| The needles are an important component in the process of knitting machine with fast speed, long operation duration, high load capacity. As vulnerable parts, there’s a great demand in the market. Contacted with the textile line, needles directly determine the quality of knitted products. Needles of poor quality in the weaving process often lead to textile line breaking or galling, so high-grade needles are in urgent need. The first step in the production of needles is die blanking operation, which plays great influence on the quality of the needle. Corner height of shearing surface, the burr size and vertical height of section directly impact the quality of knitting needles. Domestic knitting productions are mainly small and medium enterprises. Due to the cost of research and development and technology, most enterprises still adopt the ordinary punching production to process needles. But ordinary blanking technology can not meet the requirements of high-grade needles. Domestic quality of needles is generally low, showing a large gap with foreign industries. Therefore, studying on the technology of the fine blanking of needles, analyzing of manufacturability of the needles outline, summarizing the influence law of process parameters has practical value.Taking a flat knitting needle made by SK5 material as the object of study, this paper uses the HD scanner and MATLAB image processing technology to map the size of needle. This method ensures the dimensional accuracy of the needle billet modeling. This paper adopts the PRESSCAD software to design of the stock layout design proposal of punching needle and gain the maximum utilization of materials. Based on the empirical formula for the fine blanking calculation, the theoretical value of process parameter for the needle fine blanking were initially identified. The fine blanking process was defined by analyzing of processing property of the needle blanking. In addition, the fine blanking die used by ordinary punching machines were designed.All of this shows the instruction significance to the actual production.The main factors affecting the quality of the needle fine blanking in the perspective of mechanics of materials were clarified by analyzing the stress of deformation zone in fine blanking process. Increasing the hydrostatic pressure in the deformation zone can enhance the plasticity of sheet metal and improve the quality of the fine blanking of needles. Combined with the theory of fine blanking deformation and stress analysis, the needle fine blanking model established by the SolidWorks software was imported into the DEFROM software for fine blanking simulation. Equivalent stress, metal flow, die load, stress and abrasion in fine blanking process were analyzed.The needle belongs to the sheet metal parts with complex contour. It is mainly composed of the straight line, arc and corner. The plasticity of each contour is different. The average stress quality of fine blanking forming were gained by analyzing the average variation of stresses and shearing surface quality in simulation results. These outlines include the concave corner, concave arc, straight line, convex arc, convex corner arc. According to the theoretical value of needle fine blanking, setting different process parameters were set. Comparing the interstice between matrix and punch, radius, the influence law of the needle fine blanking quality of matrix radius, blank holding force, back pressure, the best range of the interstice is 0.5%～1% of thickness of plate. The amplification of corner height increases when the radius is larger than 15% of sheet. When blank holding force exceeds 150KN, the hydrostatic pressure in fine blanking deformation zone decreases. When the back pressure is 150KN, stress of sheet is evenly distributed, and the quality of needle is high. The orthogonal test was used to optimize parameter of the needle, and the optimal fine blanking technology was achieved. |
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