Search Results (13)

This study employed cold metal transfer (CMT) welding technology to repair defects in ZL114A aluminum alloy, investigating the influence of key repair welding parameters (preheating temperature, overlap amount, wire feed speed, welding speed) and ultimately obtaining defect-free repaired joints with relatively high tensile strength. Using a single-layer, single-pass bead-on-plate method, the effects of wire feed speed and welding speed on the spreading behavior of ZL114A melt on the substrate surface were studied. Through a two-pass, single-layer welding method, the influence of inter-pass overlap amount on the morphology of overlap welds was investigated. The effects of preheating temperature on the morphology, microstructure, and mechanical properties of the repaired specimens were examined by repair welding experiments on spherical crown grooves. The results indicate that to achieve favorable spreading of ZL114A droplets on the base material surface, the welding speed should be greater than 5 mm/s, and the wire feed speed should be within 7–9 m/min. When the overlap amounts are 65%, 70%, 75%, and 80%, the overlap welds are relatively flat, and lack-of-fusion defects are less likely to occur between the two weld passes. As the preheating temperature increases, the porosity defect rate in the repair weld decreases significantly, and the average grain size in the repair zone shows an increasing trend. The average grain size at the center of the repair weld is larger than that in the fusion zone. When the preheating temperature is 350 °C, no obvious porosity defects are observed in the repair weld. The proportion of high-angle grain boundaries increases significantly, and the maximum Kernel Average Misorientation (KAM) value also increases. The room-temperature tensile strength and Vickers hardness of the repaired specimens are superior to those of the original base material, with the tensile strength increasing by approximately 6 MPa and the Vickers hardness increasing by approximately 4 HV. Full article

The IC10 directionally solidified superalloy is a nickel-based alloy with high temperature resistance, and its surface integrity has a significant impact on the fatigue life of critical hot-end components in aerospace engines. This paper investigates the influence of creep-feed grinding surface integrity (surface roughness and surface hardness) on the high-temperature fatigue life of IC10 directionally solidified superalloy. High-temperature fatigue life tests were conducted on IC10 directionally solidified superalloy, and a method for evaluating the high-temperature fatigue life of the IC10 directionally solidified superalloy using surface integrity is proposed. The results indicate that as the surface roughness Ra increases from 0.60 μm to 2.15 μm, the maximum valley depth Rv of the grinding surface profile and the stress concentration factor increase, leading to more scratches and wider grooves. The fatigue fracture of IC10 consists of a fatigue source zone, a fatigue propagation zone, and an instantaneous fracture zone. With increasing surface roughness, the number of fatigue sources also increases, and the stress concentration on the grinding surface intensifies. Under the action of multiple fatigue propagation sources, the sample structure is more likely to reach a critical value and lose stability, leading to fracture and thus reducing the high-temperature fatigue life. When the surface hardness increases from 387.11 HV to 393.60 HV, the high-temperature fatigue life of IC10 improves by 68.13%; when the surface hardness increases from 401.62 HV to 418.13 HV, the high-temperature fatigue life of IC10 decreases by 73.12%. The surface integrity of the IC10 directionally solidified superalloy has a notable impact on its high-temperature fatigue life. Full article

This study presents a new gas metal arc welding (GMAW) technique that achieves both high efficiency and low heat input using a hybridization of the hot-wire method. The optimal combination of welding speed and welding current conditions was investigated using a fixed hot-wire feeding speed of 10 m/min on a butt joint with a V-shaped groove using 19 mm thick steel plates. Molten pool stability and defect formation were observed using high-speed imaging and cross-sectional observations. The power consumption and heat input were predicted prior to welding and measured in the experiments. The results indicate that a combination of a welding current of 350–500 A and welding speed of 0.3–0.7 m/min is optimal to avoid defect formation and molten metal precedence using three or four passes. The higher efficiency and lower heat input achieved by hot-wire GMAW results in a weld metal of adequate hardness, narrower heat-affected zone, smaller grain size at the fusion boundary, and lower power consumption than those obtained using tandem GMAW and high-current GMAW. Based on the experimental results, a single bevel groove, which is widely used in construction machinery welding joints, was welded using hot-wire GMAW, and we confirmed that the welding part could be welded in six passes, whereas eight passes were required with GMAW only. Full article

A hot-working die steel thick-walled tube Pilger rolling test was carried out using an LG40 Pilger mill, and the morphology and roughness evolution of the inner surface were examined using a white-light interferometer. The experimental results showed that micro-wrinkles formed on the basis of the original inner surface morphology, the altitude difference (Sz) between the peaks and valleys of the inner surface profile increased from 3.18 to 3.686 μm, and Sa increased from 0.722 to 0.892 μm in the diameter reduction zone. As the tube continued to feed into the wall thickness reduction zone, the micro-wrinkles gradually flattened, Sz and Sa were decreased to 1.625 and 0.174 respectively, and Sa maintained a slight fluctuation of 0.174~0.2 μm in the final sizing zone. From the diameters of the roller groove and taper of the mandrel, the three-dimensional strain of the tube in the wall thickness reduction zone was calculated, and the strain state of the tube in the complete deformation zone could be analyzed by finite element simulations. We found that in the diameter reduction zone, the inner surface was not supported by the mandrel and was free, while micro-wrinkles formed under circumferential compressive strain. In the wall thickness reduction zone, the deformation of the inner surface was controlled by the mandrel, and the micro-wrinkles were gradually flattened by radial compressive strain. The ratio of radial to circumferential strain was the key to flattening the micro-wrinkles, and when the ratio increased, the inner surface roughness (Sa) was reduced to 0.174 μm. In the sizing zone, the radial and circumferential strains were small, and the inner surface roughness showed no obvious fluctuation. Full article

Femtosecond laser processing technology offers a promising technique for the preparation of micro and nanostructures of single-crystal silicon carbide (SiC), thanks to its high precision and non-destructive processing. However, further research is needed to optimize processing parameters, as well as improve efficiency and quality of the process. This study conducts experiments to explore the effects of femtosecond laser ablation on single-crystal SiC. The influence and significance of parameters, such as fluence (F), repetition rate, scan speed (S), multipass scanning (c) and numerical aperture on the performance of grooves, including groove depth, groove width, heat-affected zone (HAZ) width, material removal rate (MRR) and side wall inclination angle, were studied. The results show that the influence of fluence and numerical aperture on groove depth, groove width, HAZ width, MRR and side wall inclination angle is very significant. The scan speed has a very significant effect on the groove depth, groove width, HAZ width and side wall inclination angle but has insignificant effect on the MRR. Repetition rate and multipass scanning have a very significant effect on groove depth, HAZ width, MRR and side wall inclination angle and a moderately significant effect on groove width. The experimental methods of increasing the aspect ratio and reducing the HAZ width were studied, and a significance analysis was carried out. Fluence, multipass scanning and z-layer feed have significant effects on groove depth, groove width, aspect ratio, HAZ width and MRR. The influence of polarization angle on groove depth, groove width, aspect ratio and MRR is insignificant. Full article

20Cr2Ni4A alloy is widely used in the manufacturing of heavy-duty gears, although limited information about its machinability during the form-grinding process has been reported. In this work, form-grinding trials on transmission gears of 20Cr2Ni4A alloy under various parameters were conducted. Surface morphology of the gear tooth, surface roughness distribution and microstructure evolution of the machined surface layer were comprehensively studied, and the influence of grinding parameters on grinding performance was investigated. The formation mechanisms of surface/subsurface defects during the form-grinding process, including plastic flow, deep grooves, successive crushing zone, adhesive chips and cavities, were analyzed. Results showed that the change in contact conditions between the grinding wheel and tooth surface led to the decrease in the surface roughness from tooth tip to root. Mechanical force and grinding heat promoted the deformation and refinement of the microstructure within the machined surface layer. With the increase in cutting depth and feed speed, the deformation ratio of the microstructure increased, which was also consistent with the variation trend in the form-grinding temperature. Full article

The shape and size of processed materials play a crucial role in the solid conveying characteristics of single-screw extruders. Thus, the increasing amount of plastic regrind leads to new challenges in screw extrusion. This work investigates the conveying behavior of three distinctly different material shapes in an axially as well as a helically grooved solid conveying zone. A uniform virgin polypropylene (PP) granule, an irregularly plate-shaped PP regrind and a powdery polyethylene (PE) are processed at screw speeds up to 1350 rpm. Thereby, frictionally engaged conveying in the grooves is visualized for the utilized powder. Similarly, the virgin granule is subject to forced conveying by interlocking in the grooves. The experimentally determined throughput is furthermore compared to analytical calculations which assume a so-called nut–screw conveying. It is found that these calculations perfectly predict the throughput when processing the virgin granule and the powder in a helically grooved barrel. In contrast, the analytical calculation significantly underestimates the throughput for the regrind. This underestimation is expected to be mainly caused by its plate shape and a difference in bulk density. The actual bulk density in the extruder is probably significantly higher due to both orientation and compaction effects compared to the measured bulk density that is used for the analytical calculation. Additionally, the regrind exhibits a fluctuating throughput due to the non-constant bulk density, which results from an irregular regrind shape and a broad size distribution. Full article

Single-screw extrusion at high screw speeds is established nowadays since it allows for a high mass throughput at a comparatively small extruder size. Compared to conventional extrusion at low screw speeds, a considerable non-linearity in mass throughput appears by exceeding a certain threshold screw speed. In this study, the solid conveying behavior of different plastic granules with varying geometries was investigated in a smooth, a helically and an axially grooved solid conveying zone for screw speeds up to 1350 rpm. These experimental findings are compared to classical analytical predictions in the literature. It is found for the first time that both the shape and size of the plastic granules play a decisive role in determining the threshold screw speed at which a non-linear mass throughput is observed. It is shown that small and spherical granules exhibit a later onset of non-linear throughput compared to larger lenticular and cylindrical shaped granules. Moreover, it is revealed that the mass throughput equalizes for an axially and a helically grooved solid conveying zone at high screw speeds. This is contrary to the low screw speed range where the axially grooved barrel results in a significantly higher throughput than the helically grooved barrel. Thus, the maximum throughput at high screw speeds is limited by the granule stream provided by the hopper opening and is no longer governed by the groove angle. Full article

The objective of this study was to design the die groove profile and predict the rolling force produced when employing the variable curvature rolls and mandrel for manufacturing seamless pipes using the cold pilger rolling process. The parameters of the key process design were the diameter of the initial tube and final product, as well as the feed amount, reduction area, principal deformation zone, and roller radius. The rolling forces during the pilger rolling process were theoretically calculated to enable their prediction, and the characteristics of the cold pilger rolling process were identified. The calculated values were in close agreement with the experimental data. The die groove design is important in the prediction process because the dimensional accuracy of the tubes and the life of the dies are highly dependent on this design. The presented design method can be successfully applied to fulfill this objective. The tube shape and adequate tolerance can be attained by using the proposed design method. The mechanical properties of the pipe are evaluated by calculating the Q factor. Full article

The T-joints of medium-thick 6082 Al-alloy plates created by dual pulsed gas metal arc welding (P-GMAW) and bilateral synchronous welding were investigated to improve weld quality using the adaptive deposition method, which calculates the minimum amount of deposition according to the welding condition, groove size, and cross-sectional area, effectively reducing the heat input and deformation of the welds on the basis of weld filling. The optimized linear energy with a wire feed speed (WFS) of 9.5 m/min can ensure a well-formed weld with a complete root fusion, and high-quality T-joint welds were obtained both in root openings of 0 mm and 1 mm. The biggest penetration was 4 mm, which was four times more than that of the result from a single torch welding process. When the distance between the two welding torches exceeded 20 mm, the molten pool was completely separated, and process pores were observed in the unfused root zone. Influenced by the thermal cycles in asymmetric welding, the hardness distribution changed: the width of the softer zone at the base plate with the fore arc was smaller than that zone with the rear arc. Furthermore, dual P-GMAW bilateral synchronous welding with an asymmetric heat source can further reduce the deformation of the welded joint by about 20% compared to that of symmetric welding. Full article

Regrind processing poses challenges for single-screw extruders due to the irregularly shaped particles. For grooved feed zones, the output is lessened by the reduction of bulk density in comparison to virgin material. Simultaneously, the melt temperature increases, reducing the extruder’s process window. Through experimental investigations on a test stand, a novel feed zone geometry (nominal diameter 35 mm) is developed. It aligns the regrind’s specific throughput with that of virgin material. The regrind processing window is essentially increased. As the solids conveying in the novel feed zone cannot be simulated with existing methods, numerical simulations using the discrete element method are performed. Since plastic deformation occurs in the novel feed zone geometry, a new hysteresis contact model is developed. In addition to spheres, the regrind and virgin particles are modeled as superquadrics to better approximate the irregular shape. The new contact model’s simulation results show excellent agreement with experimental compression tests. The throughput of the extruder simulations is considerably underestimated when using spheres to represent the real particles than when using irregularly shaped superquadrics. Corresponding advantages can be seen especially for virgin material. Full article

The elaboration of a modified friction-extrusion method aimed at obtaining 2017A aluminum rods of gradient microstructure is described. This was achieved by cutting spiral grooves on the face of the stamp used for alloy extrusion. The experiments were carried out at a constant material feed (~10 mm/min) and a range of tool rotation speeds (80 to 315 rpm). The microstructure observations were carried out using light microscopy (LM) and both scanning and transmission electron microscopy (SEM and TEM). The mechanical properties were assessed through hardness measurements and static tensile tests. The performed investigations show that material simultaneous radial and longitudinal flow, enforced by friction of the rotating tool head and extrusion, results in the formation of two zones of very different microstructures. At the perpendicular section, the outer zone stands out from the core due to circumferential elongation of strings of particles, while in the inner zone the particles are arranged in a more uniform way. Simultaneously, the grain size of the outer zone is refined by two to four times as compared with the inner one. The transfer from the outer zone to the core area is of gradient type. The hardness of the outer zone was found to be ~10% to ~20% higher than that of the core. Full article

In thick section laser welding, filler metal addition is usually required to improve joint fit-up tolerances or to control the chemical composition of the weld metal. With deep and narrow welds produced using an over-alloyed filler metal, it may be challenging to ensure that the filler metal and its elements are homogeneously mixed and evenly distributed throughout the fusion zone. Inhomogeneous filler metal mixing can cause unfavourable changes to weld metal chemistry and microstructure. Filler metal mixing behaviour in laser-arc hybrid and laser cold-wire welding is studied in this work. Welding tests were conducted on 10 mm thick butt-welded joints of AISI 316L austenitic stainless steel. An overmatching type 2205 duplex stainless steel filler wire was used to obtain a composition contrast between the base metal and filler metal. Energy dispersive spectroscopy (EDS) with chromium as the trace element was used for element mapping and stepwise characterization of the weld cross-section samples. Optical metallography was used to observe possible inhomogeneous filler metal mixing behaviour like local acute changes in macro- and microstructural features. The results showed a clear difference in filler metal mixing between the weld surface part (upper half) of the weld and the weld root part (lower half) in 10 mm thick welded cross-sections for closed root gap of I-groove welds or when the gap was only 0.4 mm. In narrow I-groove preparations, inhomogeneous mixing phenomena were more pronounced in laser cold-wire welds than in laser-arc hybrid welds. In both welding processes, a combination of trailing wire feeding and the use of a wider groove enabled filler metal to be introduced deeper into the bottom of the groove and improved mixing in the root portion of the welds. Full article