Injection Molding Troubleshooter

Injection Molding Troubleshooter Eliminate Surface Defects on Molded Parts Print This Article

Learn More Visible defects on the surface of a molded part appear Visit the as dull, glossy, or hazy areas, or as a rippled surface, Injection Molding called orange peel. Common points of occurrence Zone include near the sprue or behind sharp edges in areas away from the sprue. The mold and the molding process are the best places to seek out and identify the causes of these effects. Dull areas on the part Dull concentric rings can appear around the sprue like a faint halo. This is most likely to occur when the part is made from a high-viscosity, poorly flowing material such as PC, PMMA, or ABS. With this type of polymer there is the risk of the cooled surface layer near the gate being displaced by the flow of resin in the core of the part, leaving a visible defect.

Dull halos around the sprue and downstream of sharp It is frequently assumed that the defect occurs edges occur when initial during the packing and holding-pressure phase of injection speed is too high, the process. Yet in fact, dull areas near the sprue which causes displacement of invariably occur at the beginning of the filling cycle. cooled surface material. Our experiments have traced the actual cause of the Gradually increasing fill skin-layer displacement, which can be attributed to speed with a stepped injection speed—more specifically, the flow-front injection profile can fix the velocity. problem. Even when injection speed into the mold is constant, flow velocity changes. Flow velocity is very high in the area of the gate as it enters the mold, but slows down as the flow front extends away from the gate and into the cavity on a widening circle. The change in flow-front velocity can bring about the surface defects. One way to reduce the changes in speed of the flow front is to tailor the injectionspeed profile. In order to obtain a slow flow-front velocity near the sprue, it is necessary to inject in several steps, increasing gradually from a relatively low speed to ones that are faster and faster. The aim is to obtain a flow-front velocity that is uniform throughout the whole filling phase. Low melt temperature is another source of a dull surface on the part. Increasing

the barrel temperature and raising the screw backpressure can help reduce the probability of surface defects. Too low a temperature of the mold wall can also be a reason, so increasing the mold temperature is another possible solution to surface defects. There are also design-related issues that can generate a dull area near the sprue. A sharp transition between the gate and part can be remedied by providing a small radius between the gate and the part. Also, take a closer look at gate position and diameter and confirm that they are correct for the application. Dull areas occur not only near the sprue but are also frequently found downstream of sharp edges in the molded part. In such a case, the surface finish up to the sharp edge is typically very good, while behind it the surface is dull and rough. Here again, too high an injection speed or flow velocity can cause the cooled surface layer to be displaced by melt flowing underneath. A stepped or graduated injection speed profile is again recommended. The best approach is to allow flow to speed up only after the flow front has passed the sharp edge. A design-related source of trouble involves sharp transitions at edges in the molding away from the sprue area. A smoother, radiused transition in those areas is the answer. Fixing gloss variations Differences in gloss are most conspicuous on textured surfaces. Irregular gloss may appear on the molded part even though the mold has a uniform surface texture. The problem is poor replication of the mold surface in some areas of the part. Pressure on the injected melt decreases with increasing distance from the gate. If the part is not fully packed at the point farthest from the gate, where the pressure is lowest, the mold surface texture will not be reproduced exactly, resulting in a glossy surface. Hence, unwanted gloss is least likely in the areas where cavity pressure is strongest— from the gate to about half way along the flow path.

Glossy surfaces appear on this automotive part due to poor packing and poor mold surface replication. Higher melt or mold temperature, higher holding pressure, or longer hold time could help.

To fix this situation, consider raising the melt or mold temperature or the holding pressure. Extending the holding-pressure time also may increase the chances for accurate mold-surface replication. Part design can also contribute to gloss variations. For example, large changes in wall thickness can cause melt-flow irregularities and difficulties in mold-surface replication. Designing more uniform wall sections can alleviate this. Areas of excessive wall thickness or oversized ribs can also increase the risk of glossy marks. Another source is insufficient venting at the flow line.

Orange peel’s origin “Orange peel” or a rippled surface defect typically occurs at the end of the flow path in thick-walled parts molded of high-viscosity materials. During injection at low velocity, solidification occurs on the surface too quickly. The high resistance to flow produces uneven frontal flow, and the solidified outer layer will not fully contact the cavity wall. The result is ripples. These ripples will freeze and holding pressure will no longer be able to smooth them out. The solution is to raise the melt temperature and increase the injection speed. Now retired, Martin Bichler is a former long-time employee of Demag Plastics Group in Schwaig, Germany. Bichler was formerly head of application engineering and processing development. Since his retirement, he continues to work closely with Demag as an application advisor and symposium lecturer. He focuses on the basic aspects of injection molding and has published a book in English, Guide to Flawless Injection Moldings. For questions or comments on this article, contact Bob Lewis at Demag in Strongsville, Ohio. Tel: (440) 876-8960,or e-mail [email protected].

Heat/Cool Molding Thermal Cycling of Injection Molds Boosts Surface Quality Print This Article By Andy May, SABIC Innovative Plastics

Learn More In the injection molding process, tool temperature is an important factor in achieving high-quality parts. It is generally believed that higher tool temperature often results in better surface quality. Heat/cool molding technology is an approach to thermally cycling the mold surface temperature within the injection molding cycle. This requires heating the mold surface above the material’s glasstransition temperature (Tg) prior to injection, and then rapidly cooling the tool to solidify the molded part prior to ejection.

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Company Info SABIC Innovative Plastics,Pittsfield, MA

Fast4M Tooling LLC, The heat/cool molding Troy, MI process significantly improves the surface KraussMaffei Corp., Florence, appearance of injection KY molded parts. It is also Heat/cool molding process significantly possible to reduce system costs by eliminating secondary improves the surface appearance of operations such as primers and sanding to hide surface injection molded parts like these defects. In some cases, painting or powder coating can structural test parts made of 20% be eliminated altogether. Heat/cool molding also enables glass-filled Verton PC/ABS. the use of glass-reinforced structural materials in applications where a high-gloss finish is important. Other benefits of this approach include reduction of molded-in stress, reduction or elimination of jetting and visible weld lines, and increased resin flow lengths to produce thinwall parts.

SABIC Innovative Plastics began working on this technology in Japan several years ago. The first application was an automotive roof-rack rail support bracket that was converted from metal. When an 11% glass-filled Xenoy 1760 PC/PBT resin was trialed, surface aesthetics were not acceptable due to jetting and obvious weld lines. In addition, the part surface was very rough due to the glass fibers, and it required sanding prior to painting. Heat/cool technology eliminated these surface defects and the need for For SABIC’s tests, mold sanding. heating and cooling were With materials such as polycarbonate and blends like PC/ABS and regulated with an alternating temperature-control system PC/PBT, the heat/cool process is being used successfully to from Germany’s Single minimize surface-appearance issues in applications such as TV bezels, light-guide plates, car audio components, and notebook PC Temperiertechnik. It switches from super-heated water at covers. up to 400 F to cold water. HOW IT WORKS Conventional injection molding machinery can be used for heat/cool processing. However, a special auxiliary system is required for rapidly heating and cooling the mold surface. Both superheated water and steam are being used today. Some systems require an external boiler to generate steam, while others generate steam within the control unit itself. In the Pacific region, SABIC uses steam at its development centers. At the Polymer Processing Development Center (PPDC) in Pittsfield, Mass., the company is using a superheated water system from Germany’s Single Temperiertechnik (sold here by KraussMaffei) that can deliver water at 200 C (400 F). For efficient process control, the mold must be equipped with thermocouples that are close to the molding surface to monitor temperature. The injection mold, the molding machine, and the heat/cool controller must be integrated to achieve a stable process. During the development of this process at SABIC, we built our own control unit to integrate each element. At the outset of the molding cycle, steam or superheated water is circulated in the tool to heat the mold surfaces to a temperature 10° to 30° C above the Tg of the resin. Once this temperature is achieved, the injection machine is given a signal to inject plastic into the cavity. After the cavity is filled and the injection phase completed, cold water is circulated in the tool to quickly solidify the plastic and cool it sufficiently for ejection. A valve station is used to switch from steam or superheated water to cold water (and vice versa). After the part has cooled, the mold opens and the part An overview of the heat/cool process shows the temperature is ejected, and the system switches cycle relative to the injection cycle. Injection begins at the back to the mold-heating phase. “permission temperature.” FOCUS ON TOOL DESIGN The effect of heat/cool technology on overall cycle time depends on the material being processed and, more importantly, on the design and construction of the tool. The time required to heat and cool the tool is a function of the steel’s mass, so it is best to minimize the amount of steel to be thermally cycled. Cavities and cores should be inserted rather than cut into the mold plates to

help minimize mass. To reduce heat loss and improve efficiency, these inserts should be insulated from the cavity and core retainer plates using air gaps and insulation material whenever possible. Besides reducing the amount of steel mass that must alternate from hot to cold, consideration should be given to the use of metals such as beryllium-copper or other highly conductive alloys to reduce the time required to heat and cool the mold surfaces. Also, placing water lines close to the molding surfaces will help speed up response time. Many times, however, the part geometry will not allow this. Heat/cool technique (right) provides better surface appearance by eliminating Conformal flow marks and silver streaks in auto center consoles made of PC/ABS. cooling, where the pattern of water lines mirrors the part surface geometry, is an approach that is well suited to this process. Several different technologies are used to achieve conformal cooling, such as laser sintering and direct metal deposition. For a test mold, SABIC worked with Fast4M Tooling, which developed a laminate toolmaking process called Fast-Form. This technology builds the tool from a stack of thin sheets of steel, individually laser-cut and bonded with copper. This method easily incorporates conformal and “flood” cooling channels, as well as extensive venting, at low cost. THE BENEFITS Heat/cool technology can significantly enhance the aesthetics of injection molded parts. The improvement is more dramatic for parts made of amorphous resins such as PC and blends like PC/ABS and PC/PBT. When the mold surface temperature exceeds the Tg of an amorphous resin, the material does not form a skin during the injection phase and the polymer is free to move. As a result, it is not “frozen” when it touches the mold surface, unlike conventional molding. This allows for improved surface replication of the tool surface and higher gloss. For filled materials, a thin layer of polymer on the outside surface encapsulates the filler, thereby increasing gloss and reducing surface roughness. Studies have shown gloss improvement of 50% to 90%. With glass-filled materials, an improvement of 70% in Rmax—a measure of surface roughness—has been achieved. The improvement was greater than 20% for unfilled materials.

Heat/cool injection molding has a positive influence on the depth and visibility of weld lines. One test mold was used to mold three different materials using heat/cool and conventional molding techniques. Using the conventional method, weld-line depths on the surface ranged from 6 to 13 microns. On the heat/cool molded parts, the weld lines were completely invisible and no depth could be measured. This significant improvement has eliminated painting operations on some applications. Molded-in stress can cause unwanted warpage and, in some cases, a shorter part lifetime. On a conventionally molded test part, the molded-in stresses were high. Applying a solvent that is a known stress-cracking agent—carbon tetrachloride— caused cracks in the part. Parts molded with heat/cool had lower molded-in stress and applying the solvent did not result in cracks. Heat/cool molding can thus potentially eliminate the need to anneal parts before use.

Schematic of a water- temperature controller that can both heat and cool an injection mold within a single cycle. (Source: Single Temperiertechnik)

There are many benefits in part performance and appearance that can be achieved with heat/cool process technology. Although there are additional costs associated with the technology, it can be cost-effective from an overall systems standpoint, particularly if it can eliminate expensive secondary operations. About The Author Andy May is a project engineer at SABIC Innovative Plastics’ Polymer Processing Development Center in Pittsfield, Mass. He has worked extensively the last 20 years on processing, design, part performance, and tooling. He welcomes questions at [email protected].

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Injection molding From Wikipedia, the free encyclopedia Jump to: navigation, search Please wikify this article or section. Help improve this article by adding relevant internal links. (March 2008) Injection molding (British: moulding) is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Molten plastic is injected at high pressure into a mold, which is the inverse of the product's shape. After a product is designed, usually by an industrial designer or an engineer, molds are made by a moldmaker (or toolmaker) from metal, usually either steel or aluminium, and precisionmachined to form the features of the desired part. Injection molding is widely used for manufacturing a variety of parts, from the smallest component to entire body panels of cars. Injection molding is the most common method of production, with some commonly

made items including bottle caps and outdoor furniture. Injection molding typically is capable of tolerances equivalent to an IT Grade of about 9–14.

Standard two plates tooling – core and cavity are inserts in a mold base – "Family mold" of 5 different parts The most commonly used thermoplastic materials are polystyrene (low cost, lacking the strength and longevity of other materials), ABS or acrylonitrile butadiene styrene (a terpolymer or mixture of compounds used for everything from Lego parts to electronics housings), polyamide (chemically resistant, heat resistant, tough and flexible – used for combs), polypropylene (tough and flexible – used for containers), polyethylene, and polyvinyl chloride or PVC (more common in extrusions as used for pipes, window frames, or as the insulation on wiring where it is rendered flexible by the inclusion of a high proportion of plasticiser). Plastics reinforced with short fibres can also be injection molded.

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1 Equipment • 1.1 Mold • 1.2 Design • 1.3 Machining • 1.4 Cost 2 Injection process • 2.1 Injection molding cycle • 2.2 Molding trial • 2.3 Molding defects 3 History 4 See also 5 Notes 6 References

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[edit] Equipment

Paper clip mold opened in molding machine; the nozzle is visible at right Main article: Injection molding machine Injection molding machines, also known as presses, hold the molds in which the components are shaped. Presses are rated by tonnage, which expresses the amount of clamping force that the machine can exert. This force keeps the mold closed during the injection process. Tonnage can vary from less than 5 tons to 6000 tons, with the higher figures used in comparatively few manufacturing operations. The required force is determined by the material used and the size of the part, larger parts require higher clamping force. [edit] Mold Mold (Tool and/or Mold) is the common term used to describe the production tooling used to produce plastic parts in molding. Traditionally, molds have been expensive to manufacture. They were usually only used in mass production where thousands of parts were being produced. Molds are typically constructed from hardened steel, pre-hardened steel, aluminium, and/or berylliumcopper alloy. The choice of material to build a mold from is primarily one of economics, steel molds generally cost more to construct, but their longer lifespan will offset the higher initial cost over a higher number of parts made before wearing out. Pre-hardened steel molds are less wear resistant and are used for lower volume requirements or larger components. The steel hardness is typically 38-45 on the Rockwell-C scale. Hardened steel molds are heat treated after machining. These are by far the superior in terms of wear resistance and lifespan. Typical hardness ranges between 50 and 60 Rockwell-C (HRC). Aluminium molds can cost substantially less, and when designed and machined with modern computerized equipment, can be economical for molding tens or even hundreds of thousands of parts. Beryllium copper is used in areas of the mold which require fast heat removal or areas that see the most shear heat generated. The molds can be manufactured by either CNC machining or by using Electrical Discharge Machining processes [edit] Design Molds separate into two sides at a parting line, the A side, and the B side, to permit the part to be extracted. Plastic resin enters the mold through a sprue in the A plate, branches out between the two sides through channels called runners, and enters each part cavity through one or more specialized gates. Inside each cavity, the resin flows

around protrusions (called cores) and conforms to the cavity geometry to form the desired part. The amount of resin required to fill the sprue, runner and cavities of a mold is a shot. When a core shuts off against an opposing mold cavity or core, a hole results in the part. Air in the cavities when the mold closes escapes through very slight gaps between the plates and pins, into shallow plenums called vents. To permit removal of the part, its features must not overhang one another in the direction that the mold opens, unless parts of the mold are designed to move from between such overhangs when the mold opens (utilizing components called Lifters). Sides of the part that appear parallel with the direction of draw (the direction in which the core and cavity separate from each other) are typically angled slightly with (draft) to ease release of the part from the mold, and examination of most plastic household objects will reveal this. Parts with bucket-like features tend to shrink onto the cores that form them while cooling, and cling to those cores when the cavity is pulled away. The mold is usually designed so that the molded part reliably remains on the ejector (B) side of the mold when it opens, and draws the runner and the sprue out of the (A) side along with the parts. The part then falls freely when ejected from the (B) side. Tunnel gates tunnel sharply below the parting surface of the B side at the tip of each runner so that the gate is sheared off of the part when both are ejected. Ejector pins are the most popular method for removing the part from the B side core(s), but air ejection, and stripper plates can also be used depending on the application. Most ejector plates are found on the moving half of the tool, but they can be placed on the fixed half if spring loaded. For thermoplastics, coolant, usually water with corrosion inhibitors, circulates through passageways bored through the main plates on both sides of the mold to enable temperature control and rapid part solidification. To ease maintenance and venting, cavities and cores are divided into pieces, called inserts, and subassemblies, also called inserts, blocks, or chase blocks. By substituting interchangeable inserts, one mold may make several variations of the same part. More complex parts are formed using more complex molds. These may have sections called slides, that move into a cavity perpendicular to the draw direction, to form overhanging part features. Slides are then withdrawn to allow the part to be released when the mold opens. Slides are typically guided and retained between rails called gibs, and are moved when the mold opens and closes by angled rods called horn pins and locked in place by locking blocks, both of which move cross the mold from the opposite side. Some molds allow previously molded parts to be reinserted to allow a new plastic layer to form around the first part. This is often referred to as overmolding. This system can allow for production of one-piece tires and wheels. 2-shot or multi shot molds are designed to "overmold" within a single molding cycle and must be processed on specialized injection molding machines with two or more injection units. This can be achieved by having pairs of identical cores and pairs of different cavities within the mold. After injection of the first material, the component is rotated on

the core from the one cavity to another. The second cavity differs from the first in that the detail for the second material is included. The second material is then injected into the additional cavity detail before the completed part is ejected from the mold. Common applications include "soft-grip" toothbrushes and freelander grab handles. The core and cavity, along with injection and cooling hoses form the mold tool. While large tools are very heavy weighing hundreds and sometimes thousands of pounds, they usually require the use of a forklift or overhead crane, they can be hoisted into molding machines for production and removed when molding is complete or the tool needs repairing. A mold can produce several copies of the same parts in a single "shot". The number of "impressions" in the mold of that part is often incorrectly referred to as cavitation. A tool with one impression will often be called a single cavity (impression) tool. A mold with 2 or more cavities of the same parts will likely be referred to as multiple cavity tooling. Some extremely high production volume molds (like those for bottle caps) can have over 128 cavities. In some cases multiple cavity tooling will mold a series of different parts in the same tool. Some toolmakers call these molds family molds as all the parts are not the same but often part of a family of parts (to be used in the same product for example). [edit] Machining Molds are built through two main methods: standard machining and EDM. Standard Machining, in its conventional form, has historically been the method of building injection molds. With technological development, CNC machining became the predominant means of making more complex molds with more accurate mold details in less time than traditional methods. The electrical discharge machining (EDM) or spark erosion process has become widely used in mold making. As well as allowing the formation of shapes which are difficult to machine, the process allows pre-hardened molds to be shaped so that no heat treatment is required. Changes to a hardened mold by conventional drilling and milling normally require annealing to soften the steel, followed by heat treatment to harden it again. EDM is a simple process in which a shaped electrode, usually made of copper or graphite, is very slowly lowered onto the mold surface (over a period of many hours), which is immersed in paraffin oil. A voltage applied between tool and mold causes spark erosion of the mold surface in the inverse shape of the electrode. [edit] Cost The cost of manufacturing molds depends on a very large set of factors ranging from number of cavities, size of the parts (and therefore the mold), complexity of the pieces,

expected tool longevity, surface finishes and many others.

[edit] Injection process

Small injection molder showing hopper, nozzle and die area [edit] Injection molding cycle For the injection molding cycle to begin, four criteria must be met: mold open, ejector pins retracted, shot built, and carriage forward. When these criteria are met, the cycle begins with the mold closing. This is typically done as fast as possible with a slow down near the end of travel. Mold safety is low speed and low pressure mold closing. It usually begins just before the leader pins of the mold and must be set properly to prevent accidental mold damage. When the mold halves touch clamp tonnage is built. Next, molten plastic material is injected into the mold. The material travels into the mold via the sprue bushing, then the runner system delivers the material to the gate. The gate directs the material into the mold cavity to form the desired part. This injection usually occurs under velocity control. When the part is nearly full, injection control is switched from velocity control to pressure control. This is referred to as the pack/hold phase of the cycle. Pressure must be maintained on the material until the gate solidifies to prevent material from flowing back out of the cavity. Cooling time is dependent primarily on the wall thickness of the part. During the cooling portion of the cycle after the gate has solidified, plastication takes place. Plastication is the process of melting material and preparing the next shot. The material begins in the hopper and enters the barrel through the feed throat. The feed throat must be cooled to prevent plastic pellets from fusing together from the barrel heat. The barrel contains a screw that primarily uses shear to melt the pellets and consists of three sections. The first section is the feed section which conveys the pellets forward and allows barrel heat to soften the pellets. The flight depth is uniform and deepest in this section. The next section is the transition section and is responsible for melting the material through shear. The flight depth continuously decreases in this section, compressing the material. The final section is the metering section which features a shallow flight depth, improves the melt quality and color dispersion. At the front of the screw is the non-return valve which allows the screw to act as both an extruder and a plunger. When the screw is moving backwards to build a shot, the non-return assembly allows material to flow in front of the screw creating a melt pool or shot. During injection, the non-return assembly prevents the shot from flowing back into the screw sections. Once the shot has been built and the cooling time has timed out, the mold opens. Mold opening must occur slow-fast-slow. The mold must be opened slowly to release the vacuum that is caused by the injection molding process and prevent the part from staying on the stationary mold half. This is

undesirable because the ejection system is on the moving mold half. Then the mold is opened as far as needed, if robots are not being used, the mold only has to open far enough for the part to be removed. A slowdown near the end of travel must be utilized to compensate for the momentum of the mold. Without slowing down the machine cannot maintain accurate positions and may slam to a stop damaging the machine. Once the mold is open, the ejector pins are moved forward, ejecting the part. When the ejector pins retract, all criteria for a molding cycle have been met and the next cycle can begin. The basic injection cycle is as follows: Mold close – injection carriage forward – inject plastic – metering – carriage retract – mold open – eject part(s) Some machines are run by electric motors instead of hydraulics or a combination of both. The watercooling channels that assist in cooling the mold and the heated plastic solidifies into the part. Improper cooling can result in distorted molding. The cycle is completed when the mold opens and the part is ejected with the assistance of ejector pins within the mold. The resin, or raw material for injection molding, is most commonly supplied in pellet or granule form. Resin pellets are poured into the feed hopper, a large open bottomed container, which is attached to the back end of a cylindrical, horizontal barrel. A screw within this barrel is rotated by a motor, feeding pellets up the screw's grooves. The depth of the screw flights decreases toward the end of the screw nearest the mold, compressing the heated plastic. As the screw rotates, the pellets are moved forward in the screw and they undergo extreme pressure and friction which generates most of the heat needed to melt the pellets. Electric heater bands attached to the outside of the barrel assist in the heating and temperature control during the melting process. The channels through which the plastic flows toward the chamber will also solidify, forming an attached frame. This frame is composed of the sprue, which is the main channel from the reservoir of molten resin, parallel with the direction of draw, and runners, which are perpendicular to the direction of draw, and are used to convey molten resin to the gate(s), or point(s) of injection. The sprue and runner system can be cut or twisted off and recycled, sometimes being granulated next to the mold machine. Some molds are designed so that the part is automatically stripped through action of the mold. [edit] Molding trial When filling a new or unfamiliar mold for the first time, where shot size for that mold is unknown, a technician/tool setter usually starts with a small shot weight and fills gradually until the mold is 95 to 99% full. Once this is achieved a small amount of holding pressure will be applied and holding time increased until gate freeze off has occurred, then holding pressure is increased until the parts are free of sinks and part weight has been achieved. Once the parts are good enough and have passed any specific criteria, a setting sheet is produced for people to follow in the future.

Process optimization is done using the following methods. Injection speeds are usually determined by performing viscosity curves. Process windows are performed varying the melt temperatures and holding pressures. Pressure drop studies are done to check if the machine has enough pressure to move the screw at the set rate. Gate seal or gate freeze studies are done to optimize the holding time. A cooling time study is done to optimize the cooling time. [edit] Molding defects Injection molding is a complex technology with possible production problems. They can either be caused by defects in the molds or more often by part processing (molding)

Molding Defects Blister

Burn marks

Alternative name

Descriptions

Raised or layered zone on surface of the part Black or brown burnt areas on the Air Burn/ Gas part located at Burn furthest points from gate Blistering

Causes Tool or material is too hot, often caused by a lack of cooling around the tool or a faulty heater Tool lacks venting, injection speed is too high

Masterbatch isn't mixing properly, or Color streaks Colour Localized change of the material has run out and it's (US) streaks (UK) color/colour starting to come through as natural only Contamination of the material e.g. PP mixed with ABS, very dangerous Thin mica like if the part is being used for a safety Delamination layers formed in critical application as the material part wall has very little strength when delaminated as the materials cannot bond Tool damage, too much injection Excess material in speed/material injected, clamping thin layer exceeding Flash Burrs force too low. Can also be caused by normal part dirt and contaminants around tooling geometry surfaces. Particles on the tool surface, Foreign particle contaminated material or foreign Embedded Embedded (burnt material or debris in the barrel, or too much contaminates particulates other) embedded in shear heat burning the material prior the part to injection Injection speeds too slow (the plastic Directionally "off has cooled down too much during Flow marks Flow lines tone" wavy lines or injection, injection speeds must be patterns set as fast as you can get away with at all times) Deformed part by Poor tool design, gate position or Jetting turbulent flow of runner. Injection speed set too high. material polymer breakdown Polymer Excess water in the granules, from hydrolysis, degradation excessive temperatures in barrel oxidation etc Holding time/pressure too low, Localized cooling time too short, with sprueless Sink marks depression (In hot runners this can also be caused thicker zones) by the gate temperature being set

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Plastic Product Design Research

Overview The term "good" in design is fraught with subjectivity. Generally, a design should at least satisfy the needs of the customer at the lowest possible cost. Given different preferences of the customer regarding cost and quality, "good" designs can vary completely from a low cost Chery to a high cost Mercedes.

Past Advances Robust Design The term "robust" generally means that the design or process is insensitive to variation. A frequent measure of robustness is the process capability index, which is the ratio of the specification range to the observed variation. Our strategy for design is to first clarify customer's needs, then characterize the expected input variation, evaluate the value of the performance specifications, understand the functional relations between the decision variables and performance measures, estimate the expected output variation through moment matching or Monte Carlo methods, and ultimately derive a Pareto optimal set of solutions from which a preferred design may be selected. As shown in the following figure, the robustness of a design (as measured by combined yield) can generally be improved by increasing the cost (though we readily admit that the most significant gains are most frequently made through robust concept design!).

More recently, we have explored the concept of design flexibility in the event of performance failure. This concept suggests that it may be better to choose a design that is lower cost and not so robust, but may be easily improved in the event of failure. Currently, we are working to systematize these concepts in product and process design tools. Economics Cost estimation plays a vital role in product and process development. The question should not be "can it be done?" but rather "should it be done?" The cost almost always plays a significant role in the answer.

In particular, our research related to cost estimation is directed to robust product design and process development. With respect to robust design, the optimization issue is

determining the robustness to uncertainty (availability) as a function of increasing cost. In general, cost estimation is required on an application by application basis to ensure that an appropriate level of robustness is found. The following figure shows two designs with different levels of component integration. Our research has shown that the minimum cost and optimum level of component integration is a strong function of the process capability, and may not occur at total consolidation as implied by rules of Design for Manufacturing and Assembly. Quality and Design for Six Sigma With respect to process development, the optimization issue is determining the marginal cost as a function of the investment cost. In general, marginal cost can be decreased by increasing up-front investment. Cost estimation is required on an application by application basis to ensure that an appropriate level of process development is found. As shown in the following figure, there is a minimum cost of quality that may not occur at zero defect levels since the conformance costs are too high. It is our philosophy that the plateau around this minimum may be quite broad, and it is important for manufacturers to understand where they are on this figure and determine a proper balance.

Current Research Cost Optimization

We are continuing our research related to cost estimation in the following areas: 1) low volume manufacturing using rapid prototyping methods such as fused deposition modeling, 2) low level estimation of injection mold tooling and processing costs; and 3) high level estimation of production costs with varying levels of automation. We plan on embodying this research in new cost estimation and optimization tools in the next few months.

Related Publications 1. Irani, R. I., Kodiyalam, S., Kazmer, D. O., “Runner System Balancing for Injection Molds using Approximation Concepts and Numerical Optimization,” Proceeding from the 18th Annual ASME Design Automation Conference, 1992. 2. D. Kazmer, “Advanced Methods for Plastic Product Design and Process Control,” Toyota Motor and Suppliers Meeting, Lowell, MA, April 22, 2005. 3. Roser, C. and D. O. Kazmer, “Defect Cost Analysis,” Plastics Failure Analysis and Prevention", J. Moalli Ed. , 2001. 4. R. Karania and D. Kazmer, “Low Volume Plastics Manufacturing Strategies,” Submitted to ASME Journal of Mechanical Design. 5. Kazmer, D., Lotti, C., Breta, R. E. S., Zhu, L., "Tuning and Control of Dimensional Consistency in Molded Products," Advances in Polymer Technology, v. 23, n. 3, Fall, 2004, p. 163-175. 6. L. Zhu and D. O. Kazmer, “An Extended Simplex Method for Global Feasibility Evaluation,” Journal of Engineering Optimization, v. 35, n. 2, p. 165-176, 2003. 7. D. Kazmer, D. Kapoor, C. Roser, L. Zhu, and D. Hatch, “Definition and Application of A Process Flexibility Index,” ASME Journal of Manufacturing Science, v. 125, p. 164-172, 2003. 8. C. Roser, D. Kazmer, and J. Rinderle, “An Economic Design Change Method,” ASME Journal of Mechanical Design, v. 125, n. 2, p. 233-239, 2003. 9. Zhu, L. and D. Kazmer, “A Performance-Based Representation for Engineering Design,” ASME Journal of Mechanical Design, v. 123, n. 4, p. 486-493, 2001. 10. H. Xu and D. Kazmer, “Tight Tolerance Thermoforming,” International Polymer Processing, v. 16, n. 2, p. 208-215, 2001.

11. J. Reilly, M. Doyle, and D. O. Kazmer, “An Assessment of Dynamic Feed Control in Modular Tooling,” Journal of Injection Molding Technology, September, 2001, 5 (1), p. 52-61. 12. A. Fagade and D. O. Kazmer, “Early Cost Estimation for Injection Molded Parts,” Journal of Injection Molding Technology, September, 2000, 4 (3), p. 97106. 13. Xu, H. and D. O. Kazmer, “Productivity Evaluation with a Stiffness-Based Ejection Criterion of Injection Molding,” Journal of Injection Molding Technology, 1999, 3 (4), p. 211-218. 14. Kazmer, D.O. and C. Roser, “Evaluation of Product and Process Design Robustness,” Research in Engineering Design, 1999. 11 (1), p. 21-30. 15. Kazmer, D.O. and D.S. Roe, “Exploiting Melt Compressibility to Achieve Improves Weld Line Strenths,” International Journal of Plastics, Rubber and Composites Processing, 1998. 27 (6), p. 272-278. 16. Kazmer, D.O., “Best Practices for Injection Molding,” Journal of Injection Molding Technology, 1997. 1(1): p. 10-17. 17. R. Karania and D. Kazmer, “Low Volume Plastics Manufacturing Strategies,” Submitted to Design for Manufacturing Symposium at the 2005 ASME International Mechanical Engineering Congress and Exposition.. 18. David O. Kazmer, "Wall Thickness Optimization In Molded Product Design," Proceedings of the 2005 Society of Plastics Engineers Annual Technical Conference, 2005. 19. David O. Kazmer and Mahesh Munavallia, "Design and Performance Analysis Of A Self-Regulating Melt Pressure Valve," Proceedings of the 2005 Society of Plastics Engineers Annual Technical Conference, 2005. 20. D. Kazmer and L. Zhu, "An Integrated Performance Modeling System," Design for Manufacturing Symposium at the 2004 International Mechanical Engineering Congress, Anaheim, CA, 2004. 21. Karania, R., Kazmer, D., and C. Roser, "Plastic Product and Process Design Strategies," ASME DETC 9th Design for Manufacturing Conference, 2004. 22. Kazmer, D., Manek, K., Lotti, C., Breta, R. E. S., Zhu, L., "Dimensional Tolerancing and Control in Molded Products," Proceedings of the 2003 ASME

International Mechanical Engineering Congress & Exposition, Design for Manufacturing Symposium, Washington, D.C., November 16-21, 2003. 23. Zhu, L. and D. O. Kazmer, “An Evolving, Model-Based Quality Function Deployer,” ASME DETC 8th Design for Manufacturing Conference, v 3, 2003. 24. Kazmer, D., C. Roser, et al. (2003), “Hedge Strategies for Plastics Part Design,” Society of Plastics Engineers Annual Technical Conference: Product Design & Development Division, Nashville, TN. 25. Zhu, L., and D. O. Kazmer, “A Method for Multi-Criteria Decision Making,” Proceedings of the 4th National Science Foundation Design & Manufacturing Conference, 2002. San Juan, Puerto Rico 26. L. Zhu and D. O. Kazmer, “An Extended Simplex Method for Global Feasibility Evaluation,” ASME Design Automation Conference, 2002. 27. D. Kazmer, “The Development of Robust & Confident Decision Spaces,” Proceedings of the 4th National Science Foundation Design & Manufacturing Conference, 2002. San Juan, Puerto Rico. 28. Kazmer, D. O., Hatch, D., and L. Zhu“An Investigation of Variation and Uncertainty in Six Sigma,” ASME DETC 7th Design for Manufacturing Conference, v 3, p 21-29, 2002. 29. Zhu, L., and D. O. Kazmer, "An extensive simplex method mapping the global feasibility," Proceedings of the 28th Design Automation Conference, ASME Design Engineering Technical Conferences, v 2, 2002, p 765-771 Sep 29-Oct 2 2002, Montreal, Que., Canada. 30. Lang, J. and D. Kazmer, “How Increased Control in Plastic Melt Delivery Increases Productivity,” Accepted to Society of Plastics Engineers Annual Technical Conference, May 2002. 31. Kazmer, D. and L. Zhu, “Qualitative Reasoning for Decision Synthesis,” Proceedings of ASME DETC 6th Design for Manufacturing Conference, 2001. Pittsburgh, PA. 32. Doughty, M., Kazmer, D., “Dynamic Feed – Precision Molding in a Family Tool Application,” Plastics Odyssey 2001, Rochester, NY, Sept. 24-25, 2001.

33. Hawk, L, Kazmer, D., “Commercial Applications for Dynamic Feed™ Providing Dimensional Control for Each Injection Cavity,” K-Plast Processing Innovations, Düsseldorf/Neuss, Germany, 2001. 34. Kazmer, D. O., Zhu, L., Roser, C., “Some Advances in Design Representation and Feasibility Analysis,” Proceedings of the 3rd National Science Foundation Design & Manufacturing Conference, 2001. 35. Zhao, Y., Zhu, L., and D. O. Kazmer, “A Method for Multi-Criteria Decision Making,” Informs Decision Systems, 2000. Austin, TX. 36. D. O. Kazmer, A. Fagade, C. Roser, and L. Zhu, “Advances in Mechanical Systems Synthesis,” Proceedings of the 3rd National Science Foundation Design & Manufacturing Conference, 2000. Tampa, FL. 37. D. Kazmer, “Axiomatic Design Of The Injection Molding Process,” Proceedings of the First International Conference on Axiomatic Design, 2000. Cambridge, MA. 38. Kazmer, D. O., Fagade, A., Roser, C., Xu, H., and L. Zhu, "Incorporation of Engineering Analysis within Design Synthesis," Proceedings of the 2nd National Science Foundation Design & Manufacturing Conference, 2000. Monterrey, Mexico. 39. L. Zhu and D. Kazmer, “A Performance-Based Representation Of Constraint Based Reasoning And Decision Based Design,” Proceedings of the 12th Design Theory & Methodology Conference, ASME Design Engineering Technical Conferences, 2000. 40. Roser and D. Kazmer, “Flexible Design Methodology,” Proceedings of the 5th Design for Manufacturing Conference, Proceedings of the 5th Design for Manufacturing Conference, ASME Design Engineering Technical Conferences, 2000. 41. Roser and D. Kazmer, “A Method For Robust Flexible Design,” Proceedings of the Annual Technical Meeting of the Society of Plastics Engineers, Orlando, FL, 2000. 42. Fagade, A. and D. O. Kazmer, “Optimal Component Consolidation in Plastic Product Design.” Proceedings of the 4th Annual ASME Design for Manufacturing Conference, 1999. Las Vegas, NV.

43. Roser, C. and D. O. Kazmer, “Risk Effect Minimization using Flexible Design,” Proceedings of the 4th Annual ASME Design for Manufacturing Conference, 1999. Las Vegas, NV. 44. Zhu, L. and D. O. Kazmer, “A Performance-Based Representation for Engineering Design.” Proceedings of the 11th Annual ASME Design Theory and Methodology Conference, 1999. Las Vegas, NV. 45. Roser, C. and D. O. Kazmer, “Defect Cost Analysis.” in Proceeding of the Society of Plastics Engineers Annual Technical Conference, 1999. New York, NY. 46. Fagade, A. and D. O. Kazmer, “Effect of Complexity on Cost & Time to Market of Injection Molded Parts.” in Proceeding of the Society of Plastics Engineers Annual Technical Conference, 1999. New York, NY. 47. Xu, H. and D. O. Kazmer, “Validation of a Stiffness-Based Ejection Criterion for Injection Molding.” in Proceeding of the Society of Plastics Engineers Annual Technical Conference, 1999. New York, NY. 48. Fagade, A. and D.O. Kazmer. “Modeling The Effects of Complexity on Manufacturing Costs and Time-To-Market of Plastic Injection Molded Products,” in Proceedings of the Tenth Annual Conference of the Production and Operations Management Society, March 20-23, 1999. Charleston, S.C. 49. Carter, S. and D. O. Kazmer, “Studies of Plastic Boss Design and Methodologies.” in Proceeding of the Society of Plastics Engineers Annual Technical Conference, 1999. New York, NY. 50. Fagade, A. and D.O. Kazmer. “Economic Design Of Injection Molded Parts Using DFM Guidelines - A Review Of Two Methods For Tooling Cost Estimation.” in Proceeding of the Society of Plastics Engineers Annual Technical Conference, 1998. Atlanta, GA. 51. Kazmer, D. O., and C. Roser, “A Theory of Constraints for Design and Manufacture of Thermoplastic Parts.” in Proceeding of the Society of Plastics Engineers Annual Technical Conference, 1998. Atlanta, GA. 52. Kazmer, D. O., “Incorporation of Engineering Analysis into Design Synthesis,” NSF Division of Design, Manufacturing, and Industrial Innovation, Grantees Conference, Monterrey Mexico, January 1998.

53. Kazmer, D. O., “Beyond Analysis: Leveraging Computer Aided Engineering throughout Design and Processing,” First Gordon Conference for CAE in Polymer Processing, 1997. 54. Kazmer, D. O., Barkan, P., Ishii, K., “Quantifying Design and Manufacturing Robustness through Stochastic Optimization Techniques,“ Proceedings of the 22nd Annual ASME Design Automation Conference, 1996. 55. Kazmer, D. O., Roe, D. S., “Increasing Knit-Line Strength through Dynamic Control of Volumetric Shrinkage,” in Proceeding of the Society of Plastics Engineers Annual Technical Conference, 1994. 56. Kazmer, D. O., “Advanced Design Methodologies for the Blow Molding Process,” 20th Annual Structured Products Conference, Society of the Plastics Industry, 1991. 57. Hayes, C., Wood, W., Mekshat, L., Kazmer, D., “Design for Manufacturing: Future Directions for DfX,” ASME Design Engineering Technical Conferences, Salt Lake City, September, 2004. 58. Kazmer, D., “Fundamentals of Plastic Part Design and Manufacture,” National Manufacturing Week Workshop, Chicago, IL, 2003. 59. D. Kazmer, “Decision Based Design: Some Questions,” NSF Open Workshop on Decision Based Design, 2000. Baltimore, MD. 60. Kazmer, D. O., “Engineering Systems Design: Gaining Controllability of Dynamic Processes,” Dartmouth Thayer School of Engineering Jones Seminar, May 2000. 61. Danai, K., Kazmer, D. O., and B. Kim, "Polymer Part Design & Processing," University of Massachusetts Polymer Science & Engineering Symposium, 1999. 62. Kazmer, D. O., "A Theory of Constraints for Molded Part Design and Manufacture," GE Research & Development, 1998. 63. Kazmer, D.O., “Automating Molded Product Development using the Web,” Society of the Plastics Industry PlasticWorld, 1998. McCormick Center, Chicago. 64. Kazmer, D. O., “Robust Design Metrics,” GE Corporate Research & Development Center, 1996. 65. D. Kazmer, “Lean Development,” Flow Front Magazine, Moldflow Inc., April, 2005.

66. D. Kazmer, Book Review, Design of Machine Elements by M. F. Spotts, T.E. Shoup, L. E. Hornberger, Eighth Edition, Pearson Prentice Hall, Upper Saddle River, NJ, 2004 (ISBN 0-13-048989-1). Journal of Mechanical Design, 2003. 67. Kazmer, D. O., “An Optimization Primer,” paper written for Introduction to Engineering Course Reader, August 1, 2003. 68. D. Kazmer, Invention Disclosure, Method for Dynamic Cost Estimation of Injection Molded Article, 2002. 69. Kazmer, D., Hatch, D., Zhu, L., "Four Measures of System Performance," 2002. 70. Zhu, L., and D. O. Kazmer, "An Extensive Simplex Method for Mapping Global Feasibility," 2001. 71. Fagade, A., Kazmer, D., "Optimal Component Consolidation in Mechanical Systems," 2000. 72. Kazmer, D. O., Zhu, L., "A Performance Based Representation for Support of Multiple Decisions," International Application No. WO 00/72268, November 30, 2000. 73. D. Kazmer, Invention Disclosure, A Performance Orientation Chart for Decision Support, 2000. 74. Fagade, A., Kazmer, D., "Early Cost Estimation for Injection Molded Parts," 1999. 75. Fagade, A., Kapoor, D., and D. Kazmer, "A Discussion of Design and Manufacturing Complexity," 1998. 76. D. Kazmer, Invention Disclosure, Looking Glass: An Optimization System for Injection Molding, 1998. 77. Kazmer, D. O., Injection Molding Cost Estimator (Java Software), 1995. 78. Kazmer, D.O., “Injection Molding,” Encyclopedia of Chemical Processing, Marcel Dekker, Sunggyu (K.B.) Lee, Ed., 2005.