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Laser Beam of Automobile Hinges

A welding procedure for joining hinges to the reinforcement structure of car doors is evaluated

BY L. QUINTINO, P. VILAÇA, R. RODRIGUES, AND L. BORDALO

ABSTRACT. Since the establishment of a welding process was initiated. The ex- second set was performed on the actual C O2 laser beam as a heat source for perimental work was carried out on a lap door reinforcement structure. The results welding, its application has moved into joint with dissimilar thicknesses and were compiled and analyzed from the se- new areas, replacing existing joining types of parts. The hinge, was made of lection of the best welded reinforcement processes. This paper presents an auto- cast steel, with a thickness increasing lin- structures for structural integrity testing. motive application of laser beam welding early from 4.9 to 6.4 mm (0.193 to 0.252 This testing evaluated not only local joint for joining hinges to the reinforc e m e n t in.). The reinforcement structure wa s strength but also ove rall hinge perfor- structure of car doors. The objectives of made of rolled steel, 2 mm (0.079 in.) mance. The tests included shear, peeling, the investigation were to increase pro- thick, as seen in Fig. 1. bending, and fatigue tests that simulated d u c t iv i t y, improve repeatability, and One of the major difficulties in weld- normal wear and tear on doors over a maintain overall joint quality, while sat- ing these parts was lap joint accessibility. long period of service. isfying the needs for a perfect surface ap- The weld could only be performed from p e a rance and the structural reliability the top surface of the joint on the thicke r Laser Industrial Applications achieved with the gas metal hinge material. This constraint existed be- (GMAW). Experiments were carried out cause when the hinge was joined to the re- Demands for improved production in two distinct phases. The first dealt with i n f o rcement structure, the door was al- q u a l i t y, productiv i t y, and flexibility are technological feasibility and the second re a d y assembled, and thus access from the constantly enlarging the field of laser examined the influence of the main laser inside was prevented, as seen in Fig. 2. welding applications (Refs. 1–4). Th i s welding parameters on the quality of the To obtain adequate penetration and process is being used for an extensive va- joint. At the end of each phase, nonde- stability of the laser welding keyhole, it is riety of applications in the automotive , structive X-ray and metallographic analy- easier to perform the weld from the sur- s e m i c o n d u c t o r, and electronic indus- ses were applied, allowing the selection face of the thinner part. Normally, where tries. More recently, it has been used in of the best overall laser welding condi- possible, joints are designed that way. s u ch diverse fields as medical instru- tions. These conditions were then imple- Two other challenges were pre- ments manufacturing, where heart pace- mented to evaluate the structural in- sented. Lap joint welding was not easy makers and dental instruments are laser tegrity of the joints by means of typical due to the inherent root opening be- welded, and nuclear and naval equip- automotive industry tests. tween the parts. Also, the ove rall thick- ment, where containers and sheet metal ness from 6.9 to 8.4 mm (0.272 to 0.331 are also laser welded (Ref. 5). Introduction in.) was greater than typical automotive Laser beam welding applications in b o dy welding applications. the automotive industry include welding In a particular automotive plant, The first set of experiments was per- the roof to the side-panels by a car man- hinges were joined to the reinforcement formed on plain steel sheets, while the ufacturer in Ghent, Belgium (Ref. 6). Ad- structure of car doors by GMAW. How- vantages over were the for- ever, the process did not deliver particu- mation of a continuous watertight weld, larly good results. Poor weld appearance no post treatment required, and less dis- was the result of a great amount of spat- placed material resulting in better body t e r. Often the process resulted in non- a c c u ra cy. In addition, the problem of conformities in quality tests and breaks in KEY WORDS welding the zinc-coated material wa s production. over come by carefully selecting weld pa- In order to increase productivity, re- Laser Beam Welding rameters. Other car manufacturers (Ref. 7) p e a t a b i l i t y, and ove rall joint quality, Automotive Application use a laser system to assemble gear tran s - while maintaining the structural reliabil- Lap Joint mission shafts, and a particular company ity, an evaluation of the CO laser beam Dissimilar Materials (Ref. 8) laser welds automobile roofs 2 Shielding Gases using 5-axis CO2 5-kW laser equipment. Porosity Companies that produce automotive L. QUINTINO, P. VILAÇA, R. RODRIGUES, components have also been attracted to and L. BORDALO are with Instituto Superior laser beam welding for its ability to weld Técnico (STM), Portugal.

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Table 1 — Mechanical Characteristics and Norm Specifications of the Parts

Parts Material Specification Yield Tensile Strength Strength (N/mm2) (N/mm2) Door Reinforcement Fe P03A DIN EN 10130:1995 <210 270–350 Hinge St 52-3 DIN EN 10025:1990 <355 490–630 Fig. 1 — Geometry of the lap joint between the hinge (cast steel) and the sheet metal (rolled steel) of the door reinforcement pillar.

Fig. 3 — The machined hinge geometry intended to overcome the difficulties posed by the original thickness differences of the parts.

Fig. 2— Schematic of the hinge assembly in the reinforcement pillar of the door structure.

premachined precision components with The method of production of each part increase of output power over that wh i ch restricted heat input and minimal distor- influenced the joint fitup. While the would be obtained with single-mode op- tion. The advantages are single-sided ac- hinge was cast, the steel sheet was rolled e ration, but with a partial loss of beam cess, reduced flange widths and mass, and then stamped to produce the door re- c o h e r e n c e . smaller heat-affected zones, less ther- inforcement. The hinge casting produced The copper nozzle, used for plume mal distortion, increased structura l a rough finish, with a roughness value, Rz suppression conducting the flux of strength, high-speed automated process- (average peak-to-valley height) of about , had an outer diameter of ing, and good design flexibility. Gener- 44 µm, resulting in a gap value between 40 mm (1.57 in.), posing a difficult ac- ally, a number of CO2 laser welding ap- the overlapped parts varying from 0 to cessibility challenge due to the geomet- plications are now in production for the about 51 µm. Thus, in order to analyze rical configuration of the hinge and rein- welding of components such as radiator the gap influence in some hinges, surface f o rcement door structure. As for the supports, door window frames, rear shelf preparation was done by grinding it with handling system, the beam focusing and panels, and side panels (Ref. 8). 1200-grade silicon carbide. The resulting propagation optics were mounted on a roughness Rz of about 14 µm is equiva- Z - t ravel axis and the parts to be welded Experimental Procedure lent to a fine surface finish of were positioned on an X-Y gantry mo- processes. tion system. Welding trials were first performed on The mechanical ch a racteristics and As illustrated in Table 3, the first set of steel sheets and hinges using original chemical composition of the materials to experiments was made, with hinges and hinge geometry (as distinguished from a be welded are shown in Tables 1 and 2, plain sheets, using either or argon machined hinge geometry used later), to respectively. shielding. Using an existing gantry at the investigate different interface preparation Welds were executed using CO2 l a s e r work site, a clamping device wa s conditions. This was followed by trials equipment capable of generating an out- adapted to prevent misalignments and to performed on the actual door reinforce- put power of 6000 W. In practical terms, eliminate the gap between the two pieces ment using the best established interface this produced a beam net power of ap- as much as possible. condition and two different hinge proximately 4550 W, with a beam deliv- The first step was to prove the feasibil- geometries. The selection of the welding ery efficiency h = 76%, a focal length of ity of laser beam welding to join the parts parameters was based on visual, nonde- 150 mm (5.905 in.), and a focal diame- present in this specific application. As s t r u c t ive (ra d i o g raphic), and metallo- ter of 0.4 mm (0.016 in.). The laser stated before, one of the main problems g raphic analyses. The most promising s o u rce was operated with continuous was related to the surface finish of the cast conditions were selected for a final test wavelength and with multimode TEM, hinge, wh i ch considerably augmented phase aimed at assessing the structura l wh i ch produced an output that com- the joint root opening at the interface. Be- integrity of the assembled joint using typ- bined seve ral operating modes or pro- cause of the lap joint configuration, spe- ical automotive industry tests. files. Multimode operation resulted in an cial care had to be taken with maximum

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al l o wable root openings to reduce poros- times. The time had to be long enough to ity formation and increase penetration of d e velop a keyhole, but it could not be the keyhole in the sheet. To evaluate the too long since this would excessive l y influence of the root opening, a series of melt the parts and produce a melt- hinges were prepared by grinding the sur- through. A delay interval ranging from face of the hinge at the interface of the 0.5 to 1 s was used. overlapped joint, allowing comparisonof The second fixture was designed and the as-cast and ground surface finishes. To built to firmly hold the door reinforc e- compare these differences, argon wa s ment. The aspects of repeatability and chosen as the shielding gas. positioning accuracy were taken into ac- Because a minimized root opening re- count when designing this device, as sults in deeper penetration and less well as the possibility of welding both p o r o s i t y, ground hinges with original geometrical conditions of the hinge. The geometry were used to assess the influ- machined hinge was rotated 25 deg from Fig. 4 — Schematic of the two different paths ence of argon and helium as shielding the horizontal working plan to maintain for the welds. AA — Across the hinge, start- gases on the depth of penetration, with- the perpendicular position between the ing and finishing inside the plain sheet; BB — out changing the other parameters. laser beam and the surface of the hinge. starting and finishing inside the hinge. The method for visually selecting the The geometry and clamping characteris- most representative samples was based tics of the fixture are illustrated in Fig. 5. on a systematic characterization analysis To guarantee correct of the following data: laser beam stabil- placement of each pair of ity (sound and glow from keyhole break- hinges on their respective downs and/or plasma formation), width door reinforcement, the of the weld bead at the top surface (mea- hinges had to be aligned sured value), penetration (total/partial), on the same axis to allow clear burned-edges (yes/no), genera l proper door rotation. Th e shape of the bead at the top surface (con- holding device between ve x / p l a n / c o n c ave), and spatter the parts is represented in ( m a ny/few/none). After selecting the Fig. 6. most representative samples, X-radiogra- As in the case of the phy tests were made to reveal possible first set of experiments, porosity, cavities, or cracks in the weld ra d i o g raphs were made metal, as well as to determine wh i ch on visually representative hinges were to be metallographically ex- samples to reveal possi- amined, and, within these, which were ble defects in the weld. the most critical cross sections. Conse- Once more, representa- Fig. 5 — The gantry geometry used during the second set of ex- quently, the most representative and im- t ive samples were pre- periments allows different angular positions for the clamping de- portant samples were cut, mounted, pol- pared for metallogra p h i c vice of the door reinforcement pillar. ished, and etched for subsequent analysis. microscopic analysis. As a result of the first set of experi- ments, a combination of helium gas and Table 2 — Chemical Composition of the Hinge and Door Reinforcement Materials ground hinges was selected for the trials undertaken in the second set of experi- Chemical Composition (%) ments on the reinforcement structure. The number of welded hinges is de- Material C Si Mn P S Al scribed in Table 3. FeP03A 0.1 — 0.45 0.035 0.035 0.2 At this point, different hinge geometry (door reinforcement) was introduced to reduce the thickness of St 52-3 (hinge) 0.2 0.55 1.6 0.035 0.035 — the weld bead, as seen in Fig. 3. Note: FeP03A — rolled steel; St52-3 — cast steel. Both hinge geometries were welded on the original door reinforcement, wh i ch demanded the use of a new fixture. The best welding parameters achieved during the first set of experiments on sheet steel were used as a starting condition for the Table 3 — Overall Experiment Conditions for All Welding Trials Performed second set. Moreover, the group of para- meters resulting from the second set of 1st Set of Experiments 2nd Set of Experiments (hinge joined to plain sheet) (hinge joined to experiments, during wh i ch the hinges reinforcement structure) were welded to the original door rein- Hinge geometry Original Original Machined f o rcement structure suffer only minor variations in comparison to the final ones Surface finishing As cast Ground Ground from the first set. Argon 20 34 — — Shielding gases Weld beads were also made starting Helium — 10 14 6 and finishing inside the hinge, as seen in Number of welded Hinges Fig. 4. When starting welding inside the hinge, special care was taken with delay

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Seven samples, representative of the finish. This behavior was the trend ob- different conditions (Table 3), were se- tained for all 20 trials performed. Th e lected for detailed analysis from the ground surface not only produced a bet- welds made in both sets of experiments. ter fit and less energy loss by These were the welds on which the best r e f l e c t i o n / r e f raction of the beam at the visual appearance, penetration level and gap on the interface of the ove r l a p p e d stability were achieved. The correspond- parts but also hydrogen sources like the ing weld parameters and overall condi- hydroxide layer present at the surfaces, tions of these samples are described in were greatly reduced by careful surface Table 4. The only samples that had spat- preparation procedures. The final grind- Fig. 6 — To firmly hold the hinges to the door ter were those with the largest weld bead ing grade and respective cleaning, for ex- reinforcement and to ensure the smallest gap widths, as seen in Table 5. ample, were applied immediately before between them, a stud was welded to the base In fact, the only samples selected that welding executions. of the hinge and a spring ring was used to fas- exhibited spatter, Ar2 and He2, were The sample Ar2, welded under exactly ten it. those with higher heat input and lower the same conditions as Ar1 but with a velocity values, as confirmed in Fig. 7. ground surface, was intended to empha- It is well known (Ref. 8–12) that ob- size this phenomenon, as seen in Fig. 8. taining weld beads with less width, In order to complete the analysis of Analysis of Results higher velocity values should be used. the porosity formation and other impor- This increases keyhole stability and also tant characteristics, such as the penetra- Visual inspection of both sets of exper- results in less porosity formation. tion obtained in all the experiments, it is iments revealed a satisfactory appearan c e In examining the radiographic results necessary to introduce the metallo- of all weld joints where argon was used as ( Table 6), a difference was found be- graphic analysis results — Table 7, Fig. 9. a shielding gas. There was even better su- tween ground and nonground hinge sur- Concerning porosity formation when perficial finishing with helium shielding, face finishing. The amount and size of using argon shielding and lower welding wh i ch produced more stable and nar- porosity was very significant for the non- speeds, two types of porosity were en- ro wer welds with a convex upper bead. ground or as originally cast hinge surface countered. First, some very large bubbles

Fig. 7 — Nominal heat input vs. welding speed for all selected sam- ples. The best results were achieved for higher welding velocities.

Fig. 8 — Some representative X-ray results of the selected sam- ples. Porosity and lack of total penetration were investigated.

Table 4 — Weld Parameters and Overall Conditions of the Most Representative Samples of Both Sets of Experiments

Sample Hinge Hinge Hinge Power Weld Shielding Flow Total Heat Geometry Surface Joined (W) Speed Gas Rate Thickness Input Finishing To: (mm/min) (l/min) (mm) (J/mm) Ar1 original nonground plain sheet 5000 585 Ar 15 7 390 Ar2 original ground plain sheet 5000 585 Ar 15 7 390 He1 original ground plain sheet 5720 720 He 20 7 362 He2 original ground plain sheet 5740 560 He 20 8.4 467 He3 original ground reinforcement 5680 760 He 20 7 341 He4 machined ground reinforcement 5620 680 He 20 6.6 377 He5 machined ground reinforcement 5570 800 He 20 6.6 317

Observation: All welds were performed usingTEM multimode; stand-off = 6 mm; focal position = 0 mm.

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Porosity was located Table 5 — Results of the Visual Aspect Analysis of the Selected Samples either at the centerline or randomly distrib- Sample Spatter Bead Width uted through the fusion at Top zone, with a tendency Surface (mm) for concentration near the weld interface. Ar1 None 5.0 Centerline porosity Ar2 Few 5.4 He1 None 4.5 was caused by the en- He2 Few 5.3 t rapment of gas bub- He3 None 4.4 bles during solidifica- He4 None 3.3 tion and pushed by He5 None 3.1 a dvancing dendrites. The porosity located near the weld interface Table 6 — Results of the Nondestructive X- consisted of bubbles Ray Tests of Selected Samples t rapped at the begin- ning stage of solidifica- Sample Porosity Dimension Pattern Quantification tion (due to the high cooling rate). This oc- curs in the most stable Ar1 Many Medium Center location where a gas aligned can exist inside of a liq- Ar2 Some Large Random He1 Many Small Center uid phase, at the aligned solid/liquid interface, He2 Some Little Random where the surface ten- He3 No porosity — — sion of the pore surface He4 Few Little Random was at a minimum. He5 No porosity — — Concerning distrib- ution of porosity through the thickness, were located randomly along the thick- porosity was located Fig. 9 — Macrographs of cross sections of selected samples. Pene- ness direction of the weld. Second, from the bottom to the tration level, porosity location along the thickness, and HAZ exten- smaller centerline porosity occurred in top zone, depending sion are characterized. cases where full penetration was not ac- on the location of pre- complished. cipitation and on the The authors believe that in the first w i d t h - t o - p e n e t ration ratio of the weld sent in Table 7. Since determining the na- case, it was mostly hy d r o g e n - i n d u c e d bead. This can be observed in Fig. 9, ture of the HAZ is not included in the porosity and porosity formed by the un- where sample Ar2 and He2 have a width- scope of this work, only the width values stable eva p o ration of the metal over the t o - p e n e t ration ratio, respective l y, high will be discussed. front wall of the keyhole (Refs. 8, 13, and low, resulting in a different porosity Comparing samples Ar1 and Ar2, 14). In the second case, it was also pre- location. Thus, the main controlling pa- whi c h were welded with the same heat sent under the protection of a helium en- rameter was weld ve l o c i t y, because input, the following conclusions about the vironment (as can be seen in the He1 under low values of this parameter, the influence of two different interface condi- p h o t o m a c r o g raph), possibly due to key- weld pool was significantly wide, indi- tions in the over all cha r acteristics of the hole instability caused by the fact that cating a conduction mode as opposed to welds, e. g . , porosity formation, penetra- full weld penetration was not ach i e ve d a narrow one resulting from a stable key- tion level, and HAZ width can be made. (Refs. 13, 14). More genera l l y, it is pos- hole mode. The most significant differences be- sible to conclude that in all the experi- Full penetration levels were accom- tween these two samples were porosity ments performed, small centerline plished only with helium. With argon, in- formation, whi c h for Ar2 was less than for porosity located near the toe of the weld complete penetration was encountered, Ar1, and penetration level wh i ch wa s bead corresponded to cases of incom- despite the use of lower welding speeds. greater for Ar2 than for Ar1. These results plete penetra t i o n . This was confirmed by the macrographs were probably due first to the surface With helium shielding and slightly shown in Fig. 9. The explanation for this cleaning effect of the grinding process and higher welding speeds, macro- and phenomenon is the previously men- the consequent removal of hydroxides fre- aligned porosity were almost eliminated, tioned plasma plume formation with quently responsible for porosity formation but smaller pores could be detected by mi- argon shielding that resulted in signifi- in laser welding. Secondly, the most effi- croscopic examination, both on the weld cant energy absorption. As helium is less cient contact between the overlap parts re- center and near the weld interface. This re- likely to form this plasma, the energy ab- sulted in lower thermal resistance and in- duction in porosity formation and size was sorbed by the parts is higher, resulting in ferior losses in the power of the beam due to the stabilizing effect on the keyhole greater penetration. when it reached the root opening. caused by increased welding speeds. The One of the main ch a racteristics of The HAZ obtained for Ar2 shows a higher the welding speed, the more sta- overall weld quality is the width and na- width with 0.2 mm (0.008 in.) more than ble the weld pool; therefore, less gas (air, ture of the crystalline structure formed in the HAZ width for Ar1, which should not shielding gases, and plasma) was intro- the heat-affected zone (HAZ). The mea- be relevant in terms of metallurgical duced and the trapped gas, including surement of the HAZ width comes as a ch a racteristics and resulting residual metal vap o r , could escape more easily. result of the metallographic analysis, pre- stress field.

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Fig. 10 — Front and back view of the joint after tear-down test.

Fig. 11 — General and detailed view of the sagging test apparatus with force sensor and digital caliper to measure flexion.

Fig. 12 — Outside view shows the pneumatic cylinder that activates the handle, opening the door latch for the crazy chicken fatigue test. The system of door push and pull is located inside, closing with a 25 g acceleration force. The complete cycle takes about eight sec- Fig. 13 — Upper hinge deformation, top left door deformation, and onds to accomplish. top right door deformation, respectively.

The comparison between HAZ widths due to the decreasing power density of form these mechanical tests. applies only to samples welded under the the beam when it reached the surface. From the two samples selected in the same conditions of hinge geometry, sur- Thus, reliable and repeatable results previous section, He3 and He5, a deci- face finishing, shielding gas, and flow were obtained for a focal point location sion was made to test only original rate. In addition to the previous example, with a depth up to 0.5 mm (0.0197 in.) hinges. This explains why samples with it is possible to directly compare only the below the surface. the same characteristics as He5 were not samples He1 and He3, which have been It is relevant at this stage to summarize tested. welded under heat inputs of 362 and 341 the best ove rall conditions ach i e ved at After the hinges were welded to the J/mm (9194.8 and 8661.4 J/in.) respec- the end of all the trials performed. Sam- door reinforcement pillar, the two se- t ive l y. According to expected behav i o r, ples chosen were the He3 and He5, as lected doors were completely assem- the higher heat input value corresponded seen in Fig. 7. These samples had higher bled. Because it is the most used of a car’s to the greater width HAZ, as observed in welding velocity and lowest heat input four doors, the driver’s door was chosen Table 7. for the original and machined hinge for testing. Maximum penetration occurred whe n g e o m e t r y. These ch a racteristics corre- the beam was focused slightly below the sponded to total penetration, no porosity Tear-Down Test top surface of the lap joint. To find the formation, and more stable and narrower limit interval, the authors tried to lowe r welds with a convex upper bead. This test is usually done to va l i d a t e the point as much as possible to compen- spot and GMA welds. It consists of intro- sate for the power deficit in order to Mechanical Tests ducing a pneumatically activated chi s e l ach i e v e a full penetration weld. The limit into the lap joint to tear the parts apart. was found when the focal point was so After the welding trials established the The test is designed to evaluate if the as- deep into the part that no keyhole mode optimum welding conditions, mechani- sembly will fail at some constant applied was formed and a transition to conduc- cal tests were carried out to assess the fo r ce rather than to find the force at whi c h tion mode welding occurred. Results s t r u c t u ral integrity of the joint. First, a the assembly fails. The magnitude of this sh o wed that when the focal point position tear-down test, was done to evaluate the constant force is based on experience. was higher than 0.5 mm below the hinge shear strength of the joint. Next, the flex- The pneumatic chisel, with a 7.5 bar surface, not only did the keyhole become ion test (“sagging”) was done to assess the (0.75 MPa) pressure, was then inserted on unstable, but also its start up was more flexibility resistance. Finally, the fatigue the backside of a single-weld hinge to difficult. This behavior may be due to the test (“crazy chicken”) was done to simu- sever the laser welded joint, disconnect- de g r adation of the power density at the late the intensive use of a normal pro- ing the parts. top surface of the parts to be welded. duction car door. If inserting the chisel on the backside For the focal point positioned above The crazy ch i cken and sagging tests of the hinge did not break the parts, just the top surface of the hinge, no stable required complete doors. Two laser- deformed the steel sheet, the chisel was keyhole mode was ach i e ved, probably welded hinges (He3) were chosen to per- then introduced on the frontside of the

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hinge, acting directly on the weld. The load or fatigue. The test stopped at such were performed, and the Po r t u g u e s e final result was the steel sheet tore com- an early stage strictly because of the door Welding Institute ISQ for their support. pletely while leaving the weld intact, as steel sheet deformation. It is expected if seen in Fig. 10. In this case, the backside the hinges had been welded with two References of the hinge was completely raised due to parallel welds, the test results would have the plastic deformation of the less resis- been totally positive. As previously ex- 1. Lancaster, J. F. 1986. The Physics of tant steel sheet. plained, this was not possible due to spa- Welding. pp. 185–191, The International In- tial-related constraints. stitute of Welding. Flexion Test 2. Norrish, J. 1992. A dvanced We l d i n g Conclusions Processes. Institute of Physics Publishing Ltd., This test assesses the door flexion re- pp. 185–199. sistance by the application of a series of The results allow the following con- 3. Nippes, E. F. 1983. Welding, bra z i n g vertical loads to the lock end of the door, clusions: and soldering. Metals Handbook, 9th edition, measuring the elastic and plastic defor- Surface finish of the parts makes a great Vol. 6, ASM Handbook Committee, pp. mation at the hinges. The test specifica- difference in the amount of porosity for- 647–671. tion requires a maximum plastic defor- mation with laser beam welding. With im- 4. Welding processes 1991. We l d i n g mation of 1.5 mm (0.059 in.) for a 1000 pr o ved surface preparation, this phenom- H a n d b o o k. Vol. 2, 8th edition, American N (224.8 lbf) load. enon can be significantly reduced. Welding Society, Miami, Fla., pp. 713–738. According to test requirements, the Helium was found to be the most suit- 5. Santos, J. O., Quintino, L. 1998. Proces- door has to be opened 5 deg and sus- able gas for this application since it in- sos de Soldadura ( Welding Processes), Po r- pended by the two hinges when applying creased overall heat efficiency. tuguese Welding Institute (ISQ), pp. 579–632. the load. Then, load is applied to the The machined weld preparation de- 6. Holt, T. 1995. New applications in high lock, pulling the door vertically down, as livered a distinct improvement, allowing power laser welding. Welding & Metal Fabri- represented in Fig. 11. a weld procedure with higher velocities cation, 63(6): 230–234. Fuel & Metallurgical Due to the existence of just one weld, and lower heat input while maintaining Journals Ltd. a stress concentration, was created total penetration of both hinge and door 7. Kunzig, L. 1994. Laser welding of auto- around the weld when it was loaded, reinforcement structure. m o t ive and aero components. Welding & which caused bending of the steel sheet As expected, higher welding speeds , 62(1): 14–16, Fuel & Met- (structurally weaker than the hinge) and contributed to keyhole stabilization and, allurgical Journals Ltd. consequently augmented the total defor- c o n s e q u e n t l y, less porosity and a thinner 8. Gonçalves, V. 1997. Soldadura laser de mation. If this had been a normal pro- weld bead. ligações dissimilares (laser welding of dissim- duction door test, the door would have Typical hydrogen-induced porosity ilar joints). Ph. D dissertation, Technical Uni- failed, as the maximum plastic deforma- was reduced through careful grinding of versity of Lisbon, pp. 47–78. tion of 1.5 mm was achieved for a load the surface with reduced the hydroxide 9. Metzbow e r, E. 1993. Keyhole forma- of about 700 N, i.e., inferior to the 1000 layer, a hydrogen source. tion. Metall. Transactions B, 24: 875–880. N, for which the total plastic deformation As for focal point location, a depth up 10. Arata, Y. 1986. Plasma, Electron and was about 18 mm. The hinge deforma- to 0.5 mm (0.0197 in.) below the surface Beam Technology — Development and Use in tion occurred only at the upper hinge, provided reliable and repeatable results. Material Processing. pp. 378-396. ASM Inter- since this was the one subjected to ten- Although only a single laser beam national, Materials Park, Ohio. sion loading, while the lower one is in weld was made on the hinges mechani- 11. Dowden, J., Kapadia, P., Postacioglu, compression. cally tested, the weld bead did not fail, N. 1989. An analysis of the laser-plasma in- The results show that the ultimate nor was there any sign of weakness. teraction in laser keyhole welding. Journal of strength was not attained till 1700 N The performance of the doors me- Physics D., 22(6): 741–749, Applied Physics. (382.2 lbf). Since this behavior occurred chanically tested was limited by plastic 12. AGA AB. 1997. Facts about Laser with just one weld, it may be expected deformation in the welded parts and was Welding Gases, ed. Beskriv Te cknik AB, that if two parallel welds were used on not limited by the mechanical strength of Lidingo. the hinge, the static strength and defor- the joint. Failure occurred by deforma- 13. Matsunawa, A., Kim, J., Seto, N., Mizu- mation would not be a problem. tion of the base metal due to an uneven tani, M., Katayama, S., 1998. Dynamics of stress distribution in the hinge assembly, keyhole and molten pool in laser welding. Fatigue Test resulting from the fact that one of the Journal of Laser Application, 10(6): 247–254, hinges edge was welded, while the other Laser Institute of America. The fatigue test invol v ed opening and remained free to move. 14. Matsumoto, T., Fukuda, N., Kondo, Y., closing a car door up to 100,000 cyc l e s . The procedure developed accommo- Ohmoni., A., Inoue, K., Arata, Y. 1999. Study The test is controlled by pneumatic cyl i n - dated all the fabrication needs, e. g . su r f a c e on prevention of welding defects in high ders, whi c h opens the door from the out- finishing, access restrictions and durat i o n power CO2 laser materials processing. Journal side and pushes from the inside, opening of the operation, using a commerc i a l l y of Laser Application, 11(6): 258-262, Laser In- it completely — Fig. 12. Then the latter, available 6-kW CO2 laser system. stitute of America. using a cable, pulls the door and closes it. After working for approximately 20 h, Acknowledgments the test stopped after 8,666 cycles due to the deformation of the steel sheet. Th e This work was supported by AutoEu- door warped, wh i ch interfered with its ropa-Automóveis, Lda., the Volkswagen closing, as seen in Fig. 13. The sensor car plant in Palmela-Portugal. then actuated and cut the power to the The authors would like to thank Insti- PLC controlling hardware. tuto de Desenvolvimento e Inovação Tec - It is emphasized that joint did not nológica (IDIT) Fei ra - P ortugal, the tech- break in the welded zone, either by over- nology institute where all the laser welds

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