Design Guidelines: Plastic Injection Molding

Our basic guidelines for plastic injection molding include important design considerations to help improve part moldability, enhance cosmetic appearance, and reduce overall production time.

Size

Maximum Dimensions

SIZE 18.9 in. x 29.6 in. x 8 in.
VOLUME 59 cu. in.
DEPTH 4 in. from parting line
Up to 8 in. if parting line can pass through the middle of the part
PROJECTED MOLD AREA 175 sq. in.
SIZE 480mm x 751mm
VOLUME 966,837 cu. mm

DEPTH

101mm from parting line
Up to 203.2mm if the parting line can pass through the middle of the part
PROJECTED MOLD AREA 112,903 sq. mm

Typically, Proto Labs can maintain a machining tolerance of +/- 0.003 in. (0.08mm) with an included resin tolerance that can be greater than but no less than +/- 0.002 in./in. (0.002mm/mm).


Materials

  • ABS
  • ABS/PC
  • Acetal
  • Acetal Copolymer
  • Acetal Homopolymer
  • ETPU
  • HDPE
  • LCP
  • LDPE
  • LLDPE
  • Nylon 6
  • Nylon 5/12
  • PBT
  • PC/PBT
  • PEEK
  • PEI
  • PET
  • PETG
  • PMMA
  • Polycarbonate
  • Polypropylene
  • PPA
  • PPE/PS
  • PS

VIEW MATERIALS >

color resins for plastic injection molding prototyping

Surface Finishes

FINISH DESCRIPTION
PM-F0 non-cosmetic

PM-F1

low-cosmetic, most toolmarks removed
PM-F2 non-cosmetic, EDM permissible
SPI-C1 600 grit stone, 10-12 Ra
PM-T1 SPI-C1 + light bead blast
PM-T2 SPI-C1 + medium bead blast
SPI-B1 600 grit paper, 2-3 Ra
SPI-A2 grade #2 diamond buff, 1-2 Ra
adding surface finish to a mold

Draft

VERTICAL FACES
0.5°
MOST SITUATIONS
MINIMUM FOR SHUT OFF
MINIMUM FOR LIGHT TEXTURE (PM-T1)
MINIMUM FOR LIGHT TEXTURE (PM-T2) 5°+
adding draft to injection-molded parts

Adding draft angles to design, as shown on the right, helps facilitate ejection of a part from a mold, and improves overall moldability.


Undercuts

 Maximum Side Core Dimensions

WIDTH HEIGHT PULL
< 8.419 in. < 2.377 in. < 2.875 in.

 Maximum Side Core Dimensions

WIDTH HEIGHT

PULL

< 213.84mm < 60.38mm < 73.66mm
achieving undercuts with injection molding

Undercuts, such as the one shown on the left, can complicate and, in some cases, prevent part ejection, so eliminate them if possible.


Wall Thickness

MATERIAL RECOMMENDED WALL THICKNESS
ABS 0.045 in. - 0.140 in.
Acetal 0.030 in. - 0.120 in.
Acrylic 0.025 in. - 0.500 in.
Liquid Crystal Polymer 0.030 in. - 0.120 in.
Long-Fiber Reinforced Plastics 0.075 in. - 1.000 in.
Nylon 0.030 in. - 0.115 in.
Polycarbonate 0.040 in. - 0.150 in.
Polyester 0.025 in. - 0.125 in.
Polyethylene 0.030 in. - 0.200 in.
Polyphenylene Sulfide 0.020 in. - 0.180 in.
Polypropylene 0.035 in. - 0.150 in.
Polystyrene 0.035 in. - 0.150 in.
Polyurethane 0.080 in. - 0.750 in.

 Table is adapted from manufacturingcenter.com.

MATERIAL

RECOMMENDED WALL THICKNESS

ABS

1.143mm - 3.556mm

Acetal

0.762mm - 3.048mm

Acrylic 0.635mm - 12.7mm
Liquid Crystal Polymer 0.762mm - 3.048mm
Long-Fiber Reinforced Plastics 1.905m - 25.4mm
Nylon 0.762mm - 2.921mm
Polycarbonate 1.016mm - 3.81mm
Polyester 0.635mm - 3.175mm
Polyethylene 0.762mm - 5.08mm
Polyphenylene Sulfide 0.508mm - 4.572mm
Polypropylene 0.635mm - 3.81mm
Polystynene 0.889mm - 3.81mm
Polyurethane 2.032mm - 19.05mm

 Table is adapted from manufacturingcetner.com.

injection molding cosmetic defects like sink and warp

The top row represents a part designed with thick features and the resulting sink once molded. The middle row also shows a part designed with thick features, but this time the warp that occurs once molded. The bottom row demonstrates how coring out thick features helps create an optimally molded part.


Radii

Some part corners will have a radius rather than a sharp edge since we use an automated CNC milling process to make the mold for your parts. This typically does not require a change to your model, but resulting radii are identified before the mold is milled.

molding a radiused corner

press operator examines part

Free moldability analysis within hours

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