July 14, 2022

How to define the surface finish for injection molded parts

blog injection molding

Some companies have troubles to define what their product surface should be, or how to describe precisely what exactly they want to the injection mold supplier, mostly they will just say matt or polish, actually this is not clear enough to define the product surface, there are many standards for the polish or matt, and some unique patterns we call it texture.

Here is an overview of SPI-SPE standard for polishing surface

SPI Description Ra
in µm
A-1 Diamond
buff grade 3
– 0.025
mirror or optical finishes. Most time consuming. Steel grade important to
A-2 Diamond
buff grade 6
– 0.05
A-3 Diamond
buff grade 15
– 0.076
B-1 600
grit paper
– 0.076
all tool and machining marks. Provides good mold release. Light reflecting
finish on molded part, some sheen.
B-2 400
grit paper
– 0.127
B-3 320
grit paper
– 0.25
C-1 600
– 0.30
Remove all tool and machining marks. Provides good
mold release. Mute finish on molded part, no sheen.
C-2 400
– 0.71
C-3 320
– 1.07
D-1 Dry
blast glass bead 11, 200 distance at 0.7 Mpa; 5 sec
– 0.30
decorative finishes. Often used for die-cast and thermoset cooling. Helps
hide shrink marks and other imperfections. Dull, non reflecting finish on
molded or cast part.
D-2 Dry
blast 240 oxyde, 125 distance at 0.7 Mpa; 5 sec
– 0.81
D-3 Dry
blast 240 oxyde, 150 distance at 0.7 Mpa; 5 sec
– 5.84

Here is VDI standard for matt surface, Matt surface is created by erosion process, it is a light and even textured surface.
VDI standard for matt surface

It can be also unique patterns, there are many standards, mostly popular and widely recognized are MOLD-TECH and YS
YS-texture spec

Knowing these standards, you are able to communicate professionally with your injection mold supplier, like ACO Mold.

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