Written by: Matt Verlinich Published on: @November 4, 2021 Last updated: @November 4, 2021
Tools Used In This Recipe
The number one question I get from entrepreneurs is, "How much will it cost to injection mold this part?" While the price of injection molding had come down significantly in recent years, it is still a process inherently suited to production at scale. The definition of scale, whether it's 1,000 units or 10,000 units is going to depend on the part, your business model, and the supplier, so this seemingly simple question is actually quite difficult to answer.
There are many ways to get a rough idea of how much something will cost (topics for future articles), but the only real way to answer this question is to get a series of quotes. Quoting is often one of the biggest challenges for manufacturers and entrepreneurs alike, but this recipe will show you how to use Protolabs rapid quoting software to get an idea of how much your part might cost to make and if you're even ready to consider Injection Molding.
In order to work through this recipe, all you will need is a 3D model of your part in one of the following file formats: STEP (.stp/.step), SOLIDWORKS (.sldprt), IGES (.igs/.iges), Parasolid (.x_t/.x_b), PTC Creo (.prt), Autodesk Inventor (.ipt), CATIA (.CatPart), or ACIS (.sat).
Now you're ready to get started.
Step by Step
Step 1: Create an account
Go to Protolabs.com and hit the "Get a Quote" button to begin the process.
Before you can do anything you'll need to create an account.
Step 2: Create a project
Protolabs has a pretty good system for version control on the component level. I'd recommend creating a project for each assembly and/or sub-assembly. For example, if you have a jack-in-the-box the project would be for the whole product and contain each component individually (the enclosure, the crank, the puppet, etc.).
Step 3: Create a quote
Click the quote for each component/part that you would like to get a price on.
Protolabs currently offers rapid quoting for 3D printing, CNC Machining, Injection Molding, and Sheet Metal Fabrication. The quoting process is similar for each method of manufacturing, but this recipe will cover Injection Molding in particular.
Upload your part files.
Once the file uploads, select your part on the right panel to set material and manufacturing parameters.
Complete each of the fields request that appear on the left. Note: all of these fields can be adjusted after receiving an initial quote. You will likely want to do a bit of research on the specific polymers available, and understand if it's worth it to supply your own. Protolabs has a ton of good articles on material selection and other design considerations, but you'll probably want to do additional research as you get closer to production.
Now select the type of tooling you would like to use. Regardless of your selection you will receive a quote for each type of tooling. Protolabs has a handy break even point calculator which you can use after receiving the quote. We'll discuss the impact of tooling selection on break-even-point later. In general the longer the tool life, the larger the tool, and the more automation that's part of it; the more expensive the tool will be, but the cheaper the parts will be.
There are a whole host of secondary operations to choose from here. Some of these things you may be able to do yourself (assembly and laser engraving) to save a bit of capital up front, especially while prototyping, but some of these are extremely worthwhile to design into your process up front (Mold texturing and threaded inserts).
Hit the submit quote button! This will send your files out for a combination of human and automated processes to quote your parts. IM quotes typically take a day or so to turn around while other services like 3D printing are instant.
Step 4: Address manufacturability issues
It's very unlikely that you will design a part that has no suggested modifications. This step is probably one of the most valuable parts of this process because it reveals a lot of considerations which may improve the manufacturability, reliability, or unit economics of your part. You may have heard people talking about DFM (Design for Manufacture) well this is it! Click the "View Analysis" button to get started.
Each portion of the analysis has explanations associated with the reasoning for the suggested/required changes. Here are some additional useful resources from Protolabs website, but if you can't figure out a particular DFM question feel free to put some time on my calendar here.
You can submit revisions to your part in order to clear up all the manufacturability concerns. Make sure to click the "Configure Part" button in order to check that you have specified the appropriate quantity, finish, and materials you want before moving on.
Once you've confirmed all your manufacturing parameters, hit the "Review Quote" button in order to see a break down of your unit economics and breakeven points for different tooling styles.
Step 5: Analyze your unit economics
Now we finally get to the last, and one of the most critical decisions you need to make in order to determine your unit cost: what type of tooling should I choose? Tooling prices vary widely with injection molding and even more so when considering other methods of manufacture. In general the less you spend on tooling the more expensive each part will be. The critical factors in the cost of tooling are: 1) the material the tool is made out of 2) the number of cavities in the tool and 3) the amount of action/automation the tool does. Let's go over the impact of each of these factors on unit cost using Protolabs break even tool.
1) Tooling material
Tooling can be made of anything from 3D printed resin to aluminum to high grade tool steel. In general the more expensive the material the longer the tool will last, thus getting you lower unit costs over time. This is illustrated on the Protolabs quote below. The Prototype tooling has a limited lifespan , but it only costs $5,675. A comparable single cavity tool (more on that later) with an unlimited lifespan will cost you $7,665. The breakeven point is illustrated on the figure by low as the point where the blue and orange lines meet, around 1,400 units for a total cost of around $12,675 for both either tooling and 1,400 units.
If you expect your design will change quickly and you only need 50 units to test the part before needing new tooling, definitely go with the prototype tooling. If your design is ready to sell and you need to sell 1,000 units just to break even, then you might want to consider going with the single cavity, On-Demand Manufacturing tooling.
2) Decide on the number of Cavities needed
The number of cavities a tool has determines how many parts come out of tool each cycle: a single cavity too produces 1 part each time, 2 cavities produce 2 parts, etc. When volumes are low the majority of your unit cost will be dictated by the price of the tool and the value your manufacturer places on labor. In this specific example, a single cavity, unlimited-life tool costs $7,665 but a 4-cavity, unlimited-life tool costs 3.2x as much ($24,550). That means it won't be worth it to spend the money on a 4 cavity tool unless you expect needing at least 18,700 parts or you're ready and able to spend over $57,500 in total. Also notice that there is a $500 setup charge each time you'd like to produce parts from your tooling. If you're looking to order less than 1,000 parts that could be a significant contributor to your unit cost (over 5%), but if you need to order 20,000 parts in two 10,000 unit runs the effect is much less significant (<1%).
Depending on your part size, you may have multiple options for number of cavities. Make sure you check, because in this case, using a 2-cavity tool provides a happy medium in terms of the unit cost when comparing the different kinds of tooling. With a 2-cavity tool you would have to produce more than 20,000 parts in order to justify spending the additional money on a 4-cavity tool.
Most manufacturers will give you a different price for different quantity ranges ($5/part for 1,000-2,999 units, $4/part for 3,000-4,999 units, $3/part for 5,000+). This often requires you to do a bit of extra math in determining your break even point, but the "Part Price" tab allows you to see the impact of their sliding scale on part-price pretty intuitively.
Protolabs has a quick overview of the pros and cons of their "Prototype" tooling vs. "On-Demand Manufacturing" tooling.
Additional Considerations: Is injection molding really right for you?
Protolabs prices are fairly representative of the cost of injection molding; they probably won't be the cheapest option, but they won't be the most expensive either. If the prices and order quantities listed in the example above seem unreasonable to you it may not be the right time for you to consider injection molding.
Instead you may want to consider 3D printing your part in order to validate your design or get initial traction. You can use the same procedure detailed above to get an instant quote from Protolabs using a variety of materials/printing methods for the same part file you've already uploaded.
The example above was for a rubbery material known as TPE (Thermoplastic Elastomer), so using a Polyjet 3D printer I was able to get a quote for a comparable material. The Protolabs 3D printing quotes came in at $223.67 for 1 unit, $946.90 for 5 units ($189.38 each), and $9,083.50 for 50 units ($181.67 each).
For comparison, the cheapest you could make the same part at the same quantities via injection molding is $6,179.94 for 1 unit (including the $500 setup fee), $6,199.70 for 5 units ($1,239.94 each), and $6,422 for 50 units ($128.44).
In summary, for this relatively simple part it makes more sense to 3D print it when if I need ~50 units, injection mold it with prototype tooling if I need ~1,400 units, and begin considering more expensive tooling with multiple cavities above 1,400 units.
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