1.1 Die Pressing. Pressing of powders in rigid dies is carried out either in mechanical or hydraulic presses. The pressure is applied from the top, or from the top and bottom (double action presses). Die and punches are made of high-speed tool steel or (more rarely) hardmetal. Mechanical presses (pressing forces up to 1 MN) are used for small parts and high production rates. They allow a higher degree of dimensional precision and are well suited for process automation. Hydraulic presses are mainly used for simple preforms. Large presses with up to 30 MN (3000t) pressing force are used for pressing of plates which are to be rolled to sheet metal. The size and shape of the compact are limited by the capacity of the press and also by the geometry of the part.
Due to the friction between the powder and the die wall and the nature of the load distribution inside the die, the pressing density is not the same all over the compact. This is more pronounced for large parts and large part heights and can lead to crack formation and/or distortion of the pressed compact during sintering. Large and critical parts are therefore commonly pressed isostatically.
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