Simulation Simulation of Machining Processes with Virtual CNC

From Dr. Karsten Kreusch, Bosch Rexroth

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Simulation systems of CNC functionalities by means of control models are widely used. When they reach their limits, simulations based on the real CNC core can provide help. But how are the required application data implemented in the simulation scenario?

Powerful, intelligent and connective: the MTX CNC system from Rexroth.
Powerful, intelligent and connective: the MTX CNC system from Rexroth.
(Source: Bosch Rexroth)

Demanding machining technologies and complex machine kinematics require increasingly powerful numerical controls. Their commissioning and programming on the machine is not easy. However, with the simulation and virtual commissioning there are possibilities available that support the user in these tasks and can reduce time and costs. Such methods are nowadays summarized under the term “Digital Twin”. The big challenge, however, is to build up a database that maps reality with sufficient accuracy to achieve reliable and realistic simulation results. In addition to the configuration data of the CNC, this requires numerous parameters, kinematics information and geometry data of the machine to be controlled, but also of the equipment used (clamping devices, tools).

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CAD/CAM Coupling

In many cases, CNC programs for machine tools are no longer programmed manually, but with the aid of programming systems. This is because of the increased requirements arising from frequently changing part spectra, complex multi-technology machines, free-form surface machining or new machining processes. The heterogeneous software landscape of CAD/CAM and its large number of suppliers illustrates the enormous variety of available applications.

Regardless of which system is used, it must integrate as well as possible into existing IT infrastructures in order to use existing data efficiently. This can be done by using integrated CAD/CAM systems or by networking specialized CAD/CAM systems via corresponding software interfaces.

The software-supported procedure in a CNC programming system differs significantly from the manual mode of operation. It is not programmed manually, but the machining situation is defined either in a visual-interactive manner or by mean of automatic, feature-based selection of suitable processing sequences and tools. The user collects the necessary data, in particular jig and tool data, from various sources and bundles them in the CAM system. From this, for example, clamping and tool plans can be generated automatically. The actual programming of the CNC program takes place after a control and machine-specific post-processor defines the machining process.

CNC Simulation

CNC simulation is a software tool that has been established in practice for years. It is used to visualize production sequences in machine tools in a realistic way. By mapping the complete working area of the machine (including all fixtures, tools and workpieces) and the movements of the machine (including visualization of the tool path and material loading and unloading) in 3D, to the user can evaluate and optimize the process before the CNC programs are transferred to the machine.

Different CNC simulation systems are available to provide various control functionalities:

  • Reproduction of the CNC functionality by the software provider of the programming or simulation system.
  • Use of the original CNC functionality in the form of a virtual CNC running on a PC.
  • Real-time coupling of a real CNC with a simulation PC (HiL, Hardware-in-the-Loop)

Although the HiL approach can provide a map of a real control sequence in high quality, it is too complex and therefore unsuitable for use of work planning in a production plant. As an online simulation, however, it can be used directly on the machine for visualization purposes. Particularly in the case of workspaces that are difficult to access, it represents added value for the machine operator when the machine movements can be displayed in real time on the operating screen of the machine or a mobile device.

The first variant, on the other hand, is widely used in production planning because it works perfectly on a PC. The simulation of the CNC is part of many programming or simulation systems. However, due to the enormously increased functionality of modern CNC systems, it is becoming more and more difficult and expensive to simulate them. Generally, the standard control behavior can be visualized with sufficient accuracy, but special CNC functions such as spline interpolation, which would be relevant for optimizing the machining process, are usually not available.

This is where the CNC simulation using virtual CNC comes into play. Since this contains almost the same software as the real CNC, it offers the full range of functions and thus overcomes the limitations of conventional control simulations. Bosch Rexroth offers virtual machine simulation for its MTX CNC solution. In addition to the complete functionality of the CNC core and the original user interface, it also provides a 3D environment for virtual machine commissioning and testing as well as for offline simulation of the entire machine and the machining process.

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Data Consistency and Interfaces

Users choose a specific CNC programming or simulation software on the basis of a wide variety of criteria (manufacturing technology, machine types, integration capability, etc.), which leads to an extremely diverse range of products. For this reason, Bosch Rexroth also pursues a strategy of supporting open or standardized interfaces. In cooperation with the CAD/CAM software providers Moduleworks and Opus, a continuous process chain was integrated in an application of a Bosch-Rexroth plant. This involves the machining of hydraulic components on a 5-axis machining center with MTX control.

This article was first published by MM MaschinenMarkt