Figure 1. The digital twin is for preparation, simulation, and collision prevention. (Image: Heidenhain)

To learn about the use of digital twins for machining operations in industry, I interviewed Gisbert Ledvon, VP of Marketing at HEIDENHAIN Corporation, Schaumburg, Illinois.

Tech Briefs: An obvious question is, what is a digital twin?

Gisbert Ledvon: A digital twin is a realistic model of a machine on a programming station. With it, you can view a machine’s real kinematic behavior, parameters, and functions. In the machine tool world, it can be an exact duplication of the machine tool you use to manufacture complex parts. You feed the CNC code to the digital twin before you actually feed it to your machine, and it reproduces the machine’s exact motions.

Its machining simulation can therefore run just like the real machine. This provides greater shopfloor assurance that programs created with CAM systems or the programming station will run seamlessly. That saves time on setup, simulation, and shopfloor debugging, thereby increasing process reliability and manufacturing productivity.

Tech Briefs: How do you set up the model?

Ledvon: There are multiple digital twin solutions. For example, a CAD/CAM company could implement the digital twin of a machine tool within their software. They use the CAD/CAM software to simulate what the machine tool would do with the code they just generated. It could include the axes of motion to make sure there are no collisions, for example. The HEIDENHAIN digital twin includes that, but in addition, takes in detailed information about the specific mechanical components of the machine, for example, specifications of the motors used on each axis.

What are the torques, speeds, acceleration/deceleration characteristics for that motor? For the rotary axis you could add the spindle configuration — their torque specifications and rpm. HEIDENHAIN captures that information and uses it to create the digital twin. We ask the owner of the machine or the OEM to send their configuration file to our service group. We then combine their file with those mechanical specifications to create the digital twin and accurately simulate the machining process.

We then make a backup of the entire file and send it to the customer to upload into their programming station. Because the model includes the exact dynamic behavior of the machine based on speeds, feeds, and forces, they will have predictive information about how long it’s going to take to machine the part, to what accuracy and with what surface quality. They can know almost within a minute, how long it’s going to take to machine it.

It’s very important when you’re bidding on a job, to accurately estimate how long it’s going to take to machine each part. if you underestimate it, and it takes you 20 percent, 30 percent, 40 percent longer to make that part, you’re losing a significant amount of money. You can’t go back to the customer and ask for more. With a digital twin, you take a 3D model of the part, run it through the digital twin for a particular machine, or even try different machines and determine where you get the most efficiency. Because you ran it through the digital twin, your estimate will be very accurate. You won’t lose money and your customer will be happy because you delivered on time.

Figure 2. The digital twin looks exactly as if you were in front of the machine but in addition, you also have a precise 3D model of it. (Image: Heidenhain)

Tech Briefs: Does the model have to be set up differently for each different part being manufactured?

Ledvon: No, if the customer has multiple machines, you would design a digital twin for each, but once you have the model, it will work for any part that can be made with that machine.

Tech Briefs: So, the digital twin is used to run a virtual test before you do the actual machining. Is it also used to track the actual machining operations?

Ledvon: No, the digital twin is for your preparation, your simulation, and collision prevention. You want to make sure you don’t have any type of collision, especially if you’re moving in multiple axes at the same time. There is other software to monitor and control the actual machine.

Tech Briefs: What do you think are the prospects for digital twins being adopted more widely?

Ledvon: It’s becoming more and more important to utilize digital twins in industry and not just because of the process benefits. We all know that there is a labor shortage and it’s very difficult to engage young people to go back into factory environment — they think of factories as being dirty and unpleasant. But automated factories are much different than that. It is more challenging and interesting when there are exciting new machining and manufacturing processes in place.

It’s also the case that a lot of people have already left manufacturing jobs, so you might have one or two operators running multiple machines making very high value parts. You want to make sure that those parts don’t get damaged. You might have someone running three or four or five machines at the same time, making sure they’re running 24/7. And maybe you’ve never been automated before and there are multiple parts, they might be in a variety of small-sized lots or very high volumes. If you put yourself in the shoes of the people who have to manage the shop and operate and program these machines, they can easily make mistakes. So, digital twins become really important for them. They can verify everything before they start running the job, they can feel confident that when they’re setting up the machine, everything that was programmed and simulated is going to work properly. We give them a tool to feel more secure, to be more efficient, and safe.

I think it’s a big help for the shops to implement the relatively small investment in a digital twin to help the team to stay focused and efficient and make sure that this machine doesn’t get damaged. If there is a collision on a million-dollar machine, it can cost tens of thousands of dollars within a couple of days if that machine is not operating.

Tech Briefs: How would I get started if I were managing a factory and wanted to start using your digital twin software?

Ledvon: You create a compact file, a service file we call it, that collects all the data from the machine. If we don’t have all the data, our service team will reach out to the machine builder to get a model of whatever is missing in the machine envelope. It is then all put into a zip file and sent to our service department. The service department generates and makes the digital twin so it looks graphically like your machine looks inside, with all the components in that work envelope. It has all the data and the background on the parameters and the information about the torques and the motors and the speeds and all that. And we send that securely back to you to upload into your programming station. It looks exactly as if you were in front of the machine but in addition, you also have a precise 3D model of it.

You can also import details like where it’s mounted on the table and what the raw material looks like. Then you can do a simulation and follow the entire process and see if your tool path is optimized, whether you should approach the job from another side, because you might have some areas where you get some kind of vibration. Maybe you should machine from top to bottom or the reverse. You might avoid vibration or any type of surface quality issues. And you can do it all it right there in your office.

In summary I would say that for a manufacturer to have an exact digital twin for each of his machines will bring benefits that far outweigh the costs of the system.

This article was written by Ed Brown, editor of Sensor Technology. For more information, go here .