3D printing has already had a huge impact on manufacturing industry. Hand pieces that used to cost a few hundred dollars and took a few weeks can now be designed in the morning, printed at night, and delivered to customers next morning. Some companies are already using 3D printing process to make injection molding mold. It is no longer necessary to spend months waiting for manufacture of mold that can be used for production, or because of downstream design changes that result in a large amount of money invested in modifying mold, or uncertainty in production layer. Whether it's mold validation or small batch production of injection molded parts, you can quickly print 3d printed molds. If there is a problem with mold or if you need to modify design, print one, repeat verification or production.
These views have some truth. Plastic 3d printed injection mold is a bit like plastic shed in our backyard. It is cheaper than metal shed. Plastic shed is built quickly and performs well under low load. But if there is too much snow, they will break into pieces. 3d printed injection mold can be a reliable alternative if following conditions are met:
1. Small batch and relatively simple parts, product needs a relatively large draft angle.
2. Tool and mold design team is familiar with design principles of 3d printed molds.
3. With personnel and equipment for processing and assembling plastic molds

 

3d printed molds have their own place, and some companies have been successful in application of 3d printed molds. Proponents claim that 3d printed molds are up to 90% faster and 70% cheaper than traditional mold processing. In some cases this may be true, but it is important to understand advantages/disadvantages of metal molds compared to 3d printed plastic injection mold.
Real molds, real fast manufacturing company Proto Labs has been producing fast mold injection parts since 1999. It provides molds for manufacture of parts such as engineering plastics, metals, liquid silicone (LSR) and other materials. Mold is mainly machined from aluminum (in some cases with steel), can process several to 1000 parts, and delivery time is 1-15 days.
Its industrial grade 3D printing services include photo-curing (SLA), selective laser sintering (SLS) and direct metal laser sintering (DMLS). Printable materials include thermoplastics such as polypropylene and ABS, industrial grade nylon and metals such as stainless steel, aluminum alloys and titanium alloys.
Since there is such a large range of processing capabilities, why not directly print mold, but machine mold?

 

3D printing is processed layer by layer to obtain parts, which leads to a staggering effect on the surface of product. There are similar problems with directly printed molds, which require machining or sandblasting to eliminate these small, toothed edges. In addition, holes smaller than 1 mm must be drilled, larger holes require reaming or drilling, and thread features require tapping or milling. These secondary treatments greatly reduce speed advantage of 3d printed molds.

If you are designing a skateboard or plastic toolbox, 3d printed molds may be no problem. Part size is limited to 10 cubic inches (164 cubic centimeters), roughly size of grapefruit. And despite high precision of current additive equipment, it is still not comparable to machining centers and EDM equipment. The latter's cavity is typically accurate to ±0.003" (0.076 mm) and parts are up to 59 cubic inches in size, roughly six times volume of 3D printed parts.

In order to ensure good material flow performance, injection mold needs to be heated to a very high temperature. Aluminum and steel molds typically experience temperatures of 500 F (260℃) or higher, especially in high temperature plastics such as PEEK and PEI (Ultem) materials. It is easy to produce thousands of parts with these metal molds, and it can also be used as a transition mold before final mass production mold comes out. Mold materials made using SLA or similar 3D printing processes are typically photosensitive or thermosetting resins that are cured by ultraviolet light or laser light. Although these plastic molds are relatively hard, they are destroyed very quickly under thermal cycling conditions of injection molding. In fact, 3d printed molds typically fail within 100 uses in mild environments for high temperature plastics such as polyethylene and or styrene. For glass filled polycarbonate and high temperature resistant plastics, only a few parts can be produced.

Big reason for using 3d printed molds is because of its low cost. Cost of production-grade machining molds is typically $20,000 or more, which means that same size as $1,000 printing mold is comparable. However, this analogy is unfair, evaluation of printing stencil usually only considers material consumption, and does not consider labor, assembly and installation, injection systems and hardware. For example, aluminum molds cost $1,500 for production. If you need to produce more parts? With 3d printed molds, you need to reprint and assemble new molds for every 50-100 products you produce. On the other hand, aluminum molds are still in good service in production of 10,000 parts, regardless of plastic used.

Principles and practices of traditional injection mold manufacturing have been more than a century old, and industry is relatively thorough in its research. 3d printed molds is very new. For example, draft angle must be greater than or equal to 5 degrees to meet most aluminum mold requirements. Plastic molds are challenging to mold plastic parts, and extra care is required for number and mounting position of plastic molds thimbles.

 

Plastic molds (especially high injection temperatures) are somewhat more flexible in terms of increasing cavity wall thickness and reducing pressure. Design of gate is also different, tunnel and dot gates should be avoided. Direct gates, fan gates, and wing gates should be increased to three times normal size.
Flow direction of polymer in print mold should be consistent with 3D print line to avoid high packing caused by stickiness and low pressure. Cooling system can increase life of mold to a certain extent, but it does not significantly reduce number of cycles of printing mold, because heat dissipation capability of plastic molds is not as good as that of aluminum mold or steel mold.
Although fast aluminum molds have many advantages, in some cases 3d printed molds still play an important role. For manufacturers who have a 3D printer and have enough time to explore how print mold works on injection molding machine, they may think that mold should be printed directly.
Of course, mold designers must understand how to make functional molds, and cost of redesigning and manufacturing molds. Relevant technicians and equipment are also necessary – mechanical workers for mold blasting, thimble installation, injection molding machine operators, etc., because setting of these parameters is very different from traditional molds.

 

Why not print metal molds directly? DMLS uses lasers and precision optics to draw parts layer by layer on a small metal powder bed, producing fully compact commercial products for aerospace and medical applications. Some people predict that future molds for aluminum and die steel materials may be printed directly, providing ultra-efficient conformal cooling channels that will significantly reduce injection time and extend tool life. To some extent, DMLS direct printing molds are slow and expensive, usually only for very small, complex molds, or for mold inserts that are difficult to manufacture by conventional machining methods.
In general, ProtoLabs believes it is best to use DMLS, SLA or other 3D printing processes to do what they are good at: printing parts instead of molds. However, 3D printed injection mold can be a reliable alternative if following conditions are met.
1) For small batches and relatively simple parts, product requires a relatively large draft angle.
2) Tool and mold design team is familiar with design principles of 3D printed molds.
3) Personnel and equipment for processing and assembling plastic molds.
Final design considerations. If you need molds for long-term use, once 3D printed molds verify rationality of design, next step is to make molds with more permanent materials, such as aluminum or stainless steel, because plastic molds are mainly used in small batch production. Due to different design of 3D printed molds and traditional molds, a certain number of mold redesigns and tests must be considered in project time and budget.
Although 3D printing technology is outstanding, it only solves production of a small number of samples and its efficiency, cost are not at same level with mold. In small batch production, 3D printing costs are lower. However, in large-scale production, it is still based on molds.
Overall, 3D printing technology is far from comparable to mold industry. Technical differences between these two, different production directions, and different customer groups, are doomed to be not on same development track. As a result, mold industry will naturally not fall due to 3D printing technology.