Dry machining of soft metal-modified aluminum castings with carbon-coated tools

Abstract

Additions of small but effective amounts of one or more of bismuth, indium, lead and/or tin to a silicon-containing aluminum casting alloy markedly improves the dry machinability of a casting made from the modified alloy. But dry machining of such castings is synergistically improved by the use of cutting tools with cutting surfaces coated with microcrystalline diamond or diamond-like carbon coatings. The use of such carbon-coated tools enables remarkable improvement in dry machinability even at reduced levels of the soft metal in the alloy.

Description

TECHNICAL FIELD [0001] This invention pertains to the machining of silicon-containing aluminum castings without the use of a metalworking fluid for lubrication and / or cooling (dry machining). More specifically this invention pertains to the markedly improved dry machining of castings of silicon-aluminum alloys containing microstructurally-dispersed soft metal additives while using cutting tools with carbon-based coatings. BACKGROUND OF THE INVENTION [0002] Aluminum alloy castings are used in making many articles of manufacture. In the automobile industry, for example, many engine and transmission parts, chassis parts, body parts and interior parts are made of silicon-containing aluminum alloy castings. Many of these parts such as engine blocks, cylinder heads, crank cases, transmission cases and the like are initially formed as castings using sand molding, permanent mold, high pressure die casting and lost foam processes. These casting processes are capable of forming complex shapes...

AI Technical Summary

Benefits of technology

[0005] The relatively high silicon content of aluminum casting alloys increases the difficulty with which they are machined and has required the use of a machining fluid, typically a liquid based fluid. The purpose and goal of this invention is to accomplish dry machining of certain compositionally-modified aluminum alloy castings without damage of the part and with tool life that is comparable to fluid lubricated and cooled machining. This invention provides a synergistic improvement in dry machining of such castings by using a combination of a relatively small amount of soft-metal additive in the cast alloy and a carbon-coated cutting tool. Such combinations have provided benefits in dry machining tool life that were unforeseen from optimized use of either practice alone.

Problems solved by technology

The relatively high silicon content of aluminum casting alloys increases the difficulty with which they are machined and has required the use of a machining fluid, typically a liquid based fluid.

These lubricity-imparting additives are not very soluble in the solidified aluminum-rich matrix phase of the castings although they may combine with alloying constituents such as magnesium.

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