Understanding Injection Molding Quotes
Audio File: 2014 Mar 14 – Understanding Injection Molding Quotes.mp3
Audio Length: 20:19 minutes
Hi, my name is Montie Roland. And I’m with Montie Design in Morrisville, North Carolina. We’re a full-service product development firm providing engineering services, industrial design services, and prototyping. So, we can help you design it; help you think through the concept; and then build you a prototype and provide the assistance you need to make the connections you need to manufacture your product, domestically or abroad.
This morning I’d like to talk about understanding an injection mold quote. And really, this . . . when you look at it and break it down, this also applies to most other manufacturing processes, the way that it’s structured.
So, if we’re going to create an injection-molded part, we need two things upfront. One thing is we need a completed design – and that needs to be in 3-D CAD – and then we also need to know what the material . . . materials used in the product are, which is really part of the design, but let’s break it out for the purposes of this discussion. That completed design is going to include 3-D geometry that you’re going to release to the molder as a .STEP file or a .IGES file. And it’s also going to include a drawing. That drawing will include any critical dimensions, any critical to function, any inspection dimensions. Also, secondary operations – if you’ve got a drill a hole in the part; or if you’ve got to put a threaded insert in.
So the drawing is no longer what we call “fully descriptive”. Fifteen years ago, drawings had to describe everything that you wanted to control about that part. If you wanted to control the size of a radius, you needed to create a section view and show that radius. Which, you can imagine, for an injection molded part, was an onerous task, because there’s a lot of details in a part like that. So, now what’s happened is we have parts that are defined in 3-D on the CAD – it’s in SolidWorks or ProEngineer; Catia; Unigraphics; what have you. And so those parts give a tremendous amount of information to the mold maker. So, no longer is the mold maker having to interpret a drawing. A lot of their tool pass and a lot of their mold design comes from your model directly, which makes for quicker tool builds because they don’t have to model the part. And also more accurate because they’re not interpreting from a 2-D drawing.
So, .STEP file; drawing, probably in a PDF format; and then your material choice. With plastics there’s a whole bewildering array of materials. A lot of times, though, parts end up being made out of common materials, such as ABS or nylon. These materials can also be filled. You can use a mineral fill, like a talc; you can have a foaming agent if you want to have a part that is a foam part. You can also fill it with fibers – long or short. And those fibers can give materials like nylon really, really great stiffness. And so you select that material. If you have questions about that, you know, the best thing to do is ask someone who has a good background in plastics injection molding. Also, you can work with your material provider. Depending on how exotic the material is, you may have to make a choice between . . . you may have to choose a provider like RTP that provides smaller quantities if you want something that’s more of a custom material. You remember, a lot of plastics are sold by the train car load, so if you make a few thousand parts, obviously, you use a lot less than a train car load. So, a custom material means you go to someone who deals in custom materials like RTP – which drives the cost per pound up dramatically. But if you have an application where you need some exotic properties, you can get them.
So when you go out for a quote – we had another podcast for our covered . . . you know, the mechanics of that – when that quote comes back, it’s going to have several items on it. And even if those items are buried in the price, they’re still there. The first item is the cost of your tool, your capital cost. You’ve got to build a tool to make an injection molded part. That tooling price, we have seen prices fluctuate dramatically and all over the board. But, really, there’s several main options. One option is what we’ll call is a temporary tool for very low-volume manufacturing. A good example of this is Protomold. Twenty-five hundred to thirty-five hundred bucks; they can have you a tool. The parts are probably three . . . four . . . five-X; maybe eight or nine . . . ten-X what it would cost a traditional molder; however, if you only need a hundred injection molded parts, there’s no point in building a fifteen thousand dollar tool and making five thousand as a test run if you only need a hundred. So, I oftentimes . . . companies like Protomold are very good at that. And the traditional molders, they may be abroad or they may be domestic. And so, any of these folks are going to give you a quote for the tooling. And that cost will vary, depending on if it’s a temporary aluminum tool, if it’s a aluminum tool, or if it’s a steel tool. An aluminum tool may make tens of thousands to a few hundred thousand parts. A steel tool may make millions of parts. So, the choice of your tool is dependent upon the process you need . . . or, excuse me, the number of parts you need that tool to last. Often, aluminum tools are adequate until you get to a real high volume.
The other thing that happens with injection molded parts is that often your toolmaker’s going to use what’s called a mud base, rather than make a full-up tool. What that means is that they have a standard tool skeleton, let’s call it. A skeleton has a giant hole in the middle, and what they do is they build a what’s called a mud base; it’s an insert that goes in that hole in the middle and connects up to the tool. That way you don’t have to pay for the entire tool; you just pay for a small part of it, which helps keep the cost down. And that’s totally fine.
If you’re going to make a tool abroad and you want to bring it home for domestic production, you need to make sure that the molder is involved in this process so that you end up with a tool that they can actually use. It’s common for . . . issues like fittings that are commonly available in China but aren’t available here to cause problems or, you know, some configuration that your molder can’t support. So often, if you go abroad for your tools, a good choice is to let your molder source that tool for you.
So, we’ve got a capital expense of the tool. The next thing is we have an expense of setting up the molder. So, this is a . . . in [inaudible 0:08:11.8] non-recurring engineering cost where they take the tool to the machine; they pull the tool that’s in the machine out (previous job); they put yours in. Some of these tools can get big and heavy so it’s an involved process to switch them out. Then what they do is they switch out the material in the hoppers and the screws, and put the material you want in there; dial in the temperature – temperature, pressure and timing are all very important for injection molding. And so they set that up; do a few test farts. This may only take a couple of hours; however, the thing to consider is that the molder has lost use of the machine. Not only are they doing work to get your mold in place, and it’s probably . . . set up guys an expensive employee-per-hour, but they’re also losing the use of that machine. So, you’re paying for machine time (where you’re not making parts), and you’re paying for a service, which is getting your tool up and running. And so, at first you say, well, that should come out of the profit. Well, by understanding and breaking these costs down, you can make better decisions, because a lot of times what will happen is you’re right – it will get hidden in the cost of the part. But – that drives the cost of the part up. So there’s a better way to do this as far as calculating what your run’s going to cost you. So, if we know the set-up cost, and then we get a part, a cost-per-part. Now, one of the things that everybody says is, Well, if I make a hundred thousand or ten thousand, I should get a much reduced cost per part. Well, the reason why you’re cost per part goes down is that you’ve amortized the set-up costs across a number of parts. So what this means is that let’s say your set up cost is five hundred dollars. And you make five hundred parts. Then that cost gets amortized over that run, and so that’s a dollar a part you’ve added to the cost of your parts. If you make five thousand parts, then you’ve added ten cents a part to the cost of your part. If you make fifty thousand, then you’ve added one cent to the cost of your part. And if you make a hundred thousand, you’ve added half a cent to the cost of your part.
So this is important to keep in mind because if you know the cost per part, which really doesn’t change because it’s a function of machine time; machine costs you this much to rent, costs you this much in plastic per part (your part weighs so many ounces), and it takes this long. Cycle time is a HUGH issue in production. Even a small amount of reduction in cycle time can help reduce the cost of your part over time. I guess really . . . let me restate that. A small reduction in cycle time is something that can impact a lot of dollars in profit; it can have a big impact on your profit over time, because that cycle time is never going to change. The design of that part, until you make a change to it, is going to stay the same; and the cycle time is going to stay the same, as long as the design and the tools stay the same. Cycle time is a function of how long the part takes to cool. The thicker the wall, the longer the cooling time. So you can’t remove the part from the tool, from the injection molding machine, until it’s reached a minimum temperature. So that temperature comes from that plastic cooling, the outside cooling first and the inside cooling slower. If you pull it out too soon, you can imagine you can do all kind of . . . create all kind of problems with the part because it’s soft. So that change in your design to keep the walls thin helps reduce your costs, now and in the future, by reducing the cycle time, which reduces the cost per part. The cost of each part, after the machine is set up, is driven by the cycle time, the material cost (which is generally done per pound), the secondary operations that have to be performed, and then the cost of any items needed to perform those operations. So, for example, if you’re snapping a lens in, you’ve got a couple of costs: you’ve got the cost of the lens, and you’ve got the cost of the time for someone to manually snap that in.
You can mold around items in the tool. The challenge there is that you’ve got to take the time to place that item while the tool is open. So often, secondary operations are performed after the part has finished molding, because that way you’ve got an operator there anyway; they can perform that operation and you’re making use of idle time, rather than keeping the tool open while you load something in the tool. A good example’s a threaded insert. Generally, threaded inserts are added after the part’s molded, because if you add them before the part’s molded, what you have to do is keep the tool open long enough for the individual or the robot to place that threaded insert. So, instead of opening the tool, dropping out the top part, and then closing the tool immediately and start making the next part, you can create a situation where you’re loading, I don’t know, let’s say six threaded inserts and it takes two seconds, or five seconds; so, that robot’s reaching in, loading that threaded insert, but that tool is not making parts at that point. So, most of the time, you’ll . . . the molder will insert that threaded insert after the part’s out of the tool so that the injection molding machine can go ahead and start making parts.
And that’s an important consideration that your molder will help you with. But that all rolls into the cost of that. If you have to program a robot to do a secondary, you may save some money in a very long production run, but the cost of the programming the robot and setting it up still has to be amortized across that number of parts. So, there again, set up cost and then actual production part cost for that part.
Same thing holds true for other operations. So, for example, C&C; you got to set up the C&C machine. You’ve got to fixture the parts, set up that fixture. You’ve got to program the machine or transfer the program into the machine. You’ve got to do a run off. So, that situation is very comparable. You’ve got a set up cost and you’ve got a piece cost. Piece cost really doesn’t change all that much, but the set up cost just gets amortized across that piece cost. So, that’s important to keep that in mind. And, sure, if you go to a company and say, I’m going to give you an order for ten million of these – can I get a break? Okay, gotcha; they’ll give you a break. But that’s going to be a small break and that’s . . . you’re not going to see the hard cost going half or something; you may see a few percent off, just as a way to close that deal. Because, at the end of the day, it costs them time on that machine and they’re going to charge you for that time and those materials, and amortize your set up across the number of parts in that run. And, if they give you one number that says this batch of parts, this quantity, will cost you this much, then really is what they’re doing is they’re just bundling that all together. They’re putting the set up cost in, the part cost in and they’re giving you one number. In my mind, you’re much better off to break it out and have a fixed price per part, and have a fixed set up cost. And then what you can do, as the manufacturer, is to decide how many parts you want to make. If you want to make one part, you can do that. But you know what the set up cost is, you know what the piece cost is, and make one part. Now, a lot of molders probably won’t set up for one part because it’s not profitable, but you get the idea there. But that way if you want to make a hundred, you want to make five hundred, you can set up your spreadsheet and do your math. You can conserve capital where you need to and you can take advantage of that economy of scale where you need to.
So, that’s, hopefully, given you an understanding of how to price or how to work with the prices you get from the molder, and turn around and price your products. It’s really not a complicated set up. A lot of molders have switched over to giving you a set up cost plus a piece cost. And it works much better in my mind because you actually know how that price is derived, and you can pick an intermediate quantity. Say you have a price of five hundred and a price for two thousand; well, now if I need seven hundred and fifty, I can calculate out what that price would be, and do it exactly. Because I have the formula here.
So, hopefully this has been beneficial. Just one little tech tip here and as you’re working through your new product. If you like what you heard and need some of this experience and skills we have, give us a call. We will be happy to help with your next project; we’re happy to do your next project, start to finish. Our job is to be ready when you are.
This is Montie Roland, signing off.