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Rapid prototyping

The recent article on additive manufacturing in Race Engine Technology (issue 76, February 2014) by David Cooper was a good read; the possibilities of this technology are almost limitless, and con rods are perhaps an ideal opportunity for this production process.

The con rods used in Formula One are beautifully engineered and, in common with a great many racing rods, are machined all over – that is, every external surface is machined. You might imagine that this gives the mechanical engineer the maximum possible freedom in design, but there are limits as to what can be done with machining, and the rules that prohibited welding of rods caused at least one Formula One engine manufacturer to abandon well-advanced plans to race hollow con rods.

Hollow structures are often very attractive to designers as they combine stiffness and low mass. Metallic rapid prototyping methods such as direct metal laser sintering (DMLS) allow us to not only build simple hollow structures but also very complex hollow components with load-carrying internal lattice structures and small curved holes carrying coolant/lubricants.

The production processes, of which DMLS is only one, generally use finely divided powder with carefully controlled size and form, and fuses it together to form the component. In terms of a racing con rod, the main concern for the design engineer is that it is possible to remove loose powder from within the finished hollow structure.

The range of materials already commercially available suit our needs well, having been developed initially for aerospace customers, and for con rods there are various high-strength steels and titanium.

A real bonus when developing a novel, hollow con rod using rapid prototyping would be that development would be relatively fast. We can make a change to the internal structure without the need to consider new tooling, meaning that a batch consisting entirely of slightly differing and unique designs would be no more costly to ‘build’ than a batch of identical parts.

We cannot view such rapid prototyping processes as an engineer’s Utopia though; it is very likely that we would still prefer to machine many, if not all, of the external surfaces. The various rapid prototyping techniques, although suitable for making complex hollow components, are relatively slow. It lends itself therefore to small-volume production, but even there the costs would at the moment be prohibitive to all apart from those with exceptional budgets.

Motorsport has yet to go through the process of learning how best to use rapid prototyping, and finding suppliers who can make parts to the highest standard on a repeatable basis. The standard required embodies not only the obvious aims of consistent geometric accuracy and a fast, reliable service, but the less visible target of being able to achieve good material properties, particularly fatigue resistance. The initial condition of supply of the powder and its ongoing handling and condition are important aspects of making the techniques viable.

There is little doubt that we will see con rods made using such techniques in the near future, but it is also very likely that it will be some time before the speed of the production process and the associated costs are low enough to see it widely adopted for con rods.

Written by Wayne Ward

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