Design-CAD File Part Details and Tooling Part 1

During my thirty plus years in product design I have personally experienced the evolution of the design process from a lengthy manually intensive process to its current highly sophisticated, time compressed, state of the art. When I started as an industrial designer in the mid 1970's, I began designing with hand drawn sketches which were later rendered using a spectrum of colorful Magic Markers. A selected concept was eventually detailed for production molding after spending hundreds of painfully tedious hours on a drafting table. This process required multiple sheets of velum paper layered upon each other. Design changes were very slow and costly to implement, since even the slightest alteration would require dozens of part drawings to be reworked.

Most designers at that time had limited knowledge of plastics part design and tooling. Final production part drawings were often drawn out of scale, without draft or incorrect geometry. In addition, many orthographic drawings contained dimensional errors, missing dimensions or insufficient information. Tool makers were often relied upon to interpret final production drawings and make appropriate corrections for plastic production tooling. This often caused problems such as interferences due to draft or functional problems resulting from geometry alterations required for molding. All these cascading activities resulted in production delays, lost revenues and additional expenses.
Today things are very different from the "Olden Days". Today, designers are frequently expected to design a product within days or weeks, not months or years. Company executives will not tolerate costly mistakes, time delays or excuses. Efficient distribution, rapidly changing markets, daily technological breakthroughs, fluctuating prices and global competition have forced companies to strictly adhere to their business plans. These escalating pressures have been compounded with demands for higher quality products that are more complex and less expensive. A byproduct of this global technological and economic renaissance is the advancements in computer technology, which has consequently revolutionized the design process with 3D computeraided design.

It wasn't that long ago when 3D CAD was reserved for large multi-national corporations with million dollar main frame computers and very expensive custom written software. Within a relatively short time this exclusive technology was drastically improved and made available to almost anyone at a very affordable price. In less than 10 years, 3D CAD has literally transformed the design profession by infusing ongoing technological change. Consequently professional standards for designers have continually been raised, requiring an ever broader knowledge base and a comprehensive understanding of plastic part design.

Designers involved with plastics parts should have an in-depth knowledge of the process, materials and tooling to provide a quality design to their clients. In today's era when plastic parts are designed with 3D CAD, the files are typically imported to a CAM program which outputs tooling paths based on the geometry as defined in the CAD file. Unlike hand drawn blue prints or 2D CAD generated orthographic drawings, 3D geometry is literally a three dimensional model of the actual part embodied within an electronic file. Since 3D CAD is an actual mathematical representation of a physical part, all of the features defined within the CAD file are interrelated and can no longer be simply changed by interpretation. Mold makers today simply add shrinkage to the original part geometry by increasing overall size with a uniform shrinkage percentage and begin 3D CAM programming. Although gross errors and molding difficulties are typically noted by tool makers, designers are responsible for providing a part geometry that can be molded properly. Gone are the days when the toolmaker can be called upon to revise the design by blending a surface, changing draft or removing an undercut. The current product development process requires designers to provide mold makers with a completely accurate 3D CAD file of the part to be molded. Any changes to the geometry required by molding or tooling must be included within the CAD file, and is the designer's responsibility. The mold maker and molder are strictly responsible for providing parts perthe CAD file and associated specifications. Today's product designers involved in plastics part design must include adequate clearances, proper draft angles, surface geometries, shut-off angles, radii and parting line features within their CAD files before tooling begins. Although this limited list of design parameters may appear straight forward, it is deceivingly complex when applied to a specific part design. Often input from mold makers and molders are required by designers throughout the development process to derive the optimum design. We will discuss these parameters in greater detail in our next design comer. Until then, keep in touch and email me with any of your comments or questions.

Michael Paloian, Integrated Design Systems, Inc.