New strategies for designing assemblies.

Marin, Gheorghe ; Petrescu, Ligia ; Dolga, Lia 等

1. INTRODUCTION

The complex transformations, which have occurred in the field of designing and manufacturing products, consist in reducing the renewal and supply cycle, increasing requirements on functionality and technical and quality level, reducing dimensions of the production batches, parallel to the increase of the production systems flexibility. These transformations have determined factories to change their obsolete industrial strategies, to seek for permanent innovation and implementation as soon as possible of new technologies from the research-development field to the production one.

In the last decade, throughout the world, the production facilities in the goods field have been brought up-to-date beginning from the activity of designing, production planning and processes checking to the systems that provide measurements of the production process parameters or measurements of the dimensional, functional and shape product parameters.

It is well known that in the economically developed countries (which hold "de facto" the supremacy in efficiency, quality and performances), using computer in researchdesigning activity, production, process checking and quality certification has no longer been considered as a natural matter but as a necessity, a necessary prerequisite that is not always an enough condition for market survive.

This writing intends to survey the main strategies, solutions used at present in the field of computer-aided design, generally, and mechanical assemblies design, particularly.

2. NEW COMPUTER-AIDED DESIGNING STRATEGIES FOR MECHANICAL ASSEMBLIES

We can say without being wrong that a today's most widespread and appreciated working tool of engineers from all over the world is the computer. This extraordinary development of the information science is due to the unique qualities of the computer in comparison with human being (Fig. 1).

Indeed, the large successful use of the computer in almost all activity fields including engineering has been resulted from its very large memorizing capacity, impressive computing speed under computing accuracy conditions many times more than sufficient, visualization facilities as well as "patience" and "working capacities". The computer-aided industrial processes lead not only to an automation of same activities carried on by specialized employees but also to the introduction of the entire available technological knowledge for that production line in the research-designing-planning-production-checking process. (Boothroyd, G. 2005).

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Nowadays, the CAD (Computer-Aided Design) systems market is one of the largest and most dynamic in the world and there are millions of applications

Regardless of the application type or the platform which those applications are created for we can notice the permanent effort of the producing companies for developing new programs that offer the possibility to reduce to a minimum the designing time, the production expenses as well as the designing effort.

On that context (Rao, P. N. 2004), we can notice some important trends for CAD systems development:

a. Applications integration: allows the model achievement, description in detail, its analysis and finally manufacturing having one virtual model, using the same interface; in this way the operator's acquaintance with those applications is facilitated, being avoided the date files translations. The unique product model includes all the necessary information for each process and iterations take place efficiently and quickly. In fact, in this case we are considering a CAE (Computer-Aided Engineering) application including modules for geometric modeling, structural analysis, mechanism analysis and simulation, finite element analysis for different requirement types, for dynamical Internet data publishing, for documents management, etc.

b. Visualization facilities: have already reached a professional level (Shipulsky, M. 2007), including options like radiosity, ray tracing, photorealistic mapping, parametric animation, possibility to manipulate cameras, etc.

c. Interconnection and team work: in today's world of different designing systems and of necessity to convey projects, a designing environment should be as open as possible. The operations change is essential among systems that place at disposal and share resources for designing process, either among teams within the same company or among research groups from all over the world. In this way, the designing environments have modules allowing the control on the drawing standards; various symbols are stored in one single library for an easy maintenance and an efficient using (Lamarche, B.; Rivest R. 2007).

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d. Digital signature: by applying such a signature on a certain area of the project the professional people can offer the legal access to the create drawings. The digital signatures allow the authentication of the stored drawings and provide information on the designer identity and putting up-to-date made after project publication. By means of the programs, the signature falsification or modification is not possible.

e. On-line data change and Internet connection: allow the connection to different parts catalogues or the Internet seeking of a certain producer whose parts match the in-process project, in this way the designing time and efforts are shortened. When the item is found it can be included in the model (Fig. 2), thus the data change could take place among the designing team members, among corporations and even among distributors (by including URL addresses in the model).

f. Hybrid modeling: represents the capacity to model 3D solids using both wireframe entities or solids and surfaces; all these describe the same geometric solid and have the advantage of a mixed solver (parametric and functional); also, the hybrid modeling includes the capacity to edit and modify the model under various techniques not depending on the way the model was achieved but on the operator necessity at one time.

Primitives and model features handling: graphically shows the tree structure of model achievement history and allows modifications of parameters and position of any element in the tree (Fig. 3). In case of modifications causing an impossibility to achieve elements dependent on the modified one, the system warns the operator very fast.

Using subassemblies technique (modular designing): reduces the complexity of the designing process for it allows to focus the effort on a single component at a moment (different assembly parts will be modeled one by one and are to be put together in the final stage) and also for the fact that the same part may be used several times in the same assembly or in different assemblies. (one feature modification will automatically appear in all positions where the feature appears). That working way removes project date redundancy and makes fit different parts of the assembly (*** 2008).

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The assembly Part Manager (Fig. 3) allows parts achievement and their modification within the assembly by using one of the techniques "from complex to simple" (the designer makes a general assembly plan and a hasty draft of every parts and hands them over to other people to finish and at the end he is to put together all the parts) or "from simple to complex" (each part is separately designed and then it is attached to the assembly) which best suit to the chosen purpose.

g. Relative movements can be defined for the parts of an assembly and thus, there is the possibility to detect the eventual collisions that may appear among moving parts (Fig. 4). Also, there is possible to attach couplings to another subassembly so that each may have its own coupling system (very useful thing when the movement of some subassembly parts is desired).

3. CONCLUSION

The mechanical field designing is subject to some powerful pressures because of the increasing competitions and market globalization, more and more increased clients' requirements and quickly developing technology. As a result, companies have to be more productive, more responsible and flexible in order to survive and have success. The CAD mechanical packages become more efficient in terms of their cost. They are production-orientated, easy to use and allow data management, issuing materials list, parametric surfaces and solids modeling, various analysis and simulations, numeric control, etc.

There are also achieved interfaces according to the international and national standards, other applications and CAD/CAM/CAE systems, which are our next goals of research.

4. REFERENCES

Boothroyd, G. (2005). Assembly Automation And Product Design Second Edition, CRC Press Taylor& Francis Group, ISBN I-57444-643-6, Broken Sound Parkway, New York, USA.

Lamarche, B.; Rivest R. (2007). Dynamic Product Modelling with Inter-Features Associations: Comparing Customization and Automation. Computer Aided Design and Applications, Vol. 4, No. 6, (June 2007) p. (877-880), ISSN 1686-4360

Rao, P. N. (2004). ACAD/ CAM Principles and Applications, Tata McGraw Hill, ISBN 0070583730, Broken Sound Parkway, New York, USA

Shipulsky, M. (2007). Successful design for assembly, Available from: http://www.assemblymag.com/CDA/ Articles/Feature_Article/ BNP_GUID_9-5-2006_A_10000000000000059386 Accessed: 2008-04-10

*** (2008). Design for assembly, Available from: http://www.teamset.com/design-for-assembly-2.html Accessed: 2008-06-11