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Spot welding
The spot welding machine adopts the principle of double-sided double-point overcurrent welding. The two electrodes pressurize the artifact, so that the two layers of metal form some pressure contact resistance under the pressure of the two electrodes, and when the welding current flows from one electrode to the other When one electrode is formed, instantaneous thermal welding is formed at two contact resistance points. The welding current immediately flows from the other electrode to the electrode along the two artifacts, forming a loop, and will not damage the internal structure of the electrode. Welding artifact.

Chinese name

spot welding

use

Double-sided double-point overcurrent welding principle

form

Some contact resistance

press

Number of solder joints welded simultaneously



table of Contents

1 Introduction

2 Working Guidelines

3 Mechanical uses

4 Security

5 Installation and maintenance

6 Rebar spot welding



Introduction

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Spot welding can be divided into universal type (universal type) and special type according to the purpose; according to the number of welding points welded at the same time, there are single-point type, double-point type and multi-point type; according to the conductive method, there are single-side and double-side According to the transmission mode of the pressing mechanism, there are foot type, motor-cam type, pneumatic type, hydraulic type, compound type (pneumatic hydraulic type); according to the characteristics of operation, there are non-automatic and automated; according to the installed Methods are divided into fixed, mobile or portable (hanging type); according to the moving direction of the movable electrode of the welding machine (usually the upper electrode), there are vertical stroke (the electrode moves linearly), circular stroke; according to the electrical energy The supply methods are divided into industrial frequency welding machine (using 50 Hz AC power supply), pulse welding machine (DC pulse welding machine, energy storage welding machine, etc.), frequency conversion welding machine (such as low frequency welding machine).

When the artifact and electrode are fixed, the resistance of the artifact depends on its resistivity. Therefore, the resistivity is an important property of the material being welded. The metal with high resistivity has poor conductivity (such as stainless steel) and the metal with low resistivity has conductivity Good (such as aluminum alloy). Therefore, when spot welding stainless steel, it is easy to produce heat and difficult to dissipate heat. When spot welding aluminum alloy, it is difficult to produce heat and easy to dissipate heat. When spot welding, the former can use a smaller current (several thousands of amperes), and the latter must use a large current ( Tens of thousands of amps). The resistivity depends not only on the type of metal, but also on the heat treatment state, processing method and temperature of the metal.

In order to ensure the size of the nugget and the strength of the solder joint, the welding time and welding current can be complementary within a certain range. In order to obtain a certain solder joint strength, a large current and a short time (strong condition, also called hard code), or a small current and a long time (weak condition, also called soft code) can be used. used. The choice of hard or soft specifications depends on the performance, thickness and power of the welding machine used. For metals with different characteristics and thicknesses, there are upper and lower limits for current and time, which should be used first.

The electrode pressure has a significant effect on the total resistance R between the two electrodes. With the increase of the electrode pressure, R decreases significantly, and the increase in welding current is not large. It cannot affect the reduction in heat production caused by the decrease in R. Therefore, the strength of the solder joint always decreases as the welding pressure increases. The solution is to increase the welding current while increasing the welding pressure.

Classification automatic spot welding machine

Spot welding can be divided into universal (universal, special) spot welding according to the purpose;

According to the number of welding points welded at the same time: there are single-point type, double-point type, multi-point type;

According to the conductive method, it is divided into single-sided and double-sided;

According to the transmission mode of the booster mechanism, it is divided into: foot pedal, motor cam type, pneumatic type, hydraulic type, composite type (pneumatic hydraulic type);

According to operating characteristics: non-automated and automated;

According to the installation method, it is divided into: fixed, mobile or portable (hanging) spot welding;

According to the moving direction of the movable electrode (usually the upper electrode) of the welding machine, it can be divided into: vertical stroke (linear electrode movement) and circular stroke.



Working guidelines

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The process of spot welding is to turn on the cooling water; clean the surface of the weldment, after the assembly is accurate, send it between the upper and lower electrodes, and apply pressure to make the contact good; the energization makes the contact surfaces of the two artifacts heated and partially melted Nugget; maintain pressure after power off, so that the nugget cools and solidifies under pressure to form a solder joint; remove the pressure and take out the artifact. Spot welding process parameters such as welding current, electrode pressure, energizing time, and electrode working surface size have a significant impact on welding quality.

Spot welding uses the high temperature arc generated by the positive and negative poles during an instantaneous short circuit to melt the welded material between the electrodes to achieve the purpose of combining them. The structure of spot welding is very simple. To put it bluntly, it is a high-power transformer, which converts 220V AC to a low voltage, high-current power supply, which can be DC or AC. The welding transformer has its own characteristics, that is, it has the characteristics of a sharp drop in voltage.

After the electrode ignites, the voltage drops to adjust the working voltage of the welding machine. In addition to the primary 220/380 voltage conversion, the secondary coil also has taps to change the voltage, and there is also a soldering iron core to adjust the adjustable core. Welding machines are usually high-power transformers made using the principle of inductance. The inductance produces a huge voltage change when it is turned on and off. During the transient short circuit, the high voltage arc generated by the positive and negative electrodes is used to melt the solder on the electrodes. In order to achieve the purpose of combining them.

Spot welding is a resistance welding method in which a weldment is assembled with joints, pressed between two electrodes, and the base metal is melted by resistance heat to form a welding spot. Spot welding is more used for the connection of thin plates, such as aircraft skins, fire pipes of aircraft engines, car cabin shells, etc. The spot welding transformer is a spot welding appliance, and its secondary has only one loop. The upper and lower electrodes and electrode arms are used to conduct welding current and transmit power. The cooling water path passes through transformers, electrodes and other parts to avoid heating and welding. The cooling water should be passed before the power switch is turned on. The quality of the electrode directly affects the welding process, welding quality and productivity. Electrode materials are commonly made of copper, cadmium bronze, chrome bronze, etc .; electrode shapes are diverse, mainly determined by the shape of the weldment. When installing the electrode, pay attention to keeping the surface of the upper and lower electrodes parallel; the electrode plane should be kept clean and usually trimmed with emery cloth or file. Welding cycle The welding cycle of spot welding and projection welding consists of four basic stages (spot welding process):

(1) Pre-compression stage-the electrode is lowered to the stage where the current is turned on, to ensure that the electrode is pressed against the artifact, so that there is appropriate pressure between the artifact.

(2) Welding time—The welding current passes through the artifact and generates heat to form a nugget.

(3) Maintenance time-cut off the welding current and continue to maintain the electrode pressure until the nugget solidifies to a sufficient strength.

(4) Rest time-The electrode begins to rise, the electrode begins to fall again, and the next welding cycle begins.

In order to improve the performance of welded joints, it is sometimes necessary to add one or more of the following to the basic cycle:

(1) Increase the pre-pressure to eliminate the gap between the thick artifacts and make them fit closely.

(2) Use preheat pulse to improve the plasticity of the metal, make the artifact easy to fit closely and prevent splashing; doing this during convex welding can make multiple bumps evenly contact with the flat plate before welding to ensure the uniform heating of each point.



Mechanical use

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How to use spot welding:

1. During the welding process, the position of the electrode rod should be adjusted so that the electrode arms remain parallel to each other when the electrode is pressed against the weldment.

2. The current adjustment switch stage can be selected according to the thickness and material of the weldment. After booting, the power indicator should light up. The electrode pressure can be adjusted by adjusting the spring pressure nut and changing its compression degree.

3. After completing the above adjustments, you can turn on the cooling water first and then turn on the power to prepare for welding. Procedure of the welding process: the weldment is placed between the two electrodes, the foot pedal is pressed, and the upper electrode is brought into contact with the weldment and pressurized. When the foot pedal is continued to be pressed, the power contact switch is turned on, and the transformer starts to work. The circuit is energized to heat the weldment. When the electrode is lifted when the foot pedal is released after a certain time of welding, the power of the spring is first cut off and then restored to the original state, and the single-point welding process is ended.

4. Preparation and assembly of weldments: All dirt, oil, scale and rust on the steel weldments must be removed before welding. For hot rolled steel, it is best to first select the welding area by pickling, sandblasting or using a grinding wheel to remove scale. Although it is possible to clean uncleaned weldments, it will seriously reduce the service life of the electrode, and will also reduce production efficiency and spot welding quality. For thin-coated medium and low carbon steel, it can be directly welded.

In addition, when using, users can refer to the following process data:

1. Welding time: When welding medium and low carbon steel, this welding machine can use the strong specification welding method (instantaneous power-on) or the weak specification welding method (long-term power-on). In mass production, a strong standard welding method should be used, which can improve production efficiency, reduce power consumption and reduce artifact deformation.

2. Welding current: The welding current depends on the size, thickness and contact surface of the weldment. Generally, the higher the metal conductivity, the greater the electrode pressure and the shorter the welding time. The current density required at this time also increases.

3. Electrode pressure: The purpose of the electrode applying pressure to the weldment is to reduce the contact resistance of the welding point and ensure the pressure required to form the welding point.



Safety

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1. When used in the field, there should be rain, moisture, sunscreen, and the corresponding fire equipment should be installed.

2. Within 10m of the welding site, flammable and explosive materials such as oil, wood, oxygen cylinders and acetylene generators shall not be stacked.

3. Welding operations and cooperative personnel must wear the required labor protection equipment. Safety measures must be taken to prevent accidents such as electric shock, falling from high altitude and gas poisoning.

4. The copper plate connected to the secondary tap should be fastened, and the terminal should have a washer. Before closing, carefully check the wiring nuts, bolts and other parts, and ensure that they are intact, not loose or damaged. There is a protective cover at the terminal.

5. Before use, you should check and confirm that the primary and secondary wires are connected correctly, the input voltage meets the nameplate requirements of the welding machine, and know the type and scope of spot welding welding current. After connecting the power supply, it is strictly forbidden to touch the live part of the primary line. The primary and secondary wiring must be equipped with protective covers.

6. When moving spot welding, the power supply should be cut off, and the welding machine must not be moved by pulling the cable. When there is a sudden power failure during welding, the power should be cut off immediately.

7. When welding non-ferrous metals such as copper, aluminum, zinc, tin, lead, etc., it must be done in a well-ventilated place, and the welding personnel should wear gas masks or breathing filters.

8. When multiple spot welds are used together, they should be tapped on the three-phase power network to balance the three-phase load. The grounding devices of multiple welding machines shall be connected by the grounding poles respectively, and shall not be connected in series.

9. It is strictly forbidden to weld on the pressure pipeline in operation, the container equipped with flammable and explosive materials and pressure parts.

10. When welding preheated parts, baffles should be set up to isolate radiant heat from preheated welded parts.



Installation and maintenance

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In order to ensure personal safety, the welding machine must be properly grounded before use. Before using the welding machine, please use a 500V megohmmeter to test that the insulation resistance between the high-voltage side of the welding machine and the casing is not less than 2.5 megohms, and then it can be powered on. Before unpacking and inspecting, the power must be cut off during the inspection. The welding machine must be watered first, and then welded. It is strictly forbidden to work without water. The cooling water should ensure that industrial water is supplied at an inlet pressure of 0.15-0.2 MPa at 5--30 ° C. After the welding machine is completed in winter, use compressed air to blow the water in the pipe to avoid the water pipe freezing and breaking.

The wire of the welding machine should not be too thin or too long, the voltage drop during welding should not be greater than 5% of the initial voltage, and the initial voltage should not deviate from ± 10% of the power supply voltage. When operating the welding machine, gloves, apron and protective glasses should be worn to prevent sparks from splashing out. Sliding parts should be kept well lubricated, and metal splashes should be removed after use. After using the new welding machine for 24 hours, the screws of each part should be tightened once, especially paying attention to the connecting screw between the copper flexible joint and the electrode. After use, the oxidation between the electrode rod and the electrode arm should be removed frequently to ensure good contact.

When using a welding machine, if the AC contactor is found to be inappropriate, it means that the grid voltage is too low. The user should first solve the power supply problem and use it only after the power supply is normal. It should be pointed out that if the quality problems of the main parts occur within half a month of the newly purchased welding machine, the new welding machine or the main parts can be replaced. The main parts of the welding machine are guaranteed for one year and provide long-term maintenance services. Under normal circumstances, after the user informs the factory, it can be in place within three to seven days according to the distance. Damage to the welding machine due to user reasons is not covered by the warranty. The wearing parts and wearing parts are not covered by the warranty.

Since the contact area of the electrode determines the current density, the resistivity and thermal conductivity of the electrode material are related to the generation and loss of heat. Therefore, the shape and material of the electrode have a significant effect on the formation of the nugget. As the electrode tip deforms and wears, the contact area increases and the strength of the solder joint will decrease. Oxide, dirt, oil and other impurities on the artifact surface increase the contact resistance. An oxide layer that is too thick can even prevent current from passing through. Local conduction, due to excessive current density, will produce splashes and surface burns. The existence of the oxide layer will also affect the unevenness of heating of each solder joint, causing welding quality fluctuations. Therefore, thoroughly cleaning the surface of the artifact is a necessary condition to ensure high-quality joints.

Troubleshooting

1. Depress the pedal, the welding machine does not work, the power indicator does not light:

One. Check whether the power supply voltage is normal; check whether the control system is normal.

b. Check whether the contact of the foot switch, the contact of the AC contactor and the contact of the transfer switch are in good contact or burned.

2. The power indicator light is on, and the artifact is not compressed and welded:

One. Check that the foot pedal travel is in place and the foot switch is in good contact.

b. Check when the pressure rod spring screw is adjusted.

3. Accidental spatter during welding:

One. Check whether the electrode tip is severely oxidized.

b. Check whether the welding artifact is badly corroded and has poor contact.

C. Check if the adjustment switch is too high.

d. Check whether the electrode pressure is too low and the welding procedure is correct.

4. The solder joint has serious dents and is extruded:

One. Check if the current is too large.

b. Check whether the welding artifact is uneven.

C. Check whether the electrode pressure is too high and the shape and cross section of the electrode tip are appropriate.

5. Insufficient welding artifact strength:

One. Check whether the electrode pressure is too low, and check whether the electrode rod is tight.

b. Check whether the welding energy is too small, whether the welding artifact is seriously corroded, so that the welding point is poorly contacted.

C. Check whether there is excessive oxide between the electrode tip and the electrode rod, and between the electrode rod and the electrode arm.

d. Check whether the cross section of the electrode tip increases due to wear and whether the welding energy decreases.

e. Check whether the soft coupling of the electrode and copper and the bonding surface are severely oxidized.

6. Abnormal sound of AC contactor during welding:

One. Check whether the input voltage of the AC contactor is 300V lower than the self-release voltage during welding.

b. Check whether the power cord is too thin or too long, causing the line voltage to drop too much.

C. Check if the network voltage is too low to work properly.

d. Check whether the main transformer is short-circuited, resulting in excessive current.

7. Overheating phenomenon of electric welding machine:

One. Check whether the insulation resistance between the electrode holder and the main body is poor, and whether it causes a local short circuit.

b. Check whether the inlet water pressure, water flow and water supply temperature are appropriate, and check whether the waterway system is blocked by dirt, which may be caused by poor cooling