Advanced high-precision grinding method with an inclined symmetrical twin grinding-wheels design for machining tungsten carbide microprobes

In this study, an efficient grinding process technology with inclined symmetrical twin grinding-wheels design is proposed for the grinding of tungsten carbide inspection microprobes for detection circuits on printed circuit boards (PCBs). The inclined twin high-speed spindles are equipped with individual boronous polycrystalline composite diamond grinding-wheel so that the tapering and the tip-arc of precision microprobe can be fast generated through the symmetrical bilateral grinding design and circular interpolation movement track planning. To keep the twin grinding-wheels sharp, electric-discharge in situ dressing (EDID) technique is proposed, where the grinding-wheels need no loading, unloading nor calibration. A multiple resistance–capacitance (mRC) relaxation power source provides the discharge source for in-situ dressing of the twin grinding-wheels, thus creating adequate, highly consistent grinding edges and chip pockets. Also proposed are two self-adaptive strategies, grinding force feedback and spindle vibration detection, to improve grinding efficiency and prevent deterioration during grinding. Experimental results indicate that under the following conditions: wheel grain size of 25 μm, wheel speed of 30,000 rpm, workpiece speed of 500 rpm, pecking feed rate of 1.3 mm/min, and grinding depth of 10 μm/stroke, grinding time to create a probe is 2.8 min and 1.9 min in non-self-adaptive and self-adaptive modes, respectively. Grinding efficiency improves by 32% with surface roughness at Ra 0.206 µm. Compared to manual grinding (30 min/probe), grinding efficiency is improved by a factor of 15. After dressing the twin grinding-wheels once, up 46 probes grinding (average service life) can be achieved, which have commercial potential.