In Bestzeit zum Strukturbauteil

Alle technologisch aufwendigen Komponenten, etwa die Rundachsen und die Hauptspindeln, bezieht Wenzler dabei von HELLER. Die translatorischen Achsen der Maschine befinden sich im Werkzeug und die rotativen Achsen im Werkstück. Das ermöglicht die Integration von Verfahrwegen mit den Abmessungen 1500 x 1250 mm.

Wenig Masse, hohes Tempo

Andere Maschinen dieser Größe sind in der Regel auf ein hohes Zerspanvolumen ausgelegt, was sie entsprechend schwer und langsam macht. Wenzler ist einen anderen Weg gegangen und hat eine sehr agile Maschine mit geringen Massen konstruiert. Für die Größe der Maschine ist das Zerspanvolumen bei Strukturbauteilen eher klein und wird mit leichten bis mittleren Schnitten erzeugt. Jedoch muss die Maschine, die vom Zerspanungsprozess herrührenden Schwingungen aufnehmen können. Die hohe Agilität ist für geringe Nebenzeiten entscheidend.

Ein typisches Bauteil ist der Fahrschemel, der in Fahrzeugen als Hinterachsträger fungiert. Er misst bis zu 1000 x 1000 mm und wiegt zwischen 25 und 30 kg. Damit bietet sich eine automatische Be- und Entladung der Maschine an. Der Arbeitsraum der VKM ist von zwei gegenüberliegenden Seiten gut zugänglich, was eine sichere räumliche Trennung von Roboter und Werker erlaubt. 

The machines are largely designed to be turnkey solutions. “We always prefer to deliver the process, clamping fixture and tools along with the machine as a complete package. This way we know that everything will work well”, explains Wolfgang Wenzler. Together with his sister Ingrid Wenzler, they are the third generation to run the family company. “First and foremost, we remain a system provider. The requirement profile of our clients has not changed. The client still comes with a workpiece, names the quality and quantity, and wants a suitable solution from us.”

If speed is of the essence, Wenzler sometimes comes up with unconventional solutions. In the past, machines were already delivered to clients even though the design of the part had yet to be finalised and the process still had to be defined. Instead, Wenzler completed development on a TechCenter machine, which is available in Spaichingen for this purpose, and delivered the process later on. This machine was also used when a sports-car manufacturer that did not have its own parts production desperately needed 3,000 subframes. The machine manufacturer quickly became a contract manufacturer and helped its client out.

The quality of the parts and Wenzler’s inherent process know-how convinced the car manufacturer. Four years later, they turned once more to the Spaichingen-based company. Once again, it involved manufacturing subframes. The company wanted to buy a machine together with a process designed to use minimum quantity lubrication. The sports-car manufacturer wasn’t striving to start its own parts production in this way, but rather to equip one of its suppliers, a foundry, which was unable to achieve the required cycle time for the part on its own.

From 4 hours to 16 minutes

At first, the foundry needed around four hours to mechanically machine the rear-axle mount with multiple clamping setups. After some optimisations, they still needed two hours. The production goal of 4,000 pieces per year would have been at risk with this output. Based on the data, Wolfgang Wenzler analysed the part and came to the conclusion that a cycle time of 16 minutes was possible. In his opinion, this would only be achievable if MAPAL was aboard as the tool supplier for this project. The two companies have been working together for more than 40 years and have successfully completed many projects. The precision tool manufacturer from Aalen contributes its solution expertise to this partnership, which is based on trust and cooperation on an equal footing.

The special challenge here this time was the enormous time pressure as the project had to be completed within ten weeks. The “normal” timeframe for such a project is ten months. The blanks represented a further handicap. In car manufacturing, 4,000 parts are considered a small series. It would not have been economical for the foundry to invest a lot of time and money to optimise blanks like it would have for a large series. Instead, the blanks had very large sprues and required a lot of stock removal. And so a lot of aluminium still had to be machined during finishing.

Wolfgang Wenzler appreciates the cooperation with MAPAL: “It is impressive how accessible this company is. When it comes to making decisions, we reach the right people here very quickly, all the way up to management. Without long correspondence, we were given binding confirmation even by telephone, which was particularly important for this project.” MAPAL’s experience with PCD also came into play. Wenzler was able to profit from their enormous knowledge.

Three of the tool manufacturer’s technicians were involved in the project in Spaichingen. As a technical consultant for the client, Peter Krafft took care of all the questions that arose in everyday operation. Sven Frank is Global Head of MTB Management and thus responsible for machine manufacturers. Igor Ivankovic, Component Manager Chassis & Brakes, contributed his specialist knowledge about parts. “Thanks to this line-up, we were able to help very quickly; our expertise is available immediately from day one”, Frank explains. “We have also been focusing for years on process designs with minimum quantity lubrication to increase the sustainability of machining production. We were able to draw on extensive expertise.”

Four tools are the key

An analysis showed that the first four of a total of 26 tools were responsible for 60 percent of the cycle time. The others were only employed for a relatively short period of time. The tool manufacturer therefore knew where to start to improve performance. Right from the first meeting, MAPAL made concrete suggestions with regards to tool design. “You could notice that our two companies have a lot of experience in this field and all the necessary decisions can be made quickly”, Wolfgang Wenzler reports.

Die erzielten Ergebnisse sorgten bei Wolfgang Wenzler für Erleichterung: „Mit den Werkzeugen von MAPAL erzeugten wir auf Anhieb sehr gute Oberflächen, damit waren wir hochzufrieden. Das Fräsgeräusch war super satt und wir konnten sensationelle Schnittwerte fahren.“ Auch mit seiner berechneten Taktzeit hat er voll ins Schwarze getroffen. Bei der ersten Bearbeitung im Automatikbetrieb war das Bauteil ohne Optimierungen in 16 Minuten fertig. Trotz aller Erfahrung ist jedes neue Strukturbauteil für Wenzler wieder eine neue Herausforderung. Die Massenverteilung ist bei jedem Frame etwas anders, der dadurch sein ganz eigenes Schwingungsverhalten aufweist. 

Auch Peter Krafft war von der schnellen Abwicklung beeindruckt: „Die Werkzeuge kamen auf die Maschine und man konnte sofort produktiv arbeiten. Ich habe schon sehr viele Projekte betreut, aber mit so wenigen Änderungen lief es selten ab.“ Für die drastische Verkürzung der Taktzeit hat Sebastian Knaus, technischer Leiter bei Wenzler, mehrere Erklärungen: „Die Gießerei hatte zunächst nur eine langsamere Maschine zur Verfügung, auf der Standardwerkzeuge benutzt wurden, die viele Wege benötigten. Unser Performance-Ansatz war dem von vornherein überlegen. Hinzu kam, dass zuvor mit drei Aufspannungen gearbeitet wurde.“ Weil die Brücke der Wenzler VKM relativ schlank baut, konnten Bearbeitungen auch „über Kopf“ ausgeführt werden, was die Fertigung des gesamten Bauteils in einer einzigen Aufspannung ermöglichte.