Molding sand of good permeability is recommended in sand cas

Molding sand of good permeability is recommended in sand casting In deep drawing of sheet metals, a drawing ratio less than 2 is advisable. The formation of a built up edge on a cutting tool. Down cut milling is employed when deep slot milling using carbide tooth cutters. In metal forming, why are true stress and true strain, used, rather than the engineering ones, to calculate the forming forces?

Solution

1. Moulding sand must be porous enough to allow the dissolved gases to be removed from the moulds when the moulds are being poured. Hence the porosity or permeability of sand should be good.

2. To maintain the geometry, forces, metal flow and material properties of the work, we keep a limit on the drawing ratio. Also, it draws a limit in safe and fail regions.

3. Built up edge is formed when there is high local temperature and extreme pressure in the cutting and there is high friction in the tool chip interference this causes the work material to stick to cutting edge of tool and due to repititve action succesive layers of material are added to form the built up edge.

4. Down cut milling is employed because it reduces the load from the cutting and provides better finish. Also, it helps in improving tool life.

5. At any load, the true stress is the Load/crossectional area at that instant.Until and Unless thickness and width are being monitored continuously during the test, we can\'t calculate true stress. Hence, we use engineering stress in calculations. Also, it gives a much better representation of how the material behaves as it is being deformed, which explains its use in forming operations.