Material Machining Views: 7

Notes and tool selection for machining brittle materials - ceramics, glass, sapphire, quartz: Characteristics: 1) Extremely hard - ceramics HRA90+, glass Mohs 5-7; ordinary tools cannot cut them; 2) Very brittle - chipping, cracking and shattering, especially at the exit side; 3) Abrasive wear - hard material wears tools extremely fast; 4) Heavy dust - ceramic and glass dust is harmful; 5) Temperature-sensitive - large temperature changes cause heat cracks. Which tool: 1) Diamond tools (PCD or CVD diamond coating) - first choice: hardest (Mohs 10), excellent wear resistance; for ceramics, glass, sapphire; 2) Carbide - for soft ceramics (alumina, silicon nitride), but wears fast; not for glass or hard ceramics; 3) Electroplated diamond burrs - for chamfering and grinding glass and ceramics: diamond grit electroplated on the base; 4) Resin-bond diamond burrs - for finishing and polishing: good finish. Parameters: 1) speed - high: diamond tools 3000-10000rpm, electroplated diamond burrs 5000-20000rpm; 2) feed - very small, 0.01-0.05mm/rev, prevent chipping; 3) depth - very small, 0.05-0.2mm per pass, stepped; never cut deep at once. Notes: 1) prevent chipping - a) very small feed and depth; b) cut from solid toward the edge; go especially slow at the exit side; c) very sharp diamond tools; d) support - back the part, especially the exit side; e) tape the exit side; f) leave 0.05-0.1mm and finish with a tiny feed light pass; 2) prevent cracks - a) no impact or vibration; b) generous cooling (water or coolant; no dry cutting - heat cracks); c) no sudden temperature changes; d) preheat or anneal to relieve internal stress; 3) dust control - a) dust mask (ceramic and glass dust harms lungs - silicosis risk); b) wet machining or vacuum; c) safety glasses; 4) safety - a) flying fragments - glasses and gloves; b) do not touch during machining; c) sharp edges of broken material - be careful; 5) tool choice - diamond tools or electroplated diamond burrs; ordinary tools simply cannot cut; 6) measuring - brittle materials are dimensionally stable; measure after cooling; 7) finish - polish with resin-bond diamond burrs or polishing paste. Brittle materials are the hardest - mainly chipping and cracking prevention: diamond tools, very small feed and depth, generous cooling, support. For glass, use dedicated glass chamfering machines or electroplated diamond burrs.