The use of composite materials outside of aerospace and automotive applications tends to be confined to specialised machine and automation systems. These examples demonstrate that machine performance improvements can be achieved and that there is a place for this material in the machine building industry, as CompoTech’s head of business development, Humphrey Carter, explains.
The adoption of composites in the construction of manufacturing machinery, automation systems and machine tools has proved a relatively slow process for a variety of reasons. In particular, machine designers and OEMs are reluctant to abandon traditional materials of construction such as steel or aluminium. This is due partly to a lack of familiarity with the properties of composites and the manufacturing processes involved; it is also due to an overestimation of the complexities of including composites in machine designs - with limited knowledge of anisotropic material design, engineers have tended to err on the side of caution.
But such a cautious approach means that many machine designs are missing out on what could prove to be performance enhancing benefits. In reality, composite parts - particularly those manufactured using the highly automated axial fibre placement process, which is ideally suited to the construction of lightweight beams and thin-walled tubes - can revolutionise machine performance.
Composite beams, for example, offer significant physical and mechanical advantages over their steel or aluminium counterparts. Despite their initial higher cost, these advantages outweigh the initial cost premium and quickly pay back the investment in a variety of different ways.
Composite structures are lighter, stiffer and can be constructed to offer superior levels of damping, enabling machine systems to be operated at far higher speeds and with much greater accuracy and repeatability. Reduced weight and higher stiffness mean that a beam constructed from composite material has a higher natural frequency, and less energy is required to accelerate a component and subsequently to bring it to rest.
For automation systems and machine tool manufacturers under pressure to improve performance and throughput, an appropriately designed and manufactured carbon fibre-reinforced composite component can be engineered to deliver twice the stiffness of steel at a quarter of its mass. While providing vibration damping properties up to twenty times better than steel and, importantly, thermal stability in conditions of widely varying machine temperatures. In addition, composite parts offer sufficient strength and stiffness to support high levels of static and dynamic loading with minimal deflection.
Carbon composite tubes and beams are commonly manufactured using filament winding processes. These typically align fibres at an angle to the longitudinal axis of the part, with an inevitable compromise between strength, stiffness and deflection under load. A refinement of this process, used by CompoTech and called axial fibre placement aligns each fibre along the length of the component part.
The axial fibre placement process is fully automated and, as well as providing ideal fibre alignment for bending loads, also allows the creation of composite parts with a high percentage of fibres within their structure, compared with unidirectional tapes or fabrics. Because the fibres are straight, they are optimally loaded, further improving the mechanical characteristics of the finished part. Compared with conventional filament winding techniques, axial fibre placement can produce beams and tubes that are 10 to 15% stiffer in the direction of the fibre while offering 50% greater strength in bending.
As well as axial placement the specially developed production machines are designed for use with delicate and often difficult to process fibres, such as the various ultra-high modulus graphite fibres used for machine tool applications. These fibres made it possible to build composite structures that can perform, in stiffness terms, at the equivalent or higher level than steel but at around 25% of the weight.
The manufacturing process is additive in nature so many additional features, such as slots or fixings, can easily be built into the design. Fibres can be wound in such a way as to create, for example, fixing or location holes, which eliminates the need for subsequent machining while maintaining the material properties and reducing overall production costs.
Is it worth the extra cost?
When comparing the cost of steel or aluminium with composite parts, it is important to view the investment holistically and determine how initially high up-front costs can be amortised over the life of the machine. Firstly, modern composite manufacturing techniques produce accurately dimensioned components with little requirement for post processing operations. Thereby significantly narrowing the cost gap by reducing the time taken for a part to be prepared for installation into the machine.
Secondly, reducing the weight of large moving components allows designers to select smaller ancillary components such as bearings, motors and other motion components. And once a machine goes into service, the reduction in energy costs provided by this weight reduction can pay back any additional material costs well within the lifetime of a machine.
The benefits of composite structures to machine design are notably demonstrated by a recent project carried out by CompoTech for the Polish fibre laser machine manufacturer, Eagle. Their design engineers sought to reduce weight and deflection in a 3.1m long Y-axis transverse beam used in one of its laser cutter models. Following close collaboration with CompoTech, the existing steel part was replaced with a thin-walled composite design with axially placed fibres with foam and internal reinforcement, which enabled the weight of the beam to be reduced by as much as 44%, while increasing its stiffness.
Eagle was able to take advantage of these improvements to double the peak acceleration of the beam from 3g to 6g which, in turn, reduced the time required to cut a sheet of material by up to 30%. Furthermore, the extra stiffness and improved damping characteristics of the part resulted in accuracy improvements of up to 50%.
As hopefully this article has made clear, the most significant benefits of carbon fibre reinforced composite machine parts arise from improvements in speed, throughput and quality. High performance machines make money for their users. The annual productivity payback achieved through the use of composite parts can be tens or even hundreds of times greater than any one-off additional cost.
CompoTech is an expert in technically advanced, damped composite beams, tubes and connections. The company designs and manufactures structural composite industrial components, and specialises in creating innovative solutions that reduce weight and vibration, while improving stiffness, accuracy and repeatability in components for industrial automation, handling and machine systems.
