Views: 0 Author: Site Editor Publish Time: 2026-04-20 Origin: Site
If you run injection molding—especially with abrasive materials like glass-filled nylon—you know the pain. After 50,000, maybe 100,000 cycles, the cavity starts to wear. Parts show drag marks. Edges round off. Corrosion pits appear.
You’re not alone. But here’s the truth: most molds don’t die of old age. They die from surface failure.
And the solution isn’t a better steel grade (though that helps). It’s surface treatment.
In this guide, we’ll break down:
Why molds actually fail
The 5 most effective surface treatments
How to choose the right one for your specific plastic and filler
Real-world case studies
Let’s extend that tooling life.
Before picking a coating, understand the enemy. Mold surfaces fail in four primary ways:
Failure Mode | Cause | Typical Scenario |
|---|---|---|
Abrasive wear | Hard fillers scraping steel | PA66 + 30–50% glass fiber |
Corrosion | Acidic gases from degrading polymer | PVC, POM, or flame-retardant plastics |
Sticking / galling | Plastic affinity for steel | PA, POM, uncoated optical molds |
Thermal fatigue | Repeated heating & cooling cycles | High-cavitation, fast-cycling molds |
A good surface treatment addresses one or more of these—but none does everything.
How it works: In a vacuum, we vaporize a target material (Ti, Cr, Al, N) and deposit it as a thin, hard ceramic layer (2–5 µm).
Common types:
TiN (gold) – HV ~2300, general wear
CrN (silver-gray) – HV ~1800, excellent corrosion resistance
AlTiN (dark violet) – HV ~3500, high-temperature stability
Pros: Extremely hard, low friction (μ=0.3–0.4), low process temperature (<500°C), no distortion.
Cons: Thin layer – poor impact resistance; requires a perfect substrate finish.
Best for: Glass-filled plastics (GF30+), high-gloss molds (coating + post-polish).
How it works: Nitrogen diffuses into the steel surface, forming a hard compound layer (Fe₂-₃N, CrN) and a deep diffusion zone (0.1–0.5 mm).
Types: Gas (slow), Ion/Plasma nitriding (fast, low distortion), Salt bath (effective but toxic).
Hardness: HV 900–1200 (depending on steel).
Pros: Very high wear & fatigue resistance, good anti-galling, minimal distortion, low cost.
Cons: The white layer (compound zone) can be brittle on sharp edges.
Best for: General-purpose molds, slides/lifters, unfilled engineering plastics. The #1 value treatment.
How it works: Electro-deposition of chromium metal (5–50 µm).
Hardness: HV 800–1000.
Pros: Cheap, good corrosion resistance, can repair worn molds.
Cons: Micro-cracks (bad for mirror finishes), hydrogen embrittlement risk, environmental restrictions (Cr6+).
Best for: Low-cost repairs, rust protection on simple tools. Largely replaced by PVD/nitriding in modern shops.
How it works: Amorphous carbon network with diamond-like sp³ bonds.
Friction coefficient: μ = 0.05–0.1 (slipperier than Teflon).
Pros: Incredible anti-sticking properties; no mold release agent needed; excellent for optics.
Cons: Poor thermal stability (<350°C), higher cost.
Best for: Optical lenses (PMMA, PC), molds where sticking is the #1 problem.
How it works: High-temperature (~1000°C) chemical reaction deposits thick (5–20 µm) diamond or TiCN layers.
Pros: Extremely thick, chemically bonded – almost impossible to peel.
Cons: High temperature softens most mold steels (must re-heat-treat), expensive.
Best for: >50% glass fiber, metal powder-filled plastics, ceramic-filled resins.
Ask yourself one question first: What kills my mold fastest?
If your main problem is… | Choose this | Avoid this |
|---|---|---|
High glass fiber wear | CVD diamond / AlTiN (PVD) | Standard nitriding |
Corrosion (PVC, POM, flame retardants) | CrN (PVD) or hard chrome | Gas nitriding (consumes Cr, reduces corrosion resistance) |
Sticking / hard ejection | DLC or Ni-P-PTFE | Uncoated polished steel |
Thermal cracking (heat checking) | Plasma nitriding (diffusion layer stops crack propagation) | Thick hard coatings (they crack first) |
High-gloss / mirror finish | Polished + PVD (AlTiN or CrN) | CVD (too rough) |
Budget / general purpose | Plasma nitriding | Unnecessary exotic coating |
Rule #1 – Substrate matters.
A coating on soft steel (HRC <48) is like armor on a marshmallow. The coating will crack when the steel yields underneath. Use tool steel at ≥52 HRC for PVD/CVD.
Rule #2 – Pre-treatment is 80% of the result.
You cannot coat over grease, burrs, or sharp corners. Sharp edges must be radiused (R > 0.05 mm). Surface finish must match the coating’s requirement (typically Ra < 0.05 µm for PVD).
Rule #3 – Respect the temper temperature.
Never exceed the steel’s last tempering temperature. If your steel was tempered at 520°C, your coating/nitriding must run below that, or the mold will soften and distort.
Problem: SKD11 steel mold worn out after 80,000 cycles. Cavity root rounded off.
Solution: Premium ESR steel + plasma nitriding (0.2 mm case) + AlTiN PVD coating.
Result: 500,000 cycles with <20% of original wear. 6x longer life.
Problem: S136H mold showed pitting corrosion after 100,000 cycles due to HCl gas.
Solution: High-nitrogen stainless steel + low-temperature plasma nitriding (to avoid CrN precipitation).
Result: No pitting after 300,000 cycles. 3x corrosion resistance.
Problem: Mirror-finished cavity required mold release spray every cycle. Scratches appeared on optical surface.
Solution: Ultra-polish (Ra 0.01 µm) + DLC coating.
Result: Friction coefficient dropped from 0.5 to 0.1. Zero mold release needed. Improved light transmission.
There is no magic “one-size-fits-all” coating.
But here’s the practical rule followed by top molders:
For 80% of molds (unfilled plastics, general use): Plasma nitriding → lowest cost, big gain.
For glass-filled or abrasive resins: Nitriding + PVD (AlTiN or CrN) → the industry standard.
For extreme wear (>50% filler): CVD diamond.
For severe sticking or optical parts: DLC.
