Laying it on cold

A new thermal spray technology has been developed which results in metals and coatings being integrally bonded to the substrate surface. Ed Hill finds out more.   It's not often that a radically new manufacturing process is introduced into the marketplace, but Cold Spray Deposition has the potential to revolutionise the way some components are made. It also offers many repair and maintenance applications for worn parts. A form of additive manufacturing, unlike other thermal spray technologies, Cold Spray does not rely on heat to create the bond between the metal deposits and the substrate. Nick Gilfillan, managing director of Dycomet UK, which is the UK distributor and developer of the technology explains: “The process was discovered in Russia during space wind tunnel testing, but it has taken 30 years to develop into a more user-friendly portable system. The challenge was to develop a system which would create enough velocity using only compressed air.  “The process creates a supersonic gas flow into which metal particles are injected. High levels of kinetic energy are produced to create a rapid build-up of metal which is not simply added to the surface but becomes structurally integral with the substrate. The surface and particles deform when they come into contact. This happens at individual particle scale and is known as ‘plastic deformation'. Because of this minute scale, there is virtually no heat build-up in the process. This means there is no risk of high temperatures which can cause melting and, potentially, lead to material weakening or distortion. “Another benefit is that any thickness of the resultant coating can be fully-machined and the localised spray jet means adjacent areas remain unaffected by the operation.” <Higher or lower>  Two differing systems are available from Dycomet for various applications – High and Low Pressure. The high pressure system can process a wide range of materials and tends generally to be installed in larger production and factory environments. Gilfillan continues: “The high pressure system keeps heat to a minimum. It is ideal for larger structures or workpieces, and enables rapid build-up and use of a wide range of less ductile materials. It allows bi-metal components to be manufactured and can be utilised in conjunction with a wide range of materials. It can bond to all metals, glass and ceramics and it is typically used as a fixed installation. “It also enables high volume throughput capacity with continuous operation because of the benefits of a non-clogging nozzle design. High volume applications can be achieved quickly due to feed rate of 750g/min or higher. It is well-suited to large scale project applications and benefits from integrated heater which increases spray gun mobility.”  Dycomet's low pressure systems tend to be more portable and can be easily transported into workshop environments where they are used for repair and coating of smaller components. “Low Pressure Systems can be used for anti-corrosion as well as repair of damaged and worn castings and metal components. It can be manually operated or used via built-in automated port. Its portability means the process can be taken to the workpiece location. “It is suited to both temporary and permanent repairs. It can also be integrated into a production process. It is also suitable for product development and research in connection with new process innovation.”   So what types of coatings/metals can be applied and what applications are they used for, particularly when it comes to aerospace applications? “The low pressure system is suitable for applications in a range of metals, including aluminium, zinc, copper and nickel as well as tin, gold, silver and platinum,” notes Gilfillan. “Importantly, combinations of metals can also be worked with cold spray technology ensuring no risk of heat affected zones (HAZ) that can arise with high temperature alternatives. “The high pressure system is applicable to all metals, glass and ceramics including specialist materials such as stainless steel, titanium, molybdenum and MCrAly. “In the aerospace sector the cold spray process can be used for corrosion repair; bi-metal component manufacturing; gearbox repair – particularly in helicopters, and as a wear-resistant coating. It is also useful for re-defining electrical conductive pathways and/or electrical conductive areas, thermal barriers, heat sensitive zones and casting repair work of many types. We have proven applications with many leading manufacturers in the sector.”      It's early days at the moment, but Dycomet says the process also has the potential to apply metal compounds to composite materials. “Research is being carried out in these areas at various universities across the EU and there has been some recent success with metal to resin and with plastics to metal.” Gilfillan says the flexibility of Dycomet's Low Pressure system makes it versatile for many workshop environments. “The low pressure system only requires an air-line and 240V electrical supply either within a factory environment or via an external generator source. It is easily portable; the unit's maximum weight is only 18kg which allows it to be moved to any operational location. “Additionally minimal preparation time is required. Once set up, the system can be ready to operate within 10 seconds. It can be utilised as a replacement for thermal spray with many advantages. There are no naked flames or inflammable gases and the process is very directional so there is no overspray or mess. It is ideal for heat sensitive areas and materials and the big advantage is that the workpiece is immediately ready for machining or painting after it has been applied.” <Trials and research> Dycomet, which has its group headquarters in the Netherlands, has just opened a new R&D laboratory centre in Manchester to help with customer trials.  “It was established to provide an ‘application research' service encompassing application development consultancy and validation trialling service. We believe it is the first commercially available service of its kind in the UK. The centre is ideal for assessing a range of factors from adhesion and cohesion to application methodology and process needs. It also gains from close and ongoing links with appropriate academic institutions.” Gilfillan describes Cold Spray Deposition as somewhere between additive manufacturing and 3D printing. “Cold Spray offers clients a very flexible addition. It is adding metal which can be machined, but with the huge advantage of doing so without actually melting any metal – substrates rarely reach more than 60°C. Very thin coatings can also be achieved and material can be added to extremely thin substrate such as aluminium foil. It is ideal for R&D and some very specific application areas.” Gilfillan says that new applications for the process are being discovered continually, not only in aerospace, but also for automotive, turbine manufacturing and repair, among others.                                                      He concludes: “Often the process initially generates a degree of genuine amazement. However, as the understanding of the science behind it increases, so too does an awareness of the wide range of application possibilities.”    www.dycomet.co.uk