T.C. Lee

Tailor-welded blanks of different thickness ratios effects on forming limit diagrams ☆

Abstract In this paper, the objective is to study the thickness ratio effects of TWBs on forming limit diagrams (FLDs). Tailor-welded blanks (TWBs) of the same material but with different thickness combinations were welded together to form a single part before the formability tests. Thus, SPCC steel sheets of thickness 0.5, 0.6, 0.8 and 1.0xa0mm were studied and combined to form TWBs of different thickness ratios of 2 (0.5/1.0xa0mm), 1.67 (0.6/1.0xa0mm) and 1.25 (0.8/1.0xa0mm). An Nd:YAG laser was used to weld the tailor-made blanks before the formability tests of the uniaxial tensile test and the Swift test. The experimental findings show that TWBs of different dimensions and radii of cut-off yield different major strain and minor strain values of the FLD. The uniaxial tensile tests show that there are no significant differences between the tensile strengths of TWBs and their relative base metals. In addition, the FLDs of the TWBs indicate that both the level of the forming limit curves and the minimum major strain value decreases as the thickness ratio increases. This implies that the higher is the thickness ratio, the lower is the formability of the TWBs.

Study on the electro-discharge machining of a hot pressed aluminum oxide based ceramic

Abstract In this paper, the machinability of ceramics is studied according to their physical properties. Research results show that EDM is suitable for conductive ceramics. The mechanism of electro-discharge machining ceramics is investigated. The effects on material removal rate, surface roughness, and diameter of discharge points by various parameters are measured and discussed.

A study of ultrasonic-aided wire electrical discharge machining

Abstract An investigation has been made into the combined technology of ultrasonic and wire electrical discharge machining (W-EDM), in which the design of the vibrating device is described. The theory to describe the vibration modes of the wire under the action of ultrasonic has been established. Experimental results show that wire vibration induced by ultrasonic action has a significant effect on the overall performance of the W-EDM process. It was found that there exists an optimum relationship between the vibration amplitude of the wire and the discharge energy, by which the highest cutting rate and the best machined surface quality can be obtained. In addition, ultrasonic vibration reduced the residual tensile stress of the machined surface.

Mechanism of the ultrasonic machining of ceramic composites

Abstract This paper intends to further the understanding of the basic mechanism of the ultrasonic machining of ceramic composites. Models representing the shocking force and the material removal rate are deduced and verified. The principles of ultrasonic machining are also stated. The effects on the material removal rate and the surface roughness of the amplitude of the tool tip, the static load applied and the size of the abrasive are measured. It has been concluded that any increase in the amount of work/energy imparted to the machined ceramics in terms of the amplitude of the tool tip, the static load applied and the grit size of the abrasive, will result in an increase in the material removal rate and a roughening of the machined surface.

Application of the finite-element deformation method in the fine blanking process

Abstract This paper presents the theoretical analysis of the fine blanking process by the application of the rigid-plastic finite-element method. According to the characteristics of the fine blanking process, a mathematical model suitable for the theoretical analysis has been established. At the same time, a computer program with remeshing facility has been developed. From the results of the modeling, it was found that the values of σ ¯ and e ¯ within or near to the narrow clearance zone were much more greater than those at other areas. Deformation was localized and violent in the narrow clearance area, which coincided with the practical results and reflected the particular characteristics of fine blanking. Furthermore, it was also found that the values of σ ¯ and e ¯ around the edge of the punch and the d changed very severely, and that the value of e ¯ was greatest at these places: this is because the material here had been deformed severely during operation. It had also been observed that the value of e ¯ increased continuously when the fine blanking operation proceeded further, i.e., the deeper was the penetration of the punch, the greater was the degree of deformation, which further reflected the actual performance in fine blanking. The results obtained from the analysis have demonstrated that the rigid-plastic finite-element method should be a useful and practical tool to be applied to the fine blanking process.

Formability and Weld Zone Analysis of Tailor-Welded Blanks for Various Thickness Ratios

Cold-rolled steel sheets of thicknesses ranging from 0.5 to 1.0 mm were used to produce tailor-welded blanks (TWBs) with various thickness ratios. In this study, the formability of the TWBs, as well as the mechanical characteristics of the weld zones, were analyzed experimentally under the effects of various thickness ratios of TWBs. The formability of the TWBs was evaluated in terms of three measures-failure mode, forming limit diagram, and minimum major strain, whereas the mechanical characteristics of the weld zones were investigated by tensile testing, metallographic study, and microhardness measurement. In particular, circular TWBs with different radii and cutoff widths were designed where all the welds were located in the center of the blanks and perpendicular to the principal strain direction. Nd:YAG laser butt-welding was used to weld the TWB specimens of different thickness ratios. The experimental findings in this study showed that the higher the thickness ratio of the TWBs, the lower the forming limit curve level, and the lower formability. The minimum major strain was clearly inversely proportional to the thickness ratio of the TWBs. On the other hand, the results of uniaxial tensile tests clearly illustrated that there was no significant difference between the tensile strengths of the TWBs and those of the base metals. The metallographic study demonstrated a difference of grain size in the materials at base metal, heat-affected zones, and fusion zone. The microhardness measurement indicated that the hardness in the fusion zone increased by about 60% of the base metal.

Finite element analysis of polymer composites filled by interphase coated particles

Abstract The effects of different interphase properties on Young’s modulus, maximum stress concentration factor and stress distribution in glass bead-filled polycarbonate (GB/PC) and interphase-coated glass bead-filled polycarbonate (GB/INT/PC) have been investigated using the finite element method. A three-dimensional unit cell model has been built for modeling both two-phase and three-phase composites. The results from the predictive model allow the deduction of the optimum interphase properties for reduction of the stress concentration and minimization of the drop in elastic modulus of the resulting composites.

An investigation on the formation and propagation of shear band in fine-blanking process

Abstract An investigation has been made on the formation and propagation of shear band in fine-blanking process. Examinations by optical microscopy and SEM reveal that the highly elongated narrow subgrains extended in the shear direction within the band, while in the other regions, fine equiaxed cell were observed. Both the presence of white-etching trace and the distribution of surface microhardness in the shear band reveal that fine-blanking process involves large deformation and high temperature. Although strain localization is severe in the shear band, especially in the area adjacent to the edges of the punch and die, no cracking has been observed. It is indicated that high hydrostatic pressure, built up by specially designed fine-blanking fixture, plays a significant role to suppress the generation of fracture zones in the sheared surface. On the basis of present findings, the mechanisms of the formation and propagation of shear band in fine-blanking are discussed.

Spark erosion with ultrasonic frequency

Abstract In this paper, spark erosion with ultrasonic frequency is proposed, using a D.C. power supply instead of the usual pulse power supply, the pulse discharge being produced by the relative motion between the tool and the workpiece. The tool vibrates sinusoidally with ultrasonic frequency and enables the melted materials to be ejected strongly, and the eroded materials to be flushed away easily from the gap. This machining method can easily perform cutting, drilling, engraving, and the combined technology of UM and EDM.

Investigation of the surface integrity of laser-cut ceramic

Abstract This paper intends to address the effects of laser machining on ceramic surfaces by evaluating the surface integrity of machined ceramics in terms of surface morphology, and flexural strength and its variances, under various machining conditions, a Weibull modulus ‘m’ being introduced to measure the degreee of variation in strength. Experimental results show that the damage to the ceramic, and the flexural strength and its Weibull modulus, are determined by the parameters of the laser beam. In general, the thermally-affected layer and cracks in this layer of laser-cut ceramic surfaces are critical, and need to be modified properly.