This study investigated effects of the process parameters on the forging load and metal flow pattern during forging and thread-rolling these two process of LZ91 magnesium alloy small size screw by the finite element analysis. At first, Compression tests were carried out under various forming temperatures to study the flow stress. Then, FEM software DEFORM-2D is adopted to simulate forging and thread-rolling processes of small screw to analyze the formability and parameters. In one of this study, there are two stages in forging process, and found out that up-die velocity, temperatures and friction factors will affect the product quality and appearance; on the other part, it investigated the effect of friction factor and temperature under thread-rolling process, and found out that effective stress, effective strain, metal flow and height of thread will be affected. In addition, conduct forging and thread-rolling experiments by using universal testing machine with the mold self-designed, and MoS2 of lubricant, and comparing the analytical results to verify the suitability and accuracy of FEM for forging process. Finally, according to the analysis result of this study, engineers can take it as reference.

Screws are produced by four manufacturing processes : extrusion, drawing, heading and thread-rolling. This paper will develop the related manufacturing technology of LZ91 magnesium alloy screws. At first, finite element simulation is adopted to analyze the effects of each process parameters on the formability. Then, each process experiments are conduted to manufacture an M6 magnesium alloy screw. Comparisous between analytical and experimental results verify the suitability and accuracy of the analytical models. In the extrusion process, by the finite element simulations the extrusion load is obtained. Then bar extrudsion experiments with high extrusion ratioto manufacture two bars of 6.5 and 7 mm in diameter using a 350 ton extrusion machine . In the drawing process, the effects of reduction and friction factor on the optimal semi-die angle are discussed, and the relationship is found. Then a rod of 7.0 mm in diameter is drawn into 6.5 mm experimentally. In the heading process, three stages in it`s process are designed. The arc shape and axial length of the die for the first stage are found out. Finally, heading experiments are conducted and sizes between the product and the simulation results are compared. In thread-rolling process, the effects of the screw plate gap on the formability are discussed numerically. Then, thread-rolling experiments are conducted to compare the sizes of the product and the simulation results. In addition, microstructure observation and hardness test are conducted to understand the effects of drawing process on the strength of the product.