Experimental Research of the Rigidity of Fixtures With Incomplete Location for Connecting Rod Type Parts

Abstract

The use of modern machining centers with wide technological capabilities and the active development of productions with a small-scale form of organization necessitates an increase in the efficiency of fixtures capable of ensuring sufficient accuracy of machining with minimal costs.Classical approaches to the design of fixtures do not always allow machining with one installation with high-performance cutting conditions, so it is necessary to move the new approaches that allow maximum tool availability, which is important for the competitiveness of enterprises.The analysis of research and publications on numerical modeling and experimental research on the processing of parts of a complex shape that have insufficient rigidity showed that the issues of static research of the stress-deformation state of fixtures with incomplete locating have received little attention in the scientific literature.The purpose of the article is to experimentally demonstrate the possibility of machining non-separable connecting rods in machine tools with incomplete basing and fastening only on unprocessed surfaces in one installation with the achievement of all the necessary indicators of dimensional accuracy.The work presents for the first time an improved fixture with an incomplete location for machining connecting rod-type parts, and experimental studies of its stress-strain state in static mode are performed. The determined values of stresses and displacements compared with the previously proposed machine tool showed its technical advantage in bearing capacity for loads acting during machining.In this work, it was experimentally proven for the first time that the design of the improved fixture for machining connecting rods is capable of providing the necessary machining accuracy under static load and at the same time has a margin of accuracy thatexceeds the value of deformations by 1.5...2.5 times. The presented results and the positive experience of manufacturing a sample of a fixture can be used for its further research in a dynamic mode directly during machining, as well as for the design of technological equipment for parts of other classes, using an approach that involves incomplete locating of the workpiece

Experimental Evaluation of Flexible Fixture Stiffness for Steering Knuckles When Loading a Milling Machine Tool

“…Based on the results of theoretical and experimental studies, it was established that the proposed scientific approach to designing machine tools with incomplete location and ensuring the necessary stable position during processing due to clamping forces allows obtaining the specified accuracy. This proves the correctness of the working hypothesis [13,47] that devices with incomplete locations can ensure the specified processing accuracy, and this article is a logical continuation of previous research in this area and confirms this hypothesis experimentally.…”

“…The values of the maximum equivalent stresses according to the IV hypothesis of Mises's strength and maximum deflection of the elements of the "fixtureworkpiece" system were obtained. The process of FEM was carried out similarly as in [13,48], the results of which showed their adequacy in confirmation by the results of physical experiments [47]. It can be seen from the results of the stress diagrams obtained in the "machine toolworkpiece" system (Figure 7b) that all the parts of the device and the workpiece are of uniform strength, except for the pin, where the maximum Mises stress is 129 MPa, because its stretching causes this as a result of applying the necessary fastening force to ensure reliable retention of the workpiece.…”

“…The values of the maximum equivalent stresses according to the IV hypothesis of Mises's strength and maximum deflection of the elements of the "fixtureworkpiece" system were obtained. The process of FEM was carried out similarly as in [13,48], the results of which showed their adequacy in confirmation by the results of physical experiments [47]. The experimental setup (Figure 5) consists of the flexible fixture (1), which was clamped into a three-jaw chuck (2) mounted on the machine table.…”

“…This approach to the design of flexible fixtures using the example of connecting rods [13,47] and forks [48] has shown its effectiveness in terms of achieving minimum deformation rates and not exceeding their permissible values arising under the influence of loads from cutting forces acting on the surface finish in the "fixture-workpiece" system.…”

“…In previous studies [13,47] based on maximal stress and deflection evaluation by a physical measurement and FEM calculations, it was found that both of these parameters can be ensured within appropriate limits. In such a way, the proposed concept of incomplete orientation can be utilized for other complex form parts, for example, steering knuckles.…”