Tube Laser Cutting Machines: a Worthwhile Investment? Assessing the Technical Criteria, Organisation of Production, and Market/Client Targets

Tube laser cutting is an essential technology for the industrial processing and cutting of tubes and profiles. A tube laser cutting machine provides a wide range of possibilities, particularly with regards to interior openings, which are often impossible to achieve with more conventional production methods (sawing, milling, drilling, etc.).

A laser cutting machine can cut through a lot of different materials; round, square or rectangular tubes, flat sheets, L-shaped, U-shaped or specific open profiles. These materials can be all grades of steel, such as stainless, aluminium, copper, or brass.

Tubes and profiles are used in a number of fields of activity for designing and manufacturing products, in order to meet the following constraints:

• a very elaborate design, such as for example in the street, office, or interior furniture industry, the building sector (railings, fences, gates, etc.), fittings and many more.

• technical design constraints, particularly for the production of trailers or agricultural equipment, special machines, industrial buildings, the energy industry, etc.

Tube/profile cutting machines also provide a wide processing spectrum, allowing to carry out technical assemblies. As such, tube-tube or tube-sheet intersections can be assembled or pre-assembled with, for example, mortise and tenon joints, groove systems to slide sheets of metal, tabs or fixing and positioning lugs. The designer can use these technical solutions to increase productivity during the mechanical assembly and welding phases.

What aspects should you take into account before investing in a tube laser cutting machine? How can you evaluate the precision and repeatability of the machine? How can you be productive, i.e., reduce the set-up/cutting time ratio?

For the purpose of this article, Metal-Interface interviewed Davide Rebessi, a tube machine project manager at Bystronic. He shared his experience with us about the challenges encountered by manufacturers and sub-contractors working with tubes and profiles.
 

Loss of precision when cutting with a tube laser machine is caused by two main factors:

• A tube or a profile is never completely straight: i.e., there is a ‘deflection’ effect.

  The smaller the diameter/size of the tube or profile, the more this phenomenon is accentuated. This makes is difficult to cut the tube while maintaining the position of the openings, particularly in relation to the other cut shapes.

  

  
  According to Davide Rebessi, "tube laser machines can be equipped with a ‘laser scanning’ system to define the deflection of the tube and thus correct the trajectory of the laser head, in order to position it precisely according to this ‘deflection’ effect. A tolerance of approximately 0.2 mm is thus achieved."
  
  The advantage of this scanning solution is that the calculation is instantaneous, therefore resulting in almost no loss of productivity, unlike systems with mechanical probes that require a probing phase and for the settings to be adjusted by an operator.
  
  Davide Rebessi adds that, "unfortunately, the ‘scanning’ of tubes is rarely an option on machines that cut tubes with a diameter of up to 150 mm. And yet, it’s all the more important for tubes of that size, than for those with a bigger diameter!”

• The second factor is linked to the advancement of the tube during the cutting phase, which tends to reduce cutting precision.
  
  Davide Rebessi explains that, “to gain in precision, vibrations must be reduced, and the only way to achieve that is to separate the tube moving operation from the laser cutting operation. This is a choice that can be made depending on the production and the expected level of tolerance. What is more important: quality or productivity?”
   

The cutting speed of tubes and profiles is important, but it should not overshadow the equipment’s overall productivity. Indeed, the set-up time for batch runs can have a strong impact on productivity, especially for manufacturers working with small or medium-sized batches. The ratio between the laser cutting head’s operating time and the overall time, provides an interesting indication to assess performance.
 

• Tube/Profile Laser Cutting Machine Set-Up Time
  
  For small or medium-sized production runs, it is therefore essential to optimise set-up times. They will often have more impact than the cutting itself.
  
  Davide Rebessi stresses the importance of “automating the preparation and launch phases of production orders as much as possible.”
  
  He insists on 3 aspects that should be automated, particularly for manufacturers producing small and medium batches:
  “the adjustment of the laser head focal, the clamping/chuck system which must adapt to all types of tubes and profiles to be produced, and the adjustment of the manipulator that holds the tube in the machine.”

• Tube Laser Machine Production Speed During Cutting

  It is important to carefully analyse the power of the laser source and the speed of movement of the axes.
  
  Nevertheless, Davide Rebessi explains that, “for a thickness of up to 3mm, simultaneously moving the tube and the laser beam increases productivity by 8 to 10%. There are also other aspects to be analysed in detail for this.”

• Tube Laser Machine(s) Production Flow and Optimisation of the Installation Area

  Depending on the layout of manufacturer’s workshop and the space available, a machine with a fixed configuration may be inconvenient. Being able to switch the loading and unloading areas around can therefore sometimes help improve the production flow.

  On an island with several machines, positioning the laser cutters so that they are facing each other can optimise the handling of two machines in the same area. This means that a single operator can manage both machines at the same time.
   

In conclusion, here is a brief overview of some of the questions to consider when drawing up specifications for investing in a tube laser cutting machine:

• What are the production types: own product, subcontracting, production size, etc.?

• What diameters, thicknesses, profiles shapes, tube types etc. do I want to produce?

• What are my expectations in terms of precision, and particularly tolerance?

• Does the solution need to interface with my design software?

• Make a selection of parts that represent the intended production flow. Avoid extrapolating around one particular part, which may not be very representative, even if that part is currently difficult to produce.

• How can I organise my workshop and production flows, especially for loading the raw materials and unloading the cut parts?

• How can I differentiate myself from my competitors with this new tube laser machine, particularly if I’m a subcontractor? What markets and clients am I looking to develop?