Statistical Process Modelling for Machining of Inhomogeneous Mineral Subsoil (CRC 823 – SP B4)

Machining of concrete with diamond tools is characterized by the very heterogeneous structure of the workpiece as well as of the tools (cf. fig.). Complex engagement conditions arise being detectable only through statistical methods. An optimization of the machining process is difficult due to a lack of knowledge of the complex interaction.

Fig.: Diamond arrangements and examples for segments geometries

The chip removal processes during machining of the multi-phase inhomogeneous mineral material of reinforced concrete with diamond tools are examined within the scope of the Collaborative Research Center 823. This work is carried out in cooperation with the Institute of Statistics with Applications in the Field of Engineering Sciences and the Institute of Material Technology (LWT). Therefore, simulations of the process behaviour are developed based on statistical methods in order to reduce the large number of dimensions of influence to a manageable degree.

In addition to circular saws, chain saws and rope saws core drills are used in concrete processing. Core drills hold several diamond impregnated cutting segments consisting of a metal matrix and several embedded diamonds. An optimization of these tools concerning the achievable feed rate and occurring tool wear requires a detailed and sophisticated process knowledge.

The third research phase of this project is dedicated to the generalization of the models of single-grain scratch tests and single segment tests that were developed within the first two phases on complete core bits. Beside tools with randomly distributed diamonds, tools with pattern-controlled diamond arrangements are now analyzed as well. New statistical methods for lifetime models are used to determine the influence of process forces on tool wear. In particular, the breakout of individual diamond grains will be modelled. Hereby, it is taken into account that a load redistribution on the remaining diamond grains takes place. New methods for structural break detection are used to record the times at which single grains break out of the metal matrix. The final aim of the third research phase is to gain understanding of the fundamentals of the process’ and the tool’s behaviour, so that an optimized drill bit in terms of wear, energy efficiency and the achievable feed rate can be developed.

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