Understand the capabilities of polymer 3-D printing

Discover the manufacturing potential of 3-D printed bearings

By Chris Johnson October 6, 2020

The science-fiction author, Arthur C. Clarke, is credited with being the first person to describe the basic functions of a 3-D printer in 1964. However, the first 3-D printer wasn’t released until 1987 by Chuck Hull of 3-D Systems.

3-D printing technologies have evolved significantly over recent years, with much of the research effort placed in the materials science field. Along with industry pioneers, chemical companies are now entering the 3-D printing industry, accelerating the capabilities of this manufacturing process. This has enabled the development of a range of high-performance polymers with desirable mechanical characteristics similar to those of metal.

The 3-D printing market is expected to reach a value of $63.46 billion by 2025, growing at a compound annual growth rate (CAGR) of 29.48% between 2020 and 2025. Additive manufacturing (AM) has a wide range of industrial applications and plays a crucial role in automotive, electronics, aerospace and defense and health care industries.

Prototyping, designing and tooling are among the most common industrial applications in the industrial printer market. However, AM is evolving from a prototyping tool to a functional part of manufacturing. While the high entry costs previously priced smaller manufacturers out of the market, a range of affordable 3-D printers are now available. Growing expertise, new materials, faster production, the ability to fabricate larger objects and innovative finishes makes this advanced manufacturing process an attractive proposition for many manufacturers. But what are the bearing design development and production opportunities facilitated by 3-D polymer printing processes?

Design flexibility

Each AM process impacts a material’s microstructure, including size, shape and orientation of the grains or crystals. This presents various challenges and opportunities. For example, stereolithography (SLA) offers a smooth surface finish, but components tend to be less durable than parts produced with other additive technologies.

As the 3-D printing process is more widely accessible and doesn’t require expensive tooling, bearing manufacturers have the opportunity to experiment with bearings that have customized elements and enhanced performance. This affords manufacturers and design engineers the flexibility to experiment with design features that wouldn’t have been economically viable using conventional bearing manufacturing methods. With the economic barrier removed, manufacturers can provide a cost-effective low-volume production service — even for orders as low as ten bearing units.

In addition, bearing manufacturers can use an increasingly diverse range of materials. For example, 3-D printed reinforced polymers can match or be enhanced beyond conventional properties, which unlocks new design possibilities. Bowman International, a UK-based bearing manufacturer, used multi jet fusion (MJF) technology to produce a bespoke rollertrain retainer using PA11 nylon. The interlocking structure permits room for two to four more rollers, allowing for a 70% increase in load capacity, as well as boasting greater elasticity, durability and functionality.

While 3-D printed mass-produced bearings aren’t yet commonplace, polymer 3-D printing is making an impact in the rapid prototyping world. For example, in a niche aerospace project, 3-D printing may be used to achieve fast and visually appealing prototyping. This would ensure the smallest of mechanical elements, such as the bearings, functions in unison with the entire system.

Lightweight design advantages

In industries such as aerospace, automotive or medical technology, lightweight design can achieve better safety performance as well as vital cost savings. For low load, low speed applications, plastic bearings offer excellent performance characteristics and are already five times lighter than their steel counterparts.

Many industries may have historically chosen to rely on metal lightweight innovations, such as Schaeffler’s XZU conical thrust cage needle roller bearing. Another example is an aluminum wire-race 3-D printed bearing designed by German company Franke GmbH. This bearing had the requirement to have a maximum weight of 800 g, as it was destined for use in the bed of a rescue helicopter.

However, by moving away from metal and using 3-D polymer printing processes, it is possible to design an even lighter component. These designs use honeycomb-like structures, which would be difficult and time-consuming to achieve with traditional machining processes. In addition, 3-D printed high-performance thermoplastics such as carbon fiber and polyether ether ketone (PEEK) offer a feasible alternative to metal.

Opting for a 3-D printed retainer in nylon (PA66) or another polymer material, can help to reduce the weight of the whole bearing. Carbon fiber reinforced nylon is one of the most popular combinations for nylon printed materials. It offers many of the same benefits as standard nylon including high strength and stiffness, but it produces significantly lighter components.

Reduced friction

A 3-D-printed polymer cage also may reduce the wear on the rolling elements compared to a conventional steel cage. A 2018 feasibility study assessed the friction performance of a commercial deep-groove (6004) 3-D printed ball bearing. The bearing was fabricated using the MJP process using plastic material for the structure and fusible wax material for the support. The result demonstrated satisfactory durable life of the 3-D-printed ball bearing at low loads and speeds.

More recently, Igus developed its iglide tribo-filament, which is up to 50 times more wear resistant than conventional 3-D printing materials and is the world’s first to be enhanced with tribological properties. This new filament integrates lubricant in the plastic itself, making it more durable in motion applications. This is particularly advantageous for bearings. If friction is not effectively controlled, high torque bearings can increase the power required to overcome the resistance and drive the equipment. This ultimately results in a greater cost to move the load and a greater energy output required to operate the equipment.

Quality control

As with traditionally manufactured components, 3-D printed plastic bearings must undergo the same rigorous testing procedures to make sure they are fit for purpose. This is especially important for components that are safety critical, such as bearings.

Crucially, when experimenting with innovative new designs and enhanced material properties, it is essential that the final application environment is carefully considered, reaffirming the importance of bearing specialists in industry.

Adopting standards to mitigate and control risks as well as allowing more consistent quality are important steps for the future of 3-D polymer printing. New materials that adhere to standards set out by organizations such as the Food and Drug Administration (FDA), International Organization for Standardization (ISO) and ASTM, formerly known as American Society for Testing and Materials, are an important step, enabling a greater adoption of 3-D printed designs.

While 3-D printed bearings aren’t commonplace just yet, evidence shows that they could be used extensively in the future to supplement traditional bearing manufacturing techniques, to offer rapid prototyping and enhanced performance characteristics.

Author Bio: Chris Johnson is managing director at SMB Bearings. Having held this position for more than ten years, he is a specialist in bearing and lubrication services.