An evaluation of existing step solutions for automated process planning.

Schumann, Christian ; Teich, Tobias ; Militzer, Joerg 等

1. INTRODUCTION

The concept of which this paper is about was discussed in different papers on various conferences like the 18th International DAAAM Symposium (Teich et-al. 2007) or recently the German-Russian Logistics Workshop in Moscow (Teich et-al. 2008). As a short summary, the goal is the automated generation of offers to a customer in a B2B (Business to Business) environment. Therefore various theoretical and practical concepts have been revised, especially the results of the SFB 457 and resulting doctoral thesis's and habilitation treatise (Teich 2003).

One major problem is the description of the demand in a functional way, which means that the single elements of a single piece part can be identified and related to a meaning, the function of the feature. The paper is structured into three parts,

* Detailed description of requirements for data model

* Evaluation of implementation of STEP in market-leading CAD/PLM solutions (Autodesk Inventor, CATIA, PARTSolutions)

* Review of the new developed AP 224

* Conclusion derived from results

2. DETAILED DESCRIPTION OF REQUIREMENTS FOR DATA MODEL

For the automated preparation of offers, a very detailed demand is required. To accomplish our model, the supplier needs to gain all possible information for matching customer's needs. This results from the requirements determined by the concept:

* Work Scheduling has to be performed automatically as far as possible. Therefore the product has to be decomposed in its intermediate products. Intermediated products can be derived by feature separation. Therefore the product has to be described by features only.

* For determination of the raw material, the description needs to cover information about the initial shape, where all features are subtracted from.

* The description of the features has to be accomplished by a relation to other features (this doesn't apply to the initial shape).

As we talk about an ideal situation, the supplier can take for granted that he will get a 3D-drawing of the demand, enriched with data that enables him to give a detailed answer to the request.

Furthermore, the 3D-drawing has to be accomplished by using features, which is a need for the automated process planning and work scheduling later on (See also Amaitik & Kilkic 2005; 2007). Features in this context are defined as an accumulation of information which can be used for process planning. Examples are counter holes, filets etc.

These features need to be enriched by physical properties which are always related to a specific feature or a feature face. Furthermore, tolerances and feature type related attributes have to be added. Features, which include these needed information have a higher level of value according to the advanced reason they are used to.

The method we are using is FBD (Feature based design). We are not realizing Feature Recognition because of the additional complexity this will result in. The authors clearly understand that Feature Recognition and FBD need to be accomplished both to make automated offerings and especially the integration of CAD and CAP resulting from it, feasible.

As a last requirement, the language needs to be producer-independent since dependency will lead to the characteristic interface problem or to technology dependencies for companies which try to adopt our approach.

3. EVALUATION OF IMPLEMENTATION OF STEP IN MARKET-LEADING CAD/PLM SOLUTIONS

In a first face, the most reasonable standards for our model seemed to be IGES and STEP. Since IGES is only for the exchange of data between CAD (Computer Aided Design)--Systems, the second face brought our attention to STEP.

The overall objective of STEP is to provide a mechanism that describes a complete and unambiguous product definition throughout the life cycle of a product, independent of any computer system (See SCRA 2006).

The main implemented Application protocols in industry are AP 203 and 214, which are supported by the main CAD vendors for the mechanical engineering industry like CATIA, Solid Edge, Autodek Inventor or UGS (See SCRA 2006 p 142).

For our solution we decided to take a deeper look into the implementation of an independent data standard into proprietary CAD and PLM (Product Lifecycle Management) systems, especially in Autodesk Inventor, CATIA and PartSolutions.

The implementation study can be described as follows:

* All descriptions are done for a prototypical product.

* Different methods are used for describing this product

* The export is tested by interpreting the resulting STEP-file

The analysis shows the main disadvantages of STEP as it is implemented today. The evaluation is demonstrating the effect of different drawing methods (only subtractive from the raw material feature, additive with defined features only and rotation of a base shape) and compares the output in STEP-Files afterwards.

An Overview of the research work done, is shown in figure one. As stated in the requirements in chapter two, the subtractive feature drawing method is preferred by the authors. Since we also wanted to see the consequences for the output depending on the method a designer is drawing his part.

Results can be summarized shortly. The translator of each program produces boundary representation models only. Here are the elements needed for our approach, which get lost:

* material properties

* tolerances

* Feature based design history.

Especially the features used for drawing while using the subtractive drawing approach are very important for the automated process planning. Also tolerances need to be in the model of the demand to determine the resource to accomplish a process step.

It can be stated that the existing implementations are not useful for our approach. Reasons for not using the possibilities of AP 203 and 214 can be seen in the company principles of these CAD-solutions. We assume that they are not really interested in giving the drawing history in a neutral format to the outside of the system.

As a result of this, our team needed to look ahead and search for a more convenient solution, which was found by STEP AP 224.

4. REVIEW OF THE NEW PASSED ISO 10303 AP 224

The STEP AP we decided to go for is AP 224. It is called

"Mechanical product definition for process planning using machining feature". A detailed analysis of the AP brought us to this decision, leaded by the following points:

* The determination of the raw material gets possible by the definition of so called base shapes. They can be a block, a cylinder or a polygon with any number of sides. The base shape can also be defined explicit by declaring a boundary represented volume.

* The features which then can be removed by the designer are separated into machining features (for example a hole or a pocket), transition features (such as chamfers or filets) or compound features, which are machining features taken together by a path, on which the same features in terms of size and sort are arranged on the final product.

* Tolerances can be assigned to measurements (the definitions are based on ISO 1101 and ANSI Y14.5M (See SCRA 2006)).

[FIGURE 1 OMITTED]

One disadvantage can be seen in the description of dependent features, which is realized by appointing shapes which are not used to describe the features they lie inside. This disadvantage can be eliminated by generating the shapes of all features and then determine the location of the shapes described explicit by such a definition. This AP is an ISO-Standard since late 2007. Therefore implementations can only be found in some tools. Mainly Universities (See Amaitik & Kilic 2005; Amaitik & Kilic 2007; Liu et-al. 2004; Sharma et-al. 2002) and some companies have a solution based on STEP AP 224 in place (LOCAM, STEP Tools, SCRA (See SCRA 2006)). Since we don't have access to these solutions, we developed a workaround to have testing data for process planning in place. Basically we take the EXPRESS (which is the language of STEP)--schema of AP 224 and derive our instances.

5. CONCLUSION

The results from analyzing the existing implementation of STEP were not promising. Developing our own design guide and extracting information using proprietary API (Application Programming Interface) would be the result. However, using STEP AP 224 enables our approach to be realistic and achievable for the machine building branch. For other sectors the application seems easier, the definition of features not so complex (for example textile industry).

6. REFERENCES

Amaitik, S.M. & Kilic, S.E. (2005) STEP-based feature modeler for computer -aided process planning. In: International Journal of Production Research, Vol. 43, No.15, p. 3087-3101, Taylor & Francis Group Ltd., London.

Amaitik, S.M. & Kilic, S.E. (2007) An intelligent process planning system for prismatic parts using STEP features. In: International Journal of Advanced Manufacturing Technology, Vol. 31, p. 978-993, Springer-Verlag Ltd., London.

Liu, H.; Maekawa, T.; Patrikalakis, N. M.; Sachs, E. M. & Cho, W. (2004) Methods for feature-based design of heterogeneous solids. In: Computer-Aided Design, Volume 36, 2004, p. 1141-1159, Elsevier Ltd.

SCRA (2006) STEP Application Handbook, pdesinc.aticorp.org/downloadable_files/ STEPapplicationhandbook63006BF.pdf, last visited 05.28.2008.

Sharma, R. & Gao, J. X. (2002) IMPLEMENTATION OF STEP 224 IN AN AUTOMATED MANUFACTURING PLANNING SYSTEM. In: Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, Volume 216, Number 9, 2002, Professional Engineering Publishing, London.

Teich, T.; Mildenberger, U.; Richter, M.; Militzer, J. & Unger, K. (2007) Functional Characterization of Supply and Demand for Automatic Responses of ERP-Systems to Consumer Requests. In: Proceedings of the 18th DAAAM International Symposium 2007, Katalinic, B. (Ed.), Zadar, Croatia, October 24-27, 2007, pp. 745 f.

Teich, T.; Militzer, J.; Unger, K.; Gaese, T. & Winkler, S. (2008) Ein formalisierter Ansatz zur Generierung von Kundenangeboten auf Basis heuristischer Verfahren. In: Logistics and Supply Chain Management: Trends in Germany and Russia: Proceedings of the German-Russian Logistics Workshop, Publishing House of the Saint Petersburg State Polytechnical University, pp. 272-282

Teich, T. (2003) Extended Value Chain Management--ein Konzept zur Koordination von Wertschopfungsnetzen, Chemnitz: Verlag der GUC 2003, ISBN 3-934235-23-9, 690 S.