October 2009 / Volume 61 / Issue 10|
Vibratory finishing of titanium alloy parts
By Edward F. Rossman, Ph.D.
Vibratory, or mass-media, finishing is a well-established process, especially for high-volume parts production. Some part manufacturers have used vibratory finishing on small titanium alloy parts because they already own small vibrating equipment. Vibratory finishing of larger titanium alloy parts is growing and is being used on some airframe parts. Boeing specification allows vibratory finishing of titanium alloy parts.
A fellow research engineer visited an overseas titanium alloy fabrication company and saw long titanium parts— I call them 1-D parts—such as spars being vibratory finished and vibratory peened. The equipment being used could be described as a dual-shaft drive, conventional vibratory finishing system. This type of equipment has been available from a U.S. manufacturer since the late 1950s or early 1960s, but has fallen into relative disuse in recent years in the U.S.
According to Miro Oryszczak of Giant Finishing, a Chicago finishing machine designer and builder, design time is nil because all the vibratory deburring equipment is already designed. There may be some rescaling of equipment to handle various part sizes, but no new designing. The time to build and deliver a vibratory finishing machine is about 5 months. Foundations and vibration isolation are not required. The equipment generates 90 dB of sound or more, so it is usually covered with a boxlike lid that reduces the sound level to 85 dB or less. Part tubs and machine bases are integral—considered to be one piece.
Not all parts require fixturing. Some parts are deburred and finished in a free-floating mode. Some parts, however, must be rotated on special fixtures within a tub during deburring, and some must be uniquely fixtured by clamping them in fixed positions within a tub. Some fixtures can be built with adjustable ends so one fixture can handle a family of parts.
Ceramic media is the first choice for vibratory finishing. Some testing is needed to determine if a 32 μin. Ra finish (Boeing’s finish specification for deburring and sanding) can be imparted using a single media. Most companies use a second media of hardened steel to achieve a peened effect. Most titanium part drawings for military aircraft do not require shot peened parts. If a second media is required, a second machine is usually needed because of the time it takes to change from one media to another.
Oryszczak noted that the water, ceramic media fines and small amount of detergent used when vibratory finishing are not considered hazardous and do not require special waste-removal requirements and the associated expense. End users can filter the water and reuse it.
Getting a vibratory finishing operation for large titanium alloy parts up and running requires a team effort and team support. It is recommended that the team assists with vibratory finishing machine selection, fixturing concepts and design, media selection, process implementati on, possible environmental issues and developing a network of specialists to contact. CTEAbout the Author: The late Edward F. Rossman, Ph.D., was an associate technical fellow in manufacturing R&D with Boeing Integrated Defense Systems, Seattle. Rossman’s Shop Operations column is adapted from information in his book, “Creating and Maintaining a World-Class Machine Shop: A Guide to General and Titanium Machine Shop Practices,” published by Industrial Press Inc., New York. The publisher can be reached by calling (212) 889-6330 or visiting www.industrialpress.com.
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