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Articles from 1997 In May

Q & A: True interchangeability of tool components

Interchangeable core and cavity components are recognized as a way to provide value to the customer by helping maintain high levels of production and minimizing downtime. While nearly every moldmaker provides spares, there is a difference between spares and true interchangeability.

John Thirwell, vice president of marketing and sales for Caco Pacific in Covina, CA, says that it requires a completely different mindset about moldmaking to provide truly interchangeable cores and cavities.

Bill Kushmaul, CEO of Tech Mold Inc. in Tempe, AZ agrees. Although the term interchangeability is often heard among the moldmaking community, it isn't something that is necessarily important to every mold, and is generally used only with specific types of customers in certain markets.

Thirwell and Kushmaul recently discussed the concept of interchangeability and its importance in those markets with IMM.

IMM: What is the definition of interchangeability?

Kushmaul: In true interchangeability, you have a world where parts are parts. It used to be that when you provided spares for a mold, you provided a spare for cavity one, a spare for cavity two, a spare for cavity three, and so on. You could not use cavity one's spare in cavity three if cavity three went down because each one contained a minute tolerance difference.

Interchangeability means that you have spare core and cavity components that are so accurate in tolerances that it doesn't matter which spare replaces which core and cavity, or whether it's one mold or a hundred molds, it produces exactly the same part in all instances.

IMM: Why isn't interchangeability provided with every mold built?

Kushmaul: What interchangeability brings to the party is enormous, but only if a certain set of conditions exists. Interchangeability is crucial primarily for global projects involving an established product in which the manufacturer needs the highest possible quality at the lowest cost to manufacture in seeking to establish market dominance.

Thirwell: Some molded parts have wide tolerances because they are stand-alone components. They don't have to fit with other parts. Molding a letter opener has much different parameters than molding a computer keyboard, for example. There's no reason to spend the money necessary to make every letter opener's tolerance within tenths.

IMM: What are the implications of interchangeability in the global sense?

Kushmaul: It means that a customer with molding plants worldwide pumping out billions of parts - printer cartridge components, for example - can buy a mold, put it in any press anywhere in the world and make the exact same parts. If a core and cavity goes down in Asia and you're out of spares, you can borrow spares from the plant in Europe. You only need to certify the steel.

Thirwell: It makes having global operations much easier, and makes part quality in any location in the world controllable.

IMM: Can you tell us the importance of the "parts are parts" scenario to the customer?

Kushmaul: In many cases, the customer puts the plastic components through some type of automated, high-speed assembly or packaging equipment. This automated equipment is designed to handle parts with a specified tolerance, which means consistency in part dimensions is crucial to its use. Parts with varying dimensions can cause the assembly equipment to go down.

Thirwell: In the medical world, if parts are not identical there can be a health risk. Certain parts need to fit in blood analyzers and centrifuges. If there is variation within the parts that causes them not to fit properly - if they're not interchangeable - the parts can break in test and there's a high degree of contamination risk.

IMM: What do you think has driven the increased use of interchangeability?

Thirwell: Three things, really. First, molding automation. The use of robots when you want to take parts out of a mold requires that the robots grasp certain areas of the part, which means that all the parts have to be the same.

Second, the postmolding, added-value operations that are automated - such as printing, labeling, assembly, or anything else downstream from the molding machine - require a high degree of cavity-to-cavity likeness, otherwise nonconforming parts interfere with the automation processes.

Third, parts that eventually go to make an assembly of a multitude of parts have to be assembled with other parts that come from other cavities from many molds. High-speed assembly equipment is often used, and if all the parts aren't completely interchangeable, nonconforming parts cause jams in the automated equipment.

Kushmaul: In years past, we built molds using primarily manual labor and skilled craftsmen. We didn't have equipment that was accurate enough to produce the high-quality parts necessary to make interchangeability on a large scale possible. So offering that was a special thing done only rarely for certain customers.

IMM: How has that changed in the past five years?

Thirwell: In true interchangeability, there can be no hand or benching operations; no quick programming or hand finish operations can be tolerated. You must go to extremes in design and programming, and the inserts cannot be hand touched.

You must completely eliminate the human factor in production. Moldmakers will become only assemblers. They will take the part as it comes off the machine and assemble it into the mold. That's why only a handful of companies provide this service. It's costly and requires certain skills.

IMM: How has the use of automated machining and computer numeric controlled EDM, milling machines, etc. enhanced the availability and use of interchangeability?

Kushmaul: The equipment available now is so good that it plays a factor in making interchangeability a more standard practice. We don't need people with 40 years of experience to produce the components. We're trading in skills for better organization and program management. Precise machine tools require that you be better organized.

Thirwell: To provide interchangeability, you have to set up your engineering and design areas properly. It all starts with mold engineering, through extensive programming and then precision machining to produce inserts that are truly interchangeable.

CNC equipment can help tremendously, providing the CAD/CAM equipment is put to proper use and is programmed for interchangeability. Many moldmakers have CAD/CAM and CNC equipment, but they get it more for simplifying or speeding up operations, which is fine. But if the capabilities are optimized and programmed properly, then it's a tremendous help.

Kushmaul: The future of these automated machines - CNC jig grinders, CNC milling machines, and EDMs - will allow us even more interchangeability than in the past. But then you run into this problem of two worlds.

IMM: Explain what you mean by that.

Kushmaul: Currently, moldmaking is moving in two different directions at once. World one is faster, cheaper. At the other end of the spectrum you have world two, which is high quality, solids designing, and interchangeability, which are really offset by a world demand for quickness. At some point these two worlds will converge. Machinability and speed will come together, but right now there's a gap between quality and speed.

IMM: Are you saying that the technology to blend these two isn't available yet?

Kushmaul: The technology is there, it just hasn't been developed for the [moldmaking] industry. We need more extensive use of automation to achieve quality and speed.

IMM: What is the demand for moldmakers to provide true interchangeability?

Thirwell: Everyone that deals with high-end OEMs producing high-volume molds, especially for parts used in automated assemblies has to offer interchangeability because their customers demand it.

A missing link is found in closed loop control

Milko Guergov, president and CEO of M&C Advanced Processes Inc. (Wyandotte, MI), says that what he wanted to do was to bring mathematical principles and analyses to the injection molding process. In so doing, he's developed a new kind of closed loop process control system, one that has many molding machine makers, resin suppliers, molders, and moldmakers extremely excited. Why? It's because they believe Guergov may very well have finally, in one stroke, removed much of the "black art" from the science of molding.

Basically, Guergov's mathematical analysis shows that a critical variable exists in the molding process that, up until now, has largely been overlooked - there's air-pressure resistance in a mold cavity when a part is shot. The internal melt pressure of the shot must be counterbalanced to compensate for the commonly recognized shrinkage forces and the air resistance in the cavity during fill and solidification. In this way, proper control over flow, stress, sink, shrinkage, and part density can be achieved.

The method and process control for injection molding in a prepressurized cavity, according to Guergov.

Guergov's solution is to prepressurize the system with shop air, typically at 200 psi, from the injection nozzle to the mold cavities. He uses air resistance itself to build and maintain a minimum static internal melt pressure. The cavities are sealed with neoprene rubber. Air pressure is equalized from the nozzle to the cavity. Pressure transducers in the injection nozzle and at the last place to fill in the mold cavity measure all air and melt pressure displacement transitions during the fill, pack, and hold phases of the cycle in real time.

It is these real-time measurements that generate the feedback for PID calculation. It is these signals that, through a PLC, are sent to the molding machine controller and hydraulics to adjust the ram, so the internal melt pressure is maintained at desired levels that are greater than shrinkage forces and air resistance, but are small enough to prevent stress and shear. Molding is accomplished from the material's point of view, rather than from the machine's point of view.

The loop is closed from the melt to the machine. This method eliminates the need to compensate for variations either in mold temperature, resin temperature, or viscosity. And it eliminates the need for a velocity-to-pressure switchover. Molders can control the actual condition of the melt in the cavity.

Most molded parts can be produced by a single process variable, namely, the internal melt pressure profile, which - again - is based on the minimum static pressure within the melt to counterbalance shrinkage forces and air resistance. This static pressure also gives the melt more mobility, so it can feed the faster solidifying areas of the part, eliminating sink while controlling shrinkage and density.

Algorithms in Guergov's software calculate the internal melt pressure profile based on signals from the nozzle and cavity transducers, taking into account the flow rate, melt temperature, modulus, shrinkage factors, part area, and part stress levels during solidification - mostly basic specs provided by materials suppliers. The mathematics, polymer sciences, and control theories behind this system may be daunting to some, but the significant results can easily be grasped just by looking at some of the parts Guergov has shot.

GCP process control allows molders to monitor and control the internal melt pressure of the shot. Therefore, molders can control the formation, movement, and growth of the gas bubble, even in long channels. Channel walls are uniform, and there's no unintentional skin penetration. And, localized gas bubbles can be formed. These prototype handle parts were shot using dried shop air to form the channels, rather than nitrogen.

Improved Process Control

Guergov's patented process control system is trademarked "GCP." That's GCP as in gas counterpressure. In this case, though, the "gas" is air, and the "counterpressure" is used to control the molding process. And, unlike the old gas-counterpressure systems used in structural foam molding, structural properties of parts are not lost. They are improved. The GCP process in this case is for improving the conventional molding process, and is not for structural foam. By the way, the "M&C" in the company name stands for "molding and casting." For almost 23 years, Guergov has been building molds, molding machines, and diecasting equipment. He's also been involved in setting up turnkey manufacturing plants, from start to finish.

A complete GCP system, including the machine-mountable pneumatics, strain-gauge transducers, and controller, sells for about $100,000 for retrofit to existing machines. Licenses are included in the base price. Machine modification and setup can be accomplished in two to four days. It's adaptable to all molding machines and molds. Guergov estimates the cost will be two to four times less if it's sold as a standard option on new machines. Mold modification costs from about $3000 to $5000, depending on mold size. When it comes to new machines, he does not plan on going in exclusively with any one OEM. All the major players are talking to him.

The caster-mounted controller is very easy to use. Next to the main display screen are two digital transducer readouts - one for the nozzle, one for the cavity. All the operator has to do is check every now and then to make sure these two numbers are the same.

If they are, the benefits are tremendous, and not just when it comes to shrink and sink control. (Guergov intentionally short-shot parts - they have no sink marks.) Cycle times can be reduced up to 20 percent due to faster cooling with thermoplastics, or faster heating with thermosets. Remember, the cavities are pressurized with air. Molds can be run at lower temperatures. The higher internal melt pressure forces the plastic against the cavity wall, so surface appearance improves.

Warpage is reduced or eliminated because there's balanced and equalized pressure and force as the plastic cools during fill and pack. This internal pressure balancing act also helps reduce or eliminate surface stresses as surface layers of the melt cool during fill. It increases the laminar nature of flow, and improves both part structural integrity and mechanical strength.

There's more. Part weight can be reduced up to 25 percent if blowing agents are used, because densities are equalized. There are no materials limitations. Reinforcements don't show up on the surfaces of filled or reinforced parts. Clamp tonnage can be reduced. GCP even improves the environment out in the shop, since air and decomposition gases displaced in the pressurized system can be vented outside. And imagine the freedom it provides in designing new parts, since designers don't have to engineer around normal molding problems with things like ribs and bosses.

Mold modifications for GCP processing can cost from $3000 to $5000, depending on mold size. Cavities can be sealed with neoprene rubber for pressurization. This production mold is used to make flush pedals.

GCP also can improve the performance of unconventional molding systems. Take gas assist, for instance. By controlling internal melt pressure with GCP, molders can control the formation, movement, and growth of the gas bubble, even in long gas channels, so the walls of the part have uniform thickness with no skin penetration. Bubbles can be grown simultaneously with cavity filling, either through a channel or in a localized area, so there are no witness lines. GCP gas assist allows molders to use dried shop air instead of nitrogen, and "gas" injection can be through a standard ejector sleeve and pin, rather than through some fancy nozzle.

Then there's multimaterial molding. Guergov has learned that GCP can allow molding of a part with two different-but-compatible materials on a standard, single-barreled molding machine. Material combinations, like 75 percent regrind:25 percent PP or 50 percent PP:50 percent PC/ABS, can be mixed together in a single, standard machine hopper. GCP process control builds the internal melt pressure of the mixed melt so that the higher modulus material solidifies faster. Like a sponge, shrinkage squeezes out the lower modulus, still-liquid material. In turn, the higher modulus material, now the core material, is centered in the cavity by the equalized melt pressure of the still liquid, lower modulus material, now the skin. There's no core shifting. Parts with some combinations of certain PP-PC/ABS blends that Guergov shot at M&C are paintable.

GCP shows promise in improving process control in metal injection molding, which involves high-density loadings of micron-sized metal particles. And optical disk production will benefit from faster cycling of more stress-free substrates. Thin-wall, complex parts in medical and consumer electronics markets, automotive parts, even toys - GCP can help molders produce better parts, cheaper. "You can't control that which you can't measure," Guergov says. By using mathematical models, theoretical details, and common sense to find and measure a critical missing variable, he may just have brought this "black art" of molding a bit more under control.

Getting material handling right

In 1993 the folks at Osram Sylvania wanted to make room on the shop floor by installing a centralized material handling system. So they called Conair and said what they wanted - dryers, hoppers, blenders, loaders. And Osram got it. "What we realized," says Tom Nolan, senior process engineer, "was that we thought we knew what we wanted. We didn't. We should have gotten what we needed." Osram Sylvania was also confounded by another factor: Its market shifted gears. The system wasn't designed to keep up.

Osram Sylvania, based in Seymour, IN, has 50 presses, ranging from 350 to 2000 tons. Using 26 grades of engineering resins - polycarbonate, nylon, PET, polythalate carbonate, acrylic - Osram Sylvania molds car and truck headlamps, lenses, and taillights. The plant ships about 60,000 units a day. The presses gobble up a lot of resin, and because many of the headlamp applications require optical-quality molding, material temperature and moisture levels are tightly controlled.

Osram's new mezzanine houses dryers, loaders, blenders, and drying hoppers, along with conveyors that distribute blended/dried material to 30 molding machines.

Prior to 1993, the automotive headlamp industry was a relatively stable one. With product and design lives lasting about five years, it was easy for Osram Sylvania to run the same material in the same mold on the same press for months on end, sometimes years on end. Very little happened year-to-year in the automotive industry that dictated real change.

With such predictability, Osram decided a centralized material handling system was the way to go. Instead of sliding gaylords up next to the press, why not pull resin from a silo outside, dry it centrally, and then distribute it on demand? So Osram's engineers picked a corner of the plant and decided the new system would go there. Thinking it knew what this system needed, Osram called Conair (Franklin, PA) and ordered the equipment - dryers, hoppers, weigh blenders, loaders, and controllers. Conair complied and installed the equipment.

Nolan says the equipment ran - and continues to run - well. The system, however, was plagued by three overlooked items. First, each dryer serves two hoppers, so that for every dryer that went off-line, two hoppers went off-line. Second, because of the low ceiling in the corner of the plant, the weigh blenders were nudged into the rafters, making maintenance difficult. Third was "spaghetti junction," the junction plate that evolved into a maze of hoses and valves that looked like a snake pit. Nolan says they worked long and hard to overcome these hurdles.

Market Changes

But there was one change that Osram could not have planned for and Conair could not fix: market metamorphosis. After 1993, the auto industry changed the way it designs and makes headlamps. Instead of discrete and separate parts for the headlight and turn signal, designers merged the two into one modular unit. Such designs required more material and larger presses. Resin demand increased; and the hoppers and the dryers couldn't keep up.

And on top of that, says Nolan, design cycles changed from five years to two to three years. The stability Osram previously enjoyed vanished. Runs shortened and material changes became more frequent. Osram adjusted as best as it could, prospered, and in 1996 added 135,000 sq ft. Nolan was determined this time to install another centralized material handling system, one that could handle current capacity and future growth.

Hoses are connected to a quick-disconnect station on the selector plate to direct the correct material to the correct macine.

To start, Osram put the new system closer to the center of the expanded space. "The old system was shoe-horned into the corner of the plant," he says. The 30 presses (350 to 2000 tons) that were to fill the space would be placed around the new system. Next, says Nolan, Osram admitted that Conair knew more about material handling than it did. Instead of specifying particular equipment, Osram gave its requirements in terms of resin volume, resin demand, material type, material variety, number of presses, press capacity, and other factors. Conair then designed a system to meet all of those requirements.

The end product is a steel-lattice structure, about 120 by 30 ft, with stairs leading up to the mezzanine level approximately 10 ft off the ground where the dryers and hoppers are mounted. From there you can climb a short ladder to a catwalk that runs behind the hoppers; here you can easily read, access, and maintain the weigh blenders. The hoppers poke through the mezzanine floor of the structure, lower than the old version, and can pull from gaylords on the floor, or from one of eight silos outside. Conair says the new system was particularly challenging because of the long distances material has to move - up to 500 ft. The system also allows material purging, another challenge given the long distances.

The new system has hoppers of the following sizes: eight at 2000 lb, three at 1000 lb, two at 750 lb, one at 500 lb, two at 350 lb. And each has its own dryer. Nolan says he deviated from Conair's recommendations in one area - he ordered the next largest size for each hopper. Summer weather in Indiana makes drying nylon difficult; he wants the extra capacity to stay ahead of the humidity. The weigh blenders have two hoppers and weigh and mix virgin and regrind. Osram typically mixes 10 to 20 percent regrind. If there's a problem with any of the equipment, an alarm sounds on the device and on Nolan's PC in his office.

Making Connections

To replace "spaghetti junction," Osram installed Conair's vertically aligned fantail manifolds. Hoses for each press drop from the ceiling and can be attached to any valve on the selector plate. Each hose and valve has an electrical interlock. When a hose and valve are mated, the controllers check to make sure the correct material is going to the correct press. If not, an alarm is generated.

The elbows on the pipes that move the material through the plant use Conair's Pneumatic Erosion Guard (PEG), an electroless chrome plating that's supposed to last longer and leak less, especially when moving abrasive material such as nylon. Nolan says the PEG system is considerably more expensive, but if it saves him or someone else from having to replace leaking elbows 35 ft off the plant floor, it's worth it.

At the press, residence time is kept to three to 10 shots. The only space taken up beside the press is a vacuum pump that pulls material from the hoppers. The old system had one pump for every 10 presses; the new system has a pump for every three presses. All material use data are automatically sent to Nolan's PC where he can extract numbers for rates and volumes by material type.

Nolan says the system saves about 25 percent in floor space between each press. On top of that, the molder has an automated material handling system that can meet current and future capacity requirements. At $1.2 million, Osram finds it's worth it. "But the biggest difference," says Nolan, "is that we got the right one in first."

By Design: Training: Put up or Shut up

In this bimonthly column, Glenn Beall of Glenn Beall Plastics Ltd., Libertyville, IL, shares his special perspective on issues important to design engineers and the molding industry.

I had the good fortune to find a job in the plastics industry right out of college. I find it hard to believe, but that was 40 years ago. I can remember a time when there were no polycarbonates or ABS materials. In those days, everything was molded on plunger presses and Reed Prentice was king. I saw the introduction, initial rejection, and final acceptance of the in-line reciprocating screw. I made the mistake of buying one of the first CNC-controlled molding machines. That purchase put me in a position to help finance the rest of the development of that control package, while helping to train the machine manufacturer's customer service personnel. Learning about new technology has always been traumatic.

Over the years, there have been many changes in the injection molding industry. In retrospect, an equal number of things has remained exactly the same. One of those contrasts is that there has always been a shortage of technically competent people to keep up with the growth of the plastics industry. Now in the late 1990s, we know much more about the injection molding process than ever before. The problem is that what has been learned is not being taught to the plant people who are in need of the information.

The Problem of Incompetence

As a case in point, on a recent plant tour, I was asked about a 16-cavity, edge-gated project that always produced parts with sink marks. A glance at the runner indicated the nozzle opening into the sprue was only about half what it should have been. Later I was shown parts that were warped because the cavity was gated in a thin section, with the melt flowing toward a thicker wall. Neither of these parts was properly designed, but the inadequate mold design made the problem worse. Errors of this type were common when the industry was new and learning by trial and error, so this situation hasn't changed; but with what is known today, mistakes of this type must be classified as gross incompetence.

Education Isn't Free Anymore

Another contrast is that molders have always been in favor of more training opportunities for plant personnel. They have always paid lip service to education but talk was, and is, about all they were willing to pay. There are exceptions, but there are not enough molders who "walk the talk."

In the old days, everyone looked to the plastic material manufacturers to educate the processing industry. Their technical brochures and training seminars helped educate those who ran the molding plants in the rapid growth of the 1950s, '60s, and '70s. Regrettably, the material manufacturers have minimized their efforts in these areas as they downsize and concentrate on raising profit margins. The plastic material distributors are now trying to fill this void. Unfortunately, these smaller companies do not have the financial wherewithal of the larger chemical companies.

Today there are more universities offering plastics technology curricula than ever before. These institutions of higher learning do not, however, cater to plant personnel. Many liberal arts and local colleges have started full- and part-time plastics programs to service the plastics industry in their local areas. We are just now seeing the emergence of "technical universities" whose orientation is to train manufacturing personnel. However, too many of these well-intentioned ventures have declined or have been discontinued.

What went wrong with this concept that sounded so good in the beginning? What the educators heard was the plastics industry paying lip service to education. What they did not realize was that the processing industry would not support these activities on an ongoing basis. The plastics technology seminars that are now presented all across the country have become the "quick fix" for the industry. Yet seminars that are structured for plant personnel enjoy only average to poor attendance.

What Molders Must Do

It only takes the hint of a recession to prove that the plastics processing industry will not support education. This is hard to understand, as people don't have time for training when they are running shorthanded, flat-out, around-the-clock, seven days a week. A slowdown is the best time to train and upgrade staff.

Whether or not we have international customers, we are all working in a global economy. Right now, the United States is winning in the international productivity race, in spite of the fact that we are ranked 15th in the education and training of our work force. Even with NAFTA and the loss of injection molding projects to Asia, the United States has had seven years of steady economic growth. The unemployment rate is only 5.3 percent, the lowest in almost seven years. Every molder that I know complains about not being able to hire enough good operators to keep his machines running. Something has to change in order for the United States to survive and prosper in an increasingly competitive global economy.

Robots, fully automatic closed loop molding, conveyorized materials handling, and all of the other high-tech approaches to molding minimize the need for skilled operators, but do not eliminate it. Getting all of this high-tech equipment up and running, and keeping it up, takes a high level of technical competence.

The time has come for injection molders to recognize that they are going to have to start investing in their people, just the same as they now willingly invest in new equipment and buildings. There is no substitute for a well-trained work force.

More and more injection molders are willingly - or reluctantly - becoming ISO certified. One of the basic premises of ISO certification is that a molder must be able to prove that he has well-trained staff members that understand why they are doing what they are doing, and how to do it.

Progressive molders have already recognized this threat to their future profitability and have started to take action. Some larger molders now have in-plant training programs. They not only teach the basic skills of molding, setup, and quality control, but are of necessity forced to teach English, reading, writing, math, and basic work habits. Today, there are excellent video and interactive training programs that molders can use for in-plant technical training.

In various locations around the country, smaller injection molders and other processors are banding together to establish training programs at local colleges, universities, and trade schools. These teaching institutions have the advantage of already having their basic courses, such

as English comprehension, math, blueprint reading, and so forth. The Plastics Institute at Northern Illinois University and the Behrend College Plastics Lab at Penn State University at Erie are just two examples of this type. But these programs will only work as long as the industry supports them in good times and bad.

On a national level, the Society of the Plastics Industry is leading an effort toward certification of molding floor personnel, all the way from operators to setup and supervisory people. The requirements for certification will, in turn, establish benchmarks leading to a standardized curriculum for training plant personnel.

A standardized curriculum will make it much easier to get a local school to teach what is needed. The certification program will make it easier for a molder to evaluate applicants before offering them a job.

Put Up or Shut Up

All responsible injection molders have to be in favor of these SPI initiatives. If you are willing to "put your money where your mouth has always been," then call SPI's Drew Fleming at (202) 974-5246 and contribute to this program.

If you can't afford a cash contribution, then volunteer some of your time and some of your people to help with the program. If you are not willing to help at all, then stop paying lip service to education and resign yourself to the fact that you are moving toward an increasingly competitive marketplace with a technically incompetent staff.

DFM software gets cost-specific

When it comes to consumer products at the OEM level, designers and manufacturing engineers have no special affinity for injection molded plastics - they are simply another material-and-process combination within the engineering palette. Estimating the costs of tools, materials, and processing at an early stage in the design can be difficult. If the IM option doesn't look as though it will meet cost and performance specs, according to Peter Dewhurst of Boothroyd Dewhurst Inc., it is likely to be disregarded. "There is great pressure to move forward in design and get the product prototyped," Dewhurst told IMM in a recent phone interview. "That can be an obstacle to the use of injection molding. You've got to wait until designs are fairly detailed before getting quotes from moldmakers, which makes it difficult to get an accurate cost estimate in the concept design stage."

An updated geometry calculator in version 2.0 of BDI's injection molding module presents graphic icons of various part shapes. After a shape is selected, the program walks users through dimensioning and also identifies any inconsistencies in measurement.
The IM module performs volume and area calculations for a cantilever snapfit automatically after a designer inputs part dimensions.

To give designers an upfront, more accurate picture of the opportunities and costs for an injection molded part, BDI recently updated the newest module within its Design for Manufacture suite of software. Early Cost Estimating for Injection Molding (version 2.0) breaks total cost down into four areas: tooling, processing, material, and such secondary operations as printing, painting, or labeling.

In addition, the package offers estimates on the optimum number of cavities, setup time, setup cost, and cycle times. Designers can vary material choice, wall thickness, tolerances, and other parameters to quickly compare costs for candidate designs before tooling has been finalized. Users can select from aluminum, kirksite, and tool steel as potential tooling materials.

A Geometry Calculator entirely new to this version captures part volume, projected area, and complexity without the need for CAD drawings or models. Selecting various shape and feature icons prompts the program to build a volume estimate, then determines part complexity for use in calculating tooling costs. Also, projected area is calculated to determine clamping force requirements. Final results can be viewed several ways, from a single cost figure to detailed breakdowns of cost and time factors that can also be exported to spreadsheet and word processing applications.

Running an analysis is relatively simple. In the "Describe Part" window, users enter the part name, number, and production volume, then select a neat, filled, or reinforced resin from the material library. Finally, the program will ask for envelope dimensions of the part as well as average and maximum wall thickness. By choosing "optimum selection," the program automatically chooses the number of cavities for lowest part cost. "Manual" allows users to determine the number of cavities.

An "Operations" window captures details of mold type, runner systems, parting line complexity, and cavity life as well as core pulls and part tolerances. Also, additional costs such as inserts and packaging for shipment can be included.

Motivation to develop this and four other modules within the DFM family - diecasting, powder metal forming, sheet metal forming, and machining - came from observing the evolution in elegance for consumer product design. Comments Dewhurst, "Contours and sweeping geometries are possible only with net-shape processes. We wanted to let designers explore the benefits of using these processes to see if tooling investments were justified."

Currently in beta testing, the Windows-based IM module will be commercially available by late June. New for this version is a tie-in with BDI's Design for Assembly package, so that estimates from the DFM module can be imported into a total assembly analysis.

Winning designs in structural plastics

For those who wondered if gas assist was just another blip on the injection molding radar, the evidence on display at this year's Structural Plastics Conference suggests otherwise. Of the 80 products

in this year's design competition, 21 parts were molded wholly or partially with gas assist, tied with low-pressure structural foam, second only to solid-wall molding and up 10 from last year's total. This included everything from a large utility shed roof panel to an infant carrier to auto roof rails and minivan door handles.

Joe Bergen, president and CEO of Sajar Plastics (Middlefield, OH), says he thinks gas-assist molding has proven itself as a legitimate process, leading many molders to try the gas option. He also credits the decrease in litigation surrounding gas-assist technology and its licensees. "I think molders are more relaxed, more willing to try gas assist, less worried about who's suing whom," he says.

As in years past, the leading material of choice for parts in the competition was PPO/PPE, although it is not nearly as dominant as it was in past competitions. Rounding out the field were the usual suspects: polycarbonate, polyethylene, PC/ABS, ABS, urethane, and nylon.

This year's winners that were injection molded are pictured and described on these pages.

Conference Award

Instrument PanelInstrument panel. The instrument panel above, designed for Freightliner commercial trucks, is a unique blend of materials and processes - one that takes advantage of almost every molding process you can think of. It includes 16 plain injection molded parts, 10 counterpressure structural foam parts, two conventional structural foam parts, and six gas-assisted parts. Off-the-shelf parts include HVAC ducts, louvers, mounting hardware, and floor lights. The four main assemblies are bonded together with an acrylic adhesive. Consolidated Metco (Bryson City, NC) is the molder of the panel. Tom Simon, sales and marketing director at the Metco Plastics Div., says Freightliner's president saw and liked the "feel" of the dash on the model of the panel. To replicate that appearance, texture on the dash is molded in and then covered with a coat of soft-touch paint. Materials include ABS and PC/ABS for parts above the knee line. The panel also includes a bevy of extras, such as a retractable built-in trash can and scads of cup holders.

Building and Construction

SledgehammerSledgehammer. In what may be one of the most heavy duty applications of an injection molded part, Lifetime Tool (Madison Heights, MI) designed the integrally molded sledgehammers pictured on p. 46 to withstand heat, cold, and repetitive beatings. The material is Hivalloy, a filler-less engineering grade PP alloy from Montell. Dennis Siekierski, president of Lifetime Tool, says the 8-, 10-, or 12-lb heads are insert molded in a 700-ton press, giving the sledgehammer its one-piece design, an industry first. The plastic also attempts to overcome such OSHA hot buttons as cracking, splintering, and vibrating - all chronically associated with wood- or fiberglass-handled versions. And if it performs as well in the real world as it did in tests, the sledgehammer should prove a success. Siekierski says he tried more than 100 materials before settling on the Hivalloy. In third-party tests, the hammer passed 100 hits at 180F, Ð20F, and Ð40F, outperforming conventional designs.


Bristle squareBristle square. Gerber Garment Technology (Tolland, CT) makes a fabric cutter, the bed of which is composed of several of the 4-by-4-inch bristle squares pictured above. Each square needs to support the cut fabric, withstand vacuum pressure, and endure impact loading from a cutting cam device. Alliance Precision Plastics (Rochester, NY) made the complex mold and molds the part. Each square is molded from nylon and has 2450 bristles to support the cloth, and 1021 holes in the base through which the vacuum is pulled. Because the bristles are not indestructible, four feet on the bottom of each square snapfit to tracks built into the cutter, making replacement relatively simple and inexpensive.

Consumer Products

MugsMug. Coinjection molding and a proprietary phase change material provided by Phase Change Laboratories (San Diego) make the above mug a winner for designer, toolmaker, and molder Co-Mack Technology, based in Vista, CA. The inner and outer skin is molded from polypropylene, sandwiching the phase change material in between. Co-Mack reports that the phase change material holds temperature for more than an hour.


Pool PanelFlexible pool panel. After you win big bucks in the lottery and when you're ready to install your new swimming pool, be sure to check out the flexible pool panels from Horizon Plastics (Cobourg, ON) pictured at left. The living hinges in these structural foam molded panels allow pool designs to follow contours and shapes of almost any ilk. These 42-by-48-inch panels are molded from polypropylene, mainly to provide cold-weather impact for the living hinge. The hinges occur vertically every 4 inches to allow frequent twists and turns within one panel. Strips, drilled at different lengths, are attached horizontally to set the curve of each panel.


Intake ductIntake duct. To the untrained eye, this intake duct may seem pedestrian, but the beauty is in the detail. Designed by Fuji Heavy Industry and molded in Japan, this duct is molded not by lost core, but via gas assist using 40 percent glass-filled MXD6 nylon. The threads are insert molded, and postmold machining is used to open the ends of the duct. Fuji reports that it achieved a smooth finish, consistent wall thickness, and no hollow sections with a patent-pending gas-assist process.

Computers and Business Equipment

Business equipmentBusiness equipment. The label for this complex equipment is rather generic because manufacturer Lexmark International (Lexington, KY) was playing its cards close to its vest at the Structural Plastics Conference. That does not, however, detract from the significance of the design. The assembly consists of three parts, fastened to each other via molded-in mating features and thread-cutting screws.

This PPO/PPE structure uses 27 percent glass filler and 13 percent mineral filler. In the end, the frame assembly contains 65 machine interfaces and controls the positioning of all of the subsystems in the machine. Because there are only three primary parts, critical tolerances are minimized and machine-to-machine variation is reduced.

A university for moldmakers - in India

There is a severe shortage of moldmakers in North America. Organizations like the American Mold Builders Assn. (AMBA) have gone to great lengths to publicize the rewarding career opportunities moldmaking offers the young. And industry/academic teams like D-M-E and Ferris State have invested in creating programs to help train new tool builders. Yet demand still far exceeds supply. In another part of the world, in India, a successful institution exists that supplies the growing Indian industrial base and the world market with new moldmakers. It presently has 800 students.

Though it was started in 1963 with the support of the Indian national and state governments and development agencies working with the government of Switzerland, this institution has become self-reliant in a very practical manner - one that also could be used in North America. The lion's share (rather, the tiger's share) of this institution's financial support now comes from onsite custom molding, custom moldmaking, and contract manufacturing.

It's called the Nettur Technical Training Foundation (NTTF). NTTF Industries Ltd. is its manufacturing operation. NTTF's campus-like setting - complete with youth hostels and a cafeteria - sprawls over the Peenya Industrial Area in Bangalore, the largest industrial park in India, possibly the largest in Asia. Courses also are conducted at two other training centers. The core areas of training are in the fields of tool and die making, electronics, technical skills, tool design (postdiploma level), tool engineering (postgraduate level), and computer applications. Other courses include informal training programs, apprenticeship training programs, and evening courses in further education programs. Special training in courses tailor-made for specific industries also are available. All certificates and diplomas NTTF issues are recognized by industries in India and in other parts of the world.

At one center, training programs in technical skills and tool and die making are held for rural and disabled youth. NTTF even trains new entrepreneurs in courses comprised of 40 percent technical training and 60 percent management skills - everything from technical math, SPC/SQC, CNC machining, CAD, TQM, kaizen, JIT, QFD, and QMC to site selection, project appraisal and planning, modernization, materials, financial assistance, and personnel management.

Practice and Theory

The tool and die courses are a blend of practice and theory. The goal is to equip trainees with useful knowledge they can use immediately in industry. Basic training is offered free of charge. Small fees are required for the cafeteria services. Applicants must have a minimum of 10 years of formal education, at least a high school degree, and must pass an entrance exam. Preference for admission is given to meritorious students hailing from weaker economic areas.

The tool and die making diploma course is a three-year program followed by one year of in-plant training. During the course, trainees learn to design and manufacture complex tools, including press tools, plastics molds, diecasting dies, jigs and fixtures, and gauges. Advanced postgraduate courses in tool engineering and design are available, as are two-year certificate courses in moldmaking. For the final diploma-course exam, trainees must fully assemble a mold and successfully run it in a machine at NTTF Industries, all within 24 hours.

N. Reguraj is managing director. A toolmaker by trade who apprenticed under an American expert, Reguraj started India's Tool and Gage Manufacturing Assn., an organization somewhat similar to AMBA, six years ago. When he came to NTTF there were 60 students. As mentioned above, there are 800 today.

Training activities at NTTF are supported by on-site custom molding, moldmaking, and contract manufacturing. Customers include Maruti-Suzuki, India's number one carmaker.

What Reguraj brought to the table was the concept of supporting the training program through manufacturing. He felt the various governmental organizations backing NTTF could one day withdraw their support for any number of economic or political reasons. NTTF today is autonomous and is commercialized. Average annual sales for NTTF Industries is about $8 to $9 million. And, three years ago, NTTF went public. A trust holds the majority of shares and training is supported by that trust.

Reality-based Training

A tour of NTTF's impressive facilities in Bangalore is an enlightening experience. NTTF Industries is ISO 9001 and 9002 certified, and it's currently pursuing QS 9000. Its existing design center, which supports its manufacturing activities, is well equipped with CAD/CAM and CAE systems, running software from the likes of Cammand, AutoCAD, Virtual Engineer, and Moldflow. A full 90 percent of the design center's staff is NTTF grads. The design center turns jobs around from industrial designs in 20 days maximum, following established procedural details. By the second trial, 95 percent of all critical dimensions are achieved. Tolerances are generally held to within +/- 20 m. Prototyping presently is in ABS and steel tools.

Molds in Action

NTTF's Components Manufacturing Div. houses 10 hydraulic molding machines, ranging from 30 to 180 metric tons, mostly from Indian machinery OEM D.G.P. Windsor India Ltd. (Mumbai). Auxiliaries are from several sources, including dryers from Bry-Air (India) Pvt. Ltd. (Delhi). Its staff of 75 also is made up mostly of NTTF grads. Molds, built in-house for customers, are backplated for QMC. Use of hot runner systems from D-M-E, Incoe, and Mastip is prevalent. NTTF runs materials such as ABS, acetal, PC, and PP. Some 50 to 60 percent of its production is for India's growing automotive market sector. Contract-manufactured directional switch assemblies for customers like Maruti-Suzuki, India's leading carmaker, are its main product line.

NTTF produces about 38,000 of these modules every month to working tolerances ranging from within +/- .01 to .005 mm. Reject rates range from .7 percent to .4 percent. Production is supported by a fully equipped quality assurance room, housing such devices as a CEJ computerized coordinate measuring machine, a digital Nikon profile projector, and a Trimos height measurer. Its toolroom is equally well- equipped with such sophisticated equipment as Charmilles EDMs, Deckel universal milling and boring machines, Moore jig grinders, and Jung precision and surface profile grinders. Construction has begun on a new $280,000, 18,000-sq-ft design center. NTTF is purchasing three seats each of Pro-Engineer and I-Deas, one seat of Unigraphics, and one seat of Computervision. The new center also will have a selective laser sintering system for rapid prototyping. NTTF is making these investments to ensure the future success of its manufacturing and training activities.

Door-to-fascia dominion

Picture a plant that produces 100,000 assembled parts for 32 different automotive customers, then ships those subassemblies just in time. Factor in an additional requirement - known as in-line vehicle sequencing - which requires that parts come off the pallet in the same order as cars are sequenced on the customer's assembly line. Now envision shipping this quantity every day. Finally, add some of the highest quality standards imaginable to the mix. You're not dreaming - this is a typical day at Ford Automotive Products Operations' Utica Plant (APO Utica), a powerhouse in fascias and door trim panels. Ford APO ranks as the second largest automotive components manufacturer in the world. And don't be fooled by the Ford name: APO Utica not only competes with outside suppliers for Ford jobs, it recently opened its doors to "non-Ford" OEM and Tier One customers.

In case you're unfamiliar with the radical changes taking place among the Big Three, here's a short synopsis: Moving toward deintegration, today's automotive OEM has pared down its supply base while simultaneously demanding complete, bolt-on assemblies as well as design, testing, and warranty responsibility from those vendors who remain. Despite rumors to the contrary, in general, car makers confirm that they are no longer interested in piece-part manufacture. Instead, they want to become assemblers. As a result, Tier One and Two suppliers have consolidated into "systems integrators" capable of satisfying the demand. As part of this trend, APO Utica, while owned by Ford, operates as a massive Tier One with its own balance sheet.

How does such a gargantuan enterprise meet not only daily goals but also plan for the future? During our visit, it became apparent that Ford is betting heavily on both advanced technology and the power of Utica's workforce. The plant boasts nearly 3000 employees who participate in about 50 separate cross-functional teams aimed at higher productivity, more efficient plant maintenance, excellence in manufacturing, and innovative R&D.

The last time IMM visited Ford Utica, we toured the "Energy Island" (March 1996 IMM, p. 86), a centrally chilled, closed loop cooling system for LPM (low-pressure molding) presses. This second trip, conducted via golf-cart shuttle to cover the half-mile distances between different plant areas, takes in three major operations - fascia molding and assembly, a development area for the Advanced Manufacturing Engineering group, and LPM door trim panel production.

Door Panel Genius

Largest of Utica's four areas, the interior door trim panel operation (a.k.a. Area C) supplies panels for 75 percent of the Ford vehicles made for the North American market and 17 percent of all North American vehicles. That adds up to roughly 35,000 panels daily. In addition, this facility is the world's largest producer of LPM door panels, according to plant manager Don Vonk. Utica also offers every technology currently available in North America and Western Europe for door trim manufacture, including vacuum forming and low-pressure woodstock forming.

Eight JSW vertical presses currently mold Taurus/Sable door trim panels using the LPM method, essentially an injection-compression process. In one shot, polypropylene is backmolded onto a vinyl skin/olefin foam laminate, eliminating the need for secondary adhesive bonding (March 1997 IMM, p. 50). The foam is a custom material developed by supplier Toray Plastics (America) Inc.; process technology was licensed from Kasei Kogyo Co. Ltd. in Japan.

Utica commissioned two Williams-White LPM vertical presses (1325 tons) a year ago to mold front and rear door trim panels for the UN93. That's Ford lingo for the Expedition, arguably the hottest sport-utility on the market. These were the first LPM presses to be built in the United States, according to Greg Green, LPM manufacturing supervisor.

Clever process engineering and tool designs keep cycle times for the two-cavity molds to well under 2 minutes. Two foam/skin sheets are picked up and fed to the top mold half using an indexing gantry robot, then secured onto pins. At the same time, this same robot lifts completed panels out of the bottom half of the mold. During injection under low pressure, sequential valve gates release high-flow (40 MFI) polypropylene into the mold, while core and cavity remain a slight distance apart; mold halves then close completely to "squeeze" the resin into all areas of the tool. Pinch-offs trim the vinyl at the same time. At a base cost of $500,000, each tool molds a set of panels - both right and left sides - in one shot.

Another portion of the plant is devoted to taillamp molding, painting, and assembly, with annual output around 1 million parts. (Stay tuned for more details on this operation in an upcoming IMM issue.)

R&D on the Shop Floor

Utica plans to capitalize on its door panel molding expertise by driving the technology toward thinner walls, molded-in-color panels, and innovative skin materials. Joe Bonafiglia of Advanced Manufacturing Engineering (AME) works on future programs such as these in the AME development center, an area of the plant dedicated to developing new LPM applications. Here, a production-capable development press (1200 tons) manufactured entirely in North America includes a Williams-White clamp with an injection unit from Engel. Utica's AME group uses the press to conduct mold trials for production parts, to train employees, and to test advances in LPM technology.

One twist, for example, involves adapting the LPM method to horizontal molding machines. Skin-and-foam sheets would be fed by robotic gripper between mold halves prior to the injection phase, with the possibility for roll-fed operation in a future incarnation.

Another LPM project under way would replace the current vinyl skin with a thinner cover skin without foam, for lower cost and better definition on sharp contours. AME is currently working on this option for SW164, the Probe replacement coming out under the Cougar name for 1998. Bonafiglia points to a prototype, explaining benefits such as aesthetic appeal and thinner door substrates for cost reduction. Thin-wall substrates, 2.0 to 2.2 mm, take roughly 20 to 30 percent of the weight out of these developmental panels and reduce molding cycle time. A higher-flow PP was developed to meet thin-wall requirements.

For two-tone doors, such as those found on Econoline vans, AME's Aashir Patel is working on a hybrid panel molded in one shot, resulting in a molded-in-color bottom half with a vinyl-covered top. Utica is also working concurrently on materials for molded-in-color panels, aiming for better scratch resistance than current talc-filled PP.

For the Escort replacement, the CW170, Utica has developed an in-mold embossing technique. "Currently," says AME engineer Aashir Patel, "we can laser-etch any electronic image onto vinyl skin covers. These same patterns will be cut into inserts for door panel molding, so that vinyl skins can be embossed as the panel is molded." Patel and others are also working on TPO to achieve a completely recyclable olefin-based door panel.

Fascia to Fascia

Welcome to the land of the giants - 4000-ton Ube giants, to be exact. Joe Bell, fascia manufacturing supervisor, explains that this building, known as Area A, is part of a current expansion. "Utica is now in the process of converting its RIM fascia manufacturing completely to recyclable TPO for cost reduction, better molding efficiency, and paintability," says Bell. When the dust settles next year, the plant will contain 10 mammoth presses to supply 1.3 million fascias annually.

In addition to molding front and rear fascias for most of Ford's luxury vehicles, Area D also supplies parts for Taurus/Sable, Navigator, Explorer, and Mustang platforms. "Working together internally with AME has allowed us to reduce wall thicknesses and improve cycle times via sequential valve gating," Bell notes. The Taurus wraparound front fascia, for example, is a geometrically complex, 10-lb part, yet it's molded in a mere 108 seconds. Mold changes now require only 30 minutes with two employees, thanks to a quick-change system developed in-house.

AME's Gerry Dominick chose to announce a new technical development for fascias during this part of the tour. "Another example of shared internal technology will be debuting shortly. We are introducing conductive TPO resin for fascias, a filled material that significantly improves electrostatic paint transfer efficiency, resulting in reduced paint costs and improved quality." Utica developed the material using a low-cost additive. The secret, according to Dominick, is in the blending. Resin supplier D&S Plastics will compound the material for Utica, then make it available to other molders late this year. In return, APO will receive a small royalty on resin sales.

Ford Utica, Utica, MI
Square footage: 2,000,000
Markets served: Automotive
Annual sales volume: $700 million
Payroll: $230 million annually
Parts molded: Door trim panels, bumper fascias, headliners, rear lamps, package trays, instrument panels (future program), small parts
Materials processed: PC, acrylic, TPO, ABS, PP, woodstock, urethane foam, fiberglass
No. of employees: 2827 total - 346 salaried, 2481 hourly
Shifts worked: Three 8-hour shifts, six days a week
Molding machines: Six 4000-ton Ubes; eight 1200-ton JSW low-pressure presses; two 1325-ton Williams-White low-pressure presses; 11 additional molding machines ranging from 650 to 1000 tons
Secondary operations: Electrostatic painting, adhesive laminating, vibration welding, pressure bonding, heat staking, ultrasonic welding, waterjet cutting, assembly
Internal moldmaking: No
Quality: ISO 9000, Q1 (certified on all components)

Ten questions to ask before sourcing tools offshore

Thinking about partnering with a moldmaker overseas? Michael L. Hetzel, president and CEO of Broadview Injection Molding, Broadview, IL, offers the following 10 items to review with a prospective offshore tool building partner, based on his own exhaustive two-year search involving a field of 20 candidates, 10 finalists, and five visits:

1 You should plan on controlling the mold design. Does this mold supplier have the proper, compatible modem communications links and software?

2 Does this supplier have a design leader willing to make overseas calls sometimes at odd hours?

3 Does the supplier have access to the same mold materials of construction that you do? If you prefer to use Uddeholm, can your supplier comply?

4 Can you work directly with this supplier? Why pay a middleman, like a U.S. agent?

5 Is your supplier the cheapest you can find that can still provide the type and quality of mold you need?

6 Can the tooling manager at your candidate supplier speak English? What about technical English?

7 How does the supplier handle multiple slides, intricate shutoffs, cavity-to-cavity repeatability, and sampling? Send out a design and have the supplier quote your approach.

8 Have you visited your prospective supplier? Any supplier can make a beautiful brochure and show you samples, but you have to visit the plant to examine not only the toolroom, but the parking lot, the washrooms, and the administrative offices. Cultural differences aside, clues to the supplier's stability, capability, and financial resources abound.

9 Have you gotten to know the supplier's principals as well as its technical staff, in order to better understand its corporate culture?

10 Has the supplier visited your plant to see what it is going to be quoting, and to better understand your processing protocols?

Analyzing snapfit pays off for nozzle design

If you build a better subsystem, will automakers beat a path to your door? That's what happened to Bowles Fluidics Corp., a Columbia, MD-based custom molder specializing in automotive systems. The company's patented windshield washer nozzle has captured 90 percent of the domestic auto market and a good share from Japanese and European automakers as well. Designers attribute the nozzle's success, in part, to finite-element analysis early in the design cycle.

Unlike its counterparts, the Bowles nozzle has one orifice, not two, and no metal is used in the part, which eliminates the need for insert molding. As a result, it costs less to produce. But what really sets this product apart is not apparent until you wash the windshield of your car. Interior geometry causes the fluid to oscillate, spraying the windshield in a fan-shaped pattern. Patterns are customized to accommodate specific automobile models, so there are many variations. Rather than two separate streams of fluid, the result is consistent coverage that hits even those annoying squashed bugs in the corner.

A patented design for this windshield washer nozzle captured a good share of the worldwide market. Manufacturer Bowles Fluidics attributes part of the nozzle's success to early structural analysis for snapfit integrity.

Design challenges for the nozzle were more complex than its size would indicate, according to product developers. Bowles employed Pro/E for modeling, Moldflow for filling analysis, and Ansys for structural analysis and assembly simulations.

In addition to windshield washer nozzles, Bowles Fluidics also makes defroster components and air conditioner outlets. Many of its products, including the nozzles, are snapfit parts. Installation force, the amount of force required to snap the nozzle onto the mounting hole as the car travels down the assembly line, is directly related to snapfit design.

Automakers want installation force to be as low as possible. Explains Qin Zou, computer analysis and process engineering manager at Bowles, "During assembly, the people on the line have about 15 seconds to insert the nozzles. They do this 8 hours a day, so the parts must be easy to snap in. If it's too hard, the snap feature may possibly crack."

Although installation force needs to be low, the automakers also don't want the nozzle to dislodge too easily. "They don't want someone shoveling snow off the car hood to accidentally remove the nozzle, too," says Zou.

Getting the perfect level of firmness in the nozzle snap feature is a constant balancing act for engineers. In the past, problems in this area were found after a nozzle was being installed on cars. The solution meant modifying the part and the molds, an expensive and time-consuming process.

To address this while a nozzle design was still in progress, Bowles chose a CAE solution. Ansys software was selected, says Zou, because the snapfit problem is nonlinear, both in terms of geometry (large deflection) and material, and the program supports nonlinear analysis.

Now when the company gets an order for a new nozzle, designers model it in Pro/E, then transfer it to Zou for simulation. His goal is to determine the correct shape and thickness for the nozzle's cantilever snap feature so that it deflects the correct distance when a customer-specified installation force is applied. Deflection is usually in the neighborhood of 2 mm; maximum installation force is around 10 lb.

"If you think of the snap feature as a cantilever beam, what we need to do is push the beam down 2 mm without breaking it," explains Zou. "We also want the force that pushes the beam 2 mm to be no more than 10 lb. After seeing the results of simulation, I adjust the thickness or length of the beam until the snap feature performs to those specifications."

Typically this process takes Zou two or three iterations, and requires between 8 and 20 hours. If the company were to create a prototype part to evaluate installation force issues, building the prototype tool would take six to eight weeks and cost between $7000 and $18,000. Now, unless a customer wants a prototype, the company skips this step and goes directly to production tooling.