Toward Automatic Tolerancing of Mechanical Assemblies: First-Order GD&T Schema Development and Tolerance Allocation

2015 ◽  
Vol 15 (4) ◽  
Author(s):  
Payam Haghighi ◽  
Prashant Mohan ◽  
Nathan Kalish ◽  
Prabath Vemulapalli ◽  
Jami J. Shah ◽  
...  
Keyword(s):  
Feature Recognition ◽  
Reference Frames ◽  
Geometric Analysis ◽  
Tolerance Allocation ◽  
First Order ◽  
Geometric Dimensioning And Tolerancing ◽  
Mechanical Assemblies ◽  
Schema Development ◽  
Design Function ◽  
Acceptance Rates

Geometric and dimensional tolerances must be determined not only to ensure proper achievement of design function but also for manufacturability and assemblability of mechanical assemblies. We are investigating the degree to which it is possible to automate tolerance assignment on mechanical assemblies received only as STEP AP 203 (nominal) geometry files. In a previous paper, we reported on the preprocessing steps required: assembly feature recognition, pattern recognition, and extraction of both constraints and directions of control (DoC) for assembly. In this paper, we discuss first-order tolerance schema development, based purely on assemblability conditions. This includes selecting features to be toleranced, tolerance types, datums, and datum reference frames (DRFs), and tolerance value allocation. The approach described here is a combination of geometric analysis and heuristics. The assumption is that this initial geometric dimensioning and tolerancing (GD&T) specification will be sent to a stack analysis module and iterated upon until satisfactory results, such as desired acceptance rates, are reached. The paper also touches upon issues related to second-order schema development, one that takes intended design function into account.

Toward Automatic Tolerancing of Mechanical Assemblies: Assembly Analyses

2014 ◽  
Vol 14 (4) ◽  
Author(s):  
Prashant Mohan ◽  
Payam Haghighi ◽  
Prabath Vemulapalli ◽  
Nathan Kalish ◽  
Jami J. Shah ◽  
...  
Keyword(s):  
Computer Aided Design ◽  
Feature Recognition ◽  
Tolerance Analysis ◽  
Tolerance Allocation ◽  
Geometric Dimensioning And Tolerancing ◽  
Mechanical Assemblies ◽  
Loop Detection ◽  
Assembly Feature ◽  
Aided Design ◽  
Assembly Analysis

Generating geometric dimensioning and tolerancing (GD&T) specifications for mechanical assemblies is a complex and tedious task, an expertise that few mechanical engineers possess. The task is often done by trial and error. While there are commercial systems to facilitate tolerance analysis, there is little support for tolerance synthesis. This paper presents a systematic approach toward collecting part and assembly characteristics in support of automating GD&T schema development and tolerance allocation for mechanical assemblies represented as neutral B-Rep. First, assembly characteristics are determined, then a tentative schema is determined and tolerances allocated. This is followed by adaptive iterations of analyses and refinement to achieve desired goals. This paper will present the preprocessing steps for assembly analysis needed for tolerance schema generation and allocation. Assembly analysis consists of four main tasks: assembly feature recognition (AFR), pattern detection, directions of control, and loop detection. This paper starts with identifying mating features in an assembly using the computer-aided design (CAD) file. Once the features are identified, patterns are determined among those features. Next, different directions of control for each part are identified and lastly, using all this information, all the possible loops existing in an assembly are searched.

A Kinematic Based Analysis for Tolerances Within Mechanical Assemblies

1994 ◽  
Author(s):  
M. M. Ogot ◽  
B. J. Gilmore
Keyword(s):  
Sensitivity Analysis ◽  
Design Tool ◽  
Tolerance Allocation ◽  
Analytical Sensitivity ◽  
Mechanical Assemblies ◽  
Analytical Sensitivity Analysis ◽  
Design Function ◽  
Minimum Sensitivity ◽  
The Individual ◽  
The Cost

Abstract Variation of dimensions within assemblies can unexpectedly displace parts from their intended location and therefore degrade the assembly’s performance. This paper presents a design tool based on the principles of kinematics to analyze nonlinear tolerance stackup, increase the reliability of the assembly without decreasing tolerances and where necessary, judiciously allocate tolerances such that the critical parts fit relative to each other with the specified precision. Through an analytical sensitivity analysis, the procedure outlined in this paper alters the orientations of the parts to yield an assembly with the highest positional reliability. If the desired level of reliability is not met by the minimum sensitivity approach, a tolerance allocation method incorporating the above sensitivity analysis and the cost of manufacturing each dimension as a function of tolerance is applied. In addition, this approach allows the individual tolerances within the assembly to assume any distribution. The method shown by this paper allows the design engineer to consider manufacturing effects and provides an analytical basis to evaluate design function.

Automatic Detection and Extraction of Tolerance Stacks in Mechanical Assemblies

2014 ◽  
Author(s):  
Payam Haghighi ◽  
Prashant Mohan ◽  
Jami J. Shah ◽  
Joseph K. Davidson
Keyword(s):  
Global Constraints ◽  
Major Step ◽  
Local Constraints ◽  
Good Tolerance ◽  
Mechanical Assemblies ◽  
Schema Development ◽  
Assembly Features ◽  
Design Function ◽  
Assembly Feature ◽  
Part Feature

Tolerances are specified by a designer to allow reasonable freedom by a manufacturer for imperfections and inherent variability without compromising performance. It takes knowledge and experience to create a good tolerance scheme. It is a tedious process driven by the type of parts, their features and controls needed for each one of them. In this paper, we investigate the extent to which GD&T schema development can be automated. Automated tolerance schema generation, requires identifying critical tolerance loops. The tolerance loop is a loop of dimensions between faces of features governing assembly conditions. For this purpose, the first major step is to identify mating features called assembly features. Also, in order to create the tolerance chains we need Local Constraints (assembly feature relationships), Global constraints (part feature relationships) and directions of control. In addition, we have to identify feature patterns since they have associated tolerances according to Dimensioning and Tolerancing Standard ASME Y14.5M. Directions in which these loops lie are also needed; we call them Direction of Control (DoC). Then we can create the GD&T schema, allocate tolerance values, and prepare it for tolerance evaluation. In this paper, we present an approach to automatically identify the dimensional loops based on assembly requirements. Assignment of tolerance values will be covered in future works as it is based on design function.

scholarly journals Connection Between Non-Rotating Local Reference Frames by Means of the World Function

1991 ◽  
Vol 127 ◽  
pp. 262-265
Author(s):  
J.M. Gambi ◽  
P. Romero ◽  
A.San Miguel ◽  
F. Vicente
Keyword(s):  
Reference Frames ◽  
Riemann Tensor ◽  
Space Time ◽  
General Character ◽  
Order Of Approximation ◽  
First Order ◽  
The World ◽  
Local Reference ◽  
General Relativistic ◽  
World Function

AbstractBy means of the world function an approximate transformation showing the Riemann tensor between the Fermi coordinates associated to two non-rotating local reference frames is derived in a General Relativistic space-time. One of the observer’s world lines is resticted to be a time-like geodesic of the space-time, and the other is a time-like curve of a general character. The space-time where the transformation is evaluated is supposed to be of small curvature, and the calculations are carried out in a first order of approximation with respect to the Riemann tensor.

A framework for tolerance design considering systematic and random uncertainties due to operating conditions

2019 ◽  
Vol 39 (5) ◽  
pp. 854-871
Author(s):  
S. Khodaygan
Keyword(s):  
Operating Conditions ◽  
Tolerance Allocation ◽  
Manufacturing Cost ◽  
Tolerance Design ◽  
Element Analysis ◽  
Content Type ◽  
Multi Objective ◽  
Mechanical Assemblies ◽  
Conflicting Objectives ◽  
Random Uncertainties

Purpose The purpose of this paper is to present a novel Kriging meta-model assisted method for multi-objective optimal tolerance design of the mechanical assemblies based on the operating conditions under both systematic and random uncertainties. Design/methodology/approach In the proposed method, the performance, the quality loss and the manufacturing cost issues are formulated as the main criteria in terms of systematic and random uncertainties. To investigate the mechanical assembly under the operating conditions, the behavior of the assembly can be simulated based on the finite element analysis (FEA). The objective functions in terms of uncertainties at the operating conditions can be modeled through the Kriging-based metamodeling based on the obtained results from the FEA simulations. Then, the optimal tolerance allocation procedure is formulated as a multi-objective optimization framework. For solving the multi conflicting objectives optimization problem, the multi-objective particle swarm optimization method is used. Then, a Shannon’s entropy-based TOPSIS is used for selection of the best tolerances from the optimal Pareto solutions. Findings The proposed method can be used for optimal tolerance design of mechanical assemblies in the operating conditions with including both random and systematic uncertainties. To reach an accurate model of the design function at the operating conditions, the Kriging meta-modeling is used. The efficiency of the proposed method by considering a case study is illustrated and the method is verified by comparison to a conventional tolerance allocation method. The obtained results show that using the proposed method can lead to the product with a more robust efficiency in the performance and a higher quality in comparing to the conventional results. Research limitations/implications The proposed method is limited to the dimensional tolerances of components with the normal distribution. Practical implications The proposed method is practically easy to be automated for computer-aided tolerance design in industrial applications. Originality/value In conventional approaches, regardless of systematic and random uncertainties due to operating conditions, tolerances are allocated based on the assembly conditions. As uncertainties can significantly affect the system’s performance at operating conditions, tolerance allocation without including these effects may be inefficient. This paper aims to fill this gap in the literature by considering both systematic and random uncertainties for multi-objective optimal tolerance design of mechanical assemblies under operating conditions.

Preliminary Investigation on Generating an Explicit GD&T Scheme From a Process Plan

2013 ◽  
Author(s):  
Payam Haghighi ◽  
Prabath Vemulapalli ◽  
Prashant Mohan ◽  
Jami J. Shah ◽  
Joseph K. Davidson
Keyword(s):  
Reference Frames ◽  
Preliminary Investigation ◽  
Tolerance Analysis ◽  
Research Issues ◽  
Geometric Dimensioning And Tolerancing ◽  
Implicit Information ◽  
Material Condition ◽  
Geometric Tolerances ◽  
Manufacturing Tolerances ◽  
Set Up

Geometric Dimensioning and Tolerancing (GD&T) Standards have established a language for clear and concise specification of dimensional and geometric variations on manufactured parts. The language includes symbols for tolerance type, tolerance value, datum and reference frames, diameter and material condition modifiers and associativity with geometric entities. Designers use the standard to communicate their dimensional specifications to manufacturing and inspection personnel. However, process planners appear to be less formal in how tolerances are represented in process plans. Typically, they are shown only as dimensional plus/minus values. Datum Reference Frames (DRF) and geometric tolerance symbols are absent. It is believed that the latter are implicit in the set-up and fixturing prescribed in the plan. In this paper we explore how one might extract the implicit information systematically. The motivation for this effort is to verify the consistency of manufacturing tolerances with design specs and to be able to use the same tolerance analysis tools used in design. We discuss three research issues: extracting implied DRFs from set-ups and fixtures; converting plus/minus tolerances to appropriate geometric tolerances; and dealing with transient features — which are features that do not exist on the finished part used for GDT specs by the designer. We propose a new data structure, PCTF (process oriented constraint tolerance feature graph) to facilitate mapping between design and manufacturing tolerances.

Sign in / Sign up

Export Citation Format

Share Document