A NEW SYSTEM FOR CONTROLLING THE CAR SEATS WELDING POINTS

Abstract: While building a car the driver and passengers' seats have an important place on manufacturing technology, materials, design, structural reliability and price. The paper presents the fabrication technology of the Dacia SANDERO auto vehicle car seat backrest and the inspection system of the point welded areas which eliminates any rejected parts or technical hitch during the welding process.

Key words car seats, points welding, inspection machine, poke-yoke.

Introduction

The front and rear Dacia Sandero car seats are points pressure welded.

In order to realize increased productivity and quality of a number of devices fixing, monitoring and controlling the process it is needed.

Presentation of parts

The rear seat backrest parts of the Dacia Sandero car by construction point of view are made in three variants: RSB 40, RSB 60 and RSB 100. The paper presents two types and sizes RSB 40 (Figure 1) and RSB 60 (Figure 2) of the car seat backrest.

The building process consists of a metal frame that is welded pipe clamps, hinges; reinforcement bar and wire mesh for an upholstery attachment.

Version RSB 40 require for preparing reinforced backrest execution of 12 welding seams on the front and 6 welds spot on the main axis of the tube and the execution of RSB 60 need 16 welding seams on the front and 12 points welding on the main axis of the tube .

Manufacturing Technology

To achieve RSB 40 and RSB 60 backrests the following operations are executed:

Open the valve on the compressed air column. Press the button next to the gauge. Check this compressed air - 4 bar;

Valves are opened round-trip on the cooling water supply columns and the welding tongs;

It is checked according to the job with TPM (Total Productive Maintenance) of the post;

Run a sample for destructive testing;

If the result is consistent (surrender shall be made by wire breakage) to begin the work. Otherwise, it must inform the head of the team about results;

Put the preassembled backrest in the prisms of the settlement ensuring that the device is correctly positioned;

Fix by pushing his left pneumatic fasteners;

Place the back of the net for 40%, ensuring that it is positioned on aluminium and positioning the CEPI limits;

The net is fixed by pressing left pneumatic seals;

Net frame welding will run. The device will rotate as needed;

After taking the number of points, the part is automatically released;

It is 100% visually check the presence of 6 welding points and their position will be along the tube axis[1];

It is 100% visual checked of the 12 welding seams on the front of reinforcement;

The elimination part of the device and 100% visually check the presence of 6 welded seams on the back of reinforcement;

100% visual check concentricity of the two nuts from the bracket holes;

Arrange the ensemble on the support.

To be performed in the execution of welding operations device RSB 40 from Figure 3 and the fixture device RSB 60 of Figure 4 is used for the fixture.

Fig. 3. Fixture model RSB 40 - Rotating table and fixture for RSB40 B90 (Rear seat back 40, Dacia Renault project B90 - Sandero)

Fig. 4. Fixture model RSB 60 Rotating table and fixture for RSB60 B90 (Rear seat back 60, Dacia Renault project B90 - Sandero)

The process of welding for RSB60 and RSB40 types fittings will be welding equipment TECNA3322 control unit having: TE300 and clamp arm length: 250mm (Figure 5) [2].

The parameters used are: Tolerance accepted: Current Intensity: + / - 200A, welding force: + / - 10%, welding pressure: + / - 0.5bari.

Fig. 5 Welding equipment.

In Table 1 welding parameters are showed. The main welding points were the pressure P1 for model RSB 40 and P2 for model RSB 60.

Welding parameters Table

Control system (anti-foul- poka-yoke)

Poka-yoke is the system which controls the welding of the net frame for RSB40 and RSB60 backrest, this piece is composed of the sensor in the fixture, pneumatic fastening device control, connection cables, signal lamp, timer counting welded pressure points. If the number of welding points and the track is not removed from the device, the green light is shooting down and red lamp remains lit constantly. The gun is locked and the display shows "unfinished piece".

If not given all the welds that must be given outside the device, in the moment which is trying to start the new piece the  gun is locked, lamps flash on and welder must complete the unfinished piece.

Fig. 6 Control lamp for welding process

In Figure 6 is presented the control system. Poka yoke system is part of the device for fixing reinforcement and count the number of pieces made, the number of points and total points. For this system you can choose a specific program for the case being examined. For this article the B90 program settings were choose.

To achieve this control system there will be implemented additional devices, which will be added to existing devices placed in the tube welding. They will have the following functions:

They allow a rotating-tilting movement between two positions - top position (100 degrees from the horizontal) to represent the position where the operator loads the parts for welding device and a horizontal position (lid closed) to represent the position of the welder;

Closure of 'head' to the vertical position will be assisted by two gas strut (gas piston), calculated to assist and not oppose the lifting of excessive force in lowering the cap the maximum force will be established;

Newly installed devices (caps) will contain a number of sensors equals to the number of spot welds made in the device, allowing sensors to detect the upper electrode clamp throughout the performance of each spot welds, all sensors will be provided with protective elements to avoid mechanical damage to them through contact with welding parts or accidental hitting. Sensors will be connected to a "central" element installed on the cap, which will allow easier and fewer maintainability of the wire connection of sensors and PLC station. The design of the connections must take into account the movements and rotation of the device and provide protection to ensure mechanical integrity and electrical wires during handling[3];

Covers will be provided with a closing / locking of the welding position. The horizontal position will be checked by a sensor connected to the PLC station and covers can be opened only on successful completion of all welds provided for that operation;

Covers will be provided with 'windows' to avoid interference with metal fittings, wire mesh and structural elements of the current welding device, caps will be provided with guides' points to ensure correct position for welding in all welding set state.

Additional devices (caps) will be installed at these three positions:

Welding station B90 40% net to the tube, where spot welds are made in June (RSB40);

Welding mesh to the tube station B90 60%, are conducted 14 spot welds (RSB60).

Programming must include the relevant names as used for all programming elements (inputs, outputs, bit memory functions). Use a TWDLCAA40DRF Twido PLC and Magelis XBT Human Machine Interface type RT500.

Conclusions

Spot welding the valves seat pressure is a modern technology which ensures a high quality joints. Due to the large number of points made there can be missed some physical or welding points.

By implementing the new control system (poka yoke) the system will meet the intended purpose of disposing of scraps and it will pass the validation process for implementation in mass production. In addition the precise positioning of the holes in the lid will be able to control and place in the welded points.

Acknowledgements

"ACKNOWLEDGEMENT: This paper is supported by the Sectoral Operational Programme Human Resources Development (SOP HRD), ID76945 financed from the European Social Fund and by the Romanian Government

References

Georgescu, V., Mircea, O., et al.: Sudarea prin presiune. Metode clasice (Pressure welding. Classical Methods). Brasov. Lux Libris Publishing House, 2002.

Iovanas, R.: Sudarea electrica prin presiune (Pressure electric welding).  Timisoara. Sudura Publishing House, 2005

Joni, N. Trif, I. N.: Sudarea robotizata cu arc electric (Robotic arc welding . Brasov. Lux Libris Publishing House, 2005