Papers by Author: Martin Hirsch

Abstract: Blanking is one of the most widely used manufacturing technologies in sheet metalprocessing, because nearly each sheet must be trimmed out of a semi-finished part or has to beblanked after a forming process to get the precast part in the manufacturing chain. In general, a highquantity of blanked parts should be manufactured without reworking the tool. Therefore a capableprocess is indispensable to avoid inadequate part quality or premature failure of the tool because ofwear. The blanking process is affected by tool parameters, the press and the material properties ofthe blanked part.However, another important factor is the occurring temperature in the shearing zone of the sheetmetal due to the dissipation of nearly 95% of the plastic work during blanking and, in addition,frictional heating. This temperature impacts the blanking process features such as tool-wear andresulting cut edge quality. It has been presumed to be negligible by a lot of authors yet. In contrastsome publications with experimental and analytical research assume that the temperature reachesvalues up to 1000°C. Therefore, this report outlines a thermoelectric method to measure theresulting temperature distribution during the blanking process on the cutting edge of the blankingpunch. The feasibility of the investigated measurement concept is shown on a concrete example.

Abstract: The required number of punched and blanked parts in the electronic industry, such as leadframes, contact pins or plugs often reach several million pieces. According to this, the production process has been sped up to frequencies up to 2000 parts per minute. At this production rate parts of thin steel or copper sheets are produced with high-speed stamping presses and blanking tools. Because of the high gating velocities in the blanking tool there is a recurring acceleration at the moment, when the blank holder contacts the sheet metal. A second shock in the blanking tool arises, when the sheet cracks. This is also known as the impact shock during the blanking process. Trough these two impulses and through the cycle of the plunger movement a periodic oscillation arises in the tool. Horizontal vibrations can lead to an undefined position between punches and die-plate, while vertical movement leads to increased wear because of friction forces between the blanked surface and the lateral area of the punches. The goal of this project was to minimize these oscillations in cutting tools by the usage of lightweight materials in the flux of forces. An experimental cutting tool was designed with alternative top and bottom plates for the comparison of the oscillation status in the cutting process when using plates of steel, aluminium or magnesium. The centre plate of the tool remains constant. Experiments were accomplished for several velocities and tool setups with different plate materials. To determine the influence of the materials with different density and elasticity acceleration, force and acoustic emission sensors were integrated in the tool. The set of problems was investigated by analyzing the measured data and by determining the wear in practical tests.