| Summary: | 碩士 === 國立高雄應用科技大學 === 模具工程系 === 104 === The harder mold material makes it difficult to be cut through traditional machining processes. Therefore, the electrical discharge machining (EDM) or Wire-EDM are often adopted in related industrial processing. However, due to the fact of micro-cracks and pores often appearing under the workpiece surface after EDM processes, it result in the decrease of mechanical properties of the material. At the other hand, It is also common to add nickel metal in steel materials since it can improve the mechanical properties of the raw steel, and it was conjectured that nickel powder may be suitable to fulfill the micro-cracks and pores effectively. In aspect of electroplating for molds, the material of the coating matrix is often nickel, as well as alloy like nickel-cobalt and copper-nickel, etc., which indicating that the nickel is also popular in surface treating. In addition, from EDS analysis of the workpiece surface after Wire-EDM processes, the adhesive phenomenon on wire electrode material is quite evident. Thus, the idea derived from that the electrode material melts on the workpiece and forms a coating layer (or EDM cladding layer) under the high temperature of the intermittent discharging energy from EDM is then hit upon. Therefore, this thesis makes a comparison of using nickel-plated copper wire and regular brass wire in the designed Wire-EDM coating processes, to achieve surface modification through eliminating recast layer and fulfilling the micro-cracks or pores produced by Wire-EDM at one procedure, as well as the improvement of mechanical properties.
The research adopted nickel-plated copper wire form material company of conductors field, and M333 tool steel as workpiece. The goal is focused on the profile and texture of the work surface after processing, the roughness, covered ingredients and anti-abrasion performance are also concerned. The effects of machining parameters such as open-voltage〖 (O〗_V), on-time; or discharging period (T_ON), feed-rate (F) are investigated, respectively. The open-voltage is selected from 85V, 105V, and 125V, respectively. The on-time of discharging is set from 0.1μs to 0.2μs for small energy surface treatment. The pulse off-time is selected from a set of 15μs, 20μs, and 25μs. The fixed setting of feed speed is chosen from one of 0.5mm/min, 1.0 mm/min, and 2.0 mm/min. Alternative current (AC) power generator is used in conducting the experiment of Wire-EDM coating processes. It is found that the relatively optimal processing conditions for surface modification are open-voltage O_V 105V, T_ON 0.1μs, off-time T_OFF 25μs, and under the fixed feed-rate of 0.5mm/min. Under such a combination of operating condition, the most uniformly distributed and abundant alloy layer through Wire-EDM coating, or cladding, was obtained. Comparison on the mechanical properties revealed that the workpiece conducted through brass wire preserved a little stronger anti-bending strength before the yield point, but once going to plastic deformation, the nickel cladding workpiece revealed much higher stress.
|
|---|
