Mass finishing processes can be configured as either batch systems, in which batches of workpieces are added, run, and removed before the next batch is run, or as continuous systems, in which the workpieces enter at one end and leave at the other end in the finished state. They may also be sequenced, which involves running the workpieces through multiple different mass finishing processes; usually, the finish becomes progressively finer. Due to the random action of the processes, mass finishing is as much an art as it is a science.
Metal tumbling is used to burnish, deburr, clean, radius, de-flash, descale, remove rust, polish, brighten, surface harden, prepare parts for further finishing, and break off die cast runners.
The process is fairly simple: a horizontal barrel is filled with the
parts which is then rotated. Variations of this process usually include
media, water, or other lubricants. As the barrel is rotated the material
rises until gravity causes the uppermost layer to landslide down to the
other side. The barrel may also have vanes, typically made of rubber,
which run along the inside of the barrel.
As the barrel turns the vanes catch and lift the parts, which eventually slide down or fall.
In a wet processes a compound, lubricant, or barreling soap is added
to aid the finishing process, prevent rusting, and to clean parts. A
wide variety of media is available to achieved the desired finished
product. Common media materials include: sand, granite chips, slag,
steel, ceramics, and synthetics. Moreover, these materials are
available in a wide variety of shapes. Usually different shapes are used
in the same load to reach into every geometry of the part.
Barrel burnishing is a type of barreling where no cutting action is desired. The goal is to reduce minute irregularities and produce a clean, smooth surface. The parts are usually tumbled against themselves or with steel balls, shot, rounded-end pins, or ballcones to achieve this. It is also usually a wet process, that uses water and a lubricant or cleaning agent, such as soap or cream of tartar. The barrel is not loaded more than half full and if media is used then a 2:1 ratio of media to parts is maintained to keep the parts from rubbing.[3]
Vibratory finishing is a type of mass finishing manufacturing process used to deburr, radius, descale, burnish, clean, and brighten a large number of relatively small workpieces.
In this batch-type operation, specially shaped pellets of media and the workpieces are placed into the tub of a vibratory tumbler. The tub of the vibratory tumbler and all of its contents are then vibrated. The vibratory action causes the media to rub against the workpieces which yield the desired result. Depending on the application this can be either a dry or wet process.
Unlike tumbling this process can finish internal features, such as holes. Its also quicker and quieter. The process is performed in an open tub so the operator can easily observe if the required finish has been obtained.
Vibratory tumblers have an action that is similar to filing. An eccentric, rotating weight shakes the tub 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.
Vibratory finishing systems tend to produce a smooth finish because the media essentially lthe parts. 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 frequency and amplitude of the machine controls the finish of the parts. The frequencies can vary from 900 to 3600 cycles per minute (CPM) and the amplitude can vary from 0 to 3⁄16 in (4.76 mm). High frequencies, 1800 CPM or greater, and small amplitudes are used for fine finishes or delicate parts, whereas large amplitudes are used for heavier cutting. High frequencies and amplitudes can roll burrs and peen edges. The circulation of parts is best at higher frequencies, therefore, heavy pieces are run at these high frequencies with moderate amplitudes of 3⁄32 to 1⁄8 in (2.38 to 3.18 mm).
Media are designed for four things:
Media come in a wide range of materials in order to fulfill various needs.[3]
Compounds are added to mass finishing processes to assist in deburring, burnishing, cutting, cleaning, descaling, and inhibiting corrosion. They may be liquids or dry powders. They are usually broken up into four types: deburring and finishing, burnishing, cleaning, and water stabilizing.