Overmolding | Kaysun

TL;DR

What we do: TPE overmolding and insert molding for complex plastic and metal parts
Why Kaysun: Scientific molding, deep TPE expertise, precision tooling, and rapid prototyping
Outcomes: Fewer steps, stronger parts, better aesthetics, faster launches
Who we serve: Medical, automotive, defense, and consumer OEMs

What is Overmolding?

Overmolding is a multi-shot injection molding process where a base part (substrate) is coated with a second material, often TPE, for improved grip, durability, comfort, or aesthetics.

Generally speaking, the overmolding process:

Combines rigid and soft materials in one molded part
Often uses thermoplastic elastomers (TPE) over hard substrates
Improves user interface, vibration dampening, sealability, and impact resistance
Eliminates assembly steps and post-mold finishes

Download the Overmolding Fundamentals white paper → Learn best practices for material pairing and design

Overmolding vs. Insert Molding

Both overmolding and insert molding are multi-material processes, but overmolding bonds molten TPE to a molded plastic or metal part, while insert molding encases a pre-placed insert (often metal) during the injection cycle.

Kaysun has both overmolding and insert molding capabilities.

Overmolding

Insert Molding

Process

Bonding plastic substrate to plastic or metal base

Encasing pre-placed metal insert into plastic part during injection cycle

Primary Benefit

Ergonomics, aesthetics, sealing

Strength, structural bonding

Typical Material

TPE

Rigid Plastics

Benefits of Overmolding

Reduces shock and vibration
Dampens sound and provides electrical insulation
Creates moisture and chemical barriers
Enhances part feel, aesthetics, and brand appeal
Eliminates post-production coating or adhesive steps
Improves product durability and throughput

Overmolding questions?

Common Overmolding Applications

Medical: Sterilizable grips for surgical tools, sealed housings
Automotive: Connector boots, handle grips, weatherproof sensors
Industrial & Defense: Rugged handheld devices, vibration-dampening enclosures
Consumer: Appliance controls, toothbrush grips, power tools

Characteristics That Influence Successful Outcomes

Friction, hardness, TPE thickness
Chemical compatibility between TPE and substrate
Softness perception is more dependent on thickness than durometer

Substrate Compatibility

ABS, PC, PC-ABS, Nylon 6, PMMA, HDPE
Polypropylene, PPO, Copolyester, Polystyrene
Metals

Prototyping

Overmolding requires carefully designed, highly precise tools that can take months and hundreds of thousands of dollars to build. Prototyping in the earliest stages of product design and development is the most efficient way to:

Validate performance

Define realistic processes and schedules

Maximize manufacturability

Minimize expensive production tool redesign and testing

Overmolding Expertise

Not every molder can overmold. Kaysun combines:

Engineering expertise in DfM, mold flow, scientific molding, and material validation
Comprehensive tooling knowledge and collaborative design
Process development with precision control of pressure, temperature, and material flow
Vertical and horizontal presses for insert and overmold processes

What is overmolding in injection molding?

Overmolding is the process of layering a soft plastic (like TPE) over a hard plastic or metal substrate to enhance grip, protection, and performance.

When is overmolding used?

It's used when parts need better ergonomics, sealing, vibration resistance, or improved aesthetics in a single molded part.

How does overmolding differ from insert molding?

Insert molding involves placing a pre-formed component (often metal) into a mold before plastic is injected around it. Overmolding bonds two materials through sequential molding steps.

Why prototype overmolded parts?

To test for bond strength, simulate production conditions, and identify design issues early, reducing the risk of full-scale retooling.

Overmolding Durable, ergonomic, and cost-efficient solutions for better-performing parts