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VDI 3400 is a surface texture standard that assigns numerical values to different levels of mold roughness, ranging from smooth (near-mirror) finishes to coarse textures. These textures are transferred to plastic parts during injection molding, affecting both appearance and performance.
✔ Standardized Roughness Grades – Ranging from VDI 10 (smoothest) to VDI 45 (roughest).
✔ Common Applications – Used in automotive, consumer electronics, and medical device industries.
✔ Replaces Subjective Descriptions – Provides measurable benchmarks for texture specifications.
The table below shows typical VDI grades and their applications:
| VDI Grade | Roughness (Ra, μm) | Surface Appearance | Common Uses |
|---|---|---|---|
| VDI 10-12 | 0.4 - 0.8 | Mirror-like finish | High-gloss automotive trims, cosmetic packaging |
| VDI 15-18 | 0.9 - 1.2 | Slight matte finish | Electronics (laptop lids, smartphone cases) |
| VDI 21-24 | 1.3 - 2.0 | Soft-touch, fine grain | Medical devices, appliance panels |
| VDI 27-30 | 2.1 - 3.2 | Leather-like texture | Car interiors (dashboards, door handles) |
| VDI 33-45 | 3.3 - 6.3+ | Heavy grip texture | Tool handles, industrial equipment |
To achieve VDI-standard textures, mold manufacturers use different surface treatment techniques:
Uses acid to create micro-pits on the mold surface.
Cost-effective but less precise than laser methods.
High-precision CNC lasers engrave detailed patterns.
Ideal for complex designs (e.g., 3D wood grain, carbon fiber effects).
Used for hard metals like tool steel.
Produces uniform textures with high durability.
✔ Consistency – Ensures repeatable surface finishes across production batches.
✔ Better Aesthetics – Eliminates guesswork in texture matching.
✔ Functional Benefits – Improves grip, reduces fingerprints, or hides molding defects.
✔ Global Recognition – Widely accepted in Europe, Asia, and increasingly in North America.
| Standard | Region | Key Difference |
|---|---|---|
| VDI 3400 | Europe/Germany | Numeric grades (10-45) for textures |
| SPI (A-D) | USA | Letters (A=glossy, D=rough) |
| Ra (μm) | Universal | Direct roughness measurement |
Example: A "VDI 24" finish is roughly equivalent to SPI-B (semi-gloss) or Ra 2.0 μm.
Automotive: VDI 30 for leather-grain dashboards.
Electronics: VDI 18 for fingerprint-resistant laptop cases.
Medical: VDI 15 for smooth, easy-to-clean surfaces.
VDI 3400 provides a scientific, repeatable method for defining mold surface textures in injection molding. By specifying a VDI grade, manufacturers can ensure that plastic parts meet both aesthetic and functional requirements.
