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Core line, represented 25+ years
Overmolding
Overmolding molds a second material over a first, usually a soft TPE over a rigid plastic substrate, to make grips, seals, bumpers and two-color parts in one piece. It is done by pick-and-place into a second mold at moderate volume, or by two-shot molding in one machine above roughly 100,000 parts a year. TPE layers are typically 0.040–0.120 in (1–3 mm) thick.
A method under plastic injection molding, alongside insert molding.
How does overmolding work?
The schematic plays while it is on screen. Pick a phase to hold it there.
- 1
Mold the substrate
The rigid first shot, such as PP, ABS, PC or nylon, is molded in the first cavity.
- 2
Transfer
In pick-and-place, the substrate moves by hand or robot to a second mold. In two-shot, the mold rotates the substrate to the second cavity in the same press.
- 3
Close on the substrate
The second cavity seals on the substrate with sharp shutoffs so the soft material only fills where intended.
- 4
Inject the overmold
The TPE fills over the substrate, bonding chemically if the materials are compatible and locking mechanically through holes and undercuts.
- 5
Cool and eject
The finished two-material part ejects. Two-shot parts leave the press complete every cycle.
What can overmolding hold?
Typical ranges across principals. Your drawing, material and quantity set the real numbers in the quote.
| Overmold thickness | 0.040–0.120 in (1–3 mm) typical |
|---|---|
| Soft material hardness | 30–90 Shore A TPE, TPU or LSR |
| Substrate wall | 0.060–0.150 in (1.5–3.8 mm) |
| Tolerance on overmold | ±0.005 in (±0.13 mm) |
| Two-shot tooling | Often 1.5–2× a single-shot mold |
| Tooling lead time | 6–12 weeks pick-and-place; 10–16 weeks two-shot |
When is overmolding the right call?
Best for
- Soft-touch grips on tools, handles and housings
- Integrated seals and gaskets that cannot fall out
- Two-color parts and bumpers
- Removing an assembly step and a separate part number
Pick something else when
- Seals that must be replaced in service: a separate gasket
- Low volume under a few thousand parts: an assembled or adhesive-backed pad
- Metal inside plastic: insert molding
How does overmolding compare with the alternatives?
Typical values. Pick an alternative to see where each one wins.
Pick-and-place overmolding compared with
Pick-and-place overmoldingTwo-shot molding
- Precisionlooser → tighter
- Volume it pays atone-offs → millions
- Upfront toolingnone → heavy
- Shape freedomnarrow → wide
Pick-and-place overmolding · pick it when
Soft-touch grips and seals over a rigid part at moderate volume.
Two-shot molding · pick it when
Two materials at high volume, with a chemical bond made while the first shot is still hot.
MethodTypical toleranceEconomic volumeToolingLead time
- Pick-and-place overmoldingthis pageTypical tolerance±0.005 in (±0.13 mm) on the overmoldEconomic volume1,000–250,000 parts a yearToolingTwo molds, each $5,000–$60,000Lead time6–12 weeks for tooling
- Typical tolerance±0.003–0.005 in (±0.08–0.13 mm)Economic volume100,000 parts a year and upToolingOften 1.5–2× a single-shot moldLead time10–16 weeks for tooling
- Typical toleranceStack-up of both partsEconomic volumeAny volumeToolingTwo simple toolsLead timeStandard molding lead times
- Typical tolerance±0.003–0.005 in (±0.08–0.13 mm) to the insertEconomic volume5,000 parts and upTooling$8,000–$80,000+, a standard mold plus insert locatorsLead time5–12 weeks for tooling
Which design rules keep overmolding affordable?
Rules of thumb principals apply at DFM review. Each one has a reason.
RuleTargetWhy
- Material pairing
- Choose a TPE grade made for the substrate
- Chemical bonding only happens between compatible pairs, such as SEBS on PP or TPU on PC/ABS.
- Mechanical lock
- Through holes or undercuts
- Holds the overmold if the chemical bond is weak, and stops peeling at edges.
- Overmold thickness
- 0.040–0.120 in (1–3 mm), uniform
- Thin areas short-shot; thick areas sink and slow the cycle.
- Shutoff
- Sharp edge 0.015–0.030 in (0.4–0.75 mm) wide
- A clean shutoff stops soft material from flashing onto the substrate.
- Edge detail
- End the TPE in a groove, not a flat face
- A recessed edge resists peeling and hides small flash.
What drives the cost of overmolding?
In order of impact.
- 1
Two molds or one rotary mold
Pick-and-place needs two tools; two-shot needs one complex rotary tool and a two-barrel press.
- 2
Transfer labor
Pick-and-place adds a handling step per part. Two-shot removes it.
- 3
Soft material cost
Specialty bondable TPE grades cost more per pound than commodity resins.
- 4
Scrap
Bad overmolds scrap the substrate too.
Budgetary estimate for the rigid substrate, before the overmold, from the same estimator as the part builder. Change a size, the quantity or the material and the price updates.
Housing · Injection molding
Order total $24,973
- Tooling
- $17,029
- one-time, spread over the order
- Piece price
- $0.76
- before setup + tooling
- Lead time
- 6–9 weeks
- to first production
Size
Drag a row to adjust · click to type
Length140140 mm
Width90.090.0 mm
Wall2.202.20 mm
Quantity
Price per part falls as volume rises
Exact quantity1000010000 pcs
Material
Design checks pass
Open in builderBudgetary estimate for a representative part. Firm quotes come from principals after drawing review.
Overmolding questions
What is the difference between overmolding and two-shot molding?
Two-shot is one way to overmold. Pick-and-place overmolding molds the substrate, then moves it to a second mold. Two-shot molding does both shots in one press and one rotating mold, which costs more up front and less per part at high volume.
Which materials bond in overmolding?
TPE grades are formulated to bond with specific substrates: SEBS-based TPE on PP, and modified TPE or TPU on ABS, PC and PC/ABS. Nylon needs special grades. The TPE supplier's pairing chart sets the choice.
How thick should an overmold be?
Typically 0.040–0.120 in (1–3 mm), and as uniform as possible. Soft-touch grips often sit near 0.060 in (1.5 mm).
What volume justifies two-shot tooling?
Usually above about 100,000 parts a year. Below that, pick-and-place overmolding with two simpler molds tends to cost less in total.
Quote overmolding with a rep.
Send a STEP file and drawing. A rep routes the RFQ to principals that run this method every day, and brings back firm quotes.