Because of the complex constraint effects among layers in multi-layered metallic bellows hydroforming,the stress concentration and defects such as wrinkling and fracture may easily occur.It is a key to reveal the defo...Because of the complex constraint effects among layers in multi-layered metallic bellows hydroforming,the stress concentration and defects such as wrinkling and fracture may easily occur.It is a key to reveal the deformation behaviors in order to obtain a sound product.Based on the ABAQUS platform,a 3 D-FE model of the four-layered U-shaped metallic bellow hydroforming process is established and validated by experiment.The stress and strain distributions,wall thickness variations and bellow profiles of each layer in the whole process,including bulging,folding and springback stages,are studied.Then deformation behaviors of bellows under different forming conditions are discussed.It is found that the wall thinning degrees of different layer vary after hydroforming,and is the largest for the inner layer and smallest for the outer layer.At folding stage,the wall thinning degree of the crown point increases lineally,and the difference among layers increases as the process going.The displacements of the crown point decrease from the inner layer to the outer layer.After springback,the U-shaped cross section changes to a tongue shape,the change of convolution pitch is much larger than the change of convolution height,and the springback values of the inner layer are smaller than the outer layer.An increase in the internal pressure and die spacing cause the maximum wall thinning degree and springback increase.With changing of process parameters,bellows with deep convolution are easily encountered wall thinning during hydroforming and convolution distortion after springback.This research is helpful for precision forming of multi-layered bellows.展开更多
For simplified processing, micro parts are handled as linked parts. The length of the frame structure of these linked parts can change during a multi-stage production process especially when forming is included. Hence...For simplified processing, micro parts are handled as linked parts. The length of the frame structure of these linked parts can change during a multi-stage production process especially when forming is included. Hence, the positions of individual parts are not constant within the linkage. An individual referencing of the parts becomes necessary in each production step. In this paper, a visual high-speed on-line part referencing system is presented and analyzed. Especially, the trade-off between the highest possible feed velocity and the demand of high accuracy in micro production is taken into account. In addition to this general characterization application related testing with stepwise positioning is performed.展开更多
The efficient development of new materials with defined properties requires fast methods of testing low volumes of material,such as a high-throughput investigation of spherical metallic micro samples with varying comp...The efficient development of new materials with defined properties requires fast methods of testing low volumes of material,such as a high-throughput investigation of spherical metallic micro samples with varying compositions and structuring treatments.A classical material testing method for macro samples,the tensile test cannot be employed for analyzing the mechanical properties of spherical samples with diameters below 1 mm since there are currently no methods for holding and stretching them.A combination between the incremental electrohydraulic extrusion as stress actuation unit and the speckle photography as strain measuring method is presented for obtaining the required mechanical characteristics.Positive longitudinal strain is generated at stepwise extrusion through<1 mm wide forming channels using a liquid punch and the deformation is observed in situ after each forming step at the interface between the micro sample and a transparent window integrated into the forming die.The occurring local strain fields with a lateral extension down to 100 pm and high gradients require displacement measurements with high lateral resolution over a large range of local dislocations between 0.1 and>10 μm.It is unknown,whether the speckle strain measuring method is able to provide the necessary low uncertainty for the required resolution in the whole measuring range.Therefore,theoretical and experimental investigations of the deformation measurability using the speckle correlation method are presented,showing that local displacements up to 10 μm can be measured with a spatial resolution between 3 and 10μm depending on the displacement size.The dominant effect influencing the measurement uncertainty for displacements at this high spatial resolution is the speckle noise,resulting into measurement uncertainties of less than 100 μm.Hence,speckle photography is shown to be applicable for tensile test on micro samples.展开更多
基金the funds of the National Natural Science Foundation of China(No.51875456)the Natural Science Basic Research Plan in Shaanxi Province of China(No.2019JM-450)+3 种基金the Young Talent fund of University Association for Science and Technology in Shaanxi,China(No.20170518)the Key Laboratory of Advanced Manufacture Technology for Automobile Parts(Chongqing University of Technology),Ministry of Education(No.2018KLMT03)Materials Science and Engineering provincial-level superior discipline funding project of Xi'an Shiyou Universitythe Program for Young Innovative Research Team in Xi'an Shiyou University(No.2015QNKYCXTD02)。
文摘Because of the complex constraint effects among layers in multi-layered metallic bellows hydroforming,the stress concentration and defects such as wrinkling and fracture may easily occur.It is a key to reveal the deformation behaviors in order to obtain a sound product.Based on the ABAQUS platform,a 3 D-FE model of the four-layered U-shaped metallic bellow hydroforming process is established and validated by experiment.The stress and strain distributions,wall thickness variations and bellow profiles of each layer in the whole process,including bulging,folding and springback stages,are studied.Then deformation behaviors of bellows under different forming conditions are discussed.It is found that the wall thinning degrees of different layer vary after hydroforming,and is the largest for the inner layer and smallest for the outer layer.At folding stage,the wall thinning degree of the crown point increases lineally,and the difference among layers increases as the process going.The displacements of the crown point decrease from the inner layer to the outer layer.After springback,the U-shaped cross section changes to a tongue shape,the change of convolution pitch is much larger than the change of convolution height,and the springback values of the inner layer are smaller than the outer layer.An increase in the internal pressure and die spacing cause the maximum wall thinning degree and springback increase.With changing of process parameters,bellows with deep convolution are easily encountered wall thinning during hydroforming and convolution distortion after springback.This research is helpful for precision forming of multi-layered bellows.
文摘For simplified processing, micro parts are handled as linked parts. The length of the frame structure of these linked parts can change during a multi-stage production process especially when forming is included. Hence, the positions of individual parts are not constant within the linkage. An individual referencing of the parts becomes necessary in each production step. In this paper, a visual high-speed on-line part referencing system is presented and analyzed. Especially, the trade-off between the highest possible feed velocity and the demand of high accuracy in micro production is taken into account. In addition to this general characterization application related testing with stepwise positioning is performed.
基金This research is funded by Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)-project number 276397488-SFB 1232 and the support is gratefully acknowledged.
文摘The efficient development of new materials with defined properties requires fast methods of testing low volumes of material,such as a high-throughput investigation of spherical metallic micro samples with varying compositions and structuring treatments.A classical material testing method for macro samples,the tensile test cannot be employed for analyzing the mechanical properties of spherical samples with diameters below 1 mm since there are currently no methods for holding and stretching them.A combination between the incremental electrohydraulic extrusion as stress actuation unit and the speckle photography as strain measuring method is presented for obtaining the required mechanical characteristics.Positive longitudinal strain is generated at stepwise extrusion through<1 mm wide forming channels using a liquid punch and the deformation is observed in situ after each forming step at the interface between the micro sample and a transparent window integrated into the forming die.The occurring local strain fields with a lateral extension down to 100 pm and high gradients require displacement measurements with high lateral resolution over a large range of local dislocations between 0.1 and>10 μm.It is unknown,whether the speckle strain measuring method is able to provide the necessary low uncertainty for the required resolution in the whole measuring range.Therefore,theoretical and experimental investigations of the deformation measurability using the speckle correlation method are presented,showing that local displacements up to 10 μm can be measured with a spatial resolution between 3 and 10μm depending on the displacement size.The dominant effect influencing the measurement uncertainty for displacements at this high spatial resolution is the speckle noise,resulting into measurement uncertainties of less than 100 μm.Hence,speckle photography is shown to be applicable for tensile test on micro samples.
