Up to 50,000 hydraulic blocks manufactured autonomously per year

GROB G520F – twin-spindle machining centers ensure high output

Two GROB G520F twin-spindle machining centers ensure high output from the new production cells. Marcel Sütterlin says: "With this investment, we have strategically repositioned ourselves in the area of medium to high-volume production." The investment was made as part of a long-term order. The newly added annual quantities of up to 50,000 valve blocks could no longer be handled with the existing machinery. In addition to the valve blocks, other, sometimes more complex and longer steel brackets are currently being machined on the GROB twin-spindle machines. Although the design is completely different from that of the valve blocks, the brackets can be machined unattended thanks to flexible automation and automatic clamping devices.

We need more flexible manufacturing systems

Marcel Sütterlin: "As a Swiss supplier, we generally have different needs than the automotive industry. The series on our machines are often smaller and change frequently. That's why we need more flexible manufacturing systems. This is also one reason why we have designed the two GROB G520Fs as autonomous manufacturing cells rather than linking them together. This means that the two manufacturing cells are completely independent of each other and can be used more flexibly." 

Wolfgang Ulmer: "Our Swiss customers constantly challenge us in terms of precision, flexibility, and process reliability. For small and medium-sized series that require a high degree of flexibility and complexity, we developed the single-spindle G series almost 20 years ago, and Mandatec already has five of these machines in use. Our GROB G520F twin-spindle machines, on the other hand, are often used in the automotive sector for volume production. Process reliability is paramount in such an environment and is an absolute priority for GROB. Typically, our systems are fully automated and customized. In this case, Mandatec wanted to implement the automation with an external provider."

Batch sizes actually too small for twin-spindle machines

Marcel Sütterlin: "We certainly run series over several weeks or months. At the same time, however, we repeatedly receive smaller volume orders, which we then have to implement promptly on one of the two systems. This means that we use the GROB twin-spindle machines much more universally than a large-series manufacturer. The automation concept for the two production cells therefore had to be designed in such a way that we could switch from one component to another within a single day." 

Wolfgang Ulmer: "When Mandatec approached us and told us the expected series size, we were initially somewhat cautious, as we believed that the batch sizes were too small for the twin-spindle machines. However, when we saw how Mandatec designed the two production cells, creating two flexible production cells, so to speak, this actually opened up a new manufacturing perspective for us that has potential not only in Switzerland."

GROB extremely strong in the systems business

From Wolfgang Ulmer's point of view, it is necessary to take a step back at this point. GROB has grown in the automotive industry with machines such as the G series. Until 2007, GROB was primarily active in the automated systems business in the automotive sector. When GROB launched the single-spindle universal machines of the G series in 2007, the company had suppliers such as Mandatec in mind. Companies with smaller batch sizes and constantly changing components. The twin-spindle machines, on the other hand, were mostly designed for large series and a specific component, and then ran for five years or more. Wolfgang Ulmer: "One of GROB's particular strengths developed in the context of such production processes: process reliability. I think this is one of our key competencies, which also comes into its own here at Mandatec."

Evaluation: GROB with significant unique selling points

Even before investing in the two GROB G520F twin-spindle machines, Mandatec had already consistently converted its entire production area to GROB machining centers. During the evaluation, the experience gained with the existing GROB machinery was naturally taken into account. Marcel Sütterlin: "Our five existing GROB single-spindle machining centers have made an excellent impression in production, and the service has also been outstanding. This experience plays a significant role when making a new investment. Nevertheless, when making a new investment, we also have to evaluate other machine tool manufacturers and their machines. Due to the high productivity required, only twin-spindle machines were shortlisted from our point of view. In this segment, GROB machine tools definitely have unique selling points that contributed to our decision to invest in GROB machine tools again."

Autonomous Z-axes on the twin-spindle machines make all the difference

"The decisive factor," says Marcel Sütterlin, "was that the GROB G520F is designed with two controlled main spindles in the Z-axis. In contrast, most manufacturers of twin-spindle machines have Z-axes that are rigidly connected to each other." If the two main spindles in the Z-axis are rigidly connected, the tools of the two main spindles in the Z-axis must be measured and adjusted to exactly the same value. Any inaccuracies in the tool presetting will result in different values for the tool overhang at the front face. M. Sütterlin: "With GROB twin-spindle machines, a Z-axis difference can be easily corrected in the CNC control system thanks to the autonomous Z-axes. This allows us to produce with a high degree of process reliability within the tolerance limits on both spindles."

Horizontal spindle concept: overhead work possible

Another advantage of GROB twin-spindle machines is that overhead machining is possible thanks to the machine tool concept (horizontal machining center). This increases process reliability because it ensures free chip removal. No chip pockets can form on the component – an absolutely crucial factor in unattended production. Marcel Sütterlin: "In addition, as already mentioned, we have had positive experiences with GROB machining centers over the past few years. Everything is just right: the precision of the workpiece is outstanding, and process reliability is top notch. The spare parts supply and the competence of the service technicians are also excellent. You can feel GROB's proximity to the automotive industry – they offer 100 percent professional work, even in after-sales business." Based on the above aspects, the decision was ultimately made to invest in the two GROB G520F twin-spindle machining centers. Another reason for Mandatec was that GROB is a central point of contact in the machining tool machine environment.

Automation of the system

The automation concept was tailored precisely to the GROB machining centers and the changing range of parts. The central element of the automation solution is a Fanuc articulated arm robot guided on a linear axis, which picks up the raw parts stored on pallets and places them in the GROB machining center. The finished components are palletized by the robot. The workpieces are loaded and unloaded during main processing time thanks to integrated pallet changing systems.

The entire changeover process takes approximately one day.

The changeover process from one batch to the next must take no longer than one day. To achieve this goal, tooling for the new range of workpieces can be started while the process is still running. The data for the equipped tools is stored in a central database, and the CNC control system accesses this data via Balluff chips. The robot cell must also be adapted for the new component: new raw part and finished part pallets, gripper change, etc. Component-specific clamping systems are required to enable fully automated production of the components. Hydraulically operated centric clamps with jaws tailored to the valve blocks are used for the valve blocks. For the console, Mandatec technicians designed a clamping device that enables automatic loading and unloading. Once everything is set up for the new batch, production can begin. The tool sorting program optimizes tool allocation and sorting in the tool magazine to ensure that tool changes for the new component are as short as possible. Once everything is ready, the first prototypes can be milled and measured. If necessary, corrections are then made to the tools or adjustments to the CNC program before series production can finally begin. Marcel Sütterlin: "If a batch runs for a week, the process is usually economical for us."

Excellent heat dissipation of the GROB machining center

Wolfgang Ulmer: "As a machine tool manufacturer, you have to know how the machine reacts to temperature changes. Our machining centers have temperature sensors that transmit a complex temperature profile of the machining center. Depending on the temperature profile, automatic readjustments are made. Ultimately, this is based on empirical values evaluated over many years, which are stored in the control system. This makes it possible to achieve very tight tolerance ranges in the hundredths range in series production, even with changing room temperatures or when the machining center is warming up."

Conclusion from Mandatec and GROB

Marcel Sütterlin: "We have been operating the system for a year now. In general, we are very familiar with the manufacturing processes for hydraulic blocks, as this is one of our core businesses. However, we had not yet produced with twin spindles, which is why we had to familiarize ourselves with the program structure and automation processes of twin spindles. Nevertheless, with this system we have taken a step towards the "production of the future." Once the manufacturing cells are set up and all pallets with raw parts are ready, they run autonomously. This means that the semi-flexible, autonomous manufacturing cells meet our needs exactly. The two GROB G520Fs deliver the required precision in series production, a very high output due to the twin-spindle concept, and also offer a very high level of process reliability. The entire project was challenging, especially the coordination with the external supplier of the automation solution. However, this was managed excellently by all parties involved. Last but not least: our experience with GROB's service has been excellent so far. It is clear that GROB is not only at home in the automotive sector. The response times and expertise of the service technicians are simply outstanding."

"We hadn't realized that in this form before."

Wolfgang Ulmer: "Marcel Sütterlin has actually said it all. From my point of view, it should be emphasized that GROB machining centers are designed for process reliability. Precision on the workpiece is a basic requirement. As a machine tool supplier, we have learned a lot from this project. Until now, we had considered a system machine such as the GROB G520F to be a machine designed 100 percent for large series production. Mandatec convinced us otherwise and, with their approach, developed two flexible production cells from our twin-spindle system machines. We had not yet realized this in this form—it is a real advancement."

Source: SMM – Swiss Machine Market; Mandatec: Flexible automation for coarse double-spindle machines
Image source: Matthias Böhm & Nastassja Neumaier