A lot of R&D dollars are currently being allocated for making 3D printing a viable production option. Recently, Plastics Technology reported on a machine currently in development at the University of Sheffield (South Yorkshire, England), which will produce parts 100 times faster and up to three times larger than anything available at the present time. University representatives feel this will be a machine that could compete with injection molding in the realm of high volume production.
This machine, which will utilize a new form of sintering called high speed sintering or HSS, is similar to other, layer by layer, additive based production efforts. However, instead of traditional laser methods applied to existing sintering technologies, HSS will utilize infrared ink and light to bond only the targeted stock while leaving the other material unaffected. This technology is being developed by Neil Hopkinson, a member of the University of Sheffield’s Engineering Department and is expected to be ready for industrial markets by 2017.
So with this new technology, what’s not to love? High volume production of plastic parts without the need for expensive tooling. No more wait time from the completion of a design to production, just enter the program into the machine and away you go, right? Well… These topics would be great advances to the mass production of plastics parts if all of the dynamics were being discussed.
Yes, for many speed, volume, and cost effective manufacturing are the deciding factors encompassing the production of plastic parts. However, there are many other variables that come into mind when considering the mass production of most of today’s plastics.
Plastic is a fantastically durable material that we interact with on a near constant basis. Durable and more importantly, strong. This strength is obtained through injection molding by even distribution when molten plastic fills the cavity of the injection tool and cools. Exhaustive methods have been practiced and improved upon to achieve the most even flow to provide parts that are as strong as the physical properties of the chosen material will allow.
In the layer by layer processes utilized in additive manufacturing, you have an inherent structural problem. While it lends the ability to build the part without the need for tooling, it also creates a laminate weakness between layers. The individual layers do not adhere as well on the Z axis as on the X and Y planes thus creating the issue. As Nick Allen, a leader in the additive manufacturing industry, wrote in his blog, “It is comparative to a Lego wall – you place all of the bricks on top of each other, and press down: feels strong, but push the wall from the side and it breaks easily.” This is a serious problem with regards to all of the items made from plastic that require the material to maintain strength and rigidity to be functional.
Many of the plastics items that we interact with on a daily basis are items that not only require strength, but we also intermingle these items with our senses or touch and sight. From the earbuds of your iPhone to your car’s headlight lens, plastic items need to maintain a level of comfort and functionality for consumers to continue utilizing them. This is another place where injection molding holds the edge. Mold tooling can be polished to a glass like finish or textured to a near infinite number of possibilities. These finishes are then transferred to the part during the molding process with no need for any follow-up work. Whether it is an A-1 finish for that polycarbonate helmet visor or that 20 µ EDM finish found on your car’s interior trim, injection molding offers a truly finished part.
The layer by layer method utilized in additive manufacturing is an issue. This process causes surface distortion in the form of rough textures and layer lines that cannot yet be engineered out to offer specific finishes. This creates the need for expensive hand work to the parts produced to obtain the desired finish. Hand or chemical finishing can also cause loss of detail that is hard to manage creating specification failures. This is especially a problem when tight tolerances are a factor as most post-production finishing methods are very hard to reproduce.
We are still justifiably amazed by the advances of additive manufacturing, especially with regards to the ability to obtain a prototype. However, the limitations in the technology are simply too much to be ignored. While I do feel there will soon be a place for high-speed additive manufacturing, the product market that will be willing to utilize the process will be very limited. Injection molding utilizing traditional tooling remains the only method of sustained and exacting specifications for the mass production of plastic parts.
Plastics Technology, New 3D Printer Looks to Compete with Injection Molding,
Gizmodo.com, Why 3D Printing is Overhyped (I Should Know, I Do it For a Living)