What is Vibratory Finishing
Vibratory finishing is the final step in the plating process, and it includes grinding down unwanted burrs, smoothing sharp edges and providing a polished finish. The shape, material and size of vibratory media vary depending on the parts’ material, shape and strength. Choosing the right finishing media optimizes the quality of your finished product while providing cost-effective, mass-produced results.
TYPES OF FINISHING MEDIA
Finishing media materials include:
- Organic compounds
Other media, such as glass beads, are occasionally employed; however, in most cases your parts will be finished using one or more the four main media types.
CERAMICS AND PLASTIC MEDIA
Ceramic and plastic media account for eighty to ninety percent of finishing media. Ceramic media has a relatively high density, and it’s used for grinding and polishing hard metals such as steel, stainless steel and titanium. Ceramic media also includes porcelain made from pure aluminum oxide. Porcelain is used for finer grinding and produces a high gloss finish.
Ceramic media is tough and durable, but it can chip. Loose chips in the finishing media can lodge in boreholes and other small areas in metal parts.
Plastic media normally have a polyester base, but some media may be urea or formaldehyde-based. Plastic media are generally used for “softer” metals, such as aluminum, brass and zinc.
Both ceramic and plastic media are mixed with abrasives during finishing. Common abrasive types include silica, silicon carbide, aluminum oxide and zirconium. Silica, or sand, is used to debur and deflash softer metals. Silicon carbide and aluminum oxide are used for aggressive grinding, usually on harder metals. Zirconium is added to lighter plastic media to add some weight, and it’s used to finely grind all types of metals.
STEEL AND ORGANIC MEDIA
Steel media is made from both hardened carbon and stainless steel, and it’s usually used to apply pressure to debur steel parts, as well as ball burnishing and polishing of stainless steel (and occasionally aluminum).
At the far end of the steel strength spectrum lies the organic finishing medium, including corn cob granules and walnut shells. Organic media are mostly used to dry parts after vibratory finishing. It can also be used to produce a high gloss finish on stainless steel, aluminum and other metals when mixed with a polishing paste.
THE IMPORTANCE OF SHAPE
Finishing media comes in a range of sizes, from cylinders and balls to pyramids and sharp-edged stars. The shape of the parts being finished usually determines the shape of the finishing media. For general use, round, oval and cylindrical media is preferred. The rounded surfaces wear well and have less chance of lodging in parts than sharp-edged materials. Round and cylindrical ceramic media also have lower chipping rates.
Triangles, arrowheads and tri-star shapes are better suited for finishing complex parts with hard-to-reach sections, but they come with higher wear rate and are more susceptible to chipping.
Size also matters when selecting vibratory tumbling media. Smaller media has more contact with the parts’ surface area than larger materials and produces a smoother, more attractive surface. Production times are longer for small media polishing, because smaller finishing material requires gentler processing.
Larger media produces a rougher surface, but lends itself to more aggressive grinding. Large finishing material provides rapid removal of burs and is also effective for radiusing sharp edges.