Properties and deformation characteristics of mechanically worked sintered billets.

This project originated from the desire to provide the sintered preform designers in forging industries with useful information on the effects of certain process variables on the forged product and to formulate these effects into comprehensive relationships of the basic rheological characteristics of the material. A further aim was to establish a technique to theoretically demonstrate the applicability of these relationships,by analysing simple forging of sintered billets. A literature survey covering three main areas in general is presented highlighting the effects of various process variables on the mechanical properties, the deformation characteristics of various sintered materials, and the attempts to establish a yield criterion for porous materials on the basis of experimental results and theoretical analysis. The experimental programme involved the design, construction and machining, where appropriate, of a double cone powder mixer, a sintering unit, and three die compaction sets, compacts of atomised iron powder, mixed with 0.25% flake graphite were made of various heights, diameters anddensities and sintered at various sintering conditions. Further work included preparation of testpieces for compression, tension, impact, hardness, chemical analysis and metallographic tests and making of forging dies for upsetting, upset-extrusion, capped ends upsetting, triangular cavity and multi-cavity closed die forging. The programme of work involved the study of 1. The effects of sintering time and temperature on the mechanical properties of sintered iron, on the deformation characteristics and on the properties of the upset specimens. 2. The effects of aspect ratio on the deformation characteristics of sintered billets. 3. The behaviour of the material through testing specimens of various cross-sections(circular, square rectangular, triangular and semi-circular) and by changing die geometry in order to simulate effects inactual closed die forging. 4. Closed die forging simulating the production of two and four gear teeth of various widths. 5. The existing yield criteria in an attempt to improve their applicability in respect of sintered iron. 6. A finite-difference numerical technique in order to simulate the upsetting process of a variable density material. Comparison of the predicted results with those observed experimentally showed good agreement.