Machining of ZA Alloys

 

The machinability of the ZA alloys is excellent: faster and easier than any other alloy of comparable strength, including the bronzes. These zinc alloys tolerate wide variations in machining conditions without sacrificing quality.

Iron castings can contain hard spots and sand inclusions that make machining very difficult and costly. Machining zinc foundry alloys is much faster, and tool life is several times longer than cast iron.

General practice
Cutting fluids are recommended for machining zinc alloy castings.
In general, mild steel machining procedures and tooling profiles are used with zinc foundry alloy castings. High-speed cutting tools with sharp cutting edges and positive rakes are suitable. Fluted tools such as drills, taps, reamers and end mills should have large, smooth flutes to reduce friction and facilitate chip removal. Tool rake and flank faces should be ground and polished.

Drilling, tapping, reaming and turning
For drilling, the slow-spiral and fast-spiral twist drill designs for non-ferrous work are preferred.
For tapping internal threads, spiral point taps are preferred. In areas such as blind holes, the special aluminum tap geometry is an appropriate substitute. The ZA zinc foundry alloys are also readily adaptable to form tapping.
Reaming can be accomplished using the common six-fluted reamer.
Turning is facilitated by high-speed-steel turning tools with large clearance angles and positive back and side rake angles.

General speed and feed recommendations

Drilling: Drilling speeds in the range 200 to 300 fpm can be used. Feed rates as follows: 

Hole diameter Feed rate
Inches  mm  In./rev. mm/rev.
1/8 3.18 0.004  0.10
1/4 6.35 0.008 0.20
3/8 9.53 0.011 0.28
1/2  12.70 0.013 0.33
3/4 19.05 0.016 0.41

Tapping: Cutting speeds of 200 sfm are acceptable for general work.

Reaming: Feeds for reaming are similar to those for drilling. Speeds in the range 100 to 200 sfm are recommended for reaming ZA zinc foundry alloys.

Turning: Speeds and feeds are similar to those listed above for drilling. Reduced speeds and high feed rates improve chip formation.

Milling - Cutting speeds: 

General work - 350 sfm
Deep cuts - 100 sfm

Sawing: Bandsaw. Cutting speeds: 300-400 fpm

Grinding: Belts in the 40-80 grit range are acceptable for general work.

Staking: Low speed (e.g. hydraulic) or high speed (e.g. mechanical) presses can be used.

 

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