When mass finishing—finishing many parts simultaneously—in a vibratory finishing system, the tendency is to use ceramic or plastic preformed cutting media, said Steven Schneider, technical sales manager at surface finishing company Kramer Industries Inc., Piscataway, N.J. Ceramic tumbling media are made with abrasive filler, much like a grinding wheel. For plastic tumbling media, plastic is mixed with abrasive filler and cast to shape. Ceramic media use aluminum oxide as filler, and plastic media use quartz or silica for cleaner results.
“Randomly shaped media, either man-made or natural, are rarely used for precision work because they tend to jam in the holes and do not deburr into corners or recessed areas,” Schneider said. “When using ceramic media, care should be taken to avoid glazing or loading of the surface. It is a good practice to run the media with an abrasive grain occasionally to roughen the surface and clean the pores.”
The DB300 vibratory tumbler by Kramer Industries. DB tub vibrators are designed as starter machines for novices or shops on a limited budget.
Plastic tumbling media are self-cleaning due to their relatively soft bond, he said. Because adding abrasive filler to plastic media materially reduces the life of the substance, this media should be used only for mild cutting jobs that do not require adding abrasive filler.
“Plastic tumbling media are used mainly for fragile parts or soft metals,” he said. “Because plastic tumbling media weigh significantly less than stone or ceramic tumbling media, plastic is safer to use in such cases.”
There is much more to mass finishing than the selection of cutting media. For information about part details, processing speeds and costs, read “Starting Mass Finishing” in the current issue of Cutting Tool Engineering.
Related Glossary Terms
- abrasive
abrasive
Substance used for grinding, honing, lapping, superfinishing and polishing. Examples include garnet, emery, corundum, silicon carbide, cubic boron nitride and diamond in various grit sizes.
- aluminum oxide
aluminum oxide
Aluminum oxide, also known as corundum, is used in grinding wheels. The chemical formula is Al2O3. Aluminum oxide is the base for ceramics, which are used in cutting tools for high-speed machining with light chip removal. Aluminum oxide is widely used as coating material applied to carbide substrates by chemical vapor deposition. Coated carbide inserts with Al2O3 layers withstand high cutting speeds, as well as abrasive and crater wear.
- grinding
grinding
Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.
- grinding wheel
grinding wheel
Wheel formed from abrasive material mixed in a suitable matrix. Takes a variety of shapes but falls into two basic categories: one that cuts on its periphery, as in reciprocating grinding, and one that cuts on its side or face, as in tool and cutter grinding.
Author
Greg Bartlett is a former editor of Cutting Tool Engineering magazine.
