Hey there, if you’ve ever dabbled in the medical device, consumer electronics, or automotive seal parts game, you know LSR molders are the unsung heroes behind the small, flexible, safe parts that people use every single day. But here’s the thing that most folks don’t talk about enough: quality control (QC) in LSR molding isn’t just a “check the box” step—it’s what separates a supplier that cranks out parts and one that actually keeps your projects on track, compliant, and free of costly headaches. As someone who’s been running an LSR molding shop for over 10 years, I’ve seen firsthand how cutting corners on QC leads to rejected batches, client panics, and months of rework. Today, I’m breaking down exactly what goes into our QC process, why it matters, and how the right tools make all the difference.
First, let’s get on the same page about what LSR molding even is, for anyone new to this. LSR stands for liquid silicone rubber—its liquid state at room temp means it flows into super tight, detailed mold cavities before curing into that soft, durable silicone you know. The catch? It’s finicky. Temperature swings, material mix ratios, or even a tiny mold particle can turn a perfect part into a dud. That’s where QC starts long before we hit the start button on any machine. We can’t just set up a mold and hope for the best; our QC process begins with incoming goods because 90% of LSR part issues trace back to bad raw material, not the molding process itself.
Wait, let’s be real—when you’re sourcing LSR parts, you’re probably focused on lead times and cost first (no judgment, we all have budgets to hit) but skimping on QC here will blow those costs up fast. Our first QC checkpoint? Incoming LSR resin and additives. Every shipment of LSR we get comes with a COA (Certificate of Analysis) from the material maker, but we don’t just file that away. We run our own tiny batch tests in-house, checking viscosity, mix ratio (LSR is two-part, right? Part A and Part B, and if they’re off even by 1% the cure is wrong), and tensile strength. We’ve had shipments where the COA said perfect, but the actual resin cured too fast mid-mold—we caught that before it ran 10,000 parts and had to scrap the whole lot. Pro tip for buyers: never take a supplier’s word for incoming material QC; ask if they run their own tests, not just rely on raw material docs.
Next up is the actual molding process monitoring, and this is where our machines make all the difference. A few years back, we were using old, clunky molding machines that required us to manually check cycle times every hour—we missed a temperature dip once that ruined a $5k batch of medical-grade gaskets. That’s when we upgraded to TYM-W Toggle LSR Injection Molding Machine. Let me tell you, this thing is a game-changer for process QC. It has real-time sensors that track barrel temperature, injection pressure, cure time, and mold cavity pressure nonstop. If any of those variables drift even outside our pre-set tolerance (we set those super tight for medical or aerospace parts), it auto-pauses the machine and logs the error. No more manual checks, no more missed small issues that turn into big problems. We also use the TYM-W LSR Injection Molding Machine for our higher-volume runs, since it handles consistent, repeatable cycles even when we’re cranking out 50k parts a day. The toggle design is smoother than older models, so we get fewer mold shifts, which means fewer out-of-tolerance parts.
Speaking of mold shifts, mold maintenance is another make-or-break QC step that a lot of new suppliers skip. LSR is sticky, and over time, residue builds up on mold cavities, leading to flash or part distortion. We have a strict monthly mold cleaning schedule, and every mold gets a full dimensional check after 50,000 cycles. If you’re working with a supplier that doesn’t have a formal mold maintenance log, run—you’re gonna get parts that are slightly off-spec, and you won’t catch it until you assembly 1,000 of them. We also use our TYM-W55T200 2K / Double-Color Machine for parts that need two LSR materials or LSR overmolded onto plastic, and its dual injection units have built-in checks to make sure each material is injected at the right time and pressure, so no cross-contamination between the two materials. That’s a huge deal for things like baby bottle nipples that need a hard plastic core and soft silicone outer grip—cross-contamination there would mean the part doesn’t pass food safety tests.
Now, let’s talk about in-process inspection, because even with all the machine checks and mold maintenance, we don’t want to wait until the end to find a bad part. We do 100% visual inspection on every part that comes off the line for critical defects—flash, sink marks, air bubbles, or even tiny voids that you can’t see with the naked eye. For parts that need tighter dimensional tolerances (like medical device seals that have to fit perfectly inside a catheter), we use coordinate measuring machines (CMMs) to check every dimension against our CAD files. We also do functional testing—if it’s a gasket, we test its compression set to make sure it’ll seal correctly after being squeezed thousands of times; if it’s a consumer part like a phone case, we do drop tests to make sure the silicone holds up.
Wait, and let’s not forget traceability. That’s non-negotiable for regulated industries like medical or aerospace. Every single batch of parts we make has a batch number that links back to the raw material lot number, the machine that ran the batch, the operator, and all process logs. If a client has a recall or quality issue, we can pull up exactly what happened, when, and where in 5 minutes. No guessing, no finger-pointing—just clear, documented QC that keeps both us and our clients compliant. I know that sounds like extra work, but it’s saved us more than once when a client had a small issue with a batch—we could show them our QC logs, fix the root cause, and avoid a huge hassle.
A lot of newer LSR molders might say “we outsource inspection to save time” or “we only do end-of-line checks,” but that’s a recipe for disaster. Early defect detection is way cheaper than fixing a batch of 20,000 parts that’s already made. For example, a few months ago, a small startup brought us a run of LSR switches for a smart home device. They’d tried a different molder first, who only did end-of-line checks, and they found out 15% of the switches had tiny air bubbles that made them stop working. We ran in-process checks with our TYM-W machines, caught the bubble issue mid-run (it was a small material mix error), and fixed it before we even finished the batch. That startup is now a repeat client, and they told us that saved them from a product launch delay.
Now, let’s get real about what you should ask an LSR molder when you’re vetting them. Don’t just ask “how good is your quality?”—ask specific questions: What’s your incoming material QC process? Do you use real-time process monitoring machines like TYM-W Toggle LSR Injection Molding Machine? What’s your mold maintenance schedule? Do you have full traceability for all batches? What kind of testing do you do beyond just dimensional checks? Any supplier that can answer those clearly, and show you their QC logs and test results, is someone you can trust. If they hem and haw, or only have vague answers, keep looking—you don’t want to be the one stuck with bad parts.
Here’s the thing about LSR QC that a lot of people miss: it’s not one set-it-and-forget-it process. Every part is different—medical parts have stricter FDA requirements, consumer parts need to pass food safety tests, automotive parts need to handle extreme temperatures. Our QC process adapts to each project. For a medical gasket, we run additional biocompatibility tests and sterility checks. For an automotive seal, we test for UV resistance and oil compatibility. We don’t use a one-size-fits-all QC plan, because that would mean cutting corners somewhere.
I’ve been in this game long enough to see suppliers pop up that undercut everyone on price, only to go out of business 2 years later because they skipped QC to save money. The expensive part isn’t the inspection, the good machines, or the maintenance—it’s the cost of scrapping bad batches, fixing field issues, or losing clients because of poor quality. Our QC process adds a tiny bit to our upfront cost, but it saves everyone involved from huge headaches down the line.
If you’re currently working with an LSR molder that’s giving you issues—late batches, inconsistent parts, compliance headaches—or you’re looking to switch to a supplier that actually takes quality seriously, I’m here. We’ve got over 10 years of experience, all the right QC systems, and machines like the TYM-W Toggle LSR Injection Molding Machine, TYM-W LSR Injection Molding Machine, and TYM-W55T200 2K / Double-Color Machine that keep our process consistent. Whether you need small custom runs or high-volume production, we can tailor our QC to your specific requirements. Stop dealing with parts that don’t fit or fail early—let’s chat about your project, and we’ll show you exactly how we make quality part of every step of the molding process.
References:
ASTM D412 - Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers—Tension
ISO 10993 - Biological Evaluation of Medical Devices
UL 94 - Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances