Future Issues Queens Univ[Lboro8-2002] 2

7/28/2019 Future Issues Queens Univ[Lboro8-2002] 2

1/10

Proceedings of the 19th International Manufacturing Conference IMC-19 / 2002-Queens University Belfast N. Ireland

FUTURE ISSUES FOR CAD/CAM AND

INTELLIGENT CNC MANUFACTURE

Roberto S.U. Rosso Jr*, R.D. Allen, and Stephen T. Newman

Wolfson School of Mechanical and Manufacturing EngineeringLoughborough University, LE11 3TU, Leicestershire, UK

*To whom correspondence should be addressed. E-mail address: [email protected].

ABSTRACT

The search for automatic manufacture of components has been and continues to be a major goal

of researchers since CNC machines appeared in the 1980s. The ability to generate an NC tool

path is now commonplace from CAD/CAM systems, but the technology used to program NC

machines is still based on 1950s standards. Today under the IMS project named STEP-NC in

Europe and Asia, and Super Model in the USA, industrialists and academics are collaborating todeliver a new data model for CNC machines entitled the ISO14649 standard. The authors believe

that this standard will provide software vendors with the basis to meet this automatic CNC

manufacturing goal. This paper provides a futuristic view of how this standard could be used in

manufacturing and highlights the various issues for CAD/CAM vendors; machine control

vendors and manufacturing users.

KEYWORDS: STEP, CNC, CAD/CAM

1. INTRODUCTIONThe current standard to program NC machine tools has had no significant change since the

early 1950s when the first NC (numerical control) machine was developed at M.I.T.

(Massachusetts Institute of Technology), U.S.A. These early NC machines and todays NC

machines continue to use the same standard for programming namely G & M codes based on the

ISO 6893 standard [1].

Since the 1970s significant developments have been made towards more automatic and

reliable computer numerically controlled machines with new processes such as punching &

nibbling, laser cutting, and water jet cutting which are now common place. The advent of the

Computer Numerical Control (CNC) brought a massive improvement in the capabilities of these

machines. Currently CNC machines provide the ability of multi-axis, multi-tool, and multi-

processes manufacture. These capabilities have made the programming task more and more

difficult and off-line software tools for CAD/CAM a necessity for efficient code generation.Though these developments have revolutionised CNC processes and capabilities, the

programming language has basically stayed the same with G/M code programming which was

developed in the 1950s and later became the ISO 6983 standard that is based on the tool path

and machine status description.

Since the beginning of CAD and CAM software, the problem of amodels portability from

system to system was one of the key issues to spread the use of these tools. Many solutions were

proposed in the direction of a standard way of data exchange such as SET, VDA, and IGES,

which were partially successful [2] but were not totally suitable to all the needs of the

CAD/CAPP/CAM industry. Thus, the international community have developed the ISO10303

[3] set of standards, well known as STEP, which has its foundations in many of the earlier

aforementioned standards [2].


2/10


In parallel with these developments the use of solid modellers has brought the possibility

of a more realistic and reliable CAD model, however the pure geometric solid modellers (GSM)

were not developed enough to take the designers intent to the manufacture engineers. Feature

technology has been researched since 1976 [4] and was expected to fill this gap between the

design and manufacturing environment. However, neither the design intent nor the production

planning could be transferred completely to the CAM systems. Most of the information createdby the designer was lost, or needed to be re-entered, during the process-planning phase, which

included the creation of NC programs by CAM systems. Some researchers have tried to solve

this problem using feature recognition [5] [6] [7]. The key problem is in the creation and

exchange of models where different feature recognisers give different results for the same

problem. By using a design by features approach, within a GSM based CAD system, where the

modelling history is generally stored via feature design interactions. Though once the data is

exchanged from CAD to CAD or CAD to CAM the feature information is lost and then most of

the work must be done again with the additional problem of not understanding or assuming the

designers intent. This problem has been addressed in the standard ISO 10303 with the

Application Protocol 224 (AP224) [8], which provides a set of standardised machining features

for use in process planning.

2. STEP COMPLIANT NC PROGRAMMING

The software evolution for NC programming has seen a number of generations, from the

beginning of hardwired machines, with manual block to block programming, to APT

(Automated Programming Tool), ADAPT[9], AUTOMAP, COMPACT II, and UNIAPT[10] and

the extensions of APT such as EXAPT[11], EXAPT II, and EXAPT III [9] to the modern

graphic interactive Computer Aided Manufacture (CAM) systems. Today the software and

hardware available at machine tools makes it possible to simulate graphically the tool motion,

material removed, and use adaptive control for on-line improvement. The current trends are

towards open architectures such as OSACA [12] and OMAC [13] where third party software can

be used at the controller working within a standard PC operating system.

One further industrial development is the application of software controllers, where PLC

logic is captured in software rather than in hardware. Such systems for example the MDSI CNC

architecture [14], provides many opportunities to implement open control capabilities, but they

are mainly used in retrofitting applications for older CNC & NC machines. Although these

developments have improved software tools and the architecture of CNC machine tools, vendors

and users are still seeking a common language for CAD, CAPP, CAM, and CNC, which

integrates and translates the knowledge of each stage. It is with this aim that the STEP-

Compliant NC (STEP-C-NC) programming is being developed to provide consistent standards

for automatic and quality oriented CNC component manufacture. To this end in the second halfof the 1990s an effort from the international community backed by the International

Organization for Standardization started a major change in the concept of NC programming. A

new data interface called ISO 14649 [15] started to be developed under the ISO technical

Committee TC184 in the Sub-Committees SC1 and SC4 using the ISO 10303 known as STEP as

a basis. Contrary to the current NC programming standard ISO 6983, known by G/M codes, the

ISO 14649 is not a method for programming and does not describe the tool movements for a

CNC machine. Instead, ISO 14649 provides a object oriented data model for CNCs with a

detailed and structured data interface that incorporates feature based programming where there is

a range of information such as the feature to be machined, type of tools used, the operations to

perform, and the work plan [16].


3/10


Figure 1- The general structure of a STEP compliant NC code (Based on [17]).

For each operation performed on one or more features, a statement called a workingstep is

defined. These workingsteps provide the basis of the workplan to manufacture the component.

Figure 1 shows the general structure of the ISO 14649 data. Figure 2 illustrates the actual extract

of such data for a part with a workplan consisting of workingsteps, for facing, drilling, and

pocketing.

Figure 2 - Part of a STEP-C-NC code (Adapted from [18])

DATA (Information about manufacturing tasks & geometry)

Project Start Point of executions

Header (supply general information) FILE_DESCRIPTION;FILE_NAME;

FILE_SCHEMA;

Workplan & Executables:

WorkingstepsNC Functions

Program Structure

(Workplans)

Geometry & Topology description :

Reference TOPositionsAxis Placements

Directions ..

ISO 10303 Part 41

Part 42Part 511

Part 514

Technology description :

Descriptions ofWorkingsteps used in the Workplan

Association with Workingsteps&:Regions, Surfaces and Features

Tool DescriptionDimensions, Type,

Tool holder..Tool Description

Dimensions, Type,

Tool holder..

Technological Information

Cutting width, Spindle,

speed, Feed,

Finish Allowance, Tool usedTechnological Information

Cutting width, Spindle,

speed, Feed,

Finish Allowance, Tool used

Part Identification Workpiece Identification of the PartMaterial Part Material Identification

Property Parameter Material Property Parameter

Part Identification Workpiece Identification of the PartMaterial Part Material Identification

Property Parameter Material Property Parameter


4/10


3. IMPLEMENTATION FRAMEWORKS TOWARDS STEP

COMPLIANT CAD/CAM

The development of ISO 14649 provides a number of options for interpretation and

implementation of this standard within CAD/CAM systems. The implementations in this paper

are defined by the authors as ISO 14649 compliant, and referred to as STEP compliant NC(STEP-C-NC). Three frameworks are defined for STEP-C-NC as outlined below:

i) A CAD/CAM system which imports/generates a STEP-C-NC output;

ii) A CAD/CAM Systems with STEP-C-NC data support structures;

iii) A CAD/CAM environment with kernel STEP-C-NC data structure.

3.1 A CAD/CAM System which Imports/GeneratesSTEP-C-NC OutputThe first form of STEP-C-NC framework provides a CAD/CAM System with the ability to

generate ISO 14649 output. This framework can be further classified into two variants; the first

has the sole ability to export STEP-C-NC code and the second with import and export

capabilities.

3.1.1 CAD/CAM system exports STEP-C-NC dataThe first variant of this CAD/CAM framework is used in its normal operational form using

its own native feature representation and manufacturing strategies for the design and

manufacture of components. The generation of the ISO14649 output is created by mapping the

native CAD/CAM information structures onto the STEP compliant data through a post processor

specifically for ISO 14649. A major issue for this basic form of STEP compliance is that the

CAD/CAM information stored on manufacturing technology (eg. materials, tooling, clamping

and machining strategy data) has to be converted into ISO 14649 format via the post processor. It

should be noted that many of the current CAD/CAM systems will probably not have the

flexibility to incorporate this STEP output, as the output is so different to the normal G/M code

output plus further data is required on the geometry of the component not just machining data.

This framework is illustrated in figure 3.

3.1.2 CAD/CAM system imports and exports STEP-C-NC codeThe second framework is able to both import and generate STEP-C-NC output. The

imported STEP compliant data is translated into the native geometric and manufacturing data

structures of the CAD/CAM system using a reverse post-processor. The user would then use the

system in its normal operating manner, and have the ability to generate STEP-C-NC output as in

section 3.1.1.

Figure 3 Framework that exports

STEP-C-NC data

Figure 4 Variant framework

imports/exports STEP-C-NC data


5/10


3.2 A CAD/CAM System with STEP-C-NC Data Support StructuresThis framework is classified by the CAD/CAM system having a STEP-C-NC data support

structure that maybe held internally or externally to the CAD/CAM system. Two variants of this

framework are outlined below.

3.2.1 A CAD/CAM system integrated with an external STEP-C-NC data support systemIn this case, the CAD/CAM system is integrated with an external software system to

provide the STEP compliant data management support. The framework illustrated in figure 5,

shows the CAD/CAM system functioning independently to a STEP-compliant data management

system. This is used not only for importing information and generating STEP-compliant code,

but also in interpreting the native CAD/CAM geometric and manufacturing routines. In addition

it has STEP-compliant workplans and greater control to configure the output compared to using

the solutions represented in section 3.1

3.2.2 A CAD/CAM environment with both native and STEP-C-NC internal data structures

This case represents a CAD/CAM system, which has a dual internal representation ofgeometric and manufacturing data, both in the native format of the CAD/CAM system and in the

ISO 14649 format. Thus in the operational use of the system both sets of data are updated in real

time rather than generating the STEP output through a post processor or having the STEP

information structures in an external software environment. Although this framework has

essentially the same principle as in 3.2.1, it represents a significant improvement since no post-

processing is required. This framework is illustrated in figure 6.

Figure 5 An external STEP-C-NC

interfaced CAD/CAM environment

Figure 6 An internally shared STEP-C-NC

CAD/CAM environment

3.3 A CAD/CAM Environment with Kernel STEP-C-NC Data StructureThis highest level of compliance is based on a CAD/CAM system, which uses ISO 14649

and ISO 10303-224 for both geometric and manufacturing data models. The authors believe this

structure, will form the basis of new developments for CAD/CAM vendors and will also provide

the direct and simplest generation of ISO 14649 NC code. One overhead of this framework will

be the need to post process the STEP data into ISO 6983 G/M code output for conventional CNC

controllers.


6/10


Figure 7 - Framework to for an internal

STEP-compliant data structure

4. ISSUES FOR THE IMPLEMENTATION OF STEP COMPLIANT CAD/CAM

As the development of the ISO 14649 data model gains significant impetus on the way tobecoming an International Standard, the issues of how to create CAD/CAM systems that are ISO

14649 compliant and their levels of compliance will depend on the industrial use and software

vendors acceptance of the standards. These developments raise a number of issues some of

which are well recognised previously from feature based CAD/CAM plus new issues related to

the STEP standards. These issues are discussed below.

4.1 FeaturesIt is recognised that the use of features has brought many advantages to the design and

manufacturing environment. It is particularly valuable in the way it communicates in

manufacturing terms such as holes, bosses, and pockets instead of the Boolean operations using

cylinders, cubes, and other geometric entities. Features add meaning to the geometric model and

this is a major contribution of this technology.

The view of CAD/CAM developers consider design, process planning and manufacturing

as very related fields which can be considered complimentary in their use of knowledge.

However, it seems that that the use of features in CAD/CAPP and CAM shows a remarkable lack

of consensus.

Companies prefer to define theirs own set of features, sometimes slightly different from

each other. The consequence is a lack of consensus between implementations and the consequent

loss or misunderstanding of the designers intent. In the case of a design and manufacturing

environment this problem adds frustration to the user, moreover the geometric and

manufacturing models suffer from a lack consensus throughout the scientific and engineeringcommunity. To help solve this problem AP224 [8] was developed in the scope of the ISO 10303

standard. AP 224 is generally recognised as a large set of machining features that can be used to

exchange information needed to create machined mechanical parts. The ISO 14649 standard [17]

uses the ISO 10303-224 as a basis to define its features. During the development of ISO 14649

some features were re-defined resulting in the need to map from AP224 to ISO 14649 during

import export routines. It is the authors believe that the use of features defined in ISO 10303-224

should be used in order to avoid any multiple definitions.

The literature has shown the use of both, design by features and feature recognition

approaches [5][6][7][19] for the generation of features within a CAD/CAM model. A third

approach is the hybrid solution [20][21], which combines the feature recognition to understand

imported geometric models and the design by feature capabilities to provide the means to create


7/10


models or to change imported models. A fourth approach can be envisaged, which uses a

translator to exchange feature information among two or more software systems. The use of

translators to transfer geometric information based on neutral standards such as ISO AP203 [22]

and AP214 [23] or proprietary standards such as ACIS and Parasolid models plus feature

translators provides a way to import a component model to a CAD/CAM system. Since both the

geometry and the features would be available to create a model with the same type ofinformation available in the original system. There are a number of proposed solutions to use

geometry plus features either in research institutions [24] [25] or at a commercial level [26]. The

method proposed by Allen et all [24] uses the AP 224 features together with the geometric model

imported using AP203/214 as a way to have STEP compliant data to perform process planning

and to generate a STEP compliant NC program.

4.2 Machining Strategies

The ISO 14649 standard has a defined set of machining strategies that can be used in a

program. Some of them have definitions quite near to the well-recognised G-code canned cycles

in ISO 6983. Although the task is performed in a similar manner, the parameters sometimes are

different. At the highest levels of STEP-compliance it is desirable that the CAD/CAM systemshould be able to capture the machining operations/strategies according to ISO 14649. Without

this level of knowledge this system will merely be translating G and M code cycles into a basic

STEP-C-NC program resulting in much of the operation intelligence being lost.

This is not a problem at present since there are only few prototype CNC controllers [27]

[28] that are able to intelligently process a STEP-C-NC program. It should be recognised that

this would be a future drawback for the vendors, who do not follow the standard.

4.3 Generic versus Machine Specific NC ProgramsThe new data interface provides a way to create very portable programs, which means the

STEP-C-NC program can be used without change across a number of machines. The idea is

feasible in theory, since the development a controller, which has the intelligence to adapt the

program to the specific environment as proposed by Yamazaki [29] and ISO14649 compliant as

proposed by Suh [27]. Within Europe, Siemens has demonstrated the first prototype of an

industrial model of a STEP-C-NC controller for milling using their own vendor proprietary

architecture [28]. Some issues could be raised about the limits of the portability since there are

physical restrictions to machining a part. A program written to perform a task that demands a

five-axis machine tool would not work on a three-axis machine.

4.4 Process PlanningThere were many issues in the past about the way to create, store, and transfer information

about the process of machining components. The ISO 14649 [15][17][18] has a systematic anddetailed structure to solve at least the issue of storage and transfer of this information. One of its

most powerful points as mentioned in section 2 is the richness of information available in a

program written according to the new standard. In reality, the information in a STEP-C-NC

program would be recognised as a detailed process plan rather than a NC program. Details such

as the type of operation, strategy, and tool used to machine a given feature in a workingstep and

the sequence of operations given by the workplan statement. Furthermore, one of the aims of the

standard is to provide capability to be used as the basis for bi- and multi-directional data

exchange between other information systems [17]. Once a program is modified and tested at the

shop floor it can be uploaded back to the process plan database maintaining the data integrity.


8/10


4.5 CNC Machining KnowledgeFor the current generation of ISO 6983 based CNC it is generally a problem to know the

format of the program and what each canned cycle means in terms of tool behaviour. This is

more complex for the new generation of STEP-C-NC than the current CAM and CNC

controllers since it is not a matter of what is the format of the program but how the controller

would react to each instruction. It should be observed that if you have intelligent CNCcontrollers they could perform the same statement differently since the knowledge bases are

different. One new issue, which arises with the standard, is the problem that different pairs of

machine-tool/controllers would provide different tool paths. This means the knowledge

embedded in each controller needs to be available in the CAD/CAM system. Therefore

knowledge bases are expected to be very large in order to provide support for many controllers.

4.6 Validation of a STEP-Compliant Program

Machine capability data is crucial information during the simulation of an NC program.

Although ISO 14649 lets the user create programs without the need to describe the tool path,

during the simulation the user would expect to see the actual tools trajectory for a given

machine. Therefore, the CAD/CAM system must have access to the knowledge embedded in thecontroller being simulated. Presently the developed ISO 14649 solutions use their native

machining strategies, mostly based on G code canned cycles, to simulate the tool path. The

authors believe this is not the best way to perform the task since different intelligent controllers

would act in different ways. They also believe in the need of an agreement between controllers

and CAM systems vendors to solve this problem.

5. CONCLUSIONS

The recent development of the ISO 14649 standard provides a major opportunity to take

full advantage of the programming and machining capabilities of CNC controllers. This paper

outlines thee major CAD/CAM frameworks to support the implementation of the standard with

various levels of STEP compliant architecture. Issues related to the implementation of these

frameworks and their use with STEP compliant NC controllers provide a major change in the

current day use of CAD, CAPP, CAM and CNC systems. This change will bring new challenges

to industrial users and software vendors to identify the new boundaries and define intelligent

CNC manufacture in the 21st century.

6. ACKNOWLEDGMENTS

The authors wish to thank the Engineering and Physical Science Research Council

(EPSRC), Loughborough University, UDESC-State University of Santa Catarina, and ConselhoNacional de Cincia e Tecnologia (CNPq-Brazil) in support of the studentships to undertake this

research.

7. BIBLIOGRAPHY

[1] International Organization for Standartization ISO 6983/1 Numerical control of

machines Program format and definition of address words Part 1: Data format for

positioning, line and contouring control systems. First edition, 15/09/1982.

[2] Sharon J. Kemmerer (Editor), STEP The Grand Experience. Manufacturing Engineering

Laboratory. National Inst. of Standards and Technology. Gaithersburg (MD), July 1999.


9/10


[3] International Organization for Standartization-ISO10303- Industrial automation systems

and integration Product Data Representation and Exchange - Part 1: Overview and

fundamental principles. 1994.

[4] A. R. Grayer, A Computer Link Between Design and Manufacture. Ph.D. Dissertation.

University of Cambridge. September 1976.

[5] Thomas R. Kramer, A parser that converts a boundary representation into featuresrepresentation.Intl Journal of CIM. Vol. 2. No. 3. (1989) 154-163.

[6] Z. Gu, Y.F. Zhang, A. Y. C. Nee, Generic form feature recognition and operation selection

using connectionist modeling. Journal of Intelligent Manufacturing. Vol. 6, (1995), 263-

273.

[7] V. Allada and S. Amand, Feature-based Modelling Approaches for Integrated

Manufacturing: State-of-the-art Survey and Future Directions. International Journal of

Computer Integrated Manufacturing. Vol. 8, No. 6, (1995), 411-440.

[8] International Organization for Standartization - ISO 10303 - Industrial Automation

Systems and Integration -Product Data Representation and Exchange - Part 224:

Application Protocol: Mechanical Product Definition for Process Planning Using

Machining Features. December 2000.[9] Mikell P. Groover, Automation, production systems, and computer-integrated

manufacturing. 2nd Ed., London, Prentice Hall International (2001).

[10] Warren S. Seames, Computer Numerical Control: concepts and programming. 3rd Ed.,

Albany, Delmar Publishers, (1995).

[11] R. I. M. Young, Machine Tool Programming Techniques and Trends. In: Handbook of

Design, Manufacturing and Automation. Richard C. Dorf and Andrew Kusiak (Editors).

New York, John Wiley, (1994).

[12] Peter Lutz and Wolfgang Sperling,OSACA - The vendor neutral Control Architecture.In:

Facilitating Deployment of Information and Communications Technologies for

Competitive Manufacturing, Proc. of the European Conference on Integration in

Manufacturing IiM97, Dresden, Ed. by D. Fichtner, et al., Selbstverlag der TU Dresden,

1997, ISBN 3-86005-192-X

[13] Open Modular Architecture Controls Users Group. Business Justification of Open

Architecture Control. White Paper V1.0. 08/04/1999. Word Wide Web URL:

http://www.arcweb.com/omac/ guidelines/BusJustV1.pdf. Available in 07/03/2001.

[14] Manufacturing Data Systems Inc., OpenCNC Architecture. PDF document.

http://www.mdsi2.com/images/DataS_Arch.pdf. Available in 17/10/2000.

[15] International Organization for Standartization ISO/DIS 14649-1 Industrial automation

systems and integration Physical device control Data model for computerized

numerical controllers Part 1: Overview and fundamental principles. 28/09/2000.

[16] M. Weck and Jochen Wolf. STEP-NC The STEP compliant NC Programming Interface:Evaluation and Improvement of the modern Interface. In: IMS Forum. Ascona /

Switzerland, October/2001.



numerical controllers Part 10: General process data. 09/2000.



numerical controllers Part 11: Process data for milling. 09/2000.

[19] K. Case and M. S. Hounsell, Feature modelling: a validation methodology and its

evaluation.J. of Materials Processing Technology. Vol. 107 (2000), 15-23.
http://www.arcweb.com/omac/guidelines/BusJustV1.pdfhttp://www.mdsi2.com/images/DataS_Arch.pdfhttp://www.mdsi2.com/images/DataS_Arch.pdfhttp://www.arcweb.com/omac/guidelines/BusJustV1.pdf


10/10


[20] J. HAN, and A. A. G. Requicha, Integration of Feature based Design and Feature

Recognition. Computer Aided Design. Vol. 29 No.5 (1997), 393-403.

[21] T. Laako and M. Mntyl, Feature Modelling by Incremental Feature Recognition.

Computer Aided Design. Vol. 25 No. 8 (1993), 479-492.

[22] International Organization for Standartization - ISO 10303- Industrial Automation Systems

and Integration - Product Data Representation and Exchange-Part 203: ApplicationProtocol: Configuration Controlled Design First Edition; Technical Corrigendum 1: 1995.

[23] International Organization for Standartization - ISO 10303-214 Industrial Automation

System and Integration Product Data Representation and Exchange - Part 214:

Application protocol: Core data for automotive mechanical design processes. March 2001.

[24] R. D. Allen, R. S. U. Rosso Jr. and S. T. Newman. AB-CAM: an agent-based methodology

for the manufacture of STEP compliant feature based components, In: Metal Cutting and

High Speed Machining. Edited by D. Dudzinski et al., Kluwer Academic/Plenum (2002),

351-362. ISBN 0-306-46725-9

[25] Mangesh P. Bhandarkar and Rakesh Nagi, STEP-based feature extraction from STEP

geometry for Agile Manufacturing.Computers in Industry. Vol. 41 No. 1 (2000), 3-24.

[26] Anonymous ,Features and History. CAD User. Vol. 15, No. 01(2002), 20-22.[27] Suk-Hwan Suh, Jung-Hoon Cho, Hee-Dong Hong. On the architecture of intelligent STEP-

compliant CNC.Int. Journal of CIM. Vol. 15. No. 2 (2002), 168-177.

[28] Michael Weyrich, Bernard Rommel, Siegmar Haasis, Peter Muller, First Prototype of a NC

Controller based on STEP-NC. In: Sciences Days 2000. (2000), Available at the URL:

http://public.prostep.de/

[29] Kazuo Yamazaki, Yoshimaro Hanaki, Masahiro Mori, Kazusaka Tezuka. Autonomously

proficient CNC controller for high-performance machine tools based on an open

architecture concept.Annals of the CIRP. Vol. 46/1 (1997), 275-278.
http://public.prostep.de/http://public.prostep.de/

Future Issues Queens Univ[Lboro8-2002] 2

Documents

Transcript of Future Issues Queens Univ[Lboro8-2002] 2