scholarly journals Automated Iterative Tolerance Value Allocation and Analysis

2016 ◽  
Author(s):  
Deepanjan Biswas ◽  
Adarsh Venkiteswaran ◽  
Sayed Mohammad Hejazi ◽  
Jami J. Shah ◽  
Joseph K. Davidson
Keyword(s):  
Standard Deviation ◽  
Tolerance Allocation ◽  
Hill Climbing ◽  
Design Stage ◽  
Production Economics ◽  
Time Line ◽  
Loop Detection ◽  
Process Standard Deviation ◽  
Dimensional Variation ◽  
Acceptance Rates

Dimensional variation is inherent in manufacturing and it is impossible to attain exact nominal dimensions. Ideally, designer should accommodate this variation likelihood in design stage and define an allowable variation. This allowable variation is represented as tolerances and is either considered a bounded zone or a scaled allowable process standard deviation (e.g. 6 times standard deviation). The allowable tolerances are usually constrained by assemblability, functionality and manufacturing economics. Meeting these constraints simultaneously becomes a paramount task and designers usually never consider production economics when specifying tolerances. As a consequence rarely do the tolerances specified by product designer match that of the process designer. Automated tolerance value allocation can empower the product designer to include all the constraints at the design phase and reduce the overall time line between development to production. Automated tolerance allocation method described in this paper is intended for use by the designer and encompasses only 1st order tolerancing. The Critical stack detection/loop detection tool extracts the assembly level stacks that dictate assemblability. The allocation tool utilizes these stacks to distribute tolerance budget by a rule of thumb. These stacks are subjected to variation analysis to compute acceptance rates and used as feedback for iterative reallocation using a hill climbing optimization algorithm till statistical fit requirements are satisfied or allocation gets exhausted. The algorithm is tested on some case studies and presented in the paper.

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.

ESTIMATING THE PROCESS STANDARD DEVIATION BASED ON DOWNTON'S ESTIMATOR

2000 ◽  
Vol 12 (3) ◽  
pp. 357-363 ◽  
Author(s):  
Moustafa O. Abu-Shawiesh ◽  
Mokhtar B. Abdullah
Keyword(s):  
Standard Deviation ◽  
Process Standard Deviation

scholarly journals Geometrical and dimensional tolerance analysis for the radial flux type of permanent magnet generator design

2021 ◽  
Vol 12 (2) ◽  
pp. 68-80
Author(s):  
Muhammad Fathul Hikmawan ◽  
Agung Wibowo ◽  
Muhammad Kasim
Keyword(s):  
Permanent Magnet ◽  
Manufacturing Process ◽  
Cumulative Effect ◽  
Tolerance Analysis ◽  
Air Gap ◽  
Tolerance Allocation ◽  
Design Stage ◽  
Worst Case ◽  
Radial Flux ◽  
Permanent Magnet Generator

Mechanical tolerance is something that should be carefully taken into consideration and cannot be avoided in a product for manufacturing and assembly needs, especially in the design stage, to avoid excessive dimensional and geometric deviations of the components made. This paper discusses how to determine and allocate dimensional and geometric tolerances in the design of a 10 kW, 500 rpm radial flux permanent magnet generator prototype components. The electrical and mechanical design results in the form of the detailed nominal dimensions of the generator components, and the allowable air gap range are used as input parameters for tolerance analysis. The values of tolerance allocation and re-allocation process are carried out by considering the capability of the production machine and the ease level of the manufacturing process. The tolerance stack-up analysis method based on the worst case (WC) scenario is used to determine the cumulative effect on the air gap distance due to the allocated tolerance and to ensure that the cumulative effect is acceptable so as to guarantee the generator's functionality. The calculations and simulations results show that with an air gap of 1 ± 0.2 mm, the maximum air gap value obtained is 1.1785 mm, and the minimum is 0.8 mm. The smallest tolerance value allocation is 1 µm on the shaft precisely on the FSBS/SRBS feature and the rotor on the RPMS feature. In addition, the manufacturing process required to achieve the smallest tolerance allocation value is grinding, lapping, and polishing processes.

scholarly journals A Combined Upper-Sided Synthetic S2 Chart for Monitoring the Process Variance

2020 ◽  
Vol 2020 ◽  
pp. 1-6
Author(s):  
Tingting Shan ◽  
Liusan Wu ◽  
Xuelong Hu
Keyword(s):  
Steady State ◽  
Standard Deviation ◽  
Average Run Length ◽  
Process Standard Deviation ◽  
Distributed Process ◽  
Process Variance ◽  
Synthetic Chart ◽  
And Performance ◽  
Run Rules ◽  
State Average

In order to monitor the process variance, this paper proposes a combined upper-sided synthetic S2 chart for monitoring the process standard deviation of a normally distributed process. This combined upper-sided synthetic S2 chart comprises a synthetic chart and an upper-sided S2 chart. The design and performance of the proposed chart are presented, and the steady-state average run length comparisons show that the combined upper-sided synthetic S2 chart outperforms the standard synthetic S2 chart as well as several run rules S2 charts, especially for larger shifts in the process variance.

Multiobjective Optimization for Integrated Tolerance Allocation and Fixture Layout Design in Multistation Assembly

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Z. Li ◽  
L. E. Izquierdo ◽  
M. Kokkolaras ◽  
S. J. Hu ◽  
P. Y. Papalambros
Keyword(s):  
Multiobjective Optimization ◽  
Layout Design ◽  
Tolerance Allocation ◽  
Assembly Process ◽  
Optimization Strategy ◽  
Fixture Layout ◽  
Dimensional Variation ◽  
Product Variation ◽  
Multistation Assembly

Cost and dimensional variation of products are significant attributes in multistation assembly processes. These attributes depend on product∕process tolerances and fixture layouts. Typically, tolerance allocation and fixture layout design are conducted separately without considering potential interrelations. In this work, we use multiobjective optimization for integrated tolerance allocation and fixture layout design to address interactions and to quantify tradeoffs among cost, product variation, and assembly process sensitivity. A nested optimization strategy is applied to a vehicle side frame assembly. Results demonstrate the presence and quantification of tradeoffs, based on which we introduce the concept of critical variation and critical budget requirements.

Product Tolerance Allocation in Compliant Multistation Assembly Through Variation Propagation and Analytical Target Cascading

2004 ◽  
Author(s):  
Zhijun Li ◽  
Jianpeng Yue ◽  
Michael Kokkolaras ◽  
Jaime Camelio ◽  
Panos Y. Papalambros ◽  
...  
Keyword(s):  
Linear Process ◽  
Tolerance Allocation ◽  
Vehicle Body ◽  
Analytical Target Cascading ◽  
Variation Propagation ◽  
Target Cascading ◽  
Dimensional Variation ◽  
Product Variation ◽  
Multistation Assembly ◽  
Sheet Metal Assembly

Compliant sheet metal assembly is a hierarchical manufacturing process that plays a significant role in automotive product development. Parts are joined in different stations to form the final product (e.g., the vehicle body structure). Dimensional variation is a product attribute of major importance that characterizes quality, and is mainly affected by the variability of parts, fixtures, and joining methods at each of the multiple stations. The propagation of dimensional variation through the multistation assembly system is modeled as a linear process, where all three aforementioned sources of variability are taken into account at each station using finite element models. In this article we apply the analytical target cascading process to the tolerance allocation problem in multistation assembly systems. Specifically, we translate final product variation targets to tolerance specifications for subassemblies and incoming parts. We demonstrate the methodology by means of a vehicle side frame assembly example.

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