Hendrik Puls

A new experimental methodology to analyse the friction behaviour at the tool-chip interface in metal cutting

This paper investigates a new test to analyse the friction behaviour of the tool-chip interface under conditions that usually appear in metal cutting. The developed test is basically an orthogonal cutting process, that was modified to a high speed forming and friction process by using an extreme negative rake angle and a very high feed. The negative rake angle suppresses chip formation and results in plastic metal flow on the tool rake face. Through the modified kinematics and in combination with a feed velocity that is five to ten times higher than in conventional metal cutting, the shear and normal stresses are only acting in a simple inclined plane, allowing to calculate the mean friction coefficient analytically. In addition, the test setup allows to obtain the coefficient of friction for different temperatures, forces and sliding velocities. Experiments showed, that the coefficient of friction is strongly dependent on the sliding velocity for the example workpiece/tool material combination of C45E+N (AISI 1045) and uncoated cemented carbide.

Modelling and Compensation of Thermoelastic Workpiece Deformation in Dry Cutting

Dry cutting ranks among the most significant developments within manufacturing technology. Compared to wet cutting, a major problem of dry machining is a stronger heat generation and thus, workpiece warming. This leads to thermoelastic workpiece deformation. Therefore, within this work a model is developed to predict and compensate the thermoelastic workpiece deformation. At first, friction behavior and heat transfer at the tool-chip interface in the orthogonal cutting process are experimentally investigated. Based on the fundamental investigations, a multiscale model for the dry turning process is developed. It contains two submodels, a mesoscopic FE-model for the chip formation and a macroscopic FE-model for the turning process. To validate the mesoscopic FE-model, experiments of orthogonal turning are performed and the temperature fields are measured. Hereby, the occurring heat flow into the workpiece is calculated by solving the inverse heat conduction problem. The macroscopic FE-model calculates the thermoelastic workpiece deformation based on heat inputs of the mesoscopic model. By means of the developed approach, minimization and compensation strategies are developed, applied and evaluated based on complex processing examples.

FEA-Methodology for the Prediction of Aluminium Thin Walled Part Deformation in Dry Milling Operations

The presented work is a part of the EU integrated and collaborative project “Aligning, Holding and Fixing Flexible and Difficult to Handle Components” (AFFIX). The deformation of thin-walled components, caused by a thermo-mechanical load in the machining process, is a common challenge in manufacturing automotive engine heads and gearboxes. Geometrical tolerances like flatness are strongly affected by the thermo-mechanical process loads, and therefore cause production scraps and serious engine faults in case of undetected defects. To avoid long process setup times, a methodology has been developed to calculate the resulting part flatness. Based on the developed methodology a clamping strategy has been identified which minimises the resulting part deformation in milling operations and thus ensures the accuracy and quality of thin-walled aluminum power train parts.