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July/August Feature

Aero-Plast Has a High Tolerance
for Aerospace Machining

Located in Aero-Plastics' 21,000-square-foot facility in Renton, WA, are several plastic injection molding machines, Fadal machining centers, CNC lathes and EDM equipment.
Milling machines deliver performance, stability and accuracy for machining aerospace, defense and commercial plastic components.

There is more to manufacturing products for the aerospace industry than merely simple cutting and trimming. As Renton, WA-based Aero-Plastics can attest, it involves high-tolerance machining to exacting specifications.

Aero-Plastics is a two-time winner of Boeing Airplane Co.’s Supplier of the Year award. Since 1945, it has been machining parts out of various plastics and metals. An ISO 9002 and AS 9000 certified company, Aero-Plastics operates from a 21,000 square-foot facility that includes four Fadal machining centers, CNC lathes, EDM equipment and several plastic injection molding machines.

Stability: A key issue for accuracy

Machine tool stability is equally important when machining plastic parts as it is in metal parts and molds. “Our machining operations include pocketing, hole drilling and outside profiling on Teflons, acrylics, HDPE, Delrins and other plastic materials. We have to meet tolerances of up to ± 0.001 inch in order to maintain a low rejection rate of less than one-half percent,” says Ray Behrendt, shop foreman. “In machining plastic materials, high speeds, zero spindle runout and sharp tools are vitally important. The tools have to be dead sharp, or else we can’t hold the tolerances. Also, we have to use a synthetic coolant.”

When cutting any material at high speeds, vibration and spindle runout affect surface finish, accuracy and repeatability. Variation in wall thickness can also cause thin sections to become brittle.

To reduce vibration and other adverse effects, Aero-Plastics utilizes four Fadal VMCs featuring the same MP CNC control. “The control on the Fadal is very user-friendly and simple, which is an advantage in training. If you can run one, you can run them all. So we train one person on one and they can run any of the four VMCs that we have. Our programming is done with an offline CAM system and we do light editing on the control."

The MP CNC control features Parallel Processing, which utilizes up to nine microprocessors working simultaneously for fast, precision control. By dedicating one microprocessor to each axis, the MP CNC delivers a program execution speed of 3,000 blocks per second or 1,000 lines per second, virtually eliminating data starvation leading to jerking or vibration, which ultimately leads to surface blemishes on the parts.

The notion that plastic shapes are often simple and therefore easy to machine can be quickly dispelled by looking at a part nicknamed the “boomerang,” explains Josh Schleining, programmer. "It had no written dimensions and you can see by looking at it there aren’t many dimensions that are either at a right angle or parallel to any other sides on the part."

Aero-Plastics utilizes four Fadal VMC machining centers which help the company meet required tolerances of 0.001-inch for aerospace, defense and commercial plastic parts.
Limiting Set-up Time

One of Aero-Plastics’ goals is to reduce machine setups to 15 minutes or less on 80 percent of all jobs by eliminating all non-value-added steps. For example, by utilizing the VMC 4020’s 20-inch by 48-inch table size, large plastic sheets up to 1/2-inch thick can be mounted using a vacuum plate. "We’ve adapted a large vacuum plate to the table that holds the stock securely. By nesting parts, mainly fillers for aircraft, we can mount as many as 100 parts at a time ready for machining,” Behrendt explains.

Another method of reducing prep time is by using an automatic pallet changer to setup jobs offline. According to Behrendt, one benefit of utilizing the automatic pallet changer is unattended machining of parts.

“We use the pallet changer to reduce the set-up time on short runs with fixturing, by setting up all of the tooling and fixturing on the offline pallet. And we can run one part with several different setups, getting one complete part off each cycle,” he says.

Another simple technique utilizing positioning holes also has helped considerably. "We can set up each machine identically, by drilling a positioning hole into the table, so that all our plates are located in the same spot,” Behrendt says.

Preventive Maintenance

Quality control, efficiency in operations and being competitive are major issues at Aero-Plastics. Mike Hammer, president, explains, “A lot of factors affect quality, efficiency and the ability to compete, including people, training, processes and equipment. Because some of the plastic materials we machine create a lot of dust, we implemented preventive maintenance to keep the machines up and running.

“Our distributor provides the preventive maintenance program for us. Our shop features very lean manufacturing systems, integrating the reliability, ease of use and accuracy of (the machines) into our overall resource management philosophy. Every process and operation is designed to quickly deliver the best and most competitive parts to our customers.”

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Plastics Machining & Fabricating
P: (847) 634-4347
F: (847) 634-4379
P.O. BOX 1400