Transfer Molding

SIKING Differentiator

Process Overview

Silicone Transfer Molding

Transfer molding places the compound charge in a separate pot rather than directly in the mold cavity. When the press closes, a plunger forces the compound through a sprue and runner system into the sealed cavity. Because the cavity closes before material enters, parting lines are tighter and flash is significantly reduced compared to compression molding.

SIKING's transfer molding equipment shares a platform with the LSR injection system. One machine is configured for solid-compound transfer with a rear-end dual-barrel feeding system. This architecture gives SIKING shot control that most compression-only factories cannot match.

Central injection — compound enters via sprue after cavity is closed and sealed
Dual-barrel rear-end supply — consistent shot weight per cycle
Tighter parting lines: flash reduced relative to compression on equivalent geometry
Metal inserts located before fill — insert position not disturbed by compound flow
Multi-cavity tooling with simultaneous fill across all cavities

Tighter

Parting lines vs. compression

Insert

Primary application

Rare

Most competitors lack this

Transfer Molding Equipment

Competitive Context

Why Transfer Molding Is a Differentiator

Most silicone contract manufacturers offer only compression molding. Transfer molding requires different equipment, tooling design, and process engineering — it is not standard in China's silicone supply base.

Insert Integrity

In compression molding, compound is placed around the insert before the press closes, exposing the insert to lateral compound flow during fill. In transfer molding, the cavity closes around the insert first — compound enters from below. Insert location is fixed before material contacts it.

Parting Line Control

The mold is sealed before compound injection. Mating faces are held under controlled clamping force throughout fill. On precision sealing faces and cosmetic parts, this eliminates downstream deflash operations that add time and introduce dimensional risk.

Multi-Cavity Consistency

The runner system distributes compound simultaneously to all cavities. Shot weight variation — which causes weight and hardness variation across a multi-cavity compression tool — is controlled by the transfer pot volume and plunger displacement, not by operator skill.

Process Specifications

Transfer Molding Parameters

Parameter	Detail
Equipment Configuration	Dual-barrel rear-end feeding system
Compound Type	HTV Solid Silicone
Parting Line Performance	Tighter than compression on equivalent geometry
Primary Application	Metal-insert overmolding, complex geometry
Insert Compatibility	Aluminium, steel, brass, stainless steel, copper
Hardness Range (standard)	30–80 Shore A
Hardness Range (compounded)	0–90 Shore A
Tolerance	Generally tighter than compression; confirm at DFM review
Material Suppliers	Dow, Wacker ELASTOSIL, Shin-Etsu (100% imported)

Process Flow

Transfer Molding — Step by Step

1

Charge Loading

Pre-weighed compound placed in transfer pot. Metal inserts located and secured in mold cavity.

2

Mold Close

Press closes and clamps the mold. Cavity sealed around the insert before compound enters.

3

Transfer

Plunger forces compound through sprue and runner into cavity. Simultaneous fill across all cavities.

4

Cure & Demold

Part cures under heat and pressure. Mold opens. Sprue and runner separated from part.

5

Inspection

Insert position, dimensional check, and parting line inspection per drawing. Batch traceability recorded.

Best Suited For

Metal-insert overmolding (aluminium, steel, brass + silicone)
Complex geometries with undercuts or side-pull structures
Multi-cavity precision tooling requiring consistent fill
Parts with tight parting line or cosmetic sealing face requirements
Applications where parting line flash is a functional or cosmetic concern
Phone side buttons, precision seals with insert bonding

Not Suited For

Very large flat parts — compression molding handles these at lower tooling cost
Liquid silicone rubber (LSR) — requires dedicated closed-injection LSR equipment
Ultra-high volume runs where cycle time must be minimised — LSR injection is faster
Parts with no insert or parting line constraint — compression may be more cost-effective
Very thin wall structures (<0.5mm) — LSR injection preferred

Common Questions

Transfer Molding — FAQ

Why don't more factories offer transfer molding?

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Transfer molding requires dedicated equipment with a transfer pot and plunger system, distinct from standard compression press hardware. It also requires different tooling design (sprue, runner, pot geometry) and process engineering knowledge. Most silicone factories in China focus on compression molding at scale and do not invest in transfer-specific equipment. SIKING's transfer capability was built specifically for insert overmolding programmes requiring precision parting line control.

Is tooling for transfer molding more expensive than compression tooling?

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Transfer molds include a pot, sprue, and runner system that compression tools do not — this adds some tooling complexity and cost. However, the downstream savings from reduced deflash labour, tighter parting lines, and better insert position control often offset this in total programme cost. The right comparison is not tool cost alone — it is tool cost plus production scrap rate plus deflash time plus insert rework.

Can I switch a part currently compression-molded to transfer molding?

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In many cases, yes — but it requires new tooling. Transfer tooling is not interchangeable with compression tooling because the sprue and runner geometry is part of the mold design. SIKING would conduct a DFM review of your existing part before recommending a switch. If the main driver is parting line flash or insert shift, transfer molding is likely the right solution.