NEW EXPRESSION FOR A BLANKING FORCE CALCULUS OF A COSPEL USING A DIE MATRIX ANGLED

摘要

Frequently it is desired to calculate the blanking shear force of a cospel using an angled matrix as main characteristics of the cutting die. There are two reasons that support the development of this calculation: the first is that the product may change its shape or material, which makes necessary to modify the operating parameters according to the geometric size and metal composition changes. The second is that the nominal capacity of the working press is established by the manufacturer and cannot be altered to adapt to a new product, this means that any new product parameters must be adapted to the capabilities of the machine. Also, the force equation must contain the main variables of the product and not just "proportions" or "factors", allowing a better approximation of the cutting operation. In this work, a new expression for the blanking force calculus of a cospel is obtained, based on the geometric characteristics of the cutting die (punch and matrix). A matrix die angled is considered as a main characteristic of the sheet metal cutting die, maintaining the punch geometry without cut angles. Two formulas derived from analytical and graphical proposed methods are used and several blanking tests were conducted with a die designed and fabricated properly to run the laboratory tests. The graphical methods are based on a projected area of the metal cospel, obtained from the three dimensional cospel area to cut, this two dimensional projected area is utilized in the expression for the cutting force calculus. On the other hand, the analytical approach considers an area limited from a mathematical equation obtained from a model based on the geometry regions of the blanking die; this area has also utilized as the shear area in the cutting force calculus of a metal cospel. The experimental procedure consisted in reproduce the blanking operation of several metal cospels using the designed and fabricated die. The cutting force was measured using three different matrix die angles probed during the blanking tests, maintaining the same cut angle of the punch during the tests. The tests results were compared with both analytical and graphical methods showing good agreement. Similarly, the cutting force was calculated with analytical and experimental expressions obtained from the specialized literature in order to determine the degree of accuracy of the calculations.