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3D Printing Vs. Injection Molding
We are frequently approached by customers asking if it’s viable to 3D print their parts rather than injection mold them. Every part is unique and there are a variety of factors in determining whether 3D printing makes sense. Below, we’ve outlined these core considerations, such as cost, lead time, properties, and materials to help you make the right decision.
When deciding how to produce your parts, cost is likely to be your primary concern. The two main factors that determine this are your tooling cost and your part cost.
With injection molding, there is considerable upfront cost in the form of tooling. Cutting a mold can cost a few thousand dollars at a minimum, which is difficult to justify if you’re not producing a large number of parts. Adding your tooling cost to the cost of actually molding your parts can make your total unit cost unviable. 3D printing, on the other hand, has no tooling cost but will typically have a much higher part cost.
Beyond the cost of your tooling is the cost of making each individual part. For injection molding this can be anywhere from a fraction of a penny to several dollars. This is typically determined by the amount of raw material needed for each of your parts and the volume of parts you are producing.
Part cost for 3D printing is typically much higher than for injection molding. Even when 3D printing small parts in high volumes, you can typically expect each part to cost no less than ten dollars. Larger parts can cost anywhere from a few hundred to more than a thousand.
Break Even Point
With the above information it becomes apparent that the best case for 3D printing vs injection molding is in low volumes. Because of tooling costs, 3D printing will be vastly more economical when you only need a handful of parts.
But eventually, you’ll reach a break-even point at which injection molding becomes cheaper. With 3D printing, your total unit cost is essentially a flat rate. When injection molding at higher volumes, your tooling cost and your part cost eventually drop below the flat rate of 3D printing.
The total number of parts you need to produce is also a major factor in deciding whether to go with 3D printing vs injection molding. If you need more than a few hundred parts, injection molding is the way to go. Even if your parts are small, a 3D printer will take a whole day to produce just less than a hundred of them. And 3D printing a large part can take several days by itself.
Another factor that has been critical to nearly all of our customers is lead time. There are two factors that determine lead time: tooling time and cycle time. Typically, 3D printing will have a slower cycle time (print time) than injection molding. But unlike injection molding, you don’t have to wait for your tool to be cut.
Traditional injection molding requires tooling to be cut, which can take weeks or even months. This may be something to consider if you’re wanting to get your products to market quickly to capitalize on demand and don’t necessarily have time to wait. For 3D printing, since no tooling is required, a part can be printed as soon as your design is finalized.
With injection molding, you can shoot hundreds or even thousands of parts per day. Cycle times for injection molding are typically measured in seconds or, in extreme cases, minutes. 3D printing, on the other hand, has much higher cycle times or print times. Even a small part, like an electrical connector, can take an hour to print. There are some time savings when 3D printing multiple parts at the same time, but it’s still nowhere near injection molding. And as we’ve already said, large parts can take a matter of days.
Apart from cost and speed, part strength is always something you want to consider. Because of the differences in how they are made, injection molded and 3D printed parts are quite different in their mechanical properties.
Fused deposition modelling is a common 3D printing technology which creates parts in layers of thermoplastic. These layers, while firmly adhered to one another, may still delaminate if subjected to high enough shear forces. Additionally, each layer is composed of an outer boundary wall which is filled with a honeycomb pattern. This outer wall is also liable to break under too much force.
Photopolymer 3D printing technologies, such as PolyJet, MultiJet, and SLA, produce parts that are completely solid and not subject to the above concerns. However, the materials offered by these technologies tend to be brittle with low heat resistances.
On the other hand, injection molding produces homogenous plastic parts. Because there are no layer lines where they may easily split, and because the part interior is completely solid, they tend to be much stronger. Injection molding also offers a much larger variety of materials, which tend to be more durable.
Depending on your part’s intended use, materials can have a big effect on your decision to use one method of production over another.
The materials for 3D printing are limited. For the majority of 3D printers, you will only be able to run a small number of materials, and they may only be clear, opaque, and a small variety of colors. In some cases, dye may even be applied to 3D printed parts to achieve your desired color.
In contrast, injection molding is able to produce parts from nearly any thermoplastic or polymer you can think of. Additionally, injection molding may make use of additives, such as fiberglass, electrostatic dissipative materials, calcium, and more. Injection molded parts can also be made in nearly any color imaginable. And color is applied to the raw material rather than the part, which eliminates the risk of chipping a dyed or painted 3D printed surface and showing the natural color.
When to Use 3D Printing Instead of Injection Molding
While the most common considerations of using 3D printing versus injection molding are discussed above, there are a few particular examples of when you might turn to 3D printing regardless.
If the part you’ve decided to print has some complex internal geometry, you may have problems making it with injection molding. Often, injection molding cannot handle complex internal geometries due to impossible draft angles, such as with overhangs. If this geometry exists in your design, the mold may not be able to properly eject the part, causing breakage. If you choose to use inserts within your mold, this can drastically drive up the cost of cutting the mold. Additionally, even if the part can be removed, you face the possibility of air pockets or weak points being created in that part of the product. However, 3D printing can easily achieve this complex geometry thanks to its additive nature and use of removable support material.
3D Printing as Bridge Tooling
If you’re planning to ultimately go the injection molding route but need a few parts before your mold is cut, 3D printing may be a viable alternative to bridge tooling. To make sure you have parts when you need them, you can always 3D print your parts until your mold arrives.
If you need parts but your design is still liable to change, 3D printing can prove a better alternative than injection molding. Sometimes an existing mold can be altered, but this takes time. With 3D printing, you can quickly make changes that won’t cost you thousands of dollars.