•Macro-micro multi-scale simulation of fine-blanking process was performed.•Microstructure-based sub-models were generated for the microscopic simulations.•Fine-blanking ability was investigated with microscopic sub-models.•Fine-blanking surface quality of ferrite-cementite steels was well predicted.The fine-blanking process of ferrite-cementite steels was simulated with a macro-micro multi-scale approach. In the macroscopic simulation, the effects of material and blanking clearance were investigated by evaluating the damage work density of the material in the center of the fine-blanking shearing zone. A series of microstructure-based models with different particle fraction and distribution were generated as sub-models for the microscopic simulations. Microscopic damage in the sub-models was predicted with the damage work model. The simulation results indicated that an increase in particle fraction and the existence of carbide banding accelerated the microscopic damage of the material in the shearing zone during fine-blanking. Micro cracks appeared and extended along the carbide band. In addition, an increase in blanking clearance speeded up the microscopic damage accumulation at the microscale and caused early fracture of the material in the shearing zone at the macro scale. The SEM observations of various fine-blanking specimens substantiated the predictions of the simulations and suggested that severe carbide banding would change the macro crack path in the sheets, adversely affecting the quality of the blanking surface.Download high-res image (398KB)Download full-size image

The formation of the gear drum clutch involves bulk and sheet forming, and filling the tooth is a key difficulty during the forming process. In this study, four tooth extrusion processes with various extrusion ratios and preform shape were developed, and they were simulated using AFDEX software for examining how the clutch drum influenced tooth forming. Various tooth-filling results were obtained by controlling the extrusion ratio and die cavity in each process. A comparison of the deformation, material flow, and mean stress state among the processes revealed that the stress state was the main determinant of the local flowing material, and it was used to improve the degree of tooth filling. The optimal tooth-filling result was obtained using a two-step extrusion process with an appropriate extrusion ratio and a preform shape.

•An alternative quantitative evaluation method for the friction condition in cold forging by ring with boss compression test (RCT-B) was proposed.•The RCT-B method was successfully applied to determine the friction factors of four different lubricating conditions with aluminum workpieces.•By using the RCT-B method, the difference of lubrication conditions can be quantitatively evaluated by checking the inclined angle of the outer boss.Ring compression test (RCT) is a very popular method used to quantitatively evaluate friction conditions at the tool–workpiece interface by measuring the variations of the inner diameter of the ring in metal forming. There are many possibilities for measuring the inner diameter variations in RCT because of non-uniform deformation of the inner hole during the test. Such non-uniform deformation of the inner hole causes difficulties in precise measurement of the inner diameter and hence the accuracy of the derived friction coefficient. To avoid the disadvantage in dimension measurement of the conventional RCT, an alternative method for evaluating friction conditions in cold forging named ring with boss compression test (RCT-B) is proposed. By the introduction of the RCT-B concept, finite element simulation results under different friction conditions were obtained. Results showed that the shape of the outer boss remains stable during the compression deformation and allows the diameter of the outer boss to be measured more easily and accurately. The calibration curves of the RCT-B concept were constructed by using FE simulation, which cover the range of friction conditions in cold forging process. Finally, the RCT-B method was successfully applied to determine the friction factors of four different lubricating conditions in compression of aluminum rings. Furthermore, the phenomena with different lubricating conditions between the upper and lower die–workpiece interfaces were also studied using both simulation and experimental testing. The results show that it is possible to quantitatively assess the difference of friction conditions at the upper and lower die–workpiece interfaces by simply checking the inclined angle of the outer boss with the RCT-B method.

To avoid defect formation, a two-step forging process for duplex fork was developed and optimized using an unequal thickness flash. The large cross-sectional difference between the different parts of the complex shape of the duplex fork made it difficult to forge. Crack defects formed during initial forging were observed and analyzed by finite element simulation, and the metal flow lines and velocity distributions on the main cross section were studied. A non-uniform velocity distribution with a large difference in the dangerous area and large amount of oxide scale most likely caused the crack defects. An optimized two-step forging process was developed, preupsetting was used to remove the oxide scale, and final forging using a die with an unequal flash gutter depth was used to obtain a reasonable velocity distribution. The effect of different process parameters on the optimized forging process was determined. The parameters included the pre-upsetting stroke, the friction factor, the workpiece mass, and the offset of the preform, and the results were used to improve the process stability. A duplex fork of acceptable quality and without any cracks was forged in successful trial production using the optimized process in the forging plant.

Various microstructure-level finite element models were generated according to the real microstructure of DP590 steel to capture the mechanical behavior and fracture mode. The failure mode of the dual-phase (DP) steels, mainly resulting from microstructure-level inhomogeneity and initial geometrical imperfection, was predicted using the plastic strain localization theory. In addition, dog-bone-type tensile test specimens with different edge qualities were prepared and the deformation processes were recorded using a digital image correlation system. When the steel exhibited no initial geometrical imperfection, void initiation was triggered by decohesion between martensite and ferrite which was predicted based on the severe strain concentration, or tensile stress in areas where stress triaxiality and strain values were high. Final failure was caused by shear localization in the vicinity. Moreover, the initial geometrical imperfections severely affected the overall ductility and failure mode of the DP590 steel. When initial geometrical imperfections were deeply ingrained, an incipient crack began at the site of initial geometrical imperfection, and then caused progressive damage throughout the microstructure, from the area of shear localization to the final fracture. Overall, the depth of the geometrical imperfection was the critical factor in determining whether internal decohesion or a local crack plays a dominant role.

•A new plastic joining process is proposed in nail-sheet joining.•Nail forming, nail cutting and joining are completed in one press stroke.•The method of fracture control in simulation is precisely applied.•An irrelevant term is added to build functions of the three-quadrant method.In this paper, in-plane nail-sheet joints were created by multi-plate extrusion, a plastic joining method that is an alternative to traditional mechanical joining methods. Nail forming, nail cutting, nail-sheet joining and optional assembling are combined in a single press stroke in multi-plate extrusion, which can be divided into three processing periods that includes two separations. Practical experiments were performed in which compressive forces were dynamically measured at different extrusion depths. An axisymmetric model was created to simulate the process, and its results were compared with the experimental results, where both separation actions were presented. The three-quadrant method was used to estimate the exceeded length of the nail, in which an irrelevant term was required to be added to make up a four-term system which is able to create correspondence to a coordinate system with four quadrants.

Sheet-bulk metal forming is an important manufacturing process for the production of parts with three-dimensional features on a thick plate using a typical local thickening process. The process of boss extrusion is usually applied to study the filling ability by measuring the boss height. In this paper, multi-plate extrusion process is examined as an alternative to the boss extrusion process. Based on boss extrusion, multi-plate extrusion was demonstrated using three groups of experiments in which parts on the thick plate with a much higher boss were produced from sheet metal via the multi-plate method and tested for strength. A partition of the process into three periods is proposed and demonstrated empirically, during which it is shown that the key period in boss extrusion is an efficient flowing period and that extending the flowing period can aid in boss growth. The law developed may also be applied to other local thickening processes.Highlights► Two individual billets are connected by a new process without any joining or gluing. ► Three periods’ partition is made in multi-plate extrusion. ► Force and boss height grows in completely different laws in three periods. ► Period II's extension will benefit boss growing in the new process.

To improve the forging process of spur gear, the metal flow rule is investigated in detail, and a hypothesis of radial rigid-parallel-motive (RPM) flow mode is given. Based on the RPM mode a novel specific gear forging technology is put forward by introduced upend forging process and constrained divided-flow technique. Firstly, finite element method is used to simulate the upend forging pre-forming and RPM finish forging, and equivalent stress field and load-stroke curve are investigated. Secondly, a corresponding experiment is carried out with pure lead to validate the numerical simulation. Thirdly, the peak value of conventional forging process is also simulated and is used to compare with the novel forging process, and the result shows that the forming force decreases significantly, about 35%. Finally, the effect on forming load of two key process parameters (the height of gear tooth after pre-forming and friction factor) is analyzed, and the superiority of the novel forging process is further proved.

Sheet bulk metal forming processes have been widely developed to the facilitate manufacture of complicated 3D parts. However, there is still not enough know-how available. In this paper, as one of the typical sheet bulk metal forming processes, the sheet metal extrusion process was studied. A reasonable finite element method (FEM) model of sheet metal extrusion process taking the influence of flow-stress curve with wide range of plastic strain and ductile damage into consideration was established and simulated by an arbitrary Lagrangian-Eulerian (ALE) FEM implemented in MSC. Marc. Validated by comparing the results with experiment, some phenomenological characteristics, such as metal flow behavior, shrinkage cavity, and the influence of different combinations of diameter of punch, diameter of extrusion outlet, and diameter of pre-punched hole were analyzed and concluded, which can be used as theoretical fundamental for the design of the sheet metal extrusion process.

Preform design for shell nosing product without machining the inner surface after forming is an experience-extensive work. Generally, the initial design needs to be modified and simulated consequently to get proper preform and nosing die, and the iterative process is time consuming. This paper puts forward a new approach, in which the suitable initial design can be obtained by knowledge-based intelligent technology and the optimal design can be acquired by finite element method (FEM) based geometrical modification. With the CAX object model as the bridge of CAD and CAE, the CAD model with simulation knowledge can be transferred into CAE automatically, and the CAE result can be automatically utilized as well. Based on the comparison between the simulated shape and the desired shape, the dissatisfactory area will be modified. A new simulation and modification process will be carried out based on the modified design. The process is repeated iteratively to get the optimal design. This approach utilizes the commercial CAD and CAE software, without the need of complex back-forward FEM procedures. Based on the new approach, an in-home intelligent shell nosing design and optimization system is developed, and a case study proves that this system can reach a reasonable design efficiently.

In order to accurately simulate the fine-blanking process, a suitable ductile fracture is significant. So an evaluation strategy based on experimental and corresponding simulation results of tensile, compression, torsion and fine-blanking test is designed to evaluate five typical ductile fracture criteria, which are widely-used in metal forming process. The stress triaxiality and ductile damage of each test specimen are analyzed. The results show that none of these five criteria is sufficient for all tests. Furthermore, an improved fracture criterion based on Rice and Tracey model, taking the influence of both volume change and shape change of voids into account, is proposed. The characterization of this model for fine-blanking process is easily done by the tensile test and the prediction result shows good.

Two series of experiments were designed and carried out to evaluate the performance of the selected ductile fracture criterion, of which one is the experiments under monotonic loading conditions and the other is the experiments under non-proportional loading conditions. Combined with parallel numerical simulations, the experiments under monotonic loading conditions were utilized to identify the parameters of the fracture criterion with two calibration methods, a conditional one applying several experiments to calculate material constants and an optimization one of surface fitting. The prediction accuracy of fracture related state variables by using the ductile fracture criterion with different calibration methods in regard of the experimental results were estimated. It could be seen that the calibrated L-H fracture criterion via both calibration methods could be qualified for the evaluation of damage evolution in the experiments under monotonic loading conditions. The addition of pre-torsion on the tension test could shift the fracture initiation point from the center to the outside edge. While for the cases under compression-torsion loading conditions, the situation is not consistent due to the cut-off value of stress traxiality used in L-H fracture criterion. With the increase of the pre-loading amount, the prediction accuracy of the identified fracture criterion deteriorates, which is probably caused by the adoption of invariant model parameters or the error of numerical simulation of strain hardening response based on the assumption of isotropic hardening.

•A new measuring method (RCT-IB) of friction factor for bulk forming is proposed.•The geometry is designed and the dimension change can be measured more precisely.•Easily and precisely measured dimension help to reach accurate friction factor.•The unique calibration curves of RCT-IB is constructed and analyzed in detail.•Friction factors of 4 different lubricating conditions are measured successfully.To overcome the disadvantage of the bulging effect due to non-uniform deformation in dimension measurement of the conventional ring compression test (RCT), a new measuring method for the friction factor called ring compression test with inner boss (RCT-IB) was proposed. The compression behavior of the ring with an inner boss was investigated and results showed that the change of inner boss was sensitive to friction. The non-concave profile of inner boss allows the dimensional changes to be easily and precisely measured. The calibration curves of RCT-IB were constructed and compared with those of RCT showing similar level of sensitivities at most friction conditions. The RCT-IB method was successfully used to measure the friction factors under four different lubricating conditions.