Tolerance Cost in Relation to Surface Finish during Longitudinal Turning Operations

Tolerances are an important part of production where the desire to produce quality products have to be weighed against the increased production costs. The desired tolerance will influence the choice of both production method as well as the machine used. Given that machining is an adequate production method, variation of the required surface roughness will imply a variation of the part cost which needs to be taken into account during production planning. This paper presents a method for evaluating the tolerance cost in regards to surface roughness during longitudinal turning operations, thus enabling a better comparison between different production situations

Tool Life and Wear Modelling in Metal Cutting, Part 2 ─ Based on Combining the Archard and the Colding Equations

In this article an analytical and empirical model for describing tool life and tool wear in metal cutting is presented. The model is based on combining the Colding tool life equation and an extended version of the Archard wear function. It is shown that through the combining of these two models a substantial saving of resources can be achieved in terms of the workpiece material required, as well as the manpower and machine time needed for determining the model constants and the optimum cutting data to be employed

On the Machinability of Ductile and Strain Hardening Materials - Models and Methods for Analyzing Machinability

As quality and performance demands on today’s products increases, more and more advanced materials are being used during modern production. The problem is however that this in turn place new demands on the machining processes utilized. Even though a significant amount of research has been published on the machining of these materials knowledge is still limited in several crucial areas. A problem with machining research is that it often relies heavily on quantitative data primarily obtained through experimental investigations. Due to the substantial amount of potentially different machining cases it could be difficult to generalize the obtained results to other scenarios. In this dissertation it has been attempted to model the investigated phenomena through using universal physical relationships. Even though this might result in a larger modeling error for the specific case investigated the author sees a great advantage of being able to have a physical explanation to the obtained results. The aim of this dissertation has been to increase the knowledge on, and to a certain extent predict, the machinability of some common ductile and strain hardening materials. The research has focused on evaluating duplex stainless steel, Ti6Al4V and Alloy 718. However, the proposed models have been constructed in a way as to aid future implementation for other workpiece materials. A central pillar of the research has been the influence of the stagnation point and the related minimum chip thickness. This aspect influences all machining operations and could potentially have a significant impact on the machinability, not least for ductile and strain hardening materials. During this research it was found that even though cutting conditions have a major influence on the value of the minimum chip thickness, material factors such as ductility and strain hardening should not be neglected as these also influence the obtained value. In turn, it was found that the minimum chip thickness could to a certain extent be used to explain the obtained workpiece surface roughness. Also, the tool surface roughness was found to have a determinate influence on the mechanics of the machining process. During the present research it was also found that it is difficult to predict the tool life using conventional models for the investigated materials, essentially due to their high strength at elevated temperatures, adhesive behavior during machining, and low thermal conductivity. The influence of these properties commonly results in rapid and unpredictable wear of the cutting tool. Plastic deformation of the cutting tool is always a concern when machining these materials and a first step towards establishing a method for measuring the initiation of plastic deformation by using the measured cutting force has been proposed. Also, through using a proposed method for determining the potential machinability of a specific workpiece material these effects could be reduced through the use of reasonable process parameters before commencing production. Methods for improving the machining process in terms of for example part cost or sustainability has been developed as part of this research. Even though each of these methods only improves a small part of the whole production process these improvements should not be neglected as all parts of the process should be optimized in order to achieve a truly sustainable and cost efficient machining process

Machinability of duplex stainless steels - A study with focus on the tool wear behaviour

This article presents research done in order to analyse the machinability of duplex stainless steel with coated carbide tools during turning operations. Although duplex stainless steel has existed for about 70 years fairly little work has been published in the area of investigating the different aspects of the machining of these materials. In this research project three different kinds of duplex stainless steels and their properties have been examined. These materials where SAF 2507, SAF 2205 and LDX 2101 which together covers a large part of the duplex stainless steels that are commercially available today. This study focuses on analysing the tool wear behaviour in an attempt to better understand the actual wear patterns during machining, not only the more traditional ones that are in common use today. Some additional tests were also done in order to get a better understanding of the machinability of duplex stainless steel in general. Theories and concepts that are related to the analysing of machinability will be presented, most of which have been previously validated and in use for a long time. Adhesive wear of the cutting tool, in many cases severe, was to some extent found at all different cutting data investigated

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

Research solution for automatic hole quality analysis when drilling fiber-reinforced composites

Fiber-reinforced polymers are highly demanding composites in aerospace and automotive areas because of their excellent mechanical properties such as stiffness and strength-to-weight ratio. The drilling remains the major machining operation applied to composites to provide high-quality holes for joints between parts. Due to composites plied structure, the drilling is accompanied with unusual form metal cutting defects such as delamination and uncut fibers around the drilled hole. Considering that the tool life of some drills reaches over thousands of holes, the research of composites machinability becomes difficult due to demanded labor intensity in manual inspection of the hole quality. Therefore, this paper develops the research solution for automatic analysis of the hole quality in drilled fiber-reinforced materials. The paper proposes a complex of solutions aimed to speed up the analysis of the hole quality when composites drilling. The solution consists of the developed vacuum table, robot arm with high-speed camera, developed top and bottom lightning systems, and Image Processing algorithms for defect detection from captured images. The paper results show how the developed solution can be used for high routine research activities. The output data, including tested 72 cutting data parameters and full-size tool life test, allowed identifying the operational window for high-speed steel drills and the range of tool life, where drill ensures a certain hole quality. The paper shows the efficiency of the developed research solution can reach 5 s per hole including drilling and full cycle of measurements having measurement error of 1–3%

Analytical Calculation of the Ra Surface Roughness during Turning

In this article an analytical equation for calculating the theoretical arithmetic mean surface roughness, Ra, in the case of turning using a tool with a circular nose radius is presented. The calculated Ra-values are verified by experimental results obtained from machining of 7 different workpiece materials. For all measuring series results were obtained that were either better or worse than the theoretically calculated values. The presented model describes an analytical equation for calculating the theoretical Ra-value and may be practically implemented in industry