Cao Yanlong

Geometrical Simulation of Multiscale Toleranced Surface With Consideration of the Tolerancing Principle

Surface quality and accuracy are the most important factors that affect the performance and life cycle of products. Surface deviations are confirmed to be nonstationary random signals. They show characteristics of randomness, irregularity and multiscale. For precise components, those deviations, i.e., the location/orientation deviations, form deviations, waviness and roughness are constrained by different scales of tolerances. In addition, tolerancing principles are specified to deal with the relationship between geometrical and dimensional deviations of the workpiece. Conventional modeling methods are unable to express surfaces with those features. This paper proposed a new method for geometrical modeling of multiscale toleranced workpiece with consideration of tolerancing principles. The workpiece deviations are decomposed into different scale of deviations. Each scale of deviations is expressed as the products of the normalized deviations and deviation factors. To balance the conflict between computing time and accuracy, a multilevel displaying method is developed. Those deviations are presented at different levels. In the simulation, each scale of tolerances and the tolerancing principles are integrated into the geometrical model of the workpiece. At the end of this paper, a case study was carried out to validate the proposed method.

3DTS: A 3D tolerancing system based on mathematical definition *

Tolerance is almost ubiquitous during the whole product lift cycle and is imperative for seamless integration of CAD and CAM. Based on the mathematical definition of tolerance, a 3D tolerancing system, 3DTS, is presented with its design principle, system architecture and key functions. The following functional modules, tolerance modeling, semantics interpretation, 3D tolerance analysis, are described in detail. To make the tolerancing system robust and efficient, many techniques such as hierarchical tolerance representation, rule-based evaluation and non-intersection determination of tolerance zone have been devised. Tested by many samples, this system shows good robustness and practicability.

A Robust Tolerance Design Method Based on Fuzzy Quality Loss

The traditional tolerance design model ignores the impact of noise factor, so that the design may be infeasible due to variations in design constraints. Based on the analysis of fuzzy factors in tolerance design and the limitations of the traditional Taguchi squared quality loss function, a fuzzy quality loss function model utilizing fuzzy theory was introduced. Concepts on fuzzy quality loss and fuzzy quality loss cost were proposed in the model. The characteristics of the new model and the advantages over the traditional Taguchi quality loss function were analyzed. A robust tolerance design model using a fuzzy quality loss function was proposed. An example was given to illustrate the proposed model. Results and comparisons show that the method is suitable and reliable, and makes the conclusions more objective and reasonable.

A point-based variation propagation model for multi-pass machining process

In a machining process, the workpiece is usually machined by several passes to achieve the desired dimension and form. Workpiece deviation generated in the previous pass will affect the next pass. A new point-based variation propagation model for a single machining process with multi-passes was proposed in this article to investigate the relationships between different passes. The effects of locating errors, geometric errors of machine tool, and tool deflection on workpiece deviation are analyzed. Based on these analyses, a point-based variation propagation model for a machining process with multi-passes was derived. By including the influence of the tool deflection, a linkage between workpiece deviation and the cutting parameters is established. Since different passes are distinguished by their cutting parameters, the relationships between different passes are built up via this model. At the end of this article, case studies were carried out to validate the model and its application in cutting parameters’ optimization.

A robust tolerance design method based on process capability.

This paper presents a method for robust tolerance design in terms of Process Capability Indices (PCI). The component tolerance and the suitable manufacturing processes can be selected based on the real manufacturing context. The robustness of design feasibility under the effect of uncertainties is also discussed. A comparison between the results obtained by the proposed model and other methods indicates that robust and reliable tolerance can be obtained.

Fuzzy comprehensive evaluation of manufacturability in concurrent tolerance design

Tolerance design affects not only the product performance, but also the cost of a product and the manufacturing process. In this paper, a fuzzy multi-criteria evaluation model is developed to study the manufacturability evaluation in concurrent tolerance design. This model is formulated and analyzed based on fuzzy comprehensive evaluation. The manufacturability of parts can be evaluated at the design stage with consideration of the manufacturing constraints imposed. The results of the study point out the importance of early decision making capability.

Mathematical model for linear symmetry based on tolerancing principle

Tolerance is defined by graphic example and text description in the national standard and is not adaptable for expressing, processing and transferring in computers. It is essential for the integration of CAD and CAM and how to interpret its semantics is becoming a focus. Research on tolerance of mathematical model has been the topic of active research in recent years. But the models seldom consider the tolerancing principle. Thus an improved mathematical model based on independence principle (IP) and maximum material requirement (MMR) was proposed for linear symmetry tolerance. Small displacement torsor (SDT) was introduced in tolerance modeling. The constraint conditions of linear symmetry tolerance were developed systematically under IP and MMR. The corresponding mathematical models of linear symmetry of surface feature and central feature were deduced. The models can interpret the semantics of symmetry tolerance exactly and completely and can be used with the following processing. Its very important applications for seamless integration of CAD and CAM