By Henrik Lundgren, CTO at Wematter.

As an organization is about to start printing 3D plastic objects, the material and quality specifications are often rather specific. To the producers of 3D printers, these demands can be challenging to meet, and quite often, the customer has to settle for different polymers than the preferred one, or at least a different quality.

The choice of 3D printing technology

In some situations, the demands on strength of the printed parts can be very low. In these instances, a company can settle for a cheap 3D printer using  Fused Deposition Modeling (FDM) technology. An advantage of FDM technology is that there are printers for a broad range of polymers since the technology has existed for many years, and the consumer market is large. 

In most cases, the prints need to be of much higher strength and quality. 

FDM prints are nowhere near the quality of injection molded parts. They crack easily, take in water and have a whole host of other quality issues that are not acceptable for final products or prototypes. This is a problem in both industrial development and the health sector.

To achieve a higher quality equivalent to that achieved by injection molding, 3D printers are required that use Selective Laser Sintering (SLS) technology. Here the choice of polymers that can be printed is more limited. As far as we know, Wematter is the only company in the world that works with different customer companies to be able to print the customer’s polymer on a specific printer, with parameters preset to easily print with optimal quality. 

Different types of polymer

A company that has found the perfect polymer for its production process and the end product is reluctant to change the polymer. The reason is that it is a long and demanding process to find the right polymer, partly because the number of variants of polymers that exist in the world is almost infinite. The properties of the polymer can be changed by adding different additives. Fiberglass makes the polymer stronger, plasticizers make it softer and more malleable. It is also possible to make the polymer more heat-resistant or more UV-resistant, and you can control how little liquid it absorbs.

The starting point is usually that an organization chooses one of the following main types of polymers, all of which have fundamentally different properties.

• Polyamide (PA) also known as nylon
• Polypropylene (PP)
• Polyethylene Terephthalate (PETE or PET)
• High-Density Polyethylene (HDPE)
• Polyvinyl Chloride (PVC)
• Low-Density Polyethylene (LDPE)
• Polystyrene or Styrofoam (PS)
• Miscellaneous/Other which includes polycarbonate, polylactide, acrylic, acrylonitrile butadiene, styrene, and glass fibers.

Choosing the right material

Next, it is important to find a polymer quality that enables the manufacturing process to deliver objects with the right properties. Plastics are developed, manufactured and supplied by different companies and the quality can vary significantly between one polymer and another. But most polymers come in formats suitable for injection molding, and rarely in the powder form required for 3D printing.

This is where Wematter comes into play. Wematter can help companies find a polymer grade that can be printed, with exactly the right quality. Of course, some polymers simply cannot be printed with SLS, but within reason, Wematter can contact its wide network of powder suppliers and ensure that the right polymer is produced in the right format. Of course, everything depends on how large the volumes are. Small companies with low annual polymer consumption cannot count on a complete match. But even small companies can usually get close enough.

Additive manufacturing with polymers

Most polymer objects have been manufactured by injection molding because this manufacturing technology is efficient and cost-effective for producing large series of relatively simple objects.

However, the production of the molding tool required for the molding can be both expensive and time-consuming, and there are restrictions on just how complex geometries can be produced using a mold. This is where Additive Manufacturing (AM) often comes into play. SLS is particularly popular in prototyping, spare part manufacturing, component manufacturing in small or medium-sized series, and manufacturing of objects with complex geometries. In the health sector, SLS is used when manufacturing individually adapted orthoses or prostheses.

Selection of 3D printer based on material

Not all 3D printers can handle all polymer materials. In fact, many can only handle one or very few materials really well. 

Wematter offers the Gravity 3D printer which prints a variety of materials. The count is currently up to over 20, and the number grows every year. The growth is driven by Wematter’s team of material developers collaborating with customers and powder manufacturers to produce prints of exactly the quality that the customer needs.

Wematter has a unique way of working, where a team of material engineers work closely together with a hardware and a software team to optimize the performance of the material in the Gravity SLS 3D printer. When the work is completed, Wematter can offer a complete, fully integrated solution with powder, hardware and software. This is an important part of Wematter’s strategy and makes it very easy for users to create successful prints right away, without the prior knowledge otherwise required to make advanced settings on an SLS 3D printer. The Gravity SLS 3D printer system is simply preset to the right parameters for each material. In addition, Gravity comes with a quality guarantee as long as both materials and equipment are sourced from Wematter.

Wematter’s work process

Before a material is introduced to the market by Wematter, an integrated team has done basic and comprehensive work, where the materials are classified based on a Technology Readiness Level (TRL), a well-known concept in research & development. Initial lab tests “on the bench” will indicate whether or not the material will work. At this stage, the focus is mainly on two parameters: How well the powder particles move (which is key for the powder transportation inside Gravity), and the behavior of the powder when it melts, (which is decisive for the quality of the SLS 3D prints that you will produce with Gravity).

A materials engineer checks the properties of polymers under development

If the material is approved by the lab, it moves on to the prototype stage. Here, the powder comes into contact with the SLS 3D printer Gravity for the first time. The test simply consists of the powder being sintered in the printer.

The first movement test is done in a cold machine to see how the powder moves and works together with Gravity. If this looks promising, the powder is tested in a heated machine and eventually a simpler print job is carried out. As the team learns more about how the powder behaves in Gravity, the team modifies various settings and progressively more and more advanced objects can be printed, with increasingly better quality. The first prints are now delivered to the customer for a joint evaluation.

If both parties are happy with the results, the work progresses. The team prints, evaluates, and agrees on what needs to be adjusted (the powder, software or hardware), and runs new tests and new evaluations.

The prototype stage ends when the team can say with certainty that the parameters required by the customer will be reached with this particular powder.

Full system implementation

After that, a new decision is required for the team to be allowed to start “Full system implementation”, which means that you must be able to print demanding prints with the default settings, i.e. exactly as a customer would have done it. The cycle of printing and testing is made with ever more demanding challenges. The requirement is now that the powder should be able to perform optimally in every way without problems, from filling to finished printing. Full System Implementation is completed when the team can deliver precise settings and specifications on powder, software and hardware that will confidently deliver marketable parts. Multiple aspects are taken into account. Nice surface finish, strength, packing density and other mechanical properties, including making optimal use of the available construction volume.

The polymer that the customer requested

The customer who bought the Wematter 3D printing system with the request to print a specific polymer can now safely print quality prints as specified.

The powder is added to Wematter’s portfolio of materials that can be offered to the market. The materials team continues to support the marketing department and the sales department in various ways, but their powder project is completed.

Contact Wematter

Do you want to know more about our different materials? Or do you and your company have a specific material that you need to be able to print in an SLS 3D printer? Contact us today and we’ll be happy to talk more about what we do best, SLS and powder materials in combination.