Self-Adjusting Cutting Parameter Technique for Drilling Multi-Stacked Material 2015-01-2502

This study investigates the self-adjusted cutting parameter technique to improve the drilling of multi-stacked material. The technique consists in changing the cutting strategy automatically, according to the material being machined. The success of this technique relies on an accurate signal analysis, whatever the process setting. Motor current or thrust force are mostly used as incoming signals. Today, analyses are based on the thresholding method. This consists in assigning lower and upper limits for each type of material. The material is then identified when the signal level is stabilized in between one of the thresholds. Good results are observed as long as signal steps are significantly distinct. This is the case when drilling TA6V-CFRP stacks. However, thrust force level remains roughly unchanged for AA7175-CFRP stacks, leading to overlapping thresholds. These boundary limits may also change with tool geometry, wear condition, cutting parameters, etc. The thresholding method is therefore not optimal for industrial uses.

The paper presents a new method, able to differentiate composites from metallic materials, in real-time and independently of any process parameters (drill geometry, tool wear, etc.). The proposed approach based on Discrete Wavelet Transform (DWT) is able to detect specific frequency characteristics generated by material cutting. Using this method, improvements can be made to the self-adjusted cutting parameter technique for multi-stacked drilling application. Results are validated experimentally using thrust force signals measured while drilling various multi-materials under different process parameters.