TAILIEUCHUNG - Foseco Non-Ferrous Foundryman’s Handbook Part 7

Tham khảo tài liệu 'foseco non-ferrous foundryman’s handbook part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chapter 9 Pressure diecasting of aluminium alloys Introduction In high pressure diecasting usually known as pressure diecasting molten alloy is injected under pressure into a highly accurate split metal mould. It is the most widely used casting process for aluminium alloys. Production rates are fast the process can be highly automated and dimensional accuracy and surface finish are excellent. Thin-walled components are possible and little or no machining is needed on the cast component since holes grooves and recesses can be finish cast. Aluminium alloys are cast in cold-chamber diecasting machines. The die is made of tool steel usually of two cavities into which the metal is forced. The die halves are closed and locked together hydraulically to withstand the high injection pressure. Molten metal is introduced through a pouring slot into the shot tube then a steel plunger forces the liquid metal into the die cavity under a pressure of up to 100 MPa 1000 bar Fig. The pressures used are given in Table . Figure Calculation of the die opening force. Courtesy Buhler Ltd. Pressure diecasting of aluminium alloys 109 Table Guidance values for casting pressures courtesy of Buhler Ltd Casting pressure bars Al and Mg Zn Brass Standard parts up to 400 100-200 300-400 Technical parts 400-600 200-300 400-500 Pressure-tight parts 800-1000 250-400 800-1000 Chromium plating parts 220-250 Die filling times are very short castings with wall thickness of 3-4 mm are filled in less than seconds. The metal solidifies rapidly because of the good thermal contact with the water-cooled die and the die set is opened to eject the finished casting together with its sprue the process is then repeated. Cycle times depend on size and section thickness of the component being typically 40 shots per hour for a component of 5 kg. Machines are described by their locking force Fig. which determines the cross-sectional area of the casting which can be made which is in turn related

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