Renishaw has collaborated with the Bloodhound Project to produce a prototype for a critical component of its supersonic car.

The Bloodhound Project’s aim is not only to break the sound barrier but also to be the first land vehicle to exceed 1,000 miles per hour (1,609km/hr). At this speed it will be travelling the length of 4.5 football pitches every second. The majority of the cockpit and nose is made from carbon fibre reinforced epoxy. During the record attempt the car will experience more than 20,000kg of skin drag. However as the nose tip is on the ‘leading edge’ it will experience a greater proportion of this load, at up to 12,000kg per square metre.

Although the outer surfaces of the polyhedron appear flat, there are in fact subtle curves that contribute to the aerodynamics. Renishaw calibrates the laser that it uses to make the part to an accuracy of ±50 microns over the 250mm bed so it is able to reproduce accurately the geometry in the CAD model.

The hollow pocket depth is 130mm, and it tapers. If the nose tip is to be machined, as a deeper cut is made, a thicker cutter is required to maintain stiffness and this dictates the shape that can be made. With additive manufacturing, though some design rules apply, there is much more scope to manufacture novel shapes with ease.

“We believe that the key benefit of using an additive manufacturing process to produce the nose tip is the ability to create a hollow tip to minimise weight,” says Dan Johns, Materials, Process & Technologies Engineer at the Bloodhound Project. “To machine this component conventionally would be extremely challenging, result in design compromises, and waste as much as 95% of the expensive raw material.”

Titanium alloy, minimal waste

Titanium alloy, Ti-6Al-4V, is easily processed using additive manufacturing, and complexity can be built in at no additional cost. Exotic materials take the same time to process as more standard materials, and, as only the material required is consumed, it may be more cost effective than expected. The honeycomb internal structure is more complex than a uniform wall and uses less material, so is cheaper to manufacture.

The hexagonal honeycomb is an intrinsically strong design; to manufacture this on internal surfaces would be very difficult in any other way. Currently, physical manufacturing capabilities outstrip digital design capabilities. Software is rapidly improving to capitalise on this new design potential – expect to see more designs inspired by nature, as well as iterative methods such as topological optimisation.

Renishaw engineers and Bloodhound designers collaborated to model weight-reducing features in the nose tip: the resultant prototypes were printed shortly afterwards. The beauty of this supply chain is that there are no external delays: traditionally there would be hold-ups waiting for the correct material to be supplied (often with a minimum order quantity), tooling, design review and sign-off (if a significant amount of money is to be spent on the tooling, the design needs to be agreed and ‘frozen’). Additive manufacturing reduces the development and prototyping cycle from months to days, freeing engineers and allowing prototypes to be made without part-specific investment. The prototype can be tested and refined to establish further improvements.

Although great for prototypes, Renishaw is keen to emphasise that this technology can also provide a production-ready solution and currently uses it in-house to manufacture dental implant bridges and custom dental abutments, as well as mould tool inserts. The parts are ‘fully dense’ – that is to say better than castings, greater than 99.5%, and suitable for many applications. Hot isostatic pressing (HIP) is a well-established post processing technology that can be employed to ensure density and further improve material properties. This can be used if parts are likely to be pushed to their design limit.

Renishaw has a dedicated team concentrating on materials science and development to generate materials performance data and ensure that all its materials meet or exceed current industry standards for traditional methods. Renishaw also provides a design review service to anyone considering its laser melting systems as a production solution. Components or assemblies will be reviewed by Renishaw’s applications engineers who can make recommendations on DfM (Design for Manufacture), digitally process the model, and grow a sample component in one of its on-site AM250 machines. A pre-build report, inspection report, and component price estimate can also be provided on request.

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