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Plastic Injection Molding

Protomold provides quick-turn thermoplastic injection molding often used for prototyping, bridge tooling and short-run manufacturing up to 10,000+ parts. We use advanced aluminum alloy molds that allow us to eliminate the costly and time-consuming custom engineering that normally goes into the development of tooling. Protomold offer hundreds of engineering-grade resins that produce molded parts that are strong and can have excellent finishes.

Quick-turn injection molding uses the industry standard production process for parts, so it’s an excellent predictor of manufacturability when you move to large-scale production. At Protomold, we support an ever-increasing maximum part size and degree of complexity, and continue to introduce new materials that help designers and engineers make better products.
25 to 10,000+ parts
Shipped in 1 to 15 days
Molds start at $1,495
PROCESS
DESIGN GUIDELINES
Fundamentals of Molding

Design Guidelines

Size

The maximum part outline that can be molded is approximately 18.9 in. (480 mm.) by 29.6 in. (751 mm.) or roughly equivalent to 175 sq. in. (1,129 cm2). A maximum part volume of approximately 59 cu. in. Depth up to 4 in. (101 mm.) from the parting line with 3 degrees of draft, or up to 8 in. (202 mm.) total if the parting line can pass through the middle of the part, inside and outside. Deeper parts are limited to a smaller outline.
Size
Protomold size

Draft

A taper applied to the faces of the part that prevent them from being parallel to the motion of the mold opening is called draft. This keeps the part from being damaged due to scraping as the part is ejected out of the mold. Recommended draft:
  • 0.5 degrees on all vertical faces is strongly advised.
  • 2 degrees works very well in most situations.
  • 3 degrees is minimum for a shutoff (metal sliding on metal).
  • 3 degrees is required for light texture (PM-T1).
  • 5 or more degrees is required for heavy texture (PM-T2).
Draft
Protomold undrafted
Undrafted
Protomold drafted
Drafted
Protomold undrafted
Undrafted
Protomold drafted
Drafted

Tolerances

Typically, Protomold can maintain a machining tolerance of ±.003 in. (.08 mm.) with an included resin tolerance that can be greater than but no less than ±.002”in/in (.002mm/mm.).

Wall thickness

With injection-molded parts, observing proper (and uniform) wall thickness helps parts avoid potential issues such as sink marks and warpage. Recommended thicknesses vary by material:
Resin
Inches
ABS
0.045 - 0.140
Acetal
0.030 - 0.120
Acrylic
0.025 - 0.500
Liquid crystal polymer
0.030 - 0.120
Long-fiber reinforced plastics
0.075 - 1.000
Nylon
0.030 - 0.115
Polycarbonate
0.040 - 0.150
Polyester
0.025 - 0.125
Polyethylene
0.030 - 0.200
Polyphenylene sulfide
0.020 - 0.180
Polypropylene
0.025 - 0.150
Polystyrene
0.035 - 0.150
Polyurethane
0.080 - 0.750
The table* shows wall thicknesses that Protomold recommends according to resin. Please note that thin walls only work on small parts and thicker walls are required where the resin has a long way to flow. Protomold makes parts with dimensions of about 0.25 in. to 18.9 in. (6.3 mm. to 480 mm.) or more.
*Adapted from www.manufacturingcenter.com.
Wall thickness
Protomold wall thickness

Surface finish

A number of standard finishes are available for injection-molded parts at Proto Labs. Our current finishes include
non-cosmetic, low-cosmetic and EDM finishes; bead-blast texturing; and high-end mold polishing.

Standard finishes (from least to most costly):
PM-F0:
Non-cosmetic: finish to Protomold discretion
PM-F1:
Low-cosmetic: most toolmarks removed
PM-F2:
Non-cosmetic: Protomold discretion, EDM finish and/or toolmarks permissible
SPI-C1:
600 grit stone, 10-12 Ra
PM-T1:
Protomold texture, SPI-C1 followed by light bead blast
PM-T2:
Protomold texture, SPI-C1 followed by medium bead blast
SPI-B1:
600 grit paper, 2-3 Ra
SPI-A2:
Grade #2 Diamond Buff, 1-2 Ra
*“PM” in the table signifies a surface finish adjusted to fit the quick-turn injection-molding process, where SPI (The Society of the Plastics Industry) denotes an industry-standard finish.
Surface finish
Protomold PM-F0 finish
PM-F0
Protomold SPI-A2 finish
SPI-A2
Protomold T2 finish
PM-T2
Protomold PM-F0 finish
PM-F0
Protomold SPI-A2 finish
SPI-A2
Protomold T2 finish
PM-T2

Radii

Because Protomold employs an automated CNC-milling process to make the mold for your parts, some part
corners will end up with a radius rather than a sharp edge. This does not usually require a change to the model,
but the designer is made aware of these radii before the mold is made.
Radii
Protomold radii

Ejector pins

The Protomold injection-molding process uses ejector pins of various sizes to push the plastic part out of the mold
after it has solidified. The sizes and arrangement of these pins are selected to minimize the impact on your part
design. Ejector pins range in size from .063 in. (1.6 mm.) to 0.5 in. (12.7 mm), with sizes larger than 0.063
in. (0.158 cm.) preferred.
Ejector pins
Protomold ejector pins

Undercuts

Our molding process supports simple undercuts in your part geometry. Maximum side core dimensions:
Width
Height
Pull
≤ 8.419 in.
≤ 2.377 in
≤ 2.900 in.
≤ 213.84 mm.
≤60.38 mm.
≤73.66 mm.
Undercuts
Protomold undercuts

Materials

Protomold stocks hundreds of thermoplastic resins that offer a variety of benefits for many different applications
and industries. See full list of materials.
  • ABS
  • ABS/PC
  • Acetal
  • Acetal Copolymer
  • Acetal Homopolymer
  • ETPU
  • HDPE
  • LCP
  • LDPE
  • LLDPE
  • Nylon 6
  • Nylon 6/12
  • Nylon 66
  • PBT
  • PC/PBT
  • PEEK
  • PEI
  • PET
  • PETG
  • PMMA
  • Polycabonate
  • Polypropylene
  • PPA
  • PPE/PS
  • PPS
  • PS
  • PSU
  • SB
  • TPE
  • TPU
  • TPV