Printer Friendly

Building higher value into injection molds.

Moldmakers are turning to newer materials, mold components and manufacturing procedures to reduce costs and lead times and make molds that will last longer. Even more important in meeting those goals is the trend to concurrent engineering.

Many of the trends taking place in injection tooling are customer-driven. Demands for shorter lead times, easier-to-maintain tools, and extremely tight tolerances have prompted toolmakers to respond with beefed-up engineering departments and improved quality control.

Some of these trends concern technologies that are not so much "new" as gaining wider acceptance in the industry. For example, in the interest of cost and time savings, many mold shops are investing more heavily in CNC equipment, often putting those machines on 24-hr, unattended operation. And in tooling materials, stainless steel has grown in popularity because of its corrosion-resistant qualities. Aluminum, too, has carved out a niche, particularly for use in prototype molds, but also in some production applications.

One fundamental change that outweighs these incremental strides is the growth of a closer working relationship between toolmakers and their customers. To that end, engineering services have become the major focal point in many mold shops, not only in terms of CAD/CAE facilities, but also--and perhaps more significantly--in terms of how effectively those resources are used to share information between toolmakers and their customers. Several toolmakers contacted for this article spoke of having formed "strategic partnerships" with their best customers, in which the parties collaborate from the earliest stages of product and tool design, often avoiding potential production problems later on.

LARGER PIECE OF THE PIE

The significance of up-front engineering becomes evident if one looks at its increasingly hefty share of total mold costs. According to John Gravelle, president of Mar-Lee Mold Co. in Leominster, Mass., engineering costs used to account for $3000 to $5000 of the price of building a $50,000 mold. That share has increased to about 20% of the total cost today. To meet those demands, Gravelle plans to expand his engineering capacity by one-third, from four engineering workstations to six.

Gravelle sees much of the impetus for beefing up his engineering capability coming from larger corporate customers. Polaroid, for example, required toolmakers to be equipped with both CAD/CAM and IGES to qualify for its Joshua camera program. This trend has prompted Gravelle to change his focus to working primarily with such large OEMs, and consequently taking a more active role in product development and tool design.

The closer working relationship with customers has increased the importance of maintaining open lines of communication between moldmaker, molder, and customer. According to Walter Kreiseder, president of Courtesy Mold & Tool, a mold builder and custom molder in Wheeling, Ill., "Lack of communication is a serious problem. A successful situation is one in which people come together and talk, understand what each is looking for, and understand what the toolmaker, molder, and end-user can live with."

At its best, the relationship between moldmaker and customer has evolved into a long-term partnership in which both parties work together to reduce the overall cost of the mold. In one such partnership with a medical customer, Tech Mold in Tempe, Ariz., is regularly asked to participate in product design. In the past, the customer would typically develop the product internally, conduct focus-group sessions, complete the part drawing, and send it out to mold shops for bid. Today, by contrast, the moldmaker, molder, automation experts, and the customer come together as a team from the beginning of a project. "Together we work on the part until it's to everyone's liking and still serves its specified purpose," according to Vince Lomax, v.p. of Tech Mold.

REDUCING LEAD TIMES

Sophisticated engineering capabilities and strategic partnerships with customers have combined to make concurrent engineering a reality for some moldmakers and customers. Concurrent engineering combines the engineering and product-design steps, with the goal of bringing products to market sooner.

Caco-Pacific Corp., a 180-person moldmaker in Covina, Calif., performs some form of concurrent engineering with about 80% of its major customers. According to president and chairman Manfred Hoffmann, this requires what he calls "real-time engineering" over the telephone lines. Caco-Pacific has seven CAD workstations, which can receive part or mold geometries direct from a customer's CAD system via IGES. This EDI (electronic data interchange) capability allows the moldmaker to work closely with its customers despite the distances between them. As a practitioner of "paperless" engineering, Caco-Pacific can cut molds from a customer's own part-design database, eliminating the need to generate drawings.

Some top moldmakers admit to having mixed results in attempting to reduce a product's "cycle time" from initial concept to market launch. According to Klaus Cisliek, chairman of Delta Tech Mold in Arlington Heights, Ill., "There is very little room in which we can shorten our lead time. We manufacture very fast." To squeeze more time out of the mold-development cycle, Delta Tech has compressed the amount of project time spent on engineering from 30-40% to around 20-25%, says Cisliek. One way it has done this is by building pre-production tools and production tools simultaneously.

Other ways to reduce lead times have occurred on the shop floor. MarLee Mold, for example, recently started a second 12-hr shift on its CNC milling and EDM equipment, a move that Gravelle expects will save as much as 25% in lead time for a typical mold.

Moldmakers' outside suppliers are also helping to compress lead times. D-M-E Corp., Madison Heights, Mich., has instituted a Quick Deliveries Specials program to deliver machined moldbases to customers in 10 days or less. The program covers 800 of D-M-E's most frequently requested sizes of moldbases, retainer sets, and plates, with a variety of special machining, such as rough pockets, water lines, and guided ejection. According to national sales manager Glen Grosser, the program will probably provide 30-40% time savings on moldbases, freeing up moldmakers for core and cavity work.

Likewise, National Tool & Manufacturing Co., Kenilworth, N.J., has revised its manufacturing procedures to speed production of mold bases. Says marketing director Karl Budd, "In the last three or four years, we have gone to CNC machining centers. We can load up two, three, or four jobs on pallets and pump them into the machine one after the other."

ALTERNATIVES TO MACHINING

One brand-new technology that may have implications for rapid production of prototype molds is a Direct Shell Production Casting (DSPC) process being marketed by Soligen, Inc., Northridge, Calif. DSPC was originally developed to replace labor-intensive steps for investment casting of metal parts, but it reportedly also can be applied to making prototype injection molds.

The DSPC equipment consists of a shell design unit and a shell production unit. The design phase begins with a 3-D CAD drawing of the mold, which is then "swapped" into a negative image. The shell design unit then generates a solid model of a ceramic shell from that negative image, which will serve as the mold for the final plastic injection tool. A gating system is designed into the ceramic shell, through which molten metal will flow to create the injection mold.

The 3-D CAD software "slices" the solid model into a series of thin layers. The shell production unit then automatically fabricates the shell by building it up one layer at a time from ceramic powder and a liquid binder resin. The device spreads out a layer of ceramic powder and "prints" a cross-section of the part onto the powder with a stream of liquid binder that is deposited by an x-y manipulator driven by the CAD geometry. The binder hardens almost immediately; a new layer of powder is spread over the first layer and the "printing" process is repeated. Finally, the completed shell is fired, excess powder is removed, and the shell is ready to be poured with metal. Final steps involve breaking away the shell, dissolving remaining ceramic cores, and cutting off the gating structure. Completed injection molds may still require bench work, such as polishing.

There are some limitations to the process. For one thing, the present shell production unit will handle maximum dimensions of 16 x 16 x 16 in. But the process has interesting possibilities, particularly for prototype core and cavity work. Modifications can be made simply by changing the geometry on the computer screen. Molds can be ready for benchwork in as little as a week after CAD modeling. Soligen says three development units are currently operational.

Another alternative to conventional toolmaking processes that may be seeing wider use is one marketed by Keltool Inc., St. Paul, Minn. The Keltool process was originally developed by 3M Co. and first introduced to the market about 10 years ago as a method of molding cores and cavities from powdered metal, with no machining. Starting with a rigid master model (male or female) supplied by the customer, the process generates a mold which is then used to create the required number of powder metal cores or cavities. Accuracy of the process is said to be 0.0015 in./in., and the greater the amount of detail in the part, the greater the potential cost savings over conventional toolmaking methods.

The biggest limitation of the process has been that the customer had to provide the first article at the start of the process. If the customer supplied a male form, an epoxy female intermediate would have to be cast to provide the moldmaking form. The wide availability of stereolithography is now making this first step much easier, says Keltool. Using it, the cavity that would be used to generate the piece part could be generated directly from a CAD model, eliminating steps at the start of the process.

QUICK MOLD CHANGES

Interchangeable mold insert systems using common mold bases are another technique for reducing cost and lead times for new tooling, as well as for saving downtime for mold changes during molding. Recent developments have enhanced the flexibility of this approach. Pleasant Precision Inc., Huntsville, Ohio, offers "multi-position" Round Mate systems for two and four cavities. Four customers so far have bought such multi-position systems. In addition, PPI is developing a hot-manifold system and a three-plate system for its Round Mate, although neither is ready for market.

Master Unit Die Products, Greenville, Mich., has extended the range of its MUD QuickChange frame series with adapter frames to convert standard moldbases into quick-change models (see PT, June '91, p. 31). Presently, the company is developing a water jacket to fit into the standard moldbase frame, eliminating several hoses that must be connected or disconnected individually.

NEW MOLD MATERIALS

New grades of tool steels are providing increased wear and corrosion resistance. In the last five years, stainless steel has been requested more and more often, particularly for medical molds, according to Caco-Pacific's Hoffmann. Marketing and sales v.p. John Thirlwell estimates that Caco-Pacific uses stainless-steel moldbases and cavities in 95% of the medical molds that must run in clean-room environments. Cost is not really a major issue. While there may be a 20%-25% premium for stainless steel, materials typically account for only 12-22% of total mold costs, he adds.

The price difference pales further because plating costs are eliminated. According to John Gravelle of Mar-Lee Mold, plating is expensive, both in materials and waste-disposal costs. Ten years ago, Gravelle estimates, nickel plating cost 2-3|cents~/sq in. and could be stripped for 1|cent~/sq in. Today, plating costs have climbed to 8-10|cents~/sq in. and stripping costs to 30|cents~/sq in.

Paul Stoll, president of Armin Tool & Mfg. Co. in South Elgin, Ill., notes that thermal conductivity of stainless is poorer than for other steels, but adds that this disadvantage is offset by stainless' anti-corrosion properties, which help keep water lines open.

James Peters of Thyssen Specialty Steels, Carol Stream, Ill., says that benefits in lower maintenance and more consistent cooling is prompting more customers to specify entire molds of stainless steel. Thyssen is marketing a new "2316" stainless grade with a hardness of about 35 Rockwell C, suitable for molding PVC and other corrosive plastics.

High wear resistance is normally associated with low corrosion resistance and vice-versa. One relatively new tool steel that reportedly combines the two properties is Elmax from Uddeholm Corp., Rolling Meadows, Ill. (PT, Sept. '90, p. 15). Elmax, which can be hardened to 58-60 Rockwell C, is said to be suitable for long production runs in applications such as electronic parts. Its corrosion resistance makes it suitable for humid conditions and molding corrosive materials such as flame-retardant plastics and PVC, and gives it resistance to staining, rusting, and corrosion of cooling channels.

Two other new grades from Uddeholm are Vanadis 4 and Vanadis 10. These chromium-molybdenum-vanadium alloy steels reportedly combine high wear resistance and toughness. They're also said to be easier to heat treat and machine than other highly alloyed tool steels. Dimensional stability after hardening and tempering is said to be better than other high-performance cold-working tool steels.

John Worbye, product development manager of Uddeholm, also sees wider use of beryllium copper for injection molds, largely because of the extremely high thermal conductivity of these materials. Uddeholm markets Protherm and Moldmax, two beryllium copper alloys of Cleveland-based Brush Wellman Inc. Protherm is a moderate-strength material with a hardness rating of about 20 Rockwell C. For applications that require higher working hardness, Moldmax is offered in two grades of 30 and 40 Rockwell C. Recommended applications for Moldmax include molds, cores, and inserts. Other characteristics of Promax and Moldmax include good polishability, machinability, and corrosion resistance.

As cost-effective alternatives to beryllium copper, Ampco Metal Inc., Milwaukee, Wis., is marketing two relatively new copper-nickel-silicon-chromium alloys, Ampco 940 and 945. Ampco 940 is said to have very high thermal conductivity, resistance to corrosion and wear, and moderate hardness. Ampco 945 is a higher hardness version. Among the recommended applications for both grades are cores, cavities, core and ejector pins, and blow pins.

Aluminum has also been establishing a niche in injection molds. In general, aluminum tools offer advantages light weight, high cutting rates during machining, and good thermal conductivity. One newer product is QC-7 from Alcoa, Rolling Meadows, Ill., which is said to be up to 54% stronger than the 7075 aluminum alloy often used in prototype injection molds. According to product manager Michael Maloney, QC-7 offers lower machining costs and shorter lead times to make the mold. Excellent through-thickness is said improve machinability and finishing, with cutting speeds up to 40% faster than steel. Thermal conductivity is four times that of steel, reportedly reducing molding cycle times by up to 25%. Maloney says that QC-7 has shown good results in both prototype and production injection molds. He knows of customers who have experienced over 2 million cycles on injection molds of QC-7.

Another new high-strength aluminum for injection molds is Alumec 89 from Uddeholm Corp. Alumec 89 is marketed primarily for prototype and short-to-medium production runs that are not subjected to high pressures or abrasives. Among its advantages are good stability, which guarantees minimal deformation during and after machining, good corrosion resistance, and compatibility with surface treatments such as anodizing and chrome or nickel plating.

HIGHER DEMANDS FOR QUALITY

One materials-related issue that is becoming more common is customer requests for steel certification, to be performed either by an outside metrology lab or in-house by the moldmaker. "That was never part of our industry in the past," says Lomax of Tech Mold. He adds that steel certification is needed to provide a baseline for design-of-experiment procedures, which are becoming more common among plastics processors to qualify molds after completion.

Another factor placing higher quality requirements on moldmakers involves customers using high-speed automation equipment for product take-away from the mold. According to John Thirlwell of Caco-Pacific, "This demands cavity-to-cavity interchangeability, not just within each cavity of one mold but over whole series of molds." To meet demands for interchangeability, such as cases where several molds may be supplied for molding identical parts, Caco-Pacific can hold tolerances to 0.0002 in.

According to Tech Mold's Lomax, "A lot of companies will not accept a mold unless it runs at a Cpk |process capability index~ of 2.0 or better. To do that, you have to meet the mean dimension as close as possible. Parts that are just 'in tolerance' are no longer acceptable." One way of achieving that is to leave critical dimensions "steel-safe."

LOWER MAINTENANCE MOLDS

An added benefit to working to tight tolerances is that molds simply last longer. Maintenance problems are caused by molds that are under-designed or made with unacceptable tolerances, which can cause unnecessary galling and premature wear of all cavity shutoffs and parting lines, says John Thirlwell of Caco-Pacific. "We build a low-maintenance mold. It has just as many moving parts as anyone else's, but they are rugged. We guarantee interchangeability of components and have the CNC equipment to produce interchangeable parts."

To save time and cost in supplying replacement parts for molds, some moldmakers have begun to incorporate more standard components, such as side locks and leader pins, in their tools. According to Klaus Cisliek of Delta Tech Mold, "standardizing around the design is very important. We don't want to customize components. We try to incorporate more standard components from outside suppliers."

Although the cost of purchased components are a small percentage over the overall cost of the tool, they play an important role in preventing downtime, says Glenn Starkey, president of D&L Progressive Components, Wauconda, Ill. Side locks, for example, are frequently used to prevent misalignment of core and cavity inserts. "The cost of four sets may total $500, but they help to prevent wear and damage to the inserts, a repair cost of thousands of dollars, along with downtime."

Several major moldmakers say they are purchasing standard components such as these, freeing up valuable machine time for core and cavity work. Starkey adds that he works closely with tooling engineers in developing and standardizing new components into his product line. An example was the "universal mold lifter" introduced by D&L in 1991 (PT, May '91, p. 43). With the arrival of the UniLifter as a standard, off-the-shelf component, moldmakers could save an average of 15 tool-shop hours previously needed for custom designing and manufacturing lifters to aid ejection of undercut parts.

Molders themselves are doing more to make their molds last longer. Manfred Hoffmann of Caco-Pacific believes that molders are becoming more sophisticated about mold maintenance and that many have instituted regular preventive maintenance schedules for their molds (PT, Dec. '92, p. 51). To help encourage those efforts, Caco-Pacific furnishes its molds to customers complete with manuals on preventive-maintenance requirements and operating instructions.
COPYRIGHT 1993 Gardner Publications, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1993, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
Printer friendly Cite/link Email Feedback
Author:De Gaspari, John
Publication:Plastics Technology
Date:Apr 1, 1993
Words:3108
Previous Article:The 'new' imports: where they fit.
Next Article:SAE highlights new automotive plastics materials and technology.
Topics:


Related Articles
Resins flow better in TiN-coated molds.
Injection molds: product lines reviewed.
In Tokyo, a feast for injection molders.
Injection molds: product lines reviewed.
Blow molds: product lines reviewed.
Blow molds: product lines reviewed.
Why thermoforming is looking better than ever.
Novel injection molding techniques move toward commercialization.
In-mold textile laminating gives boost to injection-compression.
Thin-wall molding.

Terms of use | Copyright © 2016 Farlex, Inc. | Feedback | For webmasters