Laser Welding for Wheel Rims

FEBRUARY 201338

The use of lasers has increased andbecome widespread in many manu-facturing operations, such as mate-

rial processing, measuring, quality con-trol processing, and automation. It is acompetitive, energy-saving process withhigh user satisfaction.

Due to its many advantages, laser pro-cessing has replaced more conventionalmethods and techniques in the industry.Laser technology has become widelyused in Germany where it has been im-plemented into its automotive industries.It offers reduced labor costs, taxes, andmaterial costs as well as energy savings.Lighter, safer, and better-quality designshave been put on the market and newparts created as a result of laser process-ing. The common advantages of lasers inautomotive industrial operations includethe following (Refs. 110): High-speed operation; High reliability and repeatable quality; Multipurposes, includes welding, cut-ting, and marking; Processing using noncontact tools(since tool wear does not occur there isno need to change the tool); Automation; Enables the creation of new designs,

operations, and measurements that werepreviously deemed impossible; High-density energy transportation toa narrow point; Deep, narrow, and controllable penetration; Suitability for joining numerous mate-

rials with different characteristics; A decrease in or no need for physicalor chemical operations before and afterthe processing.

For these reasons, manufacturers inthe wheel rim industry have implementedlaser processing.

ALI . NA and H. ZDEN([email protected]) are withEge University, MechanicalEngineering, Izmir, Turkey.

The properties of laser-welded wheel rimswere considered good enough for the processto be used in production in the auto industry

BY ALI . NAAND H. ZDEN

LaserWelding Laser

Soldering

Laser SurfaceModification

Laser Marking

Laser QualityControl

Laser MonitoringMeasuring

Laser Drilling

Laser Forming

Laser Cutting

Fig. 1 Laser processing used in themanufacturing of wheel rims.

Lasers Offer Advantages forWelding Steel Wheel Rims

Ozden Feature Feb_Layout 1 1/11/13 10:52 AM Page 38

39WELDING JOURNAL

Fabricating Wheel RimsConventional Manufacturing ofSteel Wheel Rims.

Since steel wheel rims are a basicproduct of the automotive industry, man-ufacturers look for new ways to designthe rims to better compete in the mar-ketplace (Refs. 4, 5). In particular, themanufacture of steel wheel rims entailsmuch processing in production lines, andthis is a disadvantage in terms of cost. So,the use of laser welding in the manufac-turing of steel wheel rims is now beingconsidered to reduce costs.

Figure 1 shows schematically the laserprocessing used to manufacture steelwheel rims. Wheel rims consist of twobasic parts: the rim and the disk Fig. 2.The manufacturing methods and assem-bling techniques are based on cold form-ing and welding methods. Steel sheetswith good welding characteristics areused in manufacturing.

The first step in the manufacturingprocess is to obtain blanks with theproper specifications and surface quality.The prepared blanks for producing therims are rounded using a rounding ma-chine, then the ends of the materials arebanded and flattened using a press beforethe butt joining process. The flattenedends are joined with flash welding orupset butt joint welding Fig. 3. Afterthe welding operation, fins present on thesurface and at the corners of the weldsare removed with a scarfing and edge-trimming machine Fig. 4. When theseoperations are completed, the rims arererounded with a press and formed intotheir final shape with cold roller ma-chines and presses.

The disk materials, which are cut ascircular blanks, are formed with flowforming machines or presses. The centerholes, ventilation holes, and bolt holesare punched out with presses, then lathedand countersinked to precise dimensions.

The rims and disks, which are formedlast, are pressed against each other thenwelded using the submerged arc or gasmetal arc welding processes. After theseoperations, to eliminate the distortionsdue to the welding process, the wheelrims are pressed again. At the end of as-sembly, the wheel rims are painted.

Wheel Rim Manufacturing UsingLaser Welding.

There are few publications aboutusing laser processing in the manufactur-ing of wheel rims. In addition, using thelaser welding method is more commonwhen compared with other methods. Forinstance, Caprioglio developed andpatented a system to assemble rim to diskwith laser welding (Ref. 4). BBS Interna-tional GmbH uses laser welding in itswheel rim designs (Ref. 5). Dawes in hislaser welding book illustrates a laser buttjoint welded steel rim, and it is seen thatthe ductility is enough for cold forming(Ref. 6).

Laser Advantages and Disadvantages

Laser welding offers a number of ad-vantages and disadvantages compared toconventional methods, such as flash andbutt resistance welding, submerged arcwelding, and gas metal arc welding inwheel rim manufacturing.

Laser Advantages Include the Following: Since the laser head has no direct con-tact with the material, it is not necessaryto change the tools routinely; however, inflash and upset butt welding, the elec-trodes should be changed periodically. Since no flash occurs in the applica-tion of the laser welding, there is no dam-age to the machine and there is no pollu-tion in the vicinity of the operation. Because the surface of the laserwelded material is quite smooth, it is notnecessary to implement finishing opera-tions after the welding process. This savesthe added expense of these operationsnormally required after flash and butt re-sistance welding. Laser welding speed is as fast as thatfor upset butt resistance welding andfaster than submerged arc welding andgas metal arc welding. Laser welding consumes much lesselectrical power than the flash and buttresistance welding processes. For exam-ple, the butt joint welding machine usedin the Hayes Lemmerz Janta wheel rimfactory is 960 kW, but a 50-kW fiber laser(its wall-plug efficiency is more than25%) consumes only 200 kW. Lasers produce narrower weld zonescompared with the other weldingprocesses. Generally, there is no need for fillermaterial in laser welding. It is possible to apply a lap joint withlaser welding during the rim to disk weld-ing operation. Lower thermal distortions occur usinglaser welding when compared with sub-merged arc and gas metal arc welding. By using laser welding and tailored

Rim

Disk

Fig. 2 A steel wheel rim and the basicparts, rim and disk.

Fig. 3 Rim manufactur-ing process. A Bend andflattening process; B upset butt welding.

Fig. 4 Rim manufactur-ing process, weld joint withfin surface after scarfingprocess.

A B


FEBRUARY 201340

blanks, it is possible to manufacture therims with different wall thicknesses anddifferent local mechanical properties indifferent regions in accordance with theload distributions in service conditions.The weight of the parts can be reduced bythese means.

Laser Disadvantages Include theFollowing: The edges to be joined with laserwelding should have a smooth shearedzone. Before and during the weldingprocess there must be almost a zero rootopening between the abutting edges,otherwise good quality joints cannot beobtained. A fixing or clamping apparatus or aspecial construction is required in laserwelding, as is required in flash and resist-ance butt welding. Environmental conditions (dust, hu-midity, etc.) must be appropriate for thelaser.

Tests and Results

To determine whether laser welding isa practical method to use, steel wheel rim

materials were welded using laser andupset butt welding. The specimens fortesting were removed from the weldedmaterials. These specimens were sub-jected to tension and bending tests, and their Vickers hardness values weremeasured.

The material used in the experimentswas 6-mm-thick (RSt 44-2) S275J2G3(DIN EN1002) steel, the same materialused in steel wheel rim manufacturing.The mechanical and chemical propertiesof the material are shown in Tables 1 and2, respectively.

The dimensions of the welded materi-als are shown in Fig. 5. The materialwelded with butt resistance welding wassubjected to a scarfing and edge trimmingprocess after the welding operation inquestion. Welded material was cut fromthe flattened region and test sampleswere removed from the part.

The material welded with the laserwas taken from the line after the bendand flattening operations then inter-rupted from the smoothed region. Beforewelding, the material edges were milledto avoid any defects during welding dueto cutting with blades and the slitting

process. In the mechanical cuttingprocess, full flat edges could not be ob-tained and sometimes curvature oc-curred at the edges due to the force of theblades or the tools.

The prepared material was weldedwith a Trumpf HD 4006 Nd:YAG 4000-Wand Arcmate120i Fanuc robot Fig. 6.The welding process was applied double-sided. The reason for this is although thelaser has enough power for one-sidedwelding, the apparatus clamping theparts for the operation was not appropri-ate for it. A proper apparatus for buttjoints is shown in Fig. 7. During the laserwelding operation, laser power P = 2500W, focus length f = 150 mm, weldingspeed V = 8 mm/s, and Ar gas flow = 7.5L/min, BPP: 25 mm*mrad parameterswere used for the sample tests.

Weld Properties

After the laser welding process, theappearance of the weld joints was evalu-ated. No cracks were observed on the sur-face of the material due to the weldingprocess, and quite regular and smoothweld joints were obtained that required

Fig. 5 Dimensions of thewelded samples and speci-mens after laser butt jointwelding.

Fig. 6 Nd:YAG 4000-Wlaser machine and robotwelding mechanism.

Fig. 7 Clamping apertures for butt join-ing of the materials with laser.

Table 1 Mechanical Properties of (RSt 44-2) S275J2G3 Steel

Yield Strength Re (N/mm2) Tensile Strength Rm (N/mm2) Elongation-% A

min. min. maks min.275 410 510 28

Table 2 Chemical Properties of (RSt 44-2) S275J2G3 Steel

% C % Si % Mn % S ppm N % Al % Cu+Cr+Nimaks. 0.18 01.150 maks. 0.020 maks. 0.008 maks. 90 0.02 maks. 0.30


no additional processing. The width ofthe joint was 2 to 2.5 mm. The appear-ance of the laser weld is shown in Fig. 8.There is no undercut on the surface of theweld joints. A line occurred in the middleof the joint. The reason for this was theinflux of the molten metal into the keyhole, which is formed as long as the laserhead moved forward during the weldingprocess. The line is regular and continu-ous and shows that good quality jointscan be achieved. As a matter of fact, themacro view verified these assumptions.

No defects were determined in the macrosection of the weld such as porosity andincomplete fusion. A narrow HAZ wasobtained as expected. The comparison ofthe laser and butt resistance weld jointappearance is shown in Fig. 9.

Our study of the properties of thewelds started with the microhardnesstest. The fusion zone and base metal wereexamined. A 19.64 N load (F) was appliedfor 10 s in all hardness tests. When thehardness of the laser weld was comparedwith the upset butt resistance weld, the

hardness of the laser weld was approxi-mately 25 Vickers greater in the center ofthe fusion zone Fig. 10.

It had been thought that the reasonfor the higher hardness values is the ef-fect of a faster cooling rate of the fusionzone with laser welding.

The tension tests were applied in ac-cordance with 287 EN 895, 1996 standard.At the end of the tension tests, diagramshaving close properties to the base mate-rial were obtained Fig. 11. The frac-tures occurred quite far from the fusion

41WELDING JOURNAL

Fig. 8 Surface of the laser butt weld joint.

Fig. 10 Hardness profile of laser butt joint welding. WM =weld metal, HAZ = heat-affected zone, BM = base material.

Fig. 11 Force elongation diagram of the laser butt weldingjoint.

Fig. 9 A comparison of the butt resistance and laser weldedsamples.

Table 3 Tension Test Values

Tension Test Yield Tensile Elongation-% A Reduction inSpecimens No.: Strength Re Strength Area (% Z)

(N/mm2) Rm (N/mm2)1 364.58 441.14 30.01 63.02 372.16 464.09 26.2 68.23 352.3 419.24 31.06 62.5

Means 363.01 441.49 29.09 64.6


zones Fig. 12. This situation shows thatthe joints have sufficient strength. Thetest values are shown in Table 3. In orderto test the ductility of the weld specimens,three-point bending tests were carriedout according to EN 910.

The dimensions of the specimenswere 6 24 180 mm. At the end of thebending test, no cracks were observed onthe specimens as shown in Fig. 13. It hasbeen determined that there was no wors-ening of the mechanical and technologi-cal properties of the laser welded steelwheel materials after the three-pointbending tests.

Conclusion

After evaluation by tension tests, three-point bending tests, hardness tests, andmacro views, the properties of laserwelded wheel rims were considered goodenough to use this process in productionin the auto industry. Test results gave no disadvantage forthe laser welds when compared with theflash and butt resistance welds in terms ofmechanical and technological properties,and the laser welded steel wheel rimswere of good quality. The fractures oc-curred quite far from the fusion zones,and the hardness of the laser weld wasgreater in the center of the fusion zone;however, no high values were obtained.No crack was observed at the end of thebending test and the ductility was good. On account of the lower energy con-sumption, laser welding has great advan-tages. In addition, there is no need for theextra finishing process required afterflash and upset butt welding with thescarfing process, which may lead

to notching during the cold forming operation. It is possible to create new, lighter andrigid designs and optimization for wheelrims with the use of laser welding.

References

1. zden, H. 2007. Investigating fiberlasers for shipbuilding and marine con-struction. Welding Journal 86(5): 2628.

2. zden, H. 2009. Multi-laser pro-duction in the automotive industry, lasermanufacturing, laser measure, laser test-11. Automotive Symposium, TYAP-Bursa, Turkey.

3. zden, H. 2008. State of the lasertechnology and laser applications in theindustry, Cukurova University Sympo-sium, C. Faculty of Engineering andArchitecture, Adana, Turkey.

4. Caprioglio, L. 2008. Method anddevice for laser welding of a rim to disk ofa wheel for motor vehicle. U.S. PatentApplication Pub. No: US 2008/0190901A1, Rivoli (Torino).

5. BBS International GmbH,www.bbs.com. Eriim tarihi: 01.09.2009.BBS 2009 catalog.

6. Dawes, C. 1992. Laser Welding APractical Guide. Abington Publishing,UK.

7. Kleiner, M., Geiger, M., and KlausA. 2003. Manufacturing of lightweightcomponents by metal forming. CIRP An-nals Manufacturing Technology 52(3):521542.

8. Longfield, N., Lieshout, T., De Wit,I., Veldt, T. V. D., and Stam, W. 2007. Im-proving laser welding efficiency. WeldingJournal 86(5): 5254.

9. A state-of-the-art survey The

auto/steel partnership tailor weldedblank project team. June 2001. TailorWelded Blank Applications and Manufac-turing, p. 27.

10. Schlueter, H. 2007. Laser beamwelding. Welding Journal 86(5): 3739.

FEBRUARY 201342

Fig. 13 Laser welded specimens to which bending testswere applied.

Fig. 12 Tension test specimens after the test. As seen,fractures occurred at the base metal region.

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Laser Welding for Wheel Rims

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