Car manufacturer Bugatti has produced a titanium caliper with eight pistons using a 3D printer. This is not only the first caliper created using a 3D printer, but also the largest functional titanium part ever produced using an additive manufacturing method.
The caliper was produced by Bugatti in collaboration with Laser Zentrum Nord of Hamburg, which is part of the Fraunhofer-Gesellschaft. The caliper design is not new; an aluminium variant of the caliper has been used in the Bugatti Chiron for some time. The caliper in question is 41 cm long, 21 cm wide and 13.6 cm high. The front caliper of the Chiron features eight pistons, while the rear caliper has six pistons. Bugatti claims that the caliper is the largest ever produced by the automotive sector.
Weight saving of 40%
This existing caliper has now been produced in titanium by Bugatti using a 3D printer. The use of titanium instead of aluminium not only makes the caliper stronger, but also saves 40% in weight. The titanium version of the caliper weighs just 2.9 kilograms, while the aluminium model weighs 4.9 kilograms. The part is made of a titanium alloy (Ti6AI4V) that is mainly used in the aerospace industry. For instance, the material is used to produce rocket engines, wing components and the undercarriage of aircraft. The printed part has a tensile strength of 1,250 N/mm2. This means that more than 125kg of force can be exerted on one square millimetre of the material.
Calipers are traditionally turned or milled. Until now, components could not be produced from titanium, as the strength of the material makes it very difficult to impossible to mill or turn components from a titanium block. By opting for additive manufacturing, Bugatti has overcome this obstacle. A selective laser melting (SLM) printer from the Laser Zentrum Nord of Hamburg was used to produce the titanium caliper. SLM is a manufacturing process in which powder is cured at specific points using a laser to create a layer of material - in this case titanium. A new layer of powder is then applied, which is cured again. This makes it possible to build an object layer by layer. The SLM printer at the Laser Zentrum Nord of Hamburg is the world's largest 3D printer suitable for producing titanium parts. The printer is equipped with four 400-watt lasers.
Constructed from 2,213 layers
The 3D-printed titanium caliper was developed in just three months, from the initial idea to the first printed component. Printing a caliper takes a total of 45 hours. Each caliper is made up of 2,213 different layers of printed material. After printing, the caliper receives heat treatment. Here, the material is first exposed to a temperature of 700°C, after which the temperature is lowered to 100°C. This heat treatment removes residual stress and ensures shape stability.
During printing, support structures are used that allow the production of objects with overhanging elements. These support structures are removed after heat treatment, after which the surfaces of the caliper are smoothed using a combined mechanical, physical and chemical process. This process also increases fatigue strength. Finally, functional surfaces such as the contact surfaces of the pistons are machined using a five-axis milling machine, which takes another 11 hours.
Component testing
The caliper will be tested in vehicles in the first half of 2018. If these tests are completed successfully, the part can go into production. Götzke says that if the caliper is put into production, production time can be reduced. Especially the milling process can be accelerated, according to Götzke.
Author: Wouter Hoeffnagel
Source: Bugatti (pictured)
