Precision and Dynamics in Fehlmann’s New “Flagship”
A report by Fehlmann AG
A portal design and an even bigger machining area with corresponding travel distances and ball screw drive that come very close to the acceleration and rapid traverse of linear motors are the highlights of the new VERSA 945 machining center from Fehlmann. Presented for the first time at the exhibition in November 2020, it combines precision and reliability to become even more versatile.
Fehlmann AG’s first machining center series with a portal concept was the VERSA 825 back in 2009. In 2017, the company introduced the first linear motor model with the VERSA 645. These two machining centers are very similar in basic concept and portal, and have proven themselves in practice for years now. This is why Fehlmann combines the highlights of these two machining centers in the newly developed VERSA 945. The purpose of the new machining center is to offer an even more universal system in terms of dimensions and travel distances, combined with the precision, reliability, and automation options customary of Fehlmann. The list of specifications for the new machine was shaped around these principles. The machining area was defined with a workpiece diameter of 650 mm and an installation height of 650 mm with a max. workpiece height of 460 mm. The swiveling range and travel distances had to be made larger to match. The result is a Y-stroke of 800 mm and 500 mm on the Z-axis for ideal workpiece processing. The swiveling range/double-sided swivel was important to those responsible for designing the VERSA 945, and therefore another component in the list of specifications, because fewer compensation movements are done with double-sided swiveling. This helps to create precise surfaces and save quantifiable time, especially for simultaneous parts.
The overall layout was also of particular importance to the new design, as about 70% of Fehlmann’s machines are automated. About 50-60% of those are shipped automated from the factory. The VERSA 825 has satisfied these requirements for years. One side is designated solely for automation. The VERSA 945, like the VERSA 645, is accessible from the front, with the right side for automation. Fehlmann designed the opening for automation to be very generous here, because handling units, robots, and even articulated arm solutions sometimes work with very large telescopic axes. Access to the machining area can also be used on this side.
Weight-optimized and with high rigidity
The VERSA 945’s machine concept, as previously mentioned, is based on a portal design with a gray iron base. A material, says Urs Schmid, Head of Development/CTO and member of management, that is simply the better material for a high-precision machine.
The Y- and Z-axes are still in the tool axes due to the high rigidity, while the X-axis with the rotary tilting table (swiveling bridge with counter balance) is supported on the entire length of the bed. Like all VERSA models, the rotary tilting table has a direct drive. The X-slide with an extra guide carriage glides onto the machine bed with a 3-point support. This allows better vibration characteristics and more rigidity to be achieved with the rotary tilting table, as the drive is mounted on the underside and milling is done on the top.
As is currently standard, Fehlmann calculated the overall machine structure using the finite element method (FEM) in order to optimize rigidity and vibration characteristics. The result is that all moving parts are weight-optimized and made from high-strength spheroidal iron and thus have high rigidity, dynamic precision and minimal, controllable thermal growth. After tests, Fehlmann also determined that GGG 50 and GGG 60 spheroidal irons significantly enhance rigidity while keeping weight consistent.
Dynamics comparable with linear motors
The essential modifications after extensive concept studies for the VERA 945 also include the drive technology and operation. With respect to the drive, it became clear relatively quickly that the ball screw drive (BSD) was the right choice. Urs Schmied sees it as a logical consequence: “The bigger and heavy the moving axes are, the less efficient the linear motor is. On the VERSA 645, we have the linear motor in the X-axis with a magnetic force of 2.5 to. 4.0 to were necessary for the motor for the VERSA 945. This force must be able to be absorbed, the guides must be dimensioned accordingly, and the slides must be designed to be highly rigid. This is why we chose high-precision ground BSDs and double nuts for short-stroke application. This decision has the advantage that the drive concept also makes trochoidal milling, for example, possible through short-stroke application. Aside from this, with exceptionally good acceleration and 50m/min rapid traverse in all axes, there are almost no losses compared against the linear motor.”
However, this can be used to achieve a much higher feed force by comparison. And the precision, says Urs Schmid, comes from the glass scales anyway.
Fehlmann estimates the maximum pallet size that can be automated at 400 mm. Six pneumatic rotary feedthroughs are new, though, because requirements for clamping systems are always coming up. The VERSA 945 can also optionally be ordered with three hydraulic lines and one pneumatic line.
The machine’s control system is still a Heidenhain TNC 640. It is now integrated behind the screen. Right where the user will be looking for it.
Direct dialog with the control system
Fehlmann continues to rely on fast double grippers for tool-changing. The chain magazine provides 48 slots in the standard design, with an optional upgrade to 80. You can also choose to rely on a shelf magazine with 256 slots. Fehlmann is currently planning another tool magazine that will be much bigger but take up less space. It’s important in this context that the corresponding data for the tool magazine is stored in Fehlmann tool management and the Heidenhain control system. By swiveling the control system, an optimal view of the loading station is also guaranteed.
In summary, Fehlmann seems to have developed another machine concept that more than meets market requirements with the VERSA 945. Despite the most adverse of conditions, like the Covid pandemic, supply problems with the iron, etc., the prototype was still built within the set timeframe. The first individual components were already tested in February of 2020, and the new “flagship” was introduced to visitors right on time at the in-house exhibition. There are two more processing machines being built at the moment: one for trial and testing purposes and the other has already been ordered by a customer in Switzerland.
By the way
The VERSA 945 is also offered by Fehlmann as a 3-axis machine.
Fehlmann AG Maschinenfabrik
CH-5703 Seon / Switzerland
Tel. +41 62 769 11 11
New high performance machining center in portal design VERSA 945, for highly precise and dynamic 5-axis machining of workpieces with a swing circle of up to Ø 650 mm.
The cooled, torque-driven rotary tilting table is integrated along the X-axis
It became clear relatively quickly that the ball screw drive and double nut would be the best choice.
Maximum precision with high dynamics for 5-sided and 5-axis machining
Optimal access – The right side of the machine remains completely free for automation, thanks to a