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May 11, 1998

3 Min Read
Low-volume tooling idea floats this boat

ArticleImage241.gifHow many OEMs regularly make products in quantities of 100 to 1000 that require economical molded parts? With the trend toward niche marketing and customized products, it's easy to believe there may be quite a few. And for those OEMs and their moldmakers, an example we found at Nauticraft Inc. (Muskegon, MI) seems to provide an answer - a relatively simple system for creating economical, low-volume mold inserts.

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A plethora of injection molded parts helps keep Nauticraft's Excapade afloat and corrosion-free. An ingenious system of aluminum tooling inserts, developed by the company using MUD frames, also makes these parts economical to mold.

First, some background on the company. Nauticraft is an OEM staffed with experienced molders. Its product - a 12-foot, pedal-powered watercraft for fun and fitness called the Escapade - is about to hit the market. It uses a bicycle-type drive train to turn an efficient propeller for increased speed with reduced pedaling effort. Owner Curtis Chambers licensed the rights to build the boat from Harken USA. Garry Hoyt, a yacht designer from Newport, RI, designed the boat 15 years ago. It was built briefly with fiberglass, then put on the shelf. Engineers at Nauticraft modified the design from one that was not economical (fiberglass layup) to one that could be molded.

Although the 190-lb hull of the Escapade is rotationally molded, there are also roughly 135 injection molded parts on each craft - step washers, spacers, sprockets, bushings, retainer washers, eye screws, rollers, and others shown in the photo above. The drive unit contains approximately 63 of these IM parts. Most of the parts are molded in-house on a 25-ton machine. Materials range from a PTFE-filled nylon 6/6 to standard polypropylene. All are functional parts without extreme aesthetic requirements. At estimated sales levels, production requirements will range from 200 to 6500 parts per year.

To improve the economy and quality of the various molded parts, Nauticraft engineers developed a system using exchangeable inserts and three different sized frame holders. Bars of aluminum are cut to length to form the mold cavities. Using MUD (Master Unit Die) frames and inserts, pockets in the inserts receive the aluminum blocks. The system works for both single and multicavity inserts - one set is 2 by 2.75 by .75 inch thick; another is 3 by 3 by 1 inch. The largest insert, at 5 by 6 inches by variable thickness, is typically used for parts that require center-gated injection.

These inserts are essentially aluminum molds that can be made with conventional toolroom machinery such as lathes and milling machines. According to Nauticraft, the simpler mold types can be made in 1/2 to 2 days by a reasonably skilled machinist or toolmaker, bringing tooling cost down from thousands to hundreds of dollars. For example, Nauticraft produced a 2.5-inch OD step washer mold for less than $300, and a 2.5-inch-diameter drive sprocket mold for less than $1000. (This latter mold also required wire EDM to cut the sprocket tooth contour.) Total tooling costs for the 63-part pedal drive unit were less than $25,000, including the cost of a rotational mold for the housing.

Results of implementing this tooling system include both quality and economy. Prices for the boat start at an affordable $2550, giving Nauticraft a competitive advantage in the marketplace, according to sales and marketing director Hardy Bedford.

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