

Laser Metal Deposition

additive manufacturing process

melting

metal powder

high power laser beam


Input: The process of solidification and cooling occur in a closed chamber in an argon atmosphere so as to prevent oxidation of the melt pool.

process

solidification

cooling

oxidation

closed chamber

argon atmosphere

as

melt pool


Input: This process permits the use of high variety of metals and composites such as stainless steel mostly austenitic grades, which are mainly 316, SS 316L, SS 304L and other exotic metals such as titanium and its alloys, composites and functionally graded materials.

process

metals

composites

as

steel

austenitic

SS

SS

metals

as

alloys

composites

functionally graded materials


Input: A major benefit of laser additive manufacturing technology is that, it provide new chances for customization of metallic components in terms of material composition manipulation and properties, improvements in product performance, and lower overall manufacturing costs due to its unique capabilities.

laser additive manufacturing

metallic

material

components

composition

properties

performance

manufacturing costs


Input: Lots of research and discoveries has been achieved with laser metal deposition as an additive manufacturing method with the employment of stainless steel and stainless steel composite with much effort in enhancing wear resistance and strength property.

research

laser metal deposition

additive manufacturing

as

stainless steel

stainless steel

composite

wear resistance

strength property


Input: This paper presents an overview of selective laser sintering and selective laser melting process of stainless steel.

selective laser sintering

selective laser melting process

stainless steel


Input: Some recent research works on stainless steel using these powder bed additive manufacturing techniques are presented and future research need are also proposed.

research

research

stainless steel

powder bed additive manufacturing


Input: Selective Laser Sintering of Stainless Steel This additive manufacturing process is a powder based layer-additive manufacturing process where metallic components are built section by section.

Selective Laser Sintering

additive manufacturing process

manufacturing process

Stainless Steel

powder

metallic

components


Input: A moderately low laser power is used in this process as metallic material never reach a liquid phase during the heating process.

laser power

process

as

material

liquid phase

heating


Input: The process occurs at a faster rate at high temperature which is why it involves heating a powder.

process

temperature

heating

powder


Input: The process is achieved when the laser scan powder material deposited on the substrate on the 2D cross-section of the part created in 3D geometrical shape.

process

laser scan

material

substrate

2D cross-section

3D geometrical shape


Input: The process is repeated in which after the first laser scan, the powder bed is lowered by the amount of thickness of the layer produced initially, and then a new layer of powder material is spread on the powder bed again on top of the initial scanned layer until a fully dense built part is produced.

process

spread

laser scan

powder bed

powder bed

layer

layer

layer

fully dense

powder material


Input: Selective laser sintering process has the potential to become one of the most valuable additive manufacturing techniques, because it has potential to easily produced complex shapes.

Selective laser sintering process

additive manufacturing

complex shapes


Input: The Figure 1 shows the schematic diagram of the SLS process.

SLS process


Input: Schematic diagram of selective laser sintering process.

selective laser sintering process


Input: Few research investigations and studies have been done in the application of selective laser sintering with stainless steels.

research

selective laser sintering

stainless steels


Input: Stainless steel grades that has been involved in this process are the austenitic type mainly SS 316L and the precipitated hardened stainless steel grade PH.

Stainless steel

austenitic

SS

steel

process

PH

precipitated hardened


Input: Ibrahim studied the fabrication of a novel porous electrode scaffold made from stainless steel 316L powder using selective laser sintering by careful selection of process parameters and also how the property such as porosity, electrical conductivity and optical microscopy measurements were used to investigate the properties of the fabricated sample.

fabrication

selective laser sintering

porous electrode scaffold

stainless steel

powder

as

process parameters

property

properties

fabricated

electrical conductivity

optical microscopy


Input: In this investigation stainless steel, SS316L with particle size of 25 to 50 micro-meter were built with 30 W laser power and 1500 mm/s scanning speed.

stainless steel

particle

laser power

scanning speed


Input: Density and porosity properties were investigated and it was discovered that high porosity metal parts can be produced by using a low laser power and high scan speed.

Density and porosity

porosity

metal

be

laser power

scan speed


Input: This study also revealed the feasibility of producing porous metal sintered parts for electrochemical devices using the right processing parameters.

feasibility

parameters

porous metal

electrochemical devices


Input: Xie studied the mechanical and structural characteristics of porous 316L stainless steel fabricated by indirect laser sintering.

mechanical

porous

316L stainless steel

laser sintering


Input: In this investigation, a simple encapsulated method was developed to coat 316L SS powder fabricated by indirect SLS process, with ethylene-vinyl acetate copolymer resin.

simple

SLS process

encapsulated

316L SS powder

ethylene-vinyl acetate copolymer resin


Input: In this experiment, a water atomized 316L stainless steel powder with particle size of 45 micro-meter and ethylene-vinyl acetate copolymer resin were used to encapsulate the stainless steel metallic particle together.

experiment

particle

water atomized

316L stainless steel powder

stainless steel

metallic

ethylene-vinyl acetate copolymer resin


Input: The selective laser sintering method was performed in a pure argon environment on a WYS600 SLS equipment with powder bed temperature 5 0 C below the melting temperature of ethylene-vinyl acetate copolymer resin.

selective laser sintering

SLS

pure argon

C

equipment

powder bed

melting temperature

ethylene-vinyl acetate copolymer resin


Input: The processing parameters employed were scan spacing of 0.10, 0.15 and 0.20 mm, laser power ranges between 10 and 35 W at interval of 5 W, scanning speed was set between 1000 and 2000 mm/s at difference of 200 mm/s and layer thickness was set at 0.15 mm.

parameters

mm

mm

laser power

scanning speed

layer thickness

set

set


Input: Before characterization of the EVA resin, post-processing was carried out in pure hydrogen contained furnace.

resin

pure hydrogen

post-processing

furnace


Input: The EVA resin was then characterized in terms of its thermal behaviour, density, porosity, average pore size.

resin

density

porosity

average


Input: Mechanical test was performed on a CMT4305 electronic testing universal testing machine with a purpose of investigating the yield strength and young modulus.

Mechanical test

electronic testing

testing

machine

yield strength

young modulus


Input: It was discovered that the laser power and the sintering temperature are determining factor on the reduction in the porosity of the material.

laser power

sintering

reduction

porosity

material


Input: It was concluded that the characteristics of the sintered porous stainless steel 316 L produced can be use as a substitute for bones in biomedical applications.

sintered

porous

steel

be

as

biomedical applications


Input: Pal investigated the effect of post-processing and machining process parameters on the mechanical properties of stainless steel product produced by direct laser sintering.

post-processing

parameters

mechanical properties

machining

laser sintering

stainless steel


Input: A sample of stainless steel was fabricated in an argon atmosphere in a 40 degree centigrade pre-heating machining chamber with a fibre laser system having beam diameter of 0.1 mm.

sample

fabricated

stainless steel

argon atmosphere

beam diameter

machining chamber

fibre laser system

mm


Input: Processing parameters of tensile specimens were 195 W laser power, scan speed of 900 mm/s with 40 micro-meter thickness layer.

parameters

tensile specimens

laser power

scan speed

layer


Input: Tensile test was then performed with specimen dimensions 80 mm in total length, 40 mm gauge length, 5 mm gauge diameter, length of holding part was set at 20 mm and diameter 6 mm.

Tensile test

dimensions

mm

mm

mm

mm

mm gauge diameter

set

diameter


Input: It was discovered that the tensile strength of the DLMS part increased after heat treatment.

tensile strength

heat treatment


Input: Residual stresses remain in the het treated part with increased tensile strength due to rapid cooling without undergoing any post-processing stage.

Residual stresses

tensile strength

cooling

post-processing


Input: It was discovered after the analysis that the energy density will determine the mechanical property which implies that tensile strength of the stainless steel can be controlled by the combination of the machining parameters and energy density.

energy density

energy density

mechanical property

tensile strength

stainless steel

be

machining


Input: Laser power and scanning speed will also determine the extent of surface roughness of the stainless steel.

Laser power

scanning speed

surface roughness

stainless steel


Input: studied the deformation mechanism of 17-4 precipitated hardened stainless steel fabricated by direct metal laser sintering using micro pillar compression testing and transmission electron microscopy.

deformation

fabricated

precipitated hardened

steel

direct metal laser sintering

micro pillar compression testing

transmission electron microscopy


Input: 17- 4 stainless steel were first produced using direct metal laser sintering system in an argon atmosphere with spherical size of approximately 15 45 micro-meter in diameter.

stainless steel

direct metal laser sintering system

argon atmosphere

spherical

diameter


Input: Scanning speed was 750 mm/s with scanning direction made 67 degrees between successive building layers with hatch spacing was 0.11 mm.

Scanning speed

hatch spacing

scanning

mm


Input: micro compression properties of the 17-4 precipitation hardened stainless steel was evaluated.

compression

precipitation hardened

steel


Input: Outcome revealed that the microstructure and properties of the 17-4 stainless steel stainless steel specimens vary significantly from those produced by conventional manufacturing methods because of fine grain evolution that emerged.

microstructure

properties

grain evolution

17-4 stainless steel

steel

conventional manufacturing


Input: Selective Laser Melting of Stainless Steel Selective Laser Melting process is an additive manufacturing technology that can be used to produce solid metallic components from metallic powder by using a high intensity laser to melt and fuse selective region of the metallic powder layer by layer according to the computer aided design data.

Selective Laser Melting

Selective Laser Melting process

additive manufacturing

fuse

Stainless Steel

be

metallic

metallic powder

metallic powder

components

laser

computer aided design

melt

layer by layer


Input: A new layer of metal powder is applied and the build platform is being lowered by the amount of thickness of one layer.

layer

layer

metal powder

build platform


Input: The process involves building of component layer by layer by depositing a thin metallic powder on a substrate.

process

building of component layer

layer

thin metallic powder

substrate


Input: A high intensity power laser is then used to melt and fuse together a specific area of the metallic powder according to the data from the 3D CAD.

power

area

laser

melt

data

fuse

metallic powder


Input: Once the laser scanning is completed, succeeding layer of metallic powder is deposited on top and laser scans another new layer until the required component is completely built after repeated successive layer of metallic powder is deposited.

laser

laser scans

layer

layer

layer

metallic powder

metallic powder

component


Input: Once the laser scanning processes completed, loose powders are removed from the building chamber and the component can be separated from the substrate plate manually or by electrical discharge machining.

laser scanning processes

powders

be

building chamber

component

substrate plate

electrical discharge machining


Input: Schematic diagram describing the SLM process is shown in Figure 2.

SLM

process


Input: Figure 2: Schematic diagram selective laser melting process Numerous research has been conducted with the application of selective laser melting of stainless steel in the literature.

selective laser melting process

selective laser melting

research

stainless steel


Input: Jandin 2005 investigated the influence of laser power strength on the porosity of component built.

laser power strength

porosity

component


Input: In their study, ytterbium fibre laser with a wavelength of 1065 nm was used to process the 316L stainless steel powder.

fibre laser

wavelength

process

316L stainless steel powder


Input: The experiment showed that low laser power and high scanning speed caused incomplete melting of the powder material and resulted in high porosity in the components.

experiment

laser power

scanning speed

melting

powder material

porosity

components


Input: This can be improved by increasing the laser power, and decreasing the scanning speed.

be

laser power

scanning speed


Input: Wang investigated selective laser melting of stainless steel 316L with low porosity and high build rates by employing fast scanning speeds to fabricate high-density stainless steel 316L parts.

selective laser melting

fabricate

stainless steel

stainless steel

porosity

build rates

scanning speeds


Input: The aim of the study was to improve the production rate while maintaining a low porosity for the selective laser melting-built parts.

production

selective laser

porosity


Input: The study shed light on the improvement of selective laser melting build rates without any decrease in the mechanical properties or any loss of parts density of stainless steel 316L.

selective laser melting

build rates

mechanical properties

density

stainless steel


Input: Miranda investigated and developed models for predicting the physical and mechanical properties of 316L stainless steel produced by selective laser melting.

mechanical properties

316L stainless steel

selective laser melting


Input: The influence of various processing parameters on density, hardness and shear strength of 316L stainless steel were studied using statistical analysis in order to significantly determine main factors and their interactions.

parameters

density

hardness

shear strength

316L stainless steel


Input: Six different models were developed as a predictive design tool to determine the influence of these processing parameters on the shear strength, hardness and density.

as

design

parameters

shear strength

hardness

density


Input: Wang investigated the development of grain structure mechanism of 316L stainless steel fabricated by selective laser melting and mechanical property characterization.

grain structure

316L stainless steel

selective laser melting

mechanical property characterization


Input: The grain structure mechanism was studied using finite element analysis in order to reveal the growth mechanism of grains under rapid solidification condition.

grain structure

finite element analysis

mechanism

grains

rapid solidification


Input: A detailed analysis of crystal orientation of formed dendrite was performed using geometrical analysis in collaboration with experimental findings.

crystal orientation

dendrite

geometrical analysis

experimental


Input: It was discovered that rapid solidification caused by high-speed scanning resulted into sub-micron grains within the final solidified microstructure.

rapid solidification

high-speed scanning

sub-micron

grains

solidified microstructure


Input: It was also detected that grain size and densification was a dependant on high volume energy density of the laser which will significantly affect the mechanical properties of the final product formed after solidification.

grain size

densification

volume

mechanical properties

solidification

energy density

laser


Input: Casati studied the microstructure and fracture behaviour of 316L austenitic stainless steel produced by selective laser melting and discovered that severe thermal gradients and high cooling rates affects the crystal growth and orientation of grain structure after solidification.

microstructure

fracture

orientation

grain structure

solidification

316L austenitic stainless steel

selective laser melting

thermal gradients

cooling rates

crystal growth


Input: This causes material spattering and microstructure defects like pores and incomplete melted particles.

material

microstructure defects

melted

pores


Input: The influence of effect of different distribution of defects on mechanical response and failure mechanism were investigated using 316L bars with microstructure and texture built along two different orientations.

distribution

defects

mechanical response

microstructure

orientations

failure mechanism

316L bars

texture


Input: It was concluded that semi-molten metallic powder particles of stainless steel 316L were responsible for the scattering and reduced strength of the material after solidification.

semi-molten

strength

metallic powder

stainless steel

material

solidification


Input: Liu investigated the spatter behaviour of stainless steel 316L during selective laser melting process.

spatter

stainless steel

selective laser melting process


Input: It was discovered that spatter is caused as a result of negative impact of laser on the building of parts in successive layers during selective laser melting process.

spatter

building of parts

as

impact

laser

selective laser melting process


Input: Two types of spatter were identified which were droplet spatter, generated by the tearing behaviour of molten metal and powder spatter, which are produced when non-metallic powder particles around the molten pool are blown away as a result of metallic vapour impact.

spatter

droplet spatter

powder spatter

molten metal

powder particles

as

metallic

molten pool

impact


Input: It was discovered that oxygen composition increase during spatter and X-ray diffraction shows that diffraction peaks of austenite content and ferrite are low due to the formation of iron oxides.

oxygen

austenite

ferrite

iron oxides

composition

spatter

X-ray diffraction

diffraction


Input: Li investigated the deformation behaviour of stainless steel micro-lattice structures produced by selective laser melting.

Li

stainless steel

deformation

micro-lattice structures

selective laser melting


Input: Macroscopic deformation of micro-lattice structures and microscopic stress and strain evolution were studied using a full scale 3D finite element model.

Macroscopic deformation

microscopic stress

strain

micro-lattice structures

evolution

element


Input: The finite element prediction revealed that deformation of micro-lattice is significantly affected by applied boundary conditions and constitutive properties of the selective laser melted parent material.

finite element

deformation

boundary conditions

properties

micro-lattice

selective laser melted

material


Input: Zhao studied the influence of stainless steel decarburization on its youngmodulus hardness and tensile strength during selective laser melting process.

stainless steel

decarburization

selective laser melting process

youngmodulus

hardness

tensile strength


Input: The study was investigated using evolution mechanism of the chemical element during SLM.

evolution

element

SLM


Input: It was discovered that during decarburization process 21% of carbon composition was lost and as a result, it reduces the young modulus and hardness of the molten pool boundary as well as the tensile property of the stainless steel.

decarburization

carbon

as

as

as

stainless steel

young modulus

hardness

tensile property

molten pool

boundary


Input: Selective laser melting also been used to process martensitic grade of stainless steel.

Selective laser melting

process

martensitic grade

stainless steel


Input: Krakhmalev investigated the evolution of microstructure in AISI 420 martensitic stainless steel during selective laser melting.

evolution

microstructure

AISI 420

stainless steel

selective laser melting


Input: It was discovered that several upper layers which are in austenite phase posses hardness value higher than the final bulk microstructure of thermally decomposited martensite.

austenite phase

hardness

microstructure

thermally decomposited martensite


Input: Also, numerical simulation results of thermal cycles discovered that thermal process can be controlled by variation of laser energy input.

numerical simulation

thermal cycles

process

variation

laser energy

be


Input: The tribology of selective laser melting of 316Lstainless steel as a processed part under lubricated conditions was studied by Zhu.

tribology

processed

selective laser melting

steel

as


Input: The friction and wear behaviours of 316L stainless steel produced both by selective laser melting and traditional methods were studied using a ring on-disc rig under lubricated conditions.

friction

wear

316L stainless steel

selective laser melting


Input: It was discovered that the tribological performance of SLM stainless steel sample will be better if the pores can be drastically reduced with refined grains.

tribological performance

sample

grains

SLM

steel

be

be

pores


Input: Cherry investigated how processing parameters affects the microstructural and physical properties of 316L stainless steel by selective laser melting.

parameters

microstructural

physical properties

316L stainless steel

selective laser melting


Input: After systematic characterization of porosity and microstructure, it was discovered that porosity is highest at lower laser energy and decreases at higher laser energy and also laser energy density alteration resulted in production of dense parts.

porosity

porosity

microstructure

laser energy

laser energy

laser energy density

production


Input: Material hardness was also increased due to reduction in porosity.

Material

hardness

porosity

reduction


Input: Most of the research that has been done focused mostly on austenitic stainless steel grade, 316L and also on martensitic grade AISI 420.

research

austenitic stainless steel

AISI 420

martensitic grade


Input: Selective laser melting has been extensively explored with stainless steel but further study need to be done with the employment of other grades of stainless steel This review article summarizes the current state-of-the-art for biomimicry in additive manufacturing.

Selective laser melting

additive manufacturing

stainless steel

be

stainless steel

state-of-the-art

biomimicry


Input: Biomimicry is the practice of learning from and emulating nature-which can be increasingly realized in engineering applications due to progress in additive manufacturing.

Biomimicry

be

engineering

additive manufacturing


Input: AM has grown tremendously in recent years, with improvements in technology and resulting material properties sometimes exceeding those of equivalent parts produced by traditional production processes.

AM

production

technology

material properties

processes


Input: This has led to the industrial use of AM parts even in highly critical applications, most notably in aerospace, automotive and medical applications.

led

industrial

aerospace

automotive

medical applications

AM parts


Input: The ability to create parts with complex geometries is one of the most important advantages of this technology, allowing the production of complex functional objects from various materials including plastics and metals that can not be easily produced by any other means.

complex geometries

technology

production

complex functional objects

various materials

plastics

metals

be


Input: Utilizing the full complexity allowed by AM is the key to unlocking the huge potential of this technology for real world applications and biomimicry might be pivotal in this regard.

complexity

technology

biomimicry

AM

be


Input: Biomimicry may take different forms in AM, including customization of parts for individuals, or optimization for specific properties such as stiffness and light-weighting.

Biomimicry

optimization

AM

specific properties

as


Input: The optimization process often uses an iterative simulation-driven process analogous to biological evolution with an improvement in every iteration.

optimization

process

biological evolution

simulation-driven


Input: Other forms of biomimicry in AM include the incorporation of real biological inputs into designs; the use of cellular or lattice structures for various applications and customized to the application; incorporating multi-functionality into designs; the consolidation of numerous parts into one and the reduction of waste, amongst others.

biomimicry

consolidation

reduction

AM

biological inputs

designs

lattice structures

designs


Input: Numerous biomimetic design approaches may be used broadly categorized into customized/freeform, simulation-driven and lattice designs.

biomimetic design

lattice designs

be

simulation-driven


Input: not for prototyping.

prototyping


Input: The current limits of each design approach are discussed and the most exciting future opportunities for biomimetic AM applications are highlighted.

limits

design

biomimetic AM applications


Input: The beauty found in nature is often inspirational-and this inspiration has found its way into functional mechanical engineering through the latest developments in additive manufacturing.

mechanical engineering

additive manufacturing


Input: Other forms of engineering beauty are structural hierarchy, order or lack of order, and combinations with other structures.

engineering

structural hierarchy


Input: Learning from these biological structures may advance our use of efficient structures in engineering applications and may even help to provide new solutions to engineering problems, in a sustainable way.

biological structures

engineering

engineering

sustainable


Input: Biomimicry in engineering involves the study of biological systems specifically with the aim to use information learned in solving engineering problems, or for use in engineering applications.

Biomimicry

biological systems

engineering

engineering

engineering


Input: In nature, structural features from nano to micro to macro scale define an objectproperties and functionalities and vice versa.

nano

macro scale


Input: Modern engineering design has the possibility to change the structural features and properties of the objects while maintaining functionality or to apply simulation to find a design for specific required properties.

engineering

design

design

properties

properties

simulation


Input: In an ideal case, AM is able to translate innovative biomimetic design into physical objects with the desired properties and functionality.

AM

biomimetic design

properties


Input: Much of this potential has particularly realistic prospects when using AM, with its freedom of design and complex production capabilities.

AM

production

design


Input: The capability to emulate the complex structures and hence the properties of biological materials is the aim of biomimicry.

complex structures

properties

biomimicry

biological materials


Input: For example, failure of a specific design that is claimed to be biomimetic but uses no input from nature, might undermine the credibility of biomimicry.

failure

biomimicry

design

be


Input: Often structures with curves and rounded edges in any way resembling something in nature are referred to as or This is not incorrect but it must be kept in mind that no biological input is present, and as such is not truly biomimetic or bio-inspired.

rounded edges

as

be

as

biological input

biomimetic

bio-inspired


Input: Additionally, when a structure is designed for a biological application it may be termed biomimetic or bionic simply due to its intended biological role.

structure

biomimetic

designed

be


Input: Topology optimization, generative design and simulation-driven design tools used to create optimized designs using simulation often create unconventional and complex shapes and forms.

Topology optimization

design

designs

generative design

simulation-driven

simulation

complex shapes


Input: The simulation-driven design process is in reality also biomimetic or bio-inspired in the sense that it is iterative and therefore mimics aspects of natural evolutionary strategies in a short timeframe.

simulation-driven

design process

biomimetic

bio-inspired


Input: In the area of cellular or lattice structure design, some engineers refer to all porous engineered structures as biomimetic simply due to their resemblance to natural porous materials, or their similarity to the biological equivalent.

area

lattice structure design

porous

as

porous materials

biological equivalent


Input: However, cellular and lattice designs have unlimited design permutations and can therefore be tailored to the application.

lattice designs

design

be


Input: Currently, the most important application for these porous engineered structures is in dental and bone implants.

porous

dental and bone implants


Input: The latter is a biomimetic application in the sense that the structure should emulate bone for best results, in terms of mechanical properties and permeability.

biomimetic application

structure

mechanical properties

bone

permeability


Input: Finally, biomimetic lattice structures may also specifically refer to stochastic design strategies which create structures with a random distribution of strut thicknesses and lengths the randomness emulates nature.

biomimetic

distribution

stochastic design

strut thicknesses


Input: A biomimetic and bio-inspired approach to materials design has attracted great interest from scientists in diverse areas: biophysics and biomaterials, sensors and chemistry, materials science and engineering, to name a few.

biomimetic

bio-inspired

materials

biophysics

chemistry

materials

design

areas

biomaterials

sensors

engineering


Input: From 2016, with the progress in AM technology and wider understanding of the fact that complex designs can be realized in real AM products, biomimetic approaches began to be the subject of research in more than 150 papers per year.

AM technology

AM

designs

be

be

biomimetic

research


Input: Interest in lattice structures produced by AM also increased year by year.

lattice structures

AM


Input: In recent years AM has grown from a prototyping technology to a reliable direct production technique.

AM

production

prototyping


Input: In particular, metal AM has developed tremendously, up to the point where it is now possible to produce functional metal parts for critical applications in medical and aerospace industries.

metal AM

metal

medical

aerospace industries


Input: Powder bed fusion is the term used to specifically describe metal AM using a laser or electron beam to melt tracks and layers for the manufacture of detailed and complex shaped parts.

Powder bed fusion

metal AM

laser

electron beam

melt

manufacture


Input: The track-by-track and layer-by-layer PBF process allows the manufacturing of parts with intricate, complex designs.

layer-by-layer

process

manufacturing

designs


Input: Part complexity allows designs to be optimized for specific applications such as light-weighting in aerospace parts or improving bone growth and implant success in bone implants.

complexity

bone growth

designs

be

as

aerospace

implant

bone implants


Input: It has been demonstrated that the mechanical performance of PBF parts can be superior to traditionally manufactured equivalents and lots of work has been done in particular in Ti6Al4V as shown in.

mechanical

PBF

be

as

manufactured


Input: Laser powder bed fusion is limited to intricate parts typically smaller than 300 mm for larger metal parts it is possible to use wire and arc AM with a reduction in detail possible.

Laser powder bed fusion

mm

wire and arc AM

metal

reduction


Input: In addition to metals, various other materials can be reliably processed using AM including polymers, ceramics and various types of composites, as is discussed in more detail in.

metals

be

polymers

ceramics

composites

as

materials

processed

AM


Input: Metals are highly likely to have practical uses in biomimetic structural applications in military, aerospace and automotive industries due to the light-weight and strong parts that can be produced, and hence much effort has been aimed in this direction.

Metals

be

biomimetic structural applications

military

aerospace

automotive industries

light-weight


Input: However, many biological systems are based on combinations of stiff and softer materials, and often have mechanical properties more like polymers and composite materials.

biological systems

materials

mechanical properties

polymers

composite materials


Input: Therefore, many applications also exist for nature-inspired designs in materials other than metals.

designs

materials

metals


Input: Many of the examples presented in this review focus specifically on metal AM, due to their relevance for high-value functional end-use parts, but the same principles apply to all other additively manufactured materials.

metal AM

additively manufactured


Input: For products designed by biomimicry, it has been proposed that two broad approaches exist: the approach and the approach as outlined in.

designed

biomimicry

as


Input: In the first case, the designer/engineer is inspired by a biological concept or model and applies this to a new design idea.

biological concept

model

design


Input: In addition to these approaches, three major ways of obtaining a designed biomimetic model in practice exist: customized/freeform design, simulation-driven design and lattice design.

designed

design

design

lattice design

biomimetic

simulation-driven


Input: For example, lattices may be incorporated in a freeform design process or in a simulation-design process.

lattices

process

be

freeform design


Input: All these approaches may also be used with or without direct input from nature, with varying levels of biological input or bio-inspiration possible.

be

biological input

bio-inspiration


Input: Customized and freeform design involves manipulation with curved surfaces and is typically used to create custom and unique designs fit for a particular application while maintaining functionality.

Customized and freeform design

designs

curved surfaces


Input: For instance, customized implants aimed at directly replicating the bone shape for replacement, tree-like support structures, nervous-system-inspired shade or hierarchical networks where nodes constantly branch and merge.

implants

bone shape

tree-like support structures

hierarchical networks


Input: This process is the simplest of the biomimetic design methods, particularly useful for customization such as in prosthetics or implants, and is also used in artistic design.

process

biomimetic design

design

as

prosthetics

implants


Input: With reference to prosthetics and implants, the design requirement is taken from a biological shape, hence the biomimetic description.

prosthetics

implants

design

biological shape

biomimetic


Input: In addition, freeform design results in organic shapes which can often resemble natural structures.

freeform design


Input: Simulation-driven design is a very promising approach which has emerged in recent years and is especially useful for light-weight design for engineering applications.

Simulation-driven

design

design

light-weight

engineering


Input: This involves structural optimization and uses an iterative process of simulation and material removal to optimize the required material distribution or material stiffness for a given set of expected load cases.

structural optimization

process

distribution

simulation

material

material

material stiffness

set


Input: This process of stepwise optimization is similar to most evolutionary processes in nature, and removal of material in areas of low stress is a similar optimization strategy as is used in natural systems, hence the motivation to categorize this process as biomimetic.

process

optimization

processes

optimization

process

material

as

as

areas

stress


Input: The field of topology optimization in AM was reviewed recently in, where the current limits of the practical use of this technique was discussed in detail, especially with regards to overhang angle, support removal, residual stress, build quality including challenges in software tools that need to be solved for its more widespread adoption.

topology optimization

AM

limits

software

overhang angle

build

support

residual stress

be


Input: The use of additively-manufactured lattice or cellular structures is a highly relevant approach which is often combined with the former methods, i.e.

lattice

cellular structures


Input: the incorporation of lattices or cellular designs into optimized organic or topology optimized designs.

lattices

topology

cellular designs

designs


Input: Natural systems often use cellular structures and these are widely used in bio-inspiration for the use of lattices in engineering parts, hence the categorization as biomimetic.

cellular structures

bio-inspiration

lattices

engineering

as


Input: Lattices have obvious light-weighting advantages, high specific stiffness, fracture toughness, crack growth arresting, amongst other desirable and tailorable properties.

Lattices

fracture

crack growth

properties

specific stiffness


Input: One major application of cellular structures is their use in bone implants, to improve osseointegration.

cellular structures

bone implants

osseointegration


Input: The design theory for present-day AM in general was reviewed and limitations discussed in.

design

AM


Input: On the topic of biomimetic 3D printing, the review gives a detailed overview of the use of biological inputs into the design process, discusses biological study systems used in biomimicry and focusses on applications of polymer and multi-material 3D printing, but does not discuss metal AM or simulation-driven design.

biomimetic

design process

biomimicry

3D printing

multi-material 3D printing

metal AM

biological inputs

polymer

simulation-driven

design


Input: Biomimetic approaches for AM include the design of innovative materials and systems.

Biomimetic

materials

AM

design


Input: In addition to simulation-driven design of single-material parts, fracture-resistant composite materials could be designed using simulation-driven design and validated by multi-material 3D printing as demonstrated in.

simulation-driven

simulation-driven

design

design

fracture-resistant composite

be

as

multi-material 3D printing


Input: Multi-material biomimetic design for medical purposes has been demonstrated in.

Multi-material

biomimetic design

medical


Input: Not all freeform designs, lattice designs or topology optimized designs include biological input, but they are still referred to as biomimetic in a broader sense.

freeform designs

lattice designs

designs

topology

biological input

as


Input: True biological input in the AM design process is still rare in engineering due to the lack of biologists involved in engineering design in general.

biological input

AM

process

engineering

engineering

design


Input: Nevertheless, biological materials science is a mature field which focuses on studying biological systems to understand their properties and potentially employ these designs in engineering systems.

biological materials

biological systems

properties

designs

engineering


Input: Biological materials often possess superior mechanical properties due to unique combinations of hard and soft materials and gradients between them.

Biological materials

mechanical properties

materials


Input: Biologically inspired design principles have been categorized recently into fibrous, helical, gradient, layered, tubular, cellular, suture and overlapping structures.

design

tubular

fibrous

suture


Input: Besides broad design categories or guidelines, the use of X-ray tomography to study intricate details of individual biological structures in 3D for biomimetic applications is also a promising strategy to learn from nature.

design

biological structures

X-ray tomography

biomimetic applications


Input: Incorporating biological inputs into engineering design is a topic of continued effort and includes the development of biomimicry design databases.

biological inputs

engineering

design

biomimicry

databases


Input: Biomimetic design has also been named as it has been suggested that these approaches may lead to the use of the minimum required materials, which is most environmentally sustainable.

Biomimetic design

as

lead

materials

sustainable


Input: Despite the access to complexity and freedom of design, which is often cited for AM, all the biomimetic approaches discussed here have practical manufacturability limits in the context of present-day AM systems.

complexity

biomimetic

manufacturability limits

design

AM

AM


Input: A recent review paper covers the use of AM to produce bio-inspired structures with the main aim to learn about and optimize the biological structures themselves.

AM

bio-inspired structures

biological structures


Input: In the area of biomimetic cellular design, various recent reviews are useful and relevant to bone implant applications in particular, and are more generally discussed for various applications in.

area

biomimetic cellular design

bone implant applications


Input: It is therefore the aim of this present review paper to fill the gaps between these areas and address all the above biomimetic approaches in one cohesive framework.

areas

biomimetic

framework


Input: Most examples used in this paper are focused on metal AM due to its ability to produce functional end-use parts, but the principles are broadly applicable to all additively manufactured materials.

metal AM

additively manufactured


Input: While most of the discussion and examples are using laser powder bed fusion, other AM technologies are equally applicable and the design and challenges vary slightly with each technology.

laser powder bed fusion

AM technologies

design

technology


Input: For example, binder jetting has shown some promise for realization of complex designs cost effectively, but the obtained material properties require investigation.

binder jetting

designs

material properties


Input: The fields of biomimicry and AM hold a unique synergy and inter-dependence on one another.

biomimicry

AM


Input: 2 True biomimicry True biomimicry of natural form, involves the purposeful emulation of structure-function relationships in biological entities to solve engineering challenges, or to apply these to advanced engineering systems.

biomimicry

biomimicry

biological entities

engineering

engineering


Input: A review on biomimicry and bio-inspiration in the field of AM and 3D printing is provided in and focuses on explaining different potential biological study organisms and associated applications with specific biological input, mostly by polymer AM.

biomimicry

bio-inspiration

AM

3D printing

AM

biological input

polymer


Input: In addition, the review highlights the potential for different forms of AM technologies to mimic nature.

AM technologies

mimic


Input: As mentioned above, the goal of biomimetic research is to learn generic design rules from natural systems to assist the development of optimized biomimetic materials which can be used widely in engineering systems.

As

biomimetic materials

be

biomimetic

design rules

engineering


Input: To illustrate, osteoderms thin plates of dermal bone that form protective natural body armour in various animal species not only play a defensive role, but might also be involved in physiological processes such as thermoregulation.

osteoderms

dermal bone

be

as

processes


Input: The structural changes required for a physiological capacity might decrease the strength of osteoderms, rendering the structure less optimally adapted for protection than what would be expected.

capacity

structure

strength

osteoderms

be


Input: Alternatively, a bio-inspiration approach can be employed to alter specific properties of the natural structure resulting in an optimal design.

bio-inspiration

structure

be

specific properties

design


Input: Glyptodon osteoderms consists of a lattice core sandwiched between two compact layers that form a shell.

osteoderms

lattice core

compact

shell


Input: By printing and testing 3D models with varying lattice and shell parameters, the optimized shell thickness compared to lattice density and lattice strut thickness was revealed.

testing

3D models

lattice

parameters

lattice

shell

shell

lattice density


Input: Similar procedures have been used to reverse-engineer a natural structure for application as a gripping device the Aristotlelantern structure as described in.

structure

structure

as

as


Input: The mechanical properties of natural materials, particularly the superior fracture toughness, make biological structures highly suitable for biomimetic studies.

mechanical properties

materials

fracture

biomimetic studies

biological structures


Input: Nevertheless, a major advantage of AM is that a structure of interest can be further optimized by using materials that do not occur naturally in biological systems.

AM

structure

materials

biological systems

be


Input: In the case of glyptodont osteoderms, the use of biomimetic reverse-engineered metal models show remarkable strength and energy absorption capacity.

osteoderms

biomimetic

metal

strength

energy absorption capacity


Input: Besides material properties, the combination of hard and soft materials has been studied for improved fracture toughness properties using simulation-driven design tools.

material properties

materials

fracture

properties

simulation-driven

design


Input: In a recent study, pangolin scales were used as inspiration for bendable protective material for aerospace applications different combinations of hard plates and soft connecting material were 3D printed and mechanically tested.

as

bendable protective material

material

aerospace

3D printed


Input: Lastly, the microarchitecture of biological structures, which can be categorized as one of eight forms: fibrous, helical, gradient, layered, tubular, cellular, suture and overlapping, plays an important role in determining the mechanical properties of biological materials.

microarchitecture

mechanical properties

biological structures

tubular

be

as

suture

biological materials

fibrous


Input: These structural organizations can be replicated by AM to study and optimize the arrangement of biological materials as discussed in.

be

biological materials

as

AM


Input: Hierarchical structures such as functional graded materials, structures and surfaces can be produced directly by AM or in combination with other methods.

Hierarchical structures

as

be

materials

surfaces

AM


Input: For example, LPBF and femtosecond laser surface modification makes it possible to produce complex hierarchical structures for wettability applications.

LPBF

femtosecond laser

wettability

hierarchical structures


Input: Stereolithography and LPBF was applied for manufacturing of a multi-material arm orthosis; this approach can be used for manufacturing implants where the strength varies throughout the implant.

Stereolithography

LPBF

manufacturing

manufacturing

multi-material

be

implants

implant

strength


Input: In general, AM of in-situ LPBF sintered composite objects also is a form of biomimicry since biological tissues are composite materials with stiff reinforcing elements and binding medium.

AM

sintered

in-situ

biomimicry

composite

biological tissues

composite materials

reinforcing elements


Input: A pivotal tool to characterize structures for biomimicry or bio-inspiration is X-ray micro-computed tomography, as reviewed in.

tool

biomimicry

bio-inspiration

X-ray micro-computed tomography

as


Input: MicroCT is ideally suited to obtain detailed microstructural information of natural structures in 3D, which can be used to directly replicate natural structures, measure 3D design values and implement these in engineering structures as bio-inspiration, or in a broader sense to create a design principle without using any measurements.

MicroCT

microstructural

be

as

3D design values

design

engineering


Input: These three are shown in 3, using the examples of a direct replication of a structure printed on an entry-level FDM printer, a reverse-engineered design based on measurements taken from a natural structure and a generic bio-inspiration example in which honeycomb structures are used as light-weight design.

direct replication

structure

structure

bio-inspiration

FDM printer

design

honeycomb structures

design

as


Input: The main aim of direct replication is to investigate the structure of interest.

direct replication

structure


Input: For reverse-engineering, the goal is similar to that of direct replication, but the techniques make the structure more practical for direct engineering applications.

direct replication

structure

engineering


Input: The generic bio-inspiration involves using design or guidelines from nature, which might be more beneficial when limits are imposed on the structure.

bio-inspiration

limits

structure

design

be


Input: One biological structure that is of particular interest to biomimetic studies, and which has been studied extensively using microCT, is the lightweight structure of bird feathers and bones.

biological structure

biomimetic studies

microCT

lightweight structure

bird feathers


Input: Here, bio-inspiration and design rules might be applied in engineering designs for aerospace applications.

bio-inspiration

design rules

be

engineering

aerospace

designs


Input: In recent work using topology optimization techniques, an optimized light-weight structure for an airplane wing was demonstrated through simulation and optimization, with the obtained structure having a strong resemblance to the structure of bird wing bones, i.e., a solid shell and connecting rods at angles inside the hollow structure.

topology optimization

light-weight

airplane wing

simulation

optimization

structure

structure

structure

shell


Input: While the optimality of bone design had been well described analytically, this was the first example of large-scale computational structure design: the rapid increase in computing power over the last years now allows for obtaining detailed structures from simulation-driven design tools, which for the first time nears the complexity of natural systems.

bone

computational structure design

design

power

simulation-driven

complexity