What is the 3D Printing vs Injection Molding Cost-per-Unit Breakeven?
The Uses of Additive Manufacturing vs 3D Printing
Injection molding vs 3D printing represents a classic debate of 'old' vs. 'new' in today's manufacturing industry. While 3D printing is the newer technology, it cannot replace the traditional manufacturing of parts provided by injection molding or other similar techniques. However, both processes are used together to move from design to full scale production. Companies will use 3D printing as they move through prototyping and design changes, and once they’re sure of a design, they’ll move into injection molding.
As Dr. Mark Cotteleer of Deloitte Services summed up at the 2014 SIMT Additive Manufacturing Symposium, "Additive manufacturing is not a panacea. There is no reason to view it as a universal replacement for traditional manufacturing methods. [However,] we do see it as important within the constellation of manufacturing methods that businesses can deploy in pursuit of performance, innovation, and growth."
This article will go through the processes, applications, concrete examples, and real-world use cases of both manufacturing methods.
Injection molding is a manufacturing process that relies on the use of molten plastic inserted into a mold cavity, producing a part with a specific shape or geometry. Injection molding is one of the most cost-effective ways of creating plastic parts, which is why these parts are everywhere in our daily lives.
Simply put, the injection molding process can be described in 5 steps:
- Clamping (Mold Close) - This is where the mold closes and tonnage is applied. Typically a mold is divided into two halves, the A side and the B side. However, there are many cases where the mold can be divided into more sections.
- Injection – During this stage, the majority of the molten plastic is injected into the mold.
- Packing and Holding (sometimes called dwelling) – Pressure is added to the system to fill out the final parts of the mold. The pressure is then held for a set amount of time.
- Cooling – This involves the cooling of the heated plastic into the final form. The cooling stage can take seconds or minutes.
- Mold Open - Tonnage is released and the mold opens.
- Ejection – the part is removed to be further processed or shipped. This stage can be automatic or manual and marks the end of an injection cycle. The entire process is then resumed from the clamping stage for the next part.
Is injection molding additive manufacturing? Definitely not. Additive manufacturing processes refer to constructing a part on a layer-by-layer basis. More information about the injection molding process can be found in our ultimate guide to injection molding.
Due to its versatility, the injection molding process is employed in every industry including the automotive, medical, and aerospace sectors, all of which feature different certifications. All industries, however, recognize ISO 9001 certifications for quality, and FAI (first article inspection) procedures are common in the aerospace, medical, and automotive industries. Most of these same certifications and regulations also apply to 3D printed products.
The automotive industry uses injection molding for both large and small intricately designed parts. This includes bumpers, dashboards, cup holders, and mirror housings. The Production Part Approval Process (PPAP) production standard governs injection molded parts in this field, so companies that meet those standards are able to become Tier 1 suppliers.
Since this is one of the industries where consumer safety is of utmost priority, pharmaceutical and medical injection molding providers must ensure the plastic resins they use meet the industry's standards. Manufacturers can have certifications including ISO 13485 and should be able to mold in clean rooms with sterilization processes such as gamma and e beam techniques.
Parts with high tensile strength that can resist extreme temperatures, comparable to their metal alternatives, can be created via plastic injection molding. This process also allows for high-volume orders that use affordable production materials (pill bottles, for example). Injection molding can also be helpful in the production of high-grade systems like the ones related to X-ray machinery.
Aerospace companies use injection molding for products from chassis components to turbine blades to housings. Injection molding suppliers can earn AS9100 certification, and can additionally be AS9110 and AS9120 certified if they handle MRO parts or sourcing, respectively. PPAP production standards also apply in this industry, and companies producing defense products should also be ITAR compliant.
This sector uses injection molded products for food processing, storage, and consumption. Products made for this industry include straws, containers, caps, filtering components, and processing equipment components. Food and beverage companies should have FDA certification while ensuring RoHS, REACH, and NSF guidelines are also followed. They can also meet GMA safe standards, set by the Grocery Manufacturers/Food Products Association to ensure food quality.
Plastic injection molding can also be used to create custom parts in this industry. Some engineering-grade plastic resins exhibit high durability and stability, qualities complemented by excellent cost-effectiveness compared to metal and wood alternatives. Such properties are especially desirable in the case of hand tools, accessories, and fasteners.
FREE Injection Molding Design Guide
3D printing is a method belonging to the additive manufacturing family of processes, encompassing multiple technologies that can be used to create parts out of base materials. 3D printing has seen increased use since the technology has become less expensive and it has advanced enough to facilitate the manufacturing of complex geometries.
3D printing usually uses CAD data to construct the desired part on a layer-by-layer basis, fusing those layers to 'grow' the part. Some common materials used in 3D printing include polymers, composites, glass, metals, and photopolymers.
Components created via this process more often than not belong to the category of 'prototypes,' or at the very least, small-scale manufacturing. Because 3D printing has primarily become an automated process, the expertise required to operate the machinery is not that high, enabling businesses and people to engage in manufacturing experimentation.
When manufacturing small parts, the only significant recurring cost related to 3D printing is the material used. For large ones, different, more expensive machinery is required, which significantly raises the costs of the entire manufacturing process.
More details about this process, including both tools required and costs involved, can be found in our Complete 3D Printing Guide.
This type of technology, while relatively new, has made its way into every industry, but it has become especially popular in those with stringent precision requirements, such as robotics and aerospace. While many of the regulations and certifications listed for injection molding above also apply to 3D printing, it is still new enough that not many have been created specifically for this manufacturing method.
One of the most significant advantages 3D printing has given aerospace manufacturers is the ability to test functional part prototypes. Advancements in 3D printing have been spearheaded by industry leaders such as Airbus, Boeing, and Safran.
Since this is an industry where complex parts are produced in low volumes, 3D printing is a natural fit for the aerospace sector. It has helped engineers experiment with increasing aerodynamic and engine performances while attempting to reduce weight as much as possible. The materials used in this industry range from engineering-grade thermoplastics (ULTEM 1010, reinforced Nylon, PAEK, etc.) to metal powders (such as titanium, aluminum, and stainless steel).
3D printing has seen more and more uses in the robotics industry, as the parts used are usually small (and complex) enough to require only a one-time investment in a 3D printing machine. Customizable parts are a norm in this sector, as well as an emphasis on lightweight and durability. All of those qualities can be achieved through 3D printing.
This technology has seen heavy uses in the medical and dental industry, via products and processes like bio-printing, prosthetics, and custom medical devices. 3D printing can also provide patient-specific products like implants and other dental appliances, so its use is centered around the concept of personalized healthcare.
Injection molding and 3D printing manipulate plastics in different ways. Molding injects liquid into a form to cool into a solid part, while printing deposits multiple layers of melted plastic to build a piece from bottom to top. While 3D printing has allowed for innovative design implementation within hours (for small parts), plastic injection molding remains an industry standard for high-quality, reliable, large batch production.
There is no doubt that 3D printing is a cutting-edge manufacturing technique. The reality, however, is that most plastic parts you see both in daily life, and in industrial environments, are still made via plastic injection molding. However, the two manufacturing methods are regularly used, with 3D printing beginning to see particular interest from the space industry.
The question of plastic injection molding vs 3D printing comes down to your project's requirements. There are pros and cons for each process that can help guide you to a decision.
|Injection Molding Pros||Injection Molding Cons||3D Printing Pros||3D Printing Cons|
Injection Molding Pros
Fit for mass production
Injection Molding Cons
More strict design requirements compared to 3D printing
3D Printing Pros
Low costs for low volume
3D Printing Cons
Not yet fit for large parts and batches
Injection Molding Pros
Enhanced part strength
Injection Molding Cons
Expensive and time-consuming to correct mistakes
3D Printing Pros
Support for complex designs
3D Printing Cons
Long production time per piece
Injection Molding Pros
Minimal wasted material
Injection Molding Cons
More expensive if not used for large-scale orders
3D Printing Pros
Easy to quickly iterate and test part designs
3D Printing Cons
Generally rough surfaces on the constructed part
- Allows for mass production. Industrial injection molding machines are built to create multiple parts simultaneously using multi-cavity molds. This decreases the execution time for large orders and lowers costs.
- Enhanced part strength. This is due to how the process itself is executed. A single poured layer of cooled plastic adds strength to the part since there is a lower risk of fissures or points of weakness.
- Minimal wasted material. To increase the cost-effectiveness of the process, manufacturers tend to use only as much material as needed for each design. That makes plastic injection molding an efficient way of mass-producing not-too-complex parts.
- Strictere design requirements compared to 3D printing. While any part design can be created using injection molding, fitting the design around certain rules helps to avoid a far greater expense from extra complexity in the tooling to achieve those effects.For more on injection molding design guidelines, see our in-depth guide on injection molding.
- Expensive and time-consuming to correct mistakes. A part created using a mold is very hard to correct if any issues are found with the design itself. Changing your part's geometry means re-machining the mold, resulting in additional costs. If such a decision is not made early, there is also the possibility of having to redo an entire batch of parts. To avoid this, companies will often 3D print products in the design phase until they are sure they’ve reached the final form of the part.
- More expensive if not used for large-scale orders. Injection molding can be considered a cost-effective solution in the case of large batch production, but it has high setup costs, so the price per part only goes down as you manufacture more of them.
- Lower costs. This is especially the case with lower volume orders or rapid prototyping applications, as generally only one machine and a trained engineer is required to fulfill such orders.
- Support for complex designs. Due to the additive nature of the manufacturing process, it is possible to create complicated parts with a high degree of accuracy.
- Easily and quickly iterate designs. With 3D printing you can rapidly develop and test part designs since there is no need to create a mold upfront. It is even possible to fabricate multiple configurations of a design for testing purposes within the same build.
- Not fit for large parts and batches. Part size is generally confined to the size of the printer’s build area. In large designs, it is also possible for the structure to become unstable due to uneven weight distribution or uneven cooling rates which can induce warping in the part.
- Slow output. 3D printing build time generally scales linearly with increased quantity. In other words, the more parts you print, the longer it will take. The slow output of 3D printers balances the ability to support more complex designs.
- Generally rough surfaces on the constructed part. While the layers inputted by the 3D printer are quite small, they can still be noticeable. This translates into a rough surface on finished products which may not be suitable for parts where cosmetics are important. Typically parts will require additional post-processing steps, such as vapor smoothing, to smooth and improve the surface finish.
In general, the breakeven point between which of the two methods is most cost effective is reached between 250 and 2,000 parts (we explore this more in our case studies in the next section). While analyzing which one of the two processes would best fit your project or business, it is useful to also take into consideration the following:
Volume does not contribute heavily to the cost of a part, but surface area does. This is especially the case with 3D printing, as large surface areas contribute to long production time and material use. Injection molding cost, however, is not that heavily affected, since the mold has to be pre-designed anyway. This pre-design may also come in a form of a 3D printed injection mold for short run applications, though these molds don’t hold up for larger volumes.
As is the case with almost all manufacturing processes, large volume orders translate to lower costs. If we are to consider a relatively simple small part, some studies (including the one linked above), show that 3D printing costs would be in the order of 10%-20% less expensive than injection molding for production in the order of 20,000 parts or less. The 3D printing vs injection molding cost breakeven occurs at the 40,000-50,000 part mark, in this scenario. The actual numbers will most likely differ, depending mainly on the geometry of the part and the subsequent material use.
Injection molding cost is heavily influenced by product iteration. That means that with a change of design, a change of mold is also required. This puts 3D printing at a notable advantage in this comparison. No tooling costs are attached to a change of design in the case of this type of additive manufacturing technique. Plastic injection molding vs 3D printing cost breakeven is thus also affected by the possibility or expectation of such a change in part design.
In this price study, we compare three different geometries across different processes, at different quantities and recorded the price. The geometries were a drone leg (representing a typical part), a potentiometer knob (representing a small part), and a junction housing (representing a larger part). It is important to showcase different geometries because the pricing behavior per process often relies on the size and shape of the manufactured model. The amortized price per unit is recorded at doubling quantities, from 1 to 8,192 pieces, to represent the full-in price in each of the 8 technologies reviewed.
We uploaded the 3D CAD files to Xometry's Instant Quoting Engine℠, which provides instant quotes for 3D printing, CNC milling, and urethane casting in various quantities. Xometry's injection molding service typically provides quotes same-day.
Our example drone leg has a bounding box of 146.69mm x 139.57mm x 33.00mm (5.775in x 5.495in x 1.299in). A bounding box is an imaginary box around an object that shows its dimensions in image processing.
The drone leg's geometry prices out the least expensive in selective laser sintered (SLS) nylon from quantities of one ($32) to roughly 250 ($24). Around this range, another 3D printing process called HP Multi Jet Fusion (HP MJF) became slightly less expensive per part. Still, at the same time, the price per unit in injection molding hit its break-even point and quickly shows its scaling benefit. The results are clear; at around a quantity of 250, it makes sense to start considering injection molding for a project with this geometry, with scaling that quickly goes to dollars a unit. This becomes roughly $3 per piece at quantities over 8000, including the cost of tooling. Given the curve, it is clear that the pricing would amortize even further as quantities increase.
Data results for the per-unit price of the drone leg are shown below, showing doubling quantities from 1 to 8,192 pieces.
Data results for the per-unit price of the drone leg over doubling quantities from 1 to 8,192 pieces.
The potentiometer knob has a bounding box of 16.81mm x 15.20mm x 15.20mm (0.662in x 0.598in x 0.598in). It is about the same size as a thimble.
The potentiometer knob tells a different story than the drone leg. Because of its small size (about the size of a thimble), it remains cost competitive using 3D printing for quantities up to 2000 units before the break-even hit to injection molding. Note that around a quantity of 30, it is more economical to move from SLS 3D printing to HP MJF 3D printing. At $3.45 per unit, HP MJF is an excellent solution to keep small batch inventory on hand using just-in-time (JIT) methodology. However, if over 2000 are needed, then injection molding can save you thousands of dollars throughout the product's lifetime. In fact, the per-unit price without tooling amortized was less than $0.80. Savings could be even higher if a multi-cavity mold tool is chosen.
Data results for the per-unit price of the potentiometer knob are below, showing doubling quantities from 1 to 8,192 pieces.
Data results for the per-unit price of the potentiometer knob over doubling quantities from 1 to 8,192 pieces.
The junction housing has a bounding box of 215.84mm x 172.44mm x 68.18mm (8.498in x 6.789in x 2.684in). This would be considered larger on many 3D printing platforms.
The junction housing is an interesting case because it is typically considered a “larger part” on 3D printing platforms. This gives it a higher per-unit price from the get-go, and also very little discount over quantity for these processes. SLS nylon still is the cheapest at quantity one, being just above $200. Around 30 units, there is actually better pricing if the part is CNC machined. Even urethane casting and HP MJF tend to be more competitive than SLS between quantities 30 and 250. Like the other parts in this study, injection molding is ultimately the clear choice for production manufacturing. The upfront tooling to mold this piece is over $10,000, but the per-unit price is so low that at 250 units it becomes dramatically more economical, by an order of magnitude, to move to injection molding tooling.
Data results for the per-unit price of the junction housing are shown below, with doubling quantities from 1 to 8,192 pieces.
Data results for the per-unit price of the junction housing over doubling quantities from 1 to 8,192 pieces.
3D printing and injection molding are not competing, but rather complementary ways of manufacturing. Businesses (especially smaller companies that commonly use 3D printing in production) will commonly use SLS or other 3D printing techniques for rapid prototyping and low-volume production. From there they’ll switch to injection molding once the volume of parts needed is above a certain threshold. This way reduces the time and costs to mold or machine each iteration of the part design, allowing companies to develop the same products more quickly and cheaply.
The ability to produce a just-in-time quantity of parts in a short amount of time is also where 3D printing shines. Compare that with injection molding, which is typically used in mass manufacturing – i.e., producing hundreds, if not thousands, of parts inexpensively.
Although the cost per unit is an important figure, there are several hidden costs that managers should also take into consideration when making manufacturing decisions:
- Time required to manufacture and receive parts
- Potential inventory costs
- The option or flexibility to quickly change product design.
All of these play a factor in manufacturing selection and vary on a case-by-case basis. Ultimately, engineers and project managers should think critically about their project goals and determine whether a combination of processes, such as 3D and injection molding, is best for them.
Want to check out how your parts' costs compare? Talk with Xometry’s experts today. All it takes is a 3D CAD model. Xometry accepts STEP (.step, .stp), SOLIDWORKS (.sldprt), Mesh (.stl), Parasolid (.x_t, .x_b), Autodesk Inventor (.ipt), Dassault Systems (.3dxml, .catpart), PTC, Siemens (.prt), and ACIS (.sat) file types.
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