Cutting with Unbonded Grain

Cutting wire lapping (Fig. 9-11) is these days the dominant and most widespread technique. It is used especially in mass markets. Although this method has been utilised industrially for some time, knowledge of the process is still mostly of an empirical nature. Theoretical findings and process models exist only to a limited extent and are hardly accessible publicly.

The tool used in cutting wire lapping is an uncoated wire, on which a lapping suspension is supplied by means of nozzles. This suspension consists mostly of SiC particles that are found in a medium in solution. As a rule, oil or glycol is used as a medium. The lapping suspension is an essential component of the ma­chining process, since without it no material removal would be possible. Never­theless, the effects of slurry variations on the machining process are to a great ex­tent unknown [SUWA99].

The machining process takes place as follows. The abrasive medium sticks to the wire as a result of adhesion and is transported by it into the cutting gap. Mate­rial removal occurs by means of the rolling of the carbides on the workpiece. In
this way, microcracks are induced in the material, causing the silicon particles to break off [KAO98]. This method is disadvantageous with respect to its high cost as well as the ecological burden due to the used slurry and slurry disposal in par­ticular [KAO98a].

Innovative approaches thus aim to remedy these negative aspects by develop­ing slurry refreshment strategies as well as recycling measures. In addition, con­stant further development of wires and of process design is aimed at reducing the wire diameter at comparable or even higher feed velocities. The resulting reduc­tion of material loss caused by cutting diminishes, on the one hand, the manufac­turing costs per wafer, on the other hand the number of producible wafers per in­got increases. These measures will contribute to a considerable increase in cost effectiveness