ROM@IT project--the design framework of a robotic welding system.

Ciobanu, Romeo-Mihai ; Cohal, Viorel ; Sarbu, Ionel 等

1. INTRODUCTION

The implementation of flexible manufacturing systems (FMS) is in the same time a necessity and actuality, constituting "one of the roofs of protection" for an industrial company, which may enable them to successfully resist the market economy requirements (Abrudan, 1996). The robotic welding systems represent one of the particularly FMS. The harmful work atmosphere, the physical solicitation, the static and sensorial fatigue are some of the decisive elements for the automation of the welding operations. The both technical and economical advantages of robotic welding systems have already been demonstrated.

Now, the implementation of such systems in the Romanian industrial companies requires particularly studies according the both market and industrial environment requirements. Thus, ROM@IT (ROM@nian Intelligent Technology) is a proposed project regarding a robotic welding system for the Romanian industrial companies. The aim of this paper is to present some of the author's opinions regarding the design framework and defining elements of this kind of systems.

2. PROBLEM STATEMENT

The representative products to be done in the ROM@IT system are a family of commonly tanks made by the 20 OLC iron sheet and 0.75-2 mm thickness with different dimensional characteristics. These tanks can be used to storage the fuel at normal pressure for the industrial and household needs. Each tank has two cavities. On the lower (inferior) cavity there are two profiles type angle with equal wings according to the Romanian STAS 424-86, which are made by hot rolled steel sections OL 37 (STAS 500/2-80). The profiles have to be assembled by welding points and they have the roles to assure the rigidity and positioning of the tank. The two cavities have to be assembled by continuous welding on the tank contour by using the WIG method (Wolfram Inert Gas).

3. STATE OF THE ART

Within a process of manufacturing, the human actions may be included into one of the following categories:

--Category A, which provides the continuous carrying out of the technological processes.

--Category B, which is specific for the operations with discontinuous character, such as start-stop, load-unload, change-handling tools, storage-extraction, etc.

The main functions performed by the welding robots are the following:

a) Basic functions. The actually robots accomplish the welding operation as a part of the A actions category. The specific applications are regarding to the point by point welding as well as the continuous linear or complex contour welding.

b) Auxiliary functions. The robots accomplish certain auxiliary operations in the welding processes as the manipulation of pieces for automatic machines of welding, as a part of the B actions category.

The world wide achievements of robotic welding systems are multiple, complex, very efficient and represent a lot of models for the ones who initiate the implementation of these systems.

4. RESEARCH COURSE, METHOD USED AND

TECHNICAL SOLUTIONS

Our research is a development of the following methodology steps in order to conceive a robotic welding system (Cojocaru & Kovacs, 1986):

a) The study of pieces to be welded

This stage aims to group the pieces in order to emphasize the functional relationships which must be obtained by assemblage. The pieces of the tank (the two cavities and two profiles) can be grouped as the following:

--The first group contains the pieces without formed links which have to be assembled (the two cavities);

--The second group contains the ensemble made in previous assembly phases (the inferior cavity and welded profiles).

b) The study of assembly geometry

The study of assembly geometry aims to define the reference systems of pieces and assembles in order to establish the main spatial positions according the assemble geometry. In the present case we use the following reference systems:

* The main system of reference (OXZY) which is interrelated with the last element of the industrial robot.

* The secondary system of reference (O'X'Z'Y') having its origin in the centre of gravity of the assembly to be welded.

c) The study of points and contours of welding

This study has as objective the grouping of the welding points and contours, as well as the definition of the tools of welding. The welding will be done using the following procedures:

* The welding by points. Each profile will be temporarily welded by two points on the inferior cavity within a manually conformation station. Then, the first robot will execute all the basic points of welding. The number of these points will result for each specific length of profile according a constant step (for example a step of 20 ... 50 mm).

* The continuous welding. The continuous welding on the tank contour will be done by the second robot by using the WIG method in order to assemble the two cavities after the complete welding of the two profiles on the each lower cavity.

d) The study of flexibility

The study of flexibility is oriented on the following directions:

-The technological flexibility, which is the degree of adaptability of the system related to the different products to be assembled. From this point of view the proposed system is a polyvalent manufacturing line equipped in order to achieve the assembly of different variants of a basic tank, and others different products, too.

-The flexibility of substitution, which is the capacity to continue the work in a normal or reduced rhythm in the situations of some malfunctioning. From this point of view the continuity of functioning requires the implication of a human operator.

e) The definition of system configuration

We have analyzed some variants of layouts and different types of industrial robots. Based upon a certainty multi-criteria decision making process we have established the ROM@IT system layout shown in the fig. 1 with the following structure:

* OU: the first manually station which is assisted by a human operator for the conformation welding of the profiles on the lower cavity of each tank.

* P1: the first robotic welding station with a UNIMATION 6000 robot (UNIMATION INC., USA) placed on the ground for the achievement of the basic points of welding.

* P2: the second manually station assisted by the same human operator for the conformation welding of the two cavities.

* P3: the second robotic welding station with a ROMAT 320/350/410 robot (CLOOS, Germany) for the continuous welding by using the WIG method.

* P4: the delivery station of the final products (tanks). The same human operator is presented in the both manually conformation stations in order to emphasize the necessity of his/her interventions. The system presented also includes the specific storage, positioning and transportation equipments (Trif & Joni, 1994; Mudrikova et al., 2007).

The system functioning planning is shown in the fig. 2 and it is established based upon some macro-structural and micro structural analysis according the personal previous contributions (Ciobanu, 2002). The symbols used have the following significances:

t--the time coordinate; [op.sub.j]--the operations coordinate; a--the conformation welding of the profiles on the lower cavity; b--the transportation to P1; c--the welding of the each two profiles basic points; d--the transportation to P2; e--the conformation of the two cavities; f--the transportation to P3; g--the continuous welding on the tank contour; g--the delivery of the tank; 1, 2 ... n: the tank number.

5. RESULTS AND FURTHER RESEARCH

The main results of the authors' research are the following:

a) The development of a general framework in order to design a robotic welding system according the both actually knowledge, and the Romanian market and industrial requirements.

b) The application of the multi-criteria decision methods in order to establish the appropriate welding robots and system configuration.

c) The achievement of certain models of layout and functioning planning which are useful for the both producers and users of robotic welding systems as a tool of decision making process.

d) The using of Computer Aided Design for the system layout.

e) The initiation of actions in order to identify the future robotic welding processes in certain Romanian industrial companies. The further authors' researches will be oriented towards the following main directions:

a) To develop the actually design framework and collection of models for different flexible systems as welding, manufacturing, etc. for the potential industrial users and educational process, too.

b)To raise awareness and managerial support for the robotic welding systems implementation in the Romanian industry.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

6. CONCLUSION

The implementation and exploitation of the robotic welding systems is considered one of the most innovative, creative and risky actions by the technical, economical and managerial points of view. But, it is in the same time one of the key of success in the actually hard industrial environment. ROM@IT project is one of the pro-active measures in order to develop the competitiveness and performance of the Romanian industrial companies. It is very important for the both managers and employees to understand and accept the new technical systems as a fundamental way to survive an organization.

7. REFERENCES

Abrudan, I. (1996). Sisteme flexibile de fabricatie.Concepte de proiectare si management (Flexible Manufacturing Systems. Design and Management Concepts), Dacia Publishing House, ISBN 973-35-0568-4, Cluj-Napoca.

Ciobanu, R. M. (2002). Fabricatia flexibila. Elemente de concepere si proiectare (Flexible Manufacturing. Elements of design), ISBN 973-8075-36-X, Performantica Publishing House, Iasi.

Cojocaru, G & Kovacs, F. (1986). Robotii in actiune. Probleme ale sintezei sistemelor de fabricatie flexibila (Robots in Action. Syntesis Problems of the Flexible Manufacturing Systems), Facla Publishing House, Timisoara.

Mudrikova, A.; Kostal, P. & Velisek, K. (2007). Material and informational flow in flexible manufacturing cell, Annals of DAAAM for 2007 & Proceedings of the 18th International DAAAM Symposium, Katalinic, B. (Ed.), pp. 485-486, ISBN 3-901509-58-5, Zadar, Croatia, 24-27 October, DAAAM International, Vienna.

Trif, I. N. & Joni, N. (1994). Robotizarea proceselor de sudare (Robotization of the Welding Processes), Lux Libris Publishing House, ISBN 973-96308-9-8, Brasov.