Joining Sheets With Differences In Thickness And Material By Flat Hole-clinching Process

Because of unique advantages, plastic forming technologies attract a lot of attention in recent years. The existing joining by forming technologies all have limitations in the connection of metallic sheets with large differences in thickness and mechanical properties. In connection with the joining of metallic sheets with large differences in thickness and mechanical properties, this paper developed a new clinching method called flat hole-clinching(FHC) based on conventional clinching technology. The method utilizes a simple punch to force the material of one plate(the upper sheet) to flow into the cavity of a specially prepared hole on another plate(the lower sheet), forming a �nested� structure. FHC is suitable for assembling two layers of sheets with dissimilar(as well as similar) materials and thicknesses without protrusion at the joints. Two Al 6063 plates with thicknesses of 0.8mm and Al 6063 and AZ31 plates with thicknesses of 0.8 and 1.0 mm, respectively, were employed in the numerical simulation, experiments and RSA(Response Surface Analysis) to analysis flat hole-clinching with inverted conical hole, examining the impact of tool and hole geometries, material properties, and relative thicknesses on the strength of joints. Main conclusions are as follows:(1) The results confirmed that two layers of metallic sheets with dissimilar(as well as similar) materials and thicknesses can be connected reliably by FHC. It can replace the conventional clinching, with even higher joining strengths in comparison to conventional clinching. In the forming stage, FHC has a shorter punch stroke than the conventional clinching. In the pull out test FHC has a longer separation distance than the conventional clinching.(2) In FHC forming process, the lower sheet is almost not deformed. But with the increasing in yield strength of upper sheet, the deformation of material under the inverted conical hole would increase. Then the collapsed occurred and the pull out strength was decreased obviously. The pull out strength was elevated after lowering. When the thickness of lower sheet is 1.5 times or more than that of upper sheet, it is difficult to forming an �nested� structure with flat anvil mold, so it is possible to add a circular truncated cone on the anvil surface. With the decreasing in the relative thickness of the lower sheet, the pull out is gradually decreased.(3) According to the result of RSA analysis, the most influential parameter on pull out strength is the conicity ? of hole, followed by punch diameter dp, punch conicity ?, and punch corner radius R. In the joining of Al 6063/AZ31 sheets with thicknesses of 0.8 and 1.0 mm, respectively, and 6.6 Hd ?mm, the optimal parameter combination is ? ?25?, 5.6 pd ?mm, ? ?3?, and R ?0.5 mm. The strengths predicted by the regression model, numerical simulation and from the experiment using this parameter combination are 584 N, 580 N and 570 N, respectively.(4) According to the structural characteristics of FHC, and after forming the neck thickness 1?0.5Nt t, neck fracture failure mode was more prone, and when the neck thickness 10.5Nt ?t, the button separation failure mode was more prone, the flowchart of parameters design of FHC process was set up.