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GRAPHICAL ABSTRACT
ABSTRACT
It is difficult for mechanical machining to fabricate concave micro-array due to size limit and micro-tool wear. Hence, electro discharge micro-machining is proposed to fabricate concave micro-array using micro-tip array electrode. The objective is to explore the batch micro-machinability of various metallic materials such as die steel, titanium alloy and cemented carbide. First, micro-grinding with diamond wheel micro-tip was performed to fabricate pyramid micro-tip array on electrode surface; then, impulse discharge removal derived from the electrode tips was employed to gradually machine the concave micro-array on metallic surfaces; finally, micro-machined shape and corresponding machining performances were investigated. It is shown that the micro-machining performances depend on material melting point, electric conductivity, and thermal conductivity. Low melting point and electric conductivity lead to good micro-machined shape with small relative wear rate. High electric conductivity and low melting point produce small surface roughness, large micro-removal rate and discharge energy efficiency. Low thermal conductivity leads to large aspect ratio and micro-removal rate. It is confirmed that die steel produces small surface roughness, large micro-removal rate and discharge energy efficiency, whereas titanium alloy produces large aspect ratio and small relative wear rate.
Funding
National Natural Science Foundation of China [61475046]; Guangdong Science and Technology Project [2016A040403043]; Guangdong Science Foundation of China [2015A030311015]; Guangdong Science and Technology Project[2017A010102003]; Guangzhou Science and Technology Project [201508030012]; Guangdong Science and Technology Project [2014B010104003].
Nomenclature
| ap | = | cutting depth of diamond wheel (µm) |
| B | = | the width of diamond wheel (mm) |
| CH | = | the hardness of workpiece material (HRC) |
| c(T) | = | the specific heat capacity of workpiece material (J/kg · K) |
| D | = | the diameter of diamond wheel (mm) |
| Et | = | discharge energy (J) |
| G | = | the electric conductivity of workpiece material (MS/m) |
| Ge | = | discharge gap (µm) |
| H | = | the total height of micro-cavity (µm) |
| hf | = | feeding height (µm) |
| hv | = | the overlapping height of micro-cavity (µm) |
| hw | = | concave micro-array height (µm) |
| I | = | discharge current (A) |
| L | = | micro-cavity width (µm) |
| Lm | = | the latent heat of workpiece material (kJ/mol) |
| N | = | diamond wheel speed (r/min) |
| n | = | the number of spark impulse of waveform trace |
| Q | = | theoretical energy for metal melting (J) |
| q | = | the energy distribution coefficient of anode (%) |
| Ra | = | surface roughness of machined workpiece |
| rq | = | aspect ratio of concave micro-array |
| rw | = | relative wear rate (%) |
| T0 | = | initial temperature (K) |
| Tm | = | the melting point of workpiece material (K) |
| t | = | machining duration (s) |
| tL | = | the sample length of waveform trace (s) |
| V | = | the volume of micro-cavity (µm3) |
| vd | = | micro-removal rate (mm3/min) |
| vf | = | feeding speed of diamond wheel(mm/min) |
| WD | = | the energy of single impulse discharge (J) |
| η | = | discharge energy efficiency (%) |
| θ | = | the form-truing angle of diamond wheel (°) |
| λ | = | the thermal conductivity of workpiece material (W/mK) |
| ρ | = | the density of workpiece material (g/cm3) |