Computer-Aided Analysis And Process Improvement Of Filter Shell Drawing Process

Filter shell is made of steel plate in length of 0.8mm and is shaped after several drawings. For drawing and deformation extent is large that internal diameter of shell is φ107mm, total height of shell 320mm, draw ratio up to 3, it is huge challenge for drawing and shaping of filter shell. One-step shaping may cause materials near flange pile up and wrinkle since draw ratio is easy to crack and inside diameters of mould among passes are different though multi-pass drawing technology improves cracking phenomenon to some extent. As a result, wall thickness of shell is different in different positions of shell and it is likely to produce residual stress and shell is easy to generate local fatigue and finally crack under the high strength, high frequency and long-time rotary impact stress. For this purpose, main research work of the paper is as follows:(1) As the shell parts of current long-life engine oil filter cannot meet the requirements of pulse fatigue test with high strength and high pulse frequency, cracked areas of defective shell parts in pulse fatigue test were sampled in this paper for chemical component analysis and electron microscope analysis. And computer-aided engineering (CAE) finite element method was applied to conduct numerical simulation of the original forming process of the parts. It is shown in the analysis result that chemical component at the fracture meets the standard requirement and appearance of fracture is possessed of significant fatigue crack characteristics, with sea-beach pattern, so the original drawing technology is deficient in severe thinning and wrinkling. Original drawing technology is deficient in severe thinning and wrinkling. Therefore, unreasonable drawing technology is the main cause for shell cannot meet the requirement of pulse fatigue test.(2) Given thin filter wall and big draw ratio, process route, i.e. shell wafer blankingâ†'first drawingâ†'second drawingâ†'third drawingâ†'forth drawing (reverse drawing)â†'shaping and trimming, was proposed to apply and drawing technology of different procedures was calculated again and computer finite element analysis was conducted for initial design plan. According to the simulation result, several parameters like drawing coefficient, convex-concave die clearance, punch-die fillet and blank holder force were optimized purposefully. Specific parameters after optimization include circular blank diameter 387mm, the first drawing workpiece diameter 220mm, the second drawing diameter 170mm, the third drawing diameter 135mm, the fourth drawing diameter 109.8mm; roller radius of the matrix in the four drawing procedures are respectively R9, R7, R4 and R4; blank holder force in the four drawing procedures are respectively 197KN, 31KN,18KN and 11KN; optimized die is complete without crack in all passes of drawing and workpiece is good in shape and the thinnest parts can be found in fillet and straight wall of tube workpiece. Material decreases to 0.652mm and the maximum thinning rate is only 18.5%; slight wrinkle can only be found at flange fillet of drawing part, and the thickness of material in the thickest part is 0.893mm, thickening rate up to 11.6%.(3) In order to fully testify the rationality of optimized die structure and technological parameter, deep drawing die of all passes were recreated and shell pieces were produced and pulse fatigue test was performed in workpieces made by optimized drawing technology. It was shown in the result that workpiece made by optimized drawing technology successfully passed pulse fatigue test of filter, so die structure and technological parameter optimized by 3D sheet forming software DYNAFORM were logical and structure design, material selection, surface treatment method and die application maintenance for key parts and components of deep drawing die in all passes were all appropriate.