LSR Injection Molding

Process Overview

Liquid Silicone Rubber (LSR) Injection Molding

LSR injection molding uses a two-component liquid silicone system — base polymer and crosslinker — metered and mixed at a fixed ratio (typically 1:1 by weight), then injected under pressure into a heated, closed mold. The material cures rapidly at mold temperature, typically 170–200°C, and the part is demolded in a finished state requiring no post-cure deflash in most geometries.

SIKING operates two dedicated LSR injection units. Both use 100% imported LSR from Dow, Wacker ELASTOSIL, and Shin-Etsu — no domestic-compound substitution. The closed-system injection process eliminates contamination risk from open compound handling, which is especially relevant for medical-component and electronics applications.

Two dedicated LSR injection units — separate from compression and transfer equipment
Materials: Dow, Wacker ELASTOSIL, Shin-Etsu — 100% imported, no domestic compound substitution
Standard hardness range: 15–80 Shore A
Extended hardness: 0–90 Shore A with custom compounding
Precision: ±0.02mm on critical dimensions
Traceability: batch records maintained from raw material to finished part

2

Dedicated LSR injection units

±0.02mm

Precision tolerance

100%

Imported materials

LSR Injection Unit

Equipment Specifications

LSR Injection Molding Specs

Parameter	Specification
Injection Units	Two dedicated LSR injection units
Material System	Two-component liquid silicone (A+B, 1:1 ratio)
Material Suppliers	Dow, Wacker ELASTOSIL, Shin-Etsu — 100% imported
Standard Hardness Range	15–80 Shore A
Extended Hardness (custom compounding)	0–90 Shore A
Dimensional Precision	±0.02mm on critical dimensions
Mold Temperature	170–200°C (typical cure range)
Cycle Time vs. Compression	Faster cycle time due to closed-system rapid cure
Flash Generation	Minimal — closed mold system; typically no deflash required
Traceability	Batch records: material lot → job number → shipment

Buyer Implications

What This Means for Your Project

Faster Cycles, Higher Volume Capacity

LSR cures in seconds at mold temperature rather than the minutes required for HTV compression molding. For high-volume production runs, this translates to more parts per shift without adding presses. Cycle time advantage over compression is most significant on small, thin-wall parts.

Precision Without Deflash

The closed LSR mold system produces parts with minimal parting line flash. On most LSR geometries, no post-mold deflash operation is needed — the part comes out of the tool ready for inspection. This removes a processing step and the dimensional risk it introduces.

Traceability for Regulated Applications

SIKING maintains batch traceability from the incoming material lot through to the finished part shipment. For applications where supplier documentation is required — medical pathway programmes, regulated electronics — the paper trail is maintained as a standard process output, not a special request.

Process Flow

LSR Injection Molding — Step by Step

1

Material Metering

LSR components A and B metered at 1:1 ratio by weight. Pigment added where specified. Batch and lot recorded.

2

Static Mix & Injection

A+B combined via static mixer immediately before injection. Mixed material injected into closed, heated mold under controlled pressure.

3

Cure

Mold held at cure temperature (170–200°C). LSR crosslinks rapidly. Cycle time significantly shorter than compression molding.

4

Demold

Mold opens. Part demolded — typically no deflash required. Part inspected immediately after demold.

5

Inspection & Documentation

Dimensional, visual, and functional inspection. Traceability record linked to batch and production order. Pack and ship.

Tolerance Reference

LSR Dimensional Tolerances

Reference values — confirm specific tolerances at DFM review based on part geometry and wall section.

Feature	Achievable Tolerance
Critical precision dimensions	±0.02mm
General dimensions (<50mm)	±0.05mm – ±0.10mm
General dimensions (50–100mm)	±0.10mm – ±0.20mm
Wall thickness (thin wall)	0.3mm minimum (material-dependent — confirm at DFM review)
Flash (parting line)	Minimal — typically no deflash operation required

Best Suited For

Micro-precision parts requiring ±0.02mm tolerances
Thin-wall structures where compression cannot fill evenly
High-volume production where cycle time drives unit cost
Parts requiring minimal flash — no post-mold deflash operation
Medical pathway components requiring full material traceability
Optical clarity applications (transparent LSR)
Hearing aid components, surgical components, precision electronics seals

Not Suited For

Very large parts — LSR injection tooling cost is higher and shot size is limited
High-durometer silicone above 80 Shore A (standard) — compression or custom compound needed
Low-volume prototype runs where LSR tooling investment is hard to justify
Parts where a low-cost solid compound is acceptable and LSR precision is not needed
Very thick-section parts where exothermic heat from cure is a problem

Common Questions

LSR Injection Molding — FAQ

Why does SIKING use only imported LSR materials?

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Dow, Wacker ELASTOSIL, and Shin-Etsu set the global standard for LSR compound consistency, purity, and documentation. Domestic LSR compounds can vary in batch-to-batch consistency, which creates problems when customers need to validate a material specification for their application. Using 100% imported material means the compound specification is stable, the supplier data sheets are available for customer review, and the traceability chain is clean.

What hardness range can SIKING achieve in LSR?

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Standard LSR grades from Dow, Wacker, and Shin-Etsu cover 15–80 Shore A. This covers the majority of applications — soft medical seals at 20–30 Shore A, standard keypads and grips at 40–60 Shore A, and firmer sealing elements at 70–80 Shore A. For applications below 15 Shore A or above 80 Shore A, SIKING offers custom compounding to extend the range to 0–90 Shore A. Custom compounding is discussed at DFM review and involves a qualification run before production.

How is traceability maintained, and what documentation can you provide?

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SIKING maintains batch records linking the incoming material lot number to the job production order to the outgoing shipment. Standard documentation available: material test certificate, certificate of conformance, and inspection report. For customers with specific documentation requirements (e.g., incoming inspection records, IQC reports, material declarations), discuss your requirements at the quote stage so these are built into the production workflow rather than requested after the fact.