In the design of a press tool, it is necessary to assign tolerances to all the functional dimensions. The combinations of these tolerances must be sufficiently tight to guarantee that the tool will perform as intended. The performance of the tool can be judged by the dimensional quality of the component blanked out of it. A three stage progressive tool is considered for the analysis. The cumulative effect of the functional dimension tolerances on the assembly dimension tolerance is found analytically using Sure fit law and Normal law and numerically using Monte Carlo simulation technique. The goal of this paper is to design and fabricate a three stage progressive tool for producing a sheet metal component and to analyze the tolerances of progressive tool and to find their effect on the accuracy of sheet metal produced out of it. The true positional variation of the pierced holes in the blanked component is also found out experimentally by fabricating the press tool and producing a component and measuring both in Co-ordinate Measuring Machine (CMM). The results obtained using different methods are compared and discussed.
Sheet metal working by material shearing mechanisms is one of the most widely used processes in the industry. The quality and accuracy of blanked parts can be characterized according to possible defects, including dimensional, positional, form and surface errors. In a component involving piercing, blanking and bending operations, the positional error of the pierced holes with reference to the blanked contour is decided by the assembly tolerances of the press tool assembly. The assembly tolerances result from the cumulative effect of functional dimension tolerances which form the dimensional loop chain. To analyze the effect of assembly tolerance on the blanked component’s dimensional accuracy, a three stage progressive tool for producing the component is considered. A press tool is designed and fabricated for
producing a sheet metal component and a tolerance analysis is also conducted on it. The fabricated press tool and the sheet metal component that is produced out of it are inspected using CMM to validate the results obtained analytically.
METHODS AND MATERIALS
The work in this paper is divided in to three stages.
2) Tolerance analysis and
3) Fabrication of press tool.
The press tool design is divided into six divisions namely, designs of (a) Die plate (b) Punch plate (c) Piercing punch (d) Blanking punch (e) Top die shoe (f) Bottom die shoe. The tolerance analysis has to be carried out to find the true positional error of the holes analytically and numerically. The fabrication of the press tool is to be done based on the required manufacturing process for the different parts of the press tool. The component which is considered for this research work is made up of aluminium 8011 grade. The top and bottom die shoes are made up of mild steel. The punch plate and stripper plate are made up of EN 8 steel. The die plate and the punches are made up of high carbon high chromium alloy steel.
In order to validate the true positional error of the pierced holes, a press tool was fabricated as shown in fig.4 and the component produced using this tool is shown in fig
A sheet metal sample was considered and a press tool was designed and fabricated for the same. Tolerance analysis was conducted on this tool. The press tool and the sheared sample were inspected using CMM.