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Milling is seldom if ever required on zinc diecastings, as spot facing or routing is likely to be preferable. If a milling operation is required the following comments apply:

Zinc alloys are readily milled. There should be no problem with chip formation surface finish or galling provided cutters are sharp, copious cutting fluid is provided and the setup is rigid.

Cutter Design

End Milling

The common right hand spiral fluted end mill design and the special aluminum cutter design (large, highly polished flutes for non-ferrous alloys) give good results.

Plain Milling

The non-standard “high helix” and “helical aluminum” cutter designs are preferred. The higher helix angles and smaller number of teeth or flutes on these cutters give better results. Where possible, contact should be maintained between a cutter tooth and the workpiece until the next tooth is engaged. This practice reduces vibrations and chatter, which improves surface finish and prolongs the life of the cutter and machine.

Milling Direction

“Down” or “climb” milling is preferred in almost all cases for reduced burr formation. It also improves chip flow and disposal, carries cutting fluid into the cutting zone more readily and reduces sensitivity of the surface finish to cutter sharpness.

Depth of Cut

Shallow depths 0.64 mm or less are preferred. The use of shallow finishing passes after deeper roughing cuts should be considered in some cases.

Cutting Speed

Higher surface cutting speeds, such as 100 m/min can generally be used for shallow depths of cut. Cutter speeds should be reduced, to as low as 30 m/min for deep cuts.

Feed Rates

High table feed rates are preferred for both end milling and plain milling.

However, excessive feed rates can cause problems of heavy tooth loading, wear and vibration. Optimum feed rates depend on cutter diameter, width and depth of cut, number of cutter teeth, cutter speed, machine and workpiece rigidity, and other factors. In practice, the setup personnel should seek the optimum feed rate by trial, guided by the general behavior noted above.