step-nc – new data interface for nc programming

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STEP-NC New data interface for NC programming

NewsletterIssue 5, September 2003

STEP-NC is funded by the EC Growth Programme

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Dear Reader,

This is the fifth issue of the STEP-NC Newsletter, informing you about the developments in the context of theEuropean GROWTH project IMS STEP-NC. The STEP-NC project contributes to the establishment of a new

data interface for NC-Programming (ISO 14649) in replacement of the ISO 6983 Programming Code.

Should you want to become a member of the Step-NC Interest Group, then please let us know and e-mail us [email protected] . You will then receive the STEP-NC Newsletter directly as an e-mail attachment and you

will be kept informed about future information and dissemination activities.

More information and the previous STEP-NC Newsletters can be found on http://www.step-nc.org/.

In this issue you will find information on the development of the data model and the prototypeprocess chain for

turning applications. The Newsletter discusses turning-specific characteristics of STEP-NC and presents first

realisation results. The first public presentationof turning applications will take place on the FTK in Stuttgart,

Germany on October 14th

, 2003.


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Issue 5, September 2003

Introduction

Todays CAD/NC process chains have a major lack. They require a number of data conversions. Theseconversions are time-consuming, often irreversible and afflicted with information loss. The major bottleneck of this

process chain is at its end. Actual, NCs mostly require ISO 6983 as input format. This data format was suited inthe beginning of computerized machining when only simple data formats were processable. But as a

consequence of the progresses in production engineering, the higher complexity of machine tools and proceedinginformation integration within and between facilities as well as modern forms of labor organization the limited,machine-dependant data format of ISO 6983 is not appropriate anymore since it necessitates a number of postprocessors and inhibits the feedback of worker know-how (Figure 1).

STEP-NC is the backbone of the counterpart scenario for CAD/NC process chains. Since it allows direct use ofCAD data and will form the direct input format for the NC, no conversion operations are necessary. Allcomponents of the process chain are working on the same data format enabling a closed-loop process chain. Its

object-oriented information model eases the development of graphical NC editors with read-in and modifyingfunctionality as well as the development of more sophisticated applications.

Due to its high information content the STEP-NC standard is divided in one general and several technology-

specific parts. The corresponding division of the STEP-NC information model in several modules allowsapplications to support distinct technologies being in full conformance to the standard. The first workings on

STEP-NC covered milling and drilling technology. Milling and drilling applications and machining tests alreadyshowed major benefits of STEP-NC compared to the existing ISO 6983 standard. The development of the turningdata model and applications forms the next step on STEP-NCs way to a comprehensive standard data interfacefor manufacturing.

Figure 1: Comparison of process chains based on G-/M-Code (ISO 6983) and STEP-NC (ISO 14649)

actual process chain

NC

G-/M-Code

(ISO 6983)

post processor

CAM tool- path planning- cutting conditions

CLDATA / APTLike Language

CAD tool CAM tool- workplan- operations - technology - strategies

STEP-NCdatabase

Planning Level

Shop Floor

Integrated process chainwithout information loss

Bidirectionality: Feedbackof processinformation, useof worker know-how

High information contentfor sophisticated applications

Advantages :

STEP-NC process chain

NC

CAD tool

geometry data

ile, e.g. IGES

information loss

no portability

no reconversion

her0d010a.dsf, 25.09.2001 ISW

CAD:CAP:NC:

Computer Aided DesignComputer Aided PlanningNumerical Controldata flowfile transfer by ISO 10303-21or binary common databasedata file


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Data Model for Turning

To extend the usage of STEP-NC to turning processes a STEP-NC sub model for turning has been built. The ISO

document defining the STEP-NC interface for turning currently achieved its Draft International Standard (DIS)status and thus forms a stable base for turning applications.

The data model for turning extends the general process model of STEP-NC with turning-specific feature and

technology information. Like any STEP-NC process model the STEP-NC model uses the feature description ofthe CAD standard STEP defined in STEP - Mechanical Product Definition for Process Planning using MachiningFeatures (ISO 10303-224) and the STEP-NC - General Process Data (ISO 14649-10).

Turning features and operations are defined in the STEP-NC - Process Data for Turning (ISO 14649-12). Thefeatures for turning represent work piece geometry attained by conventional turning. Turning operations arestructured similar to the milling and drilling operations following the consistent STEP-NC modelling approach.

They also reference technology data and strategies for machining, approach and retract movements. Sincemilling, drilling and turning features as well as operations are based on the General Process Data of STEP-NC, allcan be referenced in a combined STEP-NC program. Thus complete machining processes are also possible with

STEP-NC.

Also contours consisting of straight and rounded segments used in common CAM editors for turning are part ofthe turning model. Moreover, STEP-NC uses the STEP description and implementation methods, which allows

use of various STEP software tools. Thus migration of turning applications to process STEP-NC data is eased.

Prototype process chain for turning

To show the benefits of STEP-NC for turning, the STEP-NC partners are implementing a prototypical STEP-NCprocess chain. Because commercial STEP-NC based CAD and CAM systems are not available up to now,existing systems were equipped with coupling modules with respect to the requirements on the process chain

(Figure 2).

Figure 2: Process chain for turning

Design

Process Planning / NC programming

Shop floor / machine tool

AP:CAD:CAM:

Application ProtocolComputer Aided DesignComputer Aided Manufacturing

NC:STEP:STEP-NC:

Numerical ControlSTandard for the Exchange of Product model dataSTEP compliant data interface for Numerical Controls

data flow

* modification of read-in STEP-NC data file* conversion to Siemens ShopTurn* manufacturing of the work piece

* input of STEP AP203 data file* feature recognition* definition of machining operations,strategies, technologies, etc.

* output of STEP-NC data file* input of existing STEP-NC data files

* 3D design of the work piece with theSTEP-enabled CAD tool CATIA V5

* output of geometry dataas STEP AP 203 data file

STEP, AP203geometry data file

CAD tool

CATIA V5

CAM tool

STEPTurn

STEP-NC-fileNC programme

conversion toolSTEP-NC -> ShopTurn

NC with ShopTurn


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The test part is designed in CATIA V5 (Figure 3) and output as STEP AP203 data file (ISO 10303-203). Thesoftware prototype STEPTurn, providing CAM functionality, reads in this data file and displays the part (Figure 4).

Feature recognition and assignment of machining operation as well as selection and input of technologyparameters and strategies is done by use of STEPTurn. At last, a STEP-NC data file is generated for output. TheSTEP-NC file is read in a conversion module to the Siemens ShopTurn data format, which is the input format to

generate tool paths for the Siemens 840D NC. The conversion of STEP-NC data files is necessary since noSTEP-NC-compliant NC is available. Additionally to the conversion editing of the STEP-NC program directly onthe machine tool is provided by the conversion module (Figure 5).

Figure 3: Test part designed in CATIA V5 Figure 4: Process Planning with STEPTurn

Figure 5: Conversion module to Siemens ShopTurn


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Having completed these steps the NC programs are available in the data format to be executed on a machinetool. For its execution the turning machine tool Boehringer NG200 is applied (Figure 6).

Figure 6: Applied Boehringer turning machine tool Figure 7: Turned work piece

Conclusion

In this newsletter the first STEP-NC implementation results up to the machining of turning work pieces werepresented.

STEP-NC enables CAD/NC process chains to close the loop from manufacturing devices to product and processplanning department. Due to its object-orientation and its high information content it eases graphical userinteraction direct on the NC and reuse of worker-know mirrored by modifications on NC programs.

The prototypical process chain presented in this newsletter is still unidirectional since there are still conversions totodays NC input format. In near future, the generation of machine-dependant tool paths will traverse to where itshould be done to the NC of the deployed machine tool.

More Information? Specific Questions?

Connect to: http://www.step-nc.org/ or e-mail to: [email protected].

Project Co-ordinator: Peter Mller, Siemens AG, Germany

Telephone ++49 / 9131 / 98-3752, Fax ++49 / 9131 / 98-2057, E-mail [email protected]

step-nc – new data interface for nc programming

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