Large-size Parts Research Articles

A novel quenching strategy for enhanced mechanical behaviour homogeneity of large-size parts via bainite kinetics acceleration: Experimental and numerical investigation

Quenching is a key process for many large-size parts in manufacturing. However, property difference between the surface and the center of the part after quenching is amplified as its part size increases because of phase transition difference. As a mesothermal phase, bainite is potential to reduce above difference through appropriate microstructure regulation. A novel quenching strategy combining the advantages of spraying schedule and phase transformation characteristic is proposed for large-size parts here to get enhanced mechanical behaviour homogeneity. In this novel strategy, an additional holding at 700 °C for 600 s was used before traditional quenching cooling process during spraying of wheel block part. The results after novel treatment shown that the differences/gaps in strength and hardness between the surface and the center was reduced, and simultaneously the strength and toughness matching of overall part was improved than 20 %. The mechanism of as-treated process was expounded in detail by bainite transformation kinetics. This additional holding can accelerate subsequent bainite formation, increase bainite volume fraction, and result in better homogeneity. These bainite with refining substructure is good to advanced strength and toughness matching. The FE model systematically considering thermal, phase transformation based on phase kinetics, and property were performed and its positive influence with new strategy on large-size parts were verified.

Microstructural causes and mechanisms of crack growth rate transition and fluctuation of additively manufactured titanium alloy

Wire and arc additive manufacturing (WAAM) enables rapid near-net-shape fabrications of large-size parts and in-situ remanufacturing in many industry sectors. A comprehensive understanding of the fatigue failure mechanism of WAAM titanium alloys is a prerequisite for their widespread use in critical structural components subject to fatigue load. Here, the fatigue crack growth behavior of WAAM TA15 material is investigated. Fatigue crack growth tests are performed using compact tension specimens sampled from different locations and with different crack orientations of the WAAM TA15 block. The fatigue crack growth rate (FCGR) data exhibit two governing rates separated by a transition stress intensity factor value, ΔKn, and the degrees of fluctuation of the FCGR data in the two regimes are notably different. A piecewise log-linear model is first proposed by incorporating the Heaviside step function and ΔKn into the classical Paris’ model, allowing for the transition ΔKn to be determined by the data. The potential causes of the transition ΔKn are phenomenologically inferred via fractography and surface roughness profiling results. The critical microstructure affecting the value of ΔKn is identified by relating the crack tip cyclic plastic zone size at ΔKn to the sizes of main microstructures. The cause of different degrees of fluctuations in the two regimes separated by ΔKn is inferred by examining the microstructures within the plastic zone. The microstructural mechanisms of the local FCGR reduction and fluctuation are further identified and explained.

A Technique for Integrated Compensation of Geometric Errors and Thermal Errors to Improve Positional Accuracy of Hole Machining in Large-Size Parts

A Technique for Integrated Compensation of Geometric Errors and Thermal Errors to Improve Positional Accuracy of Hole Machining in Large-Size Parts

A finite element model with multi-flow fields for the quenching process of mill liner component made of bainite and martensite: simulation and experimental validation

Controlling the type and location of microstructure transformation through heat treatment processes is the key to improving the property of workpieces, especially they are large-sized and highly thick irregular. Such as mill liner, the worst wear in mining machinery, of which microstructure inhomogeneity is key to developing cost-efficient mining process. In order for advanced high strength steel (AHSS) to be used in mining machinery, its microstructure uniformity must be optimized, usually by adjusting the process parameters of the heat treatment process to optimize the microstructure distribution uniformity. However, the research on the simulation of large-sized and highly thick irregular heat treatment process is limited. Previous studies usually controlled the heat transfer process by using the heat transfer coefficient as the boundary condition, but only applied to small size and simple structure of the workpiece. As the heat transfer coefficient is a process quantity, its size depends on the thermal property parameters of the fluid on both sides of the wall, the flow rate, the shape of the solid surface, the thermal property number of the material and other factors, which is not suitable for large-sized and highly thick irregular. Therefore, for the large-sized and highly thick irregular heat treatment simulation process, the equivalent heat transfer coefficient of flow field was introduced as the boundary condition, and the temperature field, microstructure field and stress field were coupled to improve the accuracy of the numerical model. The accuracy of the finite element model is verified by comparing the temperature simulation error of less than 10% through temperature measurement experiments of the quenched workpiece. The evolution process of heat transfer in large-sized and highly thick irregular water bath quenching is obtained through the finite element model data. The difference in the flow rate of the wall fluid is the fundamental reason for the difference in cooling effect, and the wetting process of the wall is the secondary reason. At the same time, the corresponding microstructure and surface hardness distribution of different cooling regions are obtained, which can provide more accurate guidance for the optimization of heat treatment process of large size and thick special-shaped parts.

Status of 3D Printing Technology for Preparing Bioceramic Materials

3D printing technology has great advantages in small batch and personalized customization, so it has attracted much attention in the biomedical field. The consumables available for 3D printing include polymer, metal, ceramic and derived materials. Biomedical ceramics, with high melting point and poor toughness, are the most difficult materials to be used in 3D printing. The progress of 3D printing ceramic preparation process using ceramic powder, ceramic slurry, ceramic wire, ceramic film and other different raw materials as consumables are reviewed, and the surface roughness, size, density and other parameters of ceramics prepared by SLS, 3DP, DIW, IJP, SL, DLP, FDM, LOM and other different processes are compared. The study also summarizes the clinical application status of 3D printed bioceramics in the field of hard tissue repair such as bone tissue engineering scaffolds and dental prostheses. The SL ceramic additive manufacturing technology based on the principle of UV polymerization has better manufacturing precision, forming quality and the ability to prepare large-size parts, and can also endow bioceramics with better biological properties, mechanical properties, antibacterial, tumor treatment and other functions by doping trace nutrients and surface functional modification. Compared with the traditional subtractive manufacturing process, the bioceramics prepared by 3D printing not only have good mechanical properties, but also often have better biocompatibility and osteoconductivity.

Novel cross wedge rolling method for producing railcar axles

Railcar axles are large-size parts manufactured in large batches using forging methods. More efficient methods of manufacturing railcar axles are currently being sought. A promising line of research in this respect is connected with the use of cross wedge rolling (CWR). Nonetheless, there exist no rolling mills that would make it possible to manufacture such large-size parts as railcar axles. A solution to this problem was inspired by the symmetric shape of a railcar axle, which makes it possible to roll this part in two passes using the same tools. Taking advantage of the potential offered by numerical modelling, simulations were made of two rolling processes for producing a railcar axle type BA302, i.e. one process was conducted with the use of two rolls and the other with two flat tools moving in the opposite directions. Numerical results demonstrated that railcar axles produced by the proposed rolling process had neither external nor internal (cracks) defects. The effectiveness of the developed CWR method was ultimately confirmed by the high quality of railcar axles that were produced (in a scale of 1:5) under industrial conditions at the Lublin University of Technology.

Homogenous strength-toughness match for 20Mn2SiCrMoV bainitic large-size parts via processing of VC particles and quenching control

Homogenous strength-toughness match for 20Mn2SiCrMoV bainitic large-size parts via processing of VC particles and quenching control

Preparation of large-size alumina ceramic parts by DLP 3D printing using high-solid-loading paste and optimizing the debinding process

Digital light processing (DLP) is a promising additive manufacturing method for creating complex structural alumina ceramic with high precision, high efficiency, and low cost. However, printing large-size parts with high feature resolution by DLP, obtaining high-performance pastes, and optimizing the debinding process are challenges that still need to be overcome. In this study, an advanced top-down Matrix-DLP technology that seamlessly connects two high-definition-resolution DLP projectors, with high resolution and a large projection area, was used to achieve fine-structured large-size alumina green bodies. The homogeneous and stable non-self-levelling alumina pastes suitable for the DLP technology were developed, with a high solid loading up to 55 vol%, viscosity of 35.0 Pa s at 30 s−1, and good rheological properties by innovatively using 2.5 wt% P5318 as surface modifiers of alumina powders and with only a 0.244% volume of bubble residue by using 0.5 wt% BYK-066N defoamer in combination with a vacuum planetary stirring defoaming process. The debinding processes were designed based on TG-DSC analysis and then optimized, and it was proved that the segmented-atmosphere debinding process was the best approach and can obtain defect- and carbon residue-free bodies with uniform grain distribution, and can also achieve non-destructive debinding for the thick-walled parts with thickness greater than 10 mm. The effects of the debinding residual carbon and the solid loading on the microstructure and properties after sintering were also investigated. Consequently, the high-precision large-size alumina ceramic with good interlayer bonding, dense microstructure, and high microhardness of 17.92 GPa was obtained.

Features of the Microstructure and Thermal Conductivity of Large-Size Parts from Pressureless Sintered AlN-Based Ceramic Composite

Features of the Microstructure and Thermal Conductivity of Large-Size Parts from Pressureless Sintered AlN-Based Ceramic Composite

Research on Flatness Measurement of Large-Size Parts Based on 3-D Machine Vision

Research on Flatness Measurement of Large-Size Parts Based on 3-D Machine Vision

A Brief Review on The Common Defects in Wire Arc Additive Manufacturing

Wire arc additive manufacturing (WAAM) process, which depends on conventional welding arc processes, is a promising option for industries when compared to typical manufacturing processes for assembling large and complicated products. WAAM process attracting manufacturing industries due to its potential to make large and complicated components with real sharp production run time with almost single step process. The process represents greater material savings, higher material buildup rate and speed, cost savings, lower cycle time, less impact on the environment, and capability of producing large size parts when evaluated with other fabrication methods. This paper focuses on WAAM process and reviews some of the common possible process defects found in variety of studies made previously to summaries a guideline for the causes of such defects and provides some prevention methods found by those studies. Of these common possible defects found in researchers works and reviewed in this work are pores, lack of fusion, cracks, and residual stress.

The surface quality, microstructure and properties of SS316L using a variable area scan strategy during quad-laser large-scale powder bed fusion

In this work, a self-developed muti-laser powder bed fusion (ML-PBF) equipment was utilized to produce a series of SS316L samples. A new scan strategy called "variable area scan" was used to investigate the dimensional accuracy, microstructure, defects, surface roughness and mechanical properties of the single-laser PBF samples, dual-laser PBF samples and quad-laser PBF samples during muti-laser PBF processing. It is found that single-laser samples and quad-laser samples have got a good surface quality and dimensional accuracy, but the size of the double laser printed samples have large deviation due to the stitching error. The OM and SEM diagrams show the complex interlacing of the melt tracks in the multi-laser junction area, and the existence of holes at the lap boundary, which is also one of the reasons for the unstable microhardness of the overlap region. As the number of lasers increases，the grain size of the region increases, and the preferred orientation of the overlapping region changes and exhibits a pronounced <100> texture, and more columnar grains along BD are generated because of a high thermal gradient. Moreover, dual-laser PBF samples even get better average tensile properties than that of single-laser PBF samples. The work can provide a practical reference for the large-size parts building during the muti-laser PBF processing.

Machining Allowance Calculation for Robotic Edge Milling an Aircraft Skin Considering the Deformation of Assembly Process

Aircraft skin parts are a typical kind of large size and thin wall parts which are easily deformed in both clamping and assembly. The edge of skin parts needs to be machined before assembly to control the clearances between adjacent skins after assembly. A frontier way is using a robot system to carry out large-range three-dimensional scanning, intelligentized calculation of machining allowance and automatic robotic edge milling. A necessary premise for robotic machining is accurately calculating the edge machining allowance of the skin part. In this article, a novel approach for accurately calculating the edge machining allowance based on onsite measurement points under the case of large bending deformation is proposed. This method solves two key problems in calculating the machining allowance. First, a method for accurately reconstructing the skin surface after assembly based on the extremely incomplete measurement points of the vacant area on a fuselage is proposed. Second, based on the reconstructed surface, a non-rigid registration method to construct the mapping relation between the skin surfaces before and after assembly is proposed to accurately calculate the edge machining allowance. To show the feasibility of the proposed method, simulations and experiments are carried out. It is proved that the proposed method can reconstruct the skin surface with a high degree of realism, and can achieve accurate non-rigid mapping between skin surfaces with large bending deformation. The skin parts are successfully milled with a robotic system based on the reconstructed surface and calculated machining allowance.

Effect of powder size segregation on the mechanical properties of hot isostatic pressing Inconel 718 alloys

Pre-alloyed powder of Inconel 718 alloy was prepared by electrode induction melting gas atomization (EIGA) and powder metallurgy (PM) Inconel 718 alloys were made through hot isostatic pressing (HIPing) route. The change in volume of large size parts (special-shaped cylindrical capsule) has a much lower effect on the alloy than the powder size. The vibration of the powder filling process over a long time causes the particle size segregation phenomenon that the proportion of coarse particle powders in top part increases, and the proportion of finer particle powders in middle and bottom part increases. This phenomenon has little effect on tensile strength of PM Inconel 718 alloys at room temperature and 650 °C, but has a significant effect on elongation, room temperature impact properties, and stress rupture life at 650 °C/725 MPa. Compared to finer particle powders, the plastic deformation of coarse particle powders is small and a large number of under-deformed powder particles are retained, forming prior particle boundaries (PPBs) and reducing the bonding strength between powder particles. In order to avoid particle size segregation, optimized process parameters and reasonable particle size should be used.

Influence of Hold Time on Dwell Fatigue Behavior in IMI834 Disc Forging

The potential cold dwell fatigue failure in the titanium components of gas turbine engines is still a troublesome industrial issue. Based on small-scale laboratory specimens tangentially extracted from a disc forging of IMI834, the influences of dwell period and microstructural conditions on dwell sensitivity have been investigated. The fatigue fracture features and deformation mechanisms were characterized using SEM, XCT and TEM. EBSD was utilized to examine the microtexture of representative locations in the disc. The results demonstrated that large differences in dwell sensitivity of the IMI834 disc depended on dwell time and crystal orientation distribution. A significant dwell effect generated in the bimodal microstructure was attributed to the intense planar slip and relatively high intensity of major texture component (5.95 times the random level), where a dwell time of 120 s was basically enough for the effect to reach a saturation. For the location with low dwell sensitivity, extending the hold time would further increase the dwell debit and strain accumulation, which was manifested in enhancing planar slip density. The quantitative influence of crystal orientation, texture intensity and dwell time have been experimentally revealed, and the results could be useful when assessing and optimizing the dwell performance of large size parts.

Re-fluidising the aged gel for high-density alumina green body

A green body with a density as high as possible is critical to diminish the crisis of deformation or cracking when large-size parts are sintered. Here, a new method, i.e., re-fluidising the aged ceramic gel is developed to prepare the high-density green body. Alumina slurry with 56 vol% solid loading and copolymers of isobutylene and maleic anhydride were aged without vaporisation and re-fluidised by non-intrusive shearing after removing the exuded water. The re-fluidised slurry was re-casted. The resultant wet gel was dried and deboned at a low temperature. The relative density of the obtained green body was 64.6%, 1.5% higher than that without aging and re-fluidising. The linear sintering shrinkage of the body decreased by 0.7%. The enhanced green density is explained from the viewpoint of the solid loading and the structure of the slurry.

An effective method for large-scale temperature simulation in SLM based on the finite difference

Numerical simulation is an effective approach to analyze the selective laser melting (SLM) process and reduce the production development cost. Based on the finite difference method (FDM), the nonuniform grid algorithm (NUGA) is developed to simulate the thermal behavior in SLM process concerning the variable thermophysical parameters of materials with different status. The NUGA can effectively improve computing efficiency, and the calculation speed using NUGA is 610 times than that without using NUGA. Different heat transfer strategies are used on each side of the two critical scanning speeds, 68.95 mm/s and 6895 mm/s, respectively, and the results of temperature calculations are highly consistent. The correctness of the heat transfer strategy under different speeds is analyzed using the NUGA. The effects of processing parameters (laser power, scanning speed and building height) on the shape and volume of the molten pool are investigated. As the scanning speed ranged from 100 mm/s to 500 mm/s, the width and depth of the molten pool decrease, while the length increases. As the laser power ranged from 100 W to 500 W, the length, width and depth of molten pool all increase. The length of the molten pool increases 11.68% from 264.94 of layer 1 to 295.88 of layer 5. The molten pool volume decreases, then increases and decreases finally from the start to the end of single molten path. The molten pool volume increases with increasing laser power and building height, while decreases with increasing scanning speed in general. The NUGA is an effective method for temperature simulation of large-size parts, which expands the application range of temperature simulation in SLM process.

Springback control and large skin manufacturing by high-speed vibration using electromagnetic forming

In this paper, a novel method of electromagnetic partitioning forming with elastic cushion is proposed. Its main principle is based on that the parts vibrate at high speed under the action of the electromagnetic force and the rebound force of the elastic pad. The state of the elastic parts inside the workpiece is changed into plastic state, and then, springback is eliminated through vibration. A common spiral coil is used to generate the magnetic field. A finite element model has been developed to analyze the effects of coil structure and coil discharge position on the stress, strain, and surface quality of the parts. It is found that a 1.5-mm bump is generated on the sheet surface, which corresponds to the middle of the coil. This is because this sheet region corresponds to the coil edges moving towards each other in opposite directions. Subsequently, the electromagnetic shielding method is used to isolate half of the spiral coil. Both the simulation and experiment demonstrated that no bulge was produced on the sheet surface. Moreover, the internal stress and springback of the parts are significantly reduced due to that the sheet vibrates at high speed. Large-scale skin was obtained after the coil was discharged multiple times in six different positions. Compared to traditional stretching, the springback of the parts is significantly reduced and the plate surface is smooth after electromagnetic forming. Consequently, the high-speed vibration induced by electromagnetic forming can reduce springback and enables the manufacturing of large size parts with smooth surface.

Realization of quenching & dynamic partitioning on large-size parts

ABSTRACT Small components can obtain microstructure of martensite and stable retained austenite (RA) by quenching and traditional partitioning (Q&P) process, thereby demonstrating excellent performances. However, the Q&P is difficult to be realized in large-size parts with complicated multiple microstructures, especially the big property differences from surface to working depth. A novel dynamic quenching–partitioning process for large products was developed by water spraying and critical bainite transformation kinetics was taken into consideration in this process. Typical as-treated microstructure is composed of triplex phases mainly including martensite, bainite and RA. Good combination of strength and toughness have been gained because of multiphase structure and film RA between bainite plate by it. Corresponding ultimate tensile strength and impact energy are 1363 MPa and 81 J at 10 mm depth from the surface as well as 1182 MPa and 65 J at 50 mm depth, respectively, keeping high strength level of over 1100 MPa and demonstrating relatively low gradients. Simulation results also showed that spraying parameters can adjust temperature variation and phase transformation near the surface, realizing the novel process in large-size parts. And it is suitable for multiphase steels, providing a new idea for large-size parts with energy and cost savings.

Effect of Slip Evacuation on the Properties of Large-Size Quartz-Ceramic Parts

Effect of Slip Evacuation on the Properties of Large-Size Quartz-Ceramic Parts