Can ISO GPS and ASME Tolerancing Systems Define the Same Functional Requirements?

Geometrical tolerances are defined in the ISO Geometrical Product Specification system that is used worldwide, but on the other hand, the ASME Y14.5 standard is used in American companies to define how far actual parts may be away from their nominal geometry. This paper aimed to investigate whether specifications defining acceptable geometrical deviations in one system can be transformed to specifications in the other system. Twelve selected cases are discussed in the paper. Particularly, two cases of size tolerance, three cases of form tolerances, one case of orientation tolerance, four cases of position tolerance (including position tolerance with MMR for the pattern of five holes) and, finally, two cases of surface profile tolerance (unequally disposed tolerance zone and dynamic profile tolerance). The issue is not only in the several different symbols and a set of different defaults, but also in the different meanings and different application contexts of some symbols that have the same graphical form. The answer to the question raised in the paper title is yes for the majority of indications specified according to ASME Y14.5 when new tools from the 2017 edition of ISO 1101 are applied.

Section Based Profile Tolerance Assessment of 3D Scanned Compressor Airfoils

This paper presents two turbomachinery-specific methods for profile tolerance assessment of compressor airfoils that process 3D scan data. This optical inspection technology digitizes the entire surface of the part into a triangulated mesh, which is aligned to nominal geometry and then processed to extract densely arranged profile sections. For the reverse engineering method, the profile sections are decomposed into thickness and camber distributions. These distributions and the camber line are used to identify the profile parameter vector of the reverse engineering model. The deviation of the actual geometry is obtained by subtracting its parameters from those of the nominal geometry. Parameter-span graphs reveal airfoil shape deviation and allow for quantification of blisk scatter. The design-like parameters are meaningful and enable an intuitive engineering judgement of the actual geometry deviation. The profile tolerance assessment method utilizes the camber line from the reverse engineering method to elegantly check against variable profile tolerance limits. The actual section is best-fitted to its nominal counterpart and assessed regarding its deviation relative to the allowed local tolerance. This ratio is plotted in a developed view summarizing the result of the profile tolerance assessment for the whole airfoil in a single graph. Thus, the condensed results allow for effective utilization of the high-resolution in airfoil sections. Ultimately, the paper widens the view from one airfoil towards the assessment of the entire blisk. The blisk data is presented by statistical processing of deviation fields of all airfoils, in terms of mean and standard deviation. These statistical quantities are plotted onto the airfoil contour to e.g. represent the average airfoil thickness of the blisk. The standard deviation plot points to airfoil sections of larger geometric scatter and reveals areas of a non-robust manufacturing process.

A Framework for Tolerance Modeling Based on Parametric Space Envelope

Geometric dimensioning and tolerancing (GD&T) tolerance standards are widely used in industries across the world. A mathematical model to formulate tolerance specifications to enable comprehensive tolerance analysis is highly desirable but difficult to build. Existing methods have limited success on this with form and profile tolerance modeling as a known challenge. In this paper, we propose a novel tolerance modeling framework and methodology based upon parametric space envelope, a purposely built variation tool constructed from base parametric curve. Under proposal, geometric variation (deviation as well as deformation) is modeled and linked to envelope boundary control points’ movement. This indirect tolerance modeling brings various benefits. It is versatile and can handle full set of tolerances specified under GD&T standards including form, profile, and runout tolerance. The proposal can deal with complex manufacturing part and is capable of providing modeling accuracy required by many applications. The proposed approach has added advantage of facilitating integration of various computer-aided systems to meet emerging industry demands on tolerancing in a new era of digital manufacturing. The proposed methodology is illustrated and verified with an industrial case example on a two-part assembly.

A High Fidelity Quality Assessment of High Pressure Turbine Blades Using Surface Curvature and Gradient-Based Adjoint

Gas turbine performance is highly dependent on the quality of the manufactured parts. Manufacturing variations in the parts can significantly alter the performance, especially efficiency and thus SFC. The legacy process is to accept variations within predefined profile tolerance limits and a few other qualitative parameters, mostly at a few, key two-dimensional aerofoil sections. With the widespread use of White light scans and other similar three-dimensional scans, this has improved to include the three-dimensional profile. The future however may lie with performance based quality assessment of manufactured parts, combined with quantitative surface quality assessment to implement an intelligent screening process for the parts. The adjoint method, typically used for shape optimization is adapted to provide a prediction of the impact on performance due to manufacturing variations. The work presented outlines a three stage quality assessment process for manufactured parts, involving three-dimensional profile tolerance based screening, followed by a surface curvature based screening and finally an Adjoint based performance prediction.

Analysis of Parameters Influencing Build Accuracy of a SLM Printed Compressor Outlet Guide Vane

The paper describes the manufacture of an outlet guide vane (OGV) of jet engines by the Selective Laser Melting (SLM) process, in view of current challenges for conventional machining approaches such as; high airfoil profile tolerances, limited tooling access and hard to machine materials like nickel-chromium-based super alloys. Within this paper, analysis was conducted to investigate the influence of build parameters on possible distortion during printing that affect the build accuracy. These parameters include the part orientation on the build plate, thickness change to the flanges and the positioning of the support structure of each part. The configurations are 3D printed using the SLM approach. The chosen material is IN625. The printed parts are 3D scanned and the results are compared to the original CAD design. The results confirmed the presence of distortions in printed parts and the effect of parameter changes. Furthermore, it was shown that improvements to the print parameters are necessary to achieve a satisfactory profile tolerance.

Gradient-Based Adjoint and Design of Experiment CFD Methodologies to Improve the Manufacturability of High Pressure Turbine Blades

The tolerance of a turbine blade aerofoil is determined by the requirements to achieve an aerodynamic performance in operation. In fact, the manufacturing tolerance applied to the profile is driven by the effects of geometrical non-conformances on the efficiency and flow capacity of the aerofoil. However, this tolerance also has an impact on the ease with which the aerofoil can be manufactured, with tighter tolerance leading to lower manufacturing conformity. This paper details the application of an adjoint RANS solver and the according series of Design of Experiments (DoE) CFD calculations for a high pressure turbine blade to the above problem. There are two aims of this work; the first is to show that simpler linear CFD perturbation can be used to evaluate the effect of the geometric non-conformance. The second is to validate the spatial geometric correlation factor of the control points used in the manufacturing process on the performance evaluation with DoE techniques. This also verified the applicability of the adjoint CFD techniques; in fact the adjoint CFD calculation is an order of magnitude less computationally expensive than a large series of DoE RANS CFD calculations. The results confirm that the peak suction area is the most critical control region for the effect on the efficiency and flow capacity. Moreover, the CFD investigations show that a significant level of correlation exists between the influence factors at different control points. This suggests that not only the amount of geometric deviation but also the stream surface variation of profile tolerance significantly influence the final aerodynamic performance. The results from this calculation allow the creation of a 3D sensitivity map which will be used during the manufacturing of the aerofoil to optimise the control of the spatial distribution of the geometric non-conformance and to directly assess the expected performance effect during the manufacturing quality inspection. The methodology detailed in this paper shows how the CFD adjoint methods could be used for improved manufacturability of turbine blades ensuring that the critical characteristic features are controlled on the surface, relaxing the profile tolerance on those surface areas where the impact on the aerodynamic performance is predicted to be lower.