Engineered Thermoplastics
Polycarbonate (PC), polyamide (PA66) and polybutylene terephthalate (PBT) are the most common rigid partners — chosen for strength, clarity or chemical resistance.
Silicone Overmolding & Bonding
Combining soft silicone with rigid plastic or metal in a single part. We plan the substrate, the bonding mechanism, the interface geometry and the verification test up front — so the joint holds in your application, not just on the sample.
Material Pairing
What Silicone Bonds To
Not every silicone bonds equally to every substrate. We match the grade to the substrate's chemistry and the part's service temperature.
Metal Inserts
Steel, brass and aluminium inserts are overmolded where the part needs a threaded, conductive or high-strength core.
Silicone-to-Silicone
Multi-shot LSR combines two silicone durometers — a firm base with a soft grip, or a colored skin over a functional core.
| Substrate | Typical part | Bonding approach | Service note |
|---|---|---|---|
| PC (polycarbonate) | Transparent housing, wearables, medical device covers | Mechanical interlock or primer + self-bonding LSR | Watch heat — PC softens at high cure temperature |
| PA66 (polyamide) | Gears, clips, structural frames, connectors | Mechanical interlock + moisture-conditioning control | PA66 is hygroscopic; dry it before molding |
| PBT (polyester) | Electrical insulators, housings, brackets | Mechanical interlock or primer | Good dimensional stability and chemical resistance |
| Metal insert (steel / brass / aluminium) | Threaded bosses, bushings, conductive cores | Insert placement + mechanical capture | Precise insert retention prevents shift and flash |
These pairings reflect materials we work with regularly. The exact grade, primer or self-bonding LSR, and the applicable pull / peel / ageing test are confirmed per part during DFM against your drawing and service conditions — we never cite a capability we have not demonstrated.
Bonding Mechanism
Two Ways We Make the Joint Hold
Mechanical Interlocking
The most reliable, process-independent bond. Undercuts, holes, grooves or knurled features physically capture the silicone, so the joint holds even under peel or shear load. This is our default where geometry allows.
Adhesive Bonding
Where a purely mechanical lock isn't possible, we use a primer or a self-bonding LSR grade selected for the specific substrate pair — applied under controlled conditions for a consistent chemical bond.
Interface Engineering
Designing the Bond Line
Substrate Temperature Control
The rigid substrate is pre-heated or cooled to the right temperature so the silicone cures against it without warping or stress.
Interface Geometry
Parting lines, shut-offs and the silicone-to-substrate contact area are designed in DFM so the bond line is clean and fully supported.
Insert Placement
Metal inserts are located and retained precisely so the overmolded silicone encapsulates them without shifting or flashing.
Verification
Proving the Bond Holds
Pull & Peel Testing
Bonded samples are pulled and peeled to confirm the joint strength meets the specification — not just that it looks bonded.
Temperature & Aging
Bonds are tested across the service temperature range and after thermal cycling to confirm they hold in the field.
Dimensional Verification
The overmolded part is measured to confirm the silicone and substrate hold their relative position and tolerance.
See the full engineering context in manufacturing engineering and our product development service.
Have a Multi-Material Part?
Send your substrate material and part idea — we'll recommend the bonding approach and quote the overmolding.
Discuss Overmolding