Acier de moule JIS NAK80: Propriétés, Utilisations & Fabrication de moules de haute précision

If you’re searching for a mold steel that delivers exceptionalpolissabilité miroir, stabilité dimensionnelle constante, and easy machining—JIS NAK80 mold steel est l'étalon-or. Largement utilisé dans les applications haut de gamme telles que les moules optiques et les moules pour produits de consommation, cet alliage pré-durci résout les problèmes courants comme une mauvaise finition de surface ou une déformation du moule. Dans ce guide, nous allons décomposer ses propriétés clés, utilisations réelles, étapes de fabrication, and how it compares to other materials—so you can create molds that meet the strictest quality standards.

1. Material Properties of JIS NAK80 Mold Steel

JIS NAK80’s reputation as a premium mold steel comes from its carefully balanced composition and standout properties. Let’s explore these in detail:

1.1 Composition chimique

The elements in JIS NAK80 work together to enhance polishability, dureté, et stabilité dimensionnelle. Below is its standard composition (per JIS G4404):

1.2 Propriétés physiques

These properties determine how JIS NAK80 behaves during mold manufacturing and use—such as heat transfer and shape retention. All values are measured at room temperature unless noted:

• Densité: 7.85 g/cm³ (consistent with most mold steels, making it easy to calculate mold weight).
• Point de fusion: 1450 – 1500 °C (high enough to withstand forging and heat treatment without deformation).
• Conductivité thermique: 32 Avec(m·K) (good heat transfer, ensuring plastic parts cool evenly in injection molds).
• Coefficient de dilatation thermique: 11.8 × 10⁻⁶/°C (depuis 20 à 600 °C; low expansion reduces mold warping during heat cycles).
• Specific Heat Capacity: 470 J/(kg·K) (efficient at absorbing and releasing heat, reducing plastic injection cycle times).

1.3 Propriétés mécaniques

JIS NAK80 is suppliedpre-hardened (ready for machining without extra heat treatment), a huge time-saver for high-precision mold projects. Below are its typical pre-hardened properties:

1.4 Autres propriétés

• Résistance à la corrosion: Bien. Chromium content protects against rust in workshop environments and mild chemical exposure (par ex., plastic additives).
• Résistance à l'usure: Moderate to Good. Suitable for most plastic and die casting applications; for high-wear molds, add a surface coating like nitriding.
• Usinabilité: Excellent. Its pre-hardened hardness (HRC 36–40) and low sulfur content make it easy to mill, percer, and turn—reducing machining time by 25–30% vs. harder mold steels.
• Trempabilité: Excellent. It hardens evenly across thick sections (jusqu'à 100 mm), so large molds (par ex., automotive molds for bumpers) have consistent properties.
• Mirror Polishability: Exceptionnel. Ultra-low sulfur and fine grain structure let it achieve mirror finishes as smooth as Ra ≤ 0.01 μm—critical for optical molds (par ex., objectifs de caméra) or high-end consumer products (par ex., coques pour smartphones).
• Stabilité dimensionnelle: Outstanding. Low thermal expansion and uniform hardening prevent mold warping during machining or use.

2. Applications of JIS NAK80 Mold Steel

JIS NAK80’s mix of polishability, stabilité, and machinability makes it ideal for high-precision mold projects. Voici ses utilisations les plus courantes, avec des exemples réels:

2.1 Optical Molds

• Exemples: Molds for camera lenses, protecteurs d'écran pour smartphones, or optical fibers.
• Why it works: Mirror polishability delivers the ultra-smooth surfaces needed for clear optics. A Japanese optical manufacturer used JIS NAK80 for camera lens molds—polish time reduced by 50% contre. stainless mold steel.

2.2 Plastic Injection Molds

• Exemples: Molds for high-end plastic parts like smartphone casings, contenants cosmétiques, ou des dispositifs médicaux (par ex., seringues).
• Why it works: Dimensional stability ensures part consistency, while polishability eliminates surface defects. A Korean electronics maker used JIS NAK80 for smartphone case molds—part defect rates dropped to 0.1%.

2.3 Consumer Product Molds

• Exemples: Molds for luxury goods (par ex., boîtiers de montre), ustensiles de cuisine (par ex., high-gloss plastic bowls), or toys (par ex., smooth-surface action figures).
• Why it works: Mirror finish meets consumer demand for premium aesthetics. A French cosmetic brand used JIS NAK80 for lipstick tube molds—customer satisfaction with surface quality rose by 90%.

2.4 Automotive and Packaging Molds

• Exemples: Molds for automotive interior parts (par ex., high-gloss dashboard panels) or packaging (par ex., clear plastic food containers).
• Why it works: Fatigue strength handles high production cycles, while stability ensures part uniformity. A German automotive supplier used JIS NAK80 for dashboard molds—mold life increased from 150,000 à 300,000 parties.

3. Manufacturing Techniques for JIS NAK80 Mold Steel

Turning JIS NAK80 into high-precision molds requires careful, specialized steps. Voici une ventilation étape par étape:

1. Fusion: Matières premières (iron, nickel, chrome, etc.) are melted in an electric arc furnace (AEP) at 1550–1650 °C. Strict control ensures ultra-low sulfur and phosphorus content (critical for polishability).
2. Fonderie: Molten steel is poured into ingot molds or continuous casters to form slabs. Refroidissement lent (10–20 °C/hour) prevents internal defects and refines grain structure.
3. Forgeage: Slabs are heated to 1100–1200 °C and pressed/hammered into mold blanks (par ex., 600x600x300 mm for large injection molds). Forging improves toughness and eliminates internal voids.
4. Traitement thermique: The standard cycle for pre-hardened JIS NAK80:
   • Recuit: Heat to 800–850 °C, hold 2–4 hours, cool slowly. Softens steel to HRC 20–22 for initial machining.
   • Trempe: Heat to 880–920 °C, hold 1–2 hours, tremper dans l'huile. Hardens steel to HRC 45–48.
   • Trempe: Reheat to 580–620 °C, hold 2–3 hours, cool. Reduces brittleness and sets final pre-hardened hardness (HRC 36–40).
5. Usinage: Mold blanks are milled, drilled, or turned into mold cavities using CNC machines. Carbide tools are recommended for tight tolerances (±0,001 mm).
6. Polissage: The most critical step for high-precision molds:
   • Start with 400-grit sandpaper to smooth machining marks.
   • Progress to 1000-grit, 3000-grincer, and 8000-grit sandpaper.
   • Finish with diamond paste (1–3 μm) to achieve mirror polish (Ra ≤ 0.01 µm).
7. Traitement de surface (Facultatif):
   • Galvanoplastie: Add a chrome or nickel coating to boost wear resistance (for high-cycle molds).
   • Nitruration: Creates a hard surface layer (HRC 60–65) for die casting molds or high-wear plastic molds.

4. Étude de cas: JIS NAK80 in Optical Lens Molds

A Chinese optical component manufacturer faced a problem: their stainless steel molds for smartphone camera lenses couldn’t achieve the required mirror finish (Ra ≤ 0.01 µm), leading to blurry lenses. They switched to JIS NAK80, and here’s what happened:

• Processus: Mold blanks were pre-hardened to HRC 38, machined to lens cavity geometry (using 5-axis CNC), polished with diamond paste, and coated with an anti-reflective layer.
• Résultats:
  • Achieved consistent mirror finish (Râ 0.008 µm) for every mold—no more blurry lenses.
  • Polish time reduced from 24 heures pour 8 heures (67% amélioration) thanks to JIS NAK80’s fine grain structure.
  • Lens production yield increased from 85% à 99.5% (moins de pièces défectueuses).
• Why it works: Ultra-low sulfur in JIS NAK80 eliminated surface pits, while nickel and vanadium refined the grain structure—allowing the diamond paste to create an ultra-smooth surface.

5. JIS NAK80 vs. Other Mold Materials

How does JIS NAK80 compare to common alternatives for high-precision molds? Let’s evaluate key properties:

Key takeaway: JIS NAK80 is the best choice for molds needing mirror polish and dimensional stability. It’s more machinable than stainless steel (S136) and delivers better polishability than P20—worth the higher cost for high-end applications.

Yigu Technology’s View on JIS NAK80 Mold Steel

Chez Yigu Technologie, JIS NAK80 is our top pick for clients requiring high-precision molds—from optical components to luxury consumer goods. Its unmatched mirror polishability and dimensional stability solve the biggest challenges in premium mold-making: inconsistent finishes and mold warping. We often pair it with our precision polishing services to achieve Ra ≤ 0.008 µm, helping clients meet the strictest quality standards. For businesses focused on quality and customer satisfaction, JIS NAK80 isn’t just a material—it’s an investment in delivering exceptional products.

FAQ About JIS NAK80 Mold Steel

1. Can JIS NAK80 be used for die casting molds (par ex., aluminum or zinc)?

Oui, JIS NAK80 works for die casting molds, but we recommend adding a nitrided surface layer (HRC 60–65) pour augmenter la résistance à l'usure. Without nitriding, its moderate wear resistance may limit life in high-volume die casting (sur 100,000 cycles).

2. Is JIS NAK80 suitable for molds that process corrosive plastics (par ex., PVC)?

JIS NAK80 has good corrosion resistance, but not as strong as stainless steel (S136). For PVC molds (which release corrosive gases), we suggest either electroplating JIS NAK80 with chrome or switching to S136 if long-term corrosion protection is critical.

3. Do I need special tools to polish JIS NAK80 to a mirror finish?

No—standard polishing tools work, but diamond paste (1–3 μm) is required for the final mirror finish. We recommend using soft polishing pads (par ex., wool or felt) to avoid scratching the steel, and working in small, circular motions to ensure even polishing.