Process Model Allows Forecasts on Wire Wear and Load
To control the multi-wire saw, many machine parameters can be adjusted. These include in particular the wire and feed speeds and the pretensioning force of the saw wire during production. Over the years, by varying these settings according to the "trial and error" principle, an apparent optimum for the production of photovoltaic wafers has developed - but a comprehensive understanding of the mechanisms within the wire field that lead to "good sawing" is still lacking.
For this purpose, a process model was developed in addition to the analysis of the machine data as well as the data by the sensor technology of the machines extended at the Fraunhofer CSP. This model describes the multi-wire saw on the basis of the most important parameters and provides important information which can hardly or not at all be measured.
As shown in the figure, force distributions during the sawing process at any position (in the saw channel) as well as the resulting material removal and wire displacements ("bow") can be determined. This information can be used to make predictions about wire wear and load, which can prevent wire breakage or minimize wire consumption, for example. In addition, the process-related damage to the silicon wafers and thus the subsequent failure probability of the processed solar cells can be estimated.