The Material Side of Robotics: Why Material Selection Matters
A robot may look like a single machine, but mechanically it is made up of a wide range of components – each with its own requirements. And with them comes a surprisingly diverse selection of materials: steel, aluminium, titanium, carbon-fibre composites, engineering plastics, elastomers, copper, ceramics and more. There is a reason for this diversity: every material has its strengths, and the right choice depends on what a particular component needs to achieve. Material selection therefore plays a key role in how individual components perform and ultimately in how efficiently, precisely and reliably a robotic system can operate.
A particularly important aspect: moving mass.
When a robot arm accelerates, its drive has to accelerate the moving mass. The required torque depends on both the amount of mass and where that mass is located relative to the axis of rotation – and the effect of distance is particularly significant. For a simple point mass, rotational inertia increases with the square of its distance from the axis of rotation. A simple example illustrates why: for a point mass, rotational inertia increases with the square of its distance from the axis of rotation. Move the same mass twice as far from the axis, and its contribution to rotational inertia becomes four times larger. Move it three times as far, and the contribution becomes nine times larger.
This is particularly relevant for moving robotic structures such as arms, wrist components or end-of-arm tooling. Reducing moving mass reduces the torque required to accelerate and decelerate these components, which can support higher dynamics and lower energy requirements. This is particularly relevant in applications involving high accelerations. Depending on the robot architecture, reducing the mass of the moving structure can also leave more of the robot’s load capacity available for payload.
This makes low-density materials attractive for moving components. But low weight alone is not enough: the material still needs to provide the stiffness and strength required for the application.
Long-term performance is a fundamental requirement
Robotic components rarely perform their task just once. They repeat the same movements over and over again – potentially millions of times. This changes the requirements placed on a material. A material that performs well under a single load may not necessarily be the right choice for a component subjected to repeated loading. Wear, fatigue and dimensional stability can become important factors, particularly in components involved in motion and force transmission. Take gears, for example. They need to transfer forces precisely while maintaining their geometry over many operating cycles. Here, wear resistance and stiffness can be just as important as low weight.
A robotic component rarely works in isolation
A robotic component has to meet a range of requirements – from weight and stiffness to strength, durability and wear resistance. The challenge is to find the material that provides the right combination of properties for the specific application.
But components do not work in isolation. They interact with other components, often made from different materials, and their properties can influence the behaviour of the overall assembly. For example, differences in thermal expansion can become relevant when components need to maintain tight tolerances and precise movement. This is why new materials need to be evaluated not only for their individual properties, but also as part of the overall component design and system. Their potential needs to be considered early in the design process, particularly when they offer a different combination of properties from conventional materials.
Materials continue to evolve
Established materials such as steel, aluminium and titanium are increasingly complemented by materials designed to combine specific properties in new ways. Carbon-fibre composites are already used where low weight and high stiffness relative to weight are important. Advanced ceramics can offer exceptional hardness, wear resistance or temperature resistance. Aluminium matrix composites (AMCs) are another example. By combining an aluminium matrix with reinforcing phases, they can offer a different balance of properties compared with conventional aluminium alloys – for example, combining low density with increased stiffness or wear resistance. Beyond this, hybrid solutions can combine different materials within a component or system – for example, metal and polymer – to make use of the specific advantages of each material. This can open up further possibilities for tailoring components to their specific requirements.
Sometimes, choosing a different material can do more than improve a single property. It can enable a different component design and with it, improve the performance of the overall system.
Rethink your material choices – it’s worth it.
About the author
Dr.-Ing Kristin Helas is Head of Product Development at CMMC GmbH, based in Chemnitz
CMMC is bringing aluminium matrix composites (AMCs) out of the niche and into series production. Using its own patented casting process, the company manufactures lightweight materials with high stiffness and wear resistance, produced entirely in Germany. CMMC is a partner in the Robot Valley network.
