Design Guidelines: Overmolding & Insert Molding

Our basic guidelines for overmolding and insert molding include important design considerations to help improve part manufacturability, enhance cosmetic appearance, and reduce overall production time.

Size

Maximum Dimensions

SIZE 8 in. x 16 in. x 8 in.
VOLUME 59 cu. in.
DEPTH 4 in. from parting line
Up to 8 in. if the parting line can pass through the middle of the part
PROJECTED MOLD AREA 175 sq. in. (plastic)
48 sq. in. (silicone rubber)
SIZE 203.2mm x 406.4mm x 203.2mm
VOLUME 966837 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 112903 sq. mm (plastic)
30968 sq. mm (silicone rubber)

Height may be limited if using a silicone as the overmold material, and deeper parts are limited to a smaller outline. Minimum part volume is 0.025 cu. in. (40.98 cu. mm). With substrate molds, we can maintain a machining tolerance of ±0.003 in. (0.08mm) with an included resin tolerance that can be greater but no less than 0.002 in./in. (0.0508mm/mm). With thermoplastic overmolds, tolerances remain the same as substrate molds, however, if the overmold is LSR, then tolerances shift to 0.025 in./in. (0.635mm).


Insert Molding Capabilities

Instead of a mold that produces a final part using two separate shots like overmolding, insert molding generally consists of a preformed part—often metal—that is loaded into a mold, where it is then overmolded with plastic to create a part with improved functional or mechanical properties. We currently accept inserts from PEM, Dodge, Tri-Star, Spirol, and Tappex.

One way insert molding is used is with threaded inserts, which reinforce the mechanical properties of plastic parts’ ability to be fastened together, especially over repeated assembly. Bushings and sleeves are another great way to increase part durability for mating components that need more abrasion resistance due to moving parts.

a three-step process to insert molding

A threaded insert is placed atop a mold core where plastic is molded over it to form the final component.


Materials

  • ABS
  • Acetal
  • HDPE
  • LCP
  • PEI
  • PMMA
  • Polycarbonate
  • Polypropylene
  • PPA

 

  • PPS
  • PS
  • PS
  • PSU
  • TPE
  • TPU
  • PEEK
  • Liquid Silicone Rubber

VIEW MATERIALS >

a two-material overmolded part

Overmolding Material Bonding

Chemical bonding between overmolded materials is possible, but material compatibility should be considered in order to achieve desired bond strength. Incorporation of an adequate mechanical bond is strongly recommended if bonding is critical to your application. An undercut is a good example of a mechanical bond.

 

Substrate Material
Overmold Material ABS Lustran ABS/PC Cycolo C2950-111 PC Lexan
940-701
PBT Valox
357-1001
PP Profax 6323 Nylon 66
Zytel 103 HSL NC010
TPU - Texin
983-000000
C C C C M M
TPV - Santoprene
101-87
M M M M C M
TPE - Santoprene
101-64
M M M M C M
LSR - Elastosil
3003/30 A/B
- - M M - M
TPC - Hytrel 3078 C C C C M M
TPE-Versaflex OM
1060X-1
C C C M M M
TPE-Versaflex OM
6240-1/td>
M M M M M C
TPE-Versaflex OM
6258-1
M M M M M C
TPE-Versaflex OM
1040X-1
C C C M M M

M = mechanical bond (recommended)
C = chemical bond

color options for overmolded parts

Surface Finishes

FINISH DESCRIPTION
PM-F0 non-cosmetic, default
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

 

build technician applies surface finish to 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 helps facilitate ejection of a part from a mold, and improves overall moldability.


Undercuts

Maximum Side Core Dimensions

WIDTH HEIGHT FULL
< 8.419 in. < 2.377 in. < 2.900 in.
WIDTH HEIGHT PULL
<213.84mm <60.38mm <73.66mm

creating undercuts for injection molding

Undercuts, such as those shown, 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.
Polystynene 0.035 in. - 0.150 in.
Polyurethane 0.080 in. - 0.750 in.

* The 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 1.905mm - 25.4mm
Nylon 0.762mm - 2.921mm
Polycarbonate 1.1016mm - 3.81mm
Polyester 0.635mm - 3.175mm
Polyethylene 0.0762mm - 5.08mm
Polyphenylene Sulfide 0.508mm - 4.572mm
Polypropylene 0.635mm - 3.81mm
Polystynene 0.89mm - 3.81mm
Polyurethane 2.032mm - 19.05mm

* The table is adapted from manufacturingcenter.com.


avoiding cosmetic defects like sink or warp in overmolded parts

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

Proper placement of corner radii can improve the moldability of parts.


press operator examines part

Free moldability analysis within hours

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