What Types of Tool Marks Can Be Removed by Dry Polishing?

1. Core Preconditions for Judgment: Two Key Indicators

To judge whether dry burnishing can eliminate tool marks, visual observation alone is insufficient. Priority should be given to the following two core indicators:

1. Original surface roughness (Ra): Reflects the height difference between peaks and valleys of tool marks, serving as the most intuitive quantitative reference.
2. Tool mark morphology: Closely-spaced continuous shallow textures differ vastly from wide and deep grooved textures in terms of removal difficulty.

Dry burnishing relies on continuous micro friction from abrasives to level texture peaks. It cannot conduct massive substrate cutting. The core process logic: flatten protruding peaks, but cannot extensively grind out deep valleys. Tool marks with excessively deep valleys can hardly be completely eliminated only by finishing burnishing.

2. Tool Marks That Can Be Stably Removed by Dry Burnishing (Feasible Mass Production Range)

2.1 Applicable Texture Morphology

• Dense, continuous, shallow spiral or concentric textures generated by CNC finish milling;
• Small tool path pitch with evenly distributed textures without independent deep grooves;
• Fine unidirectional scratch lines formed by stamping or manual grinding.

2.2 Quantitative Reference of Original Roughness (Blank Ra Value)

1. Zinc alloy, aluminum alloy, copper, tin alloy (soft alloys) Shallow tool marks with original Ra ≤ 1.6 μm can be fully faded to visually invisible through segmented dry burnishing. Trial production limit: Ra 1.6～2.0 μm. Optimize abrasives and appropriately extend cycle time; long-term mass production under this condition is not recommended.

2. 304/316 stainless steel Dense finish milling tool marks with original Ra ≤1.2 μm can be stably removed. Trial production limit: Ra 1.2～1.6 μm.

3. TC4 titanium alloy, nickel/cobalt-based superalloys Only ultra-fine finish milling textures with original Ra ≤0.8 μm are acceptable.

Workpieces with higher roughness are prohibited. Prolonged grinding easily causes surface work hardening, thermal oxidation and discoloration, and textures will appear increasingly foggy.

2.3 Necessary Supporting Conditions

• Adopt medium-soft ceramic abrasives first for texture refinement, followed by resin/plant-based abrasives for brightening;
• Use compartmentalized drum machines or fixture-type machines to avoid extra defects caused by workpiece collision;
• Operate at low speed with segmented cycles and strictly control temperature rise.

3. Tool Marks That Can Only Be Faded but Cannot Be Completely Eliminated (Risk Range, Not Recommended for Direct Mass Production)

1. Soft alloy Ra ＞2.0 μm; stainless steel Ra＞1.6 μm; titanium/superalloy Ra＞0.8 μm;
2. Rough milling textures with large tool path spacing and obvious height difference between peaks and valleys, visible continuous grooves under normal light;
3. Large step-over ball-nose roughing textures and discontinuous uneven textures formed by forming cutters.

Typical phenomenon: After long-duration burnishing, textures become lighter, but streaks can still be seen when adjusting the viewing angle, forming foggy stripes that fail to meet uniform matte or mirror standards.

Solution: Apply robotic force-controlled sanding or belt grinding in advance to reduce roughness to the safe range, then carry out dry burnishing finishing.

4. Tool Marks That Cannot Be Removed by Dry Burnishing at All (Red Line — Forbidden to Load Directly)

1. Deep grooved rough tool marks from CNC roughing and obvious stepped milling traces;
2. Intermittent pits and dented textures caused by tool chipping or chatter vibration;
3. Coarse discharge textures and deep pitting formed by electrical discharge machining (EDM);
4. Deep unidirectional coarse scratch marks from grinding (grit 180# and coarser).

Potential risks: Prolonged continuous grinding only wears workpiece edges, leads to dimensional loss and deformation of thin-walled parts. Titanium alloys and superalloys will develop hardened layers and surface thermal burns while textures remain, resulting in mass scrapping.

5. Key Additional Factors Affecting Tool Mark Removal Effect

5.1 Abrasive Selection

✅ Recommended combination: Round medium-soft ceramic abrasives (texture refinement) + resin abrasives (leveling and brightening) ❌ Not recommended: Plant-based abrasives used alone. Plant abrasives feature extremely low cutting power, suitable only for brightening and barely able to eliminate tool marks.

5.2 Texture Direction

Interlaced all-directional textures (milling spiral lines) are easier to eliminate evenly. Continuous parallel long unidirectional tool marks are more likely to leave residual streaks.

5.3 Workpiece Structure

Solid thick-walled parts allow moderately extended processing time. For thin-walled parts (wall thickness ＜1.2 mm), even textures within the qualified range require shortened single-cycle duration to prevent deformation.

5.4 Effective Compartmentation

Workpieces stack and bear uneven force inside non-compartmentalized drums, leading to inconsistent removal results within one batch. Machines with effective compartment separation deliver significantly higher polishing uniformity.

6. Quick Reference Table by Workpiece Material

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7. Recommended Standard Mass Production Process Routes

Option A (Tool marks within safe range) CNC Finish Milling → Ultrasonic Cleaning & Drying → Dry Burnishing (Medium polishing with ceramics + Fine polishing with resin) → Inspection

Option B (Relatively deep tool marks, within risk range) CNC Machining → Robotic/Belt Rough Grinding to reduce Ra → Cleaning → Dry Burnishing Finishing

Option C (Deep rough milling textures exceeding process limit) Rough Machining → Finish Milling to reduce texture height difference → Rough Sanding → Dry Burnishing Finishing

8. Conclusion

Dry burnishing is only suitable for removing dense, uniform shallow tool marks generated by finish milling. Simple judgment rule: Fine and shallow uniform textures are feasible; deep grooved rough textures cannot be removed. Soft alloys have higher tolerance, while titanium alloys and superalloys have the strictest threshold. Blank roughness testing is essential during sampling for new projects. Once original textures exceed the upper limit, do not attempt to eliminate them merely by extending burnishing time. Pre-leveling procedures must be added to balance production capacity, yield rate and overall manufacturing cost.