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Allen Pattern of Michigan: plastics bring innovations to tooling.

Allen Pattern of Michigan Plastics Bring Innovations to Tooling

Whether a pattern shop specializes in master patterns, models or production tooling, its quality reputation rests on its attention to traditional craftsmanship. Allen Pattern of Michigan, Battle Creek, MI, demonstrates that when a pattern shop moves into new tooling processes, such as plastics, the same principles apply.

While the company serves a wide range of manufacturing needs, Wendell Allen, president, says, "The skill of creating and making castings with master patterns is our focus." Indeed, Allen Pattern currently employs 17 master patternmakers, one of the largest such staffs in the U.S., allowing the company to specialize in the preparation of precision models, prototypes and masters.

This is a diverse operation, though. It also provides foundry production tooling in wood, plastic and metal. Working in aluminum, brass, bronze, iron and steel, the shop produces copes and drags, matchplates, coreboxes, shell and permanent mold equipment, all fully rigged. Foam and wax injection dies, as well as plastic molding dies, are other capabilities.

Allen's 31 years in the business (he's owned Allen Pattern for 18 years) have taught him the need to keep ahead of changing requirements in the metalcasting industry. "Our technology has changed immensely in the last seven to eight years," he comments. "We've had to tighten up our tolerance because of tighter specifications on castings. I estimate that tolerance are 25% of what they were just ten years ago."

Changing technology applies not only to tighter tolerances in traditional pattern construction, but to improvements in new tooling production processes as well. "We're using plastic instead of wood for these newer, close tolerance masters," Allen notes.

For example, Fig. 1 shows cope and drag polyurethane, reverse molds cast off the wood master patterns shown next to them. The reverse molds produce final production patterns for a high production manifold head. In Fig. 2, reverse plastic molds used to produce first-run tooling for a large low pressure die casting are shown.

Aluminum-Plastic Tooling

Allen Pattern began using fiberglass and epoxy in patternmaking during the 1960s. When polyurethane materials became available in the 1970s, the pattern shop began working with those.

In the 1980s, various improvements in polyurethane materials, equipment and processes have allowed plastics to move out of the pattern shop and onto the foundry shop floor. Once limited mostly to master patterns, plastics have moved further into production tooling. Fiberglass spray is often employed.

One polyurethane improvement, termed "the most significant development in the last three years," by Greg Allen, controller, is an aluminum powder/polyurethane material. Development began with the addition of a metal powder filler to polyurethane to manufacture a production matchplate with better abrasion resistance than straight polyurethane.

The result is a 75% aluminum, 25% polyurethane tooling process that is used for short-to-medium run (up to 10,000) production tooling. Two major advantages of this material over traditional polyurethane are thermal conductivity and polish. "For air-set or green sand molding, the release characteristics are better than unpolished or cold patterns," Allen explains. The material provides a high-strength, durable and abrasion-resistant tooling.

Though this material is not suitable for every casting application, cost savings can be substantial where applicable. For producing matchplates, Allen believes that this new material can save 40-60% over the cost of all-metal matchplates for prototyping and short-to-medium casting runs.

Construction methods, shown in Fig. 3, allow matchplates to be produced quickly and easily, on or through the plate. Lead times and labor are reduced and design changes, repair and replacement are made simpler. Mounted patterns, copes and drags also can be produced by this method.

Corebox Design

Polyurethane enabled Allen Pattern to simplify corebox design and cut co-remaking time. For cores designed with draft angles or undercuts, which normally require use of multiple cores and/or loose pieces, a flexible corebox liner can simplify the task.

This method of construction, shown in Fig. 4, eliminates the cost of multiple coreboxes and most loose pieces by constructing a flexible liner around these critical areas.

The liner will not tear because of its "memory" and elongation factor. Critical placement is retained with integrated "keys" or "locks." Figure 5 shows an example of a corebox with flexible lining, which replaced a multiple-piece corebox. Figure 6 shows another pair of plastic reverse molds.

These two new techniques demonstrate that highly practical foundry applications for plastic tooling processes are growing and that they offer flexibility, efficiency and economy to the foundry.

PHOTO : Fig. 1. Shown are cope and drag polyurethane reverse molds placed next to the wood masters.

PHOTO : Fig. 2. Plastic reverse molds for low pressure diecasting tooling are pictured.

PHOTO : Fig. 3. Steps in producing a matchplate are shown. Left: Reverse mold (top) was produced from master pattern (bottom). Center: Aluminum-polyurethane elastomer is poured into reverse mold. Inset shows how patterns with offset partings can be cast right through matchplate, if required. Right: Reverse molds are removed after proper demold time and matchplate is cleaned.

PHOTO : Fig. 4. Steps in producing coreboxes with flexible liners are shown. Left: Outer corebox (top) has been poured with solid casting material around wood master core plug (bottom), which was constructed without loose pieces, undercuts or draft. Center: Liner is poured from flexible polyurethane around core plug. Right: Outer corebox and liner are removed from core plug, ready for foundry coremaking.

PHOTO : Fig. 5. Another example of a corebox with flexible lining, which replaced a multiple-piece corebox, is shown.

PHOTO : Fig. 6. A pair of plastic reverse molds exhibiting fine detailing is shown.
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Article Details
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Author:Bralower, Paul M.
Publication:Modern Casting
Date:Jun 1, 1989
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