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The present study investigates the impact of different heat transfer approaches on the precision of geometry and solidification behavior in additively manufactured thin clad walls. Employing a 2D laser scanner to assess dimensional accuracy, the study demonstrates that thin clad walls produced on a copper base plate with forced air convection exhibit notably superior accuracy compared to those on a mild steel substrate with natural convection. Microstructure analysis unveils distinct characteristics: Thin clad walls printed with natural convection on mild steel display a coarse columnar dendritic structure marked by increasing primary dendrite arm spacing (PDAS) from bottom to top (10.4 ± 0.7 to 14.5 ± 3 µm). In contrast, forced convection leads to a fine cellular and columnar dendritic microstructure with minor PDAS variation (4.6 ± 0.9 to 7.4 ± 1.7 µm) along the entire vertical span. [ABSTRACT FROM AUTHOR]

Laser-based metal powder bed fusion (PBF-LB/M) offers great potential for producing complex and filigree sub-millimetre parts with customised shapes, such as patient-specific vascular stents. However, stent fabrication via PBF-LB/M encounters fundamental challenges, including dimensional limitations, poor surface quality, difficult support structure handling and geometrical deviations. This study addresses these challenges by investigating the potential and limitations of a novel hybrid post-processing approach. This technique uses the combination of electrochemical polishing and chemical etching and is investigated from process and design perspectives, to emphasise the interactions between the two. With the systematic application of hybrid post-processing, the strut thickness and the surface roughness were substantially reduced. Moreover, it enabled the successful removal of part-internal support structures. Furthermore, angle and orientation-dependent geometrical deviations could be compensated, highlighting the potential of achieving homogenous strut thicknesses within parts containing variable overhang angles. This study demonstrates that the usage of hybrid (electro)chemical post-processing methods with specifically tailored process parameters is a promising approach for overcoming the design- and process-related challenges in PBF-LB/M manufactured sub-millimetre parts. [ABSTRACT FROM AUTHOR]

The methodology of experiments and construction of a model for controlling the geometric accuracy indicators of forgings of massive parts of complex shapes is considered on the basis of an experimental study of the wear of ball end mills when processing samples from die material. The resulting models are used to adjust the tool path. [ABSTRACT FROM AUTHOR]

Aluminium 6061 (Al6061) is a widely used material for various industrial applications due to low density and high strength. Nevertheless, the conventional machining operations are not the best choice for the machining purposes. Therefore, amongst all the non-conventional machining operations, electric discharge machining (EDM) is opted to carry out the research due to its wide ability to cut the materials. But the high electrode wear rate (EWR) and high dimensional inaccuracy or overcut (OC) of EDM limit its usage. Consequently, nanopowder is added to the dielectric medium to address the abovementioned issues. Nanopowder mixed EDM (NPMEDM) process is a complex process in terms of performance predictability for different materials. Similarly, the interactions between the process parameters such as peak current (Ip), spark voltage (Sv), pulse on time (Pon) and powder concentration (Cp) in dielectric enhance the parametric sensitivity. In addition, the cryogenic treatment (CT) of electrodes makes the process complex limiting conventional simulation approaches for modelling inter-relationships. An alternative approach requires experimental exploration and systematic investigation to model EWR and overcutting problems of EDM. Thus, artificial neural networks (ANNs) are used for predictive modelling of the process which are integrated with multi-objective genetic algorithm (MOGA) for parametric optimization. The approach uses experimental data based on response surface methodology (RSM) design of experiments. Moreover, the process physics is thoroughly discussed with parametric effect analysis supported with evidence of microscopic images, scanning electron microscopy (SEM) and 3D surface topographic images. Based on multi-dimensional optimization results, the NT brass electrode showed an improvement of 65.02% in EWR and 59.73% in OC using deionized water. However, CT brass electrode showed 78.41% reduction in EWR and 67.79% improved dimensional accuracy in deionized water. In addition to that, CT brass electrode gave 27.69% less EWR and 81.40% improved OC in deionized water compared to kerosene oil. [ABSTRACT FROM AUTHOR]

The application of continuous natural fibers as reinforcement in composite thin-walled structures offers a feasible approach to achieve light weight and high strength while remaining environmentally friendly. In addition, additive manufacturing technology provides a favorable process foundation for its realization. In this study, the printability and energy absorption properties of 3D printed continuous fiber reinforced thin-walled structures with different configurations were investigated. The results suggested that a low printing speed and a proper layer thickness would mitigate the printing defects within the structures. The printing geometry accuracy of the structures could be further improved by rounding the sharp corners with appropriate radii. This study successfully fabricated structures with various configurations characterized by high geometric accuracy through printing parameters optimization and path smoothing. Moreover, the compressive property and energy absorption characteristics of the structures under quasi-static axial compression were evaluated and compared. It was found that all studied thin-walled structures exhibited progressive folding deformation patterns during compression. In particular, energy absorption process was achieved through the combined damage modes of plastic deformation, fiber pullout and delamination. Furthermore, the comparison results showed that the hexagonal structure exhibited the best energy absorption performance. The study revealed the structure-mechanical property relationship of 3D printed continuous fiber reinforced composite thin-walled structures through the analysis of multiscale failure characteristics and load response, which is valuable for broadening their applications. [ABSTRACT FROM AUTHOR]

Surface finishing of hard-alloy parts is investigated. The best conditions for preliminary and final finishing are established. The grid density of the resultant raster trajectory is q = 0.5–3.0 mm–1 for preliminary finishing and q = 5–7 mm–1 for final finishing. [ABSTRACT FROM AUTHOR]

Single Point Incremental Forming (SPIF) is an emerging sheet metal forming process which has been used in the prototype production of complex geometries. The geometric inaccuracies and quality of formed parts are the major obstructions in commercialization of SPIF process. The aim of presented work is to study this hindrance using experimental and numerical investigation on Aluminum Alloy 2210-O. Parametric optimization is done using Response Surface Methodology (RSM) for quality factor (surface roughness) and geometric accuracy (Maximum wall angle) while minimizing thickness reduction and forming time. For this purpose, three experimental setups were designed in this study, using tool types and tool paths. During investigation, the interaction and main effects of process parameters, viz. feed rate, spindle speed, and step increment are evaluated on surface roughness (Ra), maximum wall angle (α max) , % thickness reduction (% TR), and forming time (T) using ANOVA method. Results showed that among all the parameters of SPIF process, step increment is the most significant parameter for both forming paths using ball end and flat end tool. The comparative analysis of this study suggested that the ball end tool using the bidirectional path was better than the other setups. Furthermore, the results revealed that the ball end tool using a spiral path was better in desirability achievement (73%) as compared to the flat end tool using a spiral path (71.2%). The findings of this study are beneficial in paving a path for optimization of the SPIF process for an industrial-scale production of Al alloy AA 2219-O with desired characteristics. [ABSTRACT FROM AUTHOR]

Technological advances have increased the use of plastic-based additive manufacturing for production in a variety of industries that require high mechanical properties while maintaining geometric precision. The Arburg Plastic Freeformer (APF) process, unlike other filament-based technologies, uses standard plastic granules used in mass production in injection moulding machines. This study focuses on optimising the interaction of three critical process parameters: layer thickness (LT), droplet aspect ratio (DAR) and discharge rate (DR). Previous studies have mainly varied individual parameters to evaluate mechanical and geometrical properties. In contrast, this work analyses these parameters as a whole and evaluates their combined effects on residual porosity and geometric accuracy. APF relies heavily on supports to sustain the printed part, with a smaller achievable self-supporting overhang angle compared to the Fused Filament Fabrication (FFF) printing process. For this reason, this study investigates two compatible materials, ABS Terluran GP35 and a water-soluble PVP compound named Armat11. Cylindrical and cubic samples were 3D printed using different combinations of LT, DAR and DR. A total of 150 cubic samples were printed to assess the geometric dimensional accuracy and repeatability of printing in the plate position using permutations in the printing plate. Subsequently, 30 cylindrical samples were printed for micro-CT analysis, reconstructed by CT file segmentation and compared with the ideal CAD model, in addition to the characterisation of residual porosity. The results show that optimal combinations of LT, DAR and DR produce high density parts with repeatable geometric properties. In addition, a quantitative analytical model was developed to optimise arbitrary parameter sets. This comprehensive investigation provides important insights into the APF process and increases its potential for wider industrial applications. [ABSTRACT FROM AUTHOR]

The machining of large thin-walled rings is considered. The influence of the cutter geometry and the cutting conditions on the machining precision is analyzed by the finite-element method. Production experiments are compared with the theoretical analysis. Practical recommendations are formulated. [ABSTRACT FROM AUTHOR]

Induction heating-assisted single point incremental sheet forming was established for Ti-6Al-4V thin sheets at closed and above beta-transus temperature (980 °C). In order to eliminate geometric inaccuracy and adherence of lubricant on the surface caused by elevated temperature, a cooling lubricant system was designed for the forming tool to decrease the thermal expansion and friction. A radial basis function (RBF)-based tool path optimisation was developed to study the measured geometric accuracy, temperature, and forming force. By adjusting cooling lubricant control and integrating the RBF framework, the first optimised tool path was used to collect the results and to validate with the finite element (FE) model and theoretical geometric profiles. The output data were further studied by RBF and generate a second optimised tool path. The measured geometric coordinates revealed that the error percentage has been reduced to less than 5%. Further, the microstructure evolution analysed by scanning electron microscopy (SEM) indicated noticeable oxidation and alpha-layer for temperature around 1040 °C and the phenomenon was removed at temperature closed to 950 °C. The surface roughness and energy-dispersive X-ray analysis (EDX) revealed the optimised tool path distributed significant improvement in surface quality. The cooling lubricant system indicated optimal performance with RBF optimised tool path to support constant temperature and reduce friction and lubricant adherence on the surface. [ABSTRACT FROM AUTHOR]

The incremental sheet metal forming (ISF) process has the flexibility to manufacture components without a specific die-set. In detail, a small incremental deformation by the forming tool movement is accumulated to form a target geometry. However, the formed part's geometrical accuracy is often observed to be lower due to no external die support. This research work is aimed to replace the commonly used dies with a nickel-metal foam that acts as flexible die support in the ISF process for improving the geometrical accuracy. The pure nickel metal foam was employed with various densities such as 20, 50, and 80 pores per inch (PPI) to identify the proper flexible support configuration. The current research work is summarized in three fields: (i) at first, the indentation tests were conducted to investigate the material deformation characteristics of the nickel-metal foam. The numerical results revealed that the high-density nickel-metal foam showed good geometric accuracy compared to other configurations. (ii) according to the indentation results, the ISF experiments were carried out with a nickel-metal foam, and the shape error was estimated for the formed parts. The findings showed that the shape accuracy was improved with the use of flexible die support compared to the conventional ISF process, and (iii) to save material costs, the nickel-metal foam was reused for manufacturing new parts and confirmed the reusability. Thus, the results show that employing proper density compressed nickel-metal foam influences geometric accuracy positively and can be devised for manufacturing complex geometries in the ISF process. [ABSTRACT FROM AUTHOR]

The selection of lubricants depends on the deformation mechanism of each process which significantly affects the surface roughness. In the incremental sheet forming process, there has been little attention on this aspect. This study investigates the influence of lubricants and lubricating methods on the surface quality and geometric accuracy during the two-point incremental forming process (TPIF). By using five different lubricants and two lubricating methods, the experiments were conducted to deform the 45°-cone parts with an aluminum sheet. Then, the formed parts were analyzed in terms of surface roughness and geometric accuracy. The morphology of the formed surfaces was also observed by using the scanning electronic microscope (SEM). The experimental results showed that the mixed lubricant (graphite powder + MSo2 + machine oil) greatly improved the surface quality and geometric accuracy. Using vegetable oil as an alternative lubricant for the TPIF process induced low cost and environmental effects but provided the surface quality similar to machine oil. [ABSTRACT FROM AUTHOR]

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For heat-assisted single point incremental sheet forming (SPIF) works of Ti-6Al-4 V sheets, the use of lubricant has shown significant effects on surface quality and geometric accuracy at higher temperatures. Molybdenum disulphide (MoS2) is a common lubricant widely used in SPIF works, however, it usually indicates ineffective performance at high temperatures. This article has studied different lubricants of MoS2 lubricants and proposed a novel mixture of MoS2 to provide better surface quality and improve geometric accuracy. A forming tool with a ball-roller and water channel was designed to enable the MoS2 mixture to pass through the tool tip, allowing easy application of the lubricant on the localised area and reduce the thermal expansion on the ball-roller. Surface roughness analysis has revealed that the water-cooling MoS2 mixture performed well in reducing friction effects and achieved better geometric accuracy. Forming forces measurements, scanning electron microscope (SEM), energy-dispersive X-ray analysis (EDX) and micro-hardness tests also indicated that a higher strain hardening behaviour was detected for the water-cooling MoS2 mixture. [ABSTRACT FROM AUTHOR]

Fuel nozzle is a key part of aero-engines. Due to the particularity of fuel nozzle's working environment, the high machining requirements for the surface quality and geometric accuracy of nozzle hole were put forward. The existing process is difficult to meet the machining requirements, so a new process is proposed, which is called the flexible single-pass honing. For the novel single-pass honing tool with diameter less than 1 mm, the laws are not very clear, so studies were carried out. Firstly, a novel cutting force model of single-pass honing was established, which explains the relationship between force and machining parameters. Based on the cutting force model, the influence laws of honing parameters on surface roughness, bore diameter, and shape accuracy were explored detailedly. Finally, according to the machining requirements of fuel nozzles, the honing process optimization was carried out, and the optimal parameters were obtained. Furthermore, precision control of surface quality and geometric accuracy for fuel nozzle single-pass honing was realized. [ABSTRACT FROM AUTHOR]

Laminates of carbon fibre reinforced polymer (CFRP) and titanium (Ti) alloy are used in aerospace applications and require holes for joining to other components, which can weaken them. In this study, to determine the influences of drilling and helical milling on the geometric accuracy of holes, holes were made in a CFRP/Ti-laminated structure by these two techniques, and variations in aperture and roundness at different positions were investigated. In two processes, apertures are larger in the middle and smaller at the ends, and most are larger than the apertures of standard holes (6 mm). With drilling, roundness is relatively high at hole entrances and exits. In helical milling, the maximum roundness occurs just underneath the hole entrance, while the minimum occurs at the exit. In the drilling of Ti alloy, the maximum aperture occurs at the entrance; however, with helical milling, the hole entrance aperture is smaller. The aperture at other positions is relatively small. During drilling, the maximum roundness occurs at hole entrances, while the minimum occurs just underneath and then increases with depth. Helical milling produces a relatively large roundness at hole entrances, with consistent variation in other positions. Generally, helical milling of a laminated structure produces better geometric accuracy in holes in the Ti alloy layer, better hole roundness in the CFRP layer, and smaller roundness in the transition zone. However, drilling achieves better aperture accuracy in CFRP and smaller aperture errors in the transition zone. These results will help to produce stronger CFRP/Ti-laminated structures. [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) is a promising and flexible sheet metal forming process, which is appropriate for small batch production of complex parts and customized sheet metal parts. Although the formability of sheet metal in ISF can be significantly improved compared with conventional stamping, some low-ductility materials still cannot be formed to specific geometry through ISF at room temperature, such as magnesium alloy and titanium alloy. Besides, geometric deviation affects industrial applications. In the present work, a novel point-contact tool path (PCTP) method free of circumferential friction is developed. For better understanding the forming characteristic and deformation mechanism of this new tool path, the surface quality, geometric accuracy, and forming limit of the sheet metal are investigated through experiment and numerical simulation for different sheet materials and compared with conventional spiral tool path. Experimental results demonstrate that PCTP can obviously improve the surface quality and geometric accuracy by using small interval length. Besides, the forming limits of AA2024 and AA7075 sheets are improved dramatically due to the absence of circumferential friction, and an updated analytical model of stress triaxiality is developed based on membrane analysis to explore the increased forming limit of PCTP. This novel tool path provides a simple and feasible solution for forming low-ductility sheet metal components at room temperature. [ABSTRACT FROM AUTHOR]

Single point incremental forming is a sheet metal forming technique with great potential for use in prototyping and custom manufacture. Although this technology has undergone considerable development in recent years, it still suffers from low geometrical accuracy in terms of its application in the industry. Therefore, solutions for errors reduction or compensation are required to improve the process. In this paper, an optimization procedure of the geometric precision, based on genetic algorithm, global optimum determination by linking and interchanging kindred evaluators solver and newly developed algorithm called grasshopper optimization algorithm, is tested and doubly validated numerically and experimentally. The denture plate part simultaneously simulated and manufactured shows how it is possible to obtain sound component with reduced geometric errors such as springback, bending and pillow effect errors by properly chosen optimal process parameters. The results indicated that the reduction in the shape defects between the obtained geometry and the target model generated by computer-aided design can be achieved through coupling of numerical simulations and optimization techniques. [ABSTRACT FROM AUTHOR]

A novel method using special featured tools is proposed for double-sided incremental hole-flanging (DSIHF), which can perform successful hole-flanging in one-step due to the globally cumulated deformation mode. Tools with complementary-shape section curves are used to constrain the material flow for better part geometry. The proposed method has been verified by two cases: an axisymmetric circular flanging and an asymmetric clover flanging. Experimental results demonstrate that the new method is feasible for flanging of complex shapes with simplified tools, reduces processing time and improves geometric accuracy. Moreover, numerical simulations were conducted to show that the proposed method has a different deformation mode compared with the conventional incremental forming. Specifically, the circumferential strain becomes the dominant strain, and its value depends on the in-plane curvature and the distance from the part edge. [ABSTRACT FROM AUTHOR]

Due to the unique capability of producing parts with complex geometries and functionally graded materials, additive manufacturing (AM) is taking the leading role in the "third industrial revolution" and has attracted significant attentions in multiple industrial sectors. Part quality and energy consumption are two highly interdependent outcomes, and thus it is difficult to improve one without changing the other. However, to the best of our knowledge, prior pertinent studies usually considered and optimized quality and energy consumption individually. This proposed study aims to (1) obtain a fundamental quantitative relationship between AM process design parameters and AM part quality as well as process energy consumption, and (2) develop a general framework to optimize energy consumption in AM fabrication without compromising part quality (i.e., geometric accuracy). Linear regression models are used to capture the relationship between process design parameters and the part quality and energy consumption, respectively. Then, a non-linear optimization framework is proposed to minimize the energy consumption on the part level given specific quality requirements. A case study developed based on a fused filament fabrication (FFF) process and a specific part design is used to illustrate the effectiveness of the proposed methodology. The effects of quality requirements on the optimal energy consumption solution are also explored in the case study. [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) is considered as a flexible sheet metal forming process suitable for rapidly producing complex sheet metal parts, and the tool path has a vital impact on the forming quality. The balance between efficiency and geometric accuracy is still challenging in tool path generation algorithm for the ISF process. In the present work, a novel quadratic spiral tool path (QSTP) generation algorithm has been developed for the ISF process. For better understanding the impact of QSTP, the thickness thinning, forming cycle time, geometric accuracy, and surface quality are case-studied by using two typical parts with varied wall angle and compared with conventional spiral tool path (CSTP). Two different materials AA5052 and DC05 are used to evaluate the influences of sheet material properties. In addition, an analytical model is proposed to evaluate the surface quality of the part made by QSTP, which is also validated by experiments. Experimental results confirm that QSTP can improve surface quality and geometric accuracy, reduce horizontal forming force, and relieve severe thickness thinning compared with CSTP. Results also demonstrate that QSTP generates smoother and shorter tool path compared with CSTP, which ensures the reduction of forming cycle time. Experimental comparison in forming AA5052 and DC05 by QSTP shows that larger ratio of yield stress to Young's module of the sheet metal may cause larger geometric deviation, but the material properties do not affect the thickness thinning mode which still generally follows the Cosine law in QSTP. [ABSTRACT FROM AUTHOR]

The accuracy retentivity has become one of the most important performance index of CNC machine tools, which are affected by many complicated factors, such as stress-induced deformations, bolt preload loss, wear, and the manufacturing process itself. The long-term continuous monitoring can bridge the wide gap between the accuracy retentivity and the manufacturing processing of machine tools. In this research, a geometric accuracy monitoring approach using the discrete strain gauges is proposed. The machine basis is firstly simplified based on the structural characteristics and stress condition. And, the straightness is evaluated through the reconstructed strain field of machine tool basis. Finally, to verify the validity of our method, a vertical machining center has been monitored for 7 months using the established wireless monitoring system. [ABSTRACT FROM AUTHOR]

TRIP steels have both high strength and good ductility, and they are typically used in automotive industry for the purpose of safety and energy saving. Deforming TRIP steel by ISF is practically valuable, but the application is significantly restricted by its geometric accuracy. At present, there is not enough research on geometric accuracy for TRIP steels. In this study, we explored the geometric accuracy of ISF for TRIP590 by referring to 1060Al steel and 08F steel. We found that the accuracy of TRIP590 steel was the lowest, which was because of the phase transformation of the material which occurred during deformation. To verify this, X-ray diffraction was employed to figure out the volume fraction of retained austenite. The results have shown that there is always TRIP effect during ISF process, and the relationship between natural logarithm of austenite volume fraction and the equivalent strain is negative linear. Lastly, it is proved that multiple reverse compensations could improve the geometric accuracy for TRIP steels. [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) is an emerging forming technology that promises high flexibility and formability. These properties make it suited for small-scale and customised production. However, the poor geometric accuracy of ISF limits the wide application of this flexible forming technology. This paper presents a two-directional toolpath correction approach to enhance ISF forming accuracy using a model predictive control (MPC) algorithm. A toolpath optimisation method for vertical toolpath correction has been validated in our previous work (Lu et al., Int J Adv Manuf Technol 72:1-14, 2015), and it helps to reduce errors in the base of the test shapes to a suitable level while its major limitation is that horizontal geometric errors are relatively large. This paper extends our previous work (Lu et al., Int J Adv Manuf Technol 72:1-14, 2015) by augmenting the vertical control module with a new control module for horizontal toolpath correction. The proposed control algorithm was experimentally validated in single-point incremental sheet forming (SPIF) using two forming case studies. In the first case study (a truncated pyramid), two control approaches with different assumptions for the horizontal springback distribution along the horizontal cross-sectional profile were tested and compared. Then, the developed MPC control algorithm was applied to form a more complex asymmetric shape. The results show that the developed strategy can reduce the forming errors in the wall and base of the formed shape compared to the existing works. The ISF process with MPC control leads to significant accuracy improvement in comparison with the typical ISF process that is without toolpath control. [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) is a highly flexible sheet forming process, but it suffers from poor geometric accuracy. This paper presents a feedback control strategy using model predictive control (MPC) to obtain improved geometric accuracy in ISF. Based on the incremental deformation mechanism of ISF, a novel model for shape state prediction has been proposed. The step depth of the toolpath was optimised based on shape state feedback during the forming process. Two different cases were studied for experimental validation of the developed control strategy. Comparisons between formed parts in both controlled and uncontrolled ISF processes were implemented in terms of cross-sectional profiles, formed depth at the bottom area and global deviation distribution. Results show that the geometric accuracy in ISF with feedback control has been greatly improved at the bottom area of the formed parts compared with a standard ISF approach without control. Improved geometric accuracy has been achieved on the wall of the parts as well. [ABSTRACT FROM AUTHOR]

Two-dimensional curve offsets have a wide application area ranging from manufacturing to medical imaging. To that end, this paper concentrates on two novel techniques to produce planar curve offsets. Both methods, which are based on mathematical morphology, employ the concept that the boundaries formed by a circular structuring element whose center moves across the points on a base curve comprise the entire offsets of the progenitor. The first technique titled IMOBS was introduced in our former paper and was shown to have superior properties in terms of its high accuracy, low computational complexity, and its ability to handle complex curves if compared to the techniques available in the literature. Consequently, an all-purpose algorithm titled AMOBS is introduced to enhance further the performance of the former technique by making good use of gradient information to find globally the most suitable candidate points in the boundary data set via grid search techniques. Thus, the new paradigm is demonstrated to overcome some of the problems (like orphan curve offsets) encountered in extreme cases. Both algorithms, which have similar attributes in terms of run-time complexity and memory cost, are comparatively tested via two experimental cases where most CAD/CAM packages fail to yield acceptable results. [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) is a promising manufacturing process that features benefits of reduced forming forces, enhanced formability and greater process flexibility. It also has a great potential to achieve economic payoff for rapid prototyping applications and for small quantity production in various applications. However, limited research has been conducted from the sustainability point of view, particularly for energy consumption. More consumed energy will generate more heat and affect tool and product wear. Also, geometric accuracy is still one of the dominant limits for the further development and commercialization of the ISF technology. Therefore, the aim of this study is to investigate how different process parameters affect the consumed energy during the forming process and also find the optimal working condition for lower deformation energy with higher geometric accuracy. A Box-Behnken design of 27 tests for pyramid-forming processes have been performed for a multi-objective optimisation that considers four factors: step down, sheet thickness, tool diameter and wall angle at three levels. The deformation energy during the forming process was calculated based on the measured forming forces. It was found that the deformation energy heavily depends on the sheet thickness because of higher plastic energy required to deform the material. Increasing step-down size within a limited range or decreasing the wall angle is also an effective approach to reduce the deformation energy. Moreover, the effects of various process parameters on the global geometric accuracy have also been investigated. The geometric error has been empirically predicted by quadratic equations giving the influence of the most influential forming parameters. It was concluded that the geometric quality is largely determined by the quadratic effect of wall angle, the linear effect of sheet thickness and the interaction effect of thickness and step down. Finally, the optimal working conditions for both independent and simultaneous minimisation of deformation energy and geometric error during the pyramid-forming process are provided. [ABSTRACT FROM AUTHOR]

This paper proposes a new level of understanding of two-point incremental forming (TPIF) with partial die by means of a combined theoretical and experimental investigation. The theoretical developments include an innovative extension of the analytical model for rotational symmetric single point incremental forming (SPIF), originally developed by the authors, to address the influence of the major operating parameters of TPIF and to successfully explain the differences in formability between SPIF and TPIF. The experimental work comprised the mechanical characterization of the material and the determination of its formability limits at necking and fracture by means of circle grid analysis and benchmark incremental sheet forming tests. Results show the adequacy of the proposed analytical model to handle the deformation mechanics of SPIF and TPIF with partial die and demonstrate that neck formation is suppressed in TPIF, so that traditional forming limit curves are inapplicable to describe failure and must be replaced by fracture forming limits derived from ductile damage mechanics. The overall geometric accuracy of sheet metal parts produced by TPIF with partial die is found to be better than that of parts fabricated by SPIF due to smaller elastic recovery upon unloading. [ABSTRACT FROM AUTHOR]