High-efficiency finishing process for metal mold by large-area electron beam irradiation
Introduction
In general, the surface of metal molds is finished by hand lapping after milling and/or electrical discharge machining (EDM), in order to attain small-surface roughness without cracks and heat affected layer. This process takes a lot of time and needs special technical skills. Moreover, the automation of this polishing process is difficult, since most of the metal molds have very complicated shapes. Therefore, a high-efficient finishing process is strongly required.
In this study, a new finishing process for metal molds by large-area electron beam (EB) irradiation is proposed. The large-area EB irradiation equipment used here was recently developed for surface treatment or surface modification by the cooperative research between Okayama University and Nagata Seiki Co. Ltd. [1]. EB with high-energy density can be irradiated without focusing the beam in this method. That is, large-area EB with a maximum diameter of 60 mm can be used for melting or evaporating metal surface. Using this system, the possibility for high-efficient finishing of metal molds is experimentally discussed.
Section snippets
Large-area EB irradiation
Fig. 1 schematically illustrates the EB irradiation equipment and the generation mechanism of large-area EB [2], [3]. Fig. 2 shows the timing chart of pulse input to solenoid coil, anode, and cathode. Differently from general EB irradiation performed in a vacuum, an argon gas of about 10−2 Pa is beforehand mixed in the chamber.
At first, a magnetic field is generated by the solenoid coil set on the outer side of the chamber. At the moment when the magnetic field takes a maximum intensity, pulse
Effects of energy density
At first, an optimum condition for smoothing surface is investigated by changing the energy density of the beam. Fig. 4 shows SEM micrographs of the EB irradiated surface for various energy densities of EB. The number of irradiation is set to 30 shots under every energy density condition. The EDMed surface before irradiation is also shown for comparison. Under the small-energy density condition of 1.4 J/cm2, some melted parts can be observed on the surface [4]. In the case of 2.1 J/cm2, more
Conclusions
- (1)
The roughness of large-area EB irradiated surface becomes smaller with increasing energy density of beam and number of irradiation. Under proper conditions, the surface roughness decreases to about 0.7 μmRz in just a few minutes.
- (2)
In the smoothing process by large-area EB irradiation, the material removal by melting and evaporation occurs near the surface and resolidified layer is not formed. The thickness of removed material in this method is uniformly as small as 1 μm for 30 EB shots.
- (3)
The
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