The reconditioning by welding process applied to the crankshafts in the automotive industry can be carried out by using various reconditioning technologies that are based on different welding parameters and processes. This paper presents a comparison between Shielded Metal Arc Welding (SMAW) and Welding in Gas (WIG) reconditioning processes from the perspective of the metallographic analysis conducted on the zones resulted after the depositing process. The heat cycle resulted during the two welding processes influences in a different manner the welding behavior of the base material due to the occurrence of micro-structural changes in the main zones of the deposit. The occurred structural changes may influence to a significant degree the operating behavior of the structures repaired by welding

C. Rontescu

D. T. Cicic

G. Bălan

O. Chivu

D.T. Cicic

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The effects of reconditioning by welding of crankshafts in automotive industry

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55METALURGIJA 55 (2016) 1, 55-58O. CHIVU, C. RONTESCU, D.T. CICIC, G. BĂLANTHE EFFEC TS OF RECONDITIONING BY WELDING OF CRANKSHAFTS IN AUTOMOTIVE INDUSTRYReceived – Primljeno: 2015-02-11Accepted – Prihvaćeno: 2015-07-20Preliminary Note – Prethodno priopćenjeISSN 0543-5846METABK 55(1) 55-58 (2016)UDC – UDK 621.791.052.167.2/3:629.119:620.18=111O. Chivu, C. Rontescu, D.T. Cicic, Polytechnic University of Bucharest, Romania, G. Bălan, Romanian-German University of Sibiu, RomaniaThe reconditioning by welding process applied to the crankshafts in the automotive industry can be carried out by using various reconditioning technologies that are based on different welding parameters and processes. This pa-per presents a comparison between Shielded Metal Arc Welding (SMAW) and Welding in Gas (WIG) reconditioning processes from the perspective of the metallographic analysis conducted on the zones resulted after the depositing process. The heat cycle resulted during the two welding processes influences in a different manner the welding behavior of the base material due to the occurrence of micro-structural changes in the main zones of the deposit. The occurred structural changes may influence to a significant degree the operating behavior of the structures re-paired by welding.Key words: welding, SMAW, WIG, reconditioning, metallographic structureINTRODUCTIONDuring the working processes of the active elements used in the automotive industry the wear process may occur due to the degradation of the surface layers of the elements of the friction couples, which is characterized either by material loss, or by the plastic deformation of the contact surfaces.If equipment parts are damaged during operation, they can be replaced or reconditioned so that they can be brought to their initial dimensional value or so that they can regain their initial mechanical properties. If the replacement of the parts is expensive, they are recondi-tioned [1].During the reconditioning by welding process it is necessary to take into account the fact that the heat cy-cle the base material and the deposited material are sub-ject to (heating – melting – cooling – solidification) determines changes in the chemical composition caused by the dilution phenomenon as well as changes in the functional and technological properties, as they are the result of the structural modification in the three distinct zones (base material, heat affected zone and deposited material). Following the reconditioning process the re-conditioned element needs to have the proper dimen-sion and the required properties according to the respec-tive duty cycle [2, 3].The use of the direct current welding process with reverse or direct polarity influences the geometric char-acteristics of the beads as well as process dilution. In certain situations, such as weld deposits, the penetration should be as shallow as possible and the heat affected zone of the bead should be reduced [4].In the industrial practice concerning the crankshafts used in the automotive industry it was observed that the most frequent defects occur in the main journals and the crankpin journals (Figure 1). If the defects (e.g. crack) are not identified in time and the respective zones are not repaired, this could lead to pretty significant effects such as breakdown of the car and even worse to the loss of human lives. Considering the rather high price of a new crankshaft and after the strength and economic cal-culations are made, in most cases the people in charge make the decision to repair the non-conformity zone. Welding is the technological reconditioning process that ensures short repair time but also the convenient quality of the deposited layer [5]. EXPERIMENTAL PROCEDUREDue to the improper working conditions and to the occurrence of the wear phenomenon, the crankshaft in Figure 1 went through dimensional changes at the level of the crankpin journals. The reconditioning process consists of the depositing of the affected zones so that - following the machining process - the newly obtained zones respect the dimensions and tolerances of the shop drawing of the product, as well as the functional proper-ties of the base material.The main purpose of the experimental procedure is to analyze the reconditioning by welding possibilities of the crankshafts used in the automotive industry, by us-ing the SMAW and WIG process, based on the results obtained following the metallographic analysis in the interest zones of the deposit.56O. CHIVU et al.: THE EFFEC TS OF RECONDITIONING BY WELDING OF  CRANKSHAFTS IN AUTOMOTIVE INDUSTRY METALURGIJA 55 (2016) 1, 55-58Following the interpretation of the results obtained after the chemical composition analysis of the base ma-terial conducted with the Foundry Master equipment, it was concluded that the base material is a cast iron, type EN-GJS-600-3 according to DIN EN 1564:2012, whose chemical composition is presented in Table 1, while the mechanical characteristics are indicated in Table 2.Considering the nature of the base material and the working conditions of the crankshaft, we chose to use the following filler materials: E10-UM-60-CZ electrode with the diameter of 3,25 / mm and the metal rod type ∅ 3,2 / mm WSG-3GZ-5-T. Table 1  Chemical composition of the base material according to EN-GJS-600-3 / wt. %Base material C Si Mn P SEN-GJS-600-3 2,5 - 3,6 1,8- 2,8 0,3- 0,7 ≤ 0,08 ≤ 0,02Table 2  Material properties measured on test pieces according to DIN EN 1563:2012Material desig-nationTensile strength Rm / N/mm2Proof stress Rp0,2 / N/mm2ElongationA  / %Micro-structureEN-GJS-600-3 600 370 3 Pearlite/ferriteFor the experimental part, for both processes, we used an inverter based welding power source (Caddy TIG 2200i - ESAB). The polarities used in this experi-mental procedure were direct current negative polarity (DC-) for WIG and direct current positive polarity (DC+) for SMAW. The values of the main welding pa-rameters were: welding current intensity Is1 = 100 / A (for the marginal layers of the crankpin journals) and Is2 = 140 / A (for the facing of the crankpin journal sur-face), arc voltage Ua = 12 - 14 / V for WIG and Ua = 20 - 24 / V for SMAW.Before starting the welding process, the zones to be hard faced were machined in order to remove the worn surface layer. For the reconditioning of the crankpin journals it is necessary to take into account the applied welding order so that the value of the stresses occurred during the welding process is minimal. For these pur-poses it is recommended to carry out the depositing pro-cess applied to the journals in the following order: 1 - 3 - 4 - 2 (Figure 1). Furthermore, in order to avoid the occurrence of de-formations during the welding process and to limit the waving width of the arc during the depositing process, we resorted to the initial depositing of the marginal lay-ers on the crankpin journal and on the marginal zones of the crankpin oil holes as shown in Figure 2. The depos-iting process applied to each crankpin journal was made by dividing it into sectors and alternately depositing material on the antipodal zones [6, 7].After the depositing process, in order to perform the metallographic analysis the samples were cut using a special cutting system at low cutting speeds with con-tinuous cooling so as to prevent the analyzed zone from being affected by the heat. After the cutting process, the samples were cleaned from impurities and subject to a polishing process using metallographic paper with dif-ferent granulations; finally, the samples were subject to polishing with abrasive diamond paste [8, 9].RESULTS AND DISCUSSIONSIn order to analyze as accurately as possible the influ-ence of the reconditioning processes on the structure we made two samples for each discussed welding method. After it obtained the samples, they were subject to non-destructive testing by using the visual method and the penetrating liquid method. No non-conformities re-sulted following the test. Figure 1  Crankshaft parts: a, b, c, d, e – main journals; 1, 2, 3, 4 – crankpin journals. a) b) c) d)Figure 2  Depositing the initial beads on the marginal areas of the crankpin journal (a, b) and on the rest of the crankpin journal area (c – using SMAW, d – using WIG)57O. CHIVU et al.: THE EFFEC TS OF RECONDITIONING BY WELDING OF  CRANKSHAFTS IN AUTOMOTIVE INDUSTRYMETALURGIJA 55 (2016) 1, 55-58lyzed zones is a different one, starting from a ferrite-pearlite structure corresponding to the base material (Figure 4, a) and getting to a structure made of troostite and residual cementite corresponding to the deposited material (Figure 4, b). Furthermore, when we analyze Figure 4, c respectively Figure 4, d we observe that in the material layers corresponding to the fusion line (FL), but also to the heat affected zone (HAZ) there is a series of precipitated metal carbides that are close to the fusion line, which affect the mechanical properties of the material in these layers, specially the hardness. From the analysis of the structures presented in Fig-ure 5 we can observe that the metallographic structure of the 4 analyzed zones, just as in the WIG case, is a different structure starting from the ferrite-pearlite structure of the base material and ending with a struc-ture made of austenite and residual cementite, mar-tensite as well as a great amount of Cr metal carbides corresponding to the deposited material. As far as the reconditioning by SMAW method is concerned, we can observe that the structure of the deposited material is mainly martensitic.Furthermore, Figure 5 and Figure 6 reveals that the adherence between the base and the filler material is good, as well as that there are small nonconformities similar to porosities in the deposited material.CONCLUSIONFollowing the analysis of the obtained results we can draw the following conclusions: – the SMAW and WIG methods can be applied when reconditioning the crankshafts in the automotive in-dustry;  – the depositing method of the layers and the used procedure have a significant influence on the quality of the deposited layers; – the analysis of the metallographic structure shows that in the deposited material layer we obtain a ho-mogenous metallographic structure that only has small defects like porosities and corresponds to the increased resistance to wear of the crankshafts; – when applying the depositing process by SMAW, in the deposited layer and in HAZ we obtain martensi-tic microstructures, which can lead to a significant hardening process in these zones as well as to the occurrence of certain non-conformities like cracks during operation; – the reconditioning by welding process offers the possibility of a better control of the heat input into the reconditioned parts such as obtaining metallo-graphic microstructures with lower risk of defects occurring during the operation.The work has been funded by the Sectoral Opera-tional Programme Human Resources Development 2007-2013 of the Ministry of European Funds through the Financial Agreement POSDRU/159/1.5/S/134398.After properly processing the obtained samples we analyzed the micrographic structures obtained in the in-terest zones of the reconditioning by welding: base ma-terial (BM), the heat affected zone (HAZ), the fusion line (FL), mixed zone (MZ) as well as in the zone of deposited material (ZDM), zones presented in Figure 3.The obtained metallographic structures are present-ed in Figure 4 for the WIG samples and in Figure 5 for the SMAW sample. The analysis of the structures presented in Figure 4 reveals that the metallographic structure of the 4 ana-Figure 3  Structure of the characteristic zones of the depositing process; BM – base material; HAZ – heat affected zone; FL – fusion line; MZ – mixed zone; ZDM – zone of deposited materialc. HAZ x 200 d. FL  x 200Figure 4 Microscopic images obtained when using WIGc. HAZ  x 200 d. FL  x 200  Figure 5 Microscopic images obtained when using SMAWa. All the zones x 50 b. ZDM x 200a. All zones x 100 b. ZDM x 20058O. CHIVU et al.: THE EFFEC TS OF RECONDITIONING BY WELDING OF  CRANKSHAFTS IN AUTOMOTIVE INDUSTRY METALURGIJA 55 (2016) 1, 55-58REFERENCES[1] G. M. Dumitru, C. Radu, B. Dumitru, Recondiţionarea şi repararea produselor, Editura Printech, Bucharest, 2010, 111-115.[2]  D. Dobrotă, Structural modifications which appear in the area of welds of welded structures made of st 52.3 steel, Metalurgija 53 (2012) 2, 179-182.[3]  D. Dobrotă, Gh. Amza, Ultrasound influence on materials structure in parts reconditioned by welding with ultrasonic field, Metalurgija 52 (2013) 1, 87-89.[4]  C. Rontescu, D. T. Cicic, G. Iacobescu, C. Gh. Amza, The influence of the welding current polarity on the geometric configuration of the bead, Advanced Materials Research 1088 (2015), 797-801.[5]  D. T. Cicic, Gh. Solomon, G. Iacobescu, C. Rontescu - Me-thod of establishing the optimum technique for reconditio-ning by welding, taking into account the consumption of filler metals and electrical power, U.P.B. Sci. Bull. Series D, 73 (2011) 1, 85-98.[6]   ***Esab Welding Handbook, eighth edition – Consuma-bles for manual and automatic welding[7]   Information on http://www.esabna.com[8]   Information on http://www.twi-global.com[9]  Information on http://www.brazing.com/Note:  The responsible translator for English language is Rontescu Aurora Madalina, Bucharest, Romania, official Translator certi-fied by the Ministry of Justice

The effects of reconditioning by welding of crankshafts in automotive industry

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