Laser tube cutting: some tips
- Cutting with tilting head (3D)
- Curved tubes and laser cutting
- Application fields
The laser cutting of tubes allows the processing of all types of bar profiles. The latest generation machines also for shaped profiles with squared corners.
To determine the cutting capacity, we usually refer to the diagonal of the circle circumscribed to the profile.
In addition to the classic laser cutting parameters that are also found on the most well-known sheet metal lasers. Let’s talk about the thickness and quality of the material. The power of the resonator is decisive for the thickness, while for the quality of the material the reflective ones (copper, brass) can only be cut by resonators with fiber technology and not Co2.
As with other technologies, being able to design the pieces knowing the production process used can enhance the merits and above all minimize the limits.
In the case of laser tube cutting, the following aspects should be considered.
Radial tolerances and coaxiality
The perpendicular or inclined cut,
Bent pipes (see dedicated paragraph)
Cleaning inside the pipes
Furthermore, some characteristics of the specific machine model are sometimes also decisive.
- The fixed difference
- The weld joint search system
- The tapping unit
By linear tolerances we mean the longitudinal deviation in machining: it essentially depends on the accuracy of the machine. Most of the systems today guarantee tolerances and repeatability in the order of hundredths.
The form tolerance refers to the precision with which the figure is made (the hole, the slot or the notch). It depends both on the machine (axis positioning accuracy), on the material (the dimensional deviation from the nominal section) and on the adjustment (especially the incorrect focal length leads to an error). Normally, the form error is expected in the order of a tenth of a millimeter.
Radial tolerance is very important when you need to make through holes in which respecting coaxility is essential. Laser cutting does not perform the two holes with a single positioning but rotates the profile by 180 ° after the first hole. It is therefore clear that precision is essential to obtain a coaxial tolerance in the order of a tenth of a millimeter. Unfortunately, however, the rotation can often be eccentric given above all by profiles that are not exactly linear and in any case with their dimensional tolerance. Therefore the most advanced machines intervene with measurement systems (by contact or laser) to realign themselves and proceed with a perfect drilling.
Cutting with tilting head
The so-called 3D lasers, not to be confused with laser cutting cells (see the paragraph on curved tubes), are machines that allow the inclination of the cutting head. This peculiarity allows the designer to choose whether to always have cuts perpendicular to the thickness or not. The difference is more marked for thicknesses greater than 3 mm, sometimes radically changing the coupling in the subsequent phases. Let’s do some practical examples:
- With the tilting head it is possible to obtain a hole equal to that made by a drill. With the head always perpendicular, the diameter on the internal thickness will be less than that on the external diameter. The difference is more pronounced on tubes that have a round surface
- There is the possibility of making the initial inclined cuts in order to find the bevel for the next weld.
- Graded cutting can be performed as if it were a band saw or with the cut always perpendicular to the surface. The difference is especially marked for square and rectangle profiles rather than for tubes
Cleaning inside the pipes is essential because cutting residues accumulate during processing. There are different protection systems: from the insertion of an internal core to strong suction systems that do not allow storage on the internal side. Depending on the application of the piece it can be a decisive aspect.
The machine also allows marking by engraving on the piece. Especially for those who work within certified production systems, identification and traceability are key points.
There are specific characteristics of the single machine model that can sometimes be decisive. For example, the most recent machines equipped with more than two spindles allow the fixed waste to be reduced to almost zero for longer pieces per meter. Therefore, the waste is reduced with significant savings, especially in the case of stainless steel or aluminum alloys.
Design requirements sometimes require specific placement of the weld bead. In this case, many machines have an infrared camera that detects the bead and orients the tube automatically.
The last important feature present in some models is a tapping unit that allows the threading to be integrated into the machining cycle. In this way, a finished product is obtained without further rework, reducing processing costs.
Curved tubes and laser cutting
This article focuses on laser processing of tubes or bar profiles. Making holes or notches on pieces that will subsequently have to be curved is sometimes not possible.
The problems are different but mainly two:
- the ability to maintain the prescribed tolerances after bending, typically center distances between holes and / or phase of notches.
- the presence of holes near or in the area to be bent leads to inevitable deformations of the same holes.
Therefore, for the aforementioned cases, the technological cycle is substantially reversed. First fold the piece and then shape it as required. Unfortunately it is an operation that raises production costs.
However, tube laser cutting is no longer the ideal machine but a robotic laser cutting cell is needed. It can be considered the big sister since the tube laser cutting machines inherit the 3D and tilt head technology from the cells.
The cells or islands are born as a response to the need for drilling and trimming of cold forged pieces. The first applications were for automotive parts such as doors, hoods and other parts of the bodywork.
A cell requires the creation of one or more specific equipment to block the piece during processing. Furthermore, the cycle time is less rapid than bar cutting, ie before bending. For these reasons the costs with this process are higher but sometimes necessary.
Alternatives to processing with a laser island can be machining centers or robotic islands (anthropomorphic robots) equipped with plasma cutting units. However, even in these cases, fixing equipment is always needed and the cycle times are not comparable to the tube laser.
In addition to the laser cell described above, there are other alternatives for processing tubes.
- Cold forging
- Cutting with a band saw or disc and with subsequent drilling with a drill or milling cutter,
- Integrated cutting lines with punching and milling
The use of laser tube cutting finds application space in various sectors. Below, with a short photo gallery divided by sectors, we present some possible fields of application
- Architecture and construction with the construction of canopies, facades and canopies.
- Metalworking with the construction of frames and pylons
- Oil & Gas with heat exchangers and tanks
- Furniture with, for example, frames for chairs and tables
Agrital: our know-how
Agrital has been using this technology since 2003. It was among the first companies in Italy to have bet on this type of technology and today it can offer its customers a solid know-how on this type of processing.