Papers by Keyword: Blanking

Abstract: An oxygen-free copper has been utilized as a terminal material in the power transistors and their related electric system in the electric mobiles because of its high electric conductivity and excellent engineering durability in high current usage. The high ductility and its low mechanical strength cause large shear droop and increase of fractured surface. In this report, the shearing of oxygen-free copper was carried out using a punch with a mirror-finished surface roughness. Using the punch tip deflection as a parameter, a comparison of shearing characteristics was made between a punch with a nitrided tool surface and an untreated punch. The influence on the formation of the sheared surface was considered from an investigation of the shearing characteristics. When shearing oxygen-free copper with a thickness of 500 µm, it was shown that by providing a punch tip deflection of approximately one-tenth of the thickness in the punch stroke direction, the shear droop could be kept to 10 % or less of the plate thickness and a burnished surface ratio was approximately kept 90 %.

Abstract: To reduce emissions in the mobility sector, demand for high-strength and higher-strength steels in the automotive sector is constantly increasing, and with it the demands on the tools of the sheet metal processing industry. One important phenomenon is rapid wear which reduces the service life of blanking tools. Compensating with an increased use of lubricants is not advisable from an ecological point of view. It could be shown in literature that through texturing the lateral surfaces of blanking tools their wear behavior can be improved. In this work, machine hammer peening (MHP) was used to texture the surfaces. Compared to other deterministic texturing methods such as laser texturing, MHP has several beneficial effects. No additional surface finish is required after texturing and the surface structure is not weakened by the thermal influence. MHP machining simultaneously induces residual compressive stresses close to the surface, work-hardens the edge zone and smoothes roughness peaks. Combined with deterministic texturing in the same process step, the tribological behavior of the tool surface can be significantly improved. Based on the tribological investigations of the authors in the strip drawing test on different structuring strategies, the findings from the model test are to be transferred to the real test in this work. For this purpose, rotationally symmetrical blanking punches were textured using a specially developed texturing center. The machine hammer peening center allows surface texturing with positioning accuracies of less than 2% by controlling a rotary and feed axis in combination with frequency control of the machine hammer peening set up. A hammer head with micro-milled micro-tip was used as the texturing tool for the MHP. Different degrees of coverage with the same aspect ratio were applied to the surface. These punches were then tested on various materials on an industrial high-speed stamping press. To evaluate the effectiveness, the force curves for different blanking frequencies were analyzed and the evolution of the textured topography was continuously evaluated. The experiments reveal that the withdraw force could be reduced by 38% due to the micro texturing with a coverage of 18%. Other coverages led to an increase. By texturing the lateral surfaces of blanking punches using MHP the service life could also be significantly improved.

Abstract: In this study, the effect of die edge radius on crack initiation was discussed in finish blanking. Experiments were carried out using die with rounded cutting edge. As a result, it was confirmed that crack initiation near the punch edge occurred earlier than that near the die edge. It was also confirmed that the burnished surface increased with an increase in the die edge radius. Finite element method was carried out from the initial stage of shearing and until the punch penetration depth was achieved just before the occurrence of the cracks to investigate the distribution of the mean stress. As a result, it was confirmed that the punch stroke, where the mean stress began to increase rapidly to a positive value, increased with an increase in the die edge radius, and the punch stroke at which the mean stress increased rapidly also increased.

Abstract: Frictional forces in sheet metal blanking are central in different aspects, e.g. in wear prediction, validation of simulation models or in so called slug pulling. The latter is a phenomenon where the slug is pulled out of the die by the punch after the sheet metal is separated. This leads to process disturbances reaching from a blocked belt feeder up to severe tool damage caused by the simultaneous cutting of the slug and the sheet metal strip. A sufficiently high frictional force between the slug and the die prevents this effect. Despite its importance, this force and its causes have not yet been investigated in detail. A method was developed in this paper to measure the frictional force between slug and die. A shear cutting tool with an integrated piezoelectric load cell and an inductive position sensor was used on a stamping press to cut sheet metal made of CuSn6 (R350, thickness 1 mm). The die clearance, the punch edge radii and the lubrication conditions were varied. A larger die clearance resulted in a lower frictional force while a larger punch edge radius increased it significantly. Lubrication reduced the frictional force, especially for small die clearances. Finally, the cause of the frictional force was investigated by identifying the relevant springback modes of the slugs. This was carried out by correlating the slugs' deflection, oversize, and clean cut height with the frictional force. Especially the slug oversize, i.e. the difference between the slug's diameter and the die's inner diameter, revealed a strong correlation. Calculations showed that the deformation in radial direction is the main cause of the frictional force between slug and die. It suggests that the slug oversize is a good measure for the magnitude of the frictional force.

Abstract: The blanking operation have several die design parameters which affect the quality of the blank and its productivity. The main input parameters are sheet thickness and the punch and die clearance and the dependent output parameters are tool life and the burr height. The selected values should be in optimal value. The optimum value is achieved by using the genetic algorithm. The genetic algorithm is an optimization process to find the better results as an output. Then the development of mathematical modeling by using the equations derived from the multiple regression analysis is performed. It is achieved by converting the linear equations into the matrix form and then solving it using mathematical relations. This output is compared with the genetic algorithm results, to get the better results.

Abstract: A fine blanking process produces smoother surfaces finish than a blanking process because of a higher tri-axial compressive stress caused by v-ring and smaller punch-die clearance. This work aims to study the effect of the added v-ring design parameters on the blanking process of the SPCC sheet. Three dimension and two dimension finite element models of blanking process were used for studying the effect of v-ring design parameters on the cutting force and the quality of the surface edge respectively. The FE model of the blanking process of an isotropic elastic-plastic with ductile fracture criteria material was validated with the SPCC blanking experimental tests and the results agreed well. The influence of size and shape of v-ring on cutting forces and surfaces edge were examined using Taguchi method. Four v-ring design parameters, namely the height, the radius, the angle and the distance between die and v-ring were investigated. The Taguchi main effect analysis and ANOVA results show that the distance between die edge and V-ring is the most important factor for cutting forces. The radius of v-ring edge is the most significant factor for the length of smooth-surface and the angle of V-ring is the most important factor for burr heights.

Abstract: Currently, the shaped parts combined with straight, concave, and convex portions are increasingly fabricated. To produce the straight portion, the shearing theory is usually applied. As well as, to produce the concave and convex portions, the punching and blanking theories are usually applied. However, with the same die-cutting process parameters, the comparison of cut surface features of straight, concave, and convex portions has not been investigated yet. Therefore, in the present research, the comparison of the cut surface features in various die-cutting processes, including shearing, blanking, and punching processes are investigated. The finite element method (FEM) was used as a tool to investigate these cut surface features. The cut surface features were investigated and clearly identified via the changes of the stress distribution analyses. The results elucidated that with the same die-cutting process parameters, the different cut surface features were obtained. Specifically, the crack formations were easily generated in the case of blanking process, following by the shearing and punching processes, respectively. Therefore, the smooth cut surface was smallest in the case of blanking process, following by the shearing and punching processes, respectively. The laboratory experiments were carried out to verify the accuracy of the FEM simulation results. Based on the cut surface features, the FEM simulation results showed good agreement with the experimental results in terms of the cut surface features. Therefore, to design the die-cutting process parameters to meet the product requirements of complicated shapes, the understanding on these working process parameters being upon the shaped parts is necessarily.

Abstract: Due to a high specific strength, carbon fibre reinforced plastics (CFRP) enable material driven light-weighting of structural components. A constant increase of CFRP usage is predicted to continue in the future. At high production numbers blanking can be cost efficiently used for piercing or trimming operations of cured CFRP components. Compared with metals, sheared edges of blanked CFRP demonstrate fundamentally different morphology. Therefore, conventional characterization parameters cannot be used for an unambiguous characterization of the sheared edge quality. In the scope of this work, surface profile parameters were adopted for this purpose. The applicability of the quality parameters was successfully shown on the example of experimentally produced sheared edges. Furthermore, it was demonstrated that the proposed sheared edge quality parameters enable the quality assessment under process inherent variability of the sheared edge morphology in CFRP.

Abstract: During the forming of high-strength steels, edge cracks occur unexpectedly on sheared edges e.g. during collar forming. A non-contact measurement method based on the well-known tensile test was developed. It allows the investigation of the formation of edge cracks under tensile loads and determining general criteria to predict the formation of edge cracks during a specific forming process. The criteria are validated experimentally by means of the collar-forming test. In conjunction with the proposed line-fit-method these criteria can be implemented easily in FEM software in the near future for the prediction of edge cracks.

Abstract: Fibre reinforced plastics (FRP) are being increasingly used for advanced applications where an appropriate mechanical performance should be achieved at minimum weight. A substantial increase of the FRP usage is expected across various industries e.g. in automotive sector in the nearest future. This leads to the mass manufacturing of FRP components. Reduction of manufacturing costs of FRP components is regarded as the main enabler for the usage of this material in mass production. Although FRP components are manufactured near-net-shape, they often have to be pierced or trimmed in one of the last manufacturing steps. With rising production numbers blanking is a potentially more cost efficient technology for trimming and piercing of FRP components compared to the conventionally performed abrasive water jet cutting or machining. The mechanisms of FRP separation in blanking have not yet been researched. In particular, the influence of the fibre orientation relative to the cutting line on the cutting force is not known. In the scope of this work an experimental study of blanking of a unidirectional carbon fibre reinforced plastic with a thermoset resin at different fibre orientations to the cutting line was performed. It was shown that the cutting force decreases from the perpendicular to the parallel fibre orientation to the cutting line. A possible mechanical explanation of this dependency was formulated.