If you’re here, chances are you’re either deep in the weeds of a new product that needs that extra layer of grip, waterproofing, or durability, or you’re working with an over molding vendor and keep hearing “curing time” thrown around like it’s some black box. Let me pull back the curtain a little—this is the stuff I deal with every single day here at our over molding shop, and trust me, it’s not as mysterious as it sounds. I’m gonna keep this real, no stuffy engineering jargon that makes your eyes glaze over, just what I’ve learned from 8 years of running the oven loads, troubleshooting botched molds, and fielding 100+ texts a week from buyers panicking because their part isn’t coming out on time. Over Molding
First off, let’s get the basics straight: curing time in over molding is literally how long the second (or “overmold”) material takes to fully set, bond to the first (substrate) part, and reach its maximum strength. Yeah, it’s easy to confuse this with “cool down time” or “cycle time” when you’re quoting a job, but those are totally different. Cool down is just letting the part get cold enough to handle without burning your hands, while cycle time is the whole thing: loading substrate, injecting overmold, curing, cooling, unloading. Curing is the critical middle step that makes or breaks the part—skip a few minutes here, and you might get an overmold that peels off the first time someone uses it, or is soft and grippy when it needs to be rigid.
Now, here’s the thing no one tells you upfront: curing time isn’t a one-size-fits-all number. I wish it were, because quoting would be so much simpler, but it depends on like, a dozen factors that change with every job. Let’s break down the big ones that actually matter for you, the person ordering parts, not just the engineer hiding in the back room.
First up: the type of overmold material. This is huge. Most over molding jobs use two main types of polymers: thermoplastics (the stuff that melts when heated) and silicones (super common for medical, automotive, or kitchen parts because they’re non-toxic). Thermoplastics, like TPE, TPU, or nylon, cure way faster than silicones—usually between 1 and 10 minutes, depending on how thick the part is. Silicones? Those bad boys can take anywhere from 5 minutes up to 2 hours, sometimes even longer for thick, heavy parts. I just finished a job for a medical device client last week where we were using a platinum-cured silicone for a catheter grip, and curing time was 45 minutes per cycle. If we tried to rush that, the silicone would have been tacky, not bonded right, and the client would have had to scrap the entire batch.
Next, substrate type. What are you over molding onto? Is it a hard plastic (like ABS, polycarbonate), a metal part, or even another soft plastic? The bond between overmold and substrate is everything here. If your substrate is something like ABS, it bonds really well with most common overmold TPEs, so curing time can be a bit shorter. But if your substrate is polypropylene? Man, that’s a headache. Polypropylene is super non-porous, so the overmold has to cure long enough to actually adhere to the surface, not just sit on top. We’ve had jobs where a buyer thought curing time could be cut from 8 minutes to 4, but because the substrate was polypropylene, we had to stick to 8 minutes—cutting it short would lead to delamination, which is a disaster.
Then there’s part thickness. Thicker parts need longer curing time, period. Heat has to penetrate all the way through the overmold material to make sure every last bit is fully set, not just the outside skin. I see this all the time: a buyer will send over a design with a 10mm thick overmolded handle, and quote us a curing time of 3 minutes. That’s impossible. The outside might feel cured, but the core is still gooey. We had a client a few months back that ignored our warning, tried to run their thick handle parts at 3 minutes curing, and half of them peeled apart when their customer received them. We had to scrap 500 parts, re-run them, and push back their delivery by a week. Cost them twice as much in the long run.
Mold temperature and pressure also play a big role. We run our ovens at specific temps depending on the material—too low, and the material cures slow; too high, and you risk warping or burning the substrate. Pressure is just as important: if the mold isn’t applying enough pressure while curing, the overmold can develop voids, or the bond won’t be strong. I’ve had a few jobs where we had to adjust pressure on the mold to cut curing time by 2 minutes without compromising quality—small tweak, but makes a huge difference for lead times.
Now, let’s talk about the common myths around curing time, because everyone has one. First myth: “Higher temp = shorter curing time.” Yeah, sort of, but only up to a point. If you crank the oven temp too high, you can cause “curing shock” where the outside cures so fast it traps heat and gas in the core, leading to bubbles or weak parts. We learned that the hard way with a TPU overmold for a power tool grip a couple years back—tried to bump the temp from 180°F to 220°F to cut curing time, ended up with 20% of parts having tiny bubbles under the surface. Had to throw them all out. Never again.
Second myth: “All curing time is listed on the material data sheet.” Dude, material data sheets give general ranges, not job-specific times. A material sheet might say TPE cures in 2-8 minutes, but that’s for a 2mm thick part on an ABS substrate. If your part is 8mm thick on polypropylene, that range jumps to 6-12 minutes. Our team adjusts that number based on our actual mold specs, the size of the batch, even the humidity in the shop (yes, humidity affects curing time for some materials—high humidity can slow down silicone curing, for example).
So what does that mean for you, the person ordering over molded parts? How do you figure out the right curing time for your job, without waiting 2 weeks for us to test a sample? First, be realistic with your lead time. If you need a custom part, don’t expect us to run it in 1 day if the curing time per part is 45 minutes and you need 1000 parts. Let’s do the math: 1000 parts at 45 minutes each is 7500 minutes, which is over 124 hours— that’s like 5 and a half days of just curing time, not counting loading, unloading, and quality checks. We can’t rush that without cutting corners.
Second, be honest about your part requirements. If you need a part that’s waterproof or holds up to extreme temperatures, we’re gonna need to use a material that requires a longer curing time, no way around it. Trying to switch to a different material just to cut curing time is a bad move—you’ll end up with a part that doesn’t meet your specs. I always tell buyers: better to know upfront if the curing time is going to add a few days to your lead time than to get bad parts and have to re-order.
Another thing people don’t talk about: post-curing. Some materials need a little extra time after the initial curing to reach full strength. We call this “aging time.” For example, some silicones take 24 hours at room temp to fully cure after the oven cycle. That’s not something we can skip—if we ship the part right out of the oven, it won’t have the same tensile strength or bond strength. We had a client for a phone case who wanted their parts shipped the same day, and we had to explain that post-curing time meant we’d have to hold them for a day. They were annoyed at first, until their first batch of parts didn’t peel, so they understood.
Wait, let’s also get into what happens when curing time is wrong, because that’s the stuff that makes our phones ring at 8 PM. If curing time is too short: overmold is soft, tacky, peels off, delaminates. We had a automotive client a while back that skipped on curing time for their interior trim parts, and when they installed them, 10% of the overmold pulled off. Cost them thousands in warranty claims. If curing time is too long: overcuring. For thermoplastics, that can make the material brittle—like, snap when you bend it. For silicones, overcuring can make it stiff instead of soft and grippy. I once had a job where we left parts in the oven for 2 extra hours (mix up from a shift change), and the TPE overmold for a lawnmower handle became so brittle it cracked when the customer tested it. Total waste of materials.
Now, let’s talk about how we handle curing time here at our shop, so you know we’re not just making up numbers. First, we run a small sample for every new job—usually 10-20 parts, test them for bond strength, flexibility, and durability. We adjust curing time based on those samples. For example, last week we got a job for a set of kitchen knife handles, overmolded with a soft TPE. The initial sample at 7 minutes curing was great, but when we ran a batch of 200, we noticed a few parts had tiny gaps between overmold and substrate, so we bumped curing time to 8 minutes. No issues after that.
We also track all our curing times and part results, so if you have a similar job to one we did 6 months ago, we can pull that data and get you a pretty accurate number right away. Saves you time, saves us time, no guesswork.
So what’s the takeaway here? Curing time isn’t a boring technical detail—it’s the difference between a part that works for years and one that fails the second someone uses it. It’s not something we can cut corners on, even if you’re in a rush. The best way to work with us is to share your part specs, material needs, and lead time expectations upfront, and we’ll give you a realistic curing time, along with a timeline that actually works for your job.
If you’re working on a new project, have questions about over molding curing times, or need a quote for custom over molded parts, hit us up. We’re here to make sure your parts turn out right, on time, no headaches. Let’s chat about what you’re building.
Over Molding References:
- Rosato, D. V., & Rosato, M. G. (2000). Injection Molding Handbook. Springer.
- O’Reilly, J. (2015). Silicone Elastomers: Properties and Applications. Wiley.
- Engineering Design Handbook: Injection Molding of Thermoplastics. U.S. Army Materiel Command, 2012.
- TPE/TPU Material Selection Guide. Lubrizol Advanced Materials, 2021.
Yangzhou Dingyue Plastic & Electronics Co.,Ltd
We’re well-known as one of the leading over molding manufacturers and suppliers in China, specialized in providing high quality products and service for global clients. We warmly welcome you to buy customized over molding at competitive price from our factory.
Address: No.28 Yiju Road, Yunxi Town, Hanjiang District, Yangzhou, China.
E-mail: monica.pan@yzdingyue.com
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