Buyers searching for LSR injection molding usually already suspect liquid silicone rubber is the right process — what they need is a way to confirm it before paying for expensive tooling. This guide explains what LSR injection molding actually is, when it beats compression molding, what the tooling really costs, and the questions that separate a genuine LSR factory from one that outsources the process.
1. What LSR injection molding actually is
Liquid silicone rubber is a two-part platinum-cured silicone supplied as liquid A and B components. A meter-mix dosing unit blends them at a precise 1:1 ratio and injects the mix into a heated, closed mold (typically 150–200 °C), where it cures in 30–120 seconds depending on wall thickness. Because the material arrives as a liquid and the mold stays closed during cure, parts come out essentially flash-free, with no manual deflashing step and almost no material waste. The process is fully automated and repeatable — which is why it dominates medical, baby-care, automotive and electronics applications.
2. When LSR beats compression molding
Our compression vs injection comparison covers the full trade-off; the short version for buyers:
- Volume: above roughly 10,000 parts/year, LSR's faster cycles and zero deflashing labor usually beat compression on unit price, despite the costlier tool.
- Tolerance: LSR holds ±0.05–0.1 mm on critical dimensions because shot size and cure are machine-controlled; compression depends on operator-placed preforms and typically holds ±0.1–0.2 mm.
- Cosmetics: LSR parts have no flash line to trim, so visible surfaces stay clean — important for consumer and medical parts.
- Cleanliness: the closed, automated process is compatible with cleanroom production, which is why medical-grade and baby products default to LSR.
- Design freedom: thin walls (down to ~0.3 mm), fine details and multi-shot overmolding are practical in LSR and painful in compression.
- Stay with compression when: volumes are low, parts are large and simple (gaskets, mats), or you need many color/hardness variants — compression tooling is cheap enough to iterate. See our seals and gaskets guide for a compression-first category.
3. The tooling reality: cost and lead time
LSR tooling is where budgets surprise people. A production LSR mold is a precision tool: hardened steel, tight machining tolerances, and usually a cold-runner system that keeps the mixed silicone cool until it enters the cavity. Realistic ranges:
- Single-cavity prototype mold: roughly USD 3,000–8,000, 3–5 weeks.
- Multi-cavity production mold with cold runner: roughly USD 10,000–40,000, 5–8 weeks, depending on cavitation and complexity.
Against that, LSR cycle times of under two minutes and zero deflashing mean unit prices drop sharply at volume — the tool premium is typically recovered within the first production run of a few tens of thousands of parts. Always ask who owns the mold and where it is stored; our factory selection guide explains why tooling ownership must be in writing before payment.
4. Materials and grades
LSR is available across the same hardness range as solid silicone — see our Shore A guide — but grades matter more than buyers expect:
- Food-grade (FDA / LFGB): the baseline for kitchenware and baby products. Our food vs medical grade article details the certifications.
- Medical-grade (USP Class VI / ISO 10993): for skin-contact and healthcare devices, with full batch traceability.
- Self-adhesive grades: bond directly to PA, PBT, PC and metal substrates without primer — the enabler of LSR overmolding for waterproof buttons and sealed assemblies.
- Optical / high-clarity and fluorosilicone grades: for light guides and fuel/oil contact respectively.
5. Design rules that keep LSR parts moldable
- Uniform wall thickness (ideally 0.5–4 mm) prevents sink and cure variation; LSR flows well, so thin sections are fine, but avoid abrupt thick-to-thin transitions.
- Draft angles can be minimal (0.5–1°) because silicone is flexible and releases easily — but tell the toolmaker the demolding direction early.
- Undercuts are workable for flexible silicone, within limits; deep undercuts need sliders, which add tool cost.
- Gate location matters cosmetically — LSR gates are small, but agree the gate position on visible surfaces before tooling starts.
- Account for ~2–3% shrinkage — your supplier should compensate in the tool design, not in the part drawing.
6. How to verify a real LSR factory
Many silicone factories advertise LSR but outsource it. Before committing tooling money, ask:
- How many LSR injection machines do you own, and of what tonnage? (A real LSR shop names machine brands and clamping force without hesitating.)
- Do you make cold-runner molds in-house? Who owns the mold after payment?
- Can you send sample parts from current LSR production, with the material grade certificate?
- What is your typical scrap rate on LSR jobs, and how is it controlled?
- Do you hold ISO 9001, and can the certificate entity name match the invoicing company?
- Can you run a video call from the LSR workshop floor?
Next step: see our LSR injection molding manufacturer in China page for what we run in-house and how to send drawings for a quote within 24 hours.
Working with Tongsheng
Dongguan Tongsheng Electronic Technology Co., Ltd. has manufactured silicone rubber molds and silicone products since 2014. We run in-house CNC tooling, compression and liquid silicone injection molding, and a testing lab, from a 2,000+ sqm ISO 9001:2015 certified factory in Humen Town, Dongguan, with 100+ staff and 15 engineers. Food-grade (FDA / LFGB), medical-grade and industrial-grade compounds, Shore A 10–80, Pantone and RAL color matching.
Send 2D/3D drawings (STP, IGS, PDF) and we quote within 24 hours — request a quote, email coraycn@gmail.com, or message us on WhatsApp.