Research On Micro-Gear Fabrication By Laser Dynamic Flexible Punching

The existing micro-gears fabrication process is complicated, inefficient and not suitable for mass production, and micro-punching process has limitations of accurate alignment between micro-punch and mold and requires high precision driving device. Combining laser shock forming process and micro-punching with soft punch, the dissertation develops the laser dynamic flexible punching process to fabricate micro-gears on metal foils, with high-accuracy micro-mole fabricated by wire cut electrical discharge machining(WEDM). Its main researching is as follows:Firstly, the force effect mechanism of the laser-induced plasma and the metal workpieces’ dynamic response behavior and facture mechanism in the high-strain rate process are in-depth studied. The formulas for calculating the peak pressure of shock waves are carried out.The propagation characteristics of laser induced wave and its boost effects are also studied, providing a theoretical basis for further research on the laser dynamic flexible punching micro-gears.Secondly, laser dynamic flexible punching experiments are conducted to investigate the effects of process parameters namely laser energy, soft punch properties and blank-holder on the quality of micro-gears deeply. Micro-gears with clear outline and high accuracy are obtained under the KEYENCE VHX-1000 C microscope in the end. Results show that laser energy has a great influence on the dimensional accuracy and fracture mode of the workpiece. Furthermore, appropriate thickness and hardness of soft punch can homogenize the laser energy better in the punching process. A larger blank-holder is more beneficial to improve the punching quality, because it can provide a bigger radial thrust and the axial flow of material is hindered.Thirdly, laser dynamic flexible punching experiments are conducted to investigate the size effects, including different foils thickness and grain size, on the dimensional accuracy and rollover diameter. The dimension and rollover are observed under the KEYENCE VHX-1000 C microscope. Results show that foils thickness have a great effects on the punching quality, and punched gears of thicker foils result in worse dimensional accuracy and larger rollover diameter. The punching quality is closely related to the number of grains in the punching direction. When there are many grains locating on the cross section the foils, the slip and coordination of grains are easier during the shearing deformation, as a result of high dimensional accuracy and a bigger rollover. The cross section of the punched gears are observed by SEM. Results are that the rollover is bigger and the burr height can almost be ignored. The changes of nano-hardness and elastic modulus are measured by nano-indentation experiments. Results are that both the nano-hardness and elastic modulus increase, being in accord with the Hall-Petch relation, which is a result of grains refinement after laser shock. The laser shock effect improves the surface strength and stiffness of the gear.Fourthly, ANSYS/LS-DYNA and Ls-Prepost are employed to simulate the process of dynamic punching gears. The maximum punching force versus time is analysed. Furthermore, the effects of laser energy on displacement variation curve of cross section material in Z axial direction, deformation process of workpiece material and the pressure on the fracture surface, which is conducive to reveal the dynamic punching process and the optimize of process parameters.The study provides a new way for the manufacture of micro gears and lays a theoretical foundation.