If you can do it in in real life, you can do it with a digital twin. Digital twins validate and extend real-world CNC machines, making the creation and use of these simulations a worthwhile investment for machine shops and their customers.

Digital twins offer functionality beyond parts program validation, offline operator training and cycle time estimation. “The things that could stop the setup process and the production of parts can be simulated in the virtual world [as well],” explained Chris Pollack, technology application team manager at Siemens. “There’s not any piece of the machining process that can’t be simulated.”

Digital twin simulation capabilities

Until a digital twin is leveraged, it is not necessarily known how a part will fit in the machining space or fit in the enclosure—how the part will be held or if the tool will even reach it. “We need to prove whether the assembly and the sub-fixtures can even fit in that environment,” Pollack said.

MyVirtual Machine runs what Siemens calls its NC kernel, which differentiates it from third-party simulation packages. “The software that makes the CNC make decisions has the CNC’s brain in digital space,” Pollack continued. “We’re leveraging the brain of the CNC, because it has our kernel running inside of this environment. It’s more than just the look ahead. It’s the decision the system makes.”

The digital twin can simulate material removal, gouge detection, holder detection, fixture collision detection and more. The only limit of the digital twin is quality control of simulated parts. “The [simulated] part will always be perfect,” Pollack said.

Pollack explained that the digital twin can’t predict a hard spot. However, “[users] can implement in-process probing (Figure 1) and can validate the process for continual system checking where they simulate cutting a feature, drop a probe into it to measure it and validate it. If the virtual part is good, continue. If it isn’t good, jump back in the program, adjust the tool and rerun the part.”

Executing tool and part program management

Digital twins are what make smart virtual CNC machines virtual (Figure 2). They mimic the real-world environment. Part program and tooling management are the same as in real life; the program in the digital twin must match the real-world machine. Interfacing via network and/or a pooled server from which part programs are pulled allows the digital twin to be incorporated into the same solution as the real-world machine.

According to Pollack, the function that makes program and tooling management work is using OPC UA on the digital twin. “I can ‘handshake’ the digital twin to an external cloud-based server and can mimic the same communication that I would do in the real world,” he explained.

Digital twin sources

Who creates the digital twin—machine builders, system integrators, or end users? Pollack said that historically, machine builders didn’t make the digital twin. “Typically, [digital twins] are left to advanced end users, system integrators, or a third-party solution provider [to create],” he explained. “But there is a paradigm shift taking place right now.” The digital twin concept was an afterthought: The machine was built, commissioned, is running, then someone decides to have a digital representation for the engineering or programming department, and they would use the machine’s CAD models to create a digital twin using the software they desire.

“When we released the SINUMERIK ONE control, the first natively digital CNC, the concept of manufacturing for an OEM changed,” Pollack said. “SINUMERIK ONE allows full commissioning of machine components in a digital environment before the machine is built. Using Create MyVirtual Machine, builders can conceptually design an entire machine and run real-world parts on it in a digital world to do proof of concept. The digital twin the end user employs, Run MyVirtual Machine, organically gets created because the builder has already done the front-end work.”

Pollack explained that at least 75% of the builders who have moved to the SINUMERIK ONE control are using the digital twin from a design and engineering concept to create the machine. “It’s a tool they didn’t have before,” he explained. “Possibly 40% of our high-end users have made the switch to SINUMERIK ONE because the control is designed for high-end applications.”

Digital twin’s role in CNC machine commissioning

Machine builders and end users can now do complex setups in the virtual world that would otherwise be done in a real-world environment. All a machine builder or user has to do is import the 3-D models so the machine can be commissioned as if they were tying a real control to the machine components. “An OEM can do benchmarking to see if a new kinematic design is making part programs run faster,” explained Pollack. “Anything that can be done in the real world can be done in the smart virtual machine—without having to turn a wrench.”

OEMs and/or users can debug the programmable logic controller (PLC), add new features and can get into the backbone of the control and adjust machine parameters. “If I could do it in the real world, I can do it here,” he said. “In the real world, a probe in the spindle touches the part to set zeros and do alignments. We simulate the probe virtually. We can do that now in this virtual world.”