Deformation Of Workpiece Research Articles

Formation of a mesh of spiral wedge protrusions on the inner surface of a steel shell by local plastic deformation

Manufacture of shells with a mesh of rhombic ribbings is a complex technological task, for the solution of which it is possible to use cutting operations, electrochemical methods, laser technologies, however, all of the above methods are ineffective. Methods of processing metals by forming are also used, among which the most common is reduction. An alternative method is the local deformation of a cylindrical workpiece with a tool with a working mandrel, on which there are spiral wedge protrusions. For this, a device is used in which the working mandrel with protrusions has the ability to move along the formed cylindrical shell and make a rotational movement around an axis. Rifling with multi-start spiral riffles can be carried out using a working mandrel with a different shape of the lead-in geometry of spiral wedge protrusions and their height on its working surface, therefore, the substantiation of the shape and size of the spiral wedge protrusions is an important and urgent task.The work was carried out within the framework of the grant of the Government of the Tula region in the field of science and technology No. DS / 167.

Numerical Study of Stress-Strain State of Workpiece in Contact Problem of Surface Mandrel Drilling

In recent years, the economic factor has played an increasingly important role in the selection of technologies for manufacturing machine parts with specified values of normalized parameters of geometric accuracy and quality of working surfaces. As applied to surface plastic deformation processes, this is noticeably manifested in the search for effective friction control methods in the “tool – workpiece” pair, which ultimately determines the distribution pattern and the magnitude of stresses and strains in the workpiece and the tool. It is not possible to obtain a rigorous analytical solution to the problem of establishing a connection between surface conditions, friction, and the stress-strain state of the contacted bodies. In this regard, the construction of mathematical models comes to the fore, the solution of which is possible by numerical methods. The paper presents the results of a numerical study (computational experiment) of a finite-element model of workpiece deformation under various conditions of contact interaction and friction by one of the methods of surface plastic deformation – surface mandrel drilling. The friction coefficient has been chosen as the criterion for assessing the conditions of contact interaction and friction. It is shown that a change in the friction coefficient in the process of surface mandrel has no noticeable effect on the formation of a stress field in the deformable workpiece both in the axial, and in the radial and circumferential directions. At the same time, with an increase in the value of the friction coefficient in the “tool – workpiece” pair and with the associated increase in the force of mechanical resistance to deformation of the workpiece, their growth is observed. A computational experiment has confirmed the presence of non-contact deformations of the workpiece and tool during surface mandrel drilling, as well as as a decrease in the value of residual deformations in the workpiece with a decrease in the coefficient of friction. Balance assessment of contact surface displacements in the workpiece (the inner surface of the hole to be machined) and the tool (mandrel) has shown that the deformations of the tool in the elastic region can lead to a significant decrease in the real tightness of surface mandrel drilling.

Use of the dactyling effect to obtain a compositional structure in white iron during forming

Cast iron is traditionally used as a casting alloy for the manufacture of products operating in various industries. White cast irons are used for parts with high wear resistance due to the presence in their composite structure a large number of eutectic carbides, which are located around the dendrites of the solid solution and provide a high level of hardness and strength. The location of eutectic colonies in the form of a mesh causes a low level of ability to withstand impact loading, facilitates the chipping of individual “grains” in abrasive wear and limits the use of these alloys. The use of forming process allows us to grind the eutectic mesh in the structure of white cast iron, which significantly improves the complex of mechanical and operational properties. But the low level of plasticity of white cast iron in the cast state does not allow widespread using white cast iron plastic deformation. The possibility of hot deformation of cast iron workpieces with different speeds and schemes was investigated. The deformation rate of alloys was varied due to the use of different equipment for mass and small-series production using different types of metal forming.

Numerical and experimental verification of an iterative coupling method for analyzing the Lorentz-force-driven sheet metal stamping process

The Lorentz-force-driven stamping process is a newly developed forming process, which combines the advantages of the quasi-static stamping and electromagnetic forming to a certain extent. It involves complex physical problems such as strong electro-magneto-mechanical interactions and considerable deformation. Therefore, it is still a challenge to accurately predict the electromagnetic parameters (coil current and Lorentz force, etc.) and workpiece deformation (forming height and material flow) during the stamping process for different forming conditions. To solve this problem, taking the cylindrical cup forming of 5052-O aluminum alloy sheet metal as an example, a numerical method based on the iterative calculation of a circuit-electromagnetic model and an electromagnetic-mechanical model is developed and systematically validated. Numerical tests show that, compared with the non-iterative model, the proposed iterative mode can significantly improve the simulation accuracy for different forming conditions (such as varied discharge voltages and initial gaps between the coil and the punch). It has been confirmed that the iterative procedure can well consider the effect of the increased distance between the coil and the punch on the calculations of electromagnetic and mechanical parameters. Furthermore, numerical and experimental investigations for a Lorentz-force-driven stamping system using a discharge circuit with an additional crowbar branch are carried out, showing the simulation data of discharge current and workpiece deformation agree well with that of experiment measurement. This confirms the applicability of the proposed method to different discharge circuits.

Improvement of the deformation technology in relief rolls by asymmetric rolling realization

Among many methods of improving metal products quality, metal forming methods, applying intensive plastic deformation, take a special place. Results of a study on perfection technology of plate workpieces deforming in relief rolls presented. Application of the technology ensures receiving by a workpiece additional level of shear deformation in transverse direction due to special design features of roll profile. Besides due to various rolls rotation speeds, state of kinematic asymmetry arises, which results in additional level of shear deformation in longitudinal direction. It was revealed by Deform program simulation of metal deformed state that the workpiece is not bent practically after getting out of the relief rolls, keeping its horizontal path of motion. It was shown that the effect is reached due to relief section of the workpiece, where micro-ridges and micro-cavities are formed acting as reinforcing ribs. At that the level of deformation increases by nearly 20% comparing with symmetric rolling in relief rolls. Analysis of state of stress by calculation of Lode‒Nadai coefficient showed that in the central zone of the workpiece mainly compressing stresses are formed, reaching maximum values in the area of comb; at the inclined sections due to action of shear deformations the level of compression is decreased. The surface zones have similar stress distribution comparing with the central one ‒ in the areas of combs compressive stresses are formed, which are considerably lower comparing with those of central zone. On the inclined sections the value of Lode‒Nadai coefficient tends to zero, which gives evidence of intensification of shear deformation in these areas. Analysis of workpiece deformation after rolling in the relief rolls and having next two passes in smooth rolls showed that the proposed variant of rolling technology enables to obtain at the exit a smooth workpiece with insignificant wedging out. Since initially the technology was elaborated for multi-stand mills, these wedging outs will be completely deleted during further passes where the workpiece will have definite reduction by thickness.

ДОСЛІДЖЕННЯ ПІДШИПНИКІВ РІДИННОГО ТЕРТЯ РОБОЧИХ КЛІТЕЙ 630 СТАНУ 550

Аналіз експлуатації підшипників рідинного тертя (ПРТ) станів 630 показав, що втрати мастила на клітях 630 досягають до 10 тонн за рік. Причиною цього є недосконалість конструкції ущільнення, а це в свою чергу не забезпечує необхідний режим змащування ПРТ і призводить до високоінтенсивного зносу поверхонь втулки та вкладиша підшипника. Що призводить до виходу з ладу ПРТ раніше встановленого строку заміни втулки та вкладиша. Метою дослідження є визначення навантаженості ПРТ шляхом математичного моделювання для визначення енерго-силових параметрів прокатки на прикладі швелеру №14, визначення коефіцієнту тертя, дослідження процесу зносу поверхні втулки та вкладиша ПРТ та надання рекомендації, щодо можливого шляху удосконалення ущільнення ПРТ клітей 630. Розрахунок піддвердив перехід до граничного тертя при зносі до радіального зазору в 4 мм, що спостерігалось при експлуатації ПРТ. Запропонована удосконалена конструкція ущільнень з використанням V-подібних манжет.

Development of a New Compliant Active-Force Support System

In this article, we propose a novel compliant active-force support system (CAFS) to provide force sensing and control capabilities in support of thin-walled parts for precision machining. The CAFS is designed with a dual-feedback parallel mechanism (DFPM) driven by a piezoelectric actuator. Through displacement amplification, the DFPM enables CAFS to provide an active force support for compliant machining. Based on the input and output feedbacks of the DFPM, the contact force between CAFS and workpiece can be derived by the built force-sensing model, and the deformation of workpiece can be measured. Meanwhile, with the obtained force as feedback, the support force can be controlled by adjusting the displacement of piezoelectric actuator in real time. Without needing additional force-sensing components, a fast dynamic response can hence be achieved by the proposed CAFS. The performance of the CAFS is predicted by an established analytical model, and validated by finite-element analysis and experiment. The results show that the developed CAFS prototype with a size of 56 × 56 × 93 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> can provide a 220 N support force with a resolution of 0.35 N (0.16%). The first resonant frequency of the developed CAFS prototype can reach 4844 Hz. Closed-loop experiments further demonstrate that the proposed CAFS is capable of regulating the support force in a fast and accurate manner.

A new localization theory of thin-walled feature machining for near-net-shape part

Localization is usually required for the near-net-shape billet before machining. In conventional research, the to-be-cut features only need to be transformed into the middle of billet to leave the to-be-cut material. However, if it is applied on the thin-walled feature, the machined feature would easily be beyond tolerance due to cutting deformation. Thus, conventional localization principle is not best for the thin-walled feature before the machining. To reduce reject rate for the near-net-shape billet, a new localization theory for the thin-walled features is investigated in this article. The workpiece’s stiffness and cutting force distribution are considered in thin-walled feature localization. By the adjustment of the to-be-cut material, the cutting force is optimized to control the deformation of workpiece. Base on this principle, the cutting deformation is introduced into the constraint conditions of the localization optimization. Thus, the deviation of machined feature is prevented to be outside of tolerance as much as possible. In this work, a practical plate machining is rendered to verify this approach. It lays a theoretical foundation of thin-walled feature localization and is an effective solution for improving qualification rate of the near-net-shape part in industry.

An improved material point method for coining simulation

Extremely small time step caused by large deformation in coining process significantly increases computational time in dynamic explicit finite element method (FEM). Furthermore, negative volumes of distortion elements in the rim of coin lead to abnormal termination of simulation. In order to overcome these problems, dynamic explicit material point method (MPM) is employed for coining process. However, most of the point-to-point contact algorithms in MPM cause fake contacting detection. In addition, abundant tiny patterns on die surfaces put forward high requirement for the contact algorithm to calculate the normal vectors. A point-to-segment based contact algorithm is proposed to obtain accurate normal vectors at real physical contact point and embedded into the framework of modified update stress last (MUSL) for simulating coining. Amount of data storage and computations are reduced since the background domain only contains the deformable workpiece and one velocity field is required. The improved MPM is applied to predict insufficient filling during minting, and its performance is validated by experimental results.

Simulation Analysis of the Electromagnetic Force Distribution and Formability Parameters for Sheet Metal Electromagnetic Bulging Using a New Magnetic Field Shaper

While electromagnetic forming of aluminum alloy sheet has gained several advantages, the uneven radial deformation of the sheet is still one of the main drawback of this technology that calls for reliable and cost-effective solution. Aiming at this point, this paper presents an electromagnetic bulging system equipped with a new magnetic field shaper placed between the driving coil and the object sheet to modulate the distribution of the induced eddy current in the sheet, and hence regulating the distribution of the electromagnetic force to achieve more uniform deformation. A finite element electromagnetic-structure 2D coupling model simulating this process is developed and the effects of workpiece geometry and deformation speed on the circuit, magnetic field and structure field are considered. The coupling between the electric circuit and magnetic field; magnetic field and workpiece deformation is realized to simulate the actual system of thin plate electromagnetic bulging. The performance of the proposed system is compared with that of the traditional system through investigating the profiles of the induced eddy current, electromagnetic force and forming effect. Simulation results show that the uniformity of sheet metal forming is improved by using the proposed magnetic field shaper, and the maximum uniform deformation area is increasing from 32.1 mm to 73.8 mm, which stimulates more industrial applications of sheet metal electromagnetic forming.

On-machine ultrasonic thickness measurement and compensation of thin-walled parts machining on a CNC lathe

Aero-engine casing manufacturing requires considerable processing accuracy. In the aero casing turning process, the entire profile needs to be machined in one process to ensure the surface smoothness and control the remained wall thickness. However, the wall thickness error will be affected by tool wear and workpiece deformation in turning. This paper proposed a non-contact ultrasonic measurement system to measure the wall thickness and compensate the wall thickness error. The wall thickness of the aero casing is measured on the lathe after each turning process and compensated in the next path. Experiments validate the effectiveness of the developed method.

Integrated force interaction simulation model for milling strategy optimization of thin-walled Blisk blade machining

Complex shaped thin-walled blades that are extensively used in jet engines or stream turbines are very difficult to machine due to low rigidity of the blades, typically limited space between the blades and strict requirements on the surface quality and accuracy. The paper focuses on multi-axis machining of thin-walled and complex shaped Blisk blades made of aluminium alloys. The resulting surface quality and accuracy is mainly affected by the risk of elevated vibration occurrence, both forced and self-excited, and static deflections between the compliant tool and workpiece. An innovative integration of the transformed FE model of the blade into virtual machining simulation has been proposed, allowing to effectively solve the complex optimization task considering both the criterion of stable machining condition and static deflections as well. When choosing a machining strategy and cutting conditions, there are many variables that fundamentally affect the process. These variables are not easy to choose correctly the first time, so it is advisable to choose to use a simulation model in production preparation. The proposed simulation model allowed to effectively optimize the process parameters to keep the machining process stable and the static deformation of tool and workpiece under a defined level. The proposed model and optimization strategy was validated on a thin-walled blade machining. At the top part of the blade, the surface roughness decreased from 1.6 Ra to 0.84 Ra, and the maximum deviations from the reference model were reduced from 0.18 mm to 0.08 mm.

Plastic deformation of workpiece during unloading in plate compression

Deformation behaviour during loading and unloading is studied in compression of an aluminium plate with a high ratio between the diameter and the thickness by a DLC coated die. A compressed plate becomes thinner during unloading after the plate is compressed to a larger reduction in thickness in loading. The plastic deformation of a compressed plate during unloading is confirmed by measuring the increase of the plate diameter during unloading. The optimum profile of a die crown approaches to the reverse shape of the elastic deflection of a flat die at the loading stroke end with increasing reduction in thickness.

Modelling the Geometrical Accuracy for Different Part Geometries and Process Parameters when Broaching Fir-Tree Slots in Turbine Disks

Constructive measures in the design of aircraft engines aiming for CO2 and NOx emission reduction result in miniaturization of the components, e.g. the rotating turbine disks. The resulting filigree structures determine a reduction of the resistance against elastic workpiece deformations during the machining process. This leads to increasing demands on the cutting process to maintain the required form and position tolerances. In turbine disks, fir-tree slots as the fixing for the turbine blades are classified as safety-critical components. Currently, the profiled slots are manufactured by broaching. In order to guarantee the required component quality of the resulting fir-tree structure, it is necessary to examine the tool design systematically. By using FE simulations, it is possible to predict geometrical deviations after broaching and to perform counter measurements in tool design.In this paper, an innovative approach is presented, which combines an empirical-analytical cutting force model and numerical FE simulations to model the elastic deformations during the cutting process. Therefore, empirical cutting force information are used as input data for the dynamic FE simulations. The results are then analyzed regarding the achievable form and position tolerances when broaching profile grooves. This paper presents a parameter study on workpiece and process parameters and an evaluation of their impact regarding the geometrical accuracy in broaching.

Determination of the process damping coefficient using plain cutting tests

Process damping is an important effect to avoid chatter vibrations. It is commonly modeled as a force, which can be calculated by multiplying the indented workpiece volume with a process damping coefficient. However, the coefficient strongly varies depending on the chosen determination method. In this paper, the coefficient is determined by planing tests with a chamfered tool with negative chamfer angle and varying chamfer length (62- 275 µm). Thereby, the workpiece is indented with a defined volume. Additionally, microstructure images are created to identify workpiece deformations. The results show decreasing coefficients with increasing indentation volume due to increasing plastic deformation.

Elucidation of Mechanism Underlying Workpiece Jump in Hammer Forging

During the process of drop hammer forging, workpieces sometimes jump after strikes. The present research investigates the mechanism of the workpiece jump by means of experiments and numerical simulations. In the experiments, workpieces were struck by vertical symmetrical flat dies or vertical asymmetrical dies. A high-speed camera was used to measure the workpiece deformation, the position of workpieces during jumping and the position of the dies. Strain of lower dies and structures of the hammer were measured by strain gauges. Vibration of the antirattler under the hammer, elastic vibration of lower dies and structures of the hammer, and contact area between workpieces and dies were analyzed by numerical simulations. The results indicate that workpieces jump by adhesive force between workpieces and dies, and by elastic vibration of lower dies and structures of the hammer.

Особенности локализации деформации при термосиловой обработке

The paper considers the issues of ensuring the uniformity of strain of axisymmetric long-dimensional samples during thermal force processing (TFP), which is the simultaneous application of force and temperature effects for comprehensive improvement of geometric characteristics and physical and mechanical parameters of the workpiece material. This technology is used at various stages of technological processes of parts manufacturing, but its main task is to ensure the axis straightness and the specified distribution of residual technological stresses at the procuring stage. The disadvantage of TFP is that the axial deformation proceeds nonuniformly along the workpiece axis. The core process parameter is the deformation, the control of which is a key factor ensuring the TFP efficiency. The authors studied the plastic strain distribution over the sections of long-length workpieces with different deformation degrees. The study involved the assessment of strain uniformity over the workpiece sections, taking into account the stage of the stress-strain relation at the end of the loading cycle. Based on the concepts of plastic deformation as an auto-wave process, the authors selected the range of technological modes corresponding to the most uniform strain distribution along the workpiece axis with complete processing of the entire workpiece volume. This range corresponds to the stage of parabolic hardening of the plastic flow curve with the formation of the maximum number of stationary zones of localized plasticity. Rheological modeling allows identifying the control points that specify the boundaries of the plastic flow curve stages at various loading parameters, including temperature. To improve the reliability of determining the actual deformation under production conditions, the authors proposed modernizing the TFP process monitoring method by fixing the deformation on a limited workpiece section using the optical technique. The statistical analysis of the strain distribution over the sections for the samples confirms the correctness of this approach. The application of the proposed control method will ensure the most uniform distribution of plastic deformation due to the reliable enter of the workpiece deformation to the range of strain values corresponding to the stage of parabolic hardening of the plastic flow curve.

An adaptive fixture for suppress vibrations and measuring workpiece deformation of thin-walled casings

Thin-walled casings are key components in aerospace engines. Due to the poor rigidity, workpiece vibration and deformation become the main factors to limit cutting efficiency. Auxiliary support is usually used to increase the rigidity of the workpiece. This paper proposes a novel adaptive auxiliary fixture, which integrates vibration suppression and deformation measurement functions. The fixture provides an adaptive support force to increase the local stiffness and damping by using air cylinders. The integrated displacement sensors measure the deformation of the workpiece during and after machining. Cutting experiment verifies the effectiveness of the fixture in vibration suppressing and deformation measurements.

Experimental Study of the Dynamic Behavior of Thin-Walled Tubular Workpieces in Turning Cutting Process

Nowadays, industrialists, especially those in the automobile and aeronautical transport fields, seek to lighten the weight of different product components by developing new materials lighter than those usually used or by replacing some massive parts with thin-walled hollow parts. This lightening operation is carried out in order to reduce the energy consumption of the manufactured products while guaranteeing optimal mechanical properties of the components and increasing quality and productivity. To achieve these objectives, some research centers have focused their work on the development and characterization of new light materials and some other centers have focused their work on the analysis and understanding of the encountered problems during the machining operation of thin-walled parts. Indeed, various studies have shown that the machining process of thin-walled parts differs from that of rigid parts. This difference comes from the dynamic behavior of the thin-walled parts which is different from that of the massive parts. Therefore, the purpose of this paper is to first highlight some of these problems through the measurement and analysis of the cutting forces and vibrations of tubular parts with different thicknesses in AU4G1T351 aluminum alloy during the turning process. The experimental results highlight that the dynamic behavior of turning process is governed by large radial deformations of the thin-walled workpieces and the influence of this behavior on the variations of the chip thickness and cutting forces is assumed to be preponderant. The second objective is to provide manufacturers with a practical solution to the encountered vibration problems by improving the structural damping of thin-walled parts by additional damping. It is found that the additional structural damping increases the stability of the cutting process and reduces considerably the vibrations amplitudes.

Feed Rate Variation Strategy for Semi-Conical Shell Workpiece in Ball Head End Milling Process

The semi-conical shell workpiece is a special kind of thin-wall part that is commonly used in aerospace and mold industries. Due to the special stiffness distribution and weak rigidity for the area with a large radius, the machining quality of the semi-conical shell is sensitive to both cutting force and vibration. Conventionally, constant conservative machining parameters are chosen to ensure the workpiece deformation and surface quality, which will reduce the machining efficiency. Based on the cutting force and vibration response simulation of the whole milling process. A feed rate variation strategy is proposed for the ball head end milling process of the semi-conical shell workpiece. The cutting force, dynamic performance and stability prediction are obtained considering the shape and boundary conditions of the workpiece and the contour tool path of the milling process. Variable feed rate is used in the milling simulation to find the harmony between machining quality and efficiency. User-defined vibration amplitude and another user-defined cutting force threshold are used to find the optimal feed rate for each simulation segment. Both continuous and discrete feed rate variation strategies are proposed, and the improved discrete feed rate variation is applied in the milling experiment. About 25% of the consumed time is saved with almost the same machining quality by the experimental results.