Residual CNC cutting oil and anti-rust oil will carbonize under high friction heat during dry processing, forming permanent black films and color spots that cannot be removed on the titanium surface.
Perform ultrasonic degreasing and complete air drying before dry burnishing. Never feed workpieces with release agent, cutting fluid or hand sweat contamination.
Titanium alloy has severe work hardening characteristics. Deep CNC tool marks cannot be eliminated by dry burnishing; prolonged grinding will only harden the surface layer continuously, resulting in residual textures and foggy surfaces.
Remove thick burrs and deep tool marks via robotic sanding or manual belt grinding in advance, and only retain fine shallow textures for dry burnishing finishing.
Thin-walled titanium shells (<1.2mm wall thickness) and slender connecting rods are prohibited from free rolling in drum or vortex machines, which easily cause extrusion deformation and edge collapse. Priority shall be given to drag-type or horizontal fixture burnishing machines with independent clamping and zero workpiece collision.
Titanium parts are forbidden to be polished with iron and carbon steel. Iron debris adhered to the titanium surface will cause electrochemical corrosion spots and permanent discoloration under high temperature. Use dedicated drums and exclusive abrasives for titanium alloy and store them separately.
High-hardness brown fused alumina and rigid coarse ceramics are prohibited. Excessive cutting force will cause thermal burns and deep scratches.
Adopt medium-soft round ceramic particles with medium-fine grain size to gently fade shallow textures and reduce instantaneous friction heat. Sharp broken abrasives are strictly forbidden, as sharp edges easily scratch the high-toughness titanium surface.
Resin abrasives refine the surface texture, while walnut shell plant abrasives produce delicate matte finishes. This combination reduces dust accumulation and avoids gray fog layers formed by high-temperature oxidation of mixed titanium dust and debris.
Regularly screen broken residues and titanium debris to avoid cyclic scratching caused by mixed metal powder inside the drum. Replace the entire batch immediately when abrasives age, turn pale or generate excessive dust, as aged abrasives double grinding heat. Never use damp abrasives, as moisture accelerates titanium oxidation and discoloration under high temperature.
Small thick-walled standard parts: Compartmentalized drum machine. Compartment isolation reduces stacking extrusion and heat accumulation.
Micro jewelry & sensor parts: Low-speed vortex machine. Reduce chassis speed to lower high-speed impact heat generation.
Long parts, thin-walled parts & medical implant titanium parts: Drag-type / horizontal fixture machine with independent suspension, zero extrusion and uniform stress.
Not recommended: Large-capacity non-compartmentalized ordinary horizontal machines, which cause concentrated heat accumulation and batch yellowing due to workpiece stacking.
Titanium thermal conductivity is only 1/4 of stainless steel. Friction heat cannot dissipate quickly, and local temperature exceeding 300℃ immediately causes yellow, blue and purple oxidation color bands.
Adopt full-process variable low-speed operation, with speed reduced to 60%–70% of that for stainless steel processing. Apply segmented short-time processing: stop for 5 minutes cooling after every 10–15 minutes of grinding; continuous operation over 30 minutes is prohibited. Increase forward/reverse switching frequency to avoid fixed-point high temperature from continuous local friction. Control abrasive filling volume at 70% to reserve air circulation and heat dissipation space.
Suspended dust and fine titanium debris oxidize rapidly under friction high temperature and adhere to workpieces to form foggy surfaces. Maintain 24-hour uninterrupted dust removal to take away heat and metal dust in real time.
Stop processing immediately for cooling when the drum wall temperature exceeds 55℃. High temperature not only causes discoloration but also induces surface work hardening and reduces fatigue performance. High-temperature processing is strictly prohibited for medical and aerospace titanium parts.
Over-thick workpiece stacking causes continuous friction and overheating burns, indentation and deformation of bottom workpieces. The filling volume of each compartment shall not exceed 50% of the chamber capacity.
Spread out processed workpieces immediately for air cooling instead of closed stacking. High-temperature workpieces continue to oxidize and lose luster when exposed to air.
Drum and vortex machines are prohibited. Adopt fixture clamping to reduce abrasive immersion depth and extrusion load. Implement full-process segmented short-time processing to prevent bending and wave deformation.
Dry burnishing is only for outer surface finishing. Inner holes and threads are processed by magnetic polishing. Dry abrasive dust easily blocks holes and causes irreversible black oxidation inside holes under high temperature.
Chlorine-containing consumables and abrasives are forbidden. Chloride ions under high temperature induce titanium stress corrosion cracks and impair biocompatibility. Ensure dust-free and pollution-free processing with exclusive dedicated abrasives.
Edges feature stress concentration and are prone to edge collapse and microcracks under long-term friction. Shorten single processing duration and adopt soft plant-based abrasives to reduce grinding intensity.
Cool workpieces quickly with forced air after unloading; closed stacking and heat accumulation are prohibited. Thoroughly blow off surface dust and titanium debris with an air gun before cleaning, passivation and anodizing, as residual dust causes pinholes and color spots after high-temperature anodizing.
Oxidation discoloration cannot be repaired by secondary dry burnishing. Slight yellowing can be removed by pickling and passivation; severe blue and purple thermal burns are directly scrapped.
Apply surface protection (passivation, anodizing, coating) to finished products as soon as possible. Fresh titanium surfaces continuously form oxide films in the air, leading to gradual luster attenuation.
Ultra-fine titanium debris generated during dry burnishing is combustible metal dust. Clean dust filter elements regularly to prevent dust accumulation and spontaneous combustion.
Equip the workshop with Class D dedicated metal fire extinguishers. Water and ordinary dry powder extinguishers are prohibited for titanium fire rescue.
Ground the equipment drum and dust removal pipeline completely to eliminate static accumulation.
Operators must wear dust masks to avoid respiratory damage from long-term titanium dust inhalation.
Yellowing, bluing and purple spots: Excessive speed, long single processing time, insufficient segmented cooling and inadequate dust removal. Solutions: Reduce speed, implement segmented cooling and keep dust removal fully operational.
Large-area foggy & gray matte surface: Excessive titanium dust and unscreened broken abrasives. Solutions: Screen abrasives regularly and replace aged abrasives timely.
Dense micro scratches: Mixed processing with iron parts and sharp abrasive residues. Solutions: Use titanium-exclusive abrasives, separate processing and implement regular screening.
Bending & indentation of thin-walled parts: Stacking extrusion in free-rolling machines. Solutions: Switch to drag/horizontal fixture independent clamping processing.
Unremovable surface textures & increasingly foggy finish: Unremoved deep pre-processing tool marks and titanium work hardening. Solutions: Apply robotic sanding for pre-grinding leveling to reduce dry cutting load.
The core difficulties of TC4 titanium alloy dry burnishing focus on four major risks: high-temperature oxidation, work hardening, scratch susceptibility and dust safety. Standard operation must follow the principles of pre-grinding load reduction, low-speed segmented short-time processing, low-heat dedicated abrasives, continuous high-power dust removal, independent clamping for thin-walled parts and rapid air cooling protection after processing. Strict material separation and independent processing balance surface quality, mechanical performance and workshop production safety.
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