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Comparison between 3D printing plastic molds and traditional machining molds

Since the advent of 3D printing technology, there is no shortage of voices on the market that 3D printing is about to subvert the traditional manufacturing industry, especially the mold manufacturing industry. Traditional process injection molds often take several months to wait for the manufacture of molds that can be used for production, or because of downstream design changes resulting in a large amount of money to modify the mold or uncertainties on the production layer. And these using 3D printing technology seem to be easily solved, so it can be said that 3D printing can replace traditional mold manufacturing.

These views have some truth, but not accurate, 3D printing mold has its place, and some companies in the application of 3D printing mold are more successful. Proponents claim that 3D printing molds are up to 90 percent faster and 70 percent cheaper than traditional mold processing methods. This may be true in some cases, but it is also important to understand the advantages/disadvantages of metal molds compared to 3D-printed plastic molds.

Proto Labs engineers have been thinking about printing molds for a long time, but after 16 years in the rapid mold business, a few reasons still force them to stick to the reliable rapid injection molding process:

1, surface quality: 3D printing layer-by-layer processing parts, which will lead to the product surface having a step grain effect. There are similar problems with direct printing molds, which require machining or sandblasting to eliminate these fine, toothed edges. In addition, holes smaller than 1mm must be drilled, larger holes need to be reamed or drilled, and thread features need to be tapped or milled. These secondary processes greatly reduce the speed advantage of 3D printing molds.

2, size factor: If you want to design skateboards or plastic toolboxes, 3D printing molds may be no problem. Parts are limited to 10 cubic inches (164 cubic centimeters), roughly the size of a grapefruit. And despite the high accuracy of current additive equipment, it is still not comparable to machining centers and EDM equipment. The latter typically has cavity accuracy of ±0.003 inches (0.076 mm) and part volume of up to 59 cubic inches, roughly six times the volume of the 3D printed part.

3, high-temperature environment: To ensure good material flow performance, the injection mold needs to be heated to a very high temperature. Aluminum and steel molds typically experience temperatures of 500F(260 ° C) or higher, especially in the processing of high-temperature plastics such as PEEK and PEI(Ultem) materials. It is easy to produce thousands of parts with these metal molds and can also be used as transition molds before the final mass-production molds are produced. Mold materials manufactured using SLA or similar 3D printing processes are typically photosensitive or thermosetting resins, which are cured by ultraviolet light or laser. Although these plastic molds are relatively hard, they are damaged very quickly under the thermal cycle conditions of injection molding. 3D printed molds usually fail within 100 uses in mild environments, such as high-temperature plastics such as polyethylene and styrene. For glass filled with polycarbonate and high-temperature resistant plastics, even only a few parts can be produced.

4. Comparative cost: One of the main reasons for using 3D printing molds is its low cost. The cost of production-level machining molds is generally $20,000 or more, which means that the printing mold of $1,000 is comparable. But this analogy is not fair, the evaluation of the printing mold copy usually only considers the material consumption and does not consider the labor, assembly and installation, injection system, and hardware. ProtoLabsd’s aluminum mold, for example, costs $1,500 and can be used for production. If you need to produce more parts? With 3D printing molds, for every 50-100 products you produce, you need to re-print and assemble the machine to test the new mold. On the other hand, regardless of the plastic used, aluminum molds usually still serve well in the production of 10,000 parts.

5, Product design: the principles and practices of traditional injection mold manufacturing have a history of more than a century, and the industry has studied them thoroughly. 3D printing molds are very new. For example, the die Angle must be greater than or equal to 5 degrees to meet most aluminum die requirements. Plastic mold Injection plastic parts face challenges, the number of plastic mold thimbles and installation positions need to be extra careful.

In terms of increasing the wall thickness of the mold cavity and reducing the pressure, plastic molds (especially high injection temperature) are more flexible to some extent. Gate designs are also different, and tunnel and point gates should be avoided. The direct gate, fan gate, and wing gate should be increased to 3 times the normal size.

Real mold, real fast

Rapid manufacturing company Proto Labs has been producing rapid mold injection molded parts since 1999. It provides molds to manufacture parts in engineering plastics, metals, liquid silicone (LSR), and other materials. The mold is mainly machined using aluminum (and in some cases steel) materials and can process several to 1000 parts, and the delivery time is 1-15 days.

Its industrial-grade 3D printing services include light curing (SLA), selective laser sintering (SLS), and direct metal laser sintering (DMLS). Printable materials include thermoplastic materials like polypropylene and ABS, industrial-grade nylon, and metals (such as stainless steel, aluminum, and titanium alloys).

Since there is such a wide range of processing capabilities, why not directly print the mold, but machining the mold?

The flow direction of the polymer in the printing mold should be consistent with the 3D printing line to avoid high filling caused by viscosity and low pressure. The cooling system can improve the life of the mold to a certain extent. Still, it will not significantly reduce the number of cycles of the printing mold, because the heat dissipation capacity of the plastic mold is not as good as that of the aluminum or steel mold.


Despite the many advantages of rapid aluminum molds, there are cases where 3D-printed molds will still play an important role. For manufacturers with 3D printers and enough time to explore how the printed mold works on the injection molding machine, maybe they think they should print the mold directly.

Of course, mold designers must understand how to make functional molds, and mold redesign and production costs a lot of money. Relevant technicians and equipment are also necessary – mechanical workers for mold sandblasting, thimble installation, injection molding machine operators, etc., because the setting of these parameters is very different from that of traditional molds.

But wait — why not DMLS? Why not just print metal molds? DMLS uses lasers and precision optics to “paint” parts layer by layer on a bed of fine metal powder, producing fully dense commercial products that are widely used in aviation and medicine. Some people predict that in the future, aluminum and die steel molds may be printed directly, which can provide ultra-efficient cooling water channels, which will greatly reduce injection time and extend the service life of the mold. To some extent, DMLS is slow and expensive to print molds directly and is usually only used for very small, complex molds, or for machining mold inserts that are difficult to manufacture through traditional machining methods.


Overall, Proto Labs believes it’s best to use DMLS, SLA, or other 3D printing processes to do what they do best: print parts without molds. However, if the following conditions are met, 3D printing injection molds can be a reliable alternative.

1) Small batch and relatively simple parts, the product needs a relatively large drawing Angle.

2) The tool and mold design team should be familiar with the design principles of 3D printing molds.

3) There are personnel and equipment for processing and assembling plastic molds.

Final design considerations. Suppose you need a mold for long-term use, once the 3D printing mold has verified the rationality of the design. In that case, the next step is to use a more permanent material to make a mold, such as aluminum or stainless steel, because plastic molds are mainly used in small-batch production. Due to the different designs of 3D printing and traditional molds, the project time and budget should consider a certain number of mold redesigns and testing.

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