Detecting and preventing collisions: The earlier the better

On simpler machines, an attentive machine operator can usually visually detect potential collisions and press the emergency stop button in time. However, fast and complex movements make it impossible to manually interrupt machining on modern high-performance machines like turning-milling centers or simultaneous 5-axis machines. These machines are automatically stopped by integrated protective mechanisms in the event of a collision risk. But even if the machine is stopped manually or automatically, the result is the same: The machine is sitting idle.

To prevent machine downtime, collisions should be detected and prevented before the actual machining begins. There are three different competing solutions  that are offered by CAD/CAM and simulation software providers. All three models use digital twins of the real manufacturing environment to verify the toolpaths.

This comparison of the three variants shows that the third approach – integrated simulation and collision-checking – has many advantages:

• Additional interface operations and correction loops are avoided.
• It’s simpler, because the CAM programmer doesn’t need any special knowledge of machine code or other simulation software.
• No manual corrections to the NC code that could place process reliability at risk are necessary.
• Planning is easier, because the CAM programmer has access to all the virtual manufacturing components that are represented in virtual process libraries.
• All corrections automatically flow back into the CAM environment, so errors are never repeated.

For Model 3 – the fully integrated solution – to also function reliably on complex high-performance machines and machines with special auxiliary equipment, it must be possible to reproduce the real machining situation absolutely precisely in the virtual world with all geometry – including machines, tool assemblies, clamping devices and limit switches. Simplified substitute geometries – like symmetrical and asymmetrical machine heads – aren’t sufficient to serve as digital twins. Kinematic information needs to also be registered: i.e. reference points, tool change positions and traverse movements. This is the only way that a digital twin of the real NC code can be generated in the CAM environment.

Another advantage of the fully integrated solution: Because the CAM programmer has access to all components that are also used in real production right at his or her workstation, comprehensive options are already available for preventing collisions during planning and CAM programming – i.e., even before simulation. This saves even more time. Many errors are corrected before they can become a problem.

 

Collisions that are detected during calculation of the NC program can be identified and prevented with collision avoidance strategies. The most appropriate strategy depends primarily on the specific component geometry, the machining task and especially the available machine. This knowledge should be stored in NC templates: This means that the CAM programmer only has to select the machine and machining elements. The appropriate collision avoidance strategy – with area reduction, simultaneous 5-axis avoidance milling or indexed machining – is automatically assigned.

 

In summary: The earlier in the process chain that collisions are prevented, the better. This requires that all virtual components be precise replicas of their real twins. This enables the optimal utilization of all options for collision avoidance – from planning and CAM programming to simulation.