Custom Overmolding Solutions

Combine materials seamlessly. Reduce costs. Deliver exceptional products.

Professional overmolding services for dental, medical gas equipment, and industrial OEM brands. Bond TPE, TPU, LSR, and rigid plastics into one integrated part — eliminate assembly, improve ergonomics, and lower total cost per unit.

29 Years Injection Molding Experience Substrates: PA · PC · ABS · PP Overmolds: TPE · TPU · LSR · Silicone ISO 9001 Quality Practices

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What is Overmolding?

Overmolding is a two-stage injection molding process that bonds two materials — typically a flexible elastomer (like TPE or TPU) over a rigid plastic or metal substrate — into one fully integrated component. The result is a single part that combines the strength of a hard material with the grip, cushion, or seal of a soft one, all without the cost and complexity of post-mold assembly.

Overmolding is widely used for tool handles, medical device grips, gas regulator handwheels with soft-touch surfaces, and any product where ergonomics, sealing, or vibration damping matter. It is often compared to insert molding — the key difference is that overmolding bonds plastic to plastic (or plastic to prepared metal), while insert molding bonds plastic around a pre-made metal insert.

Problems Overmolding Solves
Eliminates multi-step assembly and adhesive bonding
Improves grip, comfort, and tactile experience
Reduces part count, BOM complexity, and labor cost
Lowers total cost per unit at volume
Improves sealing, vibration damping, and impact resistance
Enables multi-color and multi-material aesthetics

Comparison diagram showing separate plastic and metal parts on the left versus a single integrated overmolded assembly on the right, illustrating how overmolding consolidates multiple components into one part

Why Choose Weilin for Overmolding

From material compatibility analysis to final packaging, Weilin manages every stage of your overmolding project — with engineering support, honest DFM feedback, and a dedicated project manager from quote to delivery.

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Seamless Integration

Fuse multiple materials mechanically or chemically into one part — no secondary assembly, no adhesives, no fasteners.

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Material Flexibility

We work with TPE, TPU, TPV, LSR, nylon, PP, PC, ABS, and many engineered resins. Our team recommends the right combination for bond strength, cost, and performance.

Cost Efficiency

Consolidating multiple parts into one overmolded component reduces labor, assembly time, inventory, and logistics cost — especially at medium and high volumes.

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Superior Performance

Better grip, shock absorption, sealing, and impact resistance than equivalent multi-part assemblies. Soft-touch surfaces feel premium and last longer.

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Fast Turnaround

Prototypes in as little as 15 days. Production tooling typically 4–6 weeks. Rush timelines available for time-critical programs.

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Expert Support

Frank personally reviews every design in SolidWorks. Free DFM analysis with every quote, and engineering validation from first sample through production.

Common Overmolding Applications

Overmolding is the process of choice whenever a product needs both rigidity and a soft-touch, sealing, or ergonomic surface. Here are the product categories where we see the most demand.

Medical Device Handles & Grips

Dental instrument handles, patient-contact surfaces, diagnostic device grips, and sealing components. LSR (liquid silicone rubber) is the standard for biocompatible and autoclavable applications; medical-grade TPE is used for less demanding uses. Learn more about our medical plastic parts.

Common substrates: Medical-grade PC, PEI, Polysulfone
Common overmolds: LSR, medical-grade TPE, medical silicone

Medical Gas Equipment Components

Oxygen regulator handwheels, flowmeter grips, gas manifold seals, and cylinder valve ergonomic surfaces. A rigid nylon or PA+GF30% substrate provides structural strength; a TPE or TPU overmold provides grip and vibration damping under high-torque rotation. See our medical gas equipment components.

Common substrates: PA6, PA66+GF30%, POM
Common overmolds: TPE, TPU

Tool & Equipment Handles

Hand tools, power tools, and industrial equipment. A rigid nylon or ABS substrate provides structure; a TPE or TPU overmold provides grip, comfort, and vibration damping. Shore A 40–80 hardness is typical for comfortable grip.

Common substrates: ABS, Nylon (PA6, PA66), PC
Common overmolds: TPE, TPU, SEBS

Seals, Gaskets & Vibration Isolators

Fluid handling components, gas equipment fittings, industrial gaskets, and vibration isolators. TPV is the standard for chemical and temperature resistance; LSR is preferred where food or medical contact is required.

Common substrates: PP, Nylon (glass-filled), PBT
Common overmolds: TPV, LSR, EPDM-based TPE

Overmolding Material Selection Guide

Material selection is one of the most critical factors in overmolding success. The table below compares the most commonly used overmolding materials — their properties, applications, and ideal use cases.

Material	Key Properties	Common Applications	Bonding Type	Temperature Range	Hardness Range	Best For
TPE / TPU	Excellent flexibility, grip, bonding	Handles, grips, seals, medical device surfaces	Chemical + Mechanical	-40 °C to 100 °C	Shore A 30–95	Soft-touch grip, ergonomic comfort
TPV	Superior chemical resistance	Industrial seals, gas equipment gaskets	Mechanical (recommended)	-60 °C to 135 °C	Shore A 35–90	Chemical exposure, outdoor use
LSR (Liquid Silicone Rubber)	Medical-grade, heat-resistant, biocompatible	Medical devices, food-safe products	Mechanical (recommended)	-60 °C to 200 °C	Shore A 10–80	Biocompatibility, precision, sterilization
PC (Polycarbonate)	High impact strength, transparent	Device housings, transparent parts	Chemical + Mechanical	-40 °C to 130 °C	Shore D 80+	Impact protection, aesthetics
Nylon (PA)	High strength, wear-resistant	Gas regulator parts, industrial tools	Chemical + Mechanical	-40 °C to 150 °C	Shore D 70–85	High-load applications
PP (Polypropylene)	Low cost, lightweight, autoclave-compatible	Dental consumables, medical containers	Mechanical (recommended)	-20 °C to 100 °C	Shore D 65–75	Cost-sensitive, high-volume

View our complete material guide →

Overmolding Design Guide

Great overmolding begins at the CAD stage. Follow these guidelines to maximize bond strength, reduce cycle time, and avoid common molding defects.

Wall Thickness
Optimal: 1.5–3 mm (0.060"–0.120")
Why: Ensures proper material flow, bonding, and reduces shrinkage
Rule: Overmold should be thinner than substrate to prevent warpage

Corners & Radii
Minimum radius: 0.5 mm (0.020")
Purpose: Reduces localized stress, improves mold longevity
Avoid: Sharp corners — they cause cracking and poor finish

Part Size Limits
Max part size: 480 × 752 × 203 mm
Min part volume: 0.025 cu.in. (41 cu.mm)
Depth limit: 100 mm (4") from parting line
Projected area: Up to 175 sq.in.

Aluminum overmolding tools and molds used for custom overmolded plastic parts production

Tolerance Capabilities

Tolerance Type	Standard Plastic	Liquid Silicone Rubber
Plastic Substrate	±0.003" (0.08 mm)	±0.003" (0.08 mm)
Dimensional Tolerance	±0.002"/in. (0.002 mm/mm)	±0.025"/in. (0.025 mm/mm)

View our complete design guide →

Our Overmolding Process — From Design to Delivery

You get the expertise of an established manufacturer, the personal attention of a dedicated partner, and the cost-efficiency that drives your competitive advantage.

3–5 DAYS

Design Review

Our engineering team validates your design for manufacturability — checking wall thickness, radii, material compatibility, and overall geometry.

Check wall thickness, radii, and material compatibility
Identify potential issues before tooling begins
Provide free DFM (Design for Manufacturing) feedback
Optimize for cost and performance

✓ Result: Approved design ready for production

7–14 DAYS

Mold Engineering

Precision tooling with optimal material flow design.

Advanced CAD simulation for mold performance
Strategic cooling and venting system design
Material flow analysis to prevent defects
Aluminum or steel mold fabrication with tight tolerances

✓ Result: Production-ready molds tested and validated

2–3 DAYS

Material Bonding Setup

Engineer the perfect mechanical or chemical bond between substrate and overmold.

Assess material compatibility (substrate + overmold)
Design surface preparation or treatment if needed
Configure press settings for optimal bonding
Create detailed process specifications

✓ Result: Proven bonding strategy for reliable assembly

5–7 DAYS

Prototype Run

Small batch testing and validation before full production commitment.

First production run (50–100 units typical)
In-process quality checks
Physical testing: bond strength, dimensional accuracy
Visual inspection and final adjustments
Your approval before full production

✓ Result: Sample parts approved for mass production

ONGOING

Production & QA

Full-scale manufacturing with rigorous quality control from start to finish.

100% dimensional inspection via CMM or automated checks
Bond strength verification sampling
Material traceability tracking (lot numbers documented)
Final packaging and delivery
Batch production records and material certificates with every shipment

✓ Result: On-time delivery of high-quality overmolded parts

Ready to Start Your Overmolding Project?

Send us your CAD files and get a detailed quote within 24 hours — including free DFM feedback and a material recommendation.

Get a Quick Quote →

Overmolding FAQs

Common questions about overmolding costs, materials, minimum orders, and how the process compares to alternatives.

What's the difference between overmolding and insert molding?

Both processes bond two materials into a single part, but they start from different places. Insert molding begins with a pre-made component — usually a metal insert like a threaded boss, pin, or electrical contact — that's placed into the mold cavity before plastic is injected around it. Overmolding begins with a plastic substrate (the first shot) that's then overmolded with a second material (typically a softer elastomer like TPE or TPU). In short: insert molding = plastic over metal; overmolding = plastic over plastic (or over prepared metal). We offer both — see our insert molding service.

How is overmolding different from two-shot (2K) molding?

They're closely related, but the equipment and process differ. Two-shot (2K or multi-shot) molding uses a single specialized injection molding machine with two barrels that inject both materials in sequence — the part never leaves the mold between shots. Overmolding can be done in two separate steps on standard machines: first shot produces the substrate, which is then loaded into a second mold for the overmold. Two-shot is faster per part and more precise, but requires more expensive tooling and equipment. Overmolding is more flexible and cost-effective for lower volumes or more complex geometries. Our engineering team will recommend the best approach for your project.

How much does custom overmolding cost?

Overmolding cost has three components: tooling (typically $3,000–$60,000 depending on complexity and cavitation, often 20–40% higher than single-shot tooling), per-unit part cost (driven by material cost, cycle time, and volume), and any secondary operations. Simple two-material consumer parts can run well under $1 per unit at volume; complex medical or gas equipment overmolds can be several dollars per unit. Every project gets an itemized quote within 24 hours — tooling, unit cost, and lead time broken out clearly.

Which material combinations bond best for overmolding?

Bond strength depends on whether you need a chemical bond (materials fuse at a molecular level) or a mechanical bond (the overmold grips physical features like undercuts or textures). Best chemical bonds are TPE/TPU over ABS, PC, or PC/ABS — these pairs were designed for each other. LSR and TPV generally need mechanical bonding features because chemical adhesion is weaker. Rule of thumb: same-family materials (polar with polar, non-polar with non-polar) bond better. Our DFM review includes a specific bond recommendation for your substrate-overmold combination.

Can you overmold plastic over metal?

Yes. Plastic over metal is technically insert molding (not overmolding in the strictest sense), but the processes overlap and we handle both. Typical applications are threaded inserts molded into plastic bosses, electrical terminals molded into housings, or metal pins encapsulated for strain relief. Success depends on the metal being dimensionally stable at molding temperatures, having mechanical retention features (knurling, undercuts, or through-holes), and being clean of oils or contamination. See our insert molding page for details.

How long does overmolding tooling take?

Typical lead times are 4–6 weeks for overmolding tooling, plus 1–2 weeks after T1 samples are approved for first production. Aluminum prototype tooling can be produced in 2–3 weeks for design validation runs. Rush timelines are available on a project-by-project basis — tell us your target date when you request a quote.

What's the minimum order quantity for overmolding?

There is no fixed minimum at Weilin. We support everything from prototype runs of a few hundred parts for design validation through high-volume production of millions of parts per year. Lower volumes are typically run with aluminum tooling to keep tooling cost down; higher volumes justify hardened steel tooling with faster cycle times.

Can you support medical-grade overmolding projects?

We're a component-level supplier operating within our customers' quality systems — not a finished-device manufacturer. We work with biocompatible LSR (liquid silicone rubber), medical-grade TPE, and medical silicone over medical-grade PC, PEI (Ultem), or polysulfone substrates. We operate under ISO 9001 quality management practices and source ISO 10993-compatible resins on request. Our longest-running medical OEM programs are 29 years of dental consumables (US brand) and 17 years of medical gas equipment components (European brand). We do not hold ISO 13485 certification ourselves. If your project requires an ISO 13485–certified supplier, we'll tell you directly. See our medical plastic parts page for full details.

What file formats do you accept for overmolding quotes?

We accept STEP, IGES, STL, Parasolid, SolidWorks, Creo, and AutoCAD formats. 2D drawings in PDF or DWG are welcome and especially helpful when tolerances, critical features, or surface finishes need to be specified. For overmolding quotes we ask for files of both the substrate and the final overmolded geometry if available. Frank personally reviews SolidWorks files, so you get direct DFM feedback without a translation layer.