Editor's Choice

Precise part machining

November 2023 Editor's Choice Fieldbus & Industrial Networking

Having started out as a contract manufacturer in 1989, toolcraft now not only manufactures on behalf of its customers using its 60 CNC machines, but also designs, plans and builds turnkey production systems for companies in various industries, having added injection moulding, mould making and additive manufacturing technologies along the way. “Connecting machines with new technology to existing controllers at the customer’s site is not always the easiest method, but it works when you use flexible control technology,” says Andreas Bauer, division manager for robotics at toolcraft.

One automation platform for every application

This is why toolcraft relies on PC-based control, including in the production cells, which have seven-axis milling robots for machining components at CNC level. “The TwinCAT CNC was the first controller with an integrated interface to the Stäubli robot controller. This technology package made things easier for us,” recalls Bauer.

Using the machining cell designed by toolcraft, one user now mills base frames for wafer production from large silicon carbide and grey cast iron blocks. Initially, the customer was still machining the blocks with conventional five-axis CNC machines. But milling the hard material produces ultra-fine dust that penetrates every joint, linear guide and bearing, causing huge problems. The CNC machines quickly became worn out and required a major overhaul. “We knew that with the TwinCAT CNC we could achieve the required accuracy of 2/10 mm within a machining area of up to 1 m3, and we could seal the Stäubli robots and apply overpressure,” explains Daniel Distler, division manager for sales.

Next-generation CNC robot

“In collaboration with a robot supplier, we developed kinematics to increase stiffness, dust and water resistance, payload and reach. The result is the current configuration of a machining cell with a high-end CNC robot. toolcraft also uses servo drives and servomotors from Beckhoff, in addition to TwinCAT CNC,” adds Alexander Klos from the Beckhoff sales office in Nuremberg.

The robot was equipped with double-bearing gears on all axes and encoders on the drive and output sides. In addition, the spindle mount was modified. The control technology basis of the milling robot was formed by the powerful CX2040 Embedded PC in combination with the CP3921-1502-0010 CNC multi-touch Control Panel, which was connected to the embedded PC via CP-Link 4 with only one Ethernet cable. The system was rounded off by the AM8000 servomotors and the AX8000 multi-axis servo system, and also TwinCAT CNC. Other positive side effects of the new design included the internal hose assemblies, which simplified handling. In addition, no separate robot controller was required, freeing up space in the control cabinet and reducing the complexity of the project.

Straightforward conversion of the drive technology

“Although toolcraft started with TwinCAT CNC and TwinCAT Robotics uniVAL PLC, it was soon possible to switch to another robot type, with different mechanics and kinematics, using our drive and servo drive technology,” says Klos, pointing out two important properties of PC-based control – openness and flexibility. For example, it was possible to integrate the drive-side and output-side encoders of the robot axes into the software function blocks of the axis controllers without any problems.

“Direct access to all parameters and process settings has played a large part in the further improvement of the accuracy,” says Bauer. “For example, the low, but still detectable hysteresis of the gearing was further compensated via the output-side encoders and appropriate control algorithms. Even when high forces are applied, such as during solid milling, the axes are tracked with speed and precision. And the integration of measurement and calibration cycles ensures consistent properties.” toolcraft also retains flexibility in its choice of feedback systems and use of other technologies. The servo drives support many encoder interfaces, and additional options are available via EtherCAT.

It is very important for manufacturing companies to have a functioning process chain, from the CAD drawing to the machining program. As Distler says: “Our approach is to take away users’ fear of operating and programming the robots, while at the same time providing more freedom in machining.” PC-based control also helps in this area: post-processors and coordinate transformation are run on the embedded PC in parallel with the path control of the CNC robot. The machining programs can therefore be programmed in G-Code as normal, and generated from the usual CAD/CAM programs. “We want the robot to work perfectly with the user’s CAM software. toolcraft also has a flexible control platform for this purpose in the shape of PC-based control,” concludes Distler.


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