5-axis portal milling Thermally stable portal milling machine achieves maximum dimensional accuracy 

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FAULHABER Drive Systems

On the 5-axis portal milling machine FZP32 by F. Zimmermann, the Modell- und Formenbau GmbH machines vehicle models, among other things – completely from five sides without re-clamping.

In times of crisis, how should processing companies respond correctly? "Many think short-term, cut costs across the board, and even reduce staff. When the industry booms again, they are not prepared for a sudden increase in orders and often have to decline projects simply because there is no capacity available," observed Maximilian Lörzel among many market competitors. The Managing Director of Schröter Modell- und Formenbau GmbH in Oberpframmern, near Munich in Bavaria/Germany, is sitting on this day in one of the meeting rooms of F. Zimmermann GmbH, located about 230 kilometers away in Neuhausen auf den Fildern, not far from Stuttgart.

In November 2021, we faced this question: How do we respond to the COVID-19 pandemic, which worsened the order situation and forced us into short-time work? No one could assess the situation. But we knew: Eventually, the crisis will be over. And we wanted to be prepared for that.

Maximilian Lörzel, Managing Director of Schröter Modell- und Formenbau GmbH

Atypically for that time, he decided to invest in a new portal milling machine from the FZP32 series by F. Zimmermann, with a working range of 7,000 millimeters × 3,500 millimeters × 2,500 millimeters. "Certainly, it was a risk, but also a clear signal for the future, to our customers and our employees," he says today.

In 1963, Lörzel's uncle, Bruno Schröter, established the company in Munich. In the early nineties, he took over the business, which has been steadily growing since then. Today, the company manufactures components or molds for prototypes but not for series production. In addition, they produce foundry and design models, sheet metal forming tools made of aluminum or plastic, as well as machining softer materials such as foam, clay, and ureol. Schröter also processes carbon fiber and steel.

Approximately 50 percent of our customers are from the automotive industry. Among them are names like BMW, Audi, Volkswagen, Mercedes, and Porsche.

Maximilian Lörzel, Managing Director of Schröter Modell- und Formenbau GmbH

In 2022, the company milled almost 70 one-to-one models. However, his company does not want to be dependent on one industry. Diversification is important, he advises. This is why almost 40 percent of orders now come from the aerospace industry. Medical technology is a new and growing field. Here, he and his 40 employees take on the production of complex prototypes for computer tomographs or surgical robots, for example.
 Back in Neuhausen. "What makes us so successful?" Schröter's Managing Director doesn't have to think long. "We have highly qualified employees. Every one of them can both program and operate the machines. We train them ourselves and offer complete production from a single source." For design and five-axis NC programming, the company relies on the Catia and Tebis software solutions in combination with the milling machines from F. Zimmermann. Schröter has grown up with the Swabian machines. What Lörzel appreciates about them is the stability, high speed and flexibility of these systems. They work precisely and reliably. "Depending on the working time, the components hardly need to be reworked after removal from the machine, if at all. That alone saves us a lot of time and money," emphasizes the Managing Director.

In 1991, Schröter Modell- und Formenbau invested in the Swabian family company's first milling center. There are now five Zimmermann machines of different sizes in Oberpframmern - just as many can fit in the hall. "Because we use machines from the same manufacturer, we can pursue a common parts strategy," explains Lörzel. This means that if a machine breaks down, an employee can simply switch to another machine of the same size with the component. These are equipped with the same control system, comparable milling heads and simulation software from Tebis.

In more than 30 years, Schröter has replaced four machines with newer versions. "Now it's time for the fifth, and therefore the ninth Zimmermann machine," says Lörzel, looking over at Frieder Gänzle. The Managing Director of F. Zimmermann GmbH is meeting with him today for the acceptance of the new FZP32. "The old FZ37 series machine, which we are now taking out of production in Oberpframmern, is 18 years old," says Lörzel. "It is still running reliably. But of course there are always small signs of wear and tear due to its age, sometimes it was a faulty power supply unit, sometimes the graphics card."

Complete machining of vehicle models from five sides without reclamping

The new FZP32 provides him with the same workspace. Components such as vehicle models can be completely machined from five sides without reclamping. The modular design of the machine makes it possible to incorporate various options - for example, automation solutions such as shuttle tables, a positionable rotary table, dust extraction bells or a customized tool clamping system. The most important thing, however, is that Schröter is taking a significant step forward, as the new portal milling machine achieves maximum dimensional accuracy when processing workpieces. "This is due to its thermo-symmetrical design," says Zimmermann Managing Director Gänzle, explaining the special concept.

Thermosymmetry for more precision

Changing ambient temperatures and process heat inevitably influence the machine geometry in conventional portal designs. The idea of the thermo-symmetrical design is based on the fact that thermal influences can be absorbed to a considerable extent by the machine structure.

To achieve this, we have designed and intelligently arranged the structural and drive components, guides and other accuracy-defining components of the machines in our entire advanced portfolio accordingly. This allows the structure to expand in non-critical directions.

Frieder Gänzle, Managing Director of F. Zimmermann GmbH

The centrally guided Z-slider of the gantry in double bridge design has an octagonal cross-section, which makes it particularly stable. This design enables us to achieve a very high level of rigidity. And because there can be no one-sided heating, this increases accuracy enormously. Zimmermann reduces the effects of the error influencing variables to a minimum through the design of the structure. And because there are fewer lever forces compared to a serial structure with a classic guide arrangement, the machine manufacturer can build the FZP more rigidly: The octagonal Z-slide is more stable and yet slimmer. And because less mass has to be moved, the machine works faster and more dynamically - making the operator more productive. A smaller mass to be moved also requires less energy. These are clear cost benefits. What's more, the thermo-symmetrical design eliminates the need for complex cooling circuits, which also has a positive effect on costs.

Fork head in monoblock design for stable machining operations

The FZP is set up for acceptance in the hall in Neuhausen. Frieder Gänzle points to the milling head: "The VH10 is in use. The fork head is a monoblock design made of cast iron. It has a compact design, achieves high clamping forces and therefore enables stable component machining." Zimmermann equips the VH10 with optional process cooling with cooling lubricants or minimum quantity lubrication. To reduce throughput times, a powerful spindle with 34 kilowatts at a maximum speed of 24,000 revolutions per minute is installed as standard. There is also an optional dust extraction hood around the milling tool. The interference contour of the entire Z-axis is also important for customers. In addition to a high power density, the focus during development was primarily on its slim line. The closer the operator can move the milling head to the component, the shorter the tools can be used and the more material can be removed.

Especially when we run the machine for seven hours at a time at night, we have to make sure that the temperature remains stable over this long period.

Maximilian Lörzel, Managing Director of Schröter Modell- und Formenbau GmbH

The situation is even more extreme at weekends. This is because running times of up to 40 hours at a time can occur. First the system mills one side of a vehicle, then the other. If a small temperature imbalance arises due to the long running times, a small step occurs on the rear side of the model. With the new thermostable machine, reworking is almost completely eliminated. It also reduces the amount of programming required in advance, as less consideration has to be given to the thermal behavior of the machine. 
In Oberpframmern, the FZP is placed on the foundations of the old system. The size of the machine had therefore already been determined. The machine table will also be taken over. The control cabinet and media cabinet will be placed on a platform due to the limited space available. 
The investment in the new FZP was supported by the federal government in times of crisis. The aim was to make the German economy and SMEs in particular competitive again with modern technology. "Of course, that made the decision easier for us," recalls Lörzel. "And we knew that the topic would be on our to-do list for the next three to five years." He expects the FZP to have paid for itself after around eight years. "Of course, nobody knows what the market will look like in three years' time. But the order volume has been rising steadily again since summer 2022," says Lörzel. Schröter even recently acquired two new customers from the aviation industry and the medical technology sector based in the USA. German thoroughness is still in demand, he says happily.

This also fits in well with the new FZP32, on which the model and mold makers will also mill some components for helicopters and aircraft - for companies such as Airbus. Rolls Royce Triebwerkstechnik in Berlin has also recently become a customer. Typical components include covers for the engines, which have to be milled very precisely and with as few steps as possible.

Given the current order situation, we expect to produce 60 to 70 models for complete cars per year in the automotive industry. We are also using the new FZP32 for this.

Maximilian Lörzel, Managing Director of Schröter Modell- und Formenbau GmbH

Schröter is planning a two-shift utilization of the new system, possibly even a ghost shift - depending on the range of parts. This adds up to around 3,500 to 4,000 operating hours per year. 
For almost 30 years, Lörzel has not only been enthusiastic about the machines, but above all about the service: "We get an answer immediately - and not in Italian or Chinese - in case of doubt in Swabian." All of his systems are networked online with F. Zimmermann in Neuhausen. If a problem arises that he cannot solve himself with his staff, the specialists connect to the system. 
"Now we only have one challenge ahead of us," says Managing Director Lörzel. "When we built our hall in 2005, the old FZ37 was the first machine in the room - so it's right at the back. The other four milling centers are in front of it." When dismantling the old machine and installing the new one, the Managing Director and his employees therefore have to proceed skillfully - but that is actually part of the daily business.