Finite Element Investigation of Cutting Performance of Cr/W-DLC/DLC Composite Coated Cutting Tool

Coupled with a thermo-mechanical metal cutting process, rapid tool wear, higher surface roughness and mass heat are caused by the rapid plastic deformation of the workpiece and by the friction along the tool-chip interface. This phenomenon is more predominant in the machining of difficult-to-cut materials. DLC film has been applied as coating material in the machining of difficult-to-cut materials, and shows a good cutting performance. In this study, Cr/W-DLC/DLC coated tools were compared with other three coated tools (i.e., TiC-, TiAlN-, Al 2 O 3 -) to investigate the cutting performance in the machining of Al-Si alloy (AC9B). In addition, the influence of Cr/W-DLC/DLC coated tools on the cutting performance under different cutting speeds was studied. Cutting force, cutting temperature, heat transfer coefficient of the rake face of the tool, cutting deformation rate, plastic deformation of machined surface, the interface temperature and stress were investigated numerically based on Finite Element Method (FEM). Actual cutting experiments were carried out to the verification of the FEM models by means of the cutting force and cutting temperature measurement. The investigation results showed that Cr/W-DLC/DLC coated tools has the lowest cutting force and cutting temperature, good cutting deformation characteristics and lower coating-substrate interface temperature and stress, however appears the maximum value of heat partition coefficient into the cutting tool. With the increasing of cutting speeds, cutting force and cutting temperature showed an increase trend, while the plastic deformation depth of machined surface and heat partition into cutting tool all showed a decrease trend. This investigation can provide the theory basis or technical guidance for the cutting practice of Cr/W-DLC/DLC coated tools.

Thermal modelling of cutting tool temperatures and heat partition in orthogonal machining of high-strength alloy steel

Cutting temperatures and heat partition into the cutting tool are critical factors that significantly affect tool life and part accuracy during metal removal operations, especially in dry machining. Among many thermal modelling studies, uniform heat partition ratio, and/or uniform heat intensity along the tool-chip interface are frequently assumed. This assumption is not valid in actual machining and can lead to erroneous estimated results in the presence of sticking and sliding friction zones. Therefore, it is necessary to accurately predict the cutting tool temperature and heat partition during machining. This paper presents an analytical thermal modelling approach which considers the combined effect of the primary and the secondary heat sources and determines the temperature rise and non-uniform heat partition ratio along the tool-chip interface. Cutting tests were conducted on AISI/SAE 4140 high-strength alloy steel using carbide cutting tools over a wide range of cutting speeds. Cutting temperatures were measured experimentally using an infrared thermal imaging camera. Experimentally established sticking and sliding friction regions were used to evaluate non-uniform frictional heat intensity along the tool-chip interface. The temperature matching condition along the tool-chip interface leads to the solution of distributed non-uniform heat partition ratio by solving a set of linear equations through programming in MATLAB®. Experimental results show to be consistent well with those obtained from the thermal model, yielding a relative difference of predicted average tool-chip interface temperature from −0.8% to 6.3%. It is found that average heat partition into the cutting tool ( RT) varies from 35% down to 15% for the entire range of cutting speeds. These results suggest that, to address the thermal problem in metal cutting, the research and development of tooling should also focus on reducing friction on the tool rake face in addition to the contribution of the combined effect of primary and secondary heat sources on temperature rise at the tool-chip interface.

Temperature and Heat Partition Testing in the Cutting Zone for Turning AISI 321 Steel

This article shows selected results of experimental tests and the results of analytical and numerical modelling of the thermal characteristics of the cutting process. The tests were conducted for the case of the dry turning of austenitic steel AISI 321 with cutting tools with a flat rake face. The research aimed to determine the actual division of thermal fluxes in the zone of contact between the chip and the rake face. As a result of such work, a formula for a new heat partition coefficient and a formula for calculating the average contact temperature were developed. The results showed that the formulas developed can be a useful tool to estimate heat distribution in the cutting zone quickly.

Influence of AISI D2 Workpiece Roughness on Heat Partition and Plasma Channel Radius in the WEDM Process

As an important advanced machining process, in Wire Electrical Discharge Machining (WEDM) certain fundamental issues remain need to be studied in-depth, such as the effect of part surface roughness on heat transfer mechanisms. In the WEDM process, roughing cut wire goes into the workpiece to do the first shaping and in trim cut the wire sweeps on the outer surface to improve the surface roughness. In both of these two cases, the generation of sparks depends on the passing surface roughness. Therefore, with AISI D2 material and brass wire, this paper presents a study of the influence of part surface roughness on heat partition and the radius of the plasma channel in the WEDM process. Through extensive single discharge experiments, it is shown that the removal capacity per discharge can increase if the discharge occurs on a smoother surface. A Finite Element thermal model was then used for inverse fitting of the values of heat partition and radius of the plasma channel. These parameters completely define the characteristics of the heat conduction problem. The results indicate a strong correlation between an increase in heat partition ratio and a decrease in part surface roughness. The values of plasma channel radius show an increase in this value when discharging on rougher surfaces. It means that with the increasing of plasma channel radius, the heat source goes into the workpiece more dispersed. In the case of rougher surface, although the there is more area that affected by the heat source, finally the temperature of most area cannot reach to the melting point and it causes the smaller crater radius and volume, while the metal removal rate decreases. These results contribute towards a more complete understanding of the influence of surface roughness to the spark occurring.

Partition of Primary Shear Plane Heat in Orthogonal Metal Cutting

When assessing the effect of metal cutting processes on the resulting surface layer, the heat generated in the chip formation zone that is transferred into the workpiece is of major concern. Models have been developed to estimate temperature distributions in machining processes. However, most of them need information on the heat partition as input for the calculations. Based on analytical and numerical models, it is possible to determine the fraction of shear plane heat transferred into the workpiece for orthogonal cutting conditions. In the present work, these models were utilized to gain information on the significant influencing factors on heat partition, based on orthogonal cutting experiments, experimental results from the literature, and a purely model-based approach. It could be shown that the heat partition does not solely depend on the cutting velocity, the uncut chip thickness, and the thermal diffusivity—combined in the dimensionless thermal number—but the shear angle also has to be taken into account, as already proposed by some researchers. Furthermore, developed numerical models show that a more realistic representation of the process kinematics, e.g., regarding chip flow and temperature-dependent material properties, do not have a relevant impact on the heat partition. Nevertheless, the models still assume an idealized orthogonal cutting process and comparison to experimental-based findings on heat partition indicates a significant influence of the cutting edge radius and the friction on the flank face of the tool.