Oren Elliott Products, Inc. is located in Edgerton, Ohio near the Indiana border. It is a large North American supplier of air-dielectric variable capacitors, which are used in such diverse applications as magnetic resonance imagery equipment, mass spectroscopy equipment, silicon chip plasma etching and deposition devices, plus surface-to-air missile guidance systems.
One of Oren Elliott's latest products actually combines the capacitor, PC board and enclosure into a single unit. To achieve this compact design however, requires some very complex machining capability. The capacitor's body is milled from a solid block of 6061 aluminum measuring 4 inches by 4 inches by 2 inches thick. Five outside sides are faced for size, squareness, and size tolerances. Next, more than 40 holes are drilled, tapped, milled or reamed into and through the block. Finally, a central internal pocket and several multi-level pockets are milled to form the housing with finished sidewalls of only 1/16-inch thickness. Most tolerances are held to ±0.005 inch, however, the rotor-bearing bore is held to ±0.0002 inch.
One of the challenges in producing such a complex part is producing it cost effectively. The current production rate is 100 pieces per month, with 300 pieces per month expected by the end of the year. A Haas 710 VF-1, 15-hp vertical mill was dedicated to producing these parts. The part is held in a vise by a ¼-inch bite to the bottom edge of the sides. Machining the inside cavities was previously done with a 0.750-inch diameter, three-flute, tin coated carbide cutter. The engaged flute length was 1.25 inches. The depth of cut per pass was 1.25 inches plus 0.250 for the pockets. A cutter speed of 3,000 rpm was used at a 30 ipm feed rate. Climb milling is the preferred method of cut at Oren Elliott Products.
Darrel Stevens, Sales Representative from Technical Equipment Sales in Cleveland, heard about this particular application, and called on the company's production personnel. He suggested working with IMCO Carbide Tool Inc., located in Toledo, Ohio, because of its reputation for working closely with customers and dramatically improving complex machining operations. IMCO developed a new 0.750-inch diameter prototype cutter with two flutes and special chipbreaking capability. The new cutter, "STREAKERS," increased pocket cutting rpm's from 3,000 to 6,000 and increased the feed rate from 30 ipm to 120 ipm. All other parameters remained the same.
Matthew Elliott, Production Manager, conducted and recorded the test which saw a reduction of internal pocket milling time from 5 minutes, 30 seconds to 1 minute, 28 seconds, a time reduction of 75 percent. An additional benefit was improved chip removal performance, which reduced clogging by dispersing the chips away from the cutter and cutting area.