DESC:FIELD OF INVENTION

[001] The present invention relates to the field of resistance spot welding machines and more particularly relates to an automation device for converting conventional spot welding machine preferably a welding gun into an intelligent and automatic welding machine.

BACKGROUND OF INVENTION

[002] Spot welding is a very well-known technique of welding or joining the metal work pieces together. Spot welding is a type resistance heat welding wherein the work pieces to be welded are held together between the two electrodes of welding gun and electric current is passed through the same which generates the heat due to resistance of work pieces. The heat generated causes the melting of selected portion of the work piece and achieves the required joint. One of the most common application of spot welding is automotive industry where most of the parts are required to be welded quickly, precisely through automation. The spot welding method is advantageous due to its easy handling, quick and precise welding techniques. Sheet metals, vehicle body parts are mostly welded using spot welding.

[003] Spot welding process generally involves four stages; the first of which involves holding the work pieces together between the electrodes of welding gun and squeezing them together by applying required amount of pressure; second step involves passing of pre-determined amount of current through the electrodes and work-pieces for pre-determined amount of time until the melting of selected portion of the work piece and achievement of the required joint; thereafter holding the work-pieces together for some amount of time for cooling of the melted portion (solidify) and then slowly releasing the pressure over the connected work-pieces which completes the welding process. Accordingly there are various primary welding parameters in spot welding method i.e. pressure (force- start/initiation), squeeze time, weld time, welding current (current flows only during welding time), Hold time, off time and pressure (Force-stop/release). These parameters can be either fixed for a complete welding process or can be dynamic based on the type and material of the work piece.

[004] There are different types of welding guns available in the market. Primarily the spot welding guns are classified into two categories one is AC/ MFDC spot welding gun and other is Adaptive spot welding gun. AC Spot welding guns are comparatively cheaper in cost and the welding operation is carried out based on the fixed process parameters. The conventional AC spot welding guns comprises a controller which generally consists various different programs which can be selected manually with the help of switches provided on the operating pendant. Once the program is selected for a given sheet thickness the weld parameters get automatically set which are already stored for a selected program. Generally it is expected that the operator shall inspect the welding conditions such as the material to be welded, thickness of work-piece to be welded etc. and then select the appropriate program before start of each welding cycle. However since this method is more manual dependent the operator once selects the program does not change it because of various reasons and as a result same parameters are run whenever the weld start is triggered irrespective of actual sheet thickness, material to be welded. This leads to a poor quality of weld, which rises multiple welding related issues such as weak spot, spatters, spot burns etc.

[005] There is also a possibility of poor weld joint due to following conditions,
a) Change in Hardness/ Material grade/ Material composition of the work piece: There are different variants observed in sheet metal with change in Hardness/ Material grade/ Material composition, during spot welding, so it is needed to set different program depending upon the Hardness/ Material grade/ Material composition of the sheet metal. This Hardness/ Material grade/ Material composition of the sheet metal cannot be identified by the operator with naked eye, hence if the material with wrong/change in Hardness/ Material grade/ Material composition comes and if the welding program is not changed then this may lead to weak spot. b) Change in Electrode Tip & Shank Conductivity: In Spot welding, the spot welding gun consists of Electrode Tip and shank. The electrode Tip & Shank are manufactured using the Copper Alloys like- Chromium Copper, Cadmium Copper, Zirconium Copper etc. These Alloy configurations has different hardness resulting in change in conductivity. Hence the welding parameters are set for the specific Electrode Tip & Shank material composition. If the Material composition changes then the parameters are also needed to be changed. In welding shop over a period of time different improvements/ Kaizen are done in order to life enhancement of the Electrode Tip & Shank. During this improvement if the material composition changes then the welding parameters are also need to be changed. But as the change in material composition is not visually detectable and due to lack of communication of change in material, sometime the welding parameters are not changed accordingly which may lead to weak spot. These all defects ultimately leads to various failures in the final product especially in automotive industry where vehicle is subjected to continuous forces and stresses these defects leads to early failure of various components in vehicle.

[006] The other type of gun which is available in the market called as adaptive spot welding gun provides an intelligent welding method. This gun overcomes most of the disadvantages of AC spot welding gun mentioned above. These guns comprises intelligent controlling method to dynamically change the welding parameters based on different conditions such as thickness, material etc. Therefore these guns are not manual dependant for setting the welding parameters and they are capable of providing high quality of weld with minimum defects. Spot welding operation is carried depending upon the total resistance of the work piece to be welded. Adaptive controller works on the principle that, it checks the initial resistance between the two tips of electrodes and passes the current accordingly until the resistance becomes Zero. As soon as the resistance becomes near to zero the controller cutoffs the current. This happens within the weld cycle. This process ensure the weld quality in real time. However the major disadvantage of using adaptive spot welding guns is it is very costly. In automotive industry where the large number of guns are required to meet the higher production targets in lesser time, using adaptive guns becomes very costly method which also leads to increasing the total manufacturing cost of the final products. Another disadvantage of the adaptive welding is that it continues the welding operation even if any non-conducting material comes in between thereby increasing the chances of welding defects. It also requires external pendant for program or parameter setting. Adaptive gun works in two modes- Calibration mode & Master mode. We need to calibrate the Gun for the higher and the lower thickness of the work piece to be weld and generate the required graphical trend on the pendant and then set it to Master mode. The operating mode of the gun is only detectable by use of pendant hence cannot be identified by the operator. If the Adaptive gun is not set in the master mode and it operates in calibration mode then it acts like normal MFDC spot welding gun which may leads to all the defects incurred by the normal AC/MFDC Spot welding guns.

[007] Therefore currently there is no welding gun available which is cheaper in cost and is also intelligent to control the welding parameters dynamically to achieve the best welding quality. AC/MFDC spot welding guns are cheaper in price however not intelligent as adaptive welding guns and adaptive welding gun are intelligent but are at the higher price since it uses advance control system which comes at very high price and it is difficult to reduce the price of these guns.Thus, there is a need to develop a device which can make the AC welding guns more intelligent and which will improve the weld quality at lesser cost. Also such conversion/automation device needs to be retrofitted to existing AC welding guns. This can save major initial investment cost and achieve the desire weld quality.
OBJECTS OF THE INVENTION

[008] In light of the aforementioned, it is an objective of this invention to provide a cost effective way of providing a spot welding gun which can intelligently control welding parameters without any manual intervention.

[009] Another objective of the present invention is to provide a spot welding gun capable of providing good welding quality at lower cost.

[010] Still another objective of the invention is to provide an automation device which can convert the existing AC welding gun into intelligent automatic guns and can be retrofitted on the existing guns.

[011] Other objects and advantages of the present disclosure will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the present disclosure
SUMMARY OF THE INVENTION

[012] With these objectives in view, the present invention provides an automation device for welding work pieces using a welding machine comprising
a controller having memory for storing at least a welding program corresponding to pre-determined values for at least a welding parameter;
wherein said automation device is adaptable to the any AC welding machines and comprises;
a voltage measurement means to measure voltage across the work pieces to be welded;
a current measurement means to measure a current supplied through the work pieces;
further automation device comprising a measurement circuit capable to receive the measured parameters , preferably voltage from the voltage measurement means and current from the current measurement means and process the received values to calculate the resistance across the work piece;
wherein said automation device comprises a processor configured to receive the measured resistance value and to automatically select at least one program stored in the memory based on the measured resistance.

[013] To adapt said automation device to AC welding machines at least a program is used only for measuring the resistance of the work pieces and the program is modified to comprise the steps of squeezing the work pieces together and passing a current through the work pieces to determine the resistance; based on which the next appropriate welding program is selected by the processor.

[014] Further to adapt the automation device to AC welding machines the control cables of welding machine are replaced by the shielded cables and the automation device is placed close to the machine where the resistance is measured.

[015] To adapt the automation device the AC welding machine is modified to include a provision for mounting a current sensing coil for measuring the current preferably near welding machine arm.

[016] According to preferred embodiment the automation device comprises amplifier based integrated circuit for measuring the resistance across the work piece.

[017] The processor of the automation device is configured to operate a relay provided in the welding machine which instructs the welding controller to select the welding program or to change the state of the machine.
[018] According to one of the embodiment a processor is configured to select a welding program if the measured resistance of the work piece is within pre-determined range of resistance value pre-set for the corresponding program.

[019] The program stored in memory corresponds to pre-set welding parameters used for welding the work pieces wherein the pre-set welding parameters comprises at least one welding current, pressure (force- start/initiation), squeeze time, weld time, hold time, off time and pressure (Force-stop/release).

[020] The value of at least one welding parameter is different in different program.

[021] The automation device comprises a display to indicate the selected welding program and at least a welding parameter.

[022] An automation device adapted to a welding gun for atomisation of welding work pieces comprising:
a voltage sensing circuit;
a current sensing circuit;
a measurement circuit;
a processor;
at least a relay; and
a controller; wherein;
a voltage sensing circuit comprising cables mounted in an arm of the welding gun to measure voltage across the work pieces to be welded;
a current sensing circuit comprising current sensing coils mounted in an arm of the welding gun to measure the current passed through the work pieces;
a measurement circuit connected to voltage sensing circuit and current sensing circuit to receive the measured values of voltage and current from respective circuits and calculate the resistance across the work pieces;
a processor in communication with the measurement circuit to receive the calculated resistance value and is configured to select a welding program from a set of programs preset with respect to particular resistance value based on measured resistance value and instruct at least one relay of the welding gun to select a welding program or to change the state of gun;
a controller in communication with the relay to receive the instruction given by the processor i.e. to select the welding program or to change the state of gun and configured to operate the welding gun according to the instruction given by the processor.

BRIEF DESCRIPTION OF DRAWINGS

[023] The proposed invention related to the automation device for AC welding guns will now be described with the help of accompanying drawings, in which:

[024] Figure 1 illustrates the overall arrangement of components and respective connections provided in the existing AC spot welding gun.

[025] Figure 2 illustrates the block diagram of automation device developed for the AC spot welding gun according to one of the embodiment of present invention.

[026] Figure 3 illustrates the overall arrangement of components and respective connections along with automation device for AC Spot welding gun according to the present invention.

[027] Figure 4 illustrates the input signals coming to and output signals from the automation device according to present invention

DETAILED DISCRIPTION OF DRAWINGS:

[028] A preferred embodiment will now be described in detail with reference to the accompanying drawings. The preferred embodiment does not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.

[029] The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted not to unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein. The system and method of the present disclosure will be described herein below with reference to FIGURES 1 to 3.

[030] Figure 1 represents the conventional AC welding gun (100) along with its components. The AC gun primarily consist of a spot welding gun (102), welding controller (108) which contains the memory (Not shown) for storing the various programs each of which corresponds to different welding parameters for different welding conditions. The welding controller (108) is in communication with welding gun (102). Further, the AC gun (102) comprises an operating pendant (104) comprising at least 42 toggle switches for operating at least two relays (106, 107) one of which (106) is for operating the state of gun (102) i.e. Start, Stop, retract etc. and other relay (107) is use to select the pre-stored welding program from the controller (108). The operator based on the welding condition selects the appropriate welding program. The welding conditions generally includes the parameters such as material to be welded and Thickness of work piece to be welded. Therefore, as a normal operating sequence the operator is first expected to check the material, thickness of the work piece and select the appropriate welding program using operating pendant. The appropriate welding program is nothing but selection of best suited welding parameters. As explained earlier the spot welding generally comprises various welding parameters i.e. pressure (force- start/initiation), squeeze time, weld time, welding current (welding current flows during only weld time), Hold time, off time and pressure (Force-stop/release). By selecting the appropriate program operator selects the best suited welding parameters of a given work piece to get a good quality weld. It can be easily understood from this that the operation of gun is manual dependent and therefore there is a possibility of error. To eliminate this error an automation device is developed which automates the process of selection of welding programs based on welding conditions which is explained hereinafter.

[031] Fig. 2 represent a block diagram of automation device (200) and a gun (102) adapted with the proposed device according to the preferred embodiment of the present invention. It works on the principle of the Ohms Law and use the inbuilt facilities of AC spot weld gun (102) for determination of the resistance. According to the Ohm’s law the electrical resistance of any component is derived from the electrical voltage across two points divided by the current passed through those two points [R= V (Voltage)/I (Current)]. The resistance which is the sum of Resistance of both the electrodes and sheet metal parts hold between the tips for the spot welding. The electrical resistance is responsible for producing the heat in the components to be welded thereby melting the work-piece and producing the required weld. Therefore, the automation device (200) uses a voltage measurement circuit (202) to measure the voltage across the two tips of electrodes. It has a current measurement circuit (204) to measure the current passed through the work piece and two electrodes. The measured value of voltage and current are then sent to the resistance measurement circuit (206) which calculates the resistance for a given work piece and applied voltage and current. The measured resistance value is passed onto a processor (210) which is primarily a microcontroller device comprising electronic components and able to process the received data. Based on the results of processed data it operates the relays (106, 107) which in turn instructs the welding controller (108) to select the appropriate welding program or to change the state of the gun. The AC spot welding controller (108) has some pre-defined inbuilt welding programs. Generally, the gun (102) is provided with 16 inbuilt programs however the number of programs may vary based on its type. The device (200) is also provided with a screen to display (212) the program which is selected and corresponding operating parameters. Therefore, it can be understood that the programs which were previously selected by the operator are now being selected using an automation device (200). Since the resistance is ultimately derived from the material properties and thickness of work piece, Electrode Tip and shank conductivity these parameters gets automatically considered while selecting the welding parameters. This helps to run different programs depending upon the resistance of the sheet to be welded

[032] Each program stored corresponds to pre-set welding parameters. Upon selection of a particular program the particular set of welding parameters gets selected which are pre-stored in the controller (108). The program is selected based on pre-determined resistance range. For example, as represented in table 1, if the resistance falls between the range of 204 to 258 ohm then the program 5 is selected and the corresponding pre-set welding parameters are used for welding, if it falls under range of 690- 715 then program 12 is selected and so on. Therefore, it can be understood that the welding parameters changes as the resistance changes. Each parameter can be changed individually or all the parameters can be simultaneously changed based on pre-defined criteria for each resistance range. The available programs can be therefore used for setting of parameters for a particular resistance range. As illustrated in the example shown in table 1 below program 5 is utilized for the resistance range 204-258 therefore if the resistance of work piece is 250 then this program will automatically get selected. There are five corresponding welding parameters such as squeeze time, weld time, hold time, off time and welding current is pre-set for program 5. The values parameters can be individually alter based on the requirement. The five welding parameters shown here are just for illustrative purpose and the person skilled in the art can appreciate that there can be more parameters added to or removed from these. Therefore, once the program is change from one program to other, either value changes for all the welding parameter or only few parameters based on pre-determined set values.
Program No. Resistance Range (mOhms) Welding Parameters
Squeeze Time (Cycles) Weld Time
(Cycles) Hold Time (Cycles) Off Time (Cycles) Current K (Amp)
5 204-258 20 6 10 2 6.8
12 690-715 30 14 10 2 9.5
Table 1: Program no. and corresponding welding Parameters
[033] Therefore, the sequence of operating of the gun (102) equipped with automation device (200) is it first measures the resistance of the work piece held between the two tips of the spot welding gun and accordingly selects the pre-set program. The resistance is measured in real time once before start of every spot welding cycle. The current measured/ passed through the Tip of the spot welding gun is AC (Alternating Current). Since the program selection is made automatic, it no more requires external operating pendant (104) for programming/ parameter setting. It is single mode operating device. Further, the gun (102) is now capable of generating error if any non-conducting material comes in between the spot welding sheets and selects the relay (106) to change the state of gun i.e. either to stop or retract thereby preventing the possible welding defects.

[034] Fig. 3 represents the modified AC welding gun comprising automation device showing electrical connections between its components according to present invention. The proposed device cannot be directly fitted to the existing AC gun (102) as there are various challenges which needs to be overcome for adapting this automation device (200). Therefore, it requires few modifications in the gun (102) along with necessary electrical connections to operate effectively. The modifications and challenges are explained hereinafter. The modifications explained are according to the preferred embodiment of the present invention and the necessary modifications can be done using alternate methods and based on type of welding gun.

[035] The checking of the resistance needs to be carried out when the welding sheet metals are squeezed between the two electrodes. To pass the current one program out of the multiple programs stored in the controller of the AC spot welding gun is used. This activity is of very short duration (0.1 sec) with the current arrangement of AC gun (102) it is not possible to measure the resistance within such a short duration since the program of the conventional welding gun (102) takes more time to measure the resistance. The conventional AC welding gun (102) utilizes a resistor based circuit which is one of the major contributing factor for increase in the resistance measuring time. In order to reduce this measuring time the existing resistor based circuit is replaced with the appropriate operational amplifier based integrated circuit which reduces the resistance measurement time drastically and makes it possible to measure the resistance within 0.1 sec.

[036] Further, another challenge for adapting the automation device (200) to the welding gun (102) is the program 1 is used for the resistance measurement so at the end of the program there is weld over signal which forces the electrodes to open and then the next program is triggered. For every spot first the program 1 runs for checking the resistance and then depending upon the resistance respective program gets selected and then runs. The intermediate period between the switching of the program 1 to other program the electrodes are opened and again closed which results is the spot weld defect (Spot burn). To prevent this it is required to skip the first weld over signal of every spot and use the program 1 partially i.e. only squeeze & weld parameters are used i.e. only current is passed through the work pieces for a very short duration. This not only maintains the electrodes in the close condition but prevents the spot weld defects and also reduces spot cycle time (Travel time to open and again closing of the electrodes). Thereby achieving quick weld.

[037] It can be observed that for the same sheet thickness between the two electrodes the measured resistance value may not be consistent resulting in the variation in the program selection, this variation may lead to spot welding defect. To prevent this, the bare control cables of AC gun (102) are replaced by the shielded cables and the complete device (200) brought near to the gun arm where the resistance is measured, this gives the consistent reading of the resistance and the variation gets reduced drastically.

[038] The modifications includes provision for mounting the current sensing coil for which there is no facility on the electrodes of the existing AC gun (102) therefor the gun arms are required to be modified accordingly. Previously the Gun operating signals were directly provided to a solenoid valve mounting on the Gun from controller through pendant. After mounting the automation device (200) the Gun operating signals are routed through automation device (200).

[039] Figure 4 illustrates the input signals from AC welding gun (102) to the automation device (200) and output signals from the automation device (200) to the AC welding gun (102) according to an embodiment of present invention.

ADVANTAGES OF THE INVENTION
[040] Technical advancements of the system and method envisaged by the present disclosure include the realization following advantages:
1. A system that provides an automation device to convert existing AC welding guns into intelligent automatic guns at very low cost.
2. A system that provides an automation device which can be retrofitted on existing AC welding guns thereby saving large initial investment cost for implementing new intelligent adaptive welding guns.
3. A system that provides an automation device which improves the weld quality of existing AC welding gun.
4. A system that provides an automation device which can reduce the weld time required for conventional AC welding guns.
5. A system that provides an automation device which can ensures the spot welding strength despite change in the following conditions, change in the Hardness of work piece; change in the Thickness of the work piece; change in the Material grade/ Material composition of Work piece; electrode Tip & Shank conductivity; change in conductivity of current flowing path (Internal Leakages); change in spot welding contact area.

[041] Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.

[042] The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

[043] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. ,CLAIMS:We Claim:

1. An automation device for welding at least two work pieces using a welding machine comprising
a controller having a memory for storing at least a welding program corresponding to a pre-determined values for at least a welding parameter;
a voltage measurement means to measure voltage across the work pieces to be welded;
a current measurement means to measure a current supplied through the work pieces;
a measurement circuit capable to receive the measured parameters from said measurement means and process the received values to calculate the resistance across the work pieces; and
a processor configured to receive the measured resistance value and to automatically select at least one program stored in the memory based on the measured resistance.

2. An automation device as claimed in claim 1 wherein, at least one program is used for calculating the resistance across the work pieces by measuring the voltage and current passed through the work pieces to determine the resistance.

3. An automation device as claimed in claim 1 wherein, the measurement circuit comprises an amplifier based integrated circuit for measuring the resistance across the work pieces.

4. An automation device as claimed in claim 1 wherein, the controller is instructed by a relay provided in the welding machine to select the welding program or to change state of the machine.

5. An automation device as claimed in claim 1 wherein, the processor is configured to receive the measured resistance of the work piece;
decide a pre-determined range of resistance values corresponding to the measured resistance; and
select at least one welding program corresponding to the pre-determined range of resistance values.

6. An automation device as claimed in claim 1 wherein, the program stored in the memory of controller corresponds to at least one pre-set welding parameter used for welding the work pieces wherein, the pre-set welding parameter at least include welding current, pressure force at start of welding, squeeze time, weld time, hold time, off time and pressure force at stop.

7. An automation device as claimed in claim 6 wherein, at least one welding parameter has different value in different program.

8. An automation device as claimed in claim 1 wherein, the welding machine comprises a display to indicate at least the selected welding program and at least a welding parameter.

9. An automation device as claimed in claim 1 wherein, the welding machine is an existing welding machine and said automation device is adapted to the welding machine.

10. An automation device as claimed in claim 10 wherein, the welding machine comprises at least one control cable as shielded cables.

11. An automation device as claimed in claim 10, is placed close to the work pieces where the resistance is measured to avoid variations in measured resistance.

12. An automation device as claimed in claim 10 wherein, the welding machine is provided with a welding arm comprising a provision for mounting at least a current sensing coil for measuring the current or a voltage sensing coil for measuring the voltage.

13. A method of adapting an automation device to a welding machine for welding at least two work pieces comprising steps of:
providing a voltage sensing circuit comprising cable mounted in an arm of the welding machine and measuring voltage across the work pieces to be welded;
providing a current sensing circuit comprising a current sensing coil mounted in an arm of the welding machine and measuring the current passed through the work pieces;
providing a measurement circuit connected to voltage sensing circuit and current sensing circuit and receiving the measured values of the voltage and current to calculate the resistance across the work pieces;
providing a processor in communication with the measurement circuit for receiving the calculated resistance value; deciding a pre-determined range of resistance values corresponding to the measured resistance; and selecting at least one pre-set welding program corresponding to the pre-determined range of resistance values; and instructing at least one relay of the welding machine to select a welding program or to change the state of gun;
providing a controller in communication with the relay for receiving the instruction and operating the welding machine according to the instructions given by the processor.