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QUICK FACT GUIDES FOR MACHINISTS
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GUIDES |
MACHINING ALUMINUM Some of the alloys of aluminum have been machined successfully without any lubricant or cutting compound, but in order to obtain the best results, some form of lubricant is desirable. For many purposes, a soluble cutting oil is good. Tools for aluminum and its alloys should have appreciably more side and top rake than the tools for cutting steel. The front clearance of a tool most suitable for machining aluminum and its alloys should be about 8 degrees, the top rake from 30 to 50 degrees, making the total angle of the cutting edge from 25 to 55 degrees. A side rake of from 10 to 20 degrees will materially assist in the cutting action. In all cases it is essential that the cutting edges of the tools be keen, smooth, and free from grinding wheel scratches, burrs, or wire edges. Keen tool edges are best obtained by finish-grinding on a fine or very fine abrasive wheel, followed by hand-stoning with a fine or very fine oilstone. Parting tools for machining aluminum and its alloys should have from 12 to 20 degrees top rake and be stoned so that their cutting edges are keen and smooth. With such tools, the front clearance angle should be decreased to about 3 to 4 degrees. Facing tools should be ground so as to have a side rake similar in amount to that indicated for the top rake of the outside turning tools. High-carbon steel tools ground to the thin cutting edges necessary for aluminum soon fail because of brittleness. High-speed steel tools gibe much better results, except when used for machining aluminum alloys containing appreciable amounts of silicon. for the high-silicon alloys use cemented tungsten-carbide tools. Milling cutters, straddle mills, end-mills, and similar cutters work to best advantage in machining aluminum and its alloys if they are of the coarse-tooth spiral type and have a considerable amount of top rake on their cutting edges. Face milling cutters with inserted teeth are satisfactory for machining aluminum. Such cutters should be designed so that the inserted teeth have appreciable top and side rake. Excellent threads may be chased in even the softest aluminum in an engine lathe, using a single-pointed threading tool with considerable top and side rake. The tool must be ground so as to give the required thread contour. Hand and machine taps will produce smooth and accurate threads in aluminum if they are of the spiral-fluted ground-thread type. Experience has shown that such taps should have a right-hand spiral flute when intended to cut a right-hand thread, and the spiral angle should be similar to that used in an ordinary twist drill. Satisfactory taps for use in aluminum have been made by chasing threads on annealed high-carbon twist drills followed by rehardening and grinding |
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Copyright © 2002 QUICK FACT GUIDES FOR MACHINISTS
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