Improvements in additive manufacturing materials and processes make creating production-grade, functional wear parts possible while unlocking greater design flexibility.

By Preston Souza, Product Manager, igus Inc.

Historically, the choice between injection molding and additive manufacturing has been clearcut when it comes to producing functional plastic parts. The materials available for additive manufacturing didn’t have adequate mechanical or physical properties, with end-use parts unable to match the strength of injection-molded parts. And despite their ability to handle complex geometries, additive manufacturing processes were ill-suited for high-volume production runs, resulting in high piece-part costs. For these reasons, manufacturers historically used additive manufacturing and 3D printing technologies only for low-volume production or proof-of-concept efforts.

However, the gap between additive manufacturing and injection molding has started to close in some applications thanks to advancements in the tensile strength of additive materials and in-process capabilities. Nowadays, many plastic parts can be molded or printed to the same performance standards, making the choice between manufacturing processes a matter of production volume.

Despite such progress, this gap closing hasn’t been evenly distributed across all types of plastics applications. For example, in structural applications, improvements in the tensile properties of additive materials have enabled 3D-printed parts to approach parity with injection-molded parts. But for wear applications, which involve parts such as gears, lead-screw nuts, bushings, and bearings, the gap has persisted until now.

3D printing polymers pass the test for exceptional wear

Recent material advancements, such as the availability of internally lubricated materials, have resulted in wear-resistant grades of additive materials that can now match what’s only been possible for injection-molded materials. These new materials are now available for more than one additive process, including the following:

• Fused deposition modeling (FDM), the most common 3D printing process that involves depositing melted filament over a build platform layer by layer.
• Selective laser sintering (SLS), which uses high-powered lasers to sinter finely powdered material together into a solid structure.
• Digital light processing (DLP), which uses UV light to cure photopolymers one layer at a time.

These three processes can now use various proprietary formulations of base materials with internally lubricating additives and fibers to print parts with exceptional wear resistance. In many cases, the tribological properties of these resulting 3D-printed parts are comparable to, or even exceed, what standard 3D printing materials like acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and nylon have to offer.

Here are some examples, with results based on the following tests:

Linear long stroke tests. Compared to ABS, test data shows that iglide i180, an FDM material, and iglide i3, an SLS material, have lower wear coefficients by factors of 15 and 33, respectively. Such wear resistance makes iglide 3D-printed parts ideal for long-stroke applications like X-Y gantries.

Linear short stroke tests. Injection-molded and 3D-printed plain bearings made of iglide J260 have similar wear rates regardless of the manufacturing method. Tests show the iglide material’s coefficient of friction and wear rates are lower than standard ABS materials.

Drive nut tests. Compared to conventional materials, tests show that iglide offers higher wear resistance by factors of six to 18 depending on the 3D printing material and method. As an added benefit, low quantities of iglide 3D-printed drive nuts are a cost-effective alternative to injection-molded drive nuts, which require expensive tooling to produce the thread.

Rotating friction tests. The wear properties of iglide i3 exceed those of standard ABS materials by a factor of two. This improvement is because iglide polymers contain solid lubricants that lower the coefficient of friction and increase wear resistance.

Swivel tests. The tribological properties of wear-resistant filaments indicate abrasion resistance up to 50 times more than that of ABS.

Worm gear tests. After testing worm gears made from various 3D-printed and mechanically manufactured polymers in SLS 3D printing, results indicate that wear-resistant iglide i6 surpassed other materials in terms of service life. Specifically, one polyoxymethylene (POM) material exhibited high wear after 321,000 cycles, while another required downtime after 621,000 cycles. On the other hand, iglide i6 exhibited low wear after one million cycles.

Beyond exceptional performance during wear tests, these 3D printing polymers can also be formulated to have electrostatic discharge (ESD) properties, FDA approval for food-contact applications, chemical resistance, flame resistance, and more.

A note about 3D printing process selection

Of course, as with any manufacturing process, it’s not just about the materials but also the process you choose and how well you run the machines. To this end, it’s important to calibrate the 3D printing machines specifically for wear materials and understand the limits of each process to achieve an ideal 3D printing result. For example, in terms of dimensional stability, SLS processes can achieve very tight tolerances of ± 0.15 mm in all dimensions, while FDM can achieve tolerances of ± 0.2 mm.

In terms of surface quality, FDM typically yields parts with the roughest finishes, while DLP yields the best. DLP also offers the highest resolution — up to 35 µm — making this process ideal for producing small or intricate wear parts for medical applications.

In short, it’s important to consider different 3D printing processes to achieve the required physical and mechanical properties. Between the choice of material and process, you can successfully produce a wide range of wear parts, down to the finest of gears.

Greater design flexibility means endless possibilities

The successful development of wear-resistant polymer materials, in tandem with an optimized 3D printing process, opens new doors for additive manufacturing, offering unprecedented design flexibility to produce complex wear parts in low to high volumes. These components, which include gears, bearings, and other parts typically found in moving machine assemblies, can now replace wear parts that could only previously be manufactured using serial production methods. At the same time, they offer up to 50 times the service life of 3D-printed parts made from conventional materials.

With this design flexibility, there is virtually no limit to what can be 3D printed, eliminating manufacturing barriers due to the complexity of the wear part. For example, in the past, manufacturers may have had to reject customer requests for injection-molded gears. These components, in particular, tend to be very expensive to machine and often require long lead times due to the fine teeth profiles. Using wear-resistant polymers, 3D-printing complex gears in high volumes is suddenly achievable — and they can last up to one million cycles with minimal wear.

To learn more about materials and 3D-printing opportunities, visit igus.com.