CAD/CAM Trials and Demonstration

INTRODUCTION

On 2 October 1998 a number of CAD/CAM (Computer Aided Design and Manufacturing) data exchange tests were conducted at Portable Welders Ltd. (PW) to supplement tests that were being progressed with Isomatic Lab Ltd. in Bulgaria. The purpose of the tests was to assess the ability of Bentley MicroStation and AutoCAD to interchange CAD/CAM data. The possible corrupting effects of compressing exchange files and transmitting them over the Internet was included by using WINzip on a number of different file types, posting them from one E-mail address to another within PW and then de-compressing with WINzip. This was followed by a demonstration on 15 October 1998, where the same test files were E-mailed to Isomatic Lab and shown on a work station there.

Project co-ordinator Peter Burton gratefully acknowledges the financial support from the Integration in Manufacturing Group within DGIII of the European Commission. Without that support, this work would never have been undertaken. The co-ordinator acknowledges the original work on which this page is based by Alan Griffiths and Mike Bryan (Tachbrook Consulting, formerly IIC Consulating), and Dimitar Kojarov (Isomatic Lab.).

HARDWARE AND SOFTWARE CONFIGURATION

It was possible to conduct the tests on-site at PW because there is one AutoCAD V14 installation in addition to the multiple seats for MicroStation. To supplement this facility, AutoCAD V14.01 and AutoCAD Mechanical Desktop (AMD) V3 were temporarily installed. The versions of MicroStation in use were SE for 2D draughting and 95 for 3D modelling, which is an ACIS based system. The latest version that has just been released is MicroStation Modeller PE and this offers an import and export facility for STEP AP203 files. This is now Parasolids based and is accompanied by a much-improved IGES translator as well as the new STEP translator. MicroStation and AutoCAD V14 were already installed on a PC running Windows NT4. AMD V3, AutoCAD V 14.01 and the associated Data Exchange module, all of which were kindly loaned to the WIDEBEAM project by Autodesk UK, were installed on the same PC with the protection of a dongle.

SCOPE OF THE TESTS

The main formats presently used for exchanging CAD/CAM data are in prioritised order, DWG and DXF (versions 10-14) and IGES (versions 4, 5, 5.2). The pre-eminence of DWG and DXF is because the majority of data exchange is with AutoCAD systems to which the use of these formats should be limited. DWG is a binary format and therefore quite economical with respect to file size while DXF is a neutral format that results in a tripling of file size compared with DWG. Both of these formats, especially DWG, are sensitive to the version of AutoCAD with no guarantee of downwards compatible and limited upwards compatibility.

The IGES processor included in the AutoCAD Data Exchange module would only work with AMD and AutoCAD V14.01. The STEP AP203 processor could only be used to reflect solids models in and out of AMD since there was no STEP support in the version of MicroStation currently in use at PW.

The log-files of the data conversion processes were kept for later perusal.

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TEST DETAILS

The first series of tests were conducted using a test IGES V4 file as source input. This test file consists of a range of 2D geometric entities plus a broad range of dimension types and annotation styles and is shown in Appendix A. All of these different elements are laid out in a matrix of 100mm squares that makes the identification of missing data visually very easy. The IGES file had been checked with the IGES Data Analysis (IDA) IGES Parser/Verifier tool that found two identical errors relating to an instance of zero height text.

The test IGES file was first imported into MicroStation with only about 7% of the entities being converted. The same file was then imported into AutoCAD V14.01 with a virtually perfect result. There was neither loss of data nor any loss of intent, i.e. dimensions had retained their identity and had not been converted to geometry and text. The resulting AutoCAD drawing was then exported via IGES V5.2 and imported into MicroStation with only marginally more success than from the initial import. The main reason for this lack of success with MicroStation is due to a lack of familiarity with IGES and the options provided for controlling the import/export process. One of the authors has had considerable prior success with exporting CAD/CAM data to MicroStation. No documentation on MicroStation IGES was available at PW.

The test drawing in AutoCAD V14.01 was exported in a number of DXF and DWG versions and imported into MicroStation with some corruption of text and loss of intent, i.e. dimensions were not recognised as dimensions. The DWF export option in AutoCAD V14.01 was tried but this could not be imported into MicroStation.

The second series of tests were conducted using a PW drawing of a welding gun general assembly which is shown in Appendix B. It is a 2D MicroStation model and was exported in a range of DWG/DXF formats ranging from V10 to V14. It was also exported in IGES V5.0 format. Attempts were made to import all of these formats into AutoCAD V14 with either total success or total failure. The DWG/DXF V11-14 formats were all successful with no visible errors, DWG/DXF V10 format would not import.

The IGES format was successfully imported into AutoCAD V14.01 with the only visible error being a line-type that had changed from chain-dotted to dashed. This could almost certainly be corrected by changing the line-type mapping options. This model was then exported from AutoCAD V14.01 in IGES V5.2 format and imported into MicroStation with the line-type change as the only visible error. Other exchanges were attempted between different versions of AutoCAD using varying versions of DWG/DXF to assess this format's AutoCAD version sensitivity.

The third series of tests were conducted to assess the use of STEP for exchanging solids models. There was a strictly limited amount of work that was possible here since the only STEP processor available was for AMD V3. The MicroStation 95 Modeller is ACIS-based, as is AMD, therefore it was possible to export a solid model of a bent arm in SAT format and import that directly into AMD with no problems. The model was then exported from AMD in STEP AP203 format and imported back in again as a reflection test. This test failed as the reflected model did not display. It was strictly outside the scope of these tests as it did not involve MicroStation but a subsequent analysis of the STEP file revealed that it contained no geometric definitions. From a PW perspective there is no need to pursue this problem, although there is undoubtedly a very simple answer, but out of consideration to Autodesk it will be reported back.

TABULATED TEST RESULTS

SERIES 1 TESTS

Note (a) - verification of wbigstst.igs gave two errors relating to a text string defined with zero box height.

Note (b) - verification of igor1401.igs gave four errors relating to subordinate entities which were defined but not referenced.

Note (c) - wbigstst.igs and igor1401.igs were viewed with Intravision and overlaid. The only observable difference was a flipping of the angular dimension witness lines in one instance.

SERIES 2 TESTS

SERIES 3 TESTS

Note (a) - the AMD STEP pre-processor was used with default options settings and as no external documentation was available with the data exchange CD no further tests were attempted.

NB: MicroStation Modeller PE will offer STEP AP203 import and export facilities and is currently available in Beta test. It is proposed to arrange a transfer of a solids model from MicroStation Modeller PE as a STEP AP203 file to RobCAD through the good offices of Bentley Systems and Tecnomatix. As the RobCAD STEP processor is AP214 compliant it offers an opportunity to assess the cross compatibility of AP203 and AP214.

SELECTION OF EXCHANGE FORMAT

Note (a) - DWG is preferred to DXF as a DWG file is about one third the size of the equivalent DXF

OBSERVATIONS

DWG/DXF are the preferred exchange formats for PW because in the main the receiving systems are AutoCAD and because they are simple to use. DXF gives no advantage over DWG and should not be used. DWG is a proprietary format and is AutoCAD version sensitive. AutoCAD systems support several earlier DWG versions and if the system version does not give good results then the prior two versions are worth trying. If the receiving AutoCAD system has an IGES processor then for complex drawings this format might offer a better result.

If the receiving system is other than AutoCAD then IGES should be the preferred exchange format. There is little or no experience of working with IGES at PW and so it is important to arrange through the MicroStation system support some expert tuition in the use of MicroStation IGES. There appeared to be no documentation available at PW on MicroStation data exchange and it is important that this is made available.

STEP is the only viable format for exchanging solids models and so it is important for PW to install MicroStation Modeller PE as soon as is reasonably possible. This new release of the modeller has moved from being ACIS-based to Parasolids-based with the benefit of much improved data exchange facilities.

DEMONSTRATION, CONCLUSIONS, BENEFITS

The test files were E-mailed to Isomatic Lab in Bulgaria and the trial software and dongle were hand carried by air to Sofia. The plan was to demonstrate that the file transfer would still work between PW (using Bentley Microstation) and Isomatic Lab. (using AutoCAD 14.0). The test file and weld gun drawing were both read satisfactorily. Both proprietary and standard (2D) methods for exchange were demonstrated. Files larger than 2 Mbytes, even when zipped, cannot normally be E-mailed via the Internet. Some Internet Service Providers have lower limits. 3D CAD files are likely to be much larger than 2 Mbytes so the sender needs to upload files to a server from which the recipient can download, both using File Transfer Protocol (FTP). This approach is being progressed further.

The conclusions reached were that while ‘proprietary’ file formats such as ‘.dwg’ often give satisfactory results, industry-standard ‘neutral’ formats such as IGES and STEP are safer (i.e. less prone to disruption through supplier upgrades, errors etc.), providing they are easy to use and cost-effective for the SME. IGES was shown to be an excellent intermediate format for 2D drawings providing the CAD supplier conforms to the standard and supplies the converter at a reasonable cost. Autodesk proved this was possible while some problems were experienced with Bentley’s converters. The general conclusion so far was that IGES is preferable for 2D drawings and probably wireframe models, while STEP should be used for 3D solid models. This approach would also fit the way the end users, e.g. the motor industry, were likely to work in future.

The benefits of successful CAD/CAM transfer between different systems is very significant for the four WIDEBEAM partners that are in the same supply chain. Data exchange with Bulgaria is reduced from 10 days to a matter of minutes, helping to cut time to market and delivery. It is anticipated that a major customer will soon be asking all its suppliers to be compatible with its CAD/CAM systems or be removed from the suppliers list. The revenue which this represents is estimated to be 1.4 Meuro per annum.

The problems with 2D CAD data transfer with customers/suppliers are defined and a plan to address them is in place, enabling cost savings and reduction in engineering lead time. A plan is in place to transfer 3D solid models to a major customer to enable easy simulation of welding robots on production lines, improving customer satisfaction.

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Copyright for the contents of this web page is owned by the WIDEBEAM consortium. Reproduction is permitted without charge on condition that the WIDEBEAM project and the support received from the Integration in Manufacturing Group within DGIII of the European Commission are acknowledged.

Page content was last updated in November 1998. The HTML code was revised and its syntax checked on 26 July 2005 using BBEdit on an iMac  .

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