Experience gained in the automotive sector

The twenty years experience of Mussino in the construction of special machines and special equipment for the automotive sector has permitted the acquisition of specific know-how in the manufacturing process of car wheel rims.

Analysis of the current arc welding process has highlighted the presence of significant inconveniences during the welding between disk and rim (for example use and control of several simultaneous torches, weld splatter, technical process stops for maintenance, etc.).

The prior experience gained in laser technology, with the design and realisation of two automatic systems to cut and weld components for car gas exhaust systems convinced the Company to develop the use of this technology also in the wheel welding process.

Laser technology in disk/rim welding

For some years now studies and test have been carried out for the application of the laser technology for the welding between disk and rim, also as a function to the considerable advantages of this technology:

more homogeneous welding due to the uniformity of the material (there is no weld material);
continuous welding parameters control in real time;
no heat distortion;
no significant weld splatter;
considerable reduction in down times for cleaning and maintenance;
greatly reduced emission of fumes and clean working area.

These studies foresee the positioning of the laser beam on the joint to be welded in a radial manner from the exterior (fig. 1). However, there are some problems, one of which is the need to apply one or more high power laser sources to be able to melt a considerable metal thickness, and the possibility of porosity due to the high development of oil vapours between the walls of the two parts.

Fig. 1) Welding with laser beam focussed in radial direction to the joint (lap welding)

Fig. 2) Welding with laser beam focussed in contact zone between disk and rim (fill welding)

The procedure of Mussino

The procedure developed by Mussino focuses the laser beam in the contact zone between disk and rim (see fig. 2), obtaining in this way a filling weld by means of the fusion of the two elements, with practically no porosity. The use of specific patented devices guarantees the perfect coupling of the parts during the welding. Furthermore, only one laser source is used.

In order to validate the procedure, Mussino has designed a machine (see fig. 3), currently in the prototype stage and therefore without the automatisms for the wheel positioning, clamping of the same and centring of the section to be welded. However, it is pointed out that all the handling regarding the welding head, execution of the welding and related setting and control of speed have been realised with an automated system, so that the process is reliable and true.

Fig. 3) Prototype of machine for disk/rim laser welding

Welding has been carried out on wheels of different diameters (from 14" to 16").The micrographic test has highlighted a perfect fusion of the to edges to be welded and without any significant porosity (fig. 4).

Fig. 4) Welded joint micrograph

The tensile test has highlighted a joint resistance equal or over that of the base material, whereas the fatigue tests have met the quality standards required by the procurement specifications.

ADVANTAGES OF DISK/RIM LASER WELDING

The advantages of the laser technology are well-known. Regarding the disk/rim laser process we have developed, the advantages can be divided into two categories:

PRODUCT ADVANTAGES

The welding is more homogeneous because it is autogenous (there is no weld material)
Better use of the material in the joint: in our type of laser welding the material is submitted to a pure cut, whereas in arc welding the joint material is submitted to complex cut and deflection stress
No heat distortion because the heat produced is less than 1/10 in relation to arc welding
No residual wire sticking
No space occupied in the brake area.

PROCESS ADVANTAGES

More controllable welding procedure because the parameters set can be easily checked, in particular laser beam emission is continually checked in real time
Possibility to check the welding position in real time
No significant projection of melted splatter, as happens in arc welding, so that the brushing operation is no longer necessary
No process technical stops. In arc welding stops are necessary to clean the nozzles and replace them, as well as the need to clean the machine, to avoid marring its efficiency. With laser welding maintenance is weekly and does not affect the machine efficiency
The work zone is clean
The emission of fumes is negligible in relation to the current system, and the aspiration power can be reduced by 1/10
Possibility to use tailored blanks.