Cutting Precision Holes in Thermoset Fiber-Reinforced Plastics
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Precision CNC Machining

A highly flexible, plastics-specific hole-cutting tool is reported to provide significant savings on sharpening, downtime, and fixture investments.

As vital performance benefits continue to energize the manufacture of plastic composite products, stiff competition and lean profits are making contract-molding shops rethink their production techniques. One area of production that is often taken for granted, yet is crucial to the successful production of many fiber-reinforced plastic (FRP) components, is hole cutting.

A secondary machining operation, the cutting of holes in FRP is often considered a necessary evil—the responsibility of the production floor personnel who use traditional metalworking technology. Usually, that means drilling with standard drill bits in what are often very costly metalworking-style fixtures.

Yet while precision metal-machining quality is certainly desirable and attainable, the physical properties of FRP are so different from metals that the use of metalworking hole cutting techniques often turns out to be an unnecessarily expensive and less productive approach. When used for cutting holes in fiber-reinforced molded plastics, conventional drill bits require frequent sharpening, which costs precious production time. When automated drilling fixtures are called for, they may be so pricey that manufacturing plans get scrubbed.

When it comes to the finishing of FRP parts, metalworking technology may be the bane of productivity. Between downtime for frequent sharpening and a high scrap rate due to irregularly shaped holes, the cost of product loss can be painfully high.

Many FRP shops of all sizes are turning to hole-cutting technologies such as the one developed by a specialist, International Carbide Corporation (ICC), Yelm, Washington. Beginning with the advent of modern FRP and other plastics, the firm has designed and developed tools using submicron tungsten carbide cutting geometries that are superior in performance to standard carbide. From extensive metallurgical and plastics know-how, ICC developed a precision FRP hole—cutting tool-the Hole-O-MagicTM—specifically for use in cutting thermosets. The tool can be used for cutting thermoset and thermoplastic FRP, according to the company.

"Prior to using this device, we had to sharpen steel drill bits about every half hour or so," says Frank Goodin, tool room manager at Vee Engineering (Fort Wayne, Ind.), a contract manufacturer of thermoset fan shrouds, as well as noise walls for trucks, farm tractors, and other OEM heavy-duty equipment. "The time it took to sharpen bits or replace broken ones resulted in downtime, which resulted in considerable productivity losses. Plus, whenever the drill bit frayed material, we had to file the excess in order to get a clean hole for attaching hardware."

When Vee Engineering management discovered the Hole-O-MagicTM technology, they soon replaced all drill bushing hole-cutting fixtures, virtually eliminating sharpening maintenance and associated downtime. "Today we're cutting holes all day long without interruptions, and the carbide cutting tools only require a minimal amount of routine maintenance," Goodin says.

"A Canadian molding firm that makes truck parts has a plant with 25 fixtures hanging on the wall," says Bruce Mackey, ICC president. "On the floor they have one fixture fitted with Hole-O-MagicTM tools. The tooling coordinator will tell you, 'See all of those fixtures hanging on the wall? If it were not for that one on the floor, we would have to use all 25 of them to get the required volume of parts produced."

Volume flexibility and repeatability

With precision cutting abilities averaging between 2,000 and 2,500 inches of drilled material per sharpening, the technology is appropriate for large and small production runs.

"This can make a dramatic impact on the feasibility of making a product," says Mackey. "In many instances, an OEM marketing or product manager will explore costs by going to a plastic molder and asking how much they would charge per unit for a given volume. In turn, the molder will go to a secondary machining fixture supplier and ask them how much a hole-cutting fixture will cost. It could be hundreds of thousands of dollars — enough to discourage the OEM from going ahead with the project. With our tool, which basically consists of a plate mounted with appropriate hole cutters operated by hand, they could afford to make accurate pilot runs for field-testing of finished product — at nowhere near the cost of conventional metalworking-style fixtures."

Contract manufacturers like Vee Engineering view repeatability as a critical capability when it comes to cutting holes. "Now we can set up a drill fixture for a specific part with the holes located wherever the customers want them, and drill holes in the same location all day long," Frank Goodin explains. "From then on, production will continue, part after part. And because we make products for a great number of OEMs, we need to know that we're getting precision accuracy time after time."

Saving on waste

Accurate secondary machining is a major contributor to the avoidance of waste. A manufacturer of housings for outboard motors knew that story well. At one time, the company was sending five trucks loaded with scrap to the dump throughout the day. "The motor housings are hemispherical in shape," Mackey explains. "That made them difficult to relocate and re-drill. There were over 50 holes to cut. So, if they were inaccurate with one hole, the whole piece part instantly became scrap."

After acquiring the new hole-cutting technology, the outboard motor company instantly increased production volume by 400%.

"Saving on waste is a primary goal of lean manufacturing," Mackey explains. "But, usually the process takes years and includes extensive research, planning, and incremental implementation. By using this technology that was developed for secondary machining of FRP, production managers are able to lean out their operations with very dramatic results — overnight."

Mackey adds that customer loyalty is also instantaneous. "When you're able to cut on size holes with precision location accuracy at the rate of 50 inches penetration per minute at 5,000 rpm, with minimum maintenance, downtime, or cost for months, you know you're using the right technology. We have users who have produced 350,000 parts with one set of tools re-sharpened three times."

For more information on International Carbide Corporation, visit www.icctool.com.

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