2006–07 UEFA Cup qualifying rounds

This article details the 2006–07 UEFA Cup qualifying rounds.
Times are CEST , as listed by UEFA (local times, if different, are in parentheses).
Round and draw dates.
All draws held at UEFA headquarters in Nyon, Switzerland.
Matches may also be played on Tuesdays or Wednesdays instead of the regular Thursdays due to scheduling conflicts.
Teams.
Below are the 100 teams involved in the qualifying rounds, grouped by their starting rounds. The 32 winners of the second qualifying round qualified for the first round.
First qualifying round.
Summary.
!colspan="5"|Southern-Mediterranean region
!colspan="5"|Central-East region
!colspan="5"|Northern region
Matches.
"Tirana won 3–1 on aggregate."
"CSKA Sofia won 5–1 on aggregate."
"Litex Lovech won 6–0 on aggregate."
"Sarajevo won 5–0 on aggregate."
"Domžale won 7–0 on aggregate."
"Dinamo București won 9–1 on aggregate."
"APOEL won 7–1 on aggregate."
"Omonia won 4–3 on aggregate."
"Lokomotiv Sofia won 3–1 on aggregate."
"Roeselare won 7–2 on aggregate."
"Rapid București won 6–0 on aggregate."
"Vaduz won 4–1 on aggregate."
"Zimbru Chișinău won 3–2 on aggregate."
"Young Boys won 4–1 on aggregate."
"2–2 on aggregate; Videoton won on away goals."
"1–1 on aggregate; Dinamo Minsk won on away goals."
"Karvan won 2–0 on aggregate."
"2–2 on aggregate; Ameri won on away goals."
"BATE won 3–0 on aggregate."
"Basel won 3–1 on aggregate."
"Artmedia won 3–2 on aggregate."
"Drogheda United won 4–2 on aggregate."
"Brøndby won 3–1 on aggregate."
"Llanelli won 2–1 on aggregate."
"Skonto won 5–0 on aggregate."
"Åtvidaberg won 7–0 on aggregate."
"Ventspils won 4–1 on aggregate."
"Brann won 2–0 on aggregate."
"2–2 on aggregate; Randers won on away goals."
"Kaunas won 4–1 on aggregate."
"Sūduva won 2–1 on aggregate."
"Levadia Tallinn won 2–1 on aggregate."
"Start won 4–0 on aggregate."
"1–1 on aggregate; Flora Tallinn won on away goals."
"Derry City won 2–0 on aggregate."
Second qualifying round.
Summary.
!colspan="5"|Southern-Mediterranean region
!colspan="5"|Central-East region
!colspan="5"|Northern region
Matches.
"Trabzonspor won 2–1 on aggregate."
"Hapoel Tel Aviv won 4–2 on aggregate."
"1–1 on aggregate; CSKA Sofia won on away goals."
"Ethnikos Achna won 6–2 on aggregate."
"Auxerre won 5–2 on aggregate."
"Dinamo București won 2–1 on aggregate."
"Partizan won 3–2 on aggregate."
"Rapid București won 2–1 on aggregate."
"Lokomotiv Sofia won 6–0 on aggregate."
"Litex Lovech won 2–1 on aggregate."
"Kayserispor won 5–1 on aggregate."
"Artmedia won 5–3 on aggregate."
"Sion won 1–0 on aggregate."
"Grasshoppers won 3–1 on aggregate."
"Slavia Prague won 2–0 on aggregate."
"1–1 on aggregate; Chornomorets Odesa won on away goals."
"2–2 on aggregate; Basel won on away goals."
"Metalurh Zaporizhya won 3–0 on aggregate."
"Wisła Kraków won 2–1 on aggregate."
"Hertha BSC won 3–2 on aggregate."
"Rubin Kazan won 5–0 on aggregate."
"3–3 on aggregate; Marseille won on away goals."
"1–1 on aggregate; Start won 11–10 on penalties"
"Odense won 6–1 on aggregate."
"Randers won 3–2 on aggregate."
"Levadia Tallinn won 2–1 on aggregate."
"Newcastle United won 1–0 on aggregate."
"4–4 on aggregate; Åtvidaberg won on away goals."
"Molde won 2–1 on aggregate."
"Brøndby won 4–0 on aggregate."
"Club Brugge won 7–2 on aggregate."
"Derry City won 7–3 on aggregate."


Rolled throughput yield

Rolled throughput yield (RTY) in production economics is the probability that a process with more than one step will produce a defect free unit. It is the product of yields for each process step of the entire process.
For any process, it is ideal for that process to produce its product without defects and without rework. Rolled throughput yield quantifies the cumulative effects of inefficiencies found throughout the process. Rolled throughput yield and rolled throughput yield loss (RTYL) are often used in Six Sigma.


Vibratory stress relief

Vibratory Stress Relief, often abbreviated VSR, is a non-thermal stress relief method used by the metal working industry to enhance the dimensional stability and mechanical integrity of castings, forgings, and welded components, chiefly for two categories of these metal workpieces:
This stress is called "residual stress", because it remains in a solid material after the original cause of the stress has been removed. Residual stresses can occur through a variety of mechanisms including inelastic (plastic) deformations, temperature gradients (during thermal cycle), or structural changes (phase transformation). For example, heat from welding may cause localized expansion, which is taken up during welding by either the molten metal or the placement of parts being welded. When the finished weldment cools, some areas cool and contract more than others, leaving residual stresses. These stresses often lead to distortion or warping of the structure during machining, assembly, testing, transport, field-use or over time. In extreme cases, residual stress can cause structural failure.
Almost all vibratory stress relief equipment manufacturers and procedures use the workpiece's own resonant frequency to boost the loading experienced by induced vibration, so to maximize the degree of stress relief achieved. Some equipment and procedures are designed to operate near, but not at, workpiece resonances (perhaps to extend equipment life) example WIAP research, but independent research has consistently shown resonant frequency vibration to be more effective. "See references 4, 6, and 9."
The effectiveness of vibratory stress relief is highly questionable. In general, the strain amplitudes achieved during vibratory stress relief are too low to exceed the critical stress required to activate mechanical relaxation during the induced low amplitude high cycle fatigue excitation of the transducer vibrations. If the strain amplitudes were increased to a level sufficient to cause instability in the residual stresses, fatigue damage would occur. For most applications, conventional stress relief methodologies should be applied to components that require the reduction of residual stresses.
Criteria for effective VSR treatment.
Effective vibratory stress relief treatment results from a combination of factors:
Each of these changes, which often combine, i.e., peak growth AND shifting, is consistent with a lowering of the rigidity of the workpiece. The workpiece rigidity is inflated by the presence of residual stress. In the example below, which depicts a common resonance pattern change that occurs during vibratory stress relief, the large peak grew by 47%, while simultaneously shifting to the left 28-RPM, which is less than 0.75%. "See Figure 4."
The equipment used to perform this stress relief had vibrator speed regulation of ± 0.02%, and speed increment fine-tuning of 1-RPM, which allowed even subtle shifting of the peaks to be accurately tracked to their final, stable locale.
The pattern of change, i.e., how quickly the peaks grow and shift, is faster at the beginning of vibration treatment: As treatment continues, the rate of change decreases, eventually resulting in a new, stable resonance pattern. Stability of this new resonance pattern indicates that dimensional stability of the workpiece has been achieved.
The power plot is useful in both positioning and orienting the vibrator, and when adjusting the vibrator unbalance. Poor or inappropriate vibrator locations or orientations, or excessive vibrator unbalance settings, cause large peaks in the power plot. Use of higher-powered vibrator motors (above 2-kW) provides more "head-room" for peaks in power to be tolerated, and treatment to take place, which was the case here: The power peak at ≈ 3700-RPM was only half of the vibrator motor's 2.3-kW power capacity (top of the power scale).
A "Pre-Treatment Scan", which functions as a base-line, is first recorded in green. The operator uses this green data set to tune upon the resonances, and monitor the growth and shifting of the resonance peaks. After peak growth and shifting have subsided, a "Post-Treatment Scan" is made (red). This data is superimposed on the original, green, Pre-Treatment Scan data, documenting the changes in resonance pattern. The stress relief treatment resulted in 47% growth of the original, large peak, while it shifted to the left 28-RPM (less than 0.75%).
After stress relief treatment, the braces (rust-colored, structural beams), which are used to maintain the desired shape during welding, were removed. The spacing between the two "arms" remained the same; no change was detectable (measured to 1/32" or less than 1 mm), and the spacing remained so throughout assembly, testing (to 60 ton test loads), transport, and installation.
When should VSR be considered and the limits of TSR.
VSR is not accepted by the Engineering community at large as a viable method of relaxing or reducing residual stresses in components that require it. For general use, conventional residual stress relaxation methodologies are recommended.
Historically, the first type of stress relief was performed on castings by storing them outside for months or even years. This was referred to as "curing", a term used for long-term storage of freshly hewn wood. Fresh castings were referred to as being green, meaning, they were prone to distortion during precision machining, just as "green" wood bows during cutting.
Later, thermal stress relief (TSR) was developed to alleviate the lengthy time requirements of curing. It has been known for many years, however, that TSR has limitations or shortcomings, specifically:
Metal components, whose function would be enhanced by stress relief, and fall into one or more of the above categories, are strong candidates for VSR for quality-related reasons.
Further, there is a strong economic incentive to use vibratory stress relief on large workpieces, since stress relief using a furnace (thermal stress relief or TSR) is highly energy-intensive; consuming much natural gas, and hence, producing much CO2. The cost of TSR is approximately proportional to a metal component's weight or overall size, estimated to be US$2,500 for the structure pictured, plus transportation costs, which might involve special transport permits, to and from a furnace. VSR Treatment would cost a company owning appropriate equipment less than 15% as much ( ≈ $400 ) as TSR Treatment, chiefly amortization of equipment investment plus labor, and a modest amount of electrical consumption, and treatment would take less than two hours, with no transport required. However, the lack of independent data to show that this technique is effective may mean that even that lesser investment is not of any value, so use of VSR should evaluated very carefully before proceeding.
References.
PDF D. Rao, J. Ge, and L. Chen, "Vibratory Stress Relief in the Manufacturing the Rails of a Maglev System, J. of Manufacturing Science and Engineering," 126, Issue 2, 388-391 (2004)
PDF B.B. Klauba, C.M. Adams, J.T. Berry, "Vibratory Stress Relief: Methods Used to Monitor and Document Effective Treatment, A Survey of Users, and Directions for Further Research, Proc. of ASM, 7th International Conference: Trends in Welding Research" 601-606 (2005)
PDF Y. Yang, G. Jung, and R. Yancey, "Finite Element Modeling of Vibratory Stress Relief after Welding, Proc of ASM, 7th International Conference; Trends in Welding Research" 547-552 (2005)


Cellulose electrode

A cellulose electrode is a welding electrode that has a coating containing organic materials. About 30% of the coating weight is cellulose.
In some countries, paper pulp and wood powder are added to the coating in certain ratios to reduce the amount of pure cellulose.
The organic compounds in the coating decompose in the arc to form carbon monoxide, carbon dioxide and hydrogen, which increase the arc tension and thus, the welding arc becomes stronger and harder. Compared with other types of electrodes, with the same current values, a 70% deeper penetration can be obtained with cellulose electrodes.
This type of electrode is generally produced with thin or medium coating thicknesses. When the coating is thin, a light amount of slag is formed on the welding bead and the spatter loss is high. On the other hand, the gap filling and vertical down welding capability as well as penetration of the weld obtained by this electrode is good.
Since this electrode can be used in every position (particularly in vertical down), it has a wide range of applications in the ship building industry and in the welding of pipelines with a wall thickness of less than 12.5 mm. The cellulose that burns during welding forms a very good protective gaseous atmosphere.
Application.
The main features of cellulose electrodes are as follows:
The titanium compounds in the coating provide arc stability as well as help clean the slag easily. Adding a certain amount of ferromanganese to the coating makes it possible to compensate for the manganese that is lost through oxidation during welding and to deoxidize the weld pool. Since these electrodes are generally manufactured using a sodium silicate binder, they can best be used with DC(+) polarity.


Panos Kouvelis

Panos (Panagiotis) Kouvelis is the Emerson Distinguished Professor of Supply Chain, Operations, and Technology and director of "The Boeing Center for Supply Chain Innovation" at the Olin Business School at Washington University in St. Louis. He is best known for his work on supply chain management, supply chain finance, operational excellence, and risk management.
Early life and education.
Kouvelis was born in Greece. After graduating from National Technical University of Athens in 1983, he moved to the United States, where he went on to earn his MBA and MS from the Marshall School of Business at the University of Southern California. In 1988, he earned his PhD from the Management Science and Engineering department at Stanford University.
Career.
Kouvelis served as an assistant professor at the University of Texas at Austin from 1988 to 1991 and an associate professor at Duke University's Fuqua School of Business from 1992 to 1997. He visited Washington University in St. Louis from 1996 to 1997, where he accepted a full professor position in 1997. He was installed as the inaugural Emerson Distinguished Professor of Operations and Manufacturing Management in 2000. Kouvelis served as the senior associate dean and director of executive programs at the Olin Business School from 2009 to 2013, as well as area chair of the Operations and Manufacturing Management department from 2005 to 2009. He has accepted visiting professorships at the WHU-Otto Beisheim School of Management, the University of Chicago, and Hong Kong Polytechnic University.
Kouvelis is an editor for the journals Production & Operations Management, Manufacturing and Service Operations Management, and "Foundations and Trends in Technology, Information and Operations Management".
The Boeing Center for Supply Chain Innovation.
Kouvelis was a founding co-director of The Boeing Center for Technology, Information, and Manufacturing in 1997. He became the director of the center in 2000, and continues to direct it. The center was renamed to "The Boeing Center for Supply Chain Innovation". (BCSCI) in 2016.


Single-machine scheduling

Single-machine scheduling or single-resource scheduling is an optimization problem in computer science and operations research. We are given "n" jobs "J"1, "J"2, ..., "Jn" of varying processing times, which need to be scheduled on a single machine, in a way that optimizes a certain objective, such as the throughput.
Single-machine scheduling is a special case of identical-machines scheduling, which is itself a special case of optimal job scheduling. Many problems, which are NP-hard in general, can be solved in polynomial time in the single-machine case.
In the standard three-field notation for optimal job scheduling problems, the single-machine variant is denoted by 1 in the first field. For example, " 1||formula_1" is an single-machine scheduling problem with no constraints, where the goal is to minimize the sum of completion times.
The makespan-minimization problem 1||formula_2, which is a common objective with multiple machines, is trivial with a single machine, since the makespan is always identical. Therefore, other objectives have been studied.
Minimizing the sum of completion times.
The problem 1||formula_1 aims to minimize the sum of completion times. It can be solved optimally by the Shortest Processing Time First rule (SPT): the jobs are scheduled by ascending order of their processing time formula_4.
The problem 1||formula_5 aims to minimize the "weighted" sum of completion times. It can be solved optimally by the Weighted Shortest Processing Time First rule (WSPT): the jobs are scheduled by ascending order of the ratio formula_6.
The problem 1|chains|formula_5 is a generalization of the above problem for jobs with dependencies in the form of chains. It can also be solved optimally by a suitable generalization of WSPT.
Minimizing the cost of lateness.
The problem 1||formula_8 aims to minimize the maximum "lateness". For each job "j", there is a due date formula_9. If it is completed after its due date, it suffers "lateness" defined as formula_10. 1||formula_8 can be solved optimally by the Earliest Due Date First rule (EDD): the jobs are scheduled by ascending order of their deadline formula_9.
The problem 1|prec|formula_13 generalizes the 1||formula_8 in two ways: first, it allows arbitrary precedence constraints on the jobs; second, it allows each job to have an arbitrary cost function "hj", which is a function of its completion time (lateness is a special case of a cost function). The maximum cost can be minimized by a greedy algorithm known as Lawler's algorithm.
The problem 1|formula_15|formula_8 generalizes 1||formula_8 by allowing each job to have a different "release time" by which it becomes available for processing. The presence of release times means that, in some cases, it may be optimal to leave the machine idle, in order to wait for an important job that is not released yet. Minimizing maximum lateness in this setting is NP-hard. But in practice, it can be solved using a branch-and-bound algorithm.
Maximizing the profit of earliness.
In settings with deadlines, it is possible that, if the job is completed by the deadline, there is a profit "pj". Otherwise, there is no profit. The goal is to maximize the profit. Single-machine scheduling with deadlines is NP-hard; Sahni presents both exact exponential-time algorithms and a polynomial-time approximation algorithm.
Maximizing the throughput.
The problem 1||formula_18 aims to minimize the "number" of late jobs, regardless of the amount of lateness. It can be solved optimally by the Hodgson-Moore algorithm. It can also be interpreted as maximizing the number of jobs that complete on time; this number is called the throughput.
The problem 1||formula_19 aims to minimize the "weight" of late jobs. It is NP-hard, since the special case in which all jobs have the same deadline (denoted by 1|formula_20|formula_19 ) is equivalent to the Knapsack problem.
The problem 1|formula_15|formula_18 generalizes 1||formula_18 by allowing different jobs to have different "release times". The problem is NP-hard. However, when all job lengths are equal, the problem can be solved in polynomial time. It has several variants:
Jobs can have "execution intervals". For each job "j", there is a processing time "tj" and a start-time "sj", so it must be executed in the interval ["sj," "sj+tj"]. Since some of the intervals overlap, not all jobs can be completed. The goal is to maximize the number of completed jobs, that is, the throughput. More generally, each job may have several possible intervals, and each interval may be associated with a different profit. The goal is to choose at most one interval for each job, such that the total profit is maximized. For more details, see the page on interval scheduling.
More generally, jobs can have "time-windows", with both start-times and deadlines, which may be larger than the job length. Each job can be scheduled anywhere within its time-window. Bar-Noy, Bar-Yehuda, Freund, Naor and Schieber present a (1-"ε")/2 approximation.
See also.
Many solution techniques have been applied to solving single machine scheduling problems. Some of them are listed below.


Domínguez & Cía

Domínguez & Cía (BVC: DOM) is a Venezuelan company based in Caracas, founded in 1930. It is a manufacturer of plastic containers, aluminium and tin cans, and cardboard packaging.


Expandable microsphere

Expandable microspheres are microscopic spheres comprising a thermoplastic shell encapsulating a low boiling point liquid hydrocarbon. When heated to a temperature high enough to soften the thermoplastic shell, the increasing pressure of the hydrocarbon will cause the microsphere to expand. The volume can increase by 60 to 80 times.
Expandable microsphere.
The expandable microsphere is a material that can act as a blowing agent when mixed in a product and subsequently heated to cause expansion within the matrix.
The expandable microspheres are off-white, can be 6 to 40 micrometers in average diameter and have a density of 900 to 1400 kg/m3.
The expandable microspheres are used as a blowing agent in products like e.g. puff ink, automotive underbody coatings or injection molding of thermoplastics. Here the product must be heated at some point in the process for the expandable microspheres to expand.
Expanded microsphere.
The expanded microsphere is a material that has been heated to cause expansion. The product acts as a light weight filler in many products.
The expanded microspheres are white, can be 15 to 90 micrometers in average diameter and can have a density of 15 to 70 kg/m3.
The expanded microspheres are used as a lightweight filler in composite materials such as cultured marble, in waterborne paints and crack fillers/joint compound.
Characteristics.
Characteristics that make expandable microspheres unique,


Solder

Solder (; NA: ) is a fusible metal alloy used to create a permanent bond between metal workpieces. Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces after cooling. Metals or alloys suitable for use as solder should have a lower melting point than the pieces to be joined. The solder should also be resistant to oxidative and corrosive effects that would degrade the joint over time. Solder used in making electrical connections also needs to have favorable electrical characteristics.
Soft solder typically has a melting point range of , and is commonly used in electronics, plumbing, and sheet metal work. Alloys that melt between are the most commonly used. Soldering performed using alloys with a melting point above is called "hard soldering", "silver soldering", or brazing.
In specific proportions, some alloys are eutectic — that is, the alloy's melting point is the lowest possible for a mixture of those components, and coincides with the freezing point. Non-eutectic alloys can have markedly different "solidus" and "liquidus" temperatures, as they have distinct liquid and solid transitions. Non-eutectic mixtures often exist as a paste of solid particles in a melted matrix of the lower-melting phase as they approach high enough temperatures. In electrical work, if the joint is disturbed while in this "pasty" state before it fully solidifies, a poor electrical connection may result; use of eutectic solder reduces this problem. The pasty state of a non-eutectic solder can be exploited in plumbing, as it allows molding of the solder during cooling, e.g. for ensuring watertight joint of pipes, resulting in a so-called "wiped joint".
For electrical and electronics work, solder wire is available in a range of thicknesses for hand-soldering (manual soldering is performed using a soldering iron or soldering gun), and with cores containing flux. It is also available as a room temperature paste, as a preformed foil shaped to match the workpiece which may be more suited for mechanized mass-production, or in small "tabs" that can be wrapped around the joint and melted with a flame where an iron isn't usable or available, as for instance in field repairs. Alloys of lead and tin were commonly used in the past and are still available; they are particularly convenient for hand-soldering. Lead-free solders have been increasing in use due to regulatory requirements plus the health and environmental benefits of avoiding lead-based electronic components. They are almost exclusively used today in consumer electronics.
Plumbers often use bars of solder, much thicker than the wire used for electrical applications, and apply flux separately; many plumbing-suitable soldering fluxes are too corrosive (or conductive) to be used in electrical or electronic work. Jewelers often use solder in thin sheets, which they cut into snippets.
Etymology.
The word solder comes from the Middle English word , via Old French and , from the Latin , meaning "to make solid".
Composition.
Lead-based.
Tin-lead (Sn-Pb) solders, also called "soft solders", are commercially available with tin concentrations between 5% and 70% by weight. The greater the tin concentration, the greater the solder's tensile and shear strengths. Lead mitigates the formation of tin whiskers, though the precise mechanism for this is unknown. Today, many techniques are used to mitigate the problem, including changes to the annealing process (heating and cooling), addition of elements like copper and nickel, and the application of conformal coatings. Alloys commonly used for electrical soldering are 60/40 Sn-Pb, which melts at , and 63/37 Sn-Pb used principally in electrical/electronic work. The latter mixture is a eutectic alloy of these metals, which:
In the United States, since 1974, lead is prohibited in solder and flux in plumbing applications for drinking water use, per the Safe Drinking Water Act. Historically, a higher proportion of lead was used, commonly 50/50. This had the advantage of making the alloy solidify more slowly. With the pipes being physically fitted together before soldering, the solder could be wiped over the joint to ensure water tightness. Although lead water pipes were displaced by copper when the significance of lead poisoning began to be fully appreciated, lead solder was still used until the 1980s because it was thought that the amount of lead that could leach into water from the solder was negligible from a properly soldered joint. The electrochemical couple of copper and lead promotes corrosion of the lead and tin. Tin, however, is protected by insoluble oxide. Since even small amounts of lead have been found detrimental to health as a potent neurotoxin, lead in plumbing solder was replaced by silver (food-grade applications) or antimony, with copper often added, and the proportion of tin was increased (see lead-free solder).
The addition of tin—more expensive than lead—improves wetting properties of the alloy; lead itself has poor wetting characteristics. High-tin tin-lead alloys have limited use as the workability range can be provided by a cheaper high-lead alloy.
Lead-tin solders readily dissolve gold plating and form brittle intermetallics.
60/40 Sn-Pb solder oxidizes on the surface, forming a complex 4-layer structure: tin(IV) oxide on the surface, below it a layer of tin(II) oxide with finely dispersed lead, followed by a layer of tin(II) oxide with finely dispersed tin and lead, and the solder alloy itself underneath.
Lead, and to some degree tin, as used in solder contains small but significant amounts of radioisotope impurities. Radioisotopes undergoing alpha decay are a concern due to their tendency to cause soft errors. Polonium-210 is especially troublesome; lead-210 beta decays to bismuth-210 which then beta decays to polonium-210, an intense emitter of alpha particles. Uranium-238 and thorium-232 are other significant contaminants of alloys of lead.
Lead-free.
The European Union Waste Electrical and Electronic Equipment Directive and Restriction of Hazardous Substances Directive were adopted in early 2003 and came into effect on July 1, 2006, restricting the inclusion of lead in most consumer electronics sold in the EU, and having a broad effect on consumer electronics sold worldwide. In the US, manufacturers may receive tax benefits by reducing the use of lead-based solder. Lead-free solders in commercial use may contain tin, copper, silver, bismuth, indium, zinc, antimony, and traces of other metals. Most lead-free replacements for conventional 60/40 and 63/37 Sn-Pb solder have melting points from 50 to 200 °C higher, though there are also solders with much lower melting points. Lead-free solder typically requires around 2% flux by mass for adequate wetting ability.
When lead-free solder is used in wave soldering, a slightly modified solder pot may be desirable (e.g. titanium liners or impellers) to reduce maintenance cost due to increased tin-scavenging of high-tin solder.
Lead-free solder is prohibited in critical applications, such as aerospace, military and medical projects, because joints are likely to suffer from metal fatigue failure under stress (such as that from thermal expansion and contraction). Although this is a property that conventional leaded solder possess (like any metal), the point at which stress fatigue can possibly occur is substantially above the level of stresses normally encountered. Lead free solder, by contrast, will always fail eventually regardless of how low a level of stress is encountered.
Tin-silver-copper (Sn-Ag-Cu, or "SAC") solders are used by two-thirds of Japanese manufacturers for reflow and wave soldering, and by about 75% of companies for hand soldering. The widespread use of this popular lead-free solder alloy family is based on the reduced melting point of the Sn-Ag-Cu ternary eutectic behavior , which is below the 22/78 Sn-Ag (wt.%) eutectic of and the 99.3/0.7 Sn-Cu eutectic of . The ternary eutectic behavior of Sn-Ag-Cu and its application for electronics assembly was discovered (and patented) by a team of researchers from Ames Laboratory, Iowa State University, and from Sandia National Laboratories-Albuquerque.
Much recent research has focused on the addition of a fourth element to Sn-Ag-Cu solder, in order to provide compatibility for the reduced cooling rate of solder sphere reflow for assembly of ball grid arrays. Examples of these four-element compositions are 18/64/14/4 tin-silver-copper-zinc (Sn-Ag-Cu-Zn) (melting range 217–220 °C) and 18/64/16/2 tin-silver-copper-manganese (Sn-Ag-Cu-Mn; melting range of 211–215 °C).
Tin-based solders readily dissolve gold, forming brittle intermetallic joins; for Sn-Pb alloys the critical concentration of gold to embrittle the joint is about 4%. Indium-rich solders (usually indium-lead) are more suitable for soldering thicker gold layer as the dissolution rate of gold in indium is much slower. Tin-rich solders also readily dissolve silver; for soldering silver metallization or surfaces, alloys with addition of silvers are suitable; tin-free alloys are also a choice, though their wettability is poorer. If the soldering time is long enough to form the intermetallics, the tin surface of a joint soldered to gold is very dull.
Hard solder.
Hard solders are used for brazing, and melt at higher temperatures. Alloys of copper with either zinc or silver are the most common.
In silversmithing or jewelry making, special hard solders are used that will pass assay. They contain a high proportion of the metal being soldered and lead is not used in these alloys. These solders vary in hardness, designated as "enameling", "hard", "medium" and "easy". Enameling solder has a high melting point, close to that of the material itself, to prevent the joint desoldering during firing in the enameling process. The remaining solder types are used in decreasing order of hardness during the process of making an item, to prevent a previously soldered seam or joint desoldering while additional sites are soldered. Easy solder is also often used for repair work for the same reason. Flux is also used to prevent joints from desoldering.
Silver solder is also used in manufacturing to join metal parts that cannot be welded. The alloys used for these purposes contain a high proportion of silver (up to 40%), and may also contain cadmium.
Alloys.
Different elements serve different roles in the solder alloy:
Impurities.
Impurities usually enter the solder reservoir by dissolving the metals present in the assemblies being soldered. Dissolving of process equipment is not common as the materials are usually chosen to be insoluble in solder.
Board finishes vs wave soldering bath impurities buildup:
Flux.
Flux is a reducing agent designed to help reduce (return oxidized metals to their metallic state) metal oxides at the points of contact to improve the electrical connection and mechanical strength. The two principal types of flux are acid flux (sometimes called "active flux"), containing strong acids, used for metal mending and plumbing, and rosin flux (sometimes called "passive flux"), used in electronics. Rosin flux comes in a variety of "activities", corresponding roughly to the speed and effectiveness of the organic acid components of the rosin in dissolving metallic surface oxides, and consequently the corrosiveness of the flux residue.
Due to concerns over atmospheric pollution and hazardous waste disposal, the electronics industry has been gradually shifting from rosin flux to water-soluble flux, which can be removed with deionized water and detergent, instead of hydrocarbon solvents. Water-soluble fluxes are generally more conductive than traditionally used electrical / electronic fluxes and so have more potential for electrically interacting with a circuit; in general it is important to remove their traces after soldering. Some rosin type flux traces likewise should be removed, and for the same reason.
In contrast to using traditional bars or coiled wires of all-metal solder and manually applying flux to the parts being joined, much hand soldering since the mid-20th century has used flux-core solder. This is manufactured as a coiled wire of solder, with one or more continuous bodies of inorganic acid or rosin flux embedded lengthwise inside it. As the solder melts onto the joint, it frees the flux and releases that on it as well.
Operation.
The solidifying behavior depends on the alloy composition. Pure metals solidify at a certain temperature, forming crystals of one phase. Eutectic alloys also solidify at a single temperature, all components precipitating simultaneously in so-called coupled growth. Non-eutectic compositions on cooling start to first precipitate the non-eutectic phase; dendrites when it is a metal, large crystals when it is an intermetallic compound. Such a mixture of solid particles in a molten eutectic is referred to as a mushy state. Even a relatively small proportion of solids in the liquid can dramatically lower its fluidity.
The temperature of total solidification is the solidus of the alloy, the temperature at which all components are molten is the liquidus.
The mushy state is desired where a degree of plasticity is beneficial for creating the joint, allowing filling larger gaps or being wiped over the joint (e.g. when soldering pipes). In hand soldering of electronics it may be detrimental as the joint may appear solidified while it is not yet. Premature handling of such joint then disrupts its internal structure and leads to compromised mechanical integrity.
Intermetallics.
Many different intermetallic compounds are formed during solidifying of solders and during their reactions with the soldered surfaces. The intermetallics form distinct phases, usually as inclusions in a ductile solid solution matrix, but also can form the matrix itself with metal inclusions or form crystalline matter with different intermetallics. Intermetallics are often hard and brittle. Finely distributed intermetallics in a ductile matrix yield a hard alloy while coarse structure gives a softer alloy. A range of intermetallics often forms between the metal and the solder, with increasing proportion of the metal; e.g. forming a structure of . Layers of intermetallics can form between the solder and the soldered material. These layers may cause mechanical reliability weakening and brittleness, increased electrical resistance, or electromigration and formation of voids. The gold-tin intermetallics layer is responsible for poor mechanical reliability of tin-soldered gold-plated surfaces where the gold plating did not completely dissolve in the solder.
Two processes play a role in a solder joint formation: interaction between the substrate and molten solder, and solid-state growth of intermetallic compounds. The base metal dissolves in the molten solder in an amount depending on its solubility in the solder. The active constituent of the solder reacts with the base metal with a rate dependent on the solubility of the active constituents in the base metal. The solid-state reactions are more complex – the formation of intermetallics can be inhibited by changing the composition of the base metal or the solder alloy, or by using a suitable barrier layer to inhibit diffusion of the metals.
Some example interactions include:
Preform.
A preform is a pre-made shape of solder specially designed for the application where it is to be used. Many methods are used to manufacture the solder preform, stamping being the most common. The solder preform may include the solder flux needed for the soldering process. This can be an internal flux, inside the solder preform, or external, with the solder preform coated.
Similar substances.
Glass solder is used to join glasses to other glasses, ceramics, metals, semiconductors, mica, and other materials, in a process called glass frit bonding. The glass solder has to flow and wet the soldered surfaces well below the temperature where deformation or degradation of either of the joined materials or nearby structures (e.g., metallization layers on chips or ceramic substrates) occurs. The usual temperature of achieving flowing and wetting is between .


Spin welding of polymers

Spin welding is a form of friction welding used to join thermoplastic parts. The parts to be welded must be round, and in plane with each other. Like all other welding methods this process utilizes heat, time, and pressure to create a weld joint. Heat is generated via internal friction generated between the two parts when rotating and subjected to a load normal to the weld joint. This frictional heat causes the plastic to melt and a bond to be created.
Due to this process's high speeds, and high repeat ability it is favored for a high production environment. This process was initially used to weld plastic compasses under a liquid to allow the internal parts of the compass to be filled with the liquid, but it is used in a very wide range of industries and applications.
Spin welding equipment.
Spin welding machines come in two different types an inertia welding machine, and a continuous drive machine. In general, one of the parts to be welded is clamped in place, while the other is rotated. Spin welding machines consist of two tool fixtures; fixed tooling, and a driven tooling.
Tooling.
The tooling in the spin welding machine provides support for the materials being joined while under heat and pressure. Tooling can be made of metal, such as aluminum, or epoxy molding compounds depending on how the tooling will be used. Guards may be incorporated into the tooling to prevent molten material or parts from being ejected.
Lower tooling.
The lower tooling, sometimes referred to as the "nest", supports one of the parts to be welded. The part is usually placed in the nest with the walls supporting the component as close to the joint as possible to prevent distortion of the part during joining.
Upper tooling.
Depending on the design of the machine, the upper tooling may hold a part to be joined or simply apply the necessary pressure and impart rotation to one of the parts being joined. For parts that held in place by the upper tooling prior to the start of welding, press fitting the part will prevent dropping prior to welding. Drive pins, serrations, or a grit blasted finish may be used to help the upper tooling impart rotational force on the part.
Inertia welding machines.
Inertia welding machines use a motor to spin the parts to a set RPM, and then disengages the motor and relies on the internal friction of the parts to slow down the machine again. The inertial energy contained in the machine's flywheel is transferred to the weld interface through the parts. There are also two different designs for inertia welding machines. One such design disengages the clamped part, and allows the whole part to rotate until slowing to a stop, while another allows the parts to continue to rotate until cooling and solidification stops the rotation.
Continuous drive welding machines.
Continuous drive machines operate under the same principle of using a motor to spin the part up to a user determined RPM, but instead of disengaging the drive when welding begins it continues to spin the part through the whole welding cycle. The rotation is stopped via a mechanical braking system that halts the machine either gradually or instantly, this depends on the system.
Process steps.
This section outlines the overall steps of the spin welding process. This is a description of what is might be observed in a production setting when using the spin welding process.
Part preparation and loading.
Normally parts are loaded into a holding fixture. The parts may be placed in the base of the welding machine or for larger assemblies, one half may be placed in the upper fixture of the welding machine. This process can be accomplished in 2 to 5 seconds when manually loading parts
Press actuation.
The drive motors are activated, and begin to spin The speed of the drive motors can vary, based on the application, from 200 to 14,000 rpm, with a normal speed of 2,000 rpm. The drives then engage the part to be welded. This step normally only takes 1 to 2 seconds.
Welding.
The welding step consists of four main sub-steps which describe how the heat generated from friction melts the parts at their interface. These steps can be described as follows:
Phase 1.
Friction between parts begins due to rotation from motor and the downward pressure. Heat is generated until the glass transition temperature, for amorphous polymers or the melting temperature, for semicrystalline polymers, is reached.
Phase 2.
Part melting begins; material is melted and part of the melted material is extruded into the "flash".
Phase 3.
A steady state is reached between the melt layer and the amount of material squeezed into the flash. The spinning is then stopped.
Phase 4.
While the joint cools, the parts are held in contact with each other, under pressure. This ensures a solid mating at the joint while the molten material cools.
Phases 1 through 3 are usually completed in 0.5 to 2 seconds, with an additional 1 to 2 seconds required for Phase 4.
Part removal.
After weld solidification, parts are removed and any required post processing is conducted to remove the flash. Step 4 normally takes 2 to 5 seconds to complete.
Joint design.
When designing a weld joint, multiple factors are considered. Some examples of those factors include: desired weld strength, geometry of the parts, material being welded, cosmetic of the joint, whether post processing is an option or not. It is important to balance all of these factors to achieve the optimal final part.
In spin welding the most consistent variable is that at least one of the parts needs to be circular for this process to be effective. The simplest joint design in most processes, spin welding included, is a butt joint. This can be used when final part flash is acceptable, this is because there will always be internal flash as well as external flash. A separate process will need to be conducted to remove said flash, and often time the internal flash will be impossible to remove. Due to this, alternative geometries can be used that incorporate flash traps.
Other joints often utilize self-centering geometries such as angled faces, which act as pre-weld sites, and also increase the overall welding area of the joint. Also of note is the fact that when using this form of weld joint a flash trap will be difficult to utilize.
Heat generation.
Spin welding utilizes internal heat generation which is created from friction between the two parts being welded. In its simplest form spin welding utilizes three input parameters to vary the welding process. These three parameters can be varied to change the heat generation rate as well. Parameters include: weld RPM, weld pressure, and weld time. Alternatively, other factors such as cooing time, displacement, and braking speed are possible parameters that can be altered depending on the system.
Welding time.
Welding time is defined as how long the parts are rotated while in contact. While welding time does not directly affect the overall heat generation rate, it is an influential factor on how much overall heat is generated throughout the welding process. Usually when utilizing this process there is a threshold time that is necessary to reach a steady state for heat generation. This steady state is defined by when the amount of material melted is equal to the amount of material expelled by the welding pressure. To achieve a quality weld this steady state must be reached for a uniform melt layer.
Weld rotations per minute (RPM).
The most influential factor when trying to increase heat generation or generation rate is the welding RPM. Several experiments have been conducted, and in general the higher the RPM of the part the more heat that will be generated. This combined with welding time will help to determine the overall heat generated in the weld.
Generally, rotation speeds can be varied between 200-14000 RPM depending on the part and application. RPM is the main input parameter to determine heat generation in the part.
When using an inertia spin welding consideration must also be given to the run up time in order to ensure that the drive head is operating at the proper speed prior to engaging the parts.
When using direct-drive spin welding an optimum RPM should be chosen based on the optimal linear speed of the materials being joined. The required RPM can be calculated using the following equation:
formula_1
Weld pressure.
Pressure also plays a role in heat generation, it is normally a secondary parameter. In general, the higher the pressure the more heat that is generated during welding. This is due to the increase in friction by increasing contact between the parts, this falls off when the pressures become so high that the parts are unable to rotate. [Thermoplastic welding will normally use weld pressures between 72.5 psi and 290 psi.
Welding pressure is a parameter determined by the size and area of the part being welded, larger parts require higher pressures to reach the required amount of part upset.
Mathematical analysis of heat generation.
During the spin welding process there are two main phases for heat generation. The initial phase, or the solid phase is when the bulk of the heating in the part is caused by the two solid parts rubbing against one another. The heat generation can be modeled by the following:
formula_2
Where q is the heat generation rate, f is the coefficient of friction, r is the radius of the parts being welded, and ω is related to rpm by the following:
formula_3
Where Ω is the RPM of the parts being welded.
The Second phase of heat generation is phase 3 of the weld, or the steady-state phase. This is the phase of the process where there is a constant film of molten plastic at the interphase, and viscous heating is dominant. The heat generation can be modeled by the following:
formula_4
Where is the viscosity of the molten polymer, r is the part radius, ω is related to the RPM as above, and 2h is the thickness of the melt layer.
Materials.
The spin welding process can adequately join almost all thermoplastic polymers. Typical with friction welding applications, higher melting temperature materials will require more energy to melt, so they will require more welding time or higher RPMs. Common additives and filler will often alter the weldability of polymers. These additions can make the weld process more difficult, or change the intended properties of the weld.
A note on composite materials, fiber reinforced for example. The reinforcement material will not cross the weld joint, so the intended bulk material properties will vary drastically in the welded region.
A list showing the weldability of common materials is shown below:
Applications.
Spin welding creates a clean and sound weld joint that requires little post processing. Due to this most parts being welded are in the final stages of production, or are in final assembly.
The first known application of spin welding was in the assembly of compasses, however spin welding has become used in a wide variety of products. These products include but are not limited to fuel filters, check valves, truck lights, aerosol cylinders, and floats, as well as some structural components, piping, tanks, and containers.


Shear force

In solid mechanics, shearing forces are unaligned forces acting on one part of a body in a specific direction, and another part of the body in the opposite direction. When the forces are collinear (aligned with each other), they are called tension forces and compression forces. William A. Nash defines shear force in terms of planes: "If a plane is passed through a body, a force acting along this plane is called a "shear force" or "shearing force"."
Force required to shear steel.
This section calculates the force required to cut a piece of material with a shearing action. The relevant information is the area of the material being sheared, ie the area across which the shearing action takes place, and the shear strength of the material. A round bar of steel is used as an example. The shear strength is calculated from the tensile strength using a factor which relates the two strengths. In this case 0.6 applies to the example steel, known as EN8 bright, although it can vary from 0.58–0.62 depending on application.
EN8 bright has a tensile strength of 800MPa and mild steel, for comparison, has a tensile strength of 400MPa.
To calculate the force to shear a 25 mm diameter bar of EN8 bright steel;
When working with a riveted or tensioned bolted joint, the strength comes from friction between the materials bolted together. Bolts are correctly torqued to maintain the friction. The shear force only becomes relevant when the bolts are not torqued.
A bolt with property class 12.9 has a tensile strength of 1200MPa (1MPa = 1N/mm2) or 1.2kN/mm2 and the yield strength is 0.90 times tensile strength, 1080MPa in this case.
A bolt with property class 4.6 has a tensile strength of 400MPa (1MPa = 1N/mm2) or 0.4 kN/mm2 and yield strength is 0.60 times tensile strength, 240MPa in this case.


CONWIP

CONWIP (CONstant work in process) are pull-oriented production control systems. Such systems can be classified as pull and push systems (Spearman et al. 1990). In a push system, the production order is scheduled, and the material is pushed into the production line. In a pull system, the start of each product assembly process is triggered by the completion of another at the end of production line. This pull-variant is known for its ease of implementation.
CONWIP is a kind of single-stage kanban system and is also a hybrid push-pull system. While kanban systems maintain tighter control of system WIP through the individual cards at each workstation, CONWIP systems are easier to implement and adjust, since only one set of system cards is used to manage system WIP. CONWIP uses cards to control the number of WIPs. For example, no part is allowed to enter the system without a card (authority). After a finished part is completed at the last workstation, a card is transferred to the first workstation and a new part is pushed into the sequential process route. In their paper, Spearman et al. (1990) used a simulation to make a comparison among the CONWIP, kanban and push systems, and found that CONWIP systems can achieve a lower WIP level than kanban systems.
Card control policy.
In a CONWIP system, a card is shared by all kinds of products. However, Duenyas (1994) proposed a dedicated card control policy in CONWIP and he stated that this policy could perform as a multiple chain closed queuing network.


Manufacturing Enterprise Solutions Association International (MESA, also known as MESA International) is a worldwide not-for-profit community of manufacturing companies, information technology hardware and software suppliers, system integrators, consulting service providers, analysts, editors, academics, and students. MESA's goal is to help member companies improve business results and production operations through application and implementation of information technology and best management practices.
History.
MESA was initially founded, in 1992, to promote Manufacturing Execution Systems, its acronym and reach was later broadened to Manufacturing Enterprise Solutions Association to include a wider scope of functions in the entire Manufacturing enterprise value chain and the integration of plant floor devices and control systems into enterprise systems and business intelligence for higher levels of automation, visibility, optimization and orchestration of manufacturing processes.
In 2012, MESA merged with WBF (World Batch Forum), the standards organization responsible for B2MML and BatchML.
In 2012, MESA also signed on with the Open O&M group. An initiative of multiple industry standards organizations to provide a harmonized set of standards for the exchange of Operations & Maintenance (O&M) data and associated context. OpenO&M is an open, collaborative, effort composed of diverse groups of relevant organizations and subject matter experts. The members of OpenO&M initiative are ISA, MESA, MIMOSA, OAGi, and the OPC Foundation.
In 2014, MESA International signed a Memorandum of Understanding with Open Applications Group, Inc. (OAGi) making it easier for both organizations to work together and bring value to their common set of stakeholders, and formalizes the ways in which each organization can contribute to the other's committees and working groups to bring specific expertise to key initiatives.
In 2016, MESA releases the first formal definition of Smart Manufacturing in its paper “Smart Manufacturing – The Landscape Explained” which explains the relations and scope of initiatives including Industrial Internet of Things, and Industrie 4.0.
In 2017, MESA signed an MOU with The Industrial Internet Consortium (IIC). Under the agreement, the two organizations will work together to align efforts to maximize interoperability, portability, security and privacy for the industrial Internet. Joint activities will include: identifying and sharing Industrial Internet of Things (IIoT) best practices; realizing interoperability by harmonizing architecture and other elements; collaborating on standardization; and collaboration in the areas of industrial analytics and asset performance management. .
Also in 2017, In an effort to promote greater understanding of Smart Manufacturing (SM) technologies, the Manufacturing Enterprise Solutions Association (MESA) International and the Clean Energy Smart Manufacturing Innovation Institute (CESMII) announce an agreement that will provide CESMII-member access to valuable education that MESA has developed.
Activities.
MESA members participate in and contribute to a number of activities:
Participants.
MESA includes member organizations such as:
People participating in MESA are typically in roles such as:
Related organizations.
MESA works with a number of related organizations in its work to advance best practices for Operations and Maintenance, including:


Crash test

A crash test is a form of destructive testing usually performed in order to ensure safe design standards in crashworthiness and crash compatibility for various modes of transportation (see automobile safety) or related systems and components.
Data collection.
Crash tests are conducted under rigorous scientific and safety standards. Each crash test is very expensive so the maximum amount of data must be extracted from each test. Usually, this requires the use of high-speed data-acquisition, at least one triaxial accelerometer and a crash test dummy, but often includes more.
Some organizations that conduct crash tests include Calspan, an independent test laboratory in Buffalo, NY. As a result of the capabilities and expertise at Calspan, Calspan has been awarded 5 year contracts by the National Highway Traffic Safety Administration (NHTSA) to execute for the NHTSA FMVSS No. 214, Side Impact Protection Compliance Testing, FMVSS No. 301 Fuel System Integrity, and FMVSS No. 305 Electric Powered Vehicles: Electrolyte Spillage and Electrical Shock Protection vehicle crash tests. Calspan also holds the NHTSA contracts for executing New Car Assessment Program crash tests.
Also, Monash University department of Civil Engineering, routinely conducts crash tests for the purposes of roadside barrier safety and design.
Crash testing programs.
There are a number of crash test programs around the world dedicated to providing consumers with a source of comparitative information in relation to the safety performance of new and used vehicles. Examples of new car crash test programs include National Highway Traffic Safety Administration's NCAP, the Insurance Institute for Highway Safety, Australasian New Car Assessment Program, EuroNCAP and JapNCAP. Programs such as the Used Car Safety Ratings provide consumers information on the safety performance of vehicles based on real world crash data.
In 2020, EuroNCAP introduces a "mobile progressive deformable barrier (MPDB) test" first experimented on the Toyota Yaris.


3D printing speed

3D printing speed measures the amount of manufactured material over a given time period (formula_1), where the unit of time is measured in Seconds, and the unit of manufactured material is typically measured in units of either kg, mm or cm3, depending on the type of additive manufacturing technique.
The following table compares the speeds of commercially relevant 3D printing technologies.
3D printing speed refers to only the build stage, a subcomponent of the entire 3D printing process. However, the entire process spans from pre-processing to post-processing stages. The time required for printing a completed part from a data file (.stl or .obj) is calculated as the sum of time for the following stages:
Speed up.
Additive manufacturing technologies usually imply a trade off between the printing speed and quality. Improvements in speed of the entire 3D printing process can be grouped in the following two categories.
Software improvements.
Since the actual printing process is directly influenced by how the model is sliced, oriented, and filled, optimizing them results in shorter print time.
Optimal Orientation. Changing the orientation of a part can be done through either the STL file or on the CAD model. Determining the optimal part orientation is a common software solution for all additive manufacturing processes. This can lead to a significant improvement in many key factors that affect the total print time. The following factors heavily depend on part orientation:
Adaptive Slicing. Error caused by the staircase effect can be measured using several metrics, all of which refer to the difference between model surface and actual printed surface. By adaptively computing the height distribution of layers, this error can be minimized: The quality of surface increases while post-processing time decreases. The benefits of adaptive slicing depend on the proportion of the surface-to-volume ratio of the part. Efficient computation of adaptive layers is possible by analyzing the model surface over the full layer height. Several implementations are available as an open source software.
Hardware improvements.
Increasing the speed of printing through hardware can take the following forms, many of which are used by leading 3D printing companies.
Challenges.
Depending on the technology used, there are some challenges that could limit the speed of the 3D printing:
Research.
Acoustic fabrication.
Interesting features of sound waves have encouraged scientists to use it in additive manufacturing. Sound waves can form pressure fields that shape the material in the desired form in a contact-free setup. The fact that it can be applied over a large area at the same time makes it a good candidate for rapid fabrication.
The process starts by designing an acoustic hologram. An acoustic hologram is a mask that will direct the sound field to form the desired pattern. It can be fabricated in an additive fabrication combined with etching and nanoimprint methods. The process follows by placing silicone rubber particles in a liquid medium with photo-initiator agents. Then the acoustic mask is used to generate the desired pressure sound field to put the particle in the correct order. The next step is applying the UV light to solidify the final product.
Improved SLA processes.
The speed of SLA processes is limited by:
Rapid continuous additive manufacturing by inhibition patterning
Due to the mentioned effects, the printing speed with SLA methods is limited to a few millimeters to several centimeters per hour. To address this problem a system of two light sources is used, one for polymerization and one for inhibiting the polymerization to avoid adhesion and as a result print faster. This method allows us to speed up the process up to 200 cm/hr. Moreover, by controlling the intensity of each pixel in the setup topographical patterning can be created in a single exposure with no stage translation.
A mixture of photo initiators and photo inhibitors is used in the setup. The absorbance spectra of two material is orthogonal this allows to control the process with the two orthogonal light sources. As the material is generated layer by layer the tray is gradually lifted and the photo inhibitors will not allow adhesion near the window.
Rapid, large-volume, thermally controlled 3D printing, using a mobile liquid interface
Another way to address the adhesion problem is to create a dead layer which prohibits the curing process. One method to create this dead layer is to use fluorinated oil flow. This liquid is omniphobic which means that it repels all the materials and will not stick to anything. The reason to use a flow instead of a static layer is to create a larger force against the adhesion force and also help with the cooling of the cured layer (curing generates heat).
Fast 3D printing by integrating construction kit building blocks.
Dividing an Object into smaller blocks (e.g. Lego parts) before print, can lead to 2.44x increase in speed over conventional printing method. Moreover, when the object needs to be iterated to find the optimal design it is not efficient to reprint the whole object over and over again: One solution is to print the main constant structure only once and reprint only the small changing parts with high resolution. These smaller parts are mounted onto the main structure.


Multi-material 3D printing

Multi-material 3D printing is the additive manufacturing procedure of using multiple materials at the same time to fabricate an object. Similar to single material additive manufacturing it can be realised through methods such as FFF, SLA and Inkjet (material jetting) 3D printing. By expanding the design space to different materials, it establishes the possibilities of creating 3D printed objects of different color or with different material properties like elasticity or solubility. The first multi-material 3D printer Fab@Home became publicly available in 2006. The concept was quickly adopted by the industry followed by many consumer ready multi-material 3D printers.
Multi-material 3D printing Technologies.
Fused Filament Fabrication (FFF).
Fused Filament Fabrication (also known as Fused Deposition Modeling - FDM) describes the process of continuously extruding a line of thermoplastic material to form a three dimensional model. The FFF process supports a variety of materials reaching from bio degradable ones like PLA to PETG, ABS and engineering grade materials like PEEK. This technology additionally allows for the use of flexible materials like TPU. Two possible solutions to realise a multi-material FFF 3D printer are:
Single Nozzle Design.
The single nozzle design combines the different materials before or in the melting zone of the print head such that the materials are extruded through the same nozzle. For example: The different filaments can be cut and rejoined to a single strand of a mixed filament before being fed into the melting chamber. Such a technique is implemented in the Mosaic Palette. Another example is the multi-material upgrade by Prusa3d, which is mounted on top of a single material printer to add multi material capabilities. It uses a bowden style extrusion system with an additional axis to cut and select the material. To prevent impurities inside of the object a combined melting chamber has to be cleared from the previous material before a new one can be used. Depending on the implementation, the amount of waste material produced during the printing process may be significant. In some implementations, the previous material may be used as in-fill to prevent waste, or to simultaneously print a different object in which color does not matter.
Multi-Nozzle Design.
The multi-nozzle design features a separate nozzle for each material. The nozzle can either be mounted on the same print head or on independent print heads. For this approach to work the different nozzles have to be calibrated to the exact same height relative to the print surface to circumvent the interference of an inactive nozzle with the printed object. Such a design reduces the amount of waste material during the printing process significantly compared to a single nozzle design which does not use the previous material as in-fill or to print another object.
Stereolithography (SLA).
Stereolithography is the process of solidifying a photopolymer with a laser layer by layer to form a three dimensional object. To realize multi-material prints with this technology, one can use multiple reservoirs for different photopolymers. A major problem with this approach is the removal of the not yet polymerised material as the print may contain cavities filled with the old material, which should be emptied before the next material can be used. The photopolymer resins used for SLA can have highly different physical properties, generally being more brittle and having a lower heat deflection temperature. The SLA standard resins come in different colours and opacities. Besides the engineering grade materials like the ABS-like or PP-like resin, there exist bio-compatible ones used for medical applications and flexible resins.
Material Jetting.
The process of material jetting, often also called Inkjet 3D printing, is similar to the 2D Inkjet printing procedure. The print head consists of multiple small nozzles which jet droplets of photopolymers on demand. Each nozzle can extrude a different material, which allows for the creation of multi-material parts. The droplets of material are then immediately cured using a UV light source mounted to the print head. In contrast to the FFF printing process, a layer is not formed by moving the print head along a pre-calculated path, but by scanning the layer line by line. The Statasys J750, for example, allows for full colour prints. The materials supported by the material jetting printing process are similar to the ones of the SLA process and hence share similar properties. Additionally there have been advances in the field of material jetting metals by suspending nano metal particles in a fluid. After the removal of the support material the printed object has to be sintered to create a final metal part.
Binder Jetting.
A binder jetting 3D printer uses particles of a fine-grained powder, which are fused together using a binder, to form a three-dimensional object. In principle, it consists out of two separate chambers: One functions as a reservoir for the powdered material, the other one as the printing chamber. To fabricate a layer of an object a blade pushes the material out of the reservoir and spreads it over the printing surface to create a thin layer of powder. A print head similar to the one found in a 2D inkjet printer then applies the binder to the layer to solidify and bind it to the previous one. Although binder jetting does not allow for multi-material support, there exist printers, which feature a second print head to apply pigment to the layer after the binder to allow for full color prints.
Workflow.
Designing.
Designing a three dimensional object is the first step in the workflow of 3D printing. This design process can be supported by software. Such CAD software is capable of creating, managing and manipulating different 3D geometric figures while giving the user feedback through a graphical interface. Most CAD programs already support the annotation of a geometric figure with a material. The combination of different geometries then forms a single multiple material object. However, not all file formats support the annotation of materials together with the geometry of the object.
Slicing.
Slicing is the process of splitting a 3D model into layers to transform them into a sequence of G-Code instructions. These instructions can be processed by a 3D printer to manufacture the corresponding model in either a bottom-up, top-down or even left to right manner. Before generating the instructions, support structures can be added to connect overhanging sections of the model to either the printing surface or other parts of the model. The support structures have to be removed in a post processing step after the print has finished.
The slicing process for multi-material prints differs depending on the hardware used. For FFF based machines, instructions for changing the material have to be added. This comes with multiple computational challenges such as handling two print heads at the same time without them interfering with each other or clearing the melting chamber from the previous material. For SLA based multi-material prints the slicing software has to handle the additional degrees of freedom arising from the possibility of moving the print from one resin tray to the next one. The slicing procedure for material jetting printers involves the generation of multiple bitmap images representing the voxels of the object.
Post-Processing.
3D printed objects may need to be post processed before they can be used as a prototype or a finished product. Such post-processing steps may including sanding the surface of the object to make it smoother or painting it to match the colours of the design. Depending on the printing method and the objects geometry, support structures may have to be removed. The use of multi-material 3D printing reduces the amount of post processing needed for the same result, as colours can be printed directly. Furthermore, it is possible to use a water soluble material for printing the support structures, as their removal only involves placing the object into a water bath.
Applications.
Food 3D Printing.
The rising trend of food 3D printing supports the customisation of shape, colour, flavour, texture and nutrition of different meals. Multi-material 3D printing enables using multiple ingredients like peanut butter, jelly or dough in the printing process, which is essential for the creation of most foods.
Medical Applications.
Multi-material 3D printing technology is often used in the production of 3D printed prosthetics. It enables the use of different materials like a soft TPU on the contact points with the body and a stiff carbon fibre material for the corpus of the prosthetics. The prosthetics can therefore be adjusted to suit the varying needs and desires of an individual.
Another medical use case is the generation of artificial tissue structures. The research focuses on creating tissue, that mimics human tissue in terms of feel, elasticity and structure. Such artificial tissues can be used by surgeons to train and learn on realistic models, which is otherwise hard or expensive to achieve.
Current research focuses on 3D printed drug delivery systems to efficiently deploy a medication or vaccine. Through the use of multi-material printing they create biocompatible structures that can interact with the human body on a cellular level.
Physical Properties.
The capability of switching between different materials is essential for controlling the physical properties of a 3D printed object. Besides being able to manipulate the strength of an object through micro-structures, the user can switch between harder or softer materials in the printing process to affect the rigidity of the object. Hard and soft material combination is also applied to fabricate biomimetic structure with desired properties. The use of materials of different colour or elasticity can affect the looks and the haptics of the resulting object. Additionally, it is possible to reduce the amount of post-processing needed by choosing a suitable material for the support structures or the outer hull of the part.
Rapid Prototyping.
Multi-material 3D printing enables designers to rapidly manufacture and test their prototypes. The use of multiple materials in a single part enables the designer to create functional and visually appealing prototypes. An example of how 3D printing can be included in the design process is automotive design. There, it is necessary to quickly test and verify a prototype to get the design approved for production. The reduced post-processing steps induced by the multi-material 3D printing technology result in a shorter fabrication time. Additionally, multi-material 3D printing reduces the part count of the produced prototypes compared to traditional fabrication methods like milling or molding, because the assembly of multiple parts with different materials is no longer required.
File Formats.
There exist multiple file formats to represent three dimensional objects which are suitable for 3D printing. Yet not all of them support the definition of different materials in the same file as the geometry. The table below lists the most common file formats and their capabilities:


3D food printing

3D food printing is the process of manufacturing food products using a variety of additive manufacturing techniques. Most commonly, food grade syringes hold the printing material, which is then deposited through a food grade nozzle layer by layer. The most advanced 3D food printers have pre-loaded recipes on board and also allow the user to remotely design their food on their computers, phones or some IoT device. The food can be customized in shape, color, texture, flavor or nutrition, which makes it very useful in various fields such as space exploration and healthcare.
General principles.
There are three general areas that impact precise and accurate food printing: materials/ingredients (viscosity, powder size), process parameters (nozzle diameter, printing speed, printing distance), and post-processing methods (baking, microwaving, frying).
Materials and ingredients.
The type of food available to print is limited by the printing technique. For an overview of these printing techniques, please see the section "Printing Techniques" below:
Extrusion-based printing ingredients.
Common ingredients used in extrusion based printing are inherently soft enough to extrude from a syringe/printhead and possess a high enough viscosity to retain a shape. In certain cases, powdered ingredients (protein, sugar, etc.) are added to increase viscosity, e.g. adding flour to water creates a paste that can be printed. Inherently soft materials include:
Certain ingredients that are solid can be used by melting and then extruding the ingredient, e.g. chocolate.
Selective laser sintering and binder jetting ingredients.
Powdered ingredients:
Inkjet printing ingredients.
Ingredients with low viscosity are used for surface filling:
Printing techniques.
Extrusion-based printing.
Although there are different approaches to extrusion based printing, these approaches follow the same basic procedures. The platform on which food is printed consists of a standard 3-axis stage with a computer controlled extrusion head. This extrusion head pushes food materials through a nozzle typically by way of compressed air or squeezing. The nozzles can vary with respect to what type of food is being extruded or the desired printing speed (typically the smaller the nozzle the longer the food printing will take). As the food is printed, the extrusion head moves along the 3-axis stage printing the desired food. Some printed food requires additional processing such as baking or frying before consumption.
Extrusion based food printers can be purchased for household use, are typically compact in size, and have a low maintenance cost. Comparatively, extrusion based printing provides the user with more material choices. However, these food materials are usually soft, and as a result, makes printing complex food structures difficult. In addition, long fabrication times and deformations due to temperature fluctuations with additional baking or frying require further research and development to overcome.
Hot-melt and room temperature.
In Hot-melt extrusion, the extrusion head heats the food material slightly above the material's melting point. The melted material is then extruded from the head and then solidifies soon thereafter. This allows the material to be easily manipulated into the desired form or model. Foods such as chocolate are used in this technique because of its ability to melt and solidify quickly.
Other food materials do not inherently require a heating element in order to be printed. Food materials such as jelly, frosting, puree, and similar food materials with appropriate viscosity can be printed at room temperature without prior melting.
Selective laser sintering.
In selective laser sintering, powdered food materials are heated and bonded together forming a solid structure. This process is completed by bonding the powdered material layer by layer with a laser as the heat source. After a layer is completed with the desired areas bonded, it is then covered by a new unbonded layer of powder. Certain parts of this new unbonded layer are heated by the laser in order to bond it with the structure. This process continues in a vertical upwards manner until the desired food model is constructed. After construction, unbonded material can then be recycled and used to print another food model.
Selective laser sintering enables the construction of complex shapes and models and the ability to create different food textures. It is limited by the range of suitable food materials, namely powdered ingredients. Due to this limitation, selective laser sintering has been used primarily for creating sweets/candies.
Binder jetting.
Similarly to selective laser sintering, binder jetting uses powdered food materials to create a model layer by layer. Instead of using heat to bond the materials together, a liquid binder is used. After bonding the desired areas of a layer, a new layer of powder is then spread over the bonded layer covering it. Certain parts of this new layer are then bonded to the previous layer. The process is repeated until the desired food model is constructed.
As with selective laser sintering, binder jetting enables the construction of complex shapes and models and the ability to create different food textures. Likewise, it is also limited by the range of suitable food materials, namely powdered ingredients.
Inkjet printing.
Inkjet printing is used for surface filling or image decoration. By utilizing gravity, edible food ink is dropped onto the surface of the food, typically a cookie, cake, or other candy. This is a non-contact method, hence the printhead does not touch the food protecting the food from contamination during image filling. The ink droplets may consist of a broad range of colors allowing users to create unique and individualized food images. An issue with inkjet printing is the food materials being incompatible with the ink resulting in no image or high image distortion. Inkjet printers can be purchased for household or commercial use, and industrial printers are suitable for mass production.
Multi-printhead and multi-material.
In multi-printhead and multi-material printing, multiple ingredients are printed at the same time or in succession. There are different ways to support multi-material printing. In one instance, multiple printheads are used to print multiple materials/ingredients, as this can speed up production, efficiency, and lead to interesting design patterns. In another instance, there is one printhead, and when a different ingredient is required, the printer exchanges the material being printed. Multiple materials/ingredients equates to a more diverse range of meals available to print, a broader nutritional range, and is quite common for food printers.
Post-processing.
In the post-processing phase, printed food may require additional steps before consumption. This includes processing activities such as baking, frying, cleaning, etc. This phase can be one of the most critical to 3D printed food, as the printed food needs to be safe for consumption. An additional concern in post processing is the deformation of the printed food due to the strain of these additional processes. Current methods involve trial and error. That is, combining food additives with the materials/ingredients to improve the integrity of complex structures and to ensure the printed structure retains its shape. Additives such as transglutaminase and have been added to ingredients in order to help retain the printed shape while printing and after cooking.
Additionally, recent research has produced a visual simulation for baking breads, cookies, pancakes and similar materials that consist of dough or batter (mixtures of water, flour, eggs, fat, sugar and leavening agents). By adjusting certain parameters in the simulation, it shows the realistic effect that baking will have on the food. With further research and development, a visual simulation of 3D printed foods being cooked could predict what is vulnerable to deformation.
Applications.
Personal nutrition.
Personalized dietary requirements for an individual's nutritional needs has been linked to the prevention of diseases. As such, eating nutritious food is paramount to living a healthy life. 3D printed food can provide the control necessary to put a custom amount of protein, sugar, vitamins, and minerals into the foods we consume.
Another area in customized food, is elderly nutrition. The elderly sometimes cannot swallow foods, and as such require a softer pallet. However, these foods are often unappealing causing some individuals not to eat what their bodies' nutritional needs require. 3D printed food can provide a soft and aesthetically pleasing food in which the elderly can consume their bodies' dietary requirements.
In October 2019, startup company "Nourished" 3D prints personalized nutritional gummies from 28 different vitamins. Individuals take a survey, then based on their answers, a personalized nutritional gummy is printed for that individual.
Sustainability and solution for hunger.
As the world's population continues to grow, experts believe that current food supplies will not be able to supply the population. Thus, a sustainable food source is critical. Studies have shown that entomophagy, the consumption of insects, has the potential to sustain a growing population. Insects such as crickets require less feed, less water, and provide around the same amount of protein that chickens, cows, and pigs do. Crickets can be ground into a protein flour. In one study, researchers provide an overview of the process of 3D printing insect flour into foods that do not resemble insects; thus, keeping the nutritional value of the insect intact.
Space exploration.
As humans begin venturing into space for a longer time, the nutritional requirements for maintaining crew health is critical. Currently NASA is exploring ways of integrating 3D printing food into space in order to sustain the crew's dietary requirements. The vision is to 3D print powdered food layers that have a shelf life of 30 years instead of using traditional freeze dried food that have a shelf life of 5 years. In addition to dietary requirements, 3D printing food in space could provide a morale boost, as the astronauts would be able to design custom meals that are aesthetically pleasing.
In September 2019, Russian cosmonauts, along with Israeli startup Aleph Farms, grew meat from cow cells, then 3D printed the cells into steaks.
Meat bioprinting.
Livestock farming is one of the top contributors to deforestation, land degradation, water pollution and desertification. Among other reasons, this has led to the new promising technology of meat bioprinting. One alternative to livestock farming is cultured meat, also known as lab-grown meat. Cultured meat is produced by taking a small biopsy from animals, extracting the myosatellite cells and adding growth serum to multiply the cells. The resulting product is then used as a material for bioprinting meat. The post-processing phase, among other steps, includes adding flavour, vitamins and iron to the product. Yet another alternative is printing a meat analogue. Novameat, a Spanish startup has been able to print a plant-based steak and mimic the texture and appearance of real meat.
Creative food design.
Food presentation and food appearance customization for individuals is a big trend in the food industry. So far food customization and creative designs have required hand-made skills, which results in low production rate and high cost. 3D food printing can overcome this problem by providing the necessary tools for creative food design even for home users. 3D food printing has enabled some intricate designs which cannot be accomplished with traditional food manufacturing. Brand logos, text, signatures, pictures can now be printed on some food products like pastries and coffee. Complex geometric shapes have also been printed, mainly using sugar. With 3D printing, chefs can now turn their visual inspirations into signature culinary creations. Another benefit is being able to print nutritious meals in shapes that appeal to children.
Reduced food waste.
Worldwide, one third of the total food produced for consumption, around 1.6 billion tons per year, goes to waste. Food waste happens during processing, distribution and consumption. 3D food printing is a very promising way of reducing food waste during the phase of consumption, by utilizing food products like meat off-cuts, distorted fruits and vegetables, sea food by-products and perishables. These products can be processed in a suitable form for printing. Upprinting Food, a Dutch startup, has been blending and combining different ingredients from food waste to create purees which are then used as materials for 3D printing. Chefs are also creating different dishes from leftover food using 3D food printers.
Challenges.
Structure.
Unlike traditionally prepared food, the variety of food that can be manufactured using 3D printing is limited by the physical characteristics of the materials. Food materials are generally much softer than the weakest plastic used in 3D printing, making the printed structures very fragile. So far, most studies use trial and error as an approach to overcoming this challenge, but scientists are working on developing new methods that are able to predict the behavior of different materials during the printing process. These methods are developed by analyzing the rheological properties of the materials and their relation to the printing stability.
Design.
When designing a 3D model for a food product, the physical and geometrical limitations of the printing materials should be taken into account. This makes the designing process a very complex task and so far there is no available software that accounts for that. Building such software is also a complex task due to the vast variety of food materials. Considering that personal users who incorporate 3D food printing in their kitchens represent a significant part of the overall users, the design of the software interface adds to the complexity. The interface of such software should be simple and have high usability while still providing enough features and customization options for the user without causing cognitive overload.
Speed.
The current speed of 3D printing food could be sufficient for home use, but the process is very slow for mass production. Simple designs take 1 to 2 minutes, detailed designs take 3 to 7 minutes, and more intricate designs take even longer. The speed of printing food is tightly correlated to the rheological properties of the materials. Research shows that high printing speed results in low fidelity samples due to the dragging effect, while very low speed causes instability in material deposition.
In order for 3D food printing to find its way to the food industry, the printing speed needs improvement or the cost of such technology should be affordable enough for companies to operate several printers.
Multi-material printing.
The color, flavor and texture of food are of crucial importance when fabricating an edible product, thus in most cases it is required that a food printer supports multi-material printing. The current available 3D food printers are limited to using a few different materials due to the challenge of developing multiple extruder capabilities. This limits the variety of food products that can be 3D printed, leaving out complex dishes that require a lot of different materials.
Safety.
When 3D printing food, the safety is very crucial. A food printer must ensure safety along the entire path taken by the food material. Due to the possibility of food getting stuck somewhere along the path, bacteria accumulation is a major concern. Microbial stability is a crucial parameter of the quality of the printed food, thus it needs to be addressed both during the design of the printer and during the printing process. On the other hand, the materials that come into contact with the food may not be as significant of a concern since high quality printers use stainless steel and BPA-free materials.
Copyright.
Existing food products in the market such as chocolates in various shapes could easily be scanned and the obtained 3D models could be used to replicate those products. These 3D models could then be disseminated via Internet leading to copyright infringement. There are laws regulating copyright issues but it is not clear whether they will be sufficient to cover all aspects of a field like 3D food printing.


Stump gauge

A stump gauge (or wicket gauge) is an instrument used in cricket to determine the correct position for the three stumps used to form the wicket, as mandated by the Laws of Cricket. It is usually in a form of a metal (although sometimes plastic) bar with three spikes, and is used to locate and create the holes into which the spiked ends of the stumps are placed.


B-staging

B-staging is a process that utilizes heat or UV light to remove the majority of solvent from an adhesive, thereby allowing a construction to be “staged”. In between adhesive application, assembly and curing, the product can be held for a period of time, without sacrificing performance.
Attempts to use traditional epoxies in IC packaging often created expensive production bottlenecks, because, as soon as the epoxy adhesive was applied, the components had to be assembled and cured immediately. B-staging eliminates these bottlenecks by allowing the IC manufacturing to proceed efficiently, with each step performed on larger batches of product.
B stage laminates are also used in the electronic circuit board industry, where the laminates are reinforced with woven glass fibers called prepregs. This allows manufacturers to have clean and accurate setup for multilayer pressing of cores and prepregs for production of PCBs, without the need to hassle with liquid uncured epoxies.


Twister roller coaster

A twister roller coaster is the generic name given to any roller coaster layout which tends to twist or interweave its track within itself several times. It is essentially the opposite of an Out and Back roller coaster, which is often a much more simplistic layout. Twister roller coasters often have the illusion of having small or tight clearances due to the track usually travelling through several support structures. This is known as a head chopper effect.
Twister roller coasters were unheard of before the 1920s. John Miller is credited with inventing upstop wheels and secure lap bar restraints, both which led roller coaster designers to create wilder and twistier layouts.
A good example of the difference between an out and back design and twister design is layouts of Apollo's Chariot and Raging Bull, two Bolliger & Mabillard designed hypercoaster roller coasters that debuted in 1999. Apollo's Chariot uses a traditional out and back layout while Raging Bull is a twister.


Bauschinger effect

The Bauschinger effect refers to a property of materials where the material's stress/strain characteristics change as a result of the microscopic stress distribution of the material. For example, an increase in tensile yield strength occurs at the expense of compressive yield strength. The effect is named after German engineer Johann Bauschinger.
While more tensile cold working increases the tensile yield strength, the local initial compressive yield strength after tensile cold working is actually reduced. The greater the tensile cold working, the lower the compressive yield strength.
It is a general phenomenon found in most polycrystalline metals. Based on the cold work structure, two types of mechanisms are generally used to explain the Bauschinger effect:
The net result is that the yield strength for strain in the opposite direction is less than it would be if the strain had continued in the initial direction.
Mechanism of action.
Severe unidirectional cold working results in accumulation of dislocation at barriers to dislocation movement. When stresses are applied in the reverse direction, the dislocations are now aided by the back stresses that were present at the dislocation barriers previously and also because the back stresses at the dislocation barriers in the back are not likely to be strong compared to the previous case. Hence the dislocations glide easily, resulting in lower yield stress for plastic deformation for reversed direction of loading.
Consequence of Bauschinger effect.
Metal forming operations result in situations exposing the metal workpiece to stresses of reversed sign. The Bauschinger effect contributes to work softening of the workpiece, for example in straightening of drawn bars or rolled sheets, where rollers subject the workpiece to alternate bending stresses, thereby reducing the yield strength and enabling greater cold drawability of the workpiece.