4. Production of Axial-Bearing Washers with Tailored Properties by Plasma Transferred Arc Deposition Welding
Deposition welding is a particularly efficient process for applying high-performance metallic cladding to substrate materials to improve surface properties. In this way, hybrid steel components can be produced flexibly in dependence on the welding process used. There are various processes for deposition welding which have different advantages and are currently used in the industry. These include metal inert gas welding, submerged arc deposition welding, plasma powder deposition welding (PTA), laser deposition welding [
13] and electroslag welding [
14]. For maximum flexibility, a process that uses powder as a filler material is best suited. The majority of materials, which achieve maximum hardness when welded, are available as powders, since the production of solid welding rods from these materials is proven to be difficult. This is particularly true for low-alloy quenched and tempered steels with high carbon equivalent (CEV > 0.5). Welding processes with these materials are generally challenging, since these materials are classified as non-weldable or difficult to weld according to the current material data sheets [
15]. Nevertheless, it is possible to process these materials with PTA welding, which is why the process is well suited for this aim.
In the PTA welding process, an arc burns between a non-melting tungsten electrode and the workpiece. The powdery filler material is blown into the arc and reaches the workpiece completely molten. Argon is used as protective gas. The process can be automated very well by robots and enables application rates of up to 10 kg/h [
15].
In general, there is a lot of literature on plasma powder deposition welding for welding hard materials onto steel substrates in which the wear properties of new alloys for deposition cladding are primarily investigated. The influences of process parameters such as current, powder feed rate and welding speed on the dilution are also examined. A focus on the component temperature of the substrate material is not common as an influencing factor.
Motallebzadeh et al. [
16] welded a hypo-eutectic hard material alloy to a steel substrate and conducted investigations on the microstructure and tribological performance. Ferozhkhan et al. [
17] welded a stellite 6 alloy onto a stainless-steel substrate and carried out investigations on wear resistance. Sawant et al. [
18] also welded a stellite 6 alloy to an AISI 4130 steel using micro plasma powder deposition welding. In this study the influence of the energy per unit length on the mixing and microstructure was investigated. Deng et al. [
19] welded an iron-molybdenum alloy onto an AISI 1045 steel by PTA welding and investigated the microstructure.
The base material for the bearing washers is unalloyed steel AISI 1022M. The sample geometry, which is cladded, has the shape of discs with a diameter of 130 mm and a thickness of 11 mm. The steel AISI 1022M is usually used as a construction material in general mechanical engineering and in vehicle construction. The chemical composition is shown in
Table 1.
The low-alloy quenched and tempered steel AISI 5140 is used as the cladding material for PTA welding. The steel is considered difficult to weld and achieves tensile strengths of 800–1000 MPa. AISI 5140 is primarily used for drive parts such as crankshafts, front axles and steering parts. The chemical composition can be found in
Table 2.
The powder is filtered with a sieving unit. Only powder consisting of metal grains with a diameter of minimum 50 µm to maximum 150 µm is used for welding. This corresponds to the current industrial standard for additional materials in powder form that are used for welding. The welding process is carried out on a 6-axis REIS RV-16 industrial robot (Reis Robotics GmbH, Obernburg am Main, Germany) with a tilt and turn table. The PTA torch that is used is the Kennametal Stellite HPM 302 (Deloro Wear Solutions, Koblenz, Germany), the current source is the Stellite Starweld PTA 302 (Deloro Wear Solutions, Koblenz, Germany). The welding equipment can be seen in
Figure 2a.
The discs are cut with a water-cooled band saw from a long round steel. After sawing, the surfaces of the discs are cleaned with acetone. There is no further surface treatment before welding. To coat the discs, AISI 5140 is welded in a spiral until the surface of the bearing track is fully coated. This process can be seen in
Figure 2b. The entire welding process takes a total of 10 min and 35 s, which leads to a strong heating of the disc to up to 650 °C. With constant welding parameters, this strong heating leads to an ever-increasing material dilution between the cladding material and the substrate. Therefore, the current is slowly reduced from 180 A at the beginning of the welding process to only 130 A at the end of the process in order to keep the dilution as low and constant as possible. The exact course of the current intensity in the PTA welding process is shown in
Figure 3.
In order to apply the seam as homogeneously as possible and to avoid pores, the welding torch oscillates over a short distance of 4 mm with a frequency of 2 Hz at an angle of 90° to the welding direction. This slightly increases the dynamics of the weld pool and allows gases contained in the melt to escape more easily, which reduces pore formation. An overview of the general welding parameters can be found in
Table 3.
Author Contributions
H.J.M., T.H. and M.M. developed the welding process to produce large-area and crack-free deposition welds on steel discs. They also supervised the preparation of the metallographic sections and carried out the microstructure analysis; G.P., F.P. and T.C. developed the components and supervised the production. They carried out the ultrasonic tests as well as tribological investigation including the endurance tests of the finished components with final evaluation; B.-A.B., A.C. and T.M. carried out the necessary forming tests and microscopic analyses before/after the forming process as well as before/after the endurance tests including the damage analysis. In addition, they carried out the microtribological examinations. M.M., T.C. and T.M. wrote the paper.
Funding
This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) grant number 252662854. The APC was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation).
Acknowledgments
The results presented in this paper were obtained within the Collaborative Research Centre 1153 “Process chain to produce hybrid high performance components by Tailored Forming” in the subprojects A04, C01 and C03, funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—252662854. The authors thank the German Research Foundation (DFG) for their financial support of this project. The subsequent processing steps to complete the hybrid component, such as heat treatment and machining, were carried out by subprojects A02 and B04.
Conflicts of Interest
The authors declare no conflict of interest.
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Figure 1.
Process chain for manufacturing a hybrid axial bearing washer by tailored forming. (a) Plasma-transferred arc deposition welding, (b) hot forming, (c) mechanical processing and heat treatment, (d) Bearing assembly for use in a test bench.
Figure 2.
Experimental setup of PTA welding (a), PTA-process (b).
Figure 3.
Current intensity curve during cladding process.
Figure 4.
Hydraulic forming press (a), forming tool system for forging of the bearing washers (b).
Figure 5.
Height profile of the hard-faced area before (a) and after forging (b).
Figure 6.
Micrograph of the joining zone after deposition welding (a), after forging (b) and after hardening (c).
Figure 7.
Hardness gradients of the hybrid bearing washers.
Figure 8.
Results of the scratch tests: (a) industrial bearing washer made of conventional rolling bearing steel AISI 52100; (b) hybrid bearing washer without additional deformation; (c) hybrid bearing washer with additional deformation.
Figure 9.
Scanning ultrasonic microscopy of a tailored forming bearing washer: (a) after joining and before forging, showing subsurface pores aside the welding lines (indicated as white spots), (b) after forging, showing a reduction of subsurface pores (indicated as white spots); zoom images edited by inverting the color range.
Figure 10.
Assembled bearing consisting of tailored forming bearing washers, cage, and rollers (a); FE8 rig for investigation of fatigue of two tailored forming bearings simultaneously (four washers per test, (b).
Figure 11.
Bearing washers which were not forged after the cladding process after rolling contact load test (running time of 237 h).
Figure 12.
Tailored forming bearing washer after rolling contact load test (running time of 332 h).
Table 1.
Chemical composition in wt.% of AISI 1022M.
C | Si | Mn | P | S | Cr |
---|
0.17–0.24 | <0.40 | 0.40–0.70 | <0.045 | <0.045 | <0.40 |
Table 2.
Chemical composition in wt.% of AISI 5140.
C | Si | Mn | P | S | Cr |
---|
0.38–0.42 | <0.40 | 0.60–0.90 | <0.025 | <0.035 | <0.90–1.20 |
Table 3.
Welding parameters.
Parameter | Value |
---|
Shielding gas flow (Argon) | 10 min−1 |
Plasma gas flow (Argon) | 1 min−1 |
Transport gas flow (Argon) | 4 min−1 |
Welding velocity | 2 mm/s |
Working Distance | 12 mm |
Current | Dynamic, 180–130 A |
Voltage | 25–27 V (depends on current) |
Powder material | AISI 5140 atomized under argon atmosphere |
Grid size of powder particles | 0.05–0.15 mm (current industry standard) |
Powder flow rate | 15 g/min |
Table 4.
Parameters for ultrasonic microscopy.
Frequency | Focal Length in Water | Axial Resolution | Detection Limit |
---|
30 MHz | 12.7 mm | 13.68 µm | 6.59 µm |
110 MHz | 8 mm | 19.78 µm | 4.56 µm |
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