Welcome back, everybody, to the deep dive. This time, we're going to get into something I know a lot of you have been asking about, those incomplete fills, those short shots in injection molding.
Oh, yeah.
It's a pretty common problem.
Very common.
So we're going to be talking about that today, and I have an expert here with me to help break down the science and the problem solving around this issue.
Happy to be here.
All right, so let's jump right in. I think, first of all, can you tell me, just for people who might not be super familiar with this, what exactly is a short shot?
So, a short shot is when you are doing an injection molding process, and the plastic melt doesn't completely fill the mold cavity.
Okay.
So you're left with a defective part.
Right. And so we've got a ton of sources here about this. As I mentioned, a very popular topic, something that I know a lot of people have struggled with. So we're going to try to break down kind of the main culprits of this. And I think in looking at everything we have, it seems like it comes down to really three main areas that we need to look at. Material choice, mold design, and then the settings on the machine itself.
The machine settings are huge, and maybe.
We can even talk about. I've heard about some new technologies that might be helping with this as well. So we'll kind of get into all that. But first, let's talk about materials, because I think that's really the foundation, right?
Yeah, for sure. It's not just picking any plastic.
Right.
They all have different properties, and that can really affect whether you get a perfect part or a short shot.
So, like, what are some of the things that people should be thinking about when they're picking a material specifically for injection molding?
So one of the big ones is fluidity.
Okay.
Which basically means how easily the molten plastic flows through the mold.
Okay, so like water versus honey or something?
Exactly. It's like trying to fill a mold with honey versus water.
Right.
Some plastics are going to be more viscous, like honey, intense, and they're going to need more pressure to fill the mold completely.
Okay. And I've heard, like, polypropylene being one that people like to use because it flows pretty easily.
Exactly. Polypropylene is great for injection molding because it has a high fluidity, so it can easily fill even really intricate molds.
Okay. And then on the flip side, are there some that are known for maybe not being so fluid? And so those would be ones to avoid if you're having trouble with short shots.
Yeah, for sure. Nylon, for example, is not as fluid.
Right. I've heard nylon can be a real pain.
It can be. Yeah. So it needs more careful handling.
Interesting.
You got to make sure all your settings are dialed in just right.
And we'll talk about that in a little bit. And speaking of nylon, I know a lot of the sources talked about the importance of drying nylon.
Oh, yeah. That's crucial.
Like, why is that so important for that specific material?
So nylon and a few other plastics like polycarbonate, they tend to absorb moisture from the air.
Interesting.
And if that moisture isn't removed before molding, it can cause all sorts of problems.
Like what kind of problems?
Well, for one, it can turn into steam during the molding process.
Okay.
And then you get these bubbles and voids in the part, and those bubbles mean a weaker part, and they can actually contribute to short shots.
That makes sense. Yeah.
Yeah.
So it's not even just about the type of plastic, but also the condition that it's in going into the mold.
Exactly. Got to make sure it's nice and dry.
Okay. So first takeaway is material matters.
For sure.
Choose wisely, and make sure you've got it prepped and ready to go before you start molding.
Yeah, absolutely.
All right. Anything else on the material front before we move on to the mold design?
Just to really drive that point home. Even seemingly tiny variations in the Worcester content can lead to huge problems.
Really.
So, yeah, precise drying is really essential.
Okay. So don't skip on the drying step.
Don't skip on the drawing step.
All right, so we've picked our material.
We're ready to go.
We've dried it out.
Yep.
Now let's talk about getting it into the mold.
Let's do it. So now we gotta talk about mold design.
Yeah. Cause it's not just about shoving the plastic in there.
No, no, no. Even with the best material in the world, if your mold design is bad, you're gonna have short shots.
So where do we start with this? Like, what are the key things to think about?
So one of the most critical parts is the gate. The gate, that's the entry point where the plastic flows into the mold cavity.
Okay. See?
And the size of it's really important.
I bet. Too small, and it gets restricted.
Yeah, exactly. If it's too small, the plastic is going to have a hard time getting through, and that can cause pressure to build up.
But then that leads to short shot. Short shot.
Okay. So you want to make sure the gate is big enough to let the plastic flow freely.
But there's a balance. Right. Too big, and then what happens?
Yeah, if it's too big, you can get other problems. Like you might get flash. Flash, which is where the plastic squeezes out of the mold.
I've seen that. Yeah.
Yeah. It's not pretty.
So it's finding that sweet spot.
Exactly. The goldilocks zone.
Okay, what else? What about. I know. We're talking about the runners, too. Those are important, right?
Absolutely. The runners are like the highways of the mold.
Okay.
They carry the plastic from the gate to the different parts of the mold, and you want those highways to be nice and smooth.
So no traffic jams.
Exactly. No sharp turns, no bottlenecks. Just a straight shot to the destination.
And that helps to prevent short shots.
Well, if the runners are all twisty and turny, the plastic can slow down and cool off, and that increases the risk of a short shot.
Okay. And I bet trapped air can be a problem too.
Oh, yeah. Air is the enemy.
So how do you deal with that venting? Venting.
You got to give that air somewhere to escape.
So little holes or something.
Yeah. Basically, you put in these tiny channels or grooves in the mold.
Smart.
And those allow the air to escape as the plastic fills the cavity.
So it's like a pressure release valve.
Exactly.
So we've got our gate, our runners, our vents. Anything else we need to think about for the mold?
Well, there's some more advanced stuff, like collapsible cores and hot runner systems.
Okay. Those sound fancy.
They are. They're more for complex molds and high volume production.
So what do they do? Like, in a nutshell.
So collapsible cores are used for parts with really intricate internal features. Like, imagine you're molding something with a hollow section. You need a core to create that hollow space, but you also need to be able to get it out of the mold after the part cools.
Right. So it collapses in on itself or something.
Yeah, exactly. Pretty cool, huh?
That is cool. And what about hot runners?
So hot runner systems keep the plastic hot all the way through the runner system.
Okay.
So it reduces the risk of the plastic cooling down too quickly and solidifying before it fills the mold.
So it's all about keeping that flow going.
Exactly. Flow is key.
All right, so to sum up this mold design section, what are, like, the big takeaways for people to remember?
Number one, smooth flow.
Okay.
Make sure your gate is the right size, Your runners are nice and streamlined, and you've got good venting.
Got it. And then for Those tougher molds with those crazy shapes.
Don't be afraid to explore those advanced options, like collapsible cores and hot runners.
Awesome advice. Okay, so we've got our material check. Got our mold. Now it's time to fire up that machine.
Let's do it.
This is where it gets really interesting. Right. All those settings and knobs and dials.
It can be a little intimidating.
Yeah. So let's break it down. What are some of the key things that we need to pay attention to on the machine itself to make sure we're not getting those short shots?
So one of the big ones is injection pressure.
Okay. Injection pressure.
That's basically the force that's pushing the plastic into the mold.
Okay.
If you don't have enough pressure, the plastic might not be able to reach all the way into the mold cavity.
And that's how you get the short shot.
Exactly.
But too much pressure is probably not good either, right?
Yeah. Too much pressure can cause other problems, like you might get flash, or the part could warp.
Okay. So it's about finding that balance again.
Always finding that balance.
What about injection speed?
Oh, yeah. That's important too.
So how fast the plastic is actually going into the mold.
Exactly. Especially if you have a really intricate mold or. Or a material that cools quickly.
I can see that.
If you inject too slowly, the plastic might start to harden before it fills the mold completely. So you need to make sure it's flowing fast enough to reach all the nooks and crannies.
Okay. And temperature must play a role in this, too.
Huge role.
Both the temperature of the mold itself and the barrel where the plastic is melting.
Exactly. If the mold's too cold, the plastic's gonna cool down too quickly, and you could get a short shot.
Makes sense.
And if the barrel temperature is too low, the plastic might not melt properly, and then it won't flow as well.
So many things to keep in mind.
It's a lot, but once you understand how it all works together, it's pretty amazing.
So we've talked about material choice, mold design, machine settings, any other, like, secret weapons in the fight against short shots.
Well, technology is really starting to make a difference here.
Okay, like, what kind of technology?
So one of the coolest things is sandwich simulation software.
Oh, yeah, I've heard about that.
It's amazing. You can basically create a virtual model of your entire injection molding process so.
You can see how it's all going to work before you even make anything.
Exactly. You can test different materials, different mold designs, different machine settings and see how it all affects the final part. And that can help prevent short shots?
Absolutely. You can identify potential problems before they even happen.
That's so cool. And what about those sensors I've been hearing about? Are those helping too?
Yeah, those are awesome.
Little tiny sensors right in the mold.
Yeah. They can monitor things like pressure and temperature and flow rate in real time. In real time. So if something starts to go wrong.
Like a pressure drop.
Exactly. The sensor can pick that up and alert the operator.
Oh, wow.
So they can adjust the settings and hopefully prevent a short shot.
So it's like having a little detective right there inside the mold.
I like that.
All right, we got to talk about AI. Everyone's talking about AI these days. How is that impacting injection molding?
AI is playing a huge role, especially in process optimization and predictive maintenance.
Okay, what does that mean?
So with process optimization, AI can analyze data from past production runs and identify patterns and trends, and then it can use that information to suggest adjustments to the machine settings. So it's like having an AI expert constantly tweaking the process.
Exactly. And with predictive maintenance, AI can analyze data from the machines themselves to predict when maintenance might be needed.
Oh, that's smart.
Yeah. So you can avoid costly downtime and prevent defects that might be caused by a machine malfunction.
So AI is helping us make better parts and keep those machines running smoothly.
Exactly.
It seems like with all these advancements, the future of injection molding is looking pretty bright.
Oh, absolutely. It's a really exciting time to be in this industry.
Well, this has been a fascinating deep dive. I've learned so much.
Glad to hear it.
And I think the big takeaway for our listeners is that preventing short shots, it's not a one size fits all solution. It's really about understanding all the different factors that come into play.
Definitely. It's a complex process, but when you break it down, it's really not that scary.
So don't be afraid to experiment, to try new things, to keep learning.
Yeah, that's the key.
And with all the tools and technology.
Available today, the possibilities are endless.
Well said. Thank you so much for joining us on this deep dive into injection molding.
It's been a pleasure.
And for all of you listening out there, keep exploring, keep innovating, and keep pushing the boundaries of what's possible. Until next