Material Machining Views: 7

Notes and tool selection for machining zinc alloys (ZnAl4, ZnAl4Cu1, die-cast zinc): Characteristics: 1) Low melting point - about 380-420C, the lowest among common metals: melts and welds easily during cutting; 2) Low hardness - very soft, low cutting force, easy; 3) High tack - welds easily, built-up edge, poor finish; 4) Good thermal conductivity - heat dissipates; 5) Deforms easily - low strength: thin walls deform; 6) Die-cast porosity - internal pores and shrinkage: surface defects possible. Which tool: 1) Cobalt HSS or standard HSS - both fine; zinc is soft; 2) Carbide - more wear-resistant for high volume; 3) DLC coating recommended - low friction, anti-welding - ideal for zinc; 4) Single-flute - low force, good chip removal, less welding. Parameters: 1) speed - medium-high, 1500-3000rpm; not too high (excessive heat melts and welds); 2) feed - medium-large, 0.12-0.25mm/rev: less dwell, less welding and heat; 3) depth - can be large; low cutting force. Notes: 1) prevent melting/welding - a) moderate speed (avoid melt point); b) large feed - less dwell; c) DLC-coated or polished tools - less friction; d) generous cooling - semi- or full synthetic, 3%-5%; e) sharp tools - dull tools rub and weld; f) clean stuck chips promptly; 2) prevent deformation - a) light clamping; b) support thin walls; c) measure after cooling (high thermal expansion); d) do not over-clamp; 3) porosity - a) die-cast pores/shrinkage show as small pits - a material issue, not the tool; b) severe porosity: improve casting quality or change material; c) polish or grind to mask small pores; 4) finish - a) soft surface scratches easily - protect after machining; b) welding roughens the surface - anti-welding; c) final light pass improves finish; 5) measuring - a) high thermal expansion: cool to room temperature first; b) unclamp before measuring; 6) follow-up - a) zinc oxidizes after machining - surface treatment promptly (plating, painting, passivation); b) oil or dry storage. Zinc is easy to machine (soft, low force); the main issues are melting/welding and deformation - with DLC-coated tools, medium-high speed, large feed and generous cooling, quality chamfers are achievable. Our countersinks all machine zinc - ask us.