08AMR Tolerance

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.

[email protected], [email protected], [email protected],[email protected]

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

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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.

254 Materials and Product Technologies



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

Advanced Materials Research Vols. 44-46 255



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




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




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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[4] Lin K, Yan XG, Xiao J.: Research on Key Technologies of Technological Dimension Chain

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08AMR Tolerance