| 1. |
- Hosseini, Seyed, et al.
(author)
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Comparison of machining performance of stainless steel 316L produced by selective laser melting and electron beam melting
- 2022
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In: Procedia CIRP. - : Elsevier B.V.. - 2212-8271. ; , s. 72-77
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Conference paper (peer-reviewed)abstract
- Powder bed fusion processes based additively manufactured SS 316L components fall short of surface integrity requirements needed for optimal functional performance. Hence, machining is required to achieve dimensional accuracy and to enhance surface integrity characteristics. This research is focused on comparing the material removal performance of 316L produced by PBF-LB (laser) and PBF-EB (electron beam) in terms of tool wear and surface integrity. The results showed comparable surface topography and residual stress profiles. While the hardness profiles revealed work hardening at the surface where PBF-LB specimens being more susceptible to work hardening. The investigation also revealed differences in the progress of the tool wear when machining specimens produced with either PBF-LB or PBF-EB. .
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| 2. |
- Laakso, Sampsa, 1983, et al.
(author)
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Evaluation of subcooled MQL in cBN hard turning of powder-based Cr-Mo-V tool steel using simulations and experiments
- 2022
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In: International Journal of Advanced Manufacturing Technology. - : Springer Science and Business Media LLC. - 0268-3768 .- 1433-3015. ; 118:1-2, s. 511-531
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Journal article (peer-reviewed)abstract
- Metal cutting fluids for improved cooling and lubrication are an environmental risk and a health risk for workers. Minimizing water consumption in industry is also a goal for a more sustainable production. Therefore, metal cutting emulsions that contain hazardous additives and consume considerable amounts of water are being replaced with more sustainable metal cutting fluids and delivery systems, like vegetable oils that are delivered in small aerosol droplets, i.e., via minimum quantity lubrication (MQL). Since the volume of the cutting fluid in MQL is small, the cooling capacity of MQL is not optimal. In order to improve the cooling capacity of the MQL, the spray can be subcooled using liquid nitrogen. This paper investigates subcooled MQL with machining simulations and experiments. The simulations provide complementary information to the experiments, which would be otherwise difficult to obtain, e.g., thermal behavior in the tool-chip contact and residual strains on the workpiece surface. The cBN hard turning simulations and experiments are done for powder-based Cr-Mo-V tool steel, Uddeholm Vanadis 8 using MQL subcooled to −10 °C and regular MQL at room temperature. The cutting forces and tool wear are measured from the experiments that are used as the calibration factor for the simulations. After calibration, the simulations are used to evaluate the thermal effects of the subcooled MQL, and the surface residual strains on the workpiece. The simulations are in good agreement with the experiments in terms of chip morphology and cutting forces. The cutting experiments and simulations show that there is only a small difference between the subcooled MQL and regular MQL regarding the wear behavior, cutting forces, or process temperatures. The simulations predict substantial residual plastic strain on the workpiece surface after machining. The surface deformations are shown to have significant effect on the simulated cutting forces after the initial tool pass, an outcome that has major implications for inverse material modeling.
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| 3. |
- Malakizadi, Amir, 1983, et al.
(author)
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Post-processing of additively manufactured metallic alloys – A review
- 2022
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In: International Journal of Machine Tools and Manufacture. - : Elsevier BV. - 0890-6955 .- 1879-2170. ; 179
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Research review (peer-reviewed)abstract
- Additive manufacturing (AM) is characterised by several unique advantages, such as (freedom of) design, capability of fusing dissimilar materials, near-net-shape, and achieving a more sustainable production. While the increased precision of metal AM in recent years reduced the needed amount of post-processing to meet dimensional tolerance, the requirements for functional surfaces necessitate a well-understood post-processing, ranging from heat treatment to machining and finishing. The inherently rough initial (as-built) surface topography next to complex material microstructure affects the capability of post-processing/finishing operations to smooth the surface texture and obtain a favourable surface integrity. In this respect, a more fundamental understanding of the effects of material properties on post-processing/finishing is needed. Therefore, this review paper aims to establish the relationship between the characteristics of different AM technologies, microstructural properties of materials in as-built and heat-treated conditions, and the physical properties influencing the response of additively manufactured materials during post-processing/finishing operations. In particular, emphasis is placed on the physics-based understanding of how the microstructural characteristics of 316L, Ti6Al4V and Alloy 718 produced using the two principal technologies, Powder Bed Fusion (PBF) and Direct Energy Deposition (DED), influence their mechanical properties like tensile strengths, hardness and ductility. These properties are among the key factors influencing the response of material during post-processing/finishing operations involving material removal by shear deformation. This review paper also discusses the role of post-processing/finishing on fatigue performance, tribological behaviour and corrosion resistance of investigated AM materials. The paper summarises the state-of the art of post-processing/finishing operations and future research trends are highlighted.
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| 4. |
- Mallipeddi, Dinesh, 1987, et al.
(author)
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Effect of running-in - load and speed - on surface characteristics of honed gears
- 2017
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In: World Tribology Conference 2017.
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Conference paper (other academic/artistic)abstract
- The initial cycles, as in a running-in process, can influence the performance of gear. Presented here are the surface characteristics of honed spur gears, which evolved due to the combined effect of running-in load (0.9 or 1.7GPa) and speed (0.5 or 8.3m/sec). The testing is performed using an FZG test rig. Running-in effected the surface layers to a depth of 5µm. High running-in load promoted plastic deformation of asperities, created microstructural changes associated with surface cracks and relaxed residual stresses. Surface phosphorus content from EP additives was also enhanced by higher running-in load. Interestingly, running-in speed promoted micropitting than load.
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| 5. |
- Mallipeddi, Dinesh, 1987, et al.
(author)
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Effect of Running-In (Load and Speed) on Surface Characteristics of Honed Gears
- 2019
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In: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 62:3, s. 412-418
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Journal article (peer-reviewed)abstract
- The initial running-in cycles alter the surface integrity characteristics and influence gear performance. This article shows how the surface characteristics of honed spur gears evolved due to the combined effect of running-in load (0.9 or 1.7 GPa) and speed (0.5 or 8.3 m/s) in Forschungsstelle fur Zahnräder und Getriebebau tests. Running-in affected the surface layers to a depth of 5 µm. High running-in load promoted plastic deformation of asperities, created microstructural changes associated with surface cracks, and relaxed residual stresses. It also enhanced the amount of phosphorous from extreme pressure (EP) additives at the surface. The surface contact fatigue failure—that is, micropitting—was promoted by running-in speed rather than load.
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| 6. |
- Mallipeddi, Dinesh, 1987, et al.
(author)
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Influence of running-in on surface characteristics of efficiency tested ground gears
- 2017
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In: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 115, s. 45-58
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Journal article (peer-reviewed)abstract
- The effect of running-in load (0.9 or 1.7 GPa) on surface characteristics of ground spur gears, and on their development during subsequent efficiency testing (FZG rig), is examined. The effect was confined to less than 10 ism depth. Micropitting was associated with surface asperities and their plastic deformation; higher running-in load gave more micropitting, also after identical efficiency tests. Running-in increased unequal compressive residual stresses in both profile and axial directions, while after efficiency testing they approached equal levels. Deformation induced martensite is considered to form during running-in only at high load, still the amount after efficiency testing increased with running-in load. Higher surface content of phosphorous from extreme pressure additive (EP) occurred only after efficiency test following running-in at high load.
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| 7. |
- Mallipeddi, Dinesh, 1987, et al.
(author)
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Investigation of the surface integrity of mechano-chemically finished powder metallurgy gears
- 2022
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In: Procedia CIRP. - : Elsevier BV. - 2212-8271. ; 115, s. 142-147
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Conference paper (peer-reviewed)abstract
- Automotive gears are facing stringent requirements regarding weight and functional surfaces, especially in view of the electric powertrain. To achieve these demands, powder metallurgy gears need to be finished using grinding, and in certain cases, mechano-chemical treatments. With regards to the latter, five different triboconditioning strategies based on vibratory tub finishing and/or centrifugal barrel finishing were considered and their effects on the surface integrity and friction behavior were investigated. Triboconditioning improved the surface roughness after grinding and resulted in higher compressive residual stresses. Additionally, microscopic observations of the surface topography were carried out. The lowest friction coefficients were observed for triboconditioning with a doped material (tribofilm) on the finished surface.
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| 8. |
- Mallipeddi, Dinesh, 1987, et al.
(author)
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Micropitting and microstructural evolution during gear testing -from initial cycles to failure
- 2021
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In: Tribology International. - : Elsevier BV. - 0301-679X. ; 156
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Journal article (peer-reviewed)abstract
- To elucidate the micropitting mechanism, ground gears were tested using FZG test rig and the evolution of surface characteristics were followed closely from the initial 200 cycles to failure. Micropitting phenomenon was divided into three stages; running-in, steady progression and degradation. Micropitting was mainly associated with plastic deformation of asperities, which induced localized deformation bands and plastically deformed regions that were associated with cracks. Build-up of residual stresses occurred during running-in and this was correlated to the transformation of retained austenite. No further evolution occurred during steady progression stage and then the stresses decreased during degradation stage. Phosphorus content in the gear surface increased during steady progression stage and remained similar during degradation stage but with increased layer thickness.
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| 9. |
- Mallipeddi, Dinesh, 1987, et al.
(author)
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Stress distribution over gear teeth after grinding, running-in and efficiency testing
- 2015
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In: VDI-Berichte. - 0083-5560. - 9783180922553 ; 2, s. 973-984
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Conference paper (other academic/artistic)abstract
- The distribution of surface residual stresses over gear teeth were characterized by means of X-ray diffraction on case hardened gears after grinding, running-in and efficiency testing. Spur gears made of 16MnCr5 steel were tested in a FZG back to back test rig at 94Nm and 302 Nm running-in loads, and efficiency tests. After grinding a non-equal biaxial stress state was found with compressive residual stresses in profile direction more than twice those in axial direction. On one side of the teeth the stresses were uniform, while the other had gradients from tip to dedendum and in axial direction. Running-in increased the compressive stresses in both directions, but the lower load gave higher stresses in profile direction and lower in axial direction. The stresses increased further in profile direction during efficiency testing, while in profile direction they tend to decrease, totally towards rather equal stresses in both directions.
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| 10. |
- Mallipeddi, Dinesh, 1987
(author)
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Surface Integrity Characterization of Gears with respect to Running-in
- 2016
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Licentiate thesis (other academic/artistic)abstract
- A gearbox with gears of different sizes is part of a vehicle transmission system that plays an important part in transmitting the engine power to the wheels. The efficient energy transmission highly relies on the performance of gears. Together, the mesh efficiency and durability determines the gear performance.It has been reported that the final smoothening of surface by running-in process has increased the mesh efficiency of ground gears. This is not the case for superfinished gears. However, in comparison to ground, superfinished gears produced a higher overall efficiency but only at higher speeds. Micropitting is a surface contact fatigue failure which occurs in all type of gears and for all heat treatments. Depending on the initial surface micro-geometry and contact conditions used, the micropitting can initiate after a relatively short running time. Further progression of micropitting due to continuous operation leads to degradation of profile and thereby gears fail in the form of pitting, spalling or tooth breakage. The hard finishing of gear surface by different manufacturing methods, for example grinding, honing and superfinishing etc., produces a unique characteristic surfaces in terms of roughness, surface lay and residual stresses. These topographical characteristics of tooth flank affects the efficiency and durability of gears. In addition, contribution of microstructure and surface chemistry should not be neglected. Running-in process is known to alter the aforementioned surface characteristics via smoothening the surface asperities. This creates an interest to understand the initial running period with the purpose to improve efficiency and longevity of gears. The aim of this study is to investigate the effect of running-in load on the surface characteristics of gears set by generating grinding. Secondly, to follow how these characteristics influence and further develop during the initial usage. To characterize the surface layers of gears a methodology is developed by combining analytical techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).The results showed that running-in process smoothened the surface asperities through plastic deformation and the severity of deformation increased with the magnitude of the load. On the other hand, higher load produced more micropits and this trend continued for in-line efficiency testing as well. It has been found that on one side of the as-ground teeth the stresses were rather uniform while there were stress gradients from tip to dedendum and in axial direction on the other side. The deformation created by running-in increased the compressive residual stresses but only at the surface confined to 5 µm. It has also been found that surface conditioned by higher running-in load gave subsurface cracks during efficiency testing. High atomic concentration of phosphorous-containing extreme pressure additive (EP) was also observed after efficiency test that ran at high load.Keywords: Gears, running-in, micropitting, surface roughness, residual stresses, surface chemistry, surface asperities
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| 11. |
- Mallipeddi, Dinesh, 1987
(author)
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Surface Integrity of Case-hardened Gears - with Particular Reference to Running-in and Micropitting
- 2018
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Doctoral thesis (other academic/artistic)abstract
- A gearbox with gears of different sizes is part of a vehicle transmission system and plays an important part in transmitting the engine power to the wheels. The efficient energy transmission highly relies on the performance of gears. Together, the mesh efficiency and durability determines the performance of gears. The hard finishing of gear surfaces by means of different methods; grinding, honing and superfinishing etc., produces unique characteristics in terms of surface roughness, microstructure and residual stresses. These characteristics of tooth affect the gear performance. Running-in process is known to alter them along with surface chemistry and presets the gear for service. This fact creates an interest to understand the initial running-in with the purpose to improve the performance of gears. Thus, this study addressed, the influence of running-in on the evolution of surface characteristics generated by the mentioned methods, and how they developed further during initial usage, represented by efficiency test. Gears tested in a FZG back-back test rig were characterized by combining different analytical techniques. These included scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Surface roughness was found to be the most influential factor and virtually all changes were confined to ~5 μm below the surface. The running-in process smoothened the surface asperities through plastic deformation and the severity of deformation increased with load. Micropitting was also associated with asperity deformation and hence only seen in ground and honed gears, while being absent for superfinished gears. Micropitting was promoted by higher running-in load and this trend continued for subsequent efficiency testing. The running-in load also promoted the deformation bands frequently found in connection with the cracks. Compressive residual stresses beneficial for fatigue life varied between finishing methods, highest stresses recorded for honed gears. The stresses differed between profile and axial direction after manufacturing and, reached similar levels after efficiency testing, but remained compressive throughout the test. The initial increase in compressive residual stresses was linked to retained austenite transformation and its later decrease to crack formation. The indicated tribofilm formation was connected to the surface roughness and promoted by running-in load. Micropitting is a surface contact fatigue failure that occurs in all types of gears. This failure mechanism was also investigated from material perspective. Gears were tested in a sequence from 200 to 2.2 x 107 cycles. The micropitting initiated due to the deformation of asperities and associated microstructural changes; plastically deformed regions (PDR) and deformation bands (thin martensite lath with epsilon carbides precipitated at boundaries). These structural changes started already within 200 cycles and cracks occurred after 2000 cycles, signifying that micropitting can initiate already after short period of operation. Thus, the running-in of gears from materials perspective can be as short as 2000 cycles. The findings presented are expected to contribute to the technical and industrial aims for optimized gear preparation.
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| 12. |
- Mallipeddi, Dinesh, 1987, et al.
(author)
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Surface integrity of machined electron beam melted Ti6Al4V alloy manufactured with different contour settings and heat treatment
- 2020
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In: Procedia CIRP. - : Elsevier BV. - 2212-8271. ; 87:20, s. 327-332
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Conference paper (peer-reviewed)abstract
- The powder-bed-fusion-based Electron Beam Melting (EBM) is rapidly gaining interest as a feasible process in the manufacturing industry for producing intricate Ti6Al4V components. However, there is still a challenge of reducing production time and optimizing surface roughness. One way to improve surface roughness is to optimize the melting strategy, i.e. contour setting. This not only influences the obtained surface topographical features, but also the production time. Most industrial applications require subtractive post processing (machining) to obtain a desired functional surface. This paper is concerned with analysing surface and subsurface in turning of Ti6Al4V alloy, manufactured by EBM using different contour settings. Also, the effect of subsequent heat treatment, i.e. Hot Isostatic Pressing (HIP) is studied. The results indicate that avoiding of contours require a machining allowance of 1 mm to obtain surface roughness of about 0.5 µm (Sa). In case of three and five contours the machining allowance can be reduced to 0.25 mm. Microstructural differences originating from the subsequent HIP operation show no effect on machinability. Tensile residual stresses are generated when reaching down to the heat effected zone of contour settings.
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| 13. |
- Mallipeddi, Dinesh, 1987, et al.
(author)
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The effect of manufacturing method and running-in load on the surface integrity of efficiency tested ground, honed and superfinished gears
- 2019
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In: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 131, s. 277-287
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Journal article (peer-reviewed)abstract
- This study compares gear surface characteristics generated by grinding, honing and superfinishing of case-hardened steel, including the evolution during efficiency testing with two different prior running-in loads (0.9 GPa and 1.7 GPa). The most influential factor was surface roughness. Micro-pitting was associated with surface asperities and hence only seen in ground and honed gears, while being absent for super-finished gears. The micro-pitting was enhanced by running-in load, but only for rough surfaces. Deformation-induced localized microstructure impact was associated with cracks. Residual stresses reached similar levels after efficiency testing. Phosphorous content in the gear surface was connected to surface roughness and running-in load.
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| 14. |
- Pusavec, Franci, et al.
(author)
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Tribology of solid-lubricated liquid carbon dioxide assisted machining
- 2020
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In: CIRP Annals - Manufacturing Technology. - : Elsevier BV. - 1726-0604 .- 0007-8506. ; 69:1, s. 69-72
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Journal article (peer-reviewed)abstract
- An investigation is made into the lubrication capabilities of solid-lubricated liquid carbon dioxide (LCO2) in comparison to flood lubrication, straight LCO2 and oil-lubricated LCO2 (MQL). The coefficient of friction is determined via tribological experiments, similar to machining, using an open tribometer which features an uncoated carbide insert sliding against a workpiece. Tribological experiments reveal superior performance of solid-lubricated LCO2. The milling experiments as well indicate that solid-lubricated LCO2 significantly reduces wear. The machined-surface topography is examined using high-magnification SEM, which shows no presence of adhered solid particles on the workpiece surface, providing a completely dry machining process.
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| 15. |
- Sterle, Luka, et al.
(author)
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The influence of single-channel liquid CO2 and MQL delivery on surface integrity in machining of Inconel 718
- 2020
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In: Procedia CIRP. - : Elsevier BV. - 2212-8271. ; 87, s. 164-169
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Conference paper (peer-reviewed)abstract
- Sustainable machining of difficult-to-cut materials requires effective cooling and lubrication techniques. To substitute conventional flood cooling and lubrication, different techniques such as cryogenic cooling and/or minimum quantity lubrication (MQL) can be used. Liquid carbon dioxide (LCO2) can be pre-mixed with different lubricants before its delivery to the cutting zone. This article investigates the influence of this recently developed cooling and lubrication method on surface integrity characteristics in milling of Inconel 718. Surface roughness, surface topography and microstructure were evaluated for flood lubrication, dry cutting and LCO2 machining using a single-channel LCO2 and MQL strategy. Moreover, two different lubricants were evaluated for MQL: (i) conventional MQL oil and (ii) solid lubricant molybdenum di-sulphide (MoS2). In addition to being environmentally friendly, MoS2 lubricated LCO2 showed comparable surface characteristics to flood lubrication. Also, the use of lubricated LCO2 resulted in higher part surface cleanliness compared to flood lubrication.
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| 16. |
- Yang, R., et al.
(author)
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Effect of shot peening on the residual stress and mechanical behaviour of low-temperature and high-temperature annealed martensitic gear steel 18CrNiMo7-6
- 2017
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In: IOP Conference Series: Materials Science and Engineering. - 1757-8981 .- 1757-899X. ; 219:1, s. Art no: UNSP 012046-
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Conference paper (peer-reviewed)abstract
- A martensitic gear steel (18CrNiMo7-6) was annealed at 180 °C for 2h and at ∼ 750 °C for 1h to design two different starting microstructures for shot peening. One maintains the original as-transformed martensite while the other contains irregular-shaped sorbite together with ferrite. These two materials were shot peened using two different peening conditions. The softer sorbite + ferrite microstructure was shot peened using 0.6 mm conditioned cut steel shots at an average speed of 25 m/s in a conventional shot peening machine, while the harder tempered martensite steel was shot peened using 1.5 mm steel shots at a speed of 50 m/s in an in-house developed shot peening machine. The shot speeds in the conventional shot peening machine were measured using an in-house lidar set-up. The microstructure of each sample was characterized by optical and scanning electron microscopy, and the mechanical properties examined by microhardness and tensile testing. The residual stresses were measured using an Xstress 3000 G2R diffractometer equipped with a Cr Kα x-ray source. The correspondence between the residual stress profile and the gradient structure produced by shot peening, and the relationship between the microstructure and strength, are analyzed and discussed.
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