Composite materials boost machine performance

Composite materials are used in a number of high-tech industries, most notably aerospace and automotive; for example, Boeing’s Dreamliner is more than 50% composites, while high performance sports and racing cars use similar materials to save weight, reduce fuel consumption and boost acceleration and speed.

Machine builders can also incorporate composites into their designs to create lighter and stiffer parts with enhanced dampening, especially over longer operating distances, such as supporting structures for high speed pick and place or automation units. The result is machines that run faster, with higher accuracy and reliability. This, in turn, boosts productivity and quality.

Traditionally, designers and manufacturers of automation, handling and machine tools systems have selected steel or aluminium for beams, tubes or tool changers. Consequently, their areas of knowledge and experience tend to be centred around these materials. There is also a common misconception that composite parts can be more expensive and harder to manufacture.

Different properties
Composites are typically composed of a matrix such as an epoxy thermoset resin, which is reinforced with a fibre component.  As the fibre only has properties along the direction of its length it is laid down in a series of layers at different angles to create the desired properties that match the specific stress criteria of each structure.

There are many fibres to choose from, depending on requirement.  For example, although glass fibre is often used due to its low cost, it is relatively low in strength and stiffness as well as having a high density. Carbon fibre is widely recognised for its use in high strength applications with a level of stiffness, in a composite, that is comparable with aluminium, but at 50% of the weight, Graphite (also known as pitch) fibre, which is relatively unknown, is used in high stiffness applications; in a composite material its level of stiffness is comparable with steel but at just at 25% of the weight.  In each case, once the resin-fibre combination is cured with heat, it creates a material with a high strength or stiffness-to-weight ratio.

Long prismatic parts, often cylindrical, can be made using a technique called filament winding. Here, the fibre takes the form of a continuous ‘tow’, which is impregnated with resin, wound at an angle around a mandrel, then cured. The resultant structure is extremely strong, stiff and light.

CompoTech has perfected its own version of filament winding, called axial fibre placement. The technique improves bending performance by laying the fibres along the length of a cylinder under tension, rather than around its circumference. This aligns all the fibres in the axial direction, which also increases strength: stiffness is 10-15% higher, while bending strength is up to 50% higher than traditional composite laminating or standard winding.

Using various epoxy-impregnated fibres, including graphite and carbon, it is possible to create a range of cylindrical structures that are suitable for use on a range of machine and automation systems.

Application areas
Manufacturers of industrial machine tools and automation systems are under pressure to raise capacity, quality and throughput. This translates into several competing performance requirements:

• Larger machines, with moving elements that may be many metres long
• High-speed motion systems that can accelerate and decelerate rapidly
• A high degree of accuracy, repeatability and stability

In addition, designers must use suitable structural elements that are low in mass, while offering enough strength and stiffness to support both static and dynamic loads with minimal deflection. A further consideration is the ability to integrate composite structures with other machine components, which can significantly reduce overall cost of production.

Composite parts can be perfect in these applications because of their combination of high strength and low weight. For instance, a carbon fibre machine element can weigh around a quarter of a steel one, for the same strength. These materials can also be engineered to deliver up to 20 times the vibration damping properties of steel – or for zero thermal expansion in one dimension.