Stress Evaluation in the Blank Critical Region During Extrusion of the Pipe Blank into the Hole

The study assessed the stress state of the pipe blank in the process of extrusion into the hole. A finite element formulation of the research problem with the setting of boundary conditions in displacements and surface loading conditions is presented. The calculation of the workpiece was carried out in an elastic formulation using the Nastran engineering analysis application. The assessment of the stress state in the critical region is presented in two approximations with a thickening of the grid in the stress focus area. Based on the results of the distribution of equivalent stresses, an assessment of the unevenness of the stressed state of the workpiece was carried out. The presented study is important because it allows us to predict the appearance of defects in the process of forming a pipe billet during extrusion into a hole, to evaluate the power loading mode.

АNALYSIS OF THE STRESS STATE OF CYLINDRICAL ARTICLES DURING THE CRIMPING ELEMENT OF A PIPE BLANK WITH WALL THINNING

Обжим пустотелых цилиндрических заготовок позволяет получать изделия с различными сечениями в ортогональном направлении по высоте. Данная операция является весьма производительной и позволяет получать различного рода соединительные элементы. В статье рассмотрена операция обжима и одновременного утонения стенки изделия на выходе из очага деформации. В процессе обжима происходит набор толщины заготовки в деформируемой части. Ввиду этого в очаге деформации возможно возникновение значительных сжимающих и растягивающих напряжений. Возникают значительные неравномерности напряжений в детали, что плохо сказывается на их качестве. Поэтому актуален вопрос подбора параметров процесса, обеспечивающих наилучшее напряжённое состояние изделий. В статье выполнено исследование напряженного состояния в изделиях при совмещенном процессе обжима с утонением стенки. Установлены зоны с максимальными по значениям сжимающими и растягивающими напряжениями в детали. Установлено влияние коэффициента утонения стенки изделия, коэффициента обжима, контактного трения и угла конусности матрицы на сжимающие и растягивающие напряжения. Получены регрессионные зависимости для определения растягивающих и сжимающих напряжений. Это позволит установить приблизительные значения напряжений при разных ключевых технологических параметрах процесса.

Numerical Analysis of Temperature Fields and Thermal Stress Fields in Heating Process of Large-Diameter Seamless Steel Pipe Blanks

In the piercing process of large-diameter seamless steel pipe blanks after heating, severe lateral cracks easily occur on the surface of pierced pipe blanks owing to the effects of the large temperature difference and thermal stress during the heating phase, influencing the finished product ratio and the safety and stability of use. Therefore, obtaining pipe blanks with uniform temperature distributions and low thermal stress peaks is the basis for the quality assurance of seamless pipes. In this paper, a study was conducted with large-diameter TP321 seamless pipe blanks with an example. The heating process of the pipe blank was investigated from two perspectives, temperature fields and thermal stress fields. Moreover, the effects of heating rate, initial furnace temperature, and hot-charging temperature were quantitatively analyzed. It was found that the peaks of the temperature difference and thermal stress both occurred at the early stage of heating. The temperature field and thermal stress distribution of the pipe blank gradually changed during heating. At the initial stage of heating, the temperature at the outer diameter edge was the highest, and the maximum thermal stress zones were concentrated on the inner hole edge and external surface. At the late stage of heating, the highest temperature zone and the maximum thermal stress zone were both focused on the inner hole surface. Lower initial furnace temperature and higher hot-charging temperature were more conducive to decreasing the maximum temperature difference and peak thermal stress, while the changes in heating rate had insignificant effects.

Simulation of vibration piercing of pipe blank at press

In some cases, the processes of piercing or expanding pipe blanks involve the use of high-frequency active vibrations. However, due to insufficient knowledge, these processes are not widely used in the practice of seamless pipes production. In particular, the problems of increasing the efficiency of the processes of piercing or expanding a pipe blank at a piercing press using high-frequency vibrations are being solved without proper research and, as a rule, by experiments. The elaboration of modern technological processes for the production of seamless pipes using high-frequency vibrations is directly related to the choice of rational modes of metal deformation and the prediction resistance indicators of technological tools and the reliability of equipment operation. The creation of a mathematical model of the process of vibrating piercing (expansion) of an axisymmetric pipe blank at a piercing press of a pipe press facility is an actual task. A calculation scheme for the process of piercing a pipe plank has been elaborated. A dependence was obtained characterizing the speed of front of plastic deformation propagation on the speed of penetration of a vibrated axisymmetric mandrel into the pipe workpiece being pierced. The dynamic characteristics of the occurrence of wave phenomena in the metal being pierced under the influence of a vibrated tool have been determined, which significantly complements the previously known ideas about the stress-strain state of the metal in the deformation zone. The deformation fields in the zones of the disturbed region of the deformation zone were established, taking into account the high-frequency vibrations of the technological tool. It has been established that the choice of rational parameters (amplitude-frequency characteristics) of the vibration piercing process of a pipe blank results in significant increase in the efficiency of the process, the durability of the technological tool and the quality of the pierced blanks.

Microstructures and Properties of Spinning for Silicon Carbide Particle Reinforced Aluminum Composite

In this paper, 15% SiCp/2009A1 composites were subjected to multi-pass hot spinning experiments. The principle of the microstructure and properties of the materials was studied with the increase of thinning rate. The microstructures, interfaces, precipitates and their properties of the tube, which were in the states of spinning, spinning and solution heat treatment were analyzed and discussed.The research shows that it is possible to prepare spinning pipe with good shape and smooth surface by taking use of the spinning process of this paper. During the power spinning process, the force of the rotary wheel to the pipe causes the billet to produce two-way deformation, and the axial and tangential grains are obviously elongated and the flow line is formed.There are mainly Al, SiC, CuAl2and Mg2Si phases in the tube, and the spinning deformation does not change the phase composition of the composites, but the SiC distribution can be more uniform and the oxide film on the surface of the aluminum particles is broken, as a result that the oxygen element will cluster at the interface.The solution heat treatment after spinning can greatly improve the yield strength and tensile strength of SiC/Al composites with a slight decrease in plasticity. The spinning process used in this paper can not only form a composite pipe with a smaller diameter and thinner wall thickness, but it can still be applied when the diameter of the pipe blank becomes larger and the wall thickness becomes thicker.Through the research on spinning process and microstructure, the feasibility of spinning process for preparing aluminum matrix composites pipes was explored, which provided technical and theoretical support for the preparation and processing of Particulate reinforced aluminum matrix composites (PRAMCs) pipes for aviation and aerospace applications.