Intended Audience

• Drawing die manufacturers & reconditioning engineers
• Superhard material polishing technicians
• Purchasing and technical personnel looking for high-quality diamond polishing powders

1. Why Diamond Powder Selection is Critical for Drawing Die Polishing

The polishing quality of synthetic diamond (especially polycrystalline diamond, PCD) drawing dies directly determines the dimensional accuracy, surface finish of drawn products, and die service life. More than 60% of polishing success depends on the characteristics of the diamond micropowder itself – particle size distribution, crystal shape, dispersibility, and purity.

This guide summarizes real feedback from hundreds of drawing die customers, covering operating precautions and abrasive selection tips. Whether or not you use our products, you will find practical value here.

2. Pre-polishing Preparation: Cleanliness First

2.1 Die Bore Cleaning

New or reconditioned dies often carry EDM debris, oil, or oxides in the bore. Must do:

• Ultrasonic cleaning with alcohol or special cleaner for 3–5 minutes
• Blow dry with compressed air

⚠️ Any residue will scratch the inner wall during initial polishing, causing irreversible damage.

2.2 Clean Environment & Tools

• Physically separate roughing and finishing workstations
• Cover workbenches with lint-free cloth
• Before switching to a finer abrasive, wipe workpiece and tools thoroughly with a soft cloth moistened with alcohol
• A cleanroom is highly recommended for finishing stages

2.3 Temporary Rust Protection

If not polished immediately after cleaning, apply a light rust preventive oil. Remove it completely before polishing – residual oil will dilute the diamond paste or cause agglomeration.

3. Key Control Points During Polishing (with Recommended Diamond Powder Grits)

3.1 Stepwise Processing – Coarse to Fine (Never Skip Grits)

3.2 Tool & Backing Material Selection

• Use cork or bamboo sticks as backing for sandpaper or lapping paste – avoid metal sticks which cause deep scratches
• Shape the stick end to match the die bore curvature (cone or ball)
• Use different backing sticks for different grit sizes – never mix

3.3 Pressure & Time Control

• Apply light pressure throughout – especially in finishing. Excessive pressure causes thermal burns or orange peel
• Single polishing interval no longer than 15 seconds – check frequently to avoid heat buildup
• Clean thoroughly after each abrasive grade before moving to the next finer grade

3.4 Multi-Directional Polishing

After each grit, rotate the workpiece or polishing direction by 45°–90° to erase previous scratches uniformly.

3.5 Amount of Lapping Paste

A rice-grain sized drop is sufficient. Too much paste causes abrasive overlap and extra scratches.

4. Diamond Powder-Related Problems & Prevention (Core Section)

Poor polishing results are often caused by the diamond powder itself, not by technique. Use this table for quick diagnosis:

How to quickly check if your current diamond powder is qualified?

1. Request a laser particle size report – Span (D90-D10)/D50 should be ≤1.5
2. Check crystal shape under microscope – particles should be near-spherical or equiaxed, no sharp edges
3. Dispersibility test – add a small amount to alcohol, ultrasonicate – no obvious agglomeration or sedimentation
4. Purity test – ash content should be below 0.5%

5. Post-Polishing Treatment (Rust Prevention = Profit Protection)

• Thorough cleaning – Wipe die bore repeatedly with alcohol-moistened cotton balls until no black/grey residue appears
• Immediate rust protection – Spray with dedicated die anti-rust oil or wrap in vapour-phase rust preventive paper
• Storage – Keep in a clean, dry, dust-free container with stable temperature, avoid contact with other hard objects

6. Quick Troubleshooting FAQ

Q1: There are long scratches even after switching to finer powder. What should I do?
Answer: Most likely, oversized particles are present in your coarse powder, or the paste has agglomerated. Switch to a brand with narrower particle size distribution, and pre-disperse the paste on a glass plate with light stoning before use.

Q2: The surface remains hazy after long polishing. Why?
Answer: Possible causes: ① Skipping too many grit sizes (e.g., 15 μm → 3 μm); ② Insufficient finishing time; ③ Diamond concentration too low. Follow the recommended grit sequence step by step and ensure enough time for each grade.

Q3: What pressure should I use?
Answer: For manual polishing, use a pressure that feels "just slight resistance". For mechanical polishing, refer to 100–200 g/cm². Excess pressure causes burns.

Q4: Should I choose monocrystalline or polycrystalline diamond powder?
Answer: For finishing of drawing dies, polycrystalline diamond is preferred due to its self-sharpening nature and more uniform scratching. Monocrystalline can be used for roughing to lower cost.

Q5: Can you supply ready-to-use lapping pastes?
Answer: Yes. Both oil-based and water-based pre-dispersed lapping pastes with customizable diamond concentration are available.

7. Recommended Diamond Micropowder Specifications for Drawing Die Polishing

8. Summary

• Clean – Die bore, environment, tools, hands – keep everything dust-free.
• Stepwise – Follow a complete grit sequence; never skip sizes or mix different abrasives.
• Light pressure – Apply light pressure throughout, especially in finishing.
• Good abrasive – Use diamond powder with narrow size distribution, rounded crystal shape, good dispersibility and high purity.
• Rust protection – Protect immediately after polishing, otherwise the effort may be wasted.