T.H.C. Childs

Computer-aided simulation and experimental studies of chip flow and tool wear in the turning of low alloy steels by cemented carbide tools☆

Abstract A finite element modelling (FEM) analysis of chip flow has been developed on a CAD (computer-aided design) computer and used to aid studies of the wear of cemented carbide tools turning an aluminium-deoxidized and an aluminium-deoxidized, calcium-treated resulphurized low alloy steel. The latter steel formed a Ca-Mn-S deposit on the tool rake face and, at a given feed and speed, machined with 20% lower tool forces and 60-fold less crater wear than the former. Subsidiary tests showed both steels to have the same mechanical properties but that the Ca-Mn-S deposit reduced chip-tool friction; input of these data to the FEM analysis resulted in lower predicted cutting forces and temperatures for the deposit-forming steel. The temperature calculations, with a thermal activation wear model, indicate provisionally that the crater-wear-reducing properties of the deposit were multiplicatively 20-fold due to its effect as a diffusion barrier and three-fold due to lower temperatures.

Finite element simulation of chip flow in metal machining

Abstract Finite element studies of machining are becoming ever more sophisticated. A basic approach which removes the need, in an elastic–plastic analysis, to follow the development of chip formation from initial contact between work and tool, is the iterative convergence method (ICM). It develops a steady-state chip formation from an initial state of a fully formed chip loaded against a tool. It relies for its accuracy on the assumption that its simplified loading path coincides with the real developed flow at the end of the simulation. This paper examines the robustness of this assumption by studying the sensitivity of the simulation to changes of detail, within the ICM method, of how the flow develops; and it compares the simulated results with experiments. The experiment involves the turning of three free cutting steels, for which experimental flow stress variations with strain, strain rate and temperature, as well as information about the friction interaction between chip and tool, are available. The changes to the simulation method considered here are the structure of the finite element mesh, the measures of judging when the flow is fully developed, how the chip separates from the work at the cutting edge and the friction laws used during the approach to fully developed flow. It is shown that these do affect the outcomes of the simulation but within the ranges studied only to a minor extent and good agreement with experiment is achieved.

MATERIAL PROPERTY NEEDS IN MODELING METAL MACHINING

ABSTRACT Different laws of how flow stress varies with strain, strain rate, and temperature, from different authors, are reviewed and compared for their predictions of behavior in the primary and secondary shear conditions of metal machining. Despite differences in their structure, the laws give similar numerical values of flow stress in primary shear conditions, but show large differences in secondary shear. Friction laws are also discussed. There is a need to develop secondary shear yield and friction laws.

Affective Consumer Requirements: A Case Study of Moisturizer Packaging:

Tools for eliciting and managing product requirements are now well-established in some fields of engineering. These tools primarily focus on linking objective, functional customer requirements to the product’s properties. Whilst there have been advances in identifying human factors requirements, the elicitation of the customers’ subjective requirements of a product remains a challenge. This article reports a comprehensive case study in the use of affective engineering to elicit the subjective requirements for moisturizer packaging. The methodology uses focus groups and surveys to elicit subjective requirements. The results of semantic questionnaires are reduced using principal components analysis to translate the subjective requirements into values for physical properties of the packaging. The resulting requirements for surface textures, shape, and color were validated using questionnaire responses to prototype packaging. The study highlights research issues associated with recombining stimuli that have been tested separately.

Sliding friction and wear up to 600 °C of high speed steels and silicon nitrides for gas turbine bearings

Abstract The sliding friction coefficients and specific wear rates of a range of differently processed (sintered and wrought) high speed steels and (hot isostatically pressed, hot pressed and sintered) silicon nitrides have been measured in both dry and boundary lubricated conditions at temperatures from 20 to 600 °C (dry) or 200 °C (lubricated). In dry conditions, the wear of high speed steels and silicon nitrides on themselves was similar up to 400 °C, rising from 5×10 −9 mm 3 mm −1 N −1 at 20 °C to 5×10 −8 mm 3 mm −1 N −1 . However, in the range 400–600 °C, the wear rates of the silicon nitrides continued to rise, while those of the tungsten high speed steels stayed constant and those of the molybdenum steels decreased. There was no effect of processing route. The boundary lubricated testing was carried out under a synthetic ester with and without a zinc dithiophosphate (ZDDP) additive. For all the materials, the specific wear rates were in the range 10 −11 -10 −10 mm 3 mm −1 N −1 but these rates were near the measurement limit and running-in was still progressing over the 1 to 2 km sliding distance of the tests. A small amount of dry testing has been performed with silicon nitride sliding on high speed steel and on alumina and these results also are reported. A characteristic of all the dry testing was the formation of surface films from which the wear debris was formed. This perhaps explains the lack of any processing route effect.

The influence of TiC, CaF2 and MnS additives on friction and lubrication of sintered high speed steels at elevated temperature

Abstract Friction behaviours of sintered high speed steels containing TiC, CaF 2 and MnS additives and lubrication mechanisms of these additives have been investigated at sliding conditions at 600°C. Results shown that these additives strongly affected friction behaviours of the sintered high speed steels. Ceramic carbide TiC, as a bonding agent and enhancement phase, bonded the solid lubricant CaF 2 and MnS surrounding it and supported these solid lubricant particles so that friction process become stable. Fluoride calcium CaF 2 has a better high temperature lubrication properties than MnS, and that the addition of TiC + CaF 2 in the sintered high speed steels achieved excellent friction performances both a stable and a low friction coefficient value. Analysis results by X-ray indicated that the surface film appearing on worn path consists of some molten metal matters and very fine carbide particles. During sliding, the surface film separated contacts and resulted in a lower friction coefficient. Because of the sintered high speed steels usually to be used to manufacture high temperature components, these results are helpful for their engineering use.

Magnetic fluid grinding of ceramic balls

Abstract Magnetic fluid grinding is a process capable of material removal some 10 to 25 times quicker than is lapping, for the finish manufacturing of ball bearings. It is fast because balls, driven through a viscous fluid, are caused to skid against a drive shaft at speeds which can reach 10 m/s. Material removal is by abrasive wear caused by grits embedded in the drive shaft. In this paper it is shown that there is an optimum fluid viscosity: too small a viscosity does not cause skidding; too large a viscosity, although it causes skidding, prevents effective action of the grits in the shaft. Results are presented for the removal of material from silicon nitride, zirconia and alumina materials, over periods of up to 90 min. Abrasion is by plastic processes for the first two materials and by fracture for the last. Initially, wear coefficients range from 0.06 to 0.6. For all three, removal rates reduce with time probably due to loss of grits and to deterioriation of the fluids.

Kansei Engineering Toolkit for the Packaging Industry

Purpose – The purpose of this paper is to describe the Kansei engineering toolkit that has been developed to provide a set of tools and techniques to support better packaging design.Design/methodology/approach – The toolkit has its foundations in Kansei engineering but the work has extended the scope and increased reliability of results by: including structured linkages to designers; replacing “highest level Kansei” from Kansei type 1 with brand values; introducing a more structured process for the elicitation of type 2 selection of pack physical properties; reducing the complexity of the semantic differential survey used to elicit consumer perceptions; and structuring a process for selection of the Kansei words.Findings – The work has shown that the proposed toolkit is able to support the design of packaging by illustrating the process with industrial case studies.Research limitations/implications – Kansei engineering and the techniques presented in this toolkit are inevitably simplifications of the real...

Simulation analysis of machinability of leaded CrMo and MnB structural steels

Abstract The three-dimensional finite-element machining simulation method has successfully been employed to analyse machinability of both leaded CrMo an leaded MnB steels based on realistic plastic flow properties of the work-pieces and friction characteristics at the tool-chip interface. There is no remarkable difference in the predicted cutting forces, temperature rise, tool wear and surface integrity, but a slight difference can be seen. The MnB steel shows a slightly lower cutting temperature and wear rate on the rake face of a P20 carbide tool since the flow stress is smaller than that of the CrMo one. The use of a button tool is rather effective in the light of the reduction of the rake temperature and crater wear. These tendencies are in good agreement with experiments. Finally, the analysis of production cost has revealed that both steels give almost the same production cost-cutting speed characteristics below 400 m/min. However, since the material cost of the MnB steel is about 20% cheaper than that of the CrMo one, the substitution of the MnB steel for the CrMo one is cost-effective as well.

MACHINING OF CORTICAL BONE: SIMULATIONS OF CHIP FORMATION MECHANICS USING METAL MACHINING MODELS

This paper investigates chip formation in the machining of cortical bone and the application of isotropic elastic-plastic material models with a pressure dependent yield stress and a strain path dependent failure strain law to finite element calculations to predict observed behaviour. It is shown that a range of models can be created that result in segmented chip formations and a range of specific cutting forces similar to those observed experimentally. Results from the simulations provide an explanation for differences in the ratio of thrust to cutting forces observed between previous experimental studies, namely that the cutting tools used may have had different edge sharpness or degree of damage induced by the material removal process. Measurements of edge profiles from one of these studies support that explanation and emphasize the importance of tool toughness in maintaining efficient cutting of bone.