Drop-forging: outsourcing the cutting strategy

Drop-forging aluminum is a tricky business. Aluminum reacts very sensitively, and does not easily forgive errors in the production process. The Leiber Group rises to this challenge at, for instance, the company's own materials test laboratory, where extensive strength calculations and material analyses are carried out before production starts. In this context, the two-piece die molds also play a particular part. The Leiber Group makes up to 550 tool-halves each year. Every tool for the forging press has to be cut with great precision from high-strength tempering steel. The relief forms hollowed out of the mold determine the shape of the finished forging. The tiniest surface fault will therefore impair the quality of the automobile chassis components that are to be made with the mold.

"We are, of course, extremely familiar with this challenge in drop-forging," explains Hanjo Gißler, LMT Product Manager for Die and Mold Making. "The cutting tools are subjected to extreme stresses in the course of the 5-axis cutting operations performed here on the steel. In order to be able to ensure the necessary quality of detail, while at the same time achieving high efficiency in our customer's production departments, we generally have to consider the entire cutting process first. And that was exactly what happened here again," explains Gißler.

Avoiding chatter marks

Back in November 2008, experts from LMT Kieninger were present for the first successful trials at Leiber. Andreas Winkler, a specialist for die and mold-making at LMT's marketing company, Tool Systems, along with application engineer Robert Hering, introduced the LMT Fette ECP X07.20T E030-I tool and the LMT Kieninger µ-Jet range successfully to the tool makers at Leiber. "These tools made a big impression from the very beginning. At first the situation looked rather different for the LMT Kieninger EBG die-sinking cutter with indexable inserts. The surfaces it generated were in some cases better than those previously manufactured with solid carbide cutters. However, the tool had difficulties, particularly when machining tight radii (wraparound) in the die mold," added Hering. Unwanted vibrations were caused, as a result of which chatter marks were left on the mold surface. The indexable inserts used also broke several times over the full radius.

"In spite of this, we were naturally convinced from the beginning that machining the mold using an indexable insert tool offered enormous economic potential in contrast to the solid carbide tool. When a tool has become worn, if you only have to exchange an indexable insert rather than a complete cutter, then you save enormously in terms of tool costs," confirmed Harald Leiber, Design and Operating Equipment Construction Manager at the Leiber Group.

Cutting strategies for the die mold developed at LMT

After this, LMT Kieninger was able to bring all its know-how in this field to bear, and offered its customer a special service: a cast steel component that had not yet been machined, from which a die mold was to be made to Leiber's original dimensions, was brought to the Kieninger site at Lahr. Martin Weiser, application engineer and Manager of the Technology Center at LMT, explained that "Starting from that point we developed, from scratch, a complete cutting strategy at our factory, with which the capability of the indexable insert tools could be fully exploited, and optimum surfaces created". Starting with roughing followed by semi-finish machining, and on to finishing, various copying mills and indexable insert geometries from LMT Kieninger were used – and this also included the new GWR 5x cutter holder. "The new cutter holder range with carbide shafts offers longer tool life and greater process reliability, particularly when cutting deep cavities and in 5-axis machining. The conical cutter holders are matched to the usual casting angles of the workpieces. Of course, we can fully exploit these advantages, particularly with a complex die form", adds Gißler. The cutting experts then bring all the relevant process data to bear for programming the strategy. The capabilities of the machining centers present at the customer are, for instance, taken into account. Weiser explains that "The cutting figures are accurately matched to the conditions at Leiber".

Adapted for the customer’s machine tools

Developing a cutting strategy for customers on the company's machining center in Lahr – a service that is available at any time from LMT Kieninger. In fact the company concentrates quite specifically on the challenges that this presents: "For instance, we regularly change the machine that we use for this work. This gives us a very high level of expertise, and we are therefore not stuck with one particular machine. We can therefore adjust ourselves to whatever type of machine the customer has, and develop the strategy for that customer specifically," adds Gißler.

Tool costs lowered by 50 per cent

The result of these tests and calculations had been clear to see on two machine tools at Leiber since the middle of last year – and soon there will be other customers. At present, Leiber's tool makers are still using up the remaining solid carbide cutters that were employed in the past. As time goes by, cutting die molds of the sizes involved here can be completely converted to the LMT indexable insert tools. The design manager at the Leiber Group is already convinced: "On the one hand, the indexable insert tools have the same advance rate figures as the solid carbide tools used before, while the quality of the surfaces is in some cases even better. On the other hand, our tool costs are about 50 per cent lower," says Harald Leiber. The explanation is simple: the solid carbide cutters used before at Leiber were reground twice. The entire tool then had to be exchanged and replaced. The indexable inserts are now changed just as often: "But their unit price is quite different. We therefore save enormous costs every time we use a tool," concludes Leiber.