On the Cutting Edge

Text: Thomas Masuch; Pictures: Audi AG

Audi and EOS are developing reliable additive techniques in manufacturing cutting edges for press tools

At Audi Toolmaking in Ingolstadt, Germany, traditional manufacturing mingles with the future of additive production. Row upon row of press machines weighing up to 40 tons of gray iron and steel can be seen from the windows of the division’s 3D metal printing center, which opened just a few short months ago. Located right in the middle of an Audi plant that employs over 43,000 people, the center’s couch and beanbag chairs exude a startup atmosphere rather at odds with the rest of the company.

»We’ve been so busy that the furniture hasn’t seen much use,« Lars Reichelt admits with a smile. A trained mechanical engineer and tool technician, Reichelt has been in charge of establishing this center since he began working as a project lead in Additive Manufacturing at Audi Toolmaking in April 2016.

At the heart of Audi’s 3D printing center are three metal laser sintering machines. The brightly colored walls of this air-conditioned and dehumidified space still offer room for a great deal more equipment, however. The surrounding project is a high priority for Audi, with production board member Dr. Hubert Waltl having taken a personal interest in the swift assembly of this forward-thinking department in central Bavaria. While the 3D printing center is physically located within Audi Toolmaking, its team often reports directly to the board on its latest developments.

"The real challenge in this effort involved »printing« cutting edges with the necessary rigidity and material quality as efficiently as possible using 1.2709 tool steel."

GROUNDBREAKING ENDEAVOR

One groundbreaking endeavor Reichelt and his colleagues recently carried out also involved the »additive minds« from one of the leading AM technology provider EOS. This project’s stated technical objective was to »use additive methods to create reproducible cutting and hot forming tools that offer enhanced functionality and technical design«. The resulting additive operations included internally cooled cutting components for Audi’s press tools.

Here, Audi had already been using a smaller EOS M 290 unit to manufacture parts in the necessary level of quality. »We then wanted to achieve the same quality and increased layer thickness with the EOS M 400,« Reichelt explains. The components Audi is now producing in this unit’s 400 x 400 x 400 mm modeling area include cutting tools designed to remove the edges of autobody sheet metal as part of the company’s heavy press machines.

When machining aluminum, a press of this type produces tiny particles (also known as flitter) that eventually coat its cutting edge, along with the machine itself. This used to require regular cleaning of the cutting edge, which meant idle time for every machine affected.

In the design engineering department of Audi Toolmaking, the idea was thus born to use cooling and suction to improve the process and reduce the corresponding downtime. Channels positioned directly below the cutting edge now provide the cooling effect, which is meant to minimize flitter buildup. Meanwhile, Audi’s engineers also developed another tool variant in which similarly positioned suction channels reduce the amount of flitter that develops.

The real challenge in this effort involved »printing« cutting edges with the necessary rigidity and material quality as efficiently as possible using 1.2709 tool steel. During a test phase that ran from June to November 2016, more than 800 steel test cubes were 3D printed, grinding patterns evaluated, and material densities measured at EOS’s facilities in nearby Krailling. Parameters including layer thickness, laser output, speed, and track spacing were continually fine-tuned in cooperation with EOS employees until a reliable procedure was established.  

Manufacturing these cutting edges using additive techniques also makes it possible to combine different material properties in the same component. The edge itself needs to be hard and rigid, for example, while the main body material has to be a bit more ductile in order to absorb vibrations. Audi’s engineers achieved both characteristics by increasing the laser speed and incorporating more porous segments.

Reichelt is also proud of the fact that his team and the »additive minds« from EOS managed to design a process 240% more productive than the technique previously followed on the EOS M 290.

In addition to making sure Audi’s laser sintering equipment continues to run efficiently, Reichelt keeps a constant eye on the entire process chain in Additive Manufacturing. Here, direct access to computer tomography, x-ray imaging, tensile tests, and grinding patterns gives him and others at the 3D printing center a number of valuable resources in quality assurance.

PLENTY OF POTENTIAL IN POST-PROCESSING

Meanwhile, Reichelt still sees plenty of potential in the ongoing development of Additive Manufacturing, particularly in post-processing. Additive production covers more than just 3D printing, after all; it also involves activities such as eliminating powder, separating components from the modeling platform, removing support elements, and polishing or blasting the surface of printed parts.

Reichelt estimates that follow-up efforts like these account for around half of the cost of many components. »We’re slowly coming up against the machine’s physical limits in this process, but intelligent solutions should definitely make it possible to reduce post-processing costs by around 10%,« he surmises.

In Reichelt’s view, Audi’s methods in post-processing represent the current state of the art – the »benchmark in the automotive sector«, as he puts it.  The company is not one to rest on its laurels, however: Right now, Reichelt and his team are working through a list of 56 topics involving further optimizations of its Additive Manufacturing process.