Tài liệu Intelligent Set-Up Planning Systems pdf

tool cutting paths yes; PADL-1; spatially ordered representation 3-axis vertical machining centre rules; features grouping based on ADs; set-up sequencing based on criterion component l

5 Intelligent Set-Up Planning Systems for Parts Production in Manufacturing Systems

AbstractKeywords

The Machining Viewpoint • The Fixturing Viewpoint

Approach Directions of Features • Geometrical Relationships • Design Specifications • Machining Requirements • Fixturing Requirements

Set-Up Validity and Optimization • Set-Up Planning and Product Design • Set-Up Planning and Shop Floor Control

to simultaneously adopt these two views, and to achieve the integration with design evaluations and shop

S.K Ong

National University of Singapore

Andrew Y.C Nee

National University of Singapore

floor control systems This paper presents these recent developments and discusses a few open issues inset-up planning.

It can be viewed as the activity of devising means to achieve desired goals under given constraints andlimited resources [Ham and Lu, 1988]

Manufacturing planning is the process of coordinating the various activities in the design and ufacturing processes It is traditionally performed in two stages that communicate through an interfacecalled a process plan, as shown in Figure 5.1 In the first stage, an operations planner and a fixture plannercollaborate to produce a process plan, which is usually a concise document specifying a sequence of

man-FIGURE 5.1 Traditional two-stage approach to manufacturing planning.

Part and Stock Specifications and Drawings

Operations Planner

Fixture Planner

NC Programmer

Part Programs Process Plan

Stage 1 Planning Interface Stage 2 Planning

Cutter, Fixture, and Machine Tool Specifications and Drawings

Process Specifications

Set-up Specifications

Set-up Instructions

operations In the second stage, a numerical control (NC) programmer generates detailed specificationsfor each operation in the plan These are typically part programs for NC machines plus set-up instructionsfor human operators

Currently, manufacturing planning has generally been viewed as a hierarchically structured activity forachieving factory integration through bridging design and manufacturing Most current planning systems,however, are not well integrated Current efforts tend to focus on specific planning functions for specificworkpieces [ElMaraghy, 1993; Bullinger, Warnecke, and Lentes, 1986] For example, one group of researchstudies the extraction and representation of part features from solid models of workpieces [Salomons, VanHouten, and Kals, 1993; Shah, 1988; Shah, 1991], and features modeling and conversion [Bronsvoort, andJansen, 1993; Shah, Mäntylä, and Nau, 1994; Shah, 1992] A second group concentrates on Stage-I planning

artificial intelligence methods [Weill, Spur, and Eversheim, 1982; Ham and Lu, 1988; Zhang, and Alting, 1994].Another group covers systems that support the programming of machine tools and contain some automaticoperations planning facilities These micro-viewpoint planning approaches produce computer-aided sys-tems that perform individual tasks in isolation from other planning activities These computer systemstend to focus on a narrow range of activities that severely limit their applicability in practice For example,many computer-aided process planning (CAPP) systems that have been reported to date are aiming atgenerating the machining sequences of features and the selection of machining operations [Alting and Zhang,1989; Zhang, and Alting, 1994] The same can be said of the many computer-aided fixture planning (CAFP)systems that have been developed to automate the fixture design and planning process [Hargrove and Kusiak,1994; Nee and Senthil Kumar, 1991; Trappey and Liu, 1990] Other areas such as sheet metal forming processesand plastic moulding processes are all challenging domains for planning systems, but have received onlyminor attention so far [ElMaraghy, 1993]

Broadly speaking, the entire process planning domain for the machining environment can be dividedinto three levels, namely (a) operations planning, (b) set-up planning, and (c) fixture planning [Sood,Wright, and MacFarlare, 1993] The most important of these is set-up planning because almost all theprocesses in machining are set-up dependent, as illustrated in Figure 5.2 The set-up process has beenestimated to make up to 60% of the production time on a CNC turning center, and greater than 60%for a CNC machining center [Venjara, 1996] Thus, the reduction of the set-up time and cost of a set-

up plan is vital for achieving efficient production Set-up planning is a link to integrate operationsplanning with fixture planning as both activities can be considered concurrently [Ong and Nee, 1994a]

An automated process planning system should strictly encompass all three levels of planning A criticalreview shows that many of these systems do not address the entire planning problem, but insteadconcentrate on the automation of one of these planning functions Many of the reported CAPP systemscan solve the first planning function successfully, which is operations planning These systems performfunctions such as selecting the least cost operation for each feature on a workpiece, determining thefeeds, speeds, and processes for generating the individual feature, and sequencing the operations forgenerating these features [Westhoven et al., 1992; Züst and Taiber, 1990; Nevrinceanu and Donath, 1987a;Nevrinceanu, 1987b] Another group of micro-viewpoint CAFP systems solves the third planning func-tion, which is fixture planning These CAFP systems plan the locating, clamping, and supporting posi-tions, and design the fixture configurations to hold workpieces during the machining operations[Hargrove and Kusiak, 1994; Nee, and Senthill Kumar, 1991; Trappey, and Liu, 1990] Both groups ofmicro-viewpoint systems do not address planning at the higher level, i.e., set-up planning [Ong and Nee,1994b], although a few of them do perform a certain level of set-up planning in their implementation The premier set-up planning problem is automatic design of set-ups and set-up sequences As men-tioned earlier, set-up planning is a function of process planning that has been largely neglected byresearchers working on CAPP In this paper, techniques that have been applied to computer-aided set-

up planning are discussed This paper also examines the status of, and suggests some future directionsfor, research efforts in computer-aided set-up planning Tables 5.1 and 5.2 give respectively the CAPPand CAFP systems that haveincorporated set-up planning in their implementation Table 5.3 gives a list

of computer-aided set-up planning systems

5.2 Machine and Component Levels Set-Up Planning

Set-up planning can be split into (a) component set-up level, which considers the set-up planning problem

in relation to a single component, and (b) machine batch set-up level, which considers the batch andmachine requirements on the machine tools

Component set-up level planning is concerned with identifying an ordered sequence of set-ups for a workpiecewhere each set-up contains (a) regions to be machined, (b) operations to be performed, (c) possible tools andprocessing parameters for each operation, (d) regions for location, (e) regions for clamping, and (f) orientation

of the set-up Majority of the systems listed in Tables 5.1, 5.2, and 5.3 tackle the set-up planning problem atthis level Factors and constraints that are of importance at this level are essentially the design specifications

of the features on a workpiece, the geometry and topology of the workpiece, tolerance values, etc Theseconstraints are analysed to determine the relations between the features on the workpiece for formulating theset-ups that are needed to machine the required features and the sequence of generating these features Thislevel of set-up planning has a very close link with design evaluation and cost analysis of workpieces [Ong andNee, 1994a] The features on a workpiece can be redesigned by analysing the set-up plans so that fewer set-ups will be needed to machine the workpiece [Hayes, Desa, and Wright, 1989; Mäntylä, Opas, and Puhakka,1989; Ong, and Nee,1994a], thus reducing the cost of the design Table 5.4 gives two design systems that haveincorporated set-up planning during the design evaluation process based on this concept

Hayes, Desa, and Wright, [1989] reported an iterative redesign methodology as a means of using set-upplanning information to find ways of reducing the cost of a design by combining and/or eliminating set-ups

FIGURE 5.2 General operations planning and fixture planning frameworks.

3D CAD Model

Feature Recogniser

Feature-Based Model

Processes & Tools

Machine Tool Selection

Tool Path Planning

NC Part ProgramGeneration

Locating, clamping,supporting schemesdetermination

Stability Analysis

FixtureConfiguration

Assembly Sequence

SET-UP PLANNING

-Grouping of features-Sequencing of set-ups

SET-UP PLANNING

-Grouping of features-Set-up orientation-Set-up positionrelative to tools

Machining Environment

Reasoning Techniques

Level of Set-up Planning Armstrong et al.

1984.

automatic

NC code generation

directions

2 tool cutting paths

yes; PADL-1;

spatially ordered representation

3-axis vertical machining centre

rules; features grouping based on ADs; set-up sequencing based on criterion

component level; set-up forming and sequencing

Chan and

Voelcker, 1986.

process planning

fixturing machining

vise

prismatic 1 part positioning requirements

2 part clamping requirements

yes; PADL-2;

CSG solid models

3-axis vertical machining centre

level;

interactive

set-up planning Joshi et al 1988 process

planning

2 spindle axis directions

3 precedence relations

yes; BREP solid models

rules; features clustering;

set-ups sequencing based on precedence relations

component level; set-up forming and sequencing

Bond and

Chang, 1988.

process planning

2 fixturing requirements

3 spatial relations

yes; UCLA Intelligent CAD models

rules; features clustering

machine level;

set-up forming Mantyla and

Opas, 1988;

Mantyla et al

1989.

process planning - HUTCAPP

2 cutting tools

no; based models

feature-3-axis vertical machining centre

rules; features grouping based on ADs; set-ups sequencing based on number of cuts in each set-up

component level; set-up forming and sequencing

Bell and Young,

1989.

process planning - Machine Planner

machining machining

vise

2 D prismatic

1 critical tolerances

2 maximum material removal

3 clamping strategy

yes; CSG solid models

3-axis vertical machining centre

rules; features clustering based on ADs

component &

machine levels;

set-up forming and sequencing (continued)

1/2

Machining Environment

Reasoning Techniques

Level of Set-up Planning Joneja and

rules; features clustering based on ADs; set-up sequencing based on precedence relations

component level; set-up forming and sequencing

Gindy and

Ratchev, 1991.

process planning - GENPLAN

2 precedence relations of features

3 maximum number of features

no; based models

feature-3-axis vertical machining centre

rules; features clustering based on ADs

component level; set-up forming and sequencing Mayer et al,

1992.

process planning - IMPA

machining machining

vise

prismatic 1 tool directions

2 maximum material removal

3 clamping requirements

4 interference checks

yes; interface via IGES file;

BSPT data structure

3-axis vertical machining centre

rules; features clustering;

breadth-first search strategy

component level; set-up forming and sequencing Warnecke and

conversion to IAOGraphs

3-axis vertical and horizontal machines;

boring and drilling machines

rules; features clustering based on ADs; set-up sequencing based on limiting conditions set-ups

component level; set-up forming and sequencing

Delbressine

et al., 1993.

process planning - IDM

machining modular

fixture elements

prismatic 1 tolerance specifications

2 geometric reachability of features with respect to tools

yes; hybrid of BREP and CSG solid models

3-axis vertical machining centre

rules; merging

of tolerance and precedence graphs

component level; set-up forming and sequencing

TABLE 5.1 CAPP Systems with Set-up Planning (Continued)

Machining Environment

Reasoning Techniques

Level of Set-up Planning Opas, 1993;

Opas et al.,

1994.

process planning - MCOES

machining modular

fixture elements

prismatic 1 machining directions of

features

2 tolerance specifications

yes; BREP GWB modeler

3-axis vertical machining centre

3-axis vertical machining centre

rules; recursive approach

machine and component levels; set-up forming and sequencing Jung and Lee,

1994.

process planning

machining and fixturing

machining vise

prismatic 1 datum requirements

2 ADs of features

3 set-up interference

4 clamping requirements

no; based models

feature-rules; branch

& bound optimisation

component level; set-up forming and sequencing Hwang and

Miller, 1995.

process planning

2 geometric reasoning

no; based models

feature-blackboard architecture;

backtracking

component level; set-up forming and sequencing

TABLE 5.2 CAFP Systems with Set-up Planning

Machining Environment

Reasoning Techniques

Level of Set-up Planning Englert and

Wright,

1986.

fixture planning - Expert Machinist

fixturing machining

vise or toe clamps

prismatic 1 machining practices

2 ADs of features

3 maximum number of features

no; CML language

3-axis vertical machining centre

rules; tables of cuts and orientations

component level; set-up forming and sequencing Young and

Bell, 1991.

fixture planning

machining machining

vise

2 D prismatic

1 critical tolerances

2 maximum material removal

3 clamping strategy

yes; spatially divided solid models

3-axis vertical machining centre

rules; features clustering based

on ADs

component level; set-up forming and sequencing Boerma and

fixturing modular

fixture elements

prismatic 1 tolerance specifications evaluation

2 face orientation of features

3 machine tool directions

4 fixturing requirements

5 most accurate tolerance machined

yes; BREP solid models, GPM

3-axis vertical machining centre

rules; features grouping based

on tolerance relations; set- ups sequencing based on criterion

component level; set-up forming and sequencing

Ferreira and

Liu, 1988.

fixture planning

fixturing modular

fixture elements

prismatic 1 maximum number of features

machining

2 ease of fixturing

3 release of precedence relations

4 dimensional tolerances specifications

5 workpiece stability

yes; BREP solid models;

based models

feature-3-axis vertical and horizontal machines;

boring and drilling machines

rules; features clustering;

evaluate strategy

generate-and-component level; set-up forming

fixturing modular

fixture elements

prismatic 1 datum requirements

2 maximum number of features first

3 ADs of features

4 clamping requirements

machining centre

rules; tracking strategy with kinematics analysis

back-component level; set-up forming and sequencing

Lee et al 1991;

Kambhampati

et al 1993.

process planning and fixture planning - Next-Cut

fixturing and machining

modular fixture elements

prismatic 1 fixturing requirements

rules; features clustering based

on AD of features

component level; set-up forming and sequencing

1/2

TABLE 5.2 CAFP Systems with Set-up Planning (Continued)

Machining Environment

Reasoning Techniques

Level of Set-up Planning Fuh et al

1993.

fixture planning

fixturing modular

fixture elements

prismatic 1 locating datums

2 fixturing constraints

3 tool orientations

yes; CADAM 3-axis vertical

machining centre

rules; step features planning;

step-by- needed strategy

generate-when-component level; set-up forming and sequencing Dong, et al

1991; Dong

et al 1994.

fixture planning

fixturing modular

fixture elements

prismatic 1 ADs of features

2 user-defined fixturing precedence constraints

3 minimum number of orientation changes

yes; ICAD Surface Designer surface models

rules; insertion method of sequencing

component level; set-up sequencing

Yue and

Murray,

1994.

fixture planning

fixturing machining

vise

2 D prismatic

1 clamping requirements

2 tool ADs

yes; ACIS solid modeller

3-axis machining centre

rules; kinematics forces analysis

component level; set-up forming Jeng and Gill,

1995.

fixture planning

operation modular

fixture elements

prismatic 1 tool approach direction of features

2 reference and location constraints

3 good manufacturing practices

machining centre

level; set-up forming

1/2

TABLE 5.3 Set-Up Planning Systems

Machining Environment

Reasoning Techniques

Level of Set-up Planning Hayes and

Wright, 1986;

Hayes and

Wright 1988.

set-up planning - Machinist

fixturing and machining

machining vise

2 D prismatic

1 geometric features relations

2 machining heuristics

3 stock squaring-up operations

no; feature-based models

3-axis vertical machining centre

rules; features interactions graph and squaring graph merging

component level; set-up forming and sequencing Chen and

LeClair, 1994.

set-up planning - RDS

rules; neural network algorithm

component level; set-up forming and sequencing Ong, et al 1993;

Ong and Nee,

1994a; Ong and

Nee, 1994b.

set-up planning - CASP

fixturing and machining

machining vise;

modular fixture elements

prismatic 1 geometric relations

3-axis vertical machining centre

rules; fuzzy set theory modeling

component level; set-up forming and sequencing Zhang et al

1995.

set-up planning

machining prismatic 1 machining precedence feature

relations

2 ADs of features

no; feature-based models

3-axis vertical machining centre

rules;

mathematical optimization algorithm

component level; set-up forming and sequencing Mei, Zhang and

Oldham, 1995;

Mei and Zhang,

1992.

set-up planning

machining and fixturing

three-jaws chucks

rotational 1 geometric tolerance

requirements

2 workpiece support

level; set-up forming and sequencing Yut and Chang,

1995.

set-up planning

fixturing and machining

2 D prismatic

1 feasible spindle directions of operations

component level; set-up forming and sequencing Chu and Gadh,

1996.

set-up planning

fixturing and machining

machining vise

prismatic 1 ADs of features

2 fixturing and referencing requirements

3 machining heuristics

level; set-up forming and sequencing Sarma and

Wright, 1996.

set-up planning, IMADE

fixturing and machining

machining vise

prismatic 1 access directions of features

graph-theoretic model; DAG graphs

component level; set forming and sequencing

1/2

1/2

TABLE 5.4 Design Evaluation Systems with Set-up Planning

Machining Environment

Reasoning Techniques

Level of Set-up Planning Das et al.,

1994.

design

evaluation system

2 machining precedence constraints

yes; MRSEV solid models

3-axis vertical machining centre

rules; first-branch and bound approach

depth-component level; set-up forming and sequencing Hayes

fixturing and machining

machining vise

prismatic 1 tolerances specifications

2 geometric interactions

3 machining precedence

no; based models

feature-3-axis vertical machining centre

level; set-up forming and sequencing

Features can be modified and resources, such as stock from which the part is made, can be changed.Hayes and Sun (1995) recently reported a rigorous analysis of the tolerance specifications of features forgenerating redesign suggestions to enhance the cost efficiency Mäntylä, Opas, and Puhakka [1989] andDas et al [1994] have also incorporated a methodology for generating redesign suggestions, but arerestricted to minor geometrical changes such as fillets and sharp corners Ong and Nee [1994a] considered

a wider range of factors in analyzing the design of the features during set-up planning, providing feedback

on the possible changes to the surface finishes, tolerance specifications, fixturability, and geometricalshapes of the features They performed manufacturability and fixturability analysis of the features whilesimultaneously formulating a feasible set-up plan

The aim of machine batch level set-up planning is to consider batch and component set-up details toidentify the list of set-ups required by a machine batch, and the operations and fixture requirements ofeach set-up Machine batch level set-up planning considers the availability of machines and the fixturingconstraints for the machine type being considered This allows problems that relate to specific machines

to be considered in detail It introduces a useful structure in linking and interfacing with downstreamactivities such as scheduling and capacity planning Bond and Chang [1988], and Gu and Zhang [1993]have implemented set-up planning at the machine batch set-up level by considering the minimumnumber of machines that can provide most of the machining operations required by a workpiece Boththese systems performed hierarchical clustering by grouping the features that can be machined by thesame machine into clusters, and then examining the approach directions and fixturing requirements tofurther group the features into smaller clusters, as illustrated in Figure 5.3

FIGURE 5.3 Hierarchical clustering.

F3

F5

F5 F3

F3

F5 F4

after 2nd stage Tool Approach Directions

after 3rd stage Fixturing Requirements

5.3 Two Viewpoints of Set-Up Planning

Generally, set-up planning has been associated with determining the groups of features and/or operationsthat can be machined together on a particular machine and/or fixture configuration, and the sequencing

of these resultant groups However, a distinction exists in the interpretation of set-up planning by theoperations planners and the fixture designers, as illustrated in Figure 5.4 In fixture planning, set-upplanning is concerned with the grouping of features and the determination of the orientations of theworkpiece for these groups; while in process planning, set-up planning is concerned with the clustering

of features into groups and the determination of a machining sequence of these clusters of ations This difference in the concepts of set-up planning has led to a dichotomy in the research andimplementation on the automation of the set-up planning process

features/oper-The Machining Viewpoint

The objectives of process planning are essentially as follows: (a) select machining processes and tools togenerate all the features on a workpiece, (b) select machine tool(s) to perform these required operations,(c) sequence these operations, taking into account features relations, (d) generate set-ups, (e) determinethe various requirements for these set-ups, (f) select machining parameters for the operations required,(g) plan the tool paths, and (h) generate the NC part program [Ham and Lu, 1988; Ray and Feenay,1993; Hetem et al., 1995] Thus, set-up planning is a part of the generic process planning framework

not associate formulating and sequencing the set-ups as set-up planning These systems essentially mented set-up planning from the machining viewpoint Factors and criteria used are the cutting tools formachining the features, tool cutting paths, dimensional and tolerance requirements, machining directions,etc The earliest work of implementing set-up planning in a CAPP system was reported by Armstrong, Carey,and de Pennington [1984] In most of the systems listed in Table 5.1, a set-up is formed by grouping featuresthat have the same approach direction [Joneja and Chang, 1989; Hayes, and Wright, 1986; Chang, 1991],and considering the precedence relationships between the features due to constraints such as spatial andgeometrical relationships [Joshi, Vissa, and Chang, 1988; Bond and Chang, 1988; Joneja and Chang, 1989;Warnecke and Muthsam, 1992], dimensional and tolerance specifications [Bell and Young, 1989; Joneja andChang, 1991; Delbressine, de Groot, and vander Wolf, 1993; Opas, Kanerva, and Mäntylä, 1994; Nordloh,1994], geometrical accessibility [Delbressine, de Groot, and van der Wolf, 1993; Gu and Zhang, 1993], etc

imple-An assumption in these systems is that the set-up plans formed will always lead to feasible fixture tions The primary objective of these systems is to identify the operations and sequence them, together with theselection of tools and machining parameters Zhang, Nee, and Ong [1995], Delbressine, de Groot, andvan der Wolf [1993], Chen [1993a], Chen and LeClair [1994], Armstrong, Carey, and de Pennington [1984],Gindy and Ratchev [1991], Joshi, Vissa, and Chang [1988], and Bond and Chang [1988] have implemented set-

configura-up planning on this basis Young and Bell [1991] also assumed that the set-configura-up plan formed can be fixtured Thisassumption gives these systems an edge over other systems that perform computationally intensive fixturedesign and planning activities during set-up planning However, fixturing a set-up is a time-intensive activity[Wiendahl and Fu, 1992] Thus, this assumption limits the feasibility of the set-up plans and the applicability ofthese systems, as the work-holding requirements and the availability of fixturing systems are not considered

FIGURE 5.4 Set-up planning tasks—machining and fixturing viewpoints.

OrientationPlanning

OperationsGrouping

GroupsSequencing