ABSTRACTDuring the wire electrical discharge machining (WEDM) process, the vibrations of the wire generated by the gap force is the main cause of imprecision. To achieve more precise results with better accuracy, understanding of the vibration management of the wire is essential. In this article, the wire’s vibration behavior is introduced briefly, followed by an exploration of an equation, derived from Hamilton’s principle, which expresses the vibration of a wire moving axially. This equation is presented under some simplified assumptions. In addition, the relationship between the maximum amplitude of the vibration and the main relative variables is presented. The solution demonstrates that a thicker workpiece results in a larger amplitude of vibration, yet the axial speed of the wire has no impact on the maximum amplitude.

High-quality part surfaces with high surface finish and form accuracy are increasingly in demand in the mold/die and optics industries. The computer-controlled polishing (CCP) is commonly used as the final procedure to improve the surface quality. This paper presents a theoretical and experimental study on the polished profile of CCP with sub-aperture pad. A material removal model is proposed based on the evaluation of the amount of material removed from the surface along a direction orthogonal to the tool path. The model assumes that the material removal rate follows the Peterson equation. The distribution of the sliding velocity at the contact region is presented. On the basis above, the approaches to calculate the polished profiles are developed for the sub-aperture pad polishing along a straight path and a curved path. The model is validated by a series of designed polishing experiments, which reveals that polishing normal force, angular spindle velocity, feed rate and polishing path all have effects on the polished profile. The result of experiments demonstrates the capability of the model-based simulation in predicting the polished profile.

A grindability study of chopped strand mat glass fiber reinforced polymer laminates (CSM GFRP) has been carried out to evaluate the effects of abrasive types on grinding force ratio and area roughness at varying grinding parameters such as speed, feed and depth of cut. Performances of alumina (Al2O3) and cubic boron nitride (CBN) wheels were compared. Both wheels delivered the maximum grinding force ratios at low speed, high feed and low depth of cut. Alumina wheel produced smoother surface when grinding at low speed, low feed and high depth of cut. CBN wheel, on the other hand, gave smoother surface at high feed and low depth of cut conditions, regardless of speed. With CBN wheel, it is likely that a single grinding condition exists that maximizes grinding force ratio and minimizes area roughness. The findings indicate that CBN wheel exhibited higher grinding force ratio than alumina grinding wheel in general. CBN grinding wheel also outperformed alumina grinding wheel by producing smoother ground surface in most cases.

Thermography (thermal imaging) is a well-established experimental method for studying cutting tool temperature distributions. In one form, cutting edge temperatures within the chip / tool contact area are deduced from thermal images of tool faces normal to the cutting edge but offset from the contact region. In general practice, the offset is made as small as possible (<< 1 mm) and it is assumed that the observed temperature is the same as that within the contact. In this short communication an approximate analytical model is developed for the influence of the offset on the observed temperature. The predictions from the model are compared with previously unpublished existing results on the machining of Ti alloys (Ti6Al4V and Ti5Al4V) and on steel (AISI 4140). It is shown that ignoring the offset may introduce underestimates of cutting edge temperature of ≈ 30% or more. This is large compared to the usually considered uncertainties of ± 5% from camera and tool emissivity calibration. There is a need for a dedicated study of this effect.

This article correlates laboratory-based understanding in machining of titanium alloys with the industry based outputs and finds possible solutions to improve machining efficiency of titanium alloy Ti-6Al-4V. The machining outputs are explained based on different aspects of chip formation mechanism and practical issues faced by industries during titanium machining. This study also analyzed and linked the methods that effectively improve the machinability of titanium alloys. It is found that the deformation mechanism during machining of titanium alloys is complex and causes basic challenges, such as sawtooth chips, high temperature, high stress on cutting tool, high tool wear and undercut parts. These challenges are correlated and affected by each other. Sawtooth chips cause variation in cutting forces which results in high cyclic stress on cutting tools. On the other hand, low thermal conductivity of titanium alloy causes high temperature. These cause a favorable environment for high tool wear. Thus, improvements in machining titanium alloy depend mainly on overcoming the complexities associated with the inherent properties of this alloy. Vibration analysis kit, high pressure coolant, cryogenic cooling, thermally enhanced machining, hybrid machining and, use of high conductive cutting tool and tool holders improve the machinability of titanium alloy.

□ Determination of the partition ratio is fundamental to a thermo-mechanical approach to the grinding process. To establish the energy balance, accurate measurements and numerical modelling must be combined. In this work, such a method is applied to the grinding of a HVOF WC-Cr-Co hard coating. A double pole grindable thermocouple was developed to measure the temperature in the arc of cut, and its effective length. The heat flux absorbed by the workpiece is found by fitting the numerical solution to the temperature profile measured during the cooling phase, behind the contact. Identical results for the heat flux may be obtained by fitting the results to the analytical solution from moving heat source theory, but the maximum interface temperature is underestimated. A finite element solution, using MSC Marc software allows a closer approach to the maximum temperature measured at the interface during grinding, provided that the thickness of the coating is correctly modelled.

A grinding-hardening process uses the grinding heat to initiate the phase transformation in a workpiece made of quenchable steel and hence to generate its surface hardening. This paper investigates this phase transformation process and the mechanical properties of such hardened layers with the aid of experiments and the finite element analysis. It was found that the phase transformation followed a diffusionless martensitic kinetics in which the external stresses caused by the mechanical loading of the grinding wheel on the workpiece played an important role. The top hardened layer appeared to be a plastically deformed zone of uniform thickness. A metallurgical examination revealed that this layer contained refined martensitic laths, as compared with the ordinary martensite obtained by a conventional quenching method. The microstructural evolution has led to a hardness increase by 1.4 times the ordinary martensite. In addition, the grinding-hardening can promote compressive residual stresses in the ground surface, about 17% higher than the yield strength of the parent ferrite-pearlite material.

The aim of this research was to experimentally investigate and compare the wear performance of tungsten carbide drills used in conventional and modulation assisted drilling (MAD). During MAD, modulations of low frequency and high amplitude were superimposed on tool motion in the feed direction. Direct measurement of flank wear land was used as tool condition monitoring method. Since the width of flank wear was not regular along the cutting edge, the maximum flank wear, VBmax , was measured using a toolmaker's microscope. The drills were inspected under the scanning electron microscope to establish the possible wear mechanism. The results indicate that the drills used in MAD were better in resisting tool wear than those used in conventional drilling. However, at higher feed during MAD, a catastrophic failure of drill occurred due to fracture of cutting edge.

A numerical model was developed to predict the roughness profile along a line in the feed direction, in contour milling operations with cylindrical milling tools. From the model, average roughness Ra and maximum peak-to-valley roughness Rt were calculated for families of tools defined by 100,000 random combinations of radius values. Radii were selected by means of the Monte Carlo Method. Each family is defined by an average radius and a standard deviation of radius, assuming normal behavior. Histograms, roughness variation intervals, medians and modes, were calculated at different feeds. The model was validated through experimental tests. Effect of standard deviation of radius, number of teeth and tool diameter were studied. Although radius values were randomly selected according to a normal law, roughness values did not follow a normal distribution. At low standard deviations, intervals of roughness values, medians and modes vary only slightly with feed, except at very low feeds where intervals are narrow. On the contrary, at higher standard deviations, median, mode and width of roughness intervals rise as feed increases. Use of a lower number of teeth and higher tool diameter leads to narrower intervals and asymmetrical roughness frequency distributions even at high feeds, with modes near upper reference values.