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Articles from 1997 In February


The Troubleshooter, Part 12: Hot runners

This article continues our series of troubleshooting reports from one of the leading on-the-spot problem solvers in the molding industry. Bob Hatch is manager of technical service and customer support for Prime Alliance, the Des Moines-based resin distributor. Before his present assignment, Bob managed a molding operation for 25 years.

Gate dimensioning

  1. Gate diameter for hot runner molds
    • Gate diameter of 50 percent of wall thickness for easy-flow PE and PP.
    • Gate diameter of 75 percent of wall thickness for ABS, SAN, and acrylics.
    • Gate diameter of 90 percent of wall thickness for polycarbonate/acetal/ PVC/glass-filled materials and PPOs.
  2. Land length for hot runner molds
  • Land should be no more than .005 inch.
  • Check with your hot runner manufacturer for correct land length.

Problems with hot runners and heated sprue bushings always seem to be in one of three places. The first problem area is usually the gate diameter, second is the gate land, and third is the size of the nozzle orifice.

When troubleshooting hot runner problems, I start with the gate diameter and land length. The gate diameter should be at least half the wall thickness for polyethylene and polypropylene and bigger for the more shear sensitive amorphous materials such as ABS, acrylics, and polycarbonates. The land length of these hot tip gates should be .005 inch, usually indicated as a sharp edge on prints.

When the flow path is restricted because of a small gate diameter or a long land length, you will usually see higher heat settings being used by the molding technicians to get the parts to fill and pack out. The problem with this approach is that it usually causes warpage of the parts, cosmetic defects around the gate area, and long molding cycles.

If the flow path is sized correctly, you will be able to set the same heat settings on the front zone of the barrel, the nozzle, and the heated manifold, such as 450F across the board for ABS or 525F for easy-flow polycarbonate. If you find you have to run the manifold heats higher than the front zone of the barrel you probably have gate sizing problems. If you have to run the heats up on the nozzle, then the nozzle orifice probably hasn't been drilled out to match the flow tube diameter of the heated bushing (Figure 1). Notice that it isn't just sizing the nozzle orifice to match the hole in the heated sprue bushing. First you might have to increase the hole size of the sprue bushing to match the flow tube diameter, then drill the nozzle out to match that.

Figure 1. To optimize the performance of the hot runner, the sprue bushing orifice should be the same size as the main sprue bushing flow channel. Increasing the nozzle diameter reduces the pressure loss during both injection and decompression.

A case in point is a two-cavity hot runner mold that a good friend of mine is running in Arkansas. As often happens, he inherited this mold from another molder. The parts look like upside down banana split bowls (Figure 2) and the material is easy-flow polycarbonate. When he ran the mold for the first time, he found he had to run the barrel heats at a melt temperature of 610F to 620F plus all the injection speed and pressure he could muster and he still couldn't quite pack the flow lines out of one of the two parts.

The molder called the nationally known company that originally made the hot half of the mold and was advised to send the mold out to have it baked in a hot sand oven to clean out the degraded material and anything else that might be restricting material flow through the hot runner system.

He did send it out and when it came back it looked clean; but when he tried to run it, the part still wouldn't fill out. He called me for help again and I suggested he send me sample parts to see if I could find anything we had missed.

I received the parts and took a good look. The parts looked pretty good overall but, as he said, one of the parts had the flow lines he described over the phone. The flow lines looked like waves coming in off the ocean just before they crash onto the beach. It had to be a pressure loss problem. The second thing I saw was a brown streak on the part with the flow lines. The streak started at the gate and was about an inch long. It kind of looked like a candle flame because it started out with a narrow streak, spread out in the middle, then narrowed down again.

Now, I know that any blush or jetting at the gate means the gate is too small, and brown discolorations mean the material is being degraded by too much heat, but how to apply this to the problem wasn't totally clear. I knew it had something to do with the gate, so I started there. First of all, the gate didn't have the traditional recessed area and transition dimple or melt puddle like most hot runner gates. The gate was standing straight up from the part. The diameter was .105 inch, which is a little bit oversize for polycarbonate parts. We usually suggest the gate diameter should be 90 percent of the nominal wall thickness and these part walls were .105 inch thick. This would calculate out that the gate diameter should be .095 inch, so I knew the gate diameter was certainly big enough.

Then it hit me. At .105 inch in diameter, the gate size was okay, but the gate was standing straight up approximately .070 inch, not the sharp edge or .005 inch it should be.

No doubt the molder was running excessive heat in the manifold area to keep the long land gates from freezing off between shots, which was causing the polycarbonate to degrade. It was probably a combination of shear through the long land of the gate during injection and the extra heat needed to keep the gates open that were causing the brown streak and the flow lines.

I called the molder and told him what I had found, but he didn't want to get inside the manifold and start removing steel. He said something to the effect that the hot runner people should know what they're doing and that they wouldn't miss something as critical as the gate land length. I reminded him that the hot runner people probably didn't build the part of the mold that the gates are in, just the hot half. After a few quiet moments, he agreed to have the toolmakers take a look at it and see if he could get in there to remove enough steel to cut the land down to the proper dimension. I soon got a call from the toolmaker and had to convince him that the sharp edge was correct for a hot tip gate. He said he was afraid that reducing the land to a sharp edge would weaken the gate area and it would break out.

I reviewed with him how plastic flows and assured him that the maximum velocity of plastic flow is in the center of the flow channel with zero friction on the side walls, which is ideal for hot runner gates. I told him he could break the gates out if they get plugged with cold pellets or metal, but that is why melt filters are sold. Every hot runner should have a melt filter installed between the barrel and the nozzle. I guess that satisfied him or he just didn't think it would do any good to argue with me anymore; he said he would take a look and see what he could do.

A few days later, I got a call from the molder. He said the toolmaker was able to reduce the land as we wanted and the mold had been sampled with the changes. Not that I had any doubts, but I had to ask him how it ran. "Well," he said, "I'm not having any trouble filling and packing any more, but at first I was still getting the brown streak. After turning the heats down quite a bit (50 to 75 deg F) on the manifold, everything started running great."

Then he said, "You know we're 11 for 11 now," meaning this was the 11th mold I have helped him troubleshoot. He's getting pretty good at fixing up the two- and three-plate molds, but this was the first hot runner we had worked on together. I would say he's close to getting his "Official Bob Hatch Troubleshooter" diploma and badge! Not all hot runners can be fixed this easily; each has its own problems and its own way of being optimized. Sometimes it is stress concentration problems at the sharp edges of a gate recess area that causes breakage, and sometimes it is just the size of the gate and material melt flow that is causing filling problems or longer cycle times. But the majority of the time, it is the three areas covered here that cause most of the hot runner productivity problems.

TROUBLESHOOTER'S NOTEBOOK

Part: Clear polycarbonate bowl.
Tool: Two-cavity hot runner mold.
Symptoms: Burn marks, sinks, flow lines.
Problem: Mold had to run at very high heats (610F) to even fill incompletely; material was degrading, gate stood out from the part.
Solution: Reduced long land of the gate to minimize shear stresses on the material. This allowed the part to fill properly. Heat could then be turned down to eliminate burning and material degradation.

Are eco labels in your future?

The wave of environmental consciousness that's sweeping Europe and Asia may be headed to the United States. For molders and designers, especially those of computers and business equipment, it means learning new environmental lingo and molding products a little differently than before.

The root of this ecological awareness starts with eco labels. Tim Ullman is the manager for global product stewardship and compliance programs at GE Plastics (Pittsfield, MA) and spends a lot of time thinking about eco labels. He says eco labels are used predominantly in Europe and Japan right now; they present OEMs with a set of standards for energy use, material recyclability, and safety. These standards can apply to products ranging from dishwashers to diapers and lawn mowers to personal computers. They stipulate guidelines for ergonomics, electrostatic potential, height, weight, durability, labeling, resin use, and a myriad of other factors. After product testing, OEMs who meet the standards set out by the eco label they are pursuing are granted a certificate or license and can display the eco logo on their equipment. Though the label rarely carries the weight of law, it is a marketing tool for many OEMs.

There are about 12 organizations worldwide that administer and distribute eco labels. Some labels are privately administered with partial or full governmental financial support; others are administered from a government office. Eco labels are generally considered voluntary, and by European Union (EU) law, their use cannot be stipulated by member governments. However, according to an analyst at a U.S.-based computer manufacturer, European governments can adopt some or all of the guidelines of an eco label when purchasing equipment - a common practice in Europe and Asia.

The U.S. eco label, Green Seal, is seven years old and does not yet have guidelines affecting computer and business equipment. Janet Hughes, director of development at Green Seal, says the Washington D.C.-based, nonprofit organization is evaluating standards to affect information technology equipment, but she does not expect them before September 1997. The most established eco label in the U.S., Energy Star, has become a computer industry standard but only recommends guidelines for energy use.

So, if you mold computer and business equipment for European or Asian customers, eco labels could play a larger role in your business - if they don't already. But what do eco labels mean to molders? Technically, not much, but economically it could prove challenging. Most eco label guidelines do not apply to molders, but almost every eco label, according to Ullman, has one common plastics thread: The use of halogens is forbidden.

Most of the guidelines regarding halogens apply to computers, printers, computer monitors, and other such equipment. Specifically they prohibit the use of brominated flame retardants that might emit halogenated dioxins. Some guidelines also restrict the use of chloroparaffins in cabling and housings. Compliance with ISO 11469 is also required of many of the eco label guidelines.

While finding and molding a flame-retardant, halogen-free resin may not be particularly difficult, Tom Hablitzel, manager of computer products at GE Plastics, says such materials are generally more expensive than halogen-based grades. For one market that is already highly marginalized, information technology, added costs in the form of pricier resins will put more pressure on designers and molders to be more efficient. "It could have a big influence on materials specified for certain applications," Hablitzel says. "The initiative will be to take that cost out through thinner walls."

Ullman also points out that he knows of no supplier right now that makes a commercial flame-retardant ABS that is halogen-free. He says this may force many molders to use a flame-retardant, halogen-free PC/ ABS instead - which may or may not be desirable.

Molders may also be challenged by the fact that eco labels are not standardized from country to country. What may be true for one country and label may be slightly different or nonexistent for another. "While the Blue Angel label may have meaning in Germany, it may have lesser value in the U.K.," Hablitzel says. Ullman and Hablitzel say that molders should be able to develop a strategy that allows them to make parts that comply in spite of slight variations among labels; but if variations are too great, a molder could find himself with a split personality - molding the same computer monitor with different materials to comply with different guidelines in different countries. The EU is attempting to harmonize eco labels in Europe; however, Ullman points out that getting every European country on one eco label may be as difficult as getting all of Europe on one currency.

The ultimate impact of eco labels, according to an analyst for a U.S.-based computer manufacturer, may rely on consumers, not governments. The analyst says his research shows that consumers want products that are kinder and gentler to the environment, even if they don't know what an eco label is. He says, "Right now you can look at eco labels as a Good Housekeeping Seal of Approval." He says every eco label wants to have the credibility that Underwriters Laboratories gives to the customer. Eco labels are not there yet, but their credibility is growing, he says. - Jeff Sloan

Eco label web sites

Major eco labels

Country

Name

Guidelines addressed

Canada Ecologo/Environmental Choice Program CFCs
Germany ECO Circle
Test Mark
Cadmium, lead, vinyl chloride, chloroparaffins, brominated retardants, carcinogens
Germany Blue Angel Chlorine, bromine, carcinogens, cadmium, lead, chloroparaffins
Japan ECO Mark CFCs, toxic emissions
Netherlands Milieudeur Chlorine, bromine, carcinogens
Nordic Nordic Environmental Label/White Swan CFCs, cadmium, lead, chloroparaffins, PBDEs
Singapore Green Labeling Scheme Energy only, references Blue Angel
Sweden TCO '95 Chlorine, bromine, chlorinated solvents, mercury, CFCs
Taiwan ROC Green Mark CFCs
United States Green Seal None yet

Low-pressure molding trims part costs at Ford Utica

When the Taurus/ Sable platform underwent its last redesign, Ford Automotive Component Div.'s Utica plant did a little redesigning of its own. ACD Utica used a new padded trim laminate with olefin foam from Toray Plastics in its low-pressure molding (LPM) lines to produce door trim panels that were cost competitive, lighter, and easier to manufacture than previous incarnations.

According to Ford's Aashir Patel, LPM originated in Japan when Sumitomo Chemical developed a high-melt-flow PP that could be used in such a process, then patented the method, calling it Sumitomo press molding. It has been licensed to Kasai Kogyo, a Tier One supplier to Nissan. Ford ACD acquired the technology from Kasai, launching the first door panel at Utica in 1993 for the Thunderbird and making Ford the first to bring LPM to North America.

Patel related the equipment setup for Utica's LPM during a recent phone interview. Initial door panels are molded on an imported vertical press. A robotic sheet feeder places laminate sheets into the mold prior to each molding cycle.

From a processing standpoint, ACD technicians combine a vinyl skin/olefin foam laminate and PP substrate in one shot. The precut skin/foam laminate material is inserted robotically on the cavity side of an open mold. The mold closes partially, leaving a gap, and molten PP is injected behind the laminate at low pressure and 200C. No adhesives are required to bond the two materials, because the molten PP resin combines readily with the olefin foam during molding.

"Also," says Patel, "we are able to get all backside details in one shot - attachments for locator pins, wiring harnesses, hooks, etc. - Compare this to the traditional vacuum forming process: first, a rigid substrate is molded with vacuum holes, coated with adhesive, and transferred to the vacuum forming tool. A trim pad laminate is then placed above the adhesive-coated substrate, and a vacuum is drawn to bond the two components together. The additional handling increases the chance of damage to the PVC skin, says Patel, and adds time and cost. Closed loop controls maintain mold and resin temperatures and other parameters in the LPM process. "While we don't consider this a tricky process," Patel says, "doing it properly requires a certain amount of expertise. "All LPM molding at Ford Utica is performed in a building dedicated to that purpose.

Another secret to LPM success lies in the laminate material. For the Taurus/ Sable panels, olefin foam used to make the laminate was developed by Toray Plastics' PEF Div. (Front Royal, VA). According to Patel, the most common alternative to olefin foam is expanded PVC, a foam with densities four times higher than that of olefins. In addition, PP will not adhere to PVC without a synthetic backing, adding further to weight penalties. "Toray worked closely with us to meet our requirements for design and processing flexibility, weight reduction, and system cost efficiency," Patel notes, "then joined us in production start-up to ensure the foam processed properly in the tool."

Chris Workman of Toray explains how the unique foam chemistry makes it suitable for padded trim applications. "The foams are blends of two olefins - PP and PE - that are first lightly crosslinked to increase mechanical and thermal properties, then foamed into sheet stock ranging from 2 to 5 mm," he says. "They provide thermal performance to 200C, and have a specific gravity less than 1.0, making them the lightest foams available for padded trim."

Reverse engineering gets destructive

So how do you do mold verification? Do you use a laser scanner to measure part dimensions? Or look under a microscope? Perhaps you whip out the tried and true calipers and do it the old fashioned way. And just how do you get those critical inside dimensions? Have you thought about being a little more destructive? You may wish you had, because there's a way to absolutely destroy parts in order to bring them to life, verify molds, create prototypes, and build CNC tool paths.

Susan Lovelace, supervisor, material and process conformance at Cherry Electrical Products in Waukegan, IL, was looking for a "better way to use solid models to verify part quality." Cherry molds snap action switches, auto switches, gas discharge and gas plasma displays, and keyboards. The part in question is a switch housing molded from GE's Valox thermoplastic polyester, about .5 by 1 inch with 100 or so critical dimensions that had to be measured and verified to approve the mold. In the past, Cherry relied heavily on 2-D drawings, but they didn't produce the desired results. "We just couldn't get all of the dimensions we needed," Lovelace said.

Debra Kinder was in a similar boat. She's the senior quality engineer at Siemens-Furnas Controls in Batavia, IL, a manufacturer of motor controls and pressure switches. Its tool verification process was taking up to three weeks. Using mostly calipers and gauges, Kinder was trying to measure parts that were mostly nongeometric - lots of smooth lines, and sweeping curves - with few sharp corners and edges.

Lovelace and Kinder both tracked down Steve Gaspardo, owner of Gaspardo & Assoc., who has a way of not only measuring and verifying outside dimensions, but inside surfaces as well. It appears to be as effective as it is destructive; and it takes only a week.

"It's basically a 3-D Xerox machine." That's Dan Falvey, design engineer, reverse engineer, rapid prototyper, and CAD/CAM expert. He's talking about the ACSS (Automated Cross Sectional Scanning) RE1000, the device Gaspardo uses to capture, map, and digitize solid part geometry. Although Gaspardo says mold verification provides the bulk of his work, he points out that the ACSS can be used in all stages of molding, including reverse engineering, ongoing mold verification, and rapid tooling.

The ACSS works like this: You take your part or product, either fresh out of the mold or newly prototyped or just sculpted, and totally encase it in a block of epoxy so that every corner, every undercut is filled, with no voids. The epoxy needs to be a color that contrasts with the part color. Then mount the block on the aluminum base of the ACSS mill table. The ACSS uses a fly cutter to machine away thin layers of the epoxy encased part - layer thicknesses can range from .0005 to .010 of an inch. After each layer is shaved off, an optical scanner captures the exposed surface of the part and saves the data to a file. With each successive layer it captures every corner, edge, slope, angle, and dimple in the part.

The downside is that when it's done the part is destroyed. But the ACSS has a complete catalog of the part that is accurate, Gaspardo says, to within .001 inch. This captured data can be rendered in a point cloud, scaled up, scaled down, imported into a 3-D CAD package, output as an STL file for prototyping, or exported as an NC tool path to build a mold.

If it is used for mold verification, the device can also read and analyze the dimensions of the digitized part, comparing them to those of the master. It then generates a color-coded

3-D image indicating where the part is out of spec in relation to the master.

Noting how typically difficult it is to get a molded part into a database, Falvey says the ACSS system has several advantages over contemporary laser-based scanning systems. The first is that the end result is one digitized file that provides both external and internal dimensions. Falvey says most laser-based scanners provide multiple files that must be "patched" together to form a complete image; and laser-based systems do not provide internal geometry. Falvey also cites errors introduced by laser shadows, scan inaccuracies, and multipass inaccuracies. Because ACSS uses a layered scanning process, he says, the margin for error is greatly reduced. Falvey notes that undercuts, especially on anatomical figures, which are often a difficult hurdle for laser-based scanners, are easily mapped and digitized with ACSS.

The primary limitation of the ACSS, Gaspardo says, is size. The milling table can accommodate parts that fit within a volume 12 by 10.5 by 8 inches. This naturally eliminates larger parts and products, at least on the mold verification side. However, for design and prototyping, Falvey says that because the ACSS generates CAD files, any scale of product can be digitized and then scaled up or down, depending upon the application. Falvey acknowledges industry-wide hesitation to scale up electronic files, but he says, "I've not seen any scale-up problems to date."

The ACSS is also a system hog. That is, the data produced by the scanner is not the kind that can be copied to a 3.5-inch floppy on a base model home PC. Gaspardo says that depending upon how thick the milled layers are, the scanner can produce densities up to 600 dpi. When converted to a point cloud the density doubles, producing files, Gaspardo says, ranging from 5 to 60 Mb in size. To accommodate such monstrosities, Gaspardo uses a workstation PC with 2.2 Gb of storage and a Zip drive to manipulate and move data. He says he uses Pro-E for most of his CAD work.

In the end, as Kinder at Siemens-Furnas Controls points out, every dimension of the part is electronically filed. "It allows us to store parts without storing them," she says. This comes in handy, she says, when two years from now she wants to know exactly what the first part out of the mold looked like--compared to the 200,000th. Says Gaspardo, "Once you have the data and bring it into a software package, the possibilities are endless."

Falvey points out another application that does not leap immediately to mind, but may prove as useful; some of the hardest parts to measure are those with assembled pieces. He points out that the ACSS could be used to analyze snap-together parts, looking particularly at contact points, part-to-part stress, and deformations.

Though the technology the ACSS provides may cost a little more up front, Kinder and Falvey point out that the savings in time more than compensates. Gaspardo says he turns around all of his scanning and analysis within five business days, whether it's generating an STL file, color mapping, or creating a CAD file. Kinder says mold verification that used to take three weeks now takes one. "This way is more expensive than traditional methods, but sometimes time is more valuable than money," she adds.

Gaspardo says costs are comparable with laser scanning systems and vary depending upon the volume of the part when it's encased in the epoxy, the depth of the cut (which dictates total milling time), and the type of analysis required. Gaspardo says a typical mold verification analysis ranges from $2500 to $3500.

The Business of Molding #12: Quoting With Profit In Mind


Editor's note: This series of articles on business relationships of custom molders is from Bill Tobin, of WJT Assoc., a consultant in injection molding who believes in looking at the molding business in the most practical way.

There is an old saying about quoting molding services (or anything else): If you bid too high you won't get the job and you'll lose the opportunity to make money. But if you bid too low, you probably will get the job and lose money twice: once for taking on a job that loses money, and once for tying up your capacity so that you cannot bid on more profitable jobs.

If there's a lesser of two evils, it is to err on the high side of the bid and not on the low side. But there are several tricks to quoting that will help you manage your costs so that the quote stays competitive.

Resin Inventory Management

Too many people who buy computerized costing programs, or write their own, or (because they are computer disadvantaged) still do it manually, miss a chance to enhance their profits. For example, we all know it is a mistake to quote a job whose annual material consumption will be about a truckload and quote the truckload price. (If you actually buy the truckload of resin, you are turning into a bank, because you'll have to pay that invoice well before you have converted the material into product.)

However, in your company's philosophy this might be the right thing to do. Many buyers have told me the worst blind sales call they can get is from a new custom molder that calls itself a "general purpose" molder. This means the company is willing to run anything out of any material. At the last bankruptcy auction I attended, there were about 20,000 lb of resin for sale. Unfortunately, there were more than 30 different types of plastic in dozens of grades and colors. The downfall of this company was trying to be all things to all customers. There is a highly successful "custom" molder whom I know of in the Rocky Mountain area that freely tells all its customers, "We will quote any part that is either clear high-impact polystyrene or natural high-density polyethylene in the medical industry."

It has silos of HDPE and HIPS and buys resin by the railcar. It quotes the material cost at 10 percent below the annualized resin cost for each part. In this way, each part stands on its own with only a slight discount, but the molder enjoys the benefit of distributing the cost of resin across his entire customer base. He further avoids the panic or delays involved with getting extra resin when one customer wants more product.

It is simply good business to pick a market segment where you can do a good job. And it's only smart to keep the number of different resins you process down to a minimum. This allows your people to perfect the processing of what you do well. Bundling your resin inventory and distributing it over several jobs gives you an added profit margin as well as minimizing the late deliveries because you ran out of material and couldn't replace it fast enough.

As your customer base gets bigger and you can assure the resin company of reasonably continuous consumption of resin, ask your distributor for consignment shipping. This way, you don't pay for the resin until you consume it. This aids your JIT position, and only carries the burden of the warehouse cost. However, the resin supplier will always insist that its sales force do the audit, and the molder always pays for the discrepancy if the audit comes up short. The pluses: the molder will always have a minimum amount of resin on hand he is not obligated to pay for until it is brought to the molding floor. The molder will also be able to enjoy the discount of higher volume shipments. The distributor has lower shipping costs and everybody wins. The customer must pay as though each job stood on its own or was bundled with other jobs from the same customer. He is usually unaware the molder has bundled several of his customers together for the additional profit.

The Specialist Strategy

Some start-up companies have used an interesting strategy to build their business base. They go to the larger molders in the area and offer to take the jobs that use "exotic" materials as a subcontractor. This is a winning situation for everyone. If you hunt around any geographic area, you'll find many customers have placed jobs in these exotic resins with their major molders. The amount of this work is insignificant to the large molders and they take it as a courtesy to their customers. However, if you pick up a subcontract PEEK job here and there, learn how to run it, and deliver it on time, this makes you the specialist.

Soon you've got enough jobs to dedicate a machine or two to do nothing but run exotic resins (or highly polished flat lenses, or tiny parts). Since the big molder only ran these jobs as a courtesy to his customer, in time he will suggest that his customer come to you (the specialist) directly.

Many molders will nobid jobs that use PVC. Their usual excuse is that it corrodes the equipment and molds and is dangerous to their people. However, this comes out of ignorance of not knowing how to process this resin. There are several highly profitable molders who specialize in running PVC. While it isn't an exotic resin, simply being able to do this successfully can be highly profitable.

Another trick is to specialize in a specific marketplace. Usually molders in automotive cannot compete with the folks in telecommunications. Look at the accounts you make the most profit with and how you can contribute to your customer's operation. While the customer/supplier relationship is strong, it is only long term if constantly nurtured. Keep in touch with your customers, help the designers design the parts and the buyers structure the purchase orders or analyze the quotes.

Automation

Too many people are convinced that you cannot get every mold to run fully automatic. In fact, every mold can unless it requires handloaded inserts. Many molders and moldmakers don't want to invest the time in building the mold properly or won't continue refusing it until it does run fully automatic. It is amazing how much profit can be made if you don't slow the cycle down so that the operator can trim the gates, but instead off-load parts with runners attached into a container.

With an air press to degate the shot, an operator can easily outrun the molding machine and still have time left over for other work. For those jobs that automatically degate, the few thousand dollars spent on a sprue separator that feeds directly into a grinder will be paid back in a matter of months compared to the cost of manual operation.

It is becoming increasingly common for molders to have robots on machines, even with family tools. Simple end-of-arm tooling can be developed that will degate parts and then spread them far enough apart from each other to easily drop them into individual chutes. This eliminates the operator having to sort the parts into individual boxes. While the robot is relatively expensive initially, it is a one-time expense, usually requiring only new end-of-arm tooling for different parts.

When purchasing a robot, simple is better. Most tasks can be accomplished with simple robots and intelligently designed end-of-arm tooling. Only in rare instances do you need to spend for a robot an amount equal to a worker's annual pay. Even reasonably sophisticated end-of-arm tooling is dramatically cheaper than an operator, and very quickly pays for itself even in moderate-volume tooling.

Many companies have robots but don't use them. The usual excuse is that the folks on the production floor didn't (wouldn't, couldn't) read/understand the instruction manual. If the folks on the floor don't understand how to use this piece of equipment, bring in the company rep and hold an in-house workshop on its use. Tell the manufacturer you want a video tape on how to use and program it. Try to get him to provide it in the language your operators speak.

Packaging

Packaging is a cost that is normally thought of as a pass-through cost. However, profit improvements can also be found here. Look in your parking lot. How many stacks of skids are there against the warehouse wall? You may have gotten a deal by buying a truckload every few months. But how much money do you have tied up? How many different sizes of boxes and bag liners do you have? Again, the fewer, the better.

With the help of an electronic spreadsheet, you should be able to go to your cardboard supplier and negotiate an annualized contract with biweekly deliveries. While you may be charging your customer the unit cost of a box based on a single purchase of boxes for each shipment, you'll be enjoying the volume discount price and not have to take up valuable warehouse space with cardboard.

Look at the tape you're using to close your boxes. Generally, people use one of three types: Plastic tape, plain paper, or fiber-reinforced paper tape. It is also a common practice to shrink or stretch wrap the boxes to the skid. Ask yourself why you are using (expensive) reinforced paper tape when nonreinforced paper tape would do? Will the least expensive tape hold the box closed while the stretch wrap keeps the boxes on the skid? If your answer is yes, you can save a lot of money going to kraft tape instead of the more expensive reinforced paper or plastic tape.

Fully automatic molding (molding without direct operator involvement), minimizing the different kinds of material you run by specializing, consignment resin purchasing, and minimizing the variety of packaging you must maintain - all these allow you long-term lower cost contracts than continually "spot" buying for each job. There's no need to pass these additional savings onto your customers because you manage your business intelligently. Keep the cash you've worked hard to position yourself to earn. The lesson here is to use everything you have that is in best interest of your company. Quote the jobs based on the small picture, but keep in mind the big picture. - Bill Tobin

Speaking of computers. . .

Have you noticed how quickly new personal computer models and accessories appear on the market? The pace is blistering, with major OEMs churning out newer and better versions every six months or so. IT (information technology) is a growing market, and molders who want to participate can bank on compressed product development and production cycles.

In-house coloring and the right resin selection were keys to bringing the new JBL multimedia PC speakers to market on time. Ny-Glass worked with Dow and OEM Harman to speed development.

Handling IT's requirements for speed, cost, strength, and aesthetics doesn't have to be daunting, as custom molder Ny-Glass Plastics discovered. Appropriate resin selection can minimize difficulties downstream. To mold the housings for multimedia PC speakers, for example, Ny-Glass and its customer, Harman OEM Group, conferred with Dow Plastics applications development engineer Dave Jackim. "The housings needed impact resistance, aesthetic appeal, and strength," says Jackim, "but also had to fill the many ribs in the design and provide the best cost/performance balance."

Jackim recommended a polystyrene, Dow's Aim 4810, with toughness and gloss comparable to ABS and with the processing advantages of HIPS, at a lower cost than ABS. "Flow properties of the resin allowed us to gate both parts through an extremely small pin gate that left no legacy on the finished speakers," says Michael Hornak, president of Ny-Glass.

According to Dow, Aim 4810 logs in a melt flow rate of 8.5 g/10 min at 230C/3.8 kg, higher than that of most ABS grades. Aim resins are also designed for lower processing temperatures and rapid heat dissipation.

Another key to bringing this product to market quickly involved in-house coloring. "In-house coloring saves us two to three weeks over precolored resin on delivery time," says Hornak, "and by purchasing color concentrates from the same supplier as the PC manufacturer, we're assured of the best color match."

U.S. moldmakers can compete globally

Robert W. Shaw, president of Shaw Intercontinental Corp., wants to set the record straight on the perception that domestic moldmakers cannot compete with their Asian counterparts in terms of price and quality. "This kind of thinking is pervasive," he says, "but it is also dead wrong."

IMM asked Shaw to comment on this controversy because his company, a global design and engineering firm, sources molders and moldmakers (in the U.S. and overseas) for a wide variety of industries, including consumer, medical, industrial, and sporting goods concerns. Customers come to Shaw for services including product design, mold filling and structural analysis, molds, and molded parts. His working milieu gives Shaw a clear comparison of Asian and U.S. toolmakers.

"So far this year, I've worked on several projects totaling roughly half a million dollars where tooling has been sourced domestically because of superior delivery schedule and pricing," he reports. "In addition, we gained the advantage of geographic closeness, allowing us to interact more readily with the toolmaker."

Clients often give Shaw specific criteria for a tool, including the type of steel, special features, water line patterns, slides, and so forth, so that all parties quote against the same benchmark for the tool. Not all decisions are based on cost, he adds. "More complicated tools can't be forced because of pricing, because at the end of the day, what matters is productivity, not how much money was saved on the mold."

What are the hallmarks of competitive U.S. toolmakers? "Those who are contenders have a can-do attitude, for one," notes Shaw. "They are also getting automated, with CAM packages and CNC machining as the cornerstones of their operations. U.S. moldmakers also compete successfully for tools that are less intricate and in which tolerances aren't supercritical."

Team approach is another key. Shaw likes to interact with toolmakers, along with clients, to get everyone's input before anyone cuts steel. In this manner, troubleshooting is performed upfront, before small problems become production glitches.

His best advice to moldmakers: "Know what market you're in, what your strengths and weaknesses are as far as the type of tool you're willing to make." Asian and European moldmakers don't go after every job. Rather than attacking them all, Shaw suggests targeting where your expertise is, and then targeting resources you need to capitalize on that expertise.

"Bottlecap molds and automotive interior panel molds are two vastly different products, for example, requiring vastly different equipment and experience," he says. "In our business, we have opportunity to work with all of these resources and learn who is better at what. Several of our projects are split up so that each part is placed where the expertise lies."

What is Shaw looking for when he goes to source toolmakers? "I go to trade shows to learn capabilities. I check to see how we can work together, and how well we communicate personally. Are they innovative and aggressive? Does their word on delivery count? These are important questions, because our reputation is based on meeting the customer's needs."

If moldmakers find that competition from Asia is stifling, Shaw advises them to reassess their niches. "It could be that you have some very stiff competition overseas in the area you've been targeting. If that is the case, it's time to either invest in equipment and technology that will make you more competitive or apply your current resources to a different area of expertise."

Admittedly, the playing field between the U.S. and Asia is not exactly level. "There are government programs in Asia that give moldmakers there somewhat of an unfair advantage by supplying them with technology, equipment, and interest-free loans. People in the Far East recognize that this is a national business they want to develop, and the government is willing to help. Unfortunately, that's not the case here in the U.S." However, this edge can be offset at times by the cost penalty involved in bringing tools here from overseas. Duties and air freight add roughly 10 percent to the cost of tools being flown in from the Asia-Pacific region, according to Shaw.

Shaw's company attempts to work with domestic toolmakers as much as possible. "In return, we not only support the economy, we're getting our customers the best possible products at the best price, which makes great business sense." He also finds that working with toolmakers here has helped him build a network of resources, so that when he needs their expertise on specific projects, he has it.

How Gillette added rapid prototyping

As director of external technology for the Gillette Co., Robert Brown had to find a way to incorporate rapid prototyping so that it would be both useful and profitable. Because most of Gillette's products consist of molded plastics, the company was looking at RP as a way to quickly generate prototype tooling. Brown's approach, explained during a recent rapid prototyping conference at the University of Maryland, provides a blueprint for initiating technology changes at a manufacturing level.

"A technology can be successfully implemented, but whether it has a direct impact on the company's financial results is another matter," he explained to attendees at "A New Dimension in the Technological Revolution." To gather input from a busy technical staff on how RP would be used, Brown decided to experiment with a newsletter and questionnaire. "It was a means of drawing in the people that would benefit from RP and to solicit their ideas about how it should be used," he says.

Key newsletter aims and methods of achieving them included:

  • Educating staff at an early development stage in the process with useful information they might not find in trade journals and at conferences.
  • Identifying all potential users of RP by asking readers to submit names of others they believed would appreciate the newsletter.
  • Encouraging staff to become involved in the learning process by referencing additional outside sources of information.
  • Creating a forum for information exchange by feeding back results of the compiled questionnaire.

Designing the questionnaire was another matter. "We were aware that most return rates are in the 20 percent range, but we needed a much higher rate if we wanted useful information from a broad distribution of the technical staff," recalls Brown. To get that higher average return, Brown limited the questionnaire to 12 questions, most of which could be answered with a check mark. Brown offered to share the results of the compiled questionnaire with all staff members.

With these methods, Gillette achieved questionnaire return rates of 80 to 90 percent, which Brown considered spectacular. After disseminating the newsletters and compiling the questionnaire results, Brown also spent time talking to staff members, asking for opinions and comments. He also brought or sent samples of RP products so that the designers could see and feel the samples for themselves. He estimates that the total effort of writing the newsletter, gathering data from outside sources, and analyzing the questionnaire results took about half the time of one person for a year.

How did the investment pay off? "We were able to establish a strategy for RP based on the input of designers and engineers within a year," recalls Brown. "It quickly became apparent that our technical people wanted functional, high-accuracy models with which they could measure properties, study assembly, and estimate production costs." The company determined the need for rapid tooling to make several thousand prototypes under simulated processing conditions. "In the late '80s, when we were conducting this program, the layer-building RP processes available were not suitable for rapid tooling," says Brown. But the need for solid modeling CAD systems to implement any kind of RP was identified. "This was the single most valuable result of the exercise," Brown confirms.

He advises all product design groups to invest in solid modeling software, hardware, and training, then send the 3-D files to RP service bureaus to build. This was a very different conclusion from what Gillette initially considered, namely, investing heavily in RP equipment. Brown believes this strategy has had positive repercussions, both in terms of the bottom line and staff productivity. And now that intranets are here, says Brown, forums such as this one could be more easily implemented via in-house websites. - Michelle Maniscalco

Saturn bumper beam integrates technology

This January, at the North American International Automotive Show in Detroit, Saturn unveiled its mid-1997 Coupe. In addition to styling and underhood innovations, the new vehicle contains an injection molded solitary rear bumper beam that replaces a previous 19-piece aluminum and expanded PP foam bumper system.

Beneath the TPO fascia on Saturn's 1997 coupe lies a single molded rear bumper beam capable of withstanding 5 mph in both barrier and pole impact tests. Integrating design, materials, and processing expertise was the key to developing this innovation.

While consolidating parts is a major step forward, the real news centers around the beam's 5-mph impact performance, according to Saturn's Phil Minaudo. As a member of the design team that also involved material supplier GE Plastics and molder Nascote Industries, Minaudo believes this is the only injection molded rear bumper in North America that both exceeds the required FMVSS barrier impact standard and meets a 5-mph pole impact test. "Our division's philosophy is to continually aim at reducing repair costs, and a high-performance single beam helps us achieve that goal," he says.

Goal-Oriented Design

Both technology and team engineering are key elements of the development process for this breakthrough molded application. The project began when Saturn's design team set goals for a rear bumper redesign. "We wanted lower mass, low-temperature impact, fewer parts, easier assembly, and recyclability," Minaudo recalls. During the evaluation process, GE Plastics approached the Saturn team with a proposal for an injection molded beam that could be fitted with a flexible TPO fascia. Saturn engineers liked the idea, and began design work for a shockless beam with integrated fascia support and molded-in towers that crush on impact to absorb energy. (Saturn applied for a patent on this energy management system.)

Team members selected a PC/PBT alloy (Xenoy 1102) that GE developed for the application. Once the initial design was finalized, IGES files were transferred to analysts at GE for structural analysis. "We built a thin-shell finite-element model," recounts GE's Janet Rawson, bumper engineering program leader, "then performed nonlinear FEA for both the pole impact and barrier load cases. The analyses revealed high deflections during pole impact and high load transfer during barrier impact, so ribs were added or moved and wall thicknesses modified to minimize both events."

After Saturn incorporated these changes, a final CAD model was analyzed again at GE using both structural analysis and mold filling simulation. This final step helped designers select gating that optimized flow patterns, balanced the last areas to fill, and moved knit lines away from high-stress areas.

Prototype Testing

Until this point, not a single part had been tested. "We wanted to ensure that the design was completely optimized before any tooling was built to cut down on trial and error," Rawson notes. The team then built prototype tools and molded sample parts for testing. Mark Abraham at Gilbar Test & Engineering performed three different forms of dynamic impact testing in which the sample bumpers were mounted to a rigid, reinforced test cart. All tests, including center pendulum, flat barrier, and pole, took place at an impact speed of 5 mph.

How well did actual physical testing correlate with results from the many computer-aided analyses? Rawson found that a fully constrained boundary condition during analysis gave the most accurate reading. Using this condition, predicted peak loads and total energy for all three types of impacts closely reflected actual results. However, she reports that planned additional research should improve the predictive capability by developing a better failure model at high strain rates.

Intelligent Production

When all of the results were in, production tooling was cut. The mold included a valve-gated manifold. This allowed Nascote to vary timing and sequence of individual gates. Mold design also included porous metal inserts for the molded-in towers to eliminate any gas traps.

Nascote began production molding of the bumper beams in May of last year, using a 3175-ton press and a 6.6-kg shot. Before production began, however, manufacturing engineers evaluated more than 30 processing scenarios using Design of Experiments. Each setup varied mold temperature, melt temperature, injection speed, and other parameters, as well as gate sequencing.

To test bumpers resulting from each scenario, Nascote used an existing hydraulic impact tester that recorded load, energy, and displacement over time. Samples were molded, chilled at Ð20C, then mounted and impacted. (According to Minaudo, Nascote was the only molder with this capability, a key element in winning the business.) Tested bumpers that offered the best performance were sent to Gilbar for additional testing. In this manner, Nascote identified the ideal processing setup. During production, technicians still test one bumper per shift for impact performance.

Design Advantages

Aside from turning a hybrid aluminum/expanded PP assembly into a one-piece injection molded part, the new bumper design achieves several other goals of the Saturn team. Upper and lower fascia supports are integrated, for one. Mass was reduced by 1.5 kg. Once the TPO fascia is removed, the beam is completely recyclable with no extra steps necessary. Assembly time and labor were reduced as well.

What about the bottom line? Saturn invested less for the single injection molding tool, because the part provides a total energy management system. Even with another all-plastic bumper system, it would have had to invest in tooling for both a beam and a separate energy absorber.

DESIGN ANALYSIS

Part: Solitary rear bumper beam
Application: 1997 Saturn Coupe
Material: Xenoy 1102, PC/PBT alloy (GE Plastics)
Weight: 6.1 kg
Molder: Nascote Industries, Nashville, IL
Equipment: 3175-ton press

Getting what you need from a compounder

According to Michael Rosenthal, executive vice president of The Plastics Group of America (Woonsocket, RI), the economics of manufacturing resin have forced major suppliers to narrow product choices and services while raising minimum order quantities over the past few years. "Basic resin types formerly available in 50 different grades are typically offered in only 10 formulations today," he estimates. What happens to designers who want less-than-truckload quantities of something more exotic than a plain vanilla resin? They often turn to custom compounders.

"Compounders' offerings are so diverse," he says, "that although you may be working with one already, you may be unaware of what others can provide." Some compounders specialize in serving distinct markets; others perform multiple functions that range from application development to purchasing excess inventory at the end of a production run.

Custom coloring is one of the most common services compounders offer. Although you may be doing this in-house, Rosenthal suggests you consider compounders as a secondary source, especially if you run into technical problems with a particular concentrate or resin. Another instance in which to consider compounded resins is when stock grades don't offer the exact combination of cost, properties, and processing parameters you need. Adding fillers and reinforcements can modify resin flow, warpage, impact strength, density, stiffness, aesthetics, and other characteristics.

In general, says Rosenthal, compounders provide a broader variety and greater specificity of material purchasing choices than are available from the majors. The key here is that resins can be modified more cost-effectively through this channel. Rosenthal recommends the following tips for getting the most out of this relationship.

1. Do your homework to find a compounder that best suits your specific needs. Compounders with stock lines of resin are often listed in buyers guides and reference sources. Some have also posted their offerings to Internet home pages. Although most are generalists, some specialize in certain types of resins or processes. For example, if you're looking for exotic materials such as a carbon-filled flame-retardant polycarbonate, you need a specialist. But this same compounder may not have the right cost structure to economically produce large volumes of commodity products such as talc-filled polypropylene.

2.Don't equate proximity with convenience. It's a common mistake to assume that a compounder in your area can get you quicker delivery and lower cost than one across the continent. Compare the results of your research. A little research and a few phone calls can save you thousands of dollars in material and weeks on delivery.

3.Consider reprocessors. These suppliers buy molding scrap, excess inventory, and/or postconsumer scrap, then reprocess it and sell it on the open market. Others will do this on a toll basis: they'll take your scrap, reprocess it to your specs, then send it back to you for a fee. They can also add fillers or perform modifications while the material is being reprocessed to upgrade the resin's properties before you reuse it.

Many recycled-material processors specialize in particular materials, depending upon established supply sources, such as plastic film and PET bottles. Others may have a special handle on broom bristles, straws, talc-filled PP molding scrap, etc. If you can find a reprocessor who's running what you need in large volumes, you can save a bundle.

4.Use compounders to upgrade virgin resin. Again, toll processing can be advantageous. If your current needs for an application change, but you have a long-term resin supply contract that you can't (or don't want to) eliminate, compounders will gladly modify that resin to your specifications for a fee, even though they didn't sell the virgin product to you.

5.Reduce delivery hassles. Compounders can often respond more quickly than the majors, especially on small orders. Some will work with you on a just-in-time basis, serving as an off-site resin warehouse. They can also represent a useful second source of supply, providing a level of insurance in critical supply situations and serving as a bargaining chip when negotiating with existing suppliers.

6.Take advantage of technical expertise. Most compounders have enough experience with resin modifications to be able to recommend specific compounded resins for new product development or for cost cutting and performance-enhancing replacements in existing applications. As an example, it is often possible to replace engineering resins with filled PP, cutting resin costs by 50 percent or more.

Compounders earn their living by finding less expensive solutions to the problem. Most compounders will also help a molder through the fine-tuning process, setting up optimum processing parameters and running test cycles.