Scientific Molding Podcast Transcript

Kelly

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Kelly

Hello everyone, and welcome back to the Mine to Manufacturing podcast. My name is Kelly Riley and I’ll be your host for today’s episode. In previous episodes, we’ve talked about part design, mold design and tool build. Today we’re going to get into the actual manufacturing process and scientific molding. Joining us for the discussion today is Kyle, staff member of the Process engineering department here at PTI.

Welcome to the program and thank you for joining us today, Kyle.

Kyle

Hello. Thank you for having me.

Kelly

Of course. So, Kyle, tell us a bit about yourself and how you got involved in process engineering.

Kyle

Well, I’ve worked in manufacturing for six years and I’ve been at PTI for the last four years. During my time at PTI, I’ve had multiple roles in the shop at entry level, I was a press operator. Eventually a material handler became a die setter, worked in quality, process tech to a process engineer now.

Kelly

So you have seen it all in the plant?

Kyle

Yeah, it’s good. It gives me a lot of experience across different departments, helps me troubleshoot for myself and for other guys really.

Kyle

Great. Well, tell me a little bit more about the process engineering team and how many members do you have? Experience? Are you guys RJG certified? Tell me a little bit more about the team.

Kyle

Well, there are six of us process engineers total. We all have RJG certifications and altogether we have over 100 years of processing experience.

Kelly

Okay, so bringing a lot to the table.

Kyle

Definitely.

Kelly

Fantastic. Well, let’s jump right into it here. So a tool is built and now it’s on the manufacturing floor. So what happens now?

Kyle

Well, the first thing we want to do is we want to reconfirm that the press selected during the design stage is correct for this tool. So we need to look at a lot of things. But the most basic thing is the actual physical size of the molds. It needs to be able to fit between the tie bars of the selected press.

Kelly

Okay, that makes sense. And that makes sense.

Kyle

Definitely. And then we want to calculate the projected total surface area of the part in the runner, and that’s going to ensure that we have a press capable of applying enough clamping force (tonnage) to keep the mold closed during injection. That’s very important.

Kelly

Okay. And then what next?

Kyle

Finally, the last thing I would say is important is the maximum shot capacity of the screw in the barrel assembly. Ideally, we want to use around 20 to 80% of the available shot capacity. And that just helps us better utilize the design of the screw and prevent over or under heating of the material while it’s running.

Kelly

Okay. Speaking of material, how do you confirm that you’re using the right material for the job?

Kyle

Well, we study the material type. It’s processing specifications. We want to consider the melt temp, the mold temperature. That’s essential for cooling. We do the material drying time and temperature to make sure that we’re processing the material when it’s supposed to be. And then the maximum allowable moisture content.

Kelly

Okay.

Kyle

Yep. And then we can look for any other special molding, handling or storage recommendation. So this information provides us with some basic but essential parameters for processing

Kelly

Processing that specific type of material. Okay. Okay. So what happens if you determine that maybe another material is more suitable or would that be a rare occurrence or what? What about that?

Kyle

It’s a rare occurrence, but it does happen. So the material use is usually chosen at the beginning of the part design stage on the customer’s end because they kind of build the bed into the tool. Okay.

Kelly

Okay. Right.

Kyle

But on the rare occasion where a chosen material is not suitable, we can make our recommendations to our project managers who then can take their concerns back to the customer. We can find a suitable alternative additive.

Kelly

Okay.

Kyle

Or we can always send the tool to have a little work to it to help accommodate this new material.

Kelly

Okay. Is there anything else that you look at to consider before you’re developing the actual process?

Kyle

Well, yeah. You need to make sure you have all the correct auxiliary equipment there at the press. So when the job starts, you’re going to be capable of running it. So you would think, is this tool automatic? Well, if it’s automatic, then we need converters or conveyors to move the parts out and segregate bad parts. Okay. Are there hand loads?

Kyle

If it does, do they need removal fixtures to remove the parts from the hand load?

Kelly

Okay.

Kyle

And then other things like processing high heat thermolators If you’re going to need to have the mold temp over 200 degrees Fahrenheit and then, you know, hot runner systems or process monitoring and control systems like EDART from RJG.

Kelly

Kyle, you just mentioned high heat thermolators. Can you briefly talk about high temp processing?

Kyle

Yeah, of course. Hi. Temp processing is very similar to regular processing. It’s just higher temperatures. Anything over 200 degrees Fahrenheit for a mold temperature is considered high heat.

Kelly

Okay.

Kyle

And then usually any material over 600 degrees is high heat material

So it requires a dedicated area in the shop to run because it is such high temperature, it’s dangerous. You can burn yourself. It requires certain protective gear when you’re operating.

Kelly

Okay. Okay.

Kyle

Like arm sleeves or specialty gloves, and it’s mainly used for parts that need to be durable or maybe exposed to high levels of heat.

Kelly

Okay. Okay. But regardless of the temperature of the mold or the resin, you’re still going to use the same process development along the way.

Kyle

Yeah. Processing wise, we develop it the same way.

Kelly

Okay. So. So you’ve gone through all those different parameters, the molds ready for a preproduction trial, then? Then what happens?

Kyle

That’s the fun part. So in our industry, there are three main methods used to mold parts, and I’ll go over them briefly. So there’s traditional molding or D1, there’s decoupled two or D2, and then decoupled three or D3.

Kelly

Okay.

Kyle

So traditional molding is the less advanced and least consistent style molding. It’s where the fill and the pack stage occurs as one. This is kind of an older style of processing, and with the advances in technology and molding machines, it’s not really utilized today, especially in our field of medical molding.

Kelly

Where things are more technical. Okay.

Kyle

So then decouple two or D two is it allows more control of the molding process. So the difference between D two and traditional is the first stage is filling the part based off of defined shot transfer position. And the goal of this stage is to produce a part roughly 98% full with small visible shorts at the end of the fill.

Kyle

Okay, so you’re not making a full part. You want a short part, just very slightly short.

Kelly

Okay.

Kyle

And then the second stage is the pack and hold phase. It’s used to finish mold filling. It compensates for part shrinkage, and it’s to achieve the gate seal. The gate seal is the time at which the polymer at the gate is frozen and no more plastic can be packed into the cavities or flow out.

Kelly

Okay. Okay.

Kyle

Yep. And that’s important. And then D3 is first stage is filling the part to a shot position of roughly 80% full. And then we use second stage to pack the part to a set cavity pressure. And we utilize an external transfer trigger, like a cavity pressure sensor in a lower injection speed. And then the third stage is utilizing the hold pressure just to achieve the gate seal again.

Kelly

Okay. There’s a lot there.

Kyle

Yep. D2 and D3 are the most widely used methods of molding. It’s because they produce a stable and more consistent process, and that translates to manufacturing repeatability and higher quality on the shop floor.

Kelly

Right. So you’re addressing that quality issue right there.

Kyle

Right at the get go when you make the process

Kelly

Yeah…setting up the process. Okay. So that’s just a very basic understanding or a quick overview of process development. So scientific molding, where does that come into the manufacturing process and how do you implement scientific molding?

Kyle

Well, scientific molding…we use it to refine our base process. We use something called the Scientific Injection Molding Workbook or SIM.

Kelly

Okay.

Kyle

So the SIM is a series of mold machine and material tests performed press side, and they help us refine and improve the process. And it provides us real time data as we’re performing the test.

Kelly

Okay, So yeah, the process tests. You’re doing the tests in real time right there. You’re receiving the data back in the trial.

Kyle

You’re making parts, you’re looking at your changes and what it does to the part quality.

Kelly

Okay. Okay.

Kyle

And so, so.

Kelly

Lots of different tests. Are there several tests? Like how do those help the molder? We’ll get into a few of those.

Kyle

Yeah, there are a couple of important tests. The first one we perform is the injection speed linearity test, and that’s a machine test used to confirm the molding presses injection speed capabilities at different injection speeds. So this determines how much control there is over injection speed. Certain presses hydraulics take longer to ramp up to certain speeds. So depending on the part size, you may never be able to reach that speed.

Kelly

Okay.

Kyle

So it’s important that, you know, if you’re filling it two inches a second, you’re actually filling it two inches a second. And not just what the machine’s capable.

Kelly

Capable of doing…Okay. Okay.

Kyle

So then the next test would be in-mold rheology or the viscosity curve. Rheology, just being the study of the flow of matter.

Kelly

Okay.

Kyle

So this plats material viscosity or its resistance to flow versus the rate of shear using read outs from the press, including the actual injection pressure in the fill time at different fill speeds. So this helps us determine the optimum fill time and fill speed for the part.

Kelly

Okay. Is there a sequence to these tests or does it depend more on what you’re trying to accomplish? So if you have these SIM tests, you do, you know, there’s just a sequence in order of operation of the test.

Kyle

The SEM workbook gives you a step by step to process the tool scientifically.

Kelly

Okay. Okay.

Kyle

So then the next important test would be the melt temperature. A material test that confirms the material is being processed within the acceptable temperature range. It’s very important. If you’re processing the material at a wrong temperature, you’re not going to get good results.

Kelly

A good part of it.

Kyle

So we use a 30/30 method using a parameter or a probe. So we let the press run for 30 minutes, let the heat equalize and stabilize. I mean, and then we purge the press out and have 30 seconds to take accurate melt temperature.

Kelly

Of the resin. Okay. Okay.

Kyle

And then next test would be a pressure loss, which determines the amount of pressure required at each stage of the flow path from the nozzle to the screw to the runner to the gate. And finally, the filled part. So this demonstrates how much pressure each of these areas eats up and what is available to the part at the end of the fill.

Kelly

By the time you get to the end of the filled part. Okay. Okay.

Kyle

In multi cavity tools, we perform a dynamic cavity imbalance in this to test the effects of different injection speeds on the balance or the weight of a multi cavity tool. We want to make consistently the same 98 both sides of the cavity.

Kelly

Okay. Okay.

Kyle

So now we can perform a dynamic check ring repeatability study. This is a machine test measuring the variability in shot volume or the part weight during fill. So we run ten shots. We weigh them and we try to make sure that the weights are within an acceptable margin of difference.

Kelly

Okay. For each ten. Okay. Okay.

Kyle

And then finally, probably the most important is the gate seal. So as I said earlier, the gate seal, the gate is considered sealed or closed when the part no longer gains weight and no material flows back out of the mold.

Kelly

Okay.

Kyle

So that’s a set second stage pressure, which we while we increase the time intervals between shots. So by testing various pressures in the settings and the effect that they have on part appearance, we choose the best pressure setting for the part.

Kelly

For that part

Kyle

And this helps to optimize our cycle time and reduces cost.

Kelly

Okay. Okay. Yeah. Good. Ultimate. If you’re if you’re producing a lot of parts, every second in a cycle time is going to matter. Okay. And then. And you stressed the part appearance. Okay. Okay. So there’s a lot of tests there. That was, what, probably about eight, eight different tests there performed in a sequence. So each test gives you important data.

Kelly

What are what are the benefits of all of that data, then?

Kyle

This data points the processor in the right direction as to how to make a quality part consistently.

Kelly

Okay. Repeatability.

Kyle

Yep. And then after completing these tests, the process is finalized and recorded in our system.

Kelly

Okay.

Kyle

Sample parts are sent to the in-house metrology lab for measurement and the quality department reviews them for final approval.

Kelly

Okay. Okay. So you’ve got more testing based on all that data, and then it goes to quality. So based on the quality review, would you then use all that information to go back and adjust processes if needed based on what comes out of those lab results?

Kyle

Yeah, the lab results tell us important information and it tells us if we need processing changes or if we potentially need some tool work.

Kelly

Okay. Okay.

Kyle

You know, things in the spec we can do, we can start the validation effort and start performing a design of experiment or edge of failure.

Kelly

Okay. Edge of failure?

Kyle

Yeah. Exciting. Which is a study to learn how much the process affects the part. So as a good practice, we usually select three key factors like mold temperature, the hold pressure, or maybe the cooling time for these DOE interactions. And we take nine groups of sample parts total. So then these are then measured and this data again is used to kind of tell us where we want to be processing wise or as I said, if the tool needs adjusting.

Kelly

Right. Whether it’s a process adjustment, a tooling adjustment, all in the in the name of getting a quality part.

Kyle

Yep. Yeah. And process validation is very important in the medical field. PTI is a leader in medical part validations. This validation pretty much proves and tests out our process…shows that we’re consistent and that we can consistently make good parts. So if they want to go further, we have other tests, including IQ, OQ and PQ runs.

Kelly

It further refines the process. Okay. So in future episodes, we’re going to be getting more into validation. So…I guess I’m just thinking like, what would be like a key takeaway you would want our listeners to have about scientific molding and what they should be thinking about?

Kyle

Well, it’s important to understand the whole process of the Scientific Injection molding workbook. It is the starting off point for the validation process.

Kelly

Okay. So whether or not you have a tool, you’re going to validate the scientific injection molding that that workbook and this whole scientific molding process is important because regardless of validation, you want to produce a quality part every time. So customers should be looking for a molder that’s using this type of a scientific approach.

Kyle

Yep. Here at PTI, all tools are shot using the SIM workbook.

Kelly

Okay. Yeah. And then you’ve got the data from all those tests. You use that as your basis for processing and refer back to it through different part runs.

Kyle

Yep. Yep. And future validation is necessary. It’s nice to have that information ready for us.

Kelly

Locked in. Okay. Okay, great. Well, Kyle, thanks so much for sharing your team’s expertise with us today. It’s just all part of the process of producing quality parts every time. Thanks, everyone, for listening today. Meet us right back here for our next episode. If you would like more information about the scientific molding process, you can visit our website, teamPTI.com.

Kelly

And we’ve got more information there. And you can always, of course, reach out to us via the website as well. Thanks for listening. You’ve been listening to the Mind Manufacturing podcast brought to you by PTI Engineered Plastics. You can subscribe to the Mind to Manufacturing podcast wherever you listen to your podcast. And please don’t forget to leave us a review.

Kelly

Want to learn more about PTI? Engineered Plastics Custom Injection Molding Services. Please visit teampti.com and follow us on social media. Thank you for joining us today and we’ll meet you right back here for our next episode.