Appliance Design - January 2009 - (Page 28)

PLASTICS & PLASTIC PARTS Heed the Draft Fig. 1. Example of an undrafted (left) and drafted (right) part design. Remember draft angles when designing injection-molded parts. by brad cleveland Brad Cleveland is president and CEO, Protomold, Maple Plain, Minn. 28 applianceDESIGN January 2009 njection molding is the most commonly used method of manufacturing any significant volume of plastic components. The process uses metal molds to produce parts with high accuracy and cosmetic surface finishes, accommodates a vast variety of engineering-grade resins and can be highly cost effective in mid- to high-volume runs. High-volume injection molding for runs of tens of thousands or more parts uses multi-cavity, water-cooled steel molds to minimize the cycle time and, therefore, the cost of each part. Millions of shots are routinely obtained from these molds, and there simply is no other cost-effective way to achieve the same results. However, in conventional injection molding there is typically a long lead time and high cost associated with the manufacture of the mold, which has historically made injection molding a less attractive option for obtaining prototype or low volumes of plastic components. Over the past nine years it has been the mission of Protomold (a service of Proto Labs, Inc.) to reduce the cost and time associated with obtaining small quantities of injection molded parts. The company’s general approach has been I to automate most of the engineering out of the process through the use of proprietary mold design and toolpath generation software that runs on high performance computer clusters in each of its global manufacturing centers. The method also uses aluminum instead of steel for the molds, which reduces manufacturing time, costs, and helps to reduce cycle time without the need for expensive and timeconsuming cooling systems. The concept is called “rapid injection molding,” and it currently allows a lead time as short as one business day and very low tooling charges. However, there is still a universal design characteristic that Protomold or any other tooling maker requires in the design of the part to be injection molded: draft. There are several key points to consider in regards to draft and the design of injection-molded parts. Keep it simple While injection molding can produce parts of great complexity, experienced designers strive to simplify their part designs wherever possible. This helps to simplify production and reduce cost, and can even impact aeswww.applianceDESIGN.com http://www.appliancedesign.com

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Appliance Design - January 2009 Contents Editorial Shipments/Forecasts News Watch Supplier Spotlights Commercial Appliances Plastics & Parts Electronics Motors Design Marts Association Report: NAFEM Advertiser’s Index

Appliance Design - January 2009

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