Abstract
Friction and lubrication are important parameters that affect the quality of sheet metal forming; excellent lubrication conditions and less harmful friction can reduce local thinning, delay fracture, and improve surface quality. Aiming at the poor friction conditions and difficult lubrication in the flange area during deep drawing, an active pressurized forced lubrication deep drawing (FLDD) process was proposed in this paper. A hydraulic system was employed to flush high-pressure lubricating oil into the contact gap between the die and sheet in the flange area. The high-pressure hydrostatic oil film in the contact gap can reduce the real contact area and effectively improve the lubrication conditions. The equipment is simple, the cost is low, and the lubricating oil pressure can be measured and controlled. Under the conditions of 20-kN, 35-kN, and 50-kN blank holder force (BHF), FLDD testing of box parts was carried out with 5-MPa and 9-MPa pressure using water-based lubricating oil. The horizontal comparison experiment was conducted with vegetable oil and water-based lubricating oil under the same process conditions. The test results illustrated that the lubrication effect of vegetable oil was the worst, whereas the lubrication effect of water-based mineral lubricant was significantly improved after pressurization. The maximum forming height was increased by 17.97%, the maximum forming force was reduced by 8.9%, the maximum wall thickness thinning rate was decreased by 7%, and the lubrication effect at 9-MPa pressure was superior to that of 5 MPa. The FLDD process has definite application value in improving the production environment, pollution control, and automatic production.
Highlights
Friction and lubrication are unavoidable topics in sheet metal forming
In the deep drawing of axisymmetric parts, the sheet forming ability is usually indicated by the limit ratio of drawing (LRD), whose value is the ratio of blank diameter to formed cylinder diameter
In the sheet forming process, in order to reduce the adverse effect of the friction in the flange area on the material forming and die wear, liquid or solid lubricating medium is usually applied to the sheet surface before forming
Summary
Friction and lubrication are unavoidable topics in sheet metal forming. Good lubrication condition has the advantages of reducing forming force, improving forming limit, reducing wall thickness thinning rate, improving surface quality of formed parts, reducing mold wear, etc. Chen et al [14-15] used laser machining technology (LST) to manufacture triangular texture with edge length of 500 m at the flange area, it was verified that surface texture had a positive effect on reducing the contact friction coefficient and improved the forming quality through deep drawing tests and numerical analysis. Abbadeni et al [19] illustrated the lubrication mechanism of the contact zone at flange area during hydrodynamic drawing process, proposed an analytical model of the non-uniform fluid pressure distribution and the flow characteristics of the overflow lubricant film in the die cavity by means of the Reynolds equation, and the effects of BHF and fluid pressure on formability was investigated through AA5086 aluminum alloy drawing tests. The feasibility and superiority of FLDD process were verified by exploring the forming height, forming force, and wall thickness distribution
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