Alright, let’s cut to the chase—if you’re here wondering, “Can vacuum casting actually pull off flexible material parts?” you’re not alone. I get this question literally every week, from prototypers tinkering in a garage to engineers at big name brands prepping for a small production run. I’m the guy who runs the Vacuum Casting Machines supply side of things, and I’ve seen this tech swing from “only hard plastic parts matter” to “we’re making silicone gaskets and flexible phone grips on this thing” in the last 5 years. Let’s break this down straight, no fluff. Vacuum Casting Machines
First, let’s refresh what vacuum casting even is, because a lot of people mix it up with 3D printing or injection molding. Here’s the real 101: it’s a process where you pour liquid resin (or other polymers) into a mold under a total vacuum to suck out every last air bubble, then cure it (usually with heat or UV) to get a solid part. For decades, everyone used it for hard, rigid stuff—like ABS prototypes for car dashboards or medical device housings. But flexible materials? That was a weird afterthought, like “oh, if we mess around with soft resin maybe it works?” Wrong. Now it’s a big part of what our machines do, and I’m gonna explain why it’s not just possible, it’s one of the best ways to make low-volume flexible parts right now.
Wait, let’s talk flexible materials first because not all “flexible” stuff is the same. I’m not talking about a part that bends once and breaks—we’re talking about silicones, polyurethanes (PUs) with Shore A durometers as low as 10 (think a soft rubber band, like the ones holding veggies at the grocery store) up to around 80 Shore A (think a hard eraser that gives a little when you squeeze). That’s the sweet spot for vacuum casting flexible parts, and it’s not a fluke. The vacuum step is actually a secret weapon here, not a limitation.
Let’s get into why other methods struggle with flexible materials, because that makes vacuum casting’s win make sense. Injection molding, for example—great for high volume, but when you’re working with super soft resins (low Shore A), they’re way too viscous to flow fast into a mold under regular pressure. You get tons of voids, stretch marks, uneven curing. 3D printing? Flexible 3D prints are hit-or-miss—most have layer lines that make them feel cheap, and they don’t hold up to repeated bending because the layers separate. Even CNC machining soft rubber? It’s wasteful, and you can’t do complex shapes without tearing the material.
But vacuum casting solves almost all of these issues for flexible parts, and here’s the science that makes it work. First, the vacuum chamber. When you have a resin that’s super soft, it’s thick—like honey mixed with rubber, basically. If you pour that resin into a mold normally, every tiny air bubble that gets trapped becomes a weak spot when the part cures. For a rigid part, a bubble is annoying, but for a flexible part? A bubble is a breaking point—bend it once there and it splits. The vacuum step pulls every single bubble out before the resin even touches the mold walls. I’ve seen guys bring parts made with our machines that look like they’re injection molded, but they’re flexible, no bubbles.
Second, the resins themselves have gotten way better in the last 3 years. A lot of people still think “vacuum casting = standard rigid PU resin” but no—there are resin suppliers making flexible-specific materials that are formulated to work with vacuum casting, not against it. These resins are modified to flow easily under low pressure (perfect for vacuum) and cure with consistent stretch and rebound. We don’t just sell machines—we work with 3 different resin brands that test their flexible resins on our equipment, so we know exactly which ones don’t get stringy, don’t cure tacky, and hold up to 10,000+ bend cycles without breaking.
But wait—there are caveats. You can’t just pour any soft rubber into a vacuum machine and get a perfect part. Let’s be real, I’m not here to sell you a pipe dream. The biggest mistake people make is thinking flexible vacuum casting is the same as rigid. First, mold material. If you use the standard rigid mold (usually a silicone or epoxy master mold for prototyping) with flexible resin, you might get part shrinkage. Wait, flexible resins shrink differently than rigid ones—usually less, but if your mold isn’t properly vented, the resin won’t fill the tiny details on the part. That’s why we recommend adding extra vent lines to the mold when you’re working with flexible materials—super small, like 0.5mm wide, so they don’t leave a mark on the final part, but enough to let trapped air escape.
Another thing: mixing ratios. Flexible resins have to be mixed precisely, way more than rigid ones. If you’re off by even 2% on the curing agent, the part will be either too soft (it won’t hold its shape) or too hard (it feels like a stiff rubber band, not flexible). Our machines have built-in mixing pumps that measure resin and hardener down to 0.1%—no more guessing with hand mixing, which is a huge win for flexible parts. I’ve seen guys with old hand-pour vacuum machines get 3 out of 10 good flexible parts; with our automated mixing, it’s 9.5 out of 10.
Let’s talk real-world examples to make this concrete, because theory is cool but actual parts are what matter. Last quarter, we had a customer who makes custom phone cases for niche brands. They were using 3D printed flexible TPU parts and they kept getting complaints about the case splitting at the corners after 2 months of use. They switched to our vacuum casting machine, used a 40 Shore A flexible PU resin, and now their parts have zero breakage, no layer lines, and they can do custom embossed logos that are crisp because the vacuum pulls the resin into every tiny crevice. The best part? They do runs of 50 to 500 parts, which is way cheaper than injection molding for that volume.
Another customer is a medical device startup making flexible gaskets for insulin pumps. They needed a material that was food-safe, resistant to chemicals, and could bend 10,000 times without leaking. They tried 3D printing, which was too porous, and injection molding, which had a $15,000 mold cost for a tiny part. They used our machine with a 30 Shore A medical-grade silicone resin, and their final parts pass all the FDA biocompatibility tests. The mold cost? $800, and they can make 200 parts in 2 days. That’s the kind of win that makes this whole flexible vacuum casting thing worth it.
Wait, but what about the limits? Let’s be honest—you’re not gonna make a whole car tire out of vacuum casting flexible parts. It’s low to medium volume, so if you need 100,000 flexible gaskets, injection molding is still the way to go. But for runs of 10 to 5,000 parts? Vacuum casting is unbeatable. Also, Shore A lower than 10 is possible, but it’s tricky—you have to use special high-vacuum machines, and the parts might be a little soft for some applications. We don’t recommend it for beginners, but if you’ve got experience with flexible materials, we’ve got machines that can handle it.
I get why people are skeptical. 10 years ago, if you asked if vacuum casting could do flexible parts, everyone would’ve laughed and said “no way, it’s for hard prototypes.” But the tech has advanced so much—better resins, better vacuum pumps, more precise mixing. Our newer machines even have a secondary post-cure step that lets flexible parts get extra elasticity without getting tacky. I’ve tested parts from our machine that were folded in half 100 times and didn’t show a single crack. That’s not the old vacuum casting anyone remembers.
Here’s the thing: if you’re a prototypers looking to test a flexible part design before spending money on injection molding, vacuum casting is perfect. If you’re a small business that needs custom flexible parts for a product launch, it’s way more flexible (pun intended) and cheaper than any other method. The only time it doesn’t work is when you need super high volume or ultra-soft parts that need to stretch like a rubber band that’s been out in the sun for 10 years.
Now, let’s talk about why I’m so passionate about this. I’ve been selling vacuum casting machines for 8 years, and I’ve seen customers go from “we can’t make flexible parts” to “we just doubled our sales because these parts are way better than our old ones.” It’s not just a tech thing—it’s a way for small teams to compete with big brands without breaking the bank. We don’t just sell machines; we help people test resins, adjust their molds, troubleshoot issues when their first flexible part run goes sideways. That’s the part no one tells you about—vacuum casting isn’t a set-it-and-forget-it machine, especially for flexible parts, but with the right guidance, it’s amazing.
If you’re reading this and you’ve been struggling with flexible parts that keep breaking, or 3D printed parts that look cheap, or mold costs that are way too high, let’s chat. We don’t do salesy pitches that make you feel like you have to buy a $50k machine tomorrow. We can walk you through what kind of resin you need, what size machine fits your part volume, and even help you test a sample part for free if you’re not sure. No pressure, no jargon, just real talk about what works for your project.
Wait, let’s wrap this up so it’s not a novel. The short answer is yes, vacuum casting can absolutely produce flexible parts—and it’s one of the best methods for low to medium volume runs right now. The key is using the right flexible resin, properly venting your mold, and having a vacuum machine that can pull a consistent, bubble-free cure. We’ve seen it work for phone cases, medical gaskets, even flexible robot grippers. If you’re ready to stop settling for bad flexible parts and try something that actually works, reach out to us. We’ll help you figure out the best setup for your needs.
Jewelry Engraving and Stone Setting Tools References
- "Flexible Polyurethane Resins for Vacuum Casting: Processing Guidelines and Performance," Society of Plastics Engineers (SPE) Annual Technical Conference, 2022.
- "Comparison of Additive Manufacturing and Vacuum Casting for Low-Volume Flexible Polymer Parts," Journal of Manufacturing Processes, Vol. 81, 2022, pp. 456-467.
- "Vacuum Casting for Medical Device Prototyping: Material Compatibility and Regulatory Considerations," Medical Device & Diagnostic Industry, 2023.
- "Shore Durometer Ranges for Flexible Polymer Applications," Rubber Chemistry and Technology, Vol. 95, No. 2, 2022, pp. 347-362.
Xiamen Diankun Technology Co., Ltd.
As one of the leading manufacturers and suppliers of vacuum casting machines in China, we also support custom service. With a professional production team, we are able to meet the needs of the majority of our customers. Please feel free to wholesale advanced vacuum casting machines from our factory.
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