Machining chassis components is not easy, as the process usually involves difficult-to-cut materials. Many chassis components also have a long, slim shape, which makes them even more difficult to machine. Walter AG, based in Tübingen, is a sought-after solution partner in this field. The company tackles these specialised challenges with efficient tool geometries and a range of ingenious hybrid tools unrivalled on the market.
Drag bearings for the front wheels of a car are 50 cm long or longer. They are usually made from materials with difficult cutting properties. Aluminium is generally used for cars, whereas commercial vehicle chassis components are generally produced from cast iron and their dimensions are even larger.
The length and often demanding shape of the work pieces makes machining these drag bearings and other chassis components a difficult exercise. Especially since the finished parts – whether bearings, suspension arms, longitudinal swinging arms or subframes – will have to withstand exceptionally high loads: They will have to support the steering motion, compress and decompress, ensure a secure connection to the vehicle body and do their job perfectly even in the worst road conditions (to mention just a few of the demands placed on them).
The materials used to manufacture chassis components are suitably robust – and consequentiality difficult to machine. For example, the aluminium alloys, which predominate in the car sector, can produce chips that are often between 10 and 50 cm long. Removing these chips smoothly and cleanly is barely achievable.
The challenges begin much earlier, however at the clamping stage and in the spatial configuration of the machining situation. The work piece must be securely clamped and accessible for machining from all required sides. The tool must be long enough to do its job between the clamp and the component optimally. The time-honoured rule applies to clamping and tools here: As long as necessary but as short as possible. The most important thing is to get a handle on the cutting forces. The length of the pieces being machined and the tools may cause such substantial swinging movements during machining that clean and precise machining is no longer possible.
"This can be entirely or at least substantially prevented with a tool geometry specially developed for this purpose," explains Roland Hanischdörfer, PCD Special Tools Product Manager, Walter AG: "Our tools are specially designed for machining chassis components."
There are essentially two effects generated by using the correct microgeometry, which counter the undesirable swinging movements: Either the stability of the tool limits the swinging movements to a minimum or eliminates them, or the forces generated during machining cancel each other out. Which effect is produced, or whether a combination of both is employed, depends on the actual machining situation. "Our tools are able to do either," says Hanischdörfer.
Hybrid tools improve efficiency
This is not enough for the specialists at Walter, after all, their customers in the automotive sector are subject to constant competitive pressure and consequently pressure to optimise. The Tübingen-based company has therefore developed a wide range of tools to facilitate efficient machining of chassis components: Hybrid tools combining solid carbide indexable inserts with polycrystalline diamond inserts (PCD).
The carbide indexable inserts are used for roughing work to and achieve an extremely high machining volume. Their special tool geometry also produces short chips even when machining aluminium, thus solving the problem of chip removal.
In the following machining step, the hybrid tool's PCD indexable insert can be used for finishing. "The user therefore employs one and the same tool for two completely different machining stages. This reduces non-productive time as there is no need to change the tool."
According to Hanischdörfer, the PCD indexable inserts used to carry out finishing operations ensure an extremely high surface quality. Recently, Walter has also started offering PCD tools with chip breakers lasered into the diamond cutting edge. "These reduce metre-long chips to a few centimetres."
Many Walter hybrid tools can also be configured for use with minimum quantity lubrication (MQL). Instead of emulsion or oil, as is the case with conventional wet machining, an oil-air mixture cools and lubricates the machining surface and tool. This has several advantages. Firstly, using MQL brings the amount of coolant required per hour from around 500 litres down to only 10 to 20 ml. Secondly, using MQL does away with the expensive and environmentally harmful need to dispose of coolant and wet chips as special waste.
Complete machining concepts
Walter engineers have demonstrably achieved high tool life and cutting data for their hybrid tools in practical use. "Customers, who are using these tools and can see the results in their workpieces, including cutting data and tool life, are absolutely delighted," Hanischdörfer is pleased to report.
Moreover, customers are increasingly commissioning Walter to develop machining concepts based on these. "Our customers need solutions to improve their efficiency, but they do not want to have to put a lot of work into their development. We have been seeing this trend for many years now. We are therefore deploying our skills in metal machining not only to develop highly efficient tools, but also to offer our customers complete machining concepts."
There are usually two routes to this type of concept:
The automotive customer invites the Walter experts to their own premises and shows them computer images and/or prototypes of the new component. Walter develops the complete machining concept based on these, including all tools.
The user goes to their machinery manufacturer and purchases the complete machining process from them. The machinery manufacturer contacts Walter in order to define and purchase the tools required for this. Or (see above) the manufacturer develops the machining concept in collaboration with Walter.
No matter which route leads to the destination, the basis is always as detailed as possible knowledge of the existing machining processes and framework conditions at the customer's premises.
More and more users are also requiring an even more extensive service from Walter: The development of complete component cost concepts. The key point here is that the Tübingen firm can guarantee specific costs per component. This is a significant advantage in the automotive sector in particular, where the ‘cost per part’ (CPP) is the key calculation variable.
This requires extremely close collaboration between Walter and the respective user, however, as well as the extensive digitalisation and networking of all production processes. Hanischdörfer explains, "If our digital manufacturing experts have sufficient data to make the processes transparent in detail, they can unlock previously unimaginable optimisation potential and achieve amazing efficiency gains."