Vibratory finishing

Vibratory finishing is a process used to remove burrs from large numbers of relatively small workpieces.

In this batch-type operation, specially shaped abrasive pellets of nonmetallic or metallic media are placed in a Vibratory tumbler along with the parts to be deburred. The vibratory tumbler is then vibrated using various mechanical means. The impact of individual abrasives and metal particles removes the burrs and sharp edges from the parts. Depending on the application this can be either a dry or wet process.

Vibratory tumblers

Vibratory tumblers have an action that is similar to filing. The cutting media surrounds the parts. The eccentric, rotating weight shakes the tube in a circular path during which the entire load is lifted up at an angle and then dropped. As the load is falling (but not actually airborne) the tub returns to an upward position, applying an upward and angular force that causes a shearing action where the parts and media rub against each other.

Generally speaking vibratory finishing systems tend to produce a very smooth finish because it really laps the parts. The vibratory tumbler will also cut inside a tube or cup shaped piece or any spot the media can reach. Since the load is moving as a unit, very fragile parts are quite safe in the vibrator. There is no tearing action or unequal forces that tend to bend and distort parts. The larger the parts or media are, the faster the cutting action.

The speed and amplitude of the machine controls the finish of the parts. Because of this it is variable on most machines. High speeds (1800 cycles per minute) and small amplitudes are used for fine finishes or delicate parts. Large amplitudes are used for heavier cutting, varying the speed according to the finish requirement. High speeds with large amplitudes can roll burrs in and even peed metal into holes and mushroom edges. The circulation of parts is best at higher speeds; therefore, heavy pieces are run best at higher speeds with moderate amplitudes of 1/8" to 3/32". [ [http://www.kramerindustriesonline.com/finishing-guides/choosing-the-right-system.htm Surface Finishing, Vibratory Finishing, Barrel Finishing, Tumbling Barrel, Vibratory Tumblers ] ]

Media functions

*Cut - Media which cuts can remove burrs and smooth surfaces. As a carrier of abrasive grain, the large media pieces effectively increase the impact force of the abrasive on the metal part to be cut, thereby improving the efficiency of the abrasive. Cutting media develop dull, matte surfaces.

*Luster - Some grades of media are designed to promote luster on the surface of metal parts. These products are generally non-abrasive or have a very low degree of abrasiveness. They deburr by peening, rather than actually removing the burr. Media selection, therefore, will control the degree of surface luster, making the part bright and shiny or developing a very matte, dull surface characterized by a completely random scratch pattern, or anything in between.

*Parts separation - A very important function of the media is to separate parts during the deburring, cutting, surface improving or burnishing operations. The media:parts volume ratio is normally used to control the amount of part-on-part contact which will occur in a vibratory or barrel finishing operation. At low ratios, considerable part-on-part contact occurs, while at higher ratios part-on-part contact is limited.

*Scrub surfaces - Media has the unique ability of scrubbing surfaces and physically assisting compounds in their cleaning function. Both abrasive and non-abrasive media are effective in providing this action. They are effective on organic soils, as well as on scale and other inorganic residues.

Types of Media

A great variety of media is currently available on the market to provide a tremendous range of capability in cutting, deburring, smoothing surfaces, developing luster, scrubbing, and parts separation for a whole host of materials, including metals, ceramics, plastics, wood, painted, plated, and materials with other finishes on them. [ [http://www.hammondmach.com/content/view/336/5 Hammond Roto-Finish - Vibratory Media ] ] [cite news | title=Aluminum Vibratory Shaker Media | url =http://www.lsindustries.com/shakermedia.html | accessdate = 2008-07-12 ]

*Aluminum Media - Aluminum media is typically a cast part and are available in a wide variety of shapes and sizes. Aluminum scrubs the parts and works in conjunction with a compound to clean parts. Since aluminum is fairly nonabrasive it tends to remove surface impurities without affecting the parts surface qualities. Cost is typically higher than other cast media. Wear rates are lower than ceramic but higher then steel media.

*Preformed Ceramic Media - Ceramic media is manufactured by mixing clay - like materials and water with abrasives, forming this mud into shapes, drying these shapes, and firing them at high temperatures to vitrify the binder. Many of these binders are porcelain-like in nature. Variability in these products occur both with the type of binder used, firing temperatures, the amount, size and type of abrasive grains they contain, and their uniformity of firing. This type of product today is the general work horse of mass finishing systems and is the type of media generally selected because of its availability in a variety of desirable shapes and sizes, its low cost and low media wear rate.

*Preformed Resin-bonded Media - Plastic or resin-bonded media utilizes a wider range of abrasive types and sizes than preformed ceramics. The most popular grades are those using quartz as an abrasive. Aluminum oxide, silicon carbide and other abrasives are also used. Usually low cost polyester resins are employed as the binder and the various shapes are cast. Resin bonded media can develop excellent preplate finishes on any metal surface.

*Steel - Casehardened, stress-relieved steel preformed shapes are available in a variety of sizes and configurations. Balls, balls with flat spots, oval balls (footballs), diagonally cut wire similar to angle-cut cylinders, ball cones and cones (both of which are different than the standard concept of cones) and pins are the most commonly used. Steel media weighs approximately 300 pounds per cubic foot and is expensive for initial installation but, because it has a minimal attrition rate and because of its extreme cleanliness, steel media is being more widely used for light deburring applications and for cleaning. Compounds are available which keep steel burnishing media clean and bright for years so that it can rapidly clean, brighten, and deburr metal, plastic or ceramic.

*Synthetic Random-shaped Media - The most popular synthetic random media is fused aluminum oxide, which is available in a number of grades. The more loosely bound, coarse-grained materials are characterized by fast cut and high depreciation rates. Because of the dark color of fused aluminum oxide, the soil generated by this material is excessive in many applications. Fine-grained fused aluminum oxide is generally employed for burnishing and in this respect is unexcelled in many applications with the possible exception of steel. Where some light cutting is required, fine-grained aluminum oxide can develop a better luster on stainless steels and other hard surfaces than can be achieved with steel burnishing media.

*Natural Random-shaped Media - River rock, granite, quartz, limestone, emery and other naturally occurring abrasive materials are being used in vibratory and barrel finishing applications. In general, these products are not too efficient in vibratory equipment because of their high attention rates.

*Cobmeal, Walnut-Shell Flour, and Related Materials - are used for drying applications because of the natural ability of these products to absorb water from metal surfaces. These produces can also be blended with abrasives and used for fine-polishing applications in vibratory, barrel, or spindle finishing equipment.

*Other - Shoe pegs, leather, carpet tacks, and almost any solid materials conceivable have been used at one time or another in barrel or vibratory finishing for certain applications.

See also

*Barrel finishing - a process similar to vibratory finishing
*Mass finishing
*Tumble polishing

References