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Ž .Computers in Industry 42 2000 43–58www.elsevier.nlrlocatercompind

Selection of cutting tools and conditions of machining operationsusing an expert system

B. Arezoo a, K. Ridgway b, A.M.A. Al-Ahmari c,)

a Mechanical Engineering Department, UniÕersity of Sheffield, Mappin Street, Sheffield S1 3JD UKb Mechanical Engineering Department, UniÕersity of Sheffield, Mappin Street, Sheffield S1 3JD, UK

c Industrial Engineering, College of Engineering, King Saud UniÕersity, PO Box 800, Riyadh 11421, Saudi Arabia

Received 16 October 1998; accepted 30 August 1999

Abstract

This paper presents the development of a knowledge-based system for selection of cutting tools and conditions of turningŽoperations. The system developed can be used to select the toolholder, insert and cutting conditions feed, speed and depth

.of cut . It is able to analyse and optimise cutting tools and condition selection. In addition, the user or tool supplier is able tomodify and enhance the system to meet their individual requirements. This system is constructed and implemented using

Ž .Prolog. It contains an inference engine, a user interface and explanation facility a complete shell , a knowledge base, and anoptimisation model for machining conditions. The inputs to the system developed are the part and tool files, which includethe representation of the part features and cutting tools. This paper describes the application of the system developed using atypical example. q 2000 Elsevier Science B.V. All rights reserved.

Keywords: CADrCAM; Process planning; Cutting tools; Machining conditions; CIM

1. Introduction

There is no doubt that modern computing tech-nologies have made a significant impact on manufac-turing systems. These technologies have been usedfor developing many methods, techniques and toolsto support the design and manufacturing functionsw x2,6 . This includes such developments as Computer

Ž .Aided Design CAD , Computer Aided Manufactur-Ž .ing CAM , Computer Aided Process Planning

Ž . Ž .CAPP , Flexible Manufacturing Systems FMS , In-

) Corresponding author. Tel.: q966-1-4676825; fax: q966-1-4676652; e-mail: [email protected]

tegrated CADrCAM and Computer Integrated Man-Ž .ufacturing CIM .

The first step and one of the main objectives of aCIM system is to integrate the CAD and CAMcomponents. The total integration of these two com-

Ž .ponents into a common environment CADrCAMis still under development. Many of the major devel-opments have been uncoordinated and there is agreat deal of overlap in terms of their intendedfunctions. For example, the present CADrCAM sys-tems have their strength in geometrical definition,i.e., CAD component and CAM is mostly limited toNCrCNC programming. Other important intermedi-ate elements such as process planning are not in-cluded. This is due to the fact that the numerical

0166-3615r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved.Ž .PII: S0166-3615 99 00051-2

( )B. Arezoo et al.rComputers in Industry 42 2000 43–5844

information generated by a CAD system is not suffi-cient for process planning. The CAPP systems avail-able in the market are incomplete and limited whencompared to the number of CAD and CAM systemsavailable.

In automated batch production, on-line processplanning is desirable. The conflicting demands ofincreasing flexibility and efficiency on the shop floorrequire the rapid transfer of manufacturing informa-tion. Hence, there is a need for CAPP systems,which cover the whole process of decision making,from the integration of the product model through tothe generation of CNC programs. These systemsmust be capable of taking routine decisions automat-ically to ensure that the user is not an essentialbottleneck in the information flow and only requiredto act as supervisor dealing with exceptions. In thisway, process planning can be carried out quickly andaccurately to meet the demand of the automatedmachine shop.

The process planning function involves a numberw xof activities 18 :

Ø Analysis of part requirements.Ø Selection of raw workpiece.Ø Selection of manufacturing processes.Ø Selection of machine tools.Ø Selection of cutting tools.Ø Determination of machining conditions.

Despite the rapid development of system compo-nents in process planning, there has been littleprogress in the area of tool selection. The develop-ment of systems for the automatic selection of cut-ting tools for machining operations is in its infancy,and the tool selection process is still carried outmanually through extensive searching of cataloguesand manuals.

The optimum selection of cutting tools and condi-tions cannot be simply based upon the familiarity,experience and the memory of individuals. A systemis required to identify and specify various tools andto verify their suitability and availability. The currentmanual-based tool selection system equipped with asuitable methodology to handle the difficulties men-tioned earlier must be developed. This system shouldinclude the following features:Ø a cutting tool database containing details of tool-

holders and inserts;Ø a method of defining component geometry;

Ø a system to relate the component geometry to thetools in the database and select the optimum tool;

Ø a set of tool selection criteria;Ø a method of formulating the optimising cutting

conditions;Ø an interface with the end user.

The system should also have the facility to inter-face with any tool manufacture and enable them toplace their tooling system in the package. In addi-tion, the system should be flexible enough to enablethe user to feed his own shop floor experience intothe system and adapt it to specific requirements.

Using the above characteristics, an Expert Com-Ž .puter Aided Tool Selection System EXCATS com-

prising a knowledge base, inference engine, userinterface, working database and an explanation facil-ity has been developed using the Prolog language.

2. Review of previous work

Cutting tools and conditions selection, as a sub-function of process planning, is a complex taskwhich requires considerable experience and knowl-edge. The objectives of any tool selection exercise

Ž . Ž .are to select the best toolholder s and insert s fromavailable cutting tool stock, and to determine theoptimum cutting conditions. Generative tool selec-tion systems have been developed to different levelsof automation and sophistication.

The early tool selection modules employed graph-ics and presented the user with a catalogue of avail-

w xable cutting tools 16,20 . The user then selected thetools from this catalogue. These systems representthe first leÕel of automation in cutting tool selection.

The next step offered the user all combinations oftool sets, which could completely machine the com-

w xponent 15 . The user would select the best tool setaccording to his experience. The systems representthe second leÕel of automation. The above twolevels consider the geometric aspects of the compo-nent during machining and consider no cutting tech-nology.

A further step is represented by systems, whichincorporate some ‘‘tool preference criteria’’ into tool

w xselection 8,19 . These systems do not only find allcombinations of tool sets geometrically capable ofmachining the component, but also automatically

( )B. Arezoo et al.rComputers in Industry 42 2000 43–58 45

select the best set in terms of cost. These systemsrepresent the third leÕel of automation.

w xThe fourth level of automation 3 is a moreflexible system, which not only seeks the cheapestway of machining a component, but also takes theexperience of the end user into account. This level ofautomation has the advantages of the third levelsystems while avoiding their rigid system design.

Several CAPP systems have been developed forboth variant and generative methods of process plan-ning. These systems. have been reviewed and evalu-

w xated in the literature, e.g., Refs. 1,3,14,18,21 .Most tool selection modules use ‘‘minimum oper-

ational cost’’ criteria for tool selection. This criteriadoes not necessarily consider the technological con-straints involved in modern machining practice. Ex-isting systems cannot easily adapt to include theexperience of machinists within the company asthese systems always impose the ‘‘minimum cost’’criteria. This problem makes these systems too rigidand inflexible. No general solution for tool selectionis acceptable or feasible for all workshops in themetal cutting industry.

The research reviewed has demonstrated that theapplication of conventional computer systems, whichuse decision tables and decision trees, has proved tobe inflexible and inadequate for this purpose. Theuser requirements must be completely specified priorto the design of the system, otherwise the design willbe incomplete or prone to error. A further limitationof conventional programs is the mixing of data andlogic in one program such as knowledge, which is aninextricable part of the program. This renders suchknowledge inaccessible, hard to understand and ex-tremely difficult to modify without making majoralterations to the program. Hence, they are difficultto adapt to the specific needs of a company.

The field of process planning and in particulartool selection depends upon the experience of ex-perts, which cannot be converted into logic or algo-rithmic rules. Generally, in process planning, theinformation required is not always explicitly avail-able and heuristics determine the method of plan-ning. This situation is more suitable for the applica-

Ž .tion of Artificial Intelligence AI .Expert system techniques have been used in a

number of process planning systems for the selectionw xoperation sequence 12,20 . The selection modules in

these systems are either at the first level of automa-tion or similar to conventional systems, which usethe minimum cost criteria. The expert system devel-

w xoped by Mathieu et al. 12 for tools and conditionsselection for turning operations aimed to define ageneral methodology for the selection of the opti-

Žmum tool for every turning operation first level of. w xautomation . Giusti et al. 7 developed an expert

module for automatic tool selection of turning opera-tions — Computer Aided Tool Selection SystemŽ . ŽCOATS — which is a part of PICAP a process

.planing package . In this system, the analysis is toodetailed and complicated. In addition, the processplanners are skilled at judging the suitability of

Ž .cutting tools holder and insert for specific tasksrather than judging the individual parameters con-cerned with different toolholder styles and geometry,insert materials and chip-breaker geometries. A fur-ther drawback of these systems is that they provide arange of cutting conditions and no attempt is made tooptimise the conditions.

3. Development of an expert cutting tool selectionsystem

An EXpert Computer Aided Cutting Tool Selec-Ž .tion EXCATS system, which can select cutting

tools and conditions for major turning operations isdeveloped based upon several procedures. Fig. 1illustrates the general configuration of the EXCATSsystem.

In the design of EXCATS, the following proce-dures were considered.

Ø The system is based upon a generative cuttingtool selection approach.

Ø It is developed in a modular basis to accommo-date different machining operations and tool manu-facturers. Apart from higher efficiency and ease ofdevelopment, updating and maintenance, this enablesusers to acquire only those modules, which are rele-vant to their own particular requirements.

Ø It permits the user to define a core file consist-ing of cutting tools suitable for the machining appli-cations within their own company. Initial tool selec-tion is made from the tools available in the core file.

Ø For a given set of components, the system canselect the minimum number of cutting tools from


Fig. 1. The EXCATS system configuration.

any cutting tool manufacturer’s tooling system tomachine specified components.

Ø It can select cutting tools from any manufac-turer’s tooling system included in the knowledgebase.

Ø It permits the user to override the decisionsmade and carry on repeated consultations with theuser.

Ø Cutting tool selection for a particular machin-ing operation is based upon the suitability of the toolas determined by the cutting tool manufacturer andnot on the composition and properties of the cuttingtool.

Ø It selects optimised cutting parameters accord-ing to the criteria used in manufacturing industry:minimum cost per piece and maximum productionrate.

Ø It has the facility to advise the user on theselection of coolants.

ŽØ It is available for trouble shooting e.g., advise.action in case of excessive wear .

As illustrated in Fig. 1, the EXCATS system hasa user inference, knowledge base, working database,inference engine and explanation facility. These weredesigned and developed by using Prolog. The knowl-edge base comprises two kinds of information: datafiles which hold different material properties, infor-

mation of tool holders, inserts, etc., and mixture offactual, heuristic, and algorithmic knowledge of toolholder capabilities, tool selection guide lines, etc.,held in rule-based form. The rules are designed in aform, which can be changed and adapted to differentmachine shop environment. For example:

If the ‘machining operation’ is ‘external turning’andthe component is ‘clamped in a chuck’ andthe ‘stability of the operation’ is fair then‘round inserts’ are not selected.If the ‘machining operation’ is ‘internal turning’then‘solid boring bars’ are selected unlessthe ‘oÕerhang ratio’ is more than 4.The working database also holds two forms of

information. The first comprises knowledge, whichrepresents the part. The second is the information,which is inferred by the system.

The system developed concentrates on the analy-sis and optimisation of cutting tools and conditionsselection. It is assumed that the blank type and size,sequence of operations and work-holding methodsare already known or found by the user.

The cutting tools considered consist of two maincomponents, the toolholder and indexible insert. Bothare internationally coded to indicate the character-


istics of each tool. The objective of any tool selec-tion is to determine several parameters such as tool-

Žholder clamping system, type, point angle, hand of. Žcut, size, etc. , insert shape, size, grade, nose radius,

. Ž .etc. , cutting conditions feed, speed, depth of cut ,Ž .type of the coolant if required and total cost of

machining the component.The turning operation is usually divided into

roughing and finishing operations. The majority ofthe material to be machined is removed during theroughing operation, which requires maximum power.During the finishing operation a fine cut is used toprovide the required surface finish and detailed pro-file. The selection of toolholder, insert, cutting con-ditions and coolant is based upon a number offactors such as the type of operation, workpiecematerial, geometry, accuracy, finish and power andrigidity of the machine tool. These can be consideredas purely technical factors. A further aspect to cut-ting tool selection is concerned with cutting toolrationalisation. This is often the key to major eco-nomic benefits due to a reduction in cutting toolinventories and reduced tool set-up and change overtimes.

3.1. Part representation

All parts are represented in an English like syn-tax. To demonstrate the operation of the EXCATSsystem, a typical component is shown in Section 4.The part is represented separately for roughing andfinishing operations. The roughing geometries aredetermined according to the operation sequence al-ready known to the user. The finishing geometriesrepresent the exact profile of the finished part. Theelements are numbered in a clockwise manner forexternal machining and anti-clockwise for internalmachining.

To define the workpiece, the user assumes thatthe machining process is carried out against thechuck. Each element of the part is represented by apredicate representing the basic cutting action to

Ž .create the desired geometry face_in, in_copy, etc. .The first four terms of the predicates represent the Xand Y co-ordinates of the start and end points ofeach element. Additional information such as surfacefinish or tolerances are represented in the proceedingterms. For copying geometries, the system calculates

the copy angle for each geometry from the givenco-ordinates. The circular elements are divided intoquadrants and represented separately. The co-ordinates of the centre of each quadrant are repre-sented in the fifth and sixth term of their predicates.These co-ordinates are used to calculate the anglebetween the component centre line and tangent at thecircle to the start of each quadrant.

The part representation file can be created directlyw xor interactively by the user 10,17 . A section of a

typical part representation file for roughing and fin-ishing operations is shown below:

component_001 has ext_rough_ geom_1 toext_rough_ geom_7.ext_rough_ geom_1 is_a long_turn.

( )ext_rough_ geom_3 is_a in_copy 95,5,93,15 .( )ext_rough_ geom_4 is_a long_turn 93,15,67,15 .

( )ext_rough_ geom_5 is_a out_copy 67,15,65,5 .( )ext_rough_ geom_6 is_a in_arc 55,5,40,15,40,0 .

(ext_rough_ geom_7 is_a out_arc 40,15,25,)5,40,0 .

component_001 has ex_ fin_ geom_1 toex_ fin_ geom_19.

(ext_ fin_ geom_1 is_a face_in 155,55,155,27,ra)is 3.2 .

(ext_ fin_ geom_2 is_a out_champher 155,27,)153,25 .

( )ext_ fin_ geom is_a long_turn 153,25,137,25 .

3.2. Representation of toolholder

To match the capabilities of the toolholders witheach element of the component, the toolholders arerepresented in similar manner to the workpiece asdemonstrated below:

PSSN can_ext_turn long_turnand face_in

( )and out_copy max_angle, 45 .PCLN can_ext_turn long_turnand face_inand face_out

( )and out_copy max_angle, 90 .Ž .MTEN can_ext_turn long_turn See Fig. 2

( )and out_copy max_angle, 55( )and in_copy max_angle, 55 .

As the components are always described assum-ing the machining operations are against the chuck,


Fig. 2. Neutral toolholder.

then any left hand toolholder has complementarycapabilities to the corresponding right hand tool-holder. For example, for MTJNR the maximumout_copy angle is 908 and the maximum in_copyangle is 228, and the facing is clockwise. For MTJNL,the out_copy angle is 228 and the in_copy angle is228, and the facing is anti-clockwise.

3.3. Machining design assumptions

The following are examples of the machiningguidelines, which have been used for cutting tool andconditions selection:Ø EXCATS selects the minimum number of tools

which can completely machine the workpiece.Ø EXCATS selects a toolholder which accommo-

Ždates the insert with strongest largest point an-.gle shape to give maximum productivity and

lowest edge cost.Ø EXCATS selects the largest shank size which the

machine will allow to give maximum rigidity,minimum tool deflection and reduced tool over-hang ration.

Ø EXCATS selects the largest nose radius whichthe workpiece or machining condition will permit,to give high feed rate, nose strength and heatdissipation.

Ø EXCATS selects the smallest insert size that cut-ting condition will allow to give lowest edge costand tool cost per piece.

Ø EXCATS selects the greatest depth of cut whichthe workpiece or machine will permit to max-imise productivity.

Ø EXCATS selects single sided inserts for roughingoperations and double sided inserts for finishingoperations unless otherwise stated by the user.

Ø Right hand tools are preferred to left hand toolsand left hand tools are in turn preferred to neutraltools.

3.4. Cutting tool selection procedure

The cutting tools are initially selected for thefinishing operations before selecting for roughingoperations. The workpiece is first matched withavailable toolholders represented in the knowledge

Ž .base. The system selects the toolholder s , which cancompletely finish turn the workpiece and lists themin priority order in accordance with the guidelinesincorporated in the system. Following this, the ge-ometry of each element is compared with neighbour-ing elements to identify the presence of any complexgeometries such as recesses or wide grooves. Theoptimum cutting conditions are calculated, the inserttype, size, grade and chip breaking geometry areselected to meet the cutting conditions and tool-holder requirements. Tools for rough turning opera-tions are selected in a similar manner.

3.5. Selection of cutting conditions

The EXCATS system first calculates the opti-mised cutting conditions for the finishing operations.The finishing depth of cut is then subtracted from themaximum depth of cut to determine the amount ofmaterial to be removed during the roughing opera-tion. The system uses either the minimum cost orminimum machining time criteria as specified by theuser. The maximum rate of profit criteria is notincluded but can be added if required. The tool life

w xequation used is the expanded Taylor equation 4 ,which considers the feed rate and depth of cut inaddition to cutting speed. Fig. 3 shows the flowdiagram of cutting conditions selection.

The procedure for determining optimum machin-w xing conditions is taken from 9 :

VsCT x f yd z . 1Ž .The total machining cost is represented by:

C sM t q t qN t qN C . 2Ž . Ž .pc 1 m t ct t t


Fig. 3. Flow diagram for the selection of cutting conditions.

The machining time t and the number of toolsmŽ .N used for each component are found from Eqs. 3t

Ž .and 4 where the number of cuts n is represented byŽ .Eq. 5 :

p DL dc w xt s , Dg D , Dyd 3Ž .m cVf d

tmN s 4Ž .t T

dcns . 5Ž .

d

Ž . Ž . Ž .Using Eqs. 3 and 4 in Eq. 2 gives:

d Mt Cc ct tC sMt q p DL Mq q . 6Ž .pc 1 ž /ž /Vfd T T

Ž . Ž .Substituting Eq. 1 in Eq. 8 gives:

dcC sMt q p DLpc 1 ž /C

=MTqMt qC 1 1ct t

. 7Ž .xq1 yq1 zq1½ 5ž /ž /T f d

Similarly the total machining time is representedby:

p DLd Tq t 1 1c ctT s t q .t 1 xq1 yq1 zq1½ 5ž / ž /ž /C T f d

8Ž .


To obtain the minimum cost and minimum ma-Ž . Ž .chining time Eqs. 7 and 8 must be minimised. Let

K and K be the objective functions:1 2

MTqMt qC 1 1ct tK s 9Ž .1 xq1 yq1 zq1½ 5ž /ž /T f d

Tq t 1 1ctK s 10Ž .2 xq1 yq1 zq1½ 5ž / ž /ž /T f d

where:

y1-x , y , z-0. 11Ž .The objective functions can be generalised as:

KsF F F . 12Ž .1 2 3

Considering the objective functions above, it canbe seen that apart from the tool life T , only the upper

limit restrictions for feed rate and depth of cut needto be considered as these are strictly decreasingfunctions of both feed rate and depth of cut. Dy-

w xnamic programming 5,13 is applied to this problemwith the explicit optimisation rationale applied at oneor two stages depending on whether the tool life ispredefined by the user or not. Fig. 4 illustrates flowdiagrams of selection procedure of the cutting condi-tions for roughing and finishing operations.

For simplicity, the roughing operations are de-scribed first. The procedures for calculating the opti-mised cutting conditions for roughing operations areas follows.

Ø If the tool life T is predefined by the user, thenŽ .F in Eq. 12 is consistent and the procedure is:1

Ø The maximum depth of cut is set equal to d , i.e.,c

rough turning in one pass.

Fig. 4. Flow diagrams of cutting conditions selection for roughing and finishing operations.


Ø The maximum feed rate is selected.Ž .Ø The cutting speed is calculated using Eq. 1 . If

the selected conditions do not comply with theconstraints, the feed rate is first reduced incre-mentally to its lower limit and then the depth ofcut is reduced to d r2, d r3, etc., until thec c

constraints are satisfied.Ø If the tool life is not defined by the user, it is

optimised within the range 6–30 min. This achievedby minimising F while selecting the feed and depth1

as above and testing against the constraints until theoptimised cutting conditions are obtained.

The surface finish predefines the feed rate infinishing operations as it acts as a constraint. Oftenthe depth of cut is predefined by the user and hencethe tool life and cutting speed are optimised. If this isnot the case, the system optimises the depth of cut inthe range 0.25–1.5 mm or as defined by the user.

Several machining constraints are considered byw xthe EXCATS system 3 , including:

Ø Limits on the operating parameters.

V -V-Vmin max

f - f- fmin max

d -d-dmin max

Ø Limits on the feasible tool life.

T -T-Tmin max

Ø Limit on available power. The power required byin kiloWatts for a turning operation can be calcu-

w xlated using the following formula 11 :

df mck Vcps 13Ž .

60 000=Eff

w xØ Limit on tool thrust 9 .

ThsC f n1 dn2 -Th1 max

w xØ Limit on spindle torque 9 .

M sC P f n3 PdPD-Mt 2 max

w xØ Limit on the surface finish 4 .

0.0321 f 2

r sa re

4. Exemplary application of EXCATS system

To demonstrate the EXCATS system, cutting toolsand conditions are selected to machine the part shownin Fig. 5.

This component is a steel component manufac-tured to DIN standard C15, which is equivalent to040A15 in British standard, and the hardness is 120Brinel. It is designed to demonstrate the full range offeatures presented by EXCATS. In this example, it isassumed that more than one set-up is required. Thispart contains a number of internal and external ge-ometries. The first step is to represent the part inaccordance with procedure specified in Section 3.1.Fig. 6 illustrates the complete representation of thepart.

This representation is the only input to the EX-CATS concerning the part. All other representationsrelated to the component preparation are generatedautomatically by the system. Different stages of sys-tem consultation are carried out using different Pro-log files to complete the tool and conditions selec-tion. When the EXCATS starts the consultation, the

Ž .kind of job tool selection is determined. Then thetool manufacturer, type of machining operation andnumber of the machine tools are determined. Theresult of this stage is:

: Your job is Tooling system selection.: the tool manufacturing company is SandÕik.: the machining operation is turning.: the Machine tool is CNC Machine no. 1.: the Machine power in kW is 25.: the Machine Max shank capacity is 32 by 25.: the Machine Turret capacity is 10.: the Machine eff. is 0.7.: the Machine feed range in mmrreÕ is 0.1 to 1.4.: the Machine spindle speed range is 20 to 2000.: the Machine depth of cut range in mm is 0.1 to15.: the Machine and operator rate in P is 30.: the machine ‘‘tool changing time’’ for ‘‘ finish-

( )ing operations’’ in min is 15.: the Machine ‘‘tool changing time’’ for ‘‘rough-

( )ing operations’’ in min is 5.The next five questions relate to the stability

conditions of the turning operation. For example:Is the turning operation:

a: continuous turning


Fig. 5. Illustrative example.

b: interrupted turning² :Enter a . . . b : a

Is the component:a: held in the chuckb: held in the chuck and tailstockc: held in the chuck and steady rest

² :Enter a . . . c : a. . .etc.EXCATS determines this using a set of rules. The

results obtained from these questions are:: the turning operation is continuous turning.: the component is held in the chuck.

: the surface condition of the blank is bright bar.: the surface structure is light skin.: the component Length to Diameter is LrDF5.: the component is cylinder type component.: the stability of machine tool is fair.: the stability of cutting operation is reasonable.The stability of cutting conditions is established

as being ‘‘reasonable’’. If the answers to questionsof the above step were different, then the stabilityconditions would have changed. For example, if the

Ž .following question was b: interrupted turning :Is the turning operation:

a: continuous turning


Fig. 6. The component representation file.

b: interrupted turning² :Enter a . . . b : b

Then this condition would make the stability con-dition ‘‘unfavourable’’. If the answers of the user tothe next four questions were different, this wouldinvoke the following rule:

if the component is held in the chuck and tailstockand the surface structure is light scale skin

and the component is cylinder type componentand the stability of machine tool is goodthen the stability of cutting operation is faÕorable.The stability condition of the turning operation

effects the insert grade and chip breaker geometryselection. The complete rules for stability conditionsare constructed in Prolog. These rules can bechanged, added to or deleted from the knowledgebase as required.

The EXCATS system then determines the compo-nent material and hardness from which the mer-chantability group number and chip type of materialwill be retrieved using the following questions:

Is the material code:a: DIN codeb: BS codec: AISI code

² :Enter a . . . c :a: the material code is DIN code.Write the material code number: C15: the material code number is C15.Write the material hardness in BHN: 120: the material hardness in BHN is 120.: the material group number is 1.: the material is long_chipping.: the material group is steel or cast steel group.

(tool_life_exp 1,P10–P20,1214,y0.3800.y)0.1200,y0.1000

(tool_life_exp 1,P20–P30,937,y0.3400,y)0.1300,y0.100

(tool_life_exp 1,P30–P40,745,y0.3400,y)0.2300,y0.1100

EXCATS has established that the material is steel,its group number is 1, and it is long_chipping. Thenext stage involves retrieving the tool life exponentsfor all available inserts grades regardless of whichgrade will be selected later by the EXCATS system.In the ‘‘tool_life_exp’’ predicates above, the first

Ž .element 1 represents the material group number,Ž .the second element P . . . –P . . . denotes the appli-

cation area of the carbide grade, the four remainingŽelements represent the Taylor tool life exponents C,

.X, Y and Z . The complete listing of availablematerials, their merchantability group number andthe exponents for different materials are representedin Prolog files. In the following stage, the systemwill require the part file name: : the componentname is component1.


Table 1The recommendation of the system

RECOMMENDATION

EXTERNAL FINISHING OPERATION[ ] [ ]HOLDER MTJNL 20 20 K 16 ™ INSERT TNMG 16 04 12 GC415-QF

a[ ]MTJNL ext_ fin_turns geometries no 6,7,2 of 9[ ] [ ]HOLDER MTJNR 20 20 K 16 ™ INSERT TNMG 16 04 12 GC415-QF

a[ ]MTJNR ext_ fin_turn geoms no 1,2,3,4,5,6,8,10,1 of 9( )CUTTING DATA: min_cost

Tool INS DEPTH FEED VEL TLIFE POWER FINISH

MTJNL TNMG 1.5 0.19 408 26.5 7.404 Ras1.0MTJNL TNMG 1.5 0.27 391 26.5 9.257 Ras2.0MTJNL TNMG 1.5 0.30 388 26.5 9.726 Ras6.0MTJNR TNMG 1.5 0.19 408 26.5 7.404 Ras1.0MTJNR TNMG 1.5 0.27 391 26.5 9.275 Ras2.0MTJNR TNMG 1.5 0.30 387 26.5 9.726 Ras6.0

EXTERNAL ROUGHING OPERATIONS[ [ ]HOLDER PCLNR 32 25 P 12 ™ INSERT CNMG 12 04 16 GC425-QM

[ ]PCLNR ext_rough_turn geometries no 1,2,3,8[ ] [ ]HOLDER PDJNL 20 20 K 15 ™ INSERT DNMG 15 06 12 GC425-QM

[ ]PDJNL ext_roiugh_turns geometries no 5,6,2 of 7[ ] [ ]HOLDER PDJNR 20 20 K 15 ™ INSERT DNMG 15 06 12 GC425-QM

[ ]PDJNR ext_rough_turns geometries no 1,3,4,5,8,1 of 7( )CUTTING DATA: min_cost

Tool INS DEPTH FEED VEL TLIFE POWER PASS NO

PCLNR CNMG 5.58 0.30 199 13.7 24.78 first( )PCLNR CNMG 5.58 0.30 265 13.7 24.78 other passe s

PDJNL DNMG 6.70 0.25 192 15.4 24.95 first( )PDJNL DNMG 6.70 0.25 256 15.4 24.95 other passe s

PCLNR DNMG 6.70 0.25 192 15.4 24.95 first( )PCLNR DNMG 6.70 0.25 256 15.4 24.95 other passe s

INTERNAL FINISHING OPERATIONS[ ] [ ]HOLDER S 20 S-SDUCL ™ INSERT DCMM 11 03 08 GC415-QF

[ ]SDUCL fin_turns geometries no 3,4[ ] [ ]HOLDER S 20 S-SDUCR ™ INSERT DCMM 11 03 08 GC415-QF

[ ]SDUCR fin_turns geometries 1,2,4,5,6( )CUTTING DATA: min_cost

Tool INS DEPTH FEED VEL TLIFE POWER FINISH

SDUCL DCMM 1.50 0.30 330 26.5 9.70 Ras6.0SDUCL DCMM 1.50 0.30 330 26.5 9.70 Ras3SDUCR DCMM 1.50 0.30 330 26.5 9.70 Ras6.0SDUCR DCMM 1.50 0.30 330 26.5 9.70 Ras3

INTERNAL ROUGHING OPERATIONS[ ] [ ]HOLDER S 25 T-PTFNL ™ INSERT TNMG 16 04 12 GC425 -QM

[ ]PTFNL rough_turns geometries no 3,4[ ] [ ]HOLDER S 25 T-PTFNR ™ INSERT TNMG 16 04 12 GC425 -QM

[ ]PTFNR rough_turns geometries no 1,24,5,6( )CUTTING DATA: min_cost


Ž .Table 1 continued

RECOMMENDATION

INTERNAL ROUGHING OPERATIONSTool INS DEPTH FEED VEL TLIFE POWER

PTFNL TNMG 6.70 0.25 218 15.4 24.957PTFNR TNMG 6.70 0.25 218 15.4 24.957

a Two of nine and one of nine mean that the arc geometry number 9 resides on two quadrants, which are treated as two separate featuresŽ .2 and 1 an in_copy and an out_copy with an angle of 908 .

The system automatically prepares the part repre-sentation for the tool selection as follows:Ø External finishing geometries.Ø External roughing geometries.Ø Internal finishing geometries.Ø Internal roughing geometries.

Following this, EXCATS generates a completeŽlist of each operation with geometries involved total

.of four lists . These lists are called the componentŽprimary feature lists the primary or basic machining

operations in a turning operation can be divided intolongitudinal turning, facing-in, facing-out, in-copy-

. 1ing, and out-copying , which are used by EXCATSfor the tool selection. The system generates a com-

Ž .plete list for each set-up component set-up lists .Each list includes all the geometries, which are to bemachined in that set-up. These lists will be also usedto determine the existence of any recesses and theirsizes. The system has recognised a total of sixrecesses of which two are external finishing, two areexternal roughing, one is internal finishing and thelast one is internal roughing. At this stage, the partrepresentation is completed and EXCATS now re-quires the tool file name, in which the available toolsare stored. Tool preparation is the next stage of theoperation. Initially, the system breaks the capabilitiesof each tool and registers them in a single operation:: the Tool file name is tool1.

EXCATS will then group the capabilities of eachtoolholder in one single list. At this stage, the toolpreparation phase is completed and the tool selectionfor external finishing operation starts. The capabili-ties of each external finishing tool will be compared

1 Secondary turning operations are classified into three groupsgrooving, threading and parting-off. These types of operations arenot considered in this paper.

to the external finishing geometries of the compo-nent using the procedure of tool selection for exter-nal finishing operations. The component geometries,which can be machined by each tool will be regis-tered for the tool, for example:

( )MTJN,R can_ext_ fin_turn face_in no 1( )MTJN,R can_ext_ fin_turn long_turn no 2( )MTJN,R can_ext_ fin_turn out_copy no 3( )MTJN,R can_ext_ fin_turn long_turn no 4( )MTJN,R can_ext_ fin_turn out_copy no 5( )MTJN,R can_ext_ fin_turn long_turn no 6( )MTJN,R can_ext_ fin_turn long_turn no 8( )MTJN,R can_ext_ fin_turn out_copy no 1 of 9( )MTJN,R can_ext_ fin_turn long_turn no 10( )MTJN,R can_ext_ fin_turn face_out no 11Following this, EXCATS groups the geometries

in a single list for each tool. Automatic searchingwill be initiated to find a single tool to finish theexternal geometries of the component. If not success-ful, the system searches for a set of two tools, threetools, etc., until it finds a set of tools which cancompletely turn the external geometries of the com-ponent. The system determines which set is superiorusing the tool preference rules. For example:

( )if ‘MTJN’, ‘R’ can_ext_ finish_machine ‘thecomponent’

( )and ‘MTEN’,‘R’ can_ext_ finish_machine ‘thecomponent’

( )then ‘MTJN’,‘R’ has first_ext_ fin_ priority( )and ‘MTEN’,‘R’ has second_ext_ fin_ priority.

In this exemplary application, EXCATS has de-termined that ‘‘MTJNR’’ and ‘‘MTJNL’’ is the onlytool set, which has a first priority and no secondpriority; hence, it has established that this set issuperior to others. Consequently, this tool set isoffered to the user for confirmation. It will also offerthe user the possibility of an explanation or rejectionof the superior tool set and search for the next bestset using specific EXCATS menus. If the user con-


firms the EXCATS selection for external finishinggeometries, the system will determine the toolholdersize and examine the tool for possible collisions.

To ensure maximum stability of the turning opera-tion, the EXCATS system always selects the maxi-mum shank size available, which is compatible withthe machine tool size. The compatible insert size isalso selected for the toolholder. The toolholder selec-tion for the external finishing operation is completedbefore EXCATS begins the tool selection for exter-nal roughing operations. Tool selection proceduresfor the remaining operations are identical to theselection procedure for finishing operations. The userconfirms the selection of EXCATS and the systemdetermines the size of toolholders.

In this example, EXCATS cannot find a suitablesize for the ‘‘MTGNR’’ toolholder in the tool file,which does not collide with the component. Whensuch condition arises, the system will reject theselected tool sets and redo the selection proceduresas before assuming that ‘‘MTGNR’’ and ‘‘MTGNL’’are removed from the tool file.

EXCATS finds a suitable toolholder size for thisselection and the procedure for external roughinggeometries is completed. The tool selection for inter-nal finishing operations and internal roughing opera-tions follows.

The tool selection for all types of operations arecompleted. At this stage, cutting conditions optimisa-tion starts. EXCATS initially determines the objec-tive function for cutting conditions selection as:

Is the optimisation criteria:a: Minimum production costb: Minimum production timec: Fixed tool life

[ ]Enter a . . . c : aThe system defaults for ‘‘Workpiece and Machine

Ž .tool’’ WM are presented to the user and confirma-tion is requested. The maximum and minimum exter-nal and internal workpiece diameters, from whichEXCATS will calculate the maximum external andinternal depth of cut to be removed, are determined.The system will select the insert and chip-breakinggeometry using a set of rules, which are only validfor Sandvik turning inserts. Similar rules could bedeveloped for other tool manufacturers.

EXCATS retrieves the tool life exponents for thefinishing and roughing insert grades from the

database. The finishing and roughing cutting condi-tions are calculated as presented in Section 3.5. Thesystem has now determined all the required informa-tion and presents this as the recommendations of the

Žsystem in tabular forms as illustrated in Table 1 thecoding of the selected toolholders and inserts istaken from the ISO standard for external and internal

.toolholder and inserts .At the end of the consultation, EXCATS offers

the possibility of optimising the cutting conditionsŽaccording to a second objective function e.g., fixed

.tool life , starting a new consultation problem oraborting the system. If EXCATS is used to optimisethe cutting conditions according to minimum produc-tion time and fixed tool life then new cutting condi-tions will be calculated by the system.

5. Conclusion and future work

The EXCATS system, as a stand alone system,could be applied to automated manufacturing sys-tems, which aim to optimise the performance ofsimple turning operations. In addition, the systemoffers the possibility of a novel and integrated ap-proach to cutting tools and conditions selection formachining operations. It demonstrates the pivotalrole of a knowledge-based system in achieving maxi-mum flexibility in the process planning automationand development of fully integrated CIM systems.When an integrated and direct path to cutting toolselection can be provided, it is possible to moverapidly and accurately from the product design phaseto manufacture.

An effective representation of the product modelis an essential of any automated process planningsystem as any generative process planning systemrequires a detailed definition of the component ge-ometry. This requirement is successfully solved inEXCATS by adopting a methodology for componentrepresentation. To perform cutting tools and condi-tion selection for a component, the input to EXCATScomprises information related to the description ofthe component and the sequence of operations. Boththe rough blank and finished component are de-scribed in terms of the cutting operations required.


The method developed for component representationis easy to use and understand and little knowledge ofcomputers is required. The workpiece representationmethod forms a key feature in the EXCATS system.The system allows for an easy identification anddirect relationship between the cutting tool and thecomponent using operation key words, which de-scribe both the workpiece and cutting tool. All tool-holders supplied by any tool manufacturer can berepresented in this manner.

The rule-based knowledge base is designed to beadapted to different working environments. The logicof the tool selection criteria is based upon a series ofrules, which can be easily changed by users to meetspecific needs. The utilisation of the machine toolpower is optimised within the constraints imposed bythe properties of the workpiece materials, tools andtool materials.

The EXCATS system, as it stands, concentrateson the selection of cutting tools and conditions, andis incapable of the determination the machining se-quence and work holding methods, both of which areassumed to be provided by the user. When perform-ing cutting tool selection, right hand tools are pre-ferred to left hand tools and left hand tools are inturn preferred to neutral tools.

Although still in pilot form the demonstrationillustrates that the system developed can select cut-

Ž .ting tools toolholders and inserts and cutting condi-Ž .tions depth of cut, feed and cutting speed for major

turning operations. The system initially determinesall the feasible tool sets, which can completely ma-chine the component and then selects the most suit-able tool using the preference rules within theknowledge base. The tool preference rules are basedupon the recommendations of cutting tool manufac-turers. The rules can be changed by the users to suittheir own machining environment.

Future proposed developments include:Ø The integration with a similar package for milling

w xoperations 14 .Ø The integration of a CAD system for workpiece

w xrepresentation and final verification 21 .Ø The integration of a database management system

into the system developed to improve manage-ment and control of the system.

Ø Development of the system into a complete pro-cess planning system.

6. Notation

C tool life constantC constant, thrust equation1

C constant, torque equation2

C cost per componentpc

C cost of toolt

d actual depth of cutrpassD workpiece diameterD diameter of cutting tool1

d maximum depth of cut to be removedc

d maximum allowed depth of cutmax

d minimum allowed depth of cutmin

E efficiencyff

f feed rateK specific cutting forcec

L length of workpieceM total machine and operator rateM maximum torquemax

M spindle torquet

M force increase factorc

n number of cuts, rough turningn feed rate exponent for thrust equation1

n depth of cut exponent for the thrust equa-2

tionn feed rate exponent for torque equation3

N number of tools usedt

P maximum available powermax

r surface finisha

r insert nose radiuse

T tool lifeTH maximum tool thrustmax

t idle time1

t tool change over timect

t machining time per componentm

V cutting speedV maximum feasible cutting speedmax

V minimum feasible cutting speedmin

x tool life exponent, tool lifey tool life exponent, feed ratez tool life exponent, depth of cut

Acknowledgements

The authors are grateful to the anonymous re-viewers for providing very useful suggestions.


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