Updated: Jul 18, 2019
3D printing is touted to be the technology to replace injection molding. Injection molding is a highly beneficial manufacturing technology where there is a high tooling cost. The high tooling cost is acceptable when the production volume is relatively large. In metal AM set up and tooling costs are low but the variable cost is very high. But, is it possible to take advantage of each? One possible way could be using metal additive manufacturing for making molds themselves.
How can AM contribute to injection molding which is one of the most used manufacturing technique:
3D printing when compared to any other manufacturing process offers ease of design iteration for designers. In mold making, this advantage can be very well utilized as one mold can produce a large number of injection molded parts, and the design of the mold can be modified easily and printed quickly. In AM significant changes can be done to an initial insert or an individual mold with design adjustments.
Prototyping mimics full production runs. To cite an example, if a shop uses a mold insert for prototyping that is 3D printed, the same material and process can be used in a real environment as well. For parts that are destined to be injection molded at a large scale AM brings in the opportunity for designers to test the parts at near identical conditions. If any changes are required, this can be incorporated within the mold easily.
Most components can be made using a traditionally manufactured mold. But, sometimes the designs are so complex that they cannot be realized using machining. Internal channel is one such example which is difficult for a conventional manufacturing technique. The incorporation of internal channels helps to produce good quality parts and cooling channels is one of the most relevant and well-known applications for this. For example, 3D printing helps in the creation of molds with cooling channels built in. This helps to enable a faster cooling time. This helps to reduce the cycle time needed for the production of a part. Studies have shown that with the help of conformal cooling channels it is possible to reduce warpage and cooling time. Parts that are thicker consumes a lot of time to cool. In a study done, wherein conformal channels were printed using SLM, to produce tooling for support for pipette tips used in the medical industry, the overall cycle time had a significant reduction of 34.2%. (Source) Contura MTH GmbH had made molds with cooling channels which help to reduce cycle time and rejection rate. (Source)
Some mold designs are two parts mostly making it difficult to get the component produced out the mold. One of the methods adopted to sort this issue is printing a plastic part to create a ceramic mold. The original plastic melts away when the ceramic mold is heated and metal is injected into the resulting cavity during the transition to production. Metal 3D printing helps in avoiding such a complex process and saves both time and cost of making such molds.
One commercial example of using 3D printing for molds is the work of PLM Group and the Danish plastics manufacturer Vilecon who developed 3D printed molds for injection molding, especially for low series volume productions. In a study documented by the company when 3D printed molds were used in place of Aluminum molds, the costs reduced significantly by a factor of 20 from typically about 11-12,000 EUR to less than 500 EUR.
Few points have to be kept in mind while adopting 3D printing:
The limitation of materials that can be printed. The structural integrity of a 3D printed mold currently does not match that of a CNC machined part.
Financially viable for low production volume items where rapid mold making is required.
The material in usage must be resistant to heat and pressure and parts to be produced must be complex which cannot be realized using conventional process
The limitations of metal 3D printing currently hamper its usage in mold making for traditional large volume direct part production. Additive manufacturing in mold making is still at infancy but shows enough promise. These improvements in materials, as well as the technology itself, will translate into greater adoption of 3D printed molds.
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