Kinematic Synthesis of an Adjustable Knock-Out Linkage Mechanism of Screw Former

• Main Authors: Yi-ChengWu, 吳苡誠
• Other Authors: Wen-Miin Hwang
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/vwyqm2

碩士 === 國立成功大學 === 機械工程學系 === 106 === A screw former is a kind of machine for manufacturing screws by forging processes. The major function of the knock-out mechanism of a screw former is to knock out the semi-finished product from a female die. Besides, in order to manufacture screws with different length, the knock-out mechanism should be adjustable for variable knock-out strokes. For coordinating with other mechanisms in a screw former and adjusting the knock-out stroke, a knock-out mechanism must be a dwell mechanism. Thus, an adjustable knock-out mechanism consists of two sub-mechanisms: a dwell mechanism and a variable-stroke mechanism. The purpose of this thesis is to replace the cam mechanism by a linkage mechanism and redesign the adjustable knock-out mechanism for generating the same functions as an existing design. According to the structural requirements and constraints for an adjustable knock-out mechanism, five feasible six-bar linkages for the dwell mechanism are synthesized by a creative mechanism design methodology. After evaluating with the decision matrix method, the Watt-II mechanism is selected for the dwell mechanism. The dimensions of the Watt-II dwell mechanism is synthesized by an optimization method based on a geometrical design method, which is constructed on the basis of the limit position of planar four-bar linkage and relative pole method. The dimensions of the variable-stroke mechanism is also synthesized by an optimization method based on a geometrical design method, which is constructed on the basis of the initial and final positions of the variable-stroke mechanism with the longest and the shortest knock-out strokes. The new adjustable knock-out linkage mechanism for a screw former proposed in this thesis improves the mechanical performances of an existing cam-driven knock-out mechanism.