More precise components by applying some practical rules to precision processing

Components must be produced with increasing level of precision. The accuracy of the machine tools depends principally on a range of factors. In order to help designers and operators to achieve high levels of accuracy, Sirris has come up with a few practical rules.

The requirements for producing high quality components over the coming years are going to be stricter and form an even greater challenge for manufacturers. With respect specifically to energy consumption, wear patterns and functional qualities, steps probably still need to be taken for creating the next generation of products, while simultaneously maintaining the same or even lower production costs.  One of the most important factors in this story concerns the accuracy with which components can be produced. Strict tolerances and high surface quality can significantly increase the lifetime of a component, as well as making new functionalities a possibility.

The accuracy that machine tools can achieve depends principally on a number of factors. This includes the machine kinematics, which has everything to do with the type of machine. There are also many other factors, such as the temperature, tool wear, cutting conditions, machining methods applied, the accuracy of the feeler-gauges and the CAM software for example, which can all exert a significant influence depending on the type of operation and the desired level of accuracy. In order to make it easier for the machine operators to work more accurately, Sirris is currently drawing up a number of practical rules specifically for these factors.

Trying to find the last few microns

Research has already been done regarding the influence of wear and the cutting conditions with respect to the dimensional accuracy of machined parts. During the milling process, deviations are measured against the pre-set dimensions. The cutting power is also measured using an XYZ force table. By comparing these results, and with the help of the cutting forces, it can be demonstrated that it is possible to predict very accurately the level of tool deflection, and that this deflection makes the main contribution towards dimensional deviation when rough-milling is carried out. Factors such as temperature, machine kinematics, clamping, feeler-gauge accuracy and CAM, all played a much smaller role or were not even applicable.

Using the accurate cutting force calculations, this conclusion has made it possible to predict the dimensional deviations of a machined part. It is also possible to change the cutting parameters so that the cutting forces can be lower, as well as more constant, whereby deflection can be reduced considerably. This way of optimising the machining process has made it possible in practice to reduce dimensional errors by two thirds.