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| TOOL MATERIALS AND COOLANTS |
All forms of beryllium copper are machined readily with either high speed steel or carbide tools. General purpose carbide grade C-2 is recommended where carbide tools are used, and M1, M2,
T1 or T2 types of high speed tool steels are recommended when high speed steel tools are used. Coated steel tools provide the same advantage in machining beryllium copper as other alloys. Carbide tools can be used to a greater advantage if production runs are long and/or close dimensional tolerances must be maintained.
Because of the machining characteristics of all beryllium copper alloys, cutting tool life is excellent. Normally the tool life end point is a wear land of .060 inch for high speed steel tools and .015 to .030 inch for carbide tools. In many of the tests conducted to determine the proper speeds and feeds, this end point was never reached even though extremely high speeds and feeds were used.
The recommended speeds and feeds presented in this report are based on single point tool lives of sixty minutes of continuous cutting for high speed steel tools. This results in a .060 inch wear land. In the case of carbide tools, the recommended speeds and feeds reflect thirty minutes of continuous cutting with a resulting .015 inch wear land. In actual shop operations where a number of tools are used alternately, time between grindings would be 3 to 4 times these values. In such instances, a tool life in excess of 6 to 8 hours would generally indicate speeds and feeds that are too low for optimum productivity.
As, generally, wear is proportional to speed, it is not unusual for a 50 percent increase in speed to reduce tool life by 50 to 70 percent. Increasing feeds, while maintaining a fixed speed, may increase tool life up to a point but then reduce it in proportion to the feed rate. This is particularly evident at high cutting speeds.
The optimum combination of speed and feed is that which results in the greatest volume of metal removed (or greatest number of parts machined) for an allowable wear land, or for one tool change or grinding. Tool life in these terms increases greatly at moderate cutting speeds (300 ft/min) with feeds up to .020 in./rev. For higher speeds, tool life may reach a maximum and then decrease for feeds higher than .010—.015 in./rev.
Naturally, the depth of cut enters into the rate of material removal. But, except for the softer alloys, this parameter is more dependent on factors like tool and work piece rigidity and machine horsepower than on the material being machined.
The foregoing discussion is based on the results of turning experiments but, in principle, it is applicable to other operations as well.
The use of coolants is recommended for all machining operations. Chemical emulsions, water soluble oils and mineral lard oils are the most desirable of the commonly used coolants. Unless sulfurized oils are immediately rinsed from machined parts, they may cause cosmetic staining. |
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