Editor's note: Glenn Beall of Libertyville, Illinois, USA, is one of America's leading piece part design consultants. IMI asked Beall to comment on the increasing trend toward massive parts consolidation projects. Here's what he had to say.

One of the ways product designers attempt to increase productivity in an increasingly competitive world is a procedure known as "design for manufacturability and assembly," or DFMA. This is actually a very old system that has been rediscovered and updated. DFMA encompasses many good things, but as it relates to injection moulding, it has two basic parts.

Design for Manufacturability.

In basic terms, the "design for manufacturability" part of DFMA means to keep it simple so that it will be easy to manufacture. In other words, the part or product is not only designed for the marketplace, but it is also properly proportioned for the material and process being specified. As this relates to injection moulding, it means such things as uniform wall thickness, draft angles, corner radii, and so forth. All injection moulders can rejoice at this approach to designing plastic parts.

Design for Assembly

The other part of DFMA has negative connotations. Designing for assembly encourages designers to concentrate on ease of assembly while designing the product. The surest way to simplify assembly is to eliminate it. One of injection moulding's impressive advantages over other manufacturing techniques is the ability to produce extremely complex shapes. This allows the moulding of two or more parts as a single component.

These consolidation projects are nothing new. However, today, this approach to simplifying or eliminating assembly is being pursued with greater vigour than ever before. This emphasis on eliminating assembly is being driven by manufacturers' desperate attempts to reduce the number of workers they employ, as evidenced by downsizing.

Properly done, the minimizing of labour and assembly costs is good. The prevailing attitude is that if a reduction in assembly costs is good, more of the same is better. Recent advances in plastic materials, tooling, and moulding machines now allow the moulding of larger and extremely complex plastic parts. This has resulted in excessive use of consolidation projects.

The advantages of part consolidation are often cited. However, the disadvantages of parts consolidation are not being publicized. The impressive consolidation project illustrated in the figure to the right is a typical example.

This successful part was produced in one complex mould (top), instead of 21 simple moulds (bottom). The consolidated part is bigger than any of the original parts. This larger, more complex part is much more difficult to tool and to mould than any of its individual parts. The race to be first in the marketplace can always be won by several toolmakers producing one or more small, simple moulds competing against a single shop building a large complex mould.

Combining parts eliminates the tolerances that control the fit between the individual parts. The larger and more complex part must now incorporate all of the remaining precision functional dimensions that used to be shared by simpler parts. It is a well- known fact that it is easier to maintain a few close tolerances on several small parts than to hold many tight tolerances on one large, complex part.

In some cases, including this one, it becomes difficult or impractical to maintain a uniform wall thickness, or to provide adequate draft angles and radii at tooling intersections. In other words, compromises have to be made in order to reap the benefits of parts consolidation. The financial motivation that drives consolidation projects is sometimes so strong that designing for manufacturability, or keeping it simple, is compromised in favour of ease of assembly.

When Design Exceeds Capabilities

Some of the parts that moulders are now being asked to produce have become so complex that they challenge or exceed the capabilities of the injection moulding process. It is heresy to say so, but some of these engineering marvels could be produced at a lower cost and higher quality as two or more parts instead of one.

Overconsolidation is prevalent in many downsized corporations around the world. Many of the recently graduated, inexperienced engineers who design these parts have never worked in a factory. They have never built a mould, have never set up and run a moulding machine, and they won't mould the parts they design. Through no fault of their own, they do not know what is and isn't practical for efficient injection moulding. They have been led to believe, or allowed to continue to believe, that anything they can draw or get on a CAD terminal can be moulded. The indisputable advantages of parts consolidation are too good to be ignored. The process can, however, be taken too far. Moulders must watch for this and have the courage to say no to such overconsolidation projects.

Contact Information: Glenn Beall Plastics Ltd. Mr. Glenn Beall, president 32981 N. River Rd. Libertyville, Illinois 60048, USA Phone (1) 847-549-9970 Fax: (1) 847-549-9935