FIELD OF INVENTION
This invention relates to an automatic panel pre-assembly system adaptable to an existing multiple spot welding and seam welding machine having an in-built transfer line for the manufacture of 9 flute transformer radiators. More particularly, the invention relates to an automatic panel pre-assembly system and a method for pre-assembly of a radiator element.
BACKGROUND OF THE INVENTION
The formation of transformer radiator elements from panels by combination of multiple spot welding and seam welding is a well known technology. But before the said operations being undertaken, the radiator elements have to be pre assembled at different stations by placing a pair of panels on a fixture and spot welding the element at four points, near the 4 corners, by manipulating the fixture. Though the said activity eliminates any possibility of relative shifting of the panels during multi spot welding and seam welding for which a minimum of six numbers of people are to be generally employed at a separate stand alone station, time taken for pre-assembly of each element is of the order of 15 min. Further, some of the elements get damaged during material handling of the pre assembled elements by slinging. Thus, such a process of pre-assembly of the element results into much higher job cycle time and damage to element that results into leakage in some of the elements.
The sequence of operation for pre assembly of the radiator elements according to the prior art comprises.
1. Radiator elements in the form of panels having semicircular are cut out at both ends are mounted on heavy fixtures having fixed pin at one end and adjustable pin at the other end.
2. The mounted panels are spot-welded at four points, one at a time, on a general-purpose spot welding machine by manipulating the fixture.
3. The pre-assembled element is taken out of the fixture and kept on an
unloading pallet. The individual pre-assembled elements are temporality
stored in stack.
4. The built up stack of pre-assembled elements is transported to the loading
end of the welding line, by slinging the pallet to the hook of a over head
crane.
5. Each element is individually fed into a multi spot and seamwelding
machine.
Such prior art system and method therefore results into additional deployment of resources in the form of man power, working area, and material handling equipment. Further, the quality of job greatly suffers and avoidable wastage in the form of rejections and damages occurs.
It is therefore, an object of the invention to provide an automatic system for the pre-assembly of radiator panels which can be carried out on the feeding roller table of the multi spot welding machine itself, so as to reduce its cycle time.
Another object of the invention is to provide a system which reduces the rate of rejection in the pre-assembled elements which generally occurs due to relative movement of the elements between the panels and the resultant material handling.
A further object of the invention is to provide a pre-assembly system which eliminates the necessity of a separate work station and thus enhance the capability of the existing multi spot and seam welding machine through it's use as a transfer line.Still a further object of the invention is to provide an automatic panel pre-assembly system which reduces the requirement of manpower by at least six in numbers per shift due to elimination of a separate pre-assembly work center.
Yet another object of the present invention is to provide a damage proof method for pre-assembly of a radiator element.
According to this invention there is provided an automatic panel pre-assembly system which is used in conventional multi-spot welding and seam welding machine, having an in-built transfer line, and a control panel, the system characterized by feeding means connected to a job locating device, the feeding means providing at the start of each sequence of operation at least one pair of radiator panels to the job locating device; the job locating device having a slide unit with a cylindrical pin, a locking means and an adjusting means 3 (e,f,g) for adjustment and disposition of the radiator panels with the locating of a plurality of electrodes installed on a spot welding means, the spot welding means provided with a first conveyor table automatically transferring the pre-assembled radiator panels on completion of spot-welding of said atleast one pair of panels to said multi-spot welding and seam welding machine, the system being installed on a second conveyor table disposed adjacent to said in built-transfer line of the multi-spot welding and seam welding machine, the sequencing, interfacing and automatic control being monitored by a control means having a programmable logic controller, the said system has utility devices.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1- shows a radiator element for manufacture of a 9-flute transformer radiator.
Fig. 2 - shows a block diagram of an automatic pre-assembly system according
to the present invention.
Fig. 3 - shows a job locating device of the system according to the invention.
Fig. 4 - shows a spot-welding means of the system of the invention
Fig. 5 - shows an utility means in the form of a hydraulic circuit for the system.
Fig. 6 - shows a pneumatic circuit for the system of the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION
The automatic panel pre-assembly system according to the invention is properly integrated with the existing multiple spot welding and seam welding machine and comprises following means /device:
- Job locating device. (3)
- Spot welding means, (4)
- Feeding means,
- Control means, (5)
- Utilities (6,7,8)
Job locating device (3) comprising a Tin unit' (3a to 3g) provided for locating the radiator panels (1) at either end of the job, is the key element of the job locating device (3). The 'Pin Unit' constitutes of a cylindrical pin (3a) mounted on a dovetail slide means (3b) vertically having a stroke of 80 to 120mm. The stroke is obtained by means of a pneumatic cylinder 3(c). The pin (3a) will be above the table surface only when pre-assembly (locating and spot welding) operation is being carried out. The slide unit (3b) and the cylinder (3c) is mounted on a rigid vertical structure made up of plates and channels and welded on the base.
The slide unit (3b) moves on a dovetail guide way, by means of a lead screw-nut means (3d) so as to cater to job having variation in length from 1200mm to 3000mm. A handle (3e) along with a gear box (3f), is provided elevatedly on the table of the existing machine for conveniently adjusting the slide unit (3b). A scale (3g) each is provided on the bottom guide ways as well as on a top rail of the existing machine for doing the required adjustment. Further a locating means (4a) having locking pins is provided for locking the slide (3b) for each job size. After locking of the slide unit (3b), the variation of distance between the pin centers is maintained within (0.5 + job length) to (0.8 +job length). Therefore the adjustment of device is done so that a plurality of top and bottom electrodes can be aligned by means of the lead screw and nut means (3d) at the bottom and by means of a rack and pinion means (4b) at the top.
After the sheets have been placed between the two locating pins and the properly located sheets are spot welded at 4 points close to each of the corners in a spot-welding means (4). The spot welding means (4) comprises 8 Nos. electrodes mounted on atleast two pneumatic cylinders (4c, 4f). Of these 4 numbers Of electrodes are mounted on the bottom slide unit (3b) on a side opposite to that of pin unit and the other 4 are mounted on a top slide unit (4a). The top slide unit (4a) is guided on the dovetail guide ways being movable by means of a rack and pinion means (4b). A square head is provided for the motion of the top slide (4a) by means of a ratchet spanner (4c). Further a provision is made in situ for locking the slide (4a) for each job size. Locking pins elements (4d) are provided for the same. This is done such that the top and bottom electrodes are in one line. A sufficient clear space is maintained for loading of the radiator panels (1). A 600 mm gap is kept between the job and the top electrode elements in the normal un actuated position to provide an easy access for the operator for loading of the panels (1). For doing the spot welding,
first of all, the plate on which the top electrode actuating cylinders (4c) rest on is brought down by about 575 mm by main hydraulic cylinder. 4 Nos. of guide rods are provided for preventing the plate from rotating. With the electrode tips around 25 mm from the located radiator elements (1), the electrode actuating cylinders (4c, 4f) having a maximum stroke of 50mm (max) is operated. Spot welding is carried out at all the four points simultaneously. This is implemented by a suitable Programmable Logic Control panel (5).
After the welding is over, the locating pin (3a) is withdrawn by actuation of the cylinder (3c) and pre-assembled radiator elements (1) are automatically fed into the motorized part of the conveyor for subsequent operations, that is, multi-spot welding and seam welding,
An additional conveyor table is required to be placed in series with the existing one, so as to cater the space requirement of pre-assembly system.
FEEDING MEANS
At a time one pair of panels is put in between the two locating pins. Thereafter locating as well as all subsequent operations up to feeding of radiator elements (1) into the multi-spot and seam welding machine are done automatically. A motorized conveyor is used as the feeding means.
UTILITY DEVICES (6,7,8)
Chilled water circuit (6)
For cooling of the electrodes, transformers, thyristor (in the panels) and
hydraulic oil in power packs, a chilled water circuit has been built up.
Hydraulic Circuit (7)
Hydraulic circuit comprises hydraulic pumps, motors and couplings. It also houses different types of valves such as pressure relief valves, non return valves, flow control valves, direction control valves. Other safety device includes tank level indicator, pressure gauge and needle valve. It comprises of a motor, pump with an output of 11.5 Imp, hydraulic cylinders, level indicators, solenoid operated DC valve, tank , pressure gauge and filters.
PNEUMATIC CIRCUIT (8)
Pneumatic circuit comprises drum type of water drain, solenoid operated direction control valve, flow control valve, hoses and other fittings. Pneumatic system is suitably integrated with the welding controller. Pneumatic circuit powers the locating means and the main cylinders on the top plate assembly and that on the bottom plate assembly for actuating electrodes. It comprises pneumatic cylinders for locating pin vertical movement and horizontal movement, pneumatic cylinders for top electrode and bottom electrode, solenoid operated air direction control valve, speed control valve, air filter regulator lubricator unit, and air pressure regulator. CONTROL MEANS (5)
The automatic control, sequencing and interfacing with the existing machine is done by means of an ABB 86AR230 Programmable Logic Controller, through an array of sensors. The Programmable Logic Control co-ordinates the functioning and sequencing of hydraulic, pneumatic, electrical and power electronic circuitries for the automatic operation of the pre-assembly system. Suitable Spot Welder Control is provided in the system for controlling timing of squeezing, Welding, holding and off functions.
SEQUENCE OF OPERATIONS.
The sequence of operation of the pre-assembly system is as follows:
1. Activating the pneumetic cylinders of the pneumetic circuit such that the
locating pins come out automatically;
2. Manually placing the panels between the locating pins;
3. Activating the hydraulic cylinders to bring the top plate down by around
600mm;
4. Moving up the bottom electrodes of the spot-welding means to support
the panels by activating the cylinder assigned for the bottom electrodes;
5. Moving down the top electrodes by activating the cylinder assigned for the
top electrode and carrying out spot welding at four points on the panels;
6. Reactivating the cylinders causing top and bottom electrodes to retract &
top plate to move up.
7. Reactivating the assigned pneumatic cylinders so that the locating pins
get retracted.
8. Automatically feeding the pre-assembled elements via the conveyor table
to the in-built transfer line to the existing multi spot and seam welding
machine for onward operation.
The automatic pre-assembly system would allow for unhindered loading of panels and thereafter locating the same within 0.5mm. Further the same is tag welded at four points and fed into the multi spot and seam welding line.

WE CLAIM;
1. An automatic panel pre-assembly system which is used in conventional multi-spot welding and seam welding machine, having an in-built transfer line, and a control panel, the system characterized by feeding means connected to a job locating device (3), the feeding means providing at the start of each sequence of operation at least one pair of radiator panels (1) to the job locating device (3); the job locating device (3) having a slide unit (3b) with a cylindrical pin (3a), a locking means (4d) and an adjusting means 3 (e,f,g) for adjustment and disposition of the radiator panels (1) with the locating of a plurality of electrodes installed on a spot welding means (4), the spot welding means (4) provided with a first conveyor table automatically transferring the pre-assembled radiator panels (1) on completion of spot-welding of said atleast one pair of panels (1) to said multi-spot welding and seam welding machine, the system being installed on a second conveyor table disposed adjacent to said in built-transfer line of the multi-spot welding and seam welding machine, the sequencing, interfacing and automatic control being monitored by a control means (5) having a programmable logic controller, the said system has utility devices (6,7,8).
2. The system as claimed in claim 1, wherein the slide unit (3b) is movable on a dove-tail guideway by means of a lead-screw nut means (3d).
3. The system as claimed in claim 1, wherein the adjusting means comprises a handle (3c), a gear box (3f) and a scale (3g) provided on the bottom of the dove-tail guideway.
4. The system as claimed in claim 1, wherein the job locating device (3) comprises a top-slide unit (4b) movable on the top of the dovetail guideway by means of a rack and pinion means (4b).
5. The system as claimed in claim 1, wherein the spot-welding means (4) comprises electrode actuating cylinders (4c, 4f) for causing the electrodes to move upwardly and downwardly.
6. The system as claimed in claim 1, wherein the plurality of electrodes comprises atleast 8 numbers electrodes mounted equally on the top slide unit (4b) and the bottom slide unit (3b).
7. The system as claimed in claim 1, wherein the utility devices (6,7,8) comprise a chilled water circuit (6), a hydraulic circuit (7), and a pneumatic circuit (8).
8. An automatic panel pre-assembly system as substantially herein described and illustrated with reference to the accompanying drawings.