plastic Finish

SPI Mold Finish For Injection Molding Parts

Injection mold are polished as per required finish on injection molded plastic parts. Injection molding replicates the mold finish on plastic part. SPI (Society of Plastic Industry) has defined standard for injection mold finish. Designers specify spi mold finish in part drawing. This article covers various SPI mold finish for injection molded plastic parts.

Finish SPI Standard Finish Method Surface Roughness (Ra Value)
Very High Glossy Finish A1 6000 Grit diamond buff 0.012 to 0.025
High Glossy Finish A2 3000 Grit diamond buff 0.025 to 0.05
Normal Glossy Finish A3 1200 Grit diamond buff 0.05 to 0.1
Fine Semi Glossy Finish B1 600 Grit Paper 0.05 to 0.1
Medium Semi Glossy Finish B2 400 Grit Paper 0.1 to 0.15
Normal Semi Glossy Finish B3 320 Grit Paper 0.28 to 0.32
Fine Matte Finish C1 600 Grit Stone 0.35 to 0.4
Medium Matte Finish C2 400 Grit Stone 0.45 to 0.55
Normal Matte Finish C3 320 Grit Stone 0.63 to 0.70
Satin Textured Finish D1 600 stone prior to dry blast glass bead #11 0.8 to 1.0
Dry Textured Finish D2 400 stone prior to dry blast #240 oxide 1.0 to 2.8
Rough Textured Finish D3 320 stone prior to dry blast #24 oxide 3.2 to 18.0

Material Recommendations

Mold finish does not gives the same results with every material. Below table gives an idea about recommended spi mold finish for given materials.

Rating SPI Finish
X : Not Recommended 1 : Excellent 2: Good 3: Average A1 A2 A3 B1 B2 B3 C1 C2 C3 D1 D2 D3
Material SPI Finish Rating
ABS 3 3 2 2 2 1 1 1 1 1 1 2
Poly Carbonate 3 2 1 2 2 3 3 X X 1 X X
PVC X X X X 3 3 2 2 2 1 1 1
Acrylic 1 1 1 2 2 2 2 2 2 3 3 3
Acetal 3 3 2 1 1 1 1 1 1 1 1
Polyester 3 3 2 1 2 2 1 2 X 1 1
Polyethylene X 3 3 2 2 1 1 1 1 1 1

Conclusion:

To sum up, SPI finish is one of the best way to convey required finish to manufacturer. SPI mold finishes are accepted all around the word. Ra and VDI finish are good alternative to SPI Finish standard.

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