tailieunhanh - Manufacturing Processes phần 2

báo chí giả mạo) giảm nhẹ lên đến 500 C (932 F), tăng lên đến 750 C (1382 F), nhanh chóng giảm xuống 800 C (1472 F) (thường được gọi là màu xanh giòn), và vượt quá 850 C (1562 F) tăng nhanh nóng giả mạo nhiệt độ 1100 C (2012 F). Vì vậy, lợi thế đáng kể của kháng nguyên liệu thấp (áp lực công cụ thấp và tải báo chí) | PLASTIC WORKING TECHNIQUES 13-11 Fig. Effect of forging temperature on forgeability and material properties. Material AISI 1015 steel. f strain rate f limiting strain Sf flow stress Stot dimensional error FeL scale loss. K. Lange Handbook of Metal Forming McGraw-Hill 1985. press forging decreases slightly up to 500 C 932 F rises until 750 C 1 382 F drops rapidly at 800OC 1 472OF often called blue brittleness and beyond 850 C 1 562 F increases rapidly to hot forging temperature of 1 100 C 2 012 F . Therefore substantial advantages of low material resistance low tool pressures and press loads and excellent workability large flow without material failure can be realized in the hot-working range. Hot-working temperatures however also mean poor dimensional tolerance total dimensional error poor surface finish and material loss due to scale buildup. Forging temperatures above 1 300 C 2 372 F can lead to hot shortness manifested by melting at the grain boundaries. MATERIAL RESPONSE IN METAL FORMING The deformation conditions in metalworking processes span a range of deformation parameters including strain and strain rates Fig. that are much higher than those encountered in conventional testing methods Fig. . In machining the strains are high and the strain rates can Strain Fig. Range of deformation parameters for various metalworking processes. Source P F Bariani S. Bruschi and T. Dal Negro Enhancing Performances of SHPB for Determination of Flow Curves Annals of the CIRP 50 no. 1 pp. 153-156. reach 105 s while in explosive forming strains are small at high strain rates providing extremely small response times. Forging and extrusion cover a wide range of strains and strain rates. Sheet forming carried out as small strains and strain rates differs from superplastic forming at extremely low strain rates but high strains. Consequently different methods have been developed to test material response for different ranges of deformation parameters .