Injection Molding Tolerances: The Detail You Must Pay Attention to When Molding

Injection molding tolerances also be known as platic injection molding tolerances, which are a very important part of injection molding design. They are ” given by designer to designed dimensions”. Molding manufacturers should define the plastic injection molding tolerances to made the design dimensions fit the assembly requirements. It is a necessary detail to consider for every molding designer.

Tight tolerances can help designers a lot to develop complex plastic injection parts and products, especially when they are used in high-quality requirements industry such as medical, automotive, or defense applications. There has no chance to making up for mistake, especially when designer design critical-use parts, which the margins are as slim as +/- .001 inches.

How to Make Tie Tolerances During Injection Molding?

If you want to make tight tolerances, you must design them early in the part design phase. Here are some suggestions for you to achieve the tight plastic injection molding tolerances.

Start with design: Molding design engineers must consider the requirements of part geometry, overall size, and wall thickness. These factors will influence tolerance control. The thick walls may have shrink rates within the thick sections, and with the rate, it is difficult to hold tight tolerances, because the variable shrink within the section may change.

Consider the complexity of parts: The correct complex design of parts can make control of tight tolerances. Usually, complex designs have issues such as shrinking and warping. If the issues of complex designs are too lots, the part may not be repeatable. Therefore, it is necessary to consist of product design with manufacturing teams.

Injection Molding Tolerances Guide

There is a brief injection molding tolerances guide, which aims to help you know the tolerances of plastic injection molded parts. This guide is made of dimensional tolerances, straightness/flatness tolerances, hole diameter tolerances, blind hole depths tolerances, concentricity/ovality tolerances, and all of these tolerances were measured by mm.

Dimensional Tolerances

Dimension 1 to 20 (+/-mm) 21 to 100 (+/-mm) 101 to 160 (+/-mm) for each 20mm over 160 add
ABS 0.100 0.150 0.325 0.080
ABS/PC Blend 0.100 0.150 0.325 0.080
GPS 0.075 0.150 0.305 0.100
HDPE 0.125 0.170 0.375 0.100
LDPE 0.125 0.170 0.375 0.100
Mod PPO/PPE 0.100 0.150 0.325 0.080
PA 0.075 0.160 0.310 0.080
PA 30% GF 0.060 0.120 0.240 0.080
PBT 30% GF 0.060 0.120 0.240 0.080
PC 0.060 0.120 0.240 0.080
PC 20% Glass 0.050 0.100 0.200 0.080
PMMA 0.075 0.120 0.250 0.080
POM 0.075 0.160 0.310 0.080
PP 0.125 0.170 0.375 0.100
PP 20% Talc 0.125 0.170 0.375 0.100
PPS 30% GF 0.060 0.120 0.240 0.080
SAN 0.100 0.150 0.325 0.080

Straightness/Flatness Tolerances

Dimension 0-100 (+/- mm) 101-160 (+/- mm)
ABS 0.380 0.800
ABS/PC Blend 0.380 0.800
Acetal 0.300 0.500
Acrylic 0.180 0.330
GPS 0.250 0.380
Mod PPO/PPE 0.380 0.800
PA 0.300 0.500
PA 30% GF 0.150 0.200
PBT 30% GF 0.150 0.200
PC 0.150 0.200
Polycarbonate, 20% Glass 0.130 0.180
Polyethylene 0.850 1.500
Polypropylene 0.850 1.500
Polypropylene 20% Talc 0.850 1.500
PPS 30% GF 0.150 0.200
SAN 0.380 0.800

Hole Diameter Tolerances

Dimension 0-3 (+/-mm) 3.1-6 (+/-mm) 6.1-14 (+/-mm) 14-40 (+/-mm)
ABS 0.050 0.050 0.080 0.100
ABS/PC 0.050 0.050 0.080 0.100
GPS 0.050 0.050 0.050 0.090
HDPE 0.050 0.080 0.100 0.150
LDPE 0.050 0.080 0.100 0.150
PA 0.050 0.080 0.080 0.130
PA 30% GF 0.050 0.050 0.080 0.080
PBT 30% GF 0.050 0.050 0.080 0.080
PC 0.050 0.050 0.080 0.080
PC 20% GF 0.050 0.050 0.080 0.080
PMMA 0.080 0.080 0.130 0.130
POM 0.050 0.080 0.130 0.130
PP 0.050 0.080 0.150 0.150
PP 20% Talc 0.050 0.080 0.150 0.150
PPS 30% Glass 0.050 0.050 0.080 0.080
SAN 0.050 0.050 0.080 0.100

Blind Hole Depths Tolerances

Dimension 1-6 (+/-mm) 6.1-14 (+/-mm) Over 14 (+/-mm)
ABS 0.080 0.100 0.130
ABS/PC Blend 0.080 0.100 0.130
GPS 0.090 0.100 0.130
HDPE 0.100 0.120 0.150
LDPE 0.100 0.120 0.150
PA 0.100 0.100 0.130
PA 30% GF 0.050 0.080 0.100
PBT 30% GF 0.050 0.080 0.100
PC 20% GF 0.050 0.080 0.100
PMMA 0.100 0.100 0.130
POM 0.100 0.100 0.130
PP 0.100 0.120 0.150
PP 20% Talc 0.100 0.120 0.150
PPS 30% Glass 0.050 0.080 0.100
SAN 0.080 0.100 0.130

Concentricity/Ovality Tolerances

Dimension up to 100 (+/-mm)
ABS 0.230
ABS/PC Blend 0.230
GPS 0.250
HDPE 0.250
LDPE 0.250
PA 0.250
PA 30% GF 0.150
PBT 30% GF 0.150
PC 0.130
PC 20% GF 0.130
PMMA 0.250
POM 0.250
PP 0.250
PP 20% Talc 0.250
PPS 30% GF 0.130
SAN 0.230

Leave a Reply

Your email address will not be published. Required fields are marked *