Fast, cheap, good. The original challenge in manufacturing was to achieve speed and quality at low costs, and it is a common belief that it is impossible to have all three. When producing plastic parts, most engineers would say that plastic injection molding is the best solution for all three aspects, with fast production cycle times, strong materials, and low cost per part. But with the latest innovations in 3D printing, is that still true?

In April 2024, we compared the Form 4 with plastic injection molding to demonstrate how far 3D printing has advanced: that it can compete or even surpass plastic injection molding when it comes to speed and quality at lower costs. The comments were filled with many questions. Now, with the launch of the Form 4L, which has a print volume more than 4.6 times that of the Form 4, we decided to conduct this test again by producing the Form 4 Resin Mixer Latch parts with two Form 4L masked stereolithography (MSLA) 3D printers and plastic injection molding. We aimed to prove that the rapid speed of the Form 4 family of 3D printers can outpace traditional injection molding.

Below, we break down the cost details, time, and mechanical properties for the production of functional parts, while addressing audience questions about costs, post-production steps, and the mechanical properties of parts printed with 3D printers.

Production of the Form 4 Resin Mixer Latch
Manufacturing process: Plastic injection molding vs. 3D printing

The Form 4 Resin Mixer Latch is a part of the Form 4 Mixer, which is an accessory that attaches to the resin tank in the Formlabs Form 4 Series printer and enhances material performance by keeping the resin consistent within the tank during the printing process.

For this test, we timed the production of two processes in a race to produce 1,000 functional parts: an actual contract manufacturer using plastic injection molding and two large Form 4L resin 3D printers.

The mixer latch serves to secure the Resin Mixer in place on the Form 4 machine.

For plastic injection molding, we have collaborated with a contract manufacturer located in Taiwan, which has produced parts for several generations of Formlabs 3D printers, including resin tanks, cartridges, and mixers. The two-cavity mold used in this test is a real mold used for the continuous production of the Form 4 Resin Mixer Latch parts.

The plastic injection molding machine used by the contract manufacturer has a working area of about 10 square meters.

For comparison with 3D printing, we used two large Form 4L 3D printers designed for high-volume production, with a large print area and fast printing speed. The setup also includes one Form Wash L machine and one Form Cure L machine for the post-printing process.

For the material, we chose Black Resin, which is a versatile material with hardness and strength, providing parts with a matte finish, ready for presentation.

In a real injection molding environment, each production cycle takes 50 seconds and produces two parts. Speed can be increased by using molds with more cavities, which will produce more parts per cycle, or by reducing the production cycle time by modifying the process. However, this process is what we and our contract manufacturers have determined to be the most suitable for our production needs. As we will discuss shortly, injection molding will become a more cost-effective manufacturing method for this part when production volumes exceed approximately 13,000 pieces.

With the Form 4L, we print 78 parts per print job, which means 13 print jobs are needed to produce a total of 1,000 parts. The proprietary Low Force Display™ printing technology used in the Form 4 series printers allows for fast printing, with settings adjusted in the Print Settings Editor of PreForm to increase speed even further. The custom print setting with a layer height of 150 microns reduces the number of layers needed to complete the print and increases light irradiance and exposure to reduce the time taken per layer. Learn how to use the Print Settings Editor here.

Production time for parts

Both parts produced by plastic injection molding and 3D printing require some post-production steps.

Plastic injection molded parts need to have sprues and runners removed, while 3D printed parts need to be washed and cured, including the removal of supports.

In both cases, post-production steps can be carried out by operators alongside the production process, meaning that post-production will only add time to the production in the final round of the parts.

Delivery time comparison: six weeks versus within one day

Although our head-to-head competition focuses solely on production time, in reality, the timeline for production starts from the creation of the molds used in plastic injection molding. Creating molds of this size and complexity typically takes several weeks and can be expedited by paying an increased cost of about 2-3 times. From the completion of part design to the finished part, the overall timeframe generally spans about 4-6 weeks, including design for manufacturability, mold making, production, and various processes.

In contrast, 3D printing does not require tools or molds and can print parts within a single day without additional costs. This means that small-scale production using 3D printing can be completed before the mold design for injection molding is even finished.

Cost per piece analysis: 85% lower cost.

Since there are no mold costs, 3D printing is widely recognized as a low-cost method for producing small quantities of parts. This reputation also holds true in this case: at a quantity of 1,000 pieces, 3D printing is 85% cheaper than plastic injection molding.

We broke down the numbers and found that the breakeven point between these two methods is at 13,050 pieces.

Producing 1,000 pieces with outsourced plastic injection molding costs $3,920, while in-house 3D printing with Form 4L costs only $600.

The cost per piece as a function of production volume shows that 3D printing is a more cost-effective option for producing up to 13,050 pieces. Purchasing resin in bulk at a discounted price can further reduce the cost per piece of 3D printing, which may shift the breakeven point to over 40,000 pieces, depending on the amount of resin purchased.

The cost per piece of plastic injection molding varies significantly with production volume due to the high initial investment in molds. The mold used to produce this mixer latch part costs $3,600. Additionally, contract manufacturers charge $0.32 per piece for materials, labor, and overhead costs.

On the other hand, 3D printing does not require molds, so the cost per piece varies less with production volume and consists of the costs of machinery, consumables, and labor.

For this comparison, we averaged the total system costs over a period of 3 years, which includes investments in printers and operational expenses such as space, energy, maintenance, and cleaning solutions for parts. When produced in large quantities, the proportion of machine costs per piece has very little impact.

In terms of material costs, the Form 4 Resin Mixer Latch part uses 6 milliliters of Formlabs Black Resin, which costs $65 per liter when purchased in a 5-liter container, meaning the material cost per part is $0.40. As a vertically integrated manufacturer, Formlabs offers discounts for bulk orders, with prices as low as $35 per liter for resin. Therefore, for large-scale production, the cost per part can be reduced by up to 50%. Contact us to learn more about bulk resin pricing and receive a cost analysis tailored to your specific application.

For Form 4, the largest cost factor is labor, as the print area of Form 4 is smaller, allowing only half the parts to be placed per print job compared to Form 4L, meaning more than double the print jobs are needed to achieve the target number of parts.

As a result, operators need more than twice the time to prepare and perform post-printing steps for parts printed with Form 4 compared to Form 4L, and the hourly labor cost will increase accordingly.

In our model, we assume a labor rate of $30 per hour, which can be adjusted in the cost per piece calculator.

Total Cost Based on Specified Quantity:

There are several ways to calculate cost per piece; breaking down this detail is just one of them. For example, we did not include shipping and import taxes in the calculation, as this cost depends on location.

In the case of plastic injection molding, this cost can increase by about $500–1,000, while in-house 3D printing incurs no shipping costs.

Material Selection and Mechanical Properties: Suitable for Real-World Use

Viewers of the video in April 2024 questioned whether 3D printed parts could withstand real-world use. In the past, SLA resins were often too brittle for functional parts, but the new General Purpose resin from Formlabs has strength and stiffness comparable to PET.

For this test, we chose Black Resin due to its strength and stiffness that meet the requirements for the part's application. Additionally, the smooth matte black color also addresses the aesthetic aspect of the part.

The design of the latch requires a balance between stiffness and compliance: the part must be stiff enough to act as a lever and flexible enough to click in and out of position.

The mechanical properties of Black Resin meet the physical requirements for normal use of this part. For more information on this material's properties, you can download the technical data sheet of Black Resin.

A cycle tester was created to lock and unlock parts hundreds of times, and the 3D printed parts remained functional after testing was completed.

Winner: 3D printing with Form 4L

Whether you include lead time or not, 3D printing is the winner in the race to produce 1,000 pieces compared to plastic injection molding, winning by about one hour or up to six weeks. Additionally, 3D printing is up to 85% cheaper for producing 1,000 pieces and remains a more cost-effective option up to about 13,050 pieces. Finally, Black Resin has suitable mechanical properties for the practical use of this part.

However, we do not claim that 3D printing will be the winner in every case — the decision depends on design, application, and many other factors. But what was once seen as slow, costly, and inefficient for functional parts has now become a viable manufacturing option for a variety of applications.

We understand that readers with questions may want more information. You can use our interactive cost calculator to explore the differences in time, cost, and volume between 3D printing and plastic injection molding on your own, or talk to a 3D printing expert to learn how 3D printing can meet your production needs.

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References

https://formlabs.com/blog/race-to-1000-parts-3d-printing-injection-molding/