Robotized cutting of tubes and profiles: a niche market occupied by experts!

Why cut tubes and profiles using a robot?

The technological progress of the last few years now makes it possible to build highly automated and flexible tube and profile cutting machines, incorporating machinery that is increasingly sophisticated. In the conventional approach, tubes are cut by laser machines with a 5-axis head. For instance the Mazak and Bystronic machines are perfectly optimized for laser cutting, with a huge number of dedicated options. But these machines may be limited to cutting tubes with small diameters and relatively limited dimensions, due to accessibility constraints. To cut bigger tubes with larger diameters – essentially more than 400 mm – certain robot integrators design cutting cells incorporating robotized arms instead of 5-axis heads.

Since the working area of robots has a radius of more than one meter, they can cut tubes and profiles of any size without any access constraints. In addition, because these installations use a robot they are much more flexible in terms of the type of part they can cut. As well as cutting all types of tubes (round, rectangular, etc.) and profiles (H, I, L, U, etc.) they can also be used to produce chamfered parts on flat sheets.
“For example, one of our customers uses the same machine to cut chamfers on particularly thick sheets, 500 mm diameter tubes and H400 profiles,” explains Nikola Smajgert, Project Manager at Daihen Varstroj. “For the same cost, these robotized installations deliver greater flexibility and productivity than 5-axis cutting”.

Although robotized cutting of tubes and profiles constitutes a niche market, it is relevant to many industrial sectors (boiler-making, transportation and agricultural equipment, construction, etc.). Its versatility makes it possible to open up new markets to customers who make use of it as sub-contractors. However, the dimensions of these tailored installations must be perfectly adapted to customer needs.

How do robotized tube and profile cutting systems function?

There are two types of kinematics for robotized tube cutting systems:

• Systems with a rotating mandrel which brings the bars in front of the robot to facilitate cutting configurations. These machines are more complex, but deliver better quality cutting because the torch can remain vertical.
• Systems with no mandrel, suitable for profiles which do not require cutting under the bar. In that case rotation of the mandrel is not necessary and the bar can simply be pushed on rollers. However, this less expensive type of installation may not be suitable for cutting round and rectangular tubes, because robot access is very difficult at the start and end positions, and the molten material may fall onto the torch.

On these installations, plasma replaces the laser source because it has the advantage of being less expensive, effective on large diameters and very easy to integrate onto a robotized arm. Plasma can also cut very thick tubes and profiles, and so overall it is more suitable for cutting profiles.

What about precision?

One of the key points is the limited precision of a robot compared to a Cartesian head, although it is still sufficient for cutting in heavy industry and the relevant sectors.

To guarantee high precision cutting it is vital to add a trajectory adjustment strategy to compensate for the inevitable part deformations. There are several strategies. Laser or mechanical sensing provides the exact position of a bar’s characteristic points and makes it possible to recompute the trajectories according to the differences measured. Height control makes it possible to adapt the height of the torch during cutting to guarantee a constant sheet/torch distance by measuring the voltage.

No production without a specific software

Although the vast majority of robots are controlled through learning, it is not possible to envisage controlling a robotized shelf-mounted cell with more than 6 axes. Otherwise the precision of the part drawn in CAD would not be guaranteed, and the machine would be immobilized while the program was being created. As Nikola Smajgert confirms, “Without a software like Almacam, these machines would be impossible to program”.

Almacam Tube is capable of creating a robot program from a CAD assembly, completely automatically. Thanks to powerful tube and profile recognition algorithms to compute trajectories from the CAD model, intelligent nesting algorithms to optimize positioning of the parts on the bar, and algorithms to optimize robot trajectories so as to avoid collisions and singularities, programming of complex machines is child’s play!

For this automation to run smoothly, the software has to adapt to the machine, not the other way around. So Almacam 3D delivers modeling that is faithful to the machine’s kinematics to avoid collisions, take account of inevitable guidance errors and correct them thanks to precise calibration.

In addition, Almacam manages strategies for loading and unloading tubes, opening of jaws, as well as the cutting parameters chosen automatically according to the part’s material and thickness. All these strategies can be customized to suit the individual requirements of each machine.

Finally, since the software is capable of retrieving and processing production data, it seamlessly incorporates Industry 4.0 principles.

Importance of the partnership between the integrator and the vendor

For a project to succeed, the integrator’s expertise is more important than the brand of the chosen robot. So it is vital for the customer, the robot integrator and the software vendor to work closely together to define and optimize the rules defining how the machine functions. It is important to work as a partnership from the start of the project, since on these installations it may take a year to progress from initial configuration to delivery to the customer.

For example, it was thanks to many tests on real parts that Daihen Varstroj and Alma developed sensing strategies to correct robot positions according to the deformations on tubes and profiles. These deformations were inevitable since the bars were up to 12 meters long.

To sum up, it’s not by chance that Almacam Tube is the leading software for robotized cutting of tubes. This success is down to three factors:

• Very strong expertise in tube cutting at every stage of the process (importing and modifying tube assemblies, generating trajectories from the tube’s CAD model, managing cutting parameters).
• 30 years of experience in off-line programming of robots for cutting and welding (familiarity with all the robot brands and computation of trajectories without collisions or singularities).
• Tremendous flexibility of the software, capable of adapting to the needs of the manufacturer and the end user.

This is how Nikola Smajgert summarizes this from his point of view as a partner: “We are very satisfied with the services and expertise of Alma, a specialist in both software and robotics, and also perfectly familiar with every aspect of the metal-working business. Our technical cooperation with them is highly effective; we are on the same wavelength. This is very important in order for the customer’s project to succeed.”