Fredrik Schultheiss

General conception of polar diagrams for the evaluation of the potential machinability of workpiece materials

This article presents a polar diagram method developed for describing and evaluating the potential machinability of different workpiece materials. The potential machinability is examined in terms of five critical properties of the workpiece material. Two groups of materials, a group of common steel grades and the other a group of stainless steels, were examined in detail, their polar diagrams illustrating the potential for comparing the machinability of different workpiece materials. Polar diagrams are seen as being particularly helpful in setup work for the machining of new, previously unknown materials as it allows for comparison with other materials and their respective machinability.

Analytical Calculation of the True Equivalent Chip Thickness for Cutting Tools and its Influence on the Calculated Tool Life

A majority of the established systems for determination and optimization of cutting data are based on Woxén’s equivalent chip thickness, heW. In metal cutting theory and models, the equivalent chip thickness is of vital importance when the depth-of-cut ap is in the same order or smaller than the nose radius r. Woxén made considerable simplifications in his chip area model, that form the basis for calculations of the equivalent chip thickness. Basic mathematical solutions, e.g. describing the chip area on circular inserts, are lacking. This article describes the geometrical implications when machining with round inserts. The error in Woxén’s equivalent chip thickness is largest when the depth-of-cut is less than ¼ of the nose radius and are up to 40 % wrong for some combinations of cutting data in the finishing range. The presented results explain the difficulties in getting a good validity in the models used to calculate tool life in finishing machining. The error leads to an underrating of the tool load in many machining situations

Residual stress analysis of machined lead-free and lead-containing brasses

Legislations demand low lead content in drinking water and low lead leaching from the water supply facilities. Lead-free brass (LFB) can fit in. The benefits of such alloy are acknowledged in both functional and environmental points of view. The relatively high strength of LFB means that the process condition and residual stress generation can be different as compared to the conventional brass. In this study, residual stress generation for a LFB (CuZn21Si3P) and a lead-containing brass (CuZn39Pb3) in a face-turning experiment is studied. Besides stress analysis, structural characterisation is also conducted. Stress generation in the feed and cutting directions of two brasses is depicted. Machined topography is measured to evaluate the surface integrity in connection with the machining conditions. This paper is part of a Themed Issue on Brass Alloys.

Machinability of CuZn21Si3P brass

New brass alloys containing less or even no lead are being developed, decreasing the environmental impact of the material. One example of an alternative brass is CuZn21Si3P, which contains less than 0.09 wt-% Pb. The research presented in this article evaluates the machinability of CuZn21Si3P as compared to more common, lead-containing free-machining brasses. The results show a marked decrease in the machinability of CuZn21Si3P. When longitudinally turning CuZn21Si3P the cutting tool failed after 142 min of machining. This tool wear was to a large extent remedied through the use of a coating on the cutting tool. CuZn21Si3P appears as a viable substitute for lead-containing brasses, thus implying the possibility for improving the sustainability of modern production. This paper is part of a Themed Issue on Brass Alloys.

Cost Based Process Optimization by Incrementally Changing the Cutting Data during Sustainable Machining

All companies strive towards lowering their manufacturing costs. Few companies do however succeed in continuously improving their production after the launch of a new production process. This article introduces a method for companies having an established technology to optimize their production in terms of part cost without disrupting the normal, day-to-day production. By incrementally chancing the process parameters such as for example cutting data as a function of the originally selected values, it is possible to optimize the production process. This is closely related to the lean production philosophy and long term sustainability which strives towards efficient use of resources and involvement of all employees in improving the production process. In the case study presented in this article it was found that by adding extra sulfur to the cutting fluid it was possible to decrease the part cost. By using the proposed method the company was able to decrease the part cost when manufacturing a specific part with approximately 5 %.

Analysis of the minimum chip thickness during turning of duplex stainless steel

The goal of this study has been to establish a method for quantifying the minimum chip thickness, h1min, during longitudinal turning of duplex stainless steel, and explore how the value of h1min changes with varying process parameters. Based on experimental results, it was found that the tool edge radius only has a limited influence on the size of h1min up to a certain feed level after which the chip flow direction close to the nose radius will have an increasingly pronounced effect. Experimental results show that h1min may be as large as 40% of the theoretical chip thickness when machining duplex stainless steel, results which were corroborated by an finite element method (FEM) analysis. Thus, it can be concluded that a substantial amount of workpiece material will only be deformed onto the machined surface or will form the side flow and not removed as a chip.