Effect of the sector radius of a workpiece-deforming tool on the stress-strain state in the contact zone with a cylindrical surface

This paper aims to determine the effect of the sector radius of a workpiece-deforming tool on the stress-strain state in the center of elastoplastic deformation and residual stresses in the hardened zone of the surface layer of cylindrical workpieces. A mathematical model of local loading was constructed using the finite element method and AN-SYS software. This model was used to determine the values of temporary and residual stresses and deformations, as well as the depth of plastic zone, depending on the sector radius of the working tool. The simulation results showed that, under the same loading of a cylindrical surface, working tools with different sector radii create different maximum tempo-rary and residual stresses. An assessment of the stress state was carried out for situations when the surface layer of a product is treated by workpiece-deforming tools with a different shape of the working edge. It was shown that, compared to a flat tool, a decrease in the radius of the working sector from 125 to 25 mm leads to an increase in the maximum temporary and residual stresses by 1.2–1.5 times, while the plastic zone depth increases by 1.5–2.4 times. The use of a working tool with a flat surface for hardening a cylindrical workpiece ensures minimal temporary residual stresses, com-pared to those produced by a working tool with a curved surface. A decrease in the radius of the working sector leads to an increase in temporary residual stresses by 2–7%. The plastic zone depth ranges from 1.65 to 2.55 mm when chang-ing the sector radius of the working tool.

Experimental Study on Application of Tuned Mass Dampers for Chatter in Turning of a Thin-Walled Cylinder

Chatter is more likely to occur during the turning process of a thin-walled cylindrical workpiece owing to the low rigidity of such workpieces. Chatter causes intensive vibration, deterioration of the surface finish accuracy, tool damage, and tool wear. Tuned mass dampers (TMD) are usually applied as a passive damping technique to induce a large damping effect using a small mass. This study experimentally investigated the effect of the mounting arrangement and tuning parameters of the TMDs on the production of chatter during the turning process of a thin-walled cylinder, wherein multiple TMDs with extremely small mass ratios were attached to the rotating workpiece. The results of the cutting tests performed by varying the circumferential and axial mounting positions of the TMDs exhibited different characteristics of the chatter suppression effect. Conclusively, the TMDs could suppress the chatter generated by the vibration mode with circumferential nodes if they were mounted on the workpiece to avoid the coincidence of the circumferential arrangement with the pitch of the vibration nodes, regardless of the extremely small mass of the TMDs.

OPTIMUM WORKHOLDING CONDITIONS FOR PRECISION CYLINDRICAL GRINDING OPERATIONS

Grinding process is a very important process in machining industry being one of the most popular processes when high quality parts must be manufacture. Likewise, workholding is a critical issue on cylindrical grinding. The use of the driving dog is common when the workpiece is held between centers. However, one of the handicaps of this workholding is that the cylindrical workpiece cannot be ground along the complete length. In order to tackle this issue, in the present work the workpiece is held between centers avoiding the use of the driving dog. To this end, a methodology to obtain the grinding limit parameters that ensure that the transmitted torque is higher that the resistance torque is presented, being the aim of these tests is to avoid the sliding between the point and the workpiece. Finally, non-destructive tests are designed, which, using a safety coefficient of about 0.77, the tests allow the correct design of each specific grinding process. Keywords: cylindrical grinding, workholding, driving dog, sliding

Nano-Gradient Materials Prepared by Rotary Swaging

Gradient nanostructured metallic materials with a nanostructured surface layer show immense potential for various industrial applications because of their outstanding mechanical, fatigue, corrosion, tribological properties, etc. In the past several decades, various methods for fabricating gradient nanostructure have been developed. Nevertheless, the thickness of gradient microstructure is still in the micrometer scale due to the limitation of preparation techniques. As a traditional but potential technology, rotary swaging (RS) allows gradient stress and strain to be distributed across the radial direction of a bulk cylindrical workpiece. Therefore, in this review paper, we have systematically summarized gradient and even nano-gradient materials prepared by RS. We found that metals processed by RS usually possess inverse nano-gradient, i.e., nano-grains appear in the sample center, texture-gradient and dislocation density-gradient along the radial direction. Moreover, a broad gradient structure is distributed from center to edge of the whole processed rods. In addition, properties including micro-hardness, conductivity, corrosion, etc., of RS processed metals are also reviewed and discussed. Finally, we look forward to the future prospects and further research work for the RS processed materials.

Development of Calibration Knives for Hot Cutting Shears

In this paper, the problem distortion the end of a cylindrical workpiece in the cutting process on hot shears before being fed to the piercing mill is considered. To solve this problem, a new calibration of knives has been developed, and a finite element model hot cutting shears has been developed using the DEFORM-3D computer simulation software package. Modeling the cutting process using the proposed calibration has been carried out. It was found that the knife calibers geometry plays an important role in the formation end part geometry of the blank. Based on the simulation results, it was concluded that proposed calibration reduces the ovality workpiece end by almost 2 times in comparison with current calibration. Recommendations have been developed for the production of changes in the existing technology for cutting pipe billets.

EVALUATION OF DEFORMABILITY OF MATERIAL OF PREPARATIONS DURING ROLLING

The article presents the results of development and research of the technological process of cold forming rolling of aluminum billets. The main obstacle to the implementation of such processes is the danger of destruction of materials, which necessitated the study of the stress-strain state, plasticity and assessment of the deformability of the workpiece material. To experimentally determine the ductility of metals, a rolling method was developed, according to which the deformation of the free side surface of the cylindrical sample occurs under uniaxial tension. Increasing the degree of deformation and bringing the material to fracture is provided due to the increase in the radii of the rolls during rolling and deformation of the sample on the wedge. Analysis of the stress-strain state of the free side surface of the cylindrical workpiece was performed by the finite element method, which used a specialized engineering software package DEFORM 3D. As a result, a significant inhomogeneity of the stress-strain state in the deformation zone is established. The most severe stress state is observed on the free side surfaces of the workpiece, which causes the danger of its destruction in this area. The dependence between the relative compression of the workpiece during rolling and the intensity of deformation on its side surface is obtained, which allows to determine the limiting thickness of the workpiece before destruction. As a result of the assessment of the deformability of aluminum alloys during cold rolling, using the curves of limit deformations and the scalar criterion of deformation, the limits to the destruction of the intensity of deformation and the limit value of the relative compression of the workpiece. The use of constructed models makes it possible to determine the value of the used plasticity resource at intermediate stages of rolling.

Influence of Contact Positioning of Pivot Support on Machining Vibration

The authors have studied support mechanisms for the machining of thin-walled workpieces. Previous studies have shown that the newly proposed pivot support has a vibration suppression effect on flat plate workpieces. This report clarifies the guideline for determining the placement interval for deploying this support on a cylindrical workpiece. Also, a machining test was conducted to compare the damping effect of pivot support with that of conventional rigid body support. As a result, it was found that the pivot support has an equivalent vibration suppression effect as the conventional support has. By using the proposed support, installation can be simplified while maintaining the damping effect.

Prediction of Reponses in a Sustainable Dry Turning Operation: A Comparative Analysis

In a turning operation, involving removal of material from the outer diameter of a rotating cylindrical workpiece using a single-point cutting tool, there exist complex relationships between various cutting parameters and responses. In this paper, a turning operation under dry environment is considered with cutting speed, feed rate, and depth of cut as the input parameters, as well as material removal rate, average surface roughness, and cutting force as the responses. Dry turning operation reduces energy consumption and machining cost, thus eventually resulting in sustainable machining. For the considered process, the corresponding response values are envisaged using four prediction models, that is, multivariate regression analysis, fuzzy logic, artificial neural network, and adaptive neurofuzzy inference system (ANFIS), and their prediction performance is contrasted using five statistical metrics, that is, root mean squared percent error, mean absolute percentage error, root mean squared log error, correlation coefficient, and root relative squared error. It is noticed that ANFIS model consisting of the advantages features of both fuzzy logic and neural network outperforms the other prediction models with respect to the computed values of the considered statistical measures. Based on their acceptable values, it can be propounded that the ANFIS model can be effectively employed for prediction of process responses while treating different machining parameters as the input variables.