The tribological mechanisms governing microstructure evolution in incremental sheet forming (ISF) were investigated through comparative analysis of three friction modes: sliding friction (ISF-SF), rolling friction (ISF-RF), and frictionless free-deformation (ISF-FD). Systematic characterization of interfacial interactions, grain refinement mechanisms, and texture evolution demonstrated that friction-induced shear deformation served as the dominant factor in determining forming performance. Crucially, ISF-RF preserved {110} texture integrity via nondirectional shear deformation, where effective lubrication suppressed interfacial plowing, adhesion, and oxidation, thereby achieving superior surface finish and minimal twist angle in formed parts. Conversely, ISF-SF drove directional shear deformation that actively reoriented grains toward {001} texture. Reduced lubrication efficacy intensified texture strength while amplifying interfacial plowing, adhesion, oxidation, and crack propagation, ultimately increasing part twist angle. The study elucidated the mechanism by which friction governs forming performance through shear deformation: moderate deformation coupled with grain refinement enhanced formability, whereas excessive deformation led to detrimental effects, including stress concentration, interface defects, and oxidation-accelerated failure. These findings establish a microstructure-property-process relationship, advancing ISF technology towards texture-regulated friction mode selection and adaptive lubrication strategies that balance grain refinement and defect suppression. This theoretical foundation enables next-generation ISF systems with enhanced forming limits and tailorable material properties.

The multi-pass intermittent local loading process, which features a more flexible processing path, can further enhance the second material distribution during local loading, improve the formability of components, and reduce forming loads. However, the absence of compatible forming equipment makes it difficult to control the constraint in the unloaded zones during the forming process. This difficulty complicates coordination and control of deformation, particularly for asymmetric rib–web components. Additionally, the current implementation involves multi-fire heating, a long process flow, and high energy consumption, which limits the popularization and application of the local loading process. In this study, a new multi-pass local loading hydraulic forming apparatus that can quickly and reliably switch between heavy-load deformation and low-load constraint for different local loading sub-dies was developed. A 10-tonne laboratory prototype was developed, and the forming characteristics during the forming process as well as the response characteristics of the hydraulic system during the multi-pass intermittent local loading of rib–web component were investigated using numerical simulations and physical experiments. Results indicated that, compared to a whole loading process with the same initial geometry of billet, the total forming load (i.e., the sum of loaded and restrained loads) is reduced by more than 40% with the local loading process, and by nearly 50% with multi-pass local loading. The multi-pass local loading process allows for more effective control of material flow compared to single-pass local loading, leading to improved cavity filling and reduced flow line disturbance. For a large-scale, complex titanium alloy bulkhead, the cavity filling problem was addressed by optimizing the multi-pass local loading path with an unequal thickness billet. The dynamic performance of the multi-pass local loading hydraulic system was found to be robust, with stable pressure transitions during motion and load switching for the sub-die(s). The dynamic characteristic of the hydraulic cylinder when switching from non-moving/unloaded state to a moving/loading state are consistent whether a load is present or not. However, the dynamic characteristics differ when switching from a moving/loading state to non-moving/unloaded state, showing opposite behavior. The developed hydraulic drive mechanism provides a way for implementation of multi-pass local loading without auxiliary operation and extra heating. The results of the study provide a foundation for the industrial production of large-scale, complex components with reduced force requirement and low-energy consumption.

A new analytical model for geometric size and forming force prediction in incremental flanging (IF) is presented in this work. The complex deformation characteristics of IF are considered in the modeling process, which can accurately describe the strain and stress states in IF. Based on strain analysis, the model can predict the material thickness distribution and neck height after IF. By considering contact area, strain characteristics, material thickness changes, and friction, the model can predict specific moments and corresponding values of maximum axial forming force and maximum horizontal forming force during IF. In addition, an IF experiment involving different tool diameters, flanging diameters, and opening hole diameters is conducted. On the basis of the experimental strain paths, the strain characteristics of different deformation zones are studied, and the stable strain ratio is quantitatively described through two dimensionless parameters: relative tool diameter and relative hole diameter. Then, the changing of material thickness and forming force in IF, and the variation of minimum material thickness, neck height, maximum axial forming force, and maximum horizontal forming force with flanging parameters are studied, and the reliability of the analytical model is verified in this process. Finally, the influence of the horizontal forming force on the tool design and the fluctuation of the forming force are explained.

The thread rolling process has been widely applied to manufacture high-performance thread parts. In this process, the evolutions of surface and subsurface are frequently introduced, which affect the working performance of manufactured parts. In this study, an axial-infeed thread rolling process (ATRP) is employed, and the macro-meso surface characteristics under different lubrications and operating conditions are investigated. Moreover, the distributions of microstructure and hardness on the subsurface of formed tooth are analyzed in detail, along with the study of stress state and yield strength change. It is found that the MoS₂ grease is more effective in reducing the surface roughness and defects than the lubrication oil and water-base graphite during the ATRP process. Increasing rolling speed improves the quality of surface morphology and can reduce the surface roughness. On the subsurface of bottom and flank, intensive shear stress occurs in a narrow region, resulting in the elongation and refinement of the grains and increasing the low angle grain boundary fraction. Based on the grain size and plastic strain, the yield strength is predicted. The maximum yield strength and hardness on the bottom of formed tooth are improved by 41.2% and 39.4%, respectively.

Lubrication and friction conditions vary with deformation during metal forming processes. Significant macro-variations can be observed when a threshold of deformation is reached. This study shows that during the cold compression processing of #45 (AISI 1045) steel rings, the magnitude of friction and surface roughness (R_a) changes significantly upon reaching a 45% reduction in ring height. For example, the R_a of compressed ring specimens increased by approximately 55% immediately before and after reaching this threshold, compared to an 18% or 25%variation over a 35%−45% or a 45%−55% reduction in height, respectively. The ring compression test conducted by this study indicates that the Coulomb friction coefficient μ and Tresca friction factor m are 0.105 and 0.22, respectively, when the reduction in height is less than 45%; and 0.11 and 0.24, respectively, when the reduction in height is greater than 45%.