Taking CNC Multis to a New Level

A visit to EMO, should be on the top of anyone’s list to see the latest in machining technology. It’s a huge manufacturing trade show, last held in September 2017 in Hannover, Germany. For multi-spindle production machines, Hall 17, which is dedicated to multi-spindle machine tools, was a must-see for all production machining tech enthusiasts, including journalists from all over the world.

I took enough time to explore this massive hall and stopped by the Schütte booth, where complex turned rotational parts were being produced by dry-cutting on the company’s latest addition to its machine portfolio, the AC10-36 multi. The new machine offers eight spindles for more productivity for parts of up to 40 mm in diameter. It caught my eye, not because of its high complexity, but because of the speed with which it was producing parts. Within three seconds, the complete part, including front and rear machining operations, dropped out of the machine, finished and ready to be shipped to the customer.

Eight spindles make it possible. Schütte’s AC10-36 offers eight spindles and up to two counter-spindles for backworking. “For rear machining, which can be a bottleneck in production if several operations are necessary to finish the part with the counter-spindle, the AC10-36 offers two counterspindles that can work simultaneously on two workpieces, Schütte’s marketing manager, Wilfried Rupp, explains. “If the decision is to run double backworking, we have the solution. There are eight cross slide positions available, each with the possibility to have multiple tools. Two of the eight cross slides can be tooled for work on the main spindle positions or the counterspindles to give simultaneous backworking. When the front work operations are completed, both counterspindles grab one part each from positions seven and eight and two parts are completed simultaneously.

And that’s the secret behind the 3-second cycle time for the part being demonstrated in the company’s booth. After several machining operations on the main spindles including turning inner and outer diameters, profile turning, grooving and drilling, the part is transferred to the counterspindles for rear machining operations.

High-Tech Meets Traditional Design

While eight-spindle technology is nothing new – Schütte has been offering eight spindles on its G and PC-series multi-spindle machines for many years. The ACX machine, which is globally available now, is the result of ongoing developments of the company’s Generation SCX CNC six-spindle, multi-spindle automatic lathes, introduced in 2006. To learn more, I visited Schütte’s headquarters in Cologne, Germany, to experience the machine in production first-hand.

Founded in 1880, the family-run business has been producing multi-spindle automatic lathes from 1937 onwards. In 1940, the first multi-spindle automatic with an independently controlled longitudinal slide—a principle that will later become known as the "Schütte Design"—is built. The Schütte Design includes a split arrangement of the machining units for longitudinal and cross machining on two machine stands, our host, Mr. Rupp, explains. The spindle and drive head are mounted on a torsion- and vibration-resistant mineral cast compound machine base and connected by a robust longitudinal support beam. This creates a closed-loop framework that guarantees optimal force distribution and a high degree of rigidity. This design provides the machine with a high level of stability, which is reflected not least in a high material removal capacity. 

A further characteristic of multi-spindle automatics from Schütte is the ‘Schütte-Block.’ “This gives our longitudinal slides a high degree of accuracy and longevity and makes sophisticated drilling operations possible”. Often customers not too familiar with our machines, for example, those in China, ask why the company chose this particular design. The response is that it is a traditional, proven design that gives Schütte machines unparalleled accuracy and is highly valued by customers, Mr. Rupp says.

As time passed, industrial production reflected the need for more complex workpieces in smaller batches, shorter life cycles and a highly competitive environment. These needs focused the company to develop the SCX series of six spindle CNC multi-spindle machines. In the SCX series of machines, everything not directly related to the production of the workpiece has been removed from the machining area. No coolant, lubrication lines or cables are inside the work zone to collect chips. In addition, the cross and longitudinal slides are fitted with standard tool units, each with the ability to hold multiple tools. These interchangeable units can include units for turning, drilling, milling, gear hobbing, spherical and polygon turning or most any other driven or stationary need.

Why it has taken 10 years to release an eight-spindle variant of the company’s successful CNC automatic multi-spindle lathe SCX series to the market? Mr. Rupp explains as follows: “An eight-spindle machine is much more complex than a six-spindle machine. You have to program and control as many as 85 axes, which is only possible using a triple NCU in the Siemens 840D Solution Line Series. At the same time, you have to offer the same easy-to-use operator interface our customers are accustomed to.”

The configuration, operation and programming of the CNC ACX machines are carried out with the help of the SICS user interface developed by Schütte. It is optimally tuned to the range of functions of the multi-spindle automatic ACX. SICS provides operators with the respective predefined input and operating menus for their tasks. The coordination and distribution of the data to the individual control systems and channels run in the background and are not visible to the user.

The material is usually supplied to the ACX machine in the form of bar material with a diameter of as much as 42 mm. As an alternative to barstock, an automated supply of blanks or semi-manufactured parts via individual feeding devices is possible. The finished parts leave the machine depending on customer requirements via a chute, discharge conveyor or are deposited in an oriented manner in pallets. Cleaning and measuring stations can be configured according to the respective workpiece requirements and integrated in the finished part handling system.

The Eight-Spindle Advantage

The ACX machines are designed for complete machining—the front and rear side of the workpiece are completed in a single cycle. Of decisive importance is the possible simultaneous work of eight main spindles and up to two counter-spindles, Mr. Rupp explains. All spindles are equipped with liquid-cooled direct drives – keeping the thermal growth in the spindle carrier to a minimum – which permit freely selectable spindle speeds independently of one another. With a torque of 85 Nm, they feature particularly high dynamics and traction.

The machine can be operated as an eight-spindle machine for complicated parts that require extensive machining, or as a double four-spindle machine, where it actually runs as two machines working together with one another simultaneously on a single platform. Every second, a tool station always has simultaneous access to the same tools. As a result of double four-spindle machining, two finished parts are produced by the machine per drum rotation. In double rear end machining, there are eight spindle positions available for front machining the workpiece and two spindle positions for rear end machining, and they all work simultaneously.

Further productivity increases can be achieved with optionally available additional slides in positions seven and eight in the part-off position. “This feature allows the user to implement both an additional rear-end machining operation as well as simultaneous pre-part-off of a follow-up workpiece during rear-side workpiece machining,” Mr. Rupp says.

Machining Units

The basic construction of the AC10-36 follows the classical concept of the cam-controlled automatic, where eight spindles index in a precision-made spindle drum that is locked with great repeatability by a robust Hirth coupling. The cross slides for OD machining permit machining in the X, Z and Y axis on positions one through eight. The X-axis slide moves radially to the spindle centerline on linear guideways. The Z-axis motion uses a hydrostatic quill design that travels parallel to the spindle centerline and passes through the X-axis carrier at 90 degrees. Both axes are driven electromechanically. Using interpolation, these allow X-Z contour motion at all eight stations.

The modular cross slide tool turrets can bring one or more tools into the cut at any of the eight stations, potentially multiplying the number of tools that can be used at any given station. This flexibility allows for multiple operations to be performed at a single station or gives the option of having redundant tools in place for unattended operation.

Each and every cross slide can provide Y-axis machining capability as well. In addition to its linear motion, the Z axis can be arranged to swivel. This motion allows a second or third tool or more tools to be positioned on the workpiece. It also allows for Y-axis milling by interpolation between the linear X axis and the rotary C axis.

The Hirth coupling is used to accept variously configured turrets that carry cutting tools used for a given station. As on the SCX Series, the ACX standard turrets include devices for (off-center) drilling, deep-hole drilling, thread cutting, angular drilling, cross drilling, contour milling, gear hobbing, and multi-edge turning, spherical and polygon turning (cross) as well as cross slides (endworking) for driven and stationary tools. Essentially important: all units can be used independently from one another in every spindle position.

The standard connection allows any turret to be positioned on any cross slide. This modular design is suitable for both stationary and driven tools. For driven tools, an integral motor is mounted in the Z-axis quill and generates 8,500 rpm. Coolant lines are also routed through the quill, keeping the workzone clear. Through the tool coolant up to 100 bar is available.

The cross and longitudinal slide turrets use HSK or Capto cutting toolholders for solid clamping and quick change-over. Standard and accurate cutting tool interfaces encourage the use of offline tool presetters to speed up tool changes in the machine.

Free Accessible Machining Area

To accommodate change-over, anything not directly related to machining parts was eliminated from the working area of the machine. The enclosed cutting area contains no drive components or guideways, lubricating or coolant lines, or wiring. It’s a clean workzone that better facilitates access for quick-change of tooling and allows good chip removal. The open and clean workzone also gives the user freedom to add or remove various machining configurations.

“In case of chip accumulation, there are no obstructions in the material removal area due to slides, drive attachments, cables or lines,” Mr. Rupp explains. “The risk of damage to or destruction of cables or hoses through hot chips or during machine setup no longer exists. Nests of chips are also a thing of the past. This clearly improves the reliability and availability of the attachments and significantly reduces unproductive times required to remove chips and chip nests. For many shops, this is invaluable because reliable automatic operation can only be achieved if the problem of chip discharge is solved. And all of this in the knowledge that difficult-to-machine materials are increasingly being used. This is not only a real challenge with regard to the machine capacity, but also with regard to the chips, which are often long and thus difficult to discharge. The arrangement of drive and guide systems outside the machining area also effectively prevents contamination of these critical elements and thus removes the danger of premature wear.”

The ACX series from Schütte is available for worldwide distribution. It eight-spindle design serves the needs for flexible, lower-volume, higher-mix production increasingly found in metalworking shops. In addition, the eight-spindle also fills the needs for high volume production using its additional machining capabilities for complex parts.