PSI - Issue 81

Igor Stoiko et al. / Procedia Structural Integrity 81 (2026) 447–454

448

sinusoidal impact and machining loads. Li et al. (2001) presented a method to determine the optimal clamping forces for a multiple fixture subjected to quasi-static machining forces to reduce the impact on both the accuracy and location error of the part. The main processes of error compensation operations for improving machining accuracy include volumetric error modeling, measurement, compensation (Yang et al. (2018), Rahman et al. (2000)), and verification of machining accuracy through specific machining tests (Zha et al. (2020)). Conventional locating technology for such parts fails to ensure consistent accuracy, creating difficulties in performing sequential turning and grinding operations necessary to achieve IT6-IT8 precision grades and surface roughness parameters within Ra=0.63-2.5 under batch production conditions. In practical applications, it was found that the norm of the error vector is a comprehensive concept of the tool center point (Chen (2000)). Critical to curved axis manufacturing is ensuring the precision of the angle between the part's geometric axes with deviations within 10-15 arc minutes along with reliable verification of this parameter. The complexity arises from the fact that the vertex of the angle formed by the intersecting geometric axes lies within the part's body, while the part geometry and fixture design induce an imbalance in the fixture-part subsystem that continuously changes throughout the machining process. Consequently, the development and investigation of technological approaches for ensuring reliable locating, operational allowances, parameter control and tooling reliability will eliminate the identified shortcomings in curved axis manufacturing technology, representing a pressing scientific challenge. 2. Materials and Methods A curved axis is a part featuring cylindrical surfaces whose geometric axes intersect at an angle of 90°<γ<180°. This type of component is extensively utilized in the design of machinery and mechanisms for transport and technological systems, particularly agricultural equipment. These parts are employed to facilitate the rotation of machine working elements such as discs, wheels, blades and other structural components positioned at angles relative to one another. A typical design is shown in Fig. 1. The design incorporates two external surfaces of revolution A and B, whose axes intersect at a specific angle γ. Other elemen ts – cylindrical surfaces for bearing assemblies, threaded surfaces for fastening (both external and internal), face surfaces, transitional conical surfaces, holes and keyways – are employed in various combinations depending on the part's intended application. A characteristic technological feature of this part is the absence of surfaces suitable for creating coaxial center holes at points 1 and 2, which would enable the application of conventional machining technology using coaxial centers on metal-cutting machine tools which is typical for parts classified as "round bars" and, specifically, shafts. The primary and standard technical requirements for the design include ensuring: - execution of bearing mounting surfaces with accuracy no lower than IT6-IT7 grade and roughness Ra=0.63-1.25, complying with requirements for roundness deviations within half the tolerance for the corresponding dimension; - deviation of the angle between geometric axes from the nominal value within 10-20 arc minutes; - execution of other surfaces of revolution with IT7-IT9 grade accuracy and roughness Ra=2.5-6.3. Ensuring consistent achievement of specified accuracy parameters, roughness and technical requirements characterizes the operational reliability of both specific assemblies and the entire mechanism or machine. Design manufacturability is characterized by its correspondence to the current state of technology, economic efficiency, operational convenience and the extent to which it accounts for the potential application of economical and productive technological methods for its fabrication, considering the specified production volume. The specificity of structural forms creates numerous difficulties during manufacturing in ensuring appropriate angular, linear and diametric accuracy parameters. The complexity of mechanical machining lies in the need to technologically ensure the processing of high-precision surfaces of revolution (with bearing and other fits) whose geometric axes are positioned at an angle to one another. Various existing machining methods cannot adequately satisfy the technical requirements. At best, achievable accuracy and surface finish quality are one to two grades below the required parameters. When characterizing design manufacturability, it is essential to note their inherent lack of manufacturability, primarily due to the absence of surfaces for creating coaxial center holes, which would enable the use of conventional shaft and axis machining technology using coaxial centers on turning and grinding machines with traditional equipment and tooling. The absence of coaxial center holes and the use of axis contour elements for locating during sequential turning of both ends, which necessitates part repositioning into secondary datums, preclude using these datums for grinding analogous surfaces. Consequently, the grinding process requires constant adjustment, alignment of each individual part, or in many cases becomes entirely impossible, making adherence to accuracy requirements for both diametric and angular dimensions problematic. These technical accuracy requirements necessitate the creation of a technological process built upon fundamentally new theoretical and experimental locating schemes, machining methods and tooling, whose implementation will enable grinding Fig. 1. Typical curved axis design.