Page 40 - MetalForming April 2016

Mass Finishing
Table 1−Elements of a Mass-Finishing System
Mass-finishing machine
Induces the energy that creates the relative movement between workpieces and media
Grinding or polishing media
Generates the desired surface finish by constantly rubbing against the workpieces
Water
Acts as a coolant and, together with the compound, flushes out the fines from the work pieces and media
Compound
Dissolves dirt and grease, keeps the media clean and provides corrosion protection
Workpieces Drive Finishing Solution
Any surface-finishing solution evolves around the workpieces. Their material type, size, shape and above all, the finishing objectives, determine what type of finishing process must be selected.
Workpiece size is especially impor- tant. For example, the deburring and edge-radiusing of small stampings, such as chain links (Fig. 1), can take place in a small, high-energy machine with a capacity of less than 1 cu. ft. On the other hand, the polishing of large wind- power gears weighing to 5 tons requires a significantly larger machine (Fig. 2) with capacities of well over 100 cu. ft.
Fragility of the workpieces is anoth- er important factor. With delicate, high- value workpieces, part-on-part con- tact must be avoided to prevent scratches or nicks (Fig. 3). Typically, these types of workpieces mount to a fixture that prevents any part-on-part contact during finishing.
Workpiece shape influences media selection. Parts with complex geome- tries and internal passages may require completely different media shapes and sizes compared to simple forgings.
And finally, workpiece material plays a role as well. For instance, parts made from aluminum or magnesium
Fig. 3—Delicate parts, like the artificial knee joints shown here, must mount to fixtures to prevent scratches and nicks.
Table 2−Quality-Control Rules for Mass-Finishing Systems
Correct settings of the separation system
This helps minimize the time required for separating the media from the finished workpieces.
Undersized media removal
This helps minimize the time required for separating the media from the finished workpieces.
Timely media replenishment
Media are subject to constant wear. In aggressive applications the wear rate can be 5 to 10 percent. Therefore, regularly adding media to the machine is essential for process stability.
Maintaining the optimum level of media in the machine
Excessive media in the machine causes additional costs by unnecessarily increasing media consumption. Insufficient media in the machine will result in reduced quality and can cause nicking of the workpieces.
The correct dosing of compound
Excess compound can cause foaming problems, which unnecessarily increases costs. Insufficient compound will impair the finishing results, causing workpieces to come out dirty and reducing media performance.
The correct dosing of water
Excess water will dilute the cleaning effect of the compound. Insufficient water will impair finishing results, causing the workpieces to come out dirty and reducing media performance.
38 MetalForming/April 2016
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