Bugatti Produces 3D Printed Titanium Brake Calipers
Bugatti stands for high-class sports cars, such as the models Veyron and Chiron. Now Bugatti developers have joined forces with Laser Zentrum Nord to produce a 3D-printed brake caliper for the first time. The special feature of this brake caliper is that it is made of titanium.
Frank Götzke, Head of New Technologies at Bugatti Automobile’s Technical Development Department, used to work for Volkswagen Group for more than 22 years. He joined Bugatti in 2001 and, as head of chassis development, was instrumental in developing the Veyron and its current role in the development of the Chiron1. “A vehicle developer never considers his work to be concluded. This attitude applies especially to us at Bugatti," says Frank Götzke. “We are constantly developing ideas to improve our current models through model maintenance and by applying new materials and new processes. We work on technological solutions for future vehicle concepts of our brand. Since we often reach physical limits with regard to performance, we are facing particularly high demands," continues the 48-year-old engineer and trained machine tool and production technician. “That's why Bugatti always takes one step further in the development of technical solutions than other manufacturers.”
Largest Brake Calipers in a Series Vehicle
The brakes of Bugatti’s new Chiron are currently the most powerful ones in the world. To this end, the brake calipers have been completely redesigned. They are made of a high-strength aluminium alloy and are forged from a single block. With eight titanium pistons on each of the front brake calipers and six on each of the rear brake calipers, these models are also the largest brake calipers currently used in a series vehicle. The Chiron brake caliper is based on the principles of bionics and take nature as a role model. Thanks to this new design, it was possible to reduce the weight of the calipers to a minimum and ensure maximum structural rigidity at the same time. The design and function of the brakes were inspired by the designs used in racing cars.
New Titanium Brake Caliper Reduces Weight by 40 %
With the newly developed 3D printed titanium brake caliper, Bugatti is now taking things one step further and is breaking new ground. Titanium is used as an alloy under the scientific designation Ti6AI4V. In the aerospace industry it is for example used for highly stressed components such as landing gear suspensions, wings or in the engine area of aircrafts and rockets. The material is much more potent than aluminium. Even as a 3D printed component it has a tensile strength of 1,250 N/mm2, which means that one square millimeter of this titanium alloy can be exposed to a tensile force of slightly more than 125 kg without the tearing the material. The new titanium brake caliper is 41 cm long, 21 cm wide, 13.6 cm high and weighs just 2.9 kg. Compared to the currently used aluminium component, which weighs 4.9 kg, Bugatti could therefore reduce the weight by 40 %, while at the same time ensuring even greater load-bearing capacity.
The Solution: System for Selective Laser Beam Melting at Laser Zentrum Nord
However, this has so far been prevented by the fact that the extremely high strength of titanium makes it very difficult and in practice often even impossible to mill or forge such a component from a block and to machine it accordingly, as is customary with aluminium. An extremely powerful 3D printer now solves the problem and also opens up the possibility of creating far more complex and therefore considerably stiffer and firmer structures than would be possible with any conventional manufacturing process. Frank Götzke found this so-called system for selective laser beam melting at the Laser Zentrum Nord in Hamburg. “The Laser Zentrum Nord is one of many scientific institutions with which we have built up a very good cooperation over the years," explains Götzke. The institute has already gained extensive know-how in many other projects, mainly for the aviation industry, and especially in the field of titanium processing. It is also equipped with the latest technology". In recent years, the Hamburg production scientists have received several national and international, highly acclaimed innovation awards for their projects with the industry.
Only 3 Months: From the Idea to the First Printed Component
“The cooperation with Bugatti is a crucial beacon project for us, "says Prof. Dr.-Ing. Claus Emmelmann, former Managing Director of Laser Zentrum Nord GmbH and the institute’s Director since the takeover by the Fraunhofer Gesellschaft and its new designation as Fraunhofer Institute for Additive Production Technologies (Fraunhofer-IAPT). He is also Director of the Institute for Laser and System Technology at TU Hamburg (iLAS). Emmelmann is proud of his institute's collaboration with Bugatti: "When Bugatti approached us, we were immediately on fire. I know of no other automobile brand that places higher demands on its products. We were happy to accept this challenge."
The development time for the 3D printed titanium brake caliper was quite short: it took only three months from the first idea to the first printed component. Bugatti submitted the basic concept, strength and stiffness simulations and calculations, as well as the design, to Laser Zentrum Nord. The process simulation, the design of the so-called support structures, the actual pressure and the heat treatment of the component were carried out there. Bugatti took over the finishing work.
45 Hours to Produce a Brake Caliper
The special 3D printer at Laser Zentrum Nord, at the start of the project the world's largest facility suitable for titanium printing, is equipped with four lasers with an output of 400 watts each.
It takes a total of 45 hours to print one brake caliper. Titanium powder is applied layer by layer. At each layer, the four lasers melt the titanium powder according to the given form of the brake caliper. The material cools down immediately, and the brake caliper takes shape. A total of 2,213 layers are required. After finishing the last layer, the remaining titanium powder that has not been melted is removed from the construction chamber, cleaned and stored for reuse. What remains is the brake caliper, including a support structure that keeps the component in shape until it has undergone a stabilizing heat treatment, which ensures that it achieves its final strength.
To this end, the brake caliper is placed in the furnace, where it is exposed to temperatures ranging from 700 to 100 centigrade for a period of ten hours. This procedure eliminates residual stress in the components and ensure dimensional accuracy. The supporting structures are then removed, and the component is separated from the plate. In the next production step, the surfaces are ground down by a combined mechanical-physical-chemical process, which drastically increases the fatigue strength, i. e. the durability of the component in subsequent vehicle operation. Finally, the contours of all functional surfaces, such as piston chambers or threads, are machined. This is done in a 5-axis milling machine, which takes another eleven hours.
First Trials for Series Production Commenced
The result is a delicate component with a material wall thickness ranging between a minimum of just one and a maximum of four millimeters. “It was a very moving moment for our teams when they held our first 3D printed titanium brake caliper in their hands," recalls Frank Götzke. “Everybody was surprised by the low weight of the component — despite its enormous size. It is an extremely impressive technical component, and at the same time it has very aesthetic appearance."
The first trials for series production will start at a not yet determined date during the first half of this year. The engineer promises that it will then be possible to reduce production times step by step, especially during post-processing.
Götzke and his team present the results of their work to the Group and its brands. “Bugatti is spearheading the 3D printing development within the Volkswagen Group," says Götzke. “Everyone can and should benefit from our projects. This is also Bugatti's task as a corporate laboratory for applied high tech."
The 3D printed titanium brake caliper is just one example of Bugatti's current research and development work. “We have not only developed the world's largest generatively manufactured component made of titanium, but also the world's longest aluminium component ever printed in one piece in a 3D printer," says Götzke and proudly takes a 63 cm long windscreen wiper board out of the cabinet. At 0.4 kg, it weighs only half as much as a conventional aluminium lightweight die-cast circuit board, with the same stiffness. But that's another story.
This article was first published by konstruktionspraxis.
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