Integrated approach enabling robust and tolerance design in product concept development

Along with the ever-increasing customer demands, early consideration of variation in terms of robust design is important to avoid expensive iterations in the product development. However, existing methods are detached from the development process and can therefore only be applied at a late stage or only with comprehensive expert knowledge. Especially in the concept stage, where the geometry of a product is not yet defined and the optimisation potential is high, effective solution proposals for systematic consideration of variation are lacking. Therefore, this paper describes a new integrated approach facilitating robust and tolerance design in the concept stage. The novelty of the approach using ontologies and graph-based visualisation is the close linkage of product development and tolerance knowledge, which allows automation and helps to avoid time- and cost-intensive iteration loops. As a result, a robust and tolerance-compliant concept design, an initial qualitative tolerance specification and instructions for the further tolerancing process are already available at the end of the concept stage. The applicability and the benefits of the approach are illustrated by representative case studies and a user study allowing a critical comparison between the conventional, mostly subjective procedure and the presented approach.

A Knowledge-Based Engineering Workbench for Automated Tolerance Specification

Designers often lack important information about achievable manufacturing tolerances. Moreover tolerances are not considered from the beginning of product development. This often leads to inaccurately specified parts. Furthermore the full potential of the manufacturing departements is not used. This contribution tackles those areas by presenting a knowledge-based engineering workbench for automated tolerance specification, which has also been implemented using a commercial CAD system. This tool allows the designer to assign part tolerances that take into account the achievable accuracies for a specific manufacturing process, while at the same time allowing for specific part properties. The novelty of the presented approach can be found in the knowledge-based support of the product developers in tolerance specification by employing an engineering workbench. Moreover preprocessing for variation simulation and analysis is supported. It is possible to automate parts of the tolerance specification process, using the presented approach.

A rule-based exclusion method for tolerance specification of revolving components

This article proposes a novel method for tolerance specification on revolving components. The revolving parts are widely used and functionally important. An exclusion approach is introduced to construct a tolerance specification method. A functional analysis tool is developed to select features to be specified and to generate their datum reference frame. A set of rules are modelled to create suitable specification schemes. The independent axiom and entropy theory are applied for further specification refinement. A software application is developed, and an RV (RV is a code of model) reducer is used as a case study. A comparison with other specification methods is undertaken.

Implementation of Parameterized Work Piece Deviations and Measurement Uncertainties into Performant Meta-models for an Improved Tolerance Specification

Geometrical work piece deviations are unavoidable and directly affect the function and quality of technological products. Tolerance management is regarded as a crucial subtask of the development of technological products, because it ensures the function as well as a sufficient product quality while maintaining reasonable production costs. That means, that geometric tolerances as an essential part of the product description greatly affect the functional capability, manufacturability, mountability, verifiability and the costs of the final product. The research group FOR 2271 was founded to enable the computer-aided specification of tolerances, which meet the requirements of production, assembly, verification and function by close cooperation between the departments responsible for product design, assembly and metrology. The aim of this contribution is to determine the manufacturing process scatter as well as the measurement uncertainty and establish ways and means to include that information into efficient meta-models, ultimately enabling improved and accurate tolerance analyses.

Representation of Graded Materials and Structures to Support Tolerance Specification for Additive Manufacturing Application

Additive manufacturing (AM) has enabled control over heterogeneous materials and structures in ways that were not previously possible, including functionally graded materials and structures. This paper presents a novel method for representing and communicating heterogeneous materials and structures that include tolerancing of geometry and material together. The aim of this paper is to propose a means to specify nominal materials, nominal structures and allowable material variations in parts, including (a) explicit material and structural transitions (implying abrupt changes) and (b) functional transitions to support single and multiple material and structural behaviors (implying designed function-based gradients). The transition region combines bounded regions (volumes and surfaces) and material distribution and structural variation equations. Tolerancing is defined at two levels, that of the geometry including bounded regions and that of the materials. Material tolerances are defined as allowable material variations from nominal material fractions within a unit volume at a given location computed using material distribution equations. The method is described thorough several case studies of abrupt transitions, lattice-based transitions, and multimaterial and structural transitions.

Mathematical Tools for Automating Digital Fixture Setups: Constructing T-Maps and Relating Metrological Data to Coordinates for T-Maps and Deviation Spaces

Mathematical tools underlie a method that has strong potential to lower the cost of fixture-setup when finishing large castings that have machined surfaces where other components are attached. One math tool, the kinematic transformation, is used for the first time to construct Tolerance-Map® (T-Map)® models of geometric and size tolerances that are applied to planar faces and to the axes of round shapes, such as pins or holes. For any polygonal planar shape, a generic T-Map primitive is constructed at each vertex of its convex hull, and each is sheared uniquely with the kinematic transformation. All are then intersected to form the T-Map of the given shape in a single frame of reference. For an axis, the generic T-Map primitive represents each circular limit to its tolerance-zone. Both are transformed to a central frame of reference and are intersected to form the T-Map. The paper also contains the construction for the first five-dimensional (5D) T-Map for controlling the minimum wall thickness between two concentric cylinders with a least-material-condition (LMC) tolerance specification on position. It is formed by adding the dimension of size to the T-Map for an axis. The T-Maps described are consistent with geometric dimensioning and tolerancing standards and industry practice. Finally, transformations are presented to translate between small displacement torsor (SDT) coordinates and the classical coordinates for lines and planes used in T-Maps.