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8/3/2019 08AMR Tolerance
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Research on Tolerance Analysis System Based on 3D CollaborativeDesign Platform
X.Y. Shao1,a
, K. Lin2,b
, L. Gao3,c
, H.B. Qiu4,d
1,2,3,4
The State Key Laboratory of Digital Manufacturing Equipment and Technology, HuazhongUniversity of Science and Technology, 1037, Luoyu Road, Wuhan, Hubei, 430074, P. R. China.
ashaoxy@mail.hust.edu.cn, blinke1983@gmail.com, cgaoliang@mail.hust.edu.cn,dhobqiu@yahoo.com.cn
Keywords: Collaborative design Dimensional chain 3D model Geometric topology information
Abstract. Computer supported collaborative work (CSCW) technology is used to solve the
resource-sharing problems in collaborative design, analysis, and manufacture. To address this need, a
system called CollabVue for collaborative product design between designers and manufacturers is
proposed in this study. This paper first introduces the framework of tolerance analysis system basedon CollabVue, and then discusses the utilization of geometric topology information in 3D model to
resolve the problem of dimension information input and the related specific operations. Based on
object-oriented technology, a new data structure to interactively pick up and store dimension
information is established. Finally the model uses iterative method to compute technological
dimension chain equation.
Introduction
Today, global competition is increasing with pressures on prices, smaller orders, shorter life cycles,
more suppliers, more governmental regulations, and increasing material and energy costs. Rational
tolerance design, correct manufacturing process selection, and economics of processing are veryimportant role of manufacturing, especially to the implementation of CSCW, because those affect
both the functional performance and manufacturing cost of a product. In traditional practice, the
planning of the manufacturing phase and design phase are often conducted separately, this design
philosophy is called throw over the wall. More and more researchers have expressed the need of
having simultaneous selection of design and operational tolerances. Such an approach indicates that
design phase is developed concurrently with the planning of the manufacturing phase.
There are two basic processes in dimensional tolerance design (specification of permissible
variation in nominal values of constituent dimensions): tolerance analysis, and tolerance synthesis
[2]. Tolerance analysis can be defined as to deal with tolerance specifications to make a product
function well through its lifecycle and make the manufacturing of the product economical. In order to
carry out feasible and economical plans, tolerance analysis must be considered. Tolerance synthesis(also called tolerance allocation) estimates the optimum tolerances of the dimensions-members of the
tolerance chain that satisfy the critical assembly tolerances and are produced with the minimum
manufacturing cost.
In general, tolerance analysis can be divided into two categories: design tolerance analysis and
operational tolerance analysis [5, 6]. In traditional practice, design tolerance analysis is in product
design stage (CAD procedure) to distribute the functional tolerance of an assembly to the feature
relationships of the parts in the assembly. Operational tolerance analysis is in the engineering process
stage, and its focus is on obtaining an appropriate set of tolerances for different manufacturing
operations, which involve considering process capability of the manufacturing processes and
manufacturing allowance for each operation in succession[7, 8].There are three different communities (designers/draftsmen, engineering analysts, and design
researchers) using vastly different tools and techniques. The drafting community uses a manual
procedure called tolerance chart technique. This method is only a means of recording and displaying
the results of tolerance calculations, and can do only worst case analysis in only one direction at a
Advanced Materials Research Vol s. 44-46 (2008) pp 253-260online at http://www.scientific.net © (2008) Trans Tech Publications, Switzerland
All rights reserved. No part of contents of this paper may be repr oduced or transmitted in any form or by any means without the written permission of thepublisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 128.95.95.205-30/05/08,19:07:52)
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time. It requires sort of manufacturers’ experiences that are referenced to each component dimension
in the chain. The procedure is subjective to the way the particular user understands the accuracy cost
of the machining process especially in case that the tolerance chain consists of a large number of
members. Considerable dependency of the produced results on the user input, misinterpretations,
mistakes, unnecessary repetitions are unavoidable.
Many researchers investigated the representation scheme of the tolerance chart. Severalrepresentation schemes have been proposed for tolerance chart technique. Whybrew et al developed a
rooted tree scheme [1]. Each cut surface on a workpiece is uniquely identified with a label and treated
as a separate surface. These labels are the nodes on a tree. Operations are represented in the tree by
lines joining the nodes representing datum and cut faces. Some have discussed the representation
scheme based on graph theory [3]. This representation can be divided into two categories: based on
directed graph theory and based on undirected graph theory. Therefore, a graphical representation
with surfaces as nodes and relationships as arc will be used. Some investigators have reported a
representation scheme of matrix chain [4]. This method used matrix to restore surfaces and
relationships, but there is much redundant information.
This paper presents a dimensional chain calculation system based on 3D collaborative design
platform to determine a process plan and tolerances, mean sizes of operational dimensions of it. The
system uses a graph theoretic representation for tolerance chart. Furthermore, how to utilize the
geometric topology information in 3D model to process the problem of dimension information input
and the related specific operations is formulated. Finally, a mathematical model of linear equations is
built from the dimensional chains for the purpose of calculating mean sizes of operational
dimensions.
This paper is organized as follows. A 3D collaborative design platform developed by our team,
called CallabVue, was reviewed and the main contribution to tolerance chart technique was presented
in Section 2. Section 3 gave a detail description of the framework of tolerance analysis system (TAS).
An example is presented in Section 4. Conclusions and further discussion are offered in Section 5.
Methodology
Collaborative design platform. In order to solve new difficulties in modern collaborative
environment, the new collaborative environment solution should be able to :
(1) Solve the product development collaborative in lifecycle across global chains of trusted
partners, employees, suppliers, and customers.
(2) reduce development costs, increase product innovation, dramatically speeds time to market,
results in a strategic impact on revenue [3].
As such, a new solution, that is, 3D collaborative design platform, is required, as shown in Figure
1. Combining ACIS geometry modelling platform and optimal display technique of HOOPS, we have
developed prototype software, called CollabVue, with a user-friendly interface to provide the user
with an interactive windows environment so that the system can be used easily and efficiently.CollabVue can browse 3D model and read most file layouts of mainstream 3D CAD, such as
CATIA, Pre-E, UG, etc. It can support distributed workplace to cooperate work by internet. It
integrates some functions of 3D CAD, CAPP, and CAM. For example, measure, label, planning of
manufacturing, generating NC code, and so on.
CollabVue is based on hybrid representation of construction solid geometry (CSG) and boundary
representation (B-rep).The principle of this hybrid representation: by coding the geometric elements
of the B-rep representation, the mapping relation between geometric topology elements in the CSG
representation and the B-rep representation is established. According to the hybrid representation,
identified geometric topology entities uniquely, and then utilized decoding algorithm to look up
geometric topology entities, such as, point, edge, loop, face, block and body. The mapping relation
between engineering information and geometric topology information, such as, point, edge, loop etc,
is established.
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CollaborativeProductDesign
CollaborativeProduct
Development
CollaborativeProductAnalysis
CollaborativeProduct
Manufacturing
CollaborativeComponentManagement
CAD
CAM
CAPP
CAE
SCM
Fig. 1: A view of 3D collaborative design platform.
Consequently, by utilizing the operation of human-computer interaction can realize picking up
geometric topology elements.
Automatic generation tolerance chart. Tolerance chart technique is a graphical representation
of the manufacturing operation which helps to visualize the influence of the proposed manufacturing
operations on resulting dimensions and tolerances. For each step of the operation sequence,
machining accuracy is estimated and tolerance stack-ups are calculated.
In order to present the tolerance chart technique, a tolerance chart for a workpiece is shown in
Fig.2. And the manufacturing operations of the workpiece are shown in Table.1. The detailed
development and calculation of a tolerance chart can be obtained elsewhere [2]. This study uses
tolerance chart representation with the dimensional chains, as shown in Fig.2. This representation is
suitable to analyze a tolerance chart systematically because the information of dimensional chains is
explicit.
The tasks of tolerance charting can be summarized as follows:
(1) Dimensional chains should be identified for all design tolerance analysis and operational
tolerance analysis.
(2) Reasonable economical stock removal should be determined for each operation, and as large
as possible for each operation.(3) Mean sizes of design dimension must be determined.
The constraints for the above tasks are:
(1) Design dimension (including both mean sizes and tolerances).
(2) Process or machine capability of each operation.
This study investigated a method of automatic generating tolerance chart. Fig.3 describes a
sequence of operations from design phase to manufacturing phase. After computer aided design, the
features are created; the process planner can work on the component to generate plans, routes,
processes, and operations. By accessing database of technical resource, the process planner can select
manufacturing operations, cutting tools, and cutting parameters, etc. When process planning created,
the NC programmer can work with it collaboratively.
We could manipulate 3D solid model of workpiece to generate manufacturing operation. First,select manufacturing operations from database of technical resource by select menu, for example, R.
Turing. At the same time, select a surface of 3D solid model of the part as datum, for example, surface
D, as shown in Fig.2. Surface is uniquely identified with Part ID. Then, select another surface as cut
surface. If manufacturing operation is not change, e.g. Seq.No.1 and 2, don’t access database of
technical resource by operating menu. Otherwise operate the menu until all the processes are
completed.
Computing dimensional chains required a large number of data, such as mean sizes of design
dimension, economical stock removal, and so on. As mentioned before, by utilizing the operation of
human-computer interaction can realize picking up geometric topology elements. Because B-rep
representation contains topology relation of geometric elements, net relation is constructed by
starting with vertex of B-rep representation, and ending with body. A vertex is defined by
three-coordinate, X, Y, and Z. As a result of topology relation, edge, loop, face, block and body could
be computed throughout X, Y, and Z in the numerical. The dimension of a component’s 3D model
can formulate the distance of two surfaces, or dimension of a surface itself. After selected datum and
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cut surface, system can calculate automatically the distance of them by converted to computation of
three-coordinate.
.
Table.1: Process sequence of the workpiece
Fig.2: Tolerance chart of workpiece.
Computer Aided Design
Operationsselection
RoutePlanning
OperationPlanning
Computer Aided
Manufacturing
Selectmanufacturing
operationsGeneratesequence
process,selectmachiners
Select cutting parameter
CallabVue
Database of technical resoure
Fig.3: A sequence operation of automatic generation tolerance chart.
The data relevant to design tolerance can require by manipulating 3D model using the informationof geometric topology elements. The data relevant to manufacturing operation through the database
of process, and the rest needed manual inputting.
Tolerance analysis software system design
Framework of tolerance analysis system. The TAS was developed embedding in 3D collaborative
design platform, CollabVue, include three independent functional modules. The framework of TAS is
illustrated in Fig.4.
The main three modules of TAS depict the main function.
(1) Data input module
Tolerance analysis requires a large amount of information, such as the operation of each face, theeconomical stock removal. This module mainly solved generation tolerance chart and data inputting
simultaneously. Some data required by manipulating 3D model using the information of geometric
topology elements, some through the database of process, and the rest needed manual inputting.
(2) Find dimensional chain module.
The algorithm relatively perfect and the detailed development can be obtained elsewhere [2, 5, 6].
(3) Calculation module.
To effectively solve the problem of traditional algorithm needing calibration, adjustment, revising,
this study introduced a practical method for calculating the technical dimension chain by gradually
solving the equation, finding a dimension chain equation with one unknown quantity, figuring out
this unknown quantity, and then repeating this process until all the technical dimensions calculated.
Fig. 5 describes the flow of this practical method.Data restore. Based on object-oriented technology, this paper proposed a new data structure to
pick up interactively and store dimensional information. A class named CDim storing dimension
information is realized by C++ language. As mentioned before, there are three categories dimension:
Seq.No. Operation Name1 R. Turing
2 R. Turing
3 R. Turing& F. Turing
4 R. Turing
5 F. Turing
6 F.Turing
7 Grinding
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design dimension, operational dimension, and process redundancy. However, the essential of three
categories dimension is the same. In order to find dimensional chain, this new data structure should
contain datum surface, process surface, mean sizes of design dimensions, dimension tolerance, etc.
ToleranceAnalysisSystem
Find
Dimensional
ChainModule
CaculationModule
Manipulating
3DModel
GeometricTopology
Elements
Database of Technical Resource
DataInput
Module
Fig. 4: The framework of TAS.
Fig. 5: Flow of calculation module.
Traditional method of calculating dimensional chains is by matrix operation, and matrix stocking
in the computer always used linked list. However, this paper introduced a practical method for
calculating the technical dimension chain by gradually solving the equation. And there is no needing
to use matrix operation. So we used array to restore the data revenant to calculating dimensional
chains.
Case Study
Based on what is introduced in this paper, a software program is developed. Fig. 6 shows the primary
interface of TAS. A case will be presented where operational tolerance is analyzed with the
application of the system. The case study concerns a workpiece shown in Fig.2. And Table.1 showed
process sequence of this workpiece. In this example, the designers and manufacturers implemented
this system to generate tolerance chart automatically, analyze operational dimension.
The left region of Fig.6 showed topology of the part. On the right of Fig.6, upper region was used to
display 3D model. The table in the bottom of Fig. 6 is a Microsoft control, Flex. All information
shown in the table stored in class CDim, for example, datum, cut surface, mean sizes of dimension,
etc. From this table, process planner can easily get information about manufacturing operation.
Find the array of
dimensional chains
For i=1: k
k is number of
dimensional chains
The unknown dimension
is only one
i=k
Calculating unknown
manufacturing dimension
End
Yes
Yes
No
i=i+1
No
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TSA shows the potential benefits as follow:
(1) Reduced rework in computing dimension chains, cutting tool and cutting parameter selection.
(2) Optimized manufacturing operation sequence and friendly user-interface.
(3) Designers and manufacturers implemented TAS collaboratively.
Fig. 6: Primary interface of TAS
Discussion
Tolerance analysis requires mass information, and traditional tolerance analysis software inputs these
information all by hand [5,6,7], which is both time consuming and problematic. The new method
considered in this paper have primarily concentrated on generation tolerance chart and data inputting
simultaneously. Because some data required by manipulating 3D model using the information of
geometric topology elements, some through the database of process, and the rest needed manual
inputting.Another disadvantage of traditional tolerance analysis software is that the iterative analysis
technique is time-consuming for adjustment and revising, and it often depends on the skill and
experience of the user [5,6]. This paper introduces a practical method for calculating the technical
dimension chain and it keeps from the matrix operation and checking process excess material. As
compared to traditional algorithm, the practical method proposed in this paper need not adjustment
and revision. The number of iterations is much less than that of the traditional algorithm.
Conclusion
To respond to new business requirements of effective collaboration throughout the entire product
lifecycle to leverage core competencies, a framework of tolerance analysis based on 3D collaborative
design platform has been proposed in this study. The key technique has been developed. This paper discusses the utilization of geometric topology information in 3D solid model to process the problem
of dimension information input and the related specific operations. Based on object-oriented
technology, a new data structure to interactively pick up and store dimension information is
established. Finally, the model uses iterative method to compute technological dimension chain
equation.
Future study will focus on the development of 2D tolerance analysis and spatial tolerance analysis
embedding in 3D collaborative design platform, CollabVue. An optimum algorithm will be used to
optimize tolerance assignment.
Acknowledgment
This research has been supported by Natural Science Foundation of China under grant No. 50705032,
and the Hi-Tech Research and Development Program of China under grant No. 2007AA04Z120 (863
Program).
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Advanced Materials Research Vols. 44-46 259
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