Meissen, Germany, is best known as the site of Europe’s oldest porcelain manufacturer, but among its other industrial businesses is Kersten Maschinenbau, a specialty mechanical engineering company established in 1965. Following German reunification in 1990, the company was operating two small milling centers, with 12 employees, as producing parts and components developed into the main area of business.
In 2004, Kersten moved into a new office and manufacturing plant, and contacted machine-builder WFL MillTurn Technologies to assist its transition to complete machining. The first WFL M65 MillTurn machine started service at Kersten in 2006 – primarily producing shafts and parts for generators and gearboxes for wind-power manufacturers.
Unlimited range of parts
Kersten Maschinenbau customers produce electric machinery, generators and motors companies, rail engines, couplings and gears, and more. “This broad range ensures both flexibility and security,” said CEO Udo Kersten. “As a supplier, we have a wide range of customers, which means that we deal with an extremely diverse range of parts. To manage this, we have a high degree of vertical integration – cutting of blanks, welding, heat treatment, and assembly of components. Three high-precision coordinate measuring machines ensure that all manufactured parts also can be measured and shipped with records.
“The mechanical departments comprising turning, drilling, milling, and complete machining, as well as grinding with cylindrical and surface grinding machines, form the core of the manufacturing process. All our machines feature various options so that we can react with maximum flexibility when presented with new customer workpieces,” he added.
The world of complete machining
Currently Kersten Maschinenbau has four MillTurn machine models in use. One of the latest additions is the M80X MillTurn with a 4500-mm center distance. Quite simply, flexibility and precision were the main requirements for the new model. Starting with the pick-up magazine, a self-centering steady rest with a large clamping range, through to the extended X-travel, it covers the widest possible variety of machining options. Other requirements included stability, multiple technologies and high accuracy.
However, the flexibility to use a wide selection of tools in the machines also was particularly important. As a result, MillTurn impressed with its excellent handling of the large number of standard tools (up to 900 mm long) and the ability to accommodate large boring bars using the prismatic tool interface.
“The versatility of the prismatic tool magazine and the generously dimensioned tool changer provide us with many options here,” Udo Kersten explained. “On top of that, another major concern was the large Y-travel. Ultimately, however, it was the overall concept or package, which had already shown its worth in previous years, that was once again decisive.”
“All MillTurn models are currently designed for shaft part production, although the machining of chuck parts is also possible. We are currently focusing on the machining of shafts, rollers, bushings and bores. These workpiece groups are mainly run on the MillTurns – the different turning length options were important to us,” Udo Kersten commented.
The smallest complete machining center, a M50 MillTurn, with a turning length of 3000 mm, fulfils the requirements for the parts to be machined on it.
Reinforcement on the side of the internal machining options played a major role in the last purchase decision. A specially damped system boring bar for vibration-free finishing also was included in the acquisition of the M80X MillTurn. This allows automatic tool-head change at the boring bar tip, making it possible to machine complex internal contours.
The longer the boring bar, the more Z-travel is needed. The M80X MillTurn with 4500 mm machining length met this requirement and allows use of vibration damped boring bars up to 1700 mm long and weighing 200 kg. Compared to the standard M80 model, the X-stroke of the M80X has been extended by 150 mm, for a total of 1050 mm. The longer X-stroke allows use of longer tools, especially for deep cross holes.
Currently, textile industry components are being produced on the M80X MillTurn, specifically, workpieces for yarn production in textile machines. “Here we produce workpieces with long, slim boring bars that have very high accuracy and run-out requirements. A particularly high standard of internal contour machining is also required,” concludes Udo Kersten. At the end of 2020, the M80X MillTurn began producing components for yarn winders.
Technological flexibility
From a technological point of view, Kersten Maschinenbau claims it can perform any kind of mechanical machining, including internal grooves, serrations and gears. External gears are milled, and the internal gears are punched. For gear milling, the advantages of the MillTurn milling unit concept with a high-torque gear shaft come into their own. On the one hand, when pre-machining with large tools, it provides a very high torque combined with high power, while on the other hand, the high speeds during finishing of the gears ensure short machining times.
The technologically optimal torque power curve of the milling unit ensures perfect cutting conditions in every speed range. Combined with WFL’s FLANX gear cutting software, this results in an extremely flexible and efficient solution. A slotting tool with an 800-mm deep nut, developed in-house by Kersten, is used on the M50 MillTurn.
“The stability of the MillTurn machines means that we can keep trying and implementing things like this. These machines have such great stability that they are a natural fit for such applications,” according to Udo Kersten.
With the scope of work projects undertaken by Kersten Maschinenbau, both the variety of workpieces and the batch sizes can vary. The most common batch sizes are 20 to 100 pieces, so the company focuses on flexible and customer-specific order processing. It can basically handle everything from individual pieces to large batches.
The two most recently acquired machines – the M50 MillTurn and the M80X MillTurn – marked an expansion of the plant’s machinery. Since 2013, an M120 MillTurn with 6500 mm turning length has also been working reliably in a three-shift system. To date, no machine has been decommissioned.
Each new purchase involved a capacity expansion, but with a view to exploiting the additional technological potential of the newer machine models. “Technological progress was important to us here,” according to Udo Kersten. “It is crucial that we are always at the cutting edge of technology.”
From programming to production
Kersten’s machine programming and workpiece simulation is performed using TopSolid CAM. The shop has two programmers working on the MillTurns, and WFL provides 3D models of the machines, which can be virtually mapped in TopSolid CAM. The existing postprocessor serves as a link to convert the TopSolid CAM programs into ISO codes required by the control system.
Many different factors are required to run a simulation accurately: the machine model, clamping devices, the blank or component data and tools. At the same time, Kersten has been working on a digitalization program, as part of which the tool organization is optimized in order to have available all the necessary 3D models. The challenge is to capture more than 20,000 tool items, from which about 150,000 variations of complete tools can be generated.
Kersten is currently making progress in digitizing tool data. In the CAM system, the 3D digitized tools then can be loaded, and the simulation created in the program.
Complete machining ensures higher accuracy and eliminates reclamping errors, and as the complexity of the workpieces increases, they can be reproduced more effectively. Five different axes can be used for machining and interpolation in a single clamping. Lead times are shortened, idle times are eliminated, storage space is saved and ultimately the throughput becomes faster and more efficient.
“We have been won over by the numerous benefits of complete machining ever since we purchased our first complete machining center in 2004. We have clearly seen that it has major advantages over conventional manufacturing,” concluded Udo Kersten.