英文版;Rong Shijie introduces you to what is a spot welding robot, the intermediate links and matters to be aware of, as well as the details of use, which are described in detail below.





In the production process of automobiles, spot welding is an important process. At present, there are more than 2000 solder joints in the galvanized sheet fuel trucks, and some models even have more than 5,000 solder joints.

Spot welding is a high-speed, economical joining method that is suitable for the manufacture of sheet metal parts that can be stamped and rolled using lap joints, joints that are not required to be airtight, and thickness less than 3 mm.

Spot welding is the welding of individual points of the weldment on the contact surface of the joint.

Spot welding requires that the metal has good plasticity.



1, the basic knowledge of spot welding

Spot welding is usually divided into two categories: double-sided spot welding and single-sided spot welding.

In double-sided spot welding, the electrodes are fed from the sides of the workpiece to the weld. A typical double-sided spot welding method is the most common method, in which case there are electrode indentations on both sides of the workpiece. The conductive plate of the large soldering area is used as the lower electrode, which can eliminate or reduce the indentation of the workpiece below.

Commonly used for spot welding of decorative panels. Simultaneously welding two or more spot welds for double-sided spot welding, using a transformer to connect the electrodes in parallel. At this time, the impedance of all current paths must be substantially equal, and the surface state, material thickness, and electrode pressure of each welded portion. All need to be the same, in order to ensure that the current through each solder joint is basically the same, using double-sided multi-point spot welding of multiple transformers.


Spot welding usually uses lap joints and flange joints, which can consist of two or more workpieces of equal or unequal thickness.

When designing a spot welded structure, the accessibility of the electrode must be considered, ie the electrode must be able to easily reach the welded part of the workpiece. Factors such as margins, lap joints, dot pitch, assembly gap, and solder joint strength should also be considered.

The minimum margin depends on the type of metal being soldered, the thickness and the soldering conditions. Smaller values may be obtained for metals with high yield strength, thin parts, or when strong conditions are used.

The point distance is the center distance between two adjacent points, and the minimum value is related to the thickness of the metal to be welded, the conductivity, the surface cleanliness, and the diameter of the nugget.

The minimum value of the specified point distance is mainly considering the influence of the splitting. When strong conditions and large electrode pressure are used, the dot pitch can be appropriately reduced. When using thermal expansion monitoring or a controller capable of sequentially changing the current at each point, and other devices that can effectively compensate for the effects of shunting, the dot pitch can be unlimited.

The assembly clearance must be as small as possible, since relieving pressure by the gap will consume a portion of the electrode pressure, reducing the actual weld pressure. The unevenness of the gap will cause the welding pressure to fluctuate, which will cause a significant difference in the strength of each solder joint. Excessive gap will also cause severe splash. The allowable gap value depends on the stiffness and thickness of the workpiece, and the stiffness and thickness are larger. The smaller the allowable gap is, usually 0.1-2 mm.

The shear strength of a single solder joint depends on the area of the nugget at the junction of the two plates. In order to ensure the joint strength, in addition to the nugget diameter, the penetration rate and the indentation depth should also meet the requirements. The expression of the penetration rate is: η =h/δ-c×100%. The penetration rate on both boards is only allowed between 20-80%.

The maximum penetration of magnesium alloys is only allowed to be 60%. Titanium alloys are allowed up to 90%. When welding workpieces of different thicknesses, the minimum penetration rate on each workpiece may be 20% of the thickness of the thin part in the joint, and the indentation depth shall not exceed 15% of the thickness of the sheet if the thickness ratio of the two workpieces is greater than 2:1, or When the weld is applied in an inaccessible area and the flat electrode is used on one side of the workpiece, the depth of the indentation can be increased to 20-25%.

The strength of the spot welded joint when subjected to a tensile load in the direction of the vertical panel is the positive tensile strength. Since the sharp corners formed between the two plates around the nugget can cause stress concentration, and the actual strength of the nugget is lowered, the spot welded joint is generally not loaded as such. Generally, the ratio of the tensile strength to the shear strength is used as an index for judging the ductility of the joint. The larger the ratio, the better the ductility of the joint.

The joint strength formed by multiple solder joints also depends on the pitch and solder joint distribution. The dot-to-hour joint will affect its strength due to the split, which in turn limits the number of welds that can be arranged. Therefore, it is necessary to balance the dot pitch and the number of solder joints in order to obtain the maximum joint strength, and the multi-row solder joints are preferably staggered rather than rectangularly arranged.


Where welding is required to ensure the strength, the spacing of the welding will be relatively close, but considering the possible shunting of the welding, the welding point should be considered when the welding is not strong, so it is not as close as possible, reasonable arrangement Solder joints can get better results. Generally speaking, the three-layer solder joint is slightly farther than the two-layer solder joint.

The principle of application of solder joints is generally not more than 5mm, and the proportion of welded plate thickness is not more than 1:3. Exceeding this value will cause the weld nugget not to be at the center of the solder joint or even to weld through the thin plate. The thickest and thinnest three-layer welding cannot exceed the principle of 1:3.


The number of solder joints should be based on whether the joint strength meets the requirements. Excessive and excessive solder joints can only increase the cost of soldering. At the same time, the solder joint strength is reduced due to the increased shunting of solder joints.

Solder joint location is the result of process and product design coordination. Important solder joint locations should be set by CAE calculation results. The following table shows the shear strength requirements for different material thickness solder joints:


When welding, the surface of the weldment is cleaned first, then the welded plate is lapped and assembled, pressed between the two columnar copper electrodes, and pressed by a pressure P. When a sufficient current is passed, the contact at the plate A large amount of resistive heat is generated, and the metal in the hottest region of the center is quickly heated to a highly plastic or molten state to form a lenticular liquid molten pool. Continue to maintain the pressure P, disconnect the current, and after the metal cools, form a solder joint. Galvanized steel sheets are roughly classified into electrogalvanized steel sheets and hot dip galvanized steel sheets, and the former is thinner than the latter.

For electrodes for spot welding galvanized steel sheets, it is recommended to use two types of electrode alloys. Class 1 alloys can be used when the appearance of the spot weld is high. It is recommended to use a tapered electrode shape with a taper angle of 120 to 140 degrees.

When using a welding tong, it is recommended to use a spherical electrode with a face radius of 25-50mm. In order to improve the service life of the electrode, a composite electrode embedded with a tungsten electrode tip can be used, and an electrode body made of a type 2 electrode alloy can enhance the heat dissipation of the tungsten electrode tip.


Usually, according to the material and thickness of the workpiece, referring to the welding condition table of the material, the shape and size of the end face of the electrode are first determined. Secondly, the electrode pressure and welding time are preliminarily selected, then the welding current is adjusted, and the sample is welded at different currents. After checking the diameter of the nugget meets the requirements, the electrode pressure, welding time and current are adjusted within an appropriate range to carry out the sample. Welding and inspection until the quality of the solder joints fully meets the requirements specified in the technical conditions.

The most commonly used method for inspecting specimens is the tearing method. The markings for high quality solder joints are: round holes in one piece of the torn sample and round bosses on the other. Thick plates or quenched materials sometimes cannot tear round holes and bosses, but the diameter of the nugget can be judged by the sheared fracture. If necessary, low-power measurement, pull test and X-ray test are also required to determine the penetration rate, shear strength and presence or absence of shrinkage cavities, cracks, and the like. When selecting the process parameters for the sample, the difference between the sample and the workpiece in the shunt, the influence of the ferromagnetic material, and the assembly gap should be fully considered and adjusted appropriately.

The diameter of the solder joint is calculated by dividing the measured value of the long axis plus the measured value of the vertical axis of the long axis, and d = (a + b) / 2


Spot welding of aluminum alloy

The application of aluminum alloy is very extensive, and it is divided into two categories: cold work strengthening and heat treatment strengthening. The weldability of aluminum alloy spot welding is poor, especially for heat-treated aluminum alloys. The reasons for this and the technical measures to be taken are as follows:

(1) Higher conductivity and thermal conductivity must use larger current and shorter time to achieve sufficient heat to form nugget; reduce surface overheating, avoid electrode adhesion and electrode copper ion to pure aluminum The coating layer diffuses and reduces the corrosion resistance of the joint.

(2) The plastic temperature range is narrow and the linear expansion coefficient is large. It is necessary to use a large electrode pressure, and the electrode follow-up property is good, so as to avoid cracks caused by excessive tensile stress when the nugget is solidified. For aluminum alloys with large crack tendencies, such as LF6, LY12, LC4, etc., it is necessary to increase the forging pressure to make the nugget have sufficient plastic deformation and reduce tensile stress to avoid cracking. When the curved electrode is difficult to withstand a large forging pressure, it is also possible to use a method of adding a slow pulse after the welding pulse to avoid cracking. For large thickness aluminum alloys, two methods can be used together.

(3) The surface is easy to form an oxide film, which must be cleaned before welding, otherwise it will easily cause splash and nugget formation (when the tearing is checked, the shape of the nugget is irregular, the boss and the hole are not round), so that the solder joint The strength is reduced. Uneven cleaning will cause unstable solder joint strength.

For the above reasons, spot welding aluminum alloys should use welders with the following characteristics:

1) can provide high current in a short time

2) The current waveform is preferably characterized by slow rise and fall

3) Precise control of process parameters without being affected by grid voltage fluctuations

4) can provide the shape and saddle electrode pressure

5) The inertia and friction of the machine head are small, and the electrode followability is good.

At present, most of the domestic use of 300-600KVA DC pulse, three-phase low-frequency and secondary rectification welder, individually up to 1000KVA, have the above characteristics. Single-phase AC welders are also used, but only for unimportant workpieces.

The electrode of the spot-welded aluminum alloy shall be a type 1 electrode alloy with a spherical end face to facilitate the solidification of the nugget and heat dissipation.

Due to the large current density and the presence of an oxide film, electrode sticking is likely to occur during spot welding of aluminum alloy. Electrode adhesion not only affects the appearance quality, but also reduces joint strength due to current reduction. To do this, the electrode needs to be trimmed frequently. The number of points that can be welded after each trimming of the electrode is related to the welding conditions, the type of metal to be welded, the cleaning condition, the presence or absence of current waveform modulation, the electrode material and its cooling condition. Usually spot welding pure aluminum is 5-10 points, spot welding LF6, LY12 is 25-30 points.

The anti-transparent aluminum LF21 has low strength, good ductility after ductility, and no cracking, and usually uses a constant electrode pressure. Hard aluminum (such as LY11, LY12), super-hard aluminum (such as LC4, LC5) has high strength, poor ductility, and is prone to cracks. The pressure of the price curve must be taken. However, for thin parts, using large welding pressure or double pulse heating with slow cooling pulses, cracks are not inevitable.

When using valence pressure, it is important that the forging pressure lags behind the moment of power failure, usually 0-2 weeks. Forging pressure is added too early (before power failure), which is equal to increasing the welding pressure, which will affect the heating, resulting in the decrease and fluctuation of the solder joint strength. When the forging pressure is added too late, cracks have formed during the cooling of the nugget, and the forging pressure has not been helpful. Sometimes it is necessary to apply the forging pressure in advance at the time of power failure. This is because the electromagnetic valve is delayed in operation, or the forging pressure is slow due to the unsmooth passage of the gas passage, and it is not applied in advance to prevent cracks.


2, spot welding robot system



(1) Robot body

(2) Servo/pneumatic spot welding tongs

(3) Electrode dresser

(4) Pipeline package

(5) Welding tongs control cable

(6) Water and gas unit

(7) Welding tongs cold water pipe

(8) Welding clamp return pipe

(9) Spot welding controller cold water pipe (not required for air cooling)

(10) chiller

(11) Spot welding controller

(12) Robot Transformer

(13) Welding cable

(14) Robot controller

(15) Welding controller communication cable

(16) (17) (18) Robot Cable

(19) Servo encoder cable

(20) Robot Teach Pendant

(21) Cooling water switch

(22) Power supply

According to the load of the body-in-white spot welding tongs and the arm span statistics, it is generally required that the selected robot load is above 180KG, and the arm span of 2.5M or more can meet the requirements of most spot welding stations, if there is a replacement gun or a built-in pipeline package. , the load is correspondingly increased by 20KG.




The welding controller is divided into two types: power frequency and medium frequency. The welding controller has the following functions:

1. Through the primary and secondary closed-loop to achieve precise control of current, the control accuracy exceeds the ordinary similar products, which can effectively avoid defects such as solder joints, soldering and soldering.

2, solder joint counter function, effectively prevent leakage welding, and can automatically carry out electrode grinding and electrode life maintenance to ensure the diameter of the solder joint.

3. Independently monitor the growth of the weld nugget and independently compensate for the changes in the actual weld nugget and the required weld nugget.

4. Ensure the diameter of each solder joint.

5. Automatically compensate for welding disturbances.

6. Adaptive change of welding time and current during welding.

7. Store measurement data and curves online.



The IF welding controller transformer is smaller and lighter, can provide continuous high energy, and the current adjustment is faster and more accurate. It can be applied to: galvanized sheet, high-strength steel sheet, aluminum alloy sheet, 3-layer board welding and large throat wide welding tongs.



It has a compact pulse form, no inductive losses, less than 1 millisecond adjustment, no current peaks, no extra cooling time, providing higher energy and reducing electrode heat and mechanical stress. The IF is 30 – 50% longer than the power frequency electrode and provides 20 – 32% energy savings.





In addition, the IF welding controller has the following features: precise adjustment of welding parameters (dynamic adjustment and adaptive adjustment); no material overheating (less spatter).

Spot welding tongs: used to pressurize the welded workpiece (plate). The welding tongs used by robots are usually transformers and tongs mounted together as a whole, called "integrated welding tongs." In practical applications, it is necessary to make a special design for the welding tongs according to the particularity of the position of the spotting, in order to ensure that the welding tongs reach the position of the welding points.

Robotic spot welding tongs must be adapted to the welding specifications required for spot welding workpieces. The basic principles are:

1. Determine the maximum short-circuit current and maximum pressing force of the electrode of the welding tong according to the material and the thickness of the workpiece;

2. According to the shape of the workpiece and the position of the solder joint on the workpiece, determine the throat depth, throat width, electrode grip, maximum stroke, working stroke, etc. of the welding tongs;

3, the position distribution of all the solder joints on the integrated workpiece, determine which kind of welding tongs to choose, usually there are four kinds of welding tongs are more common, namely: C type single stroke welding tongs, C type double stroke welding tongs, X type single stroke welding Pliers, X-type double stroke welding tongs;

4. Under the above conditions, reduce the weight of the welding tongs as much as possible.


Advantages of servo welding tongs compared to pneumatic welding tongs:

1. The robot and the welding tongs synchronously coordinate the movement, greatly improving the production cycle.

2. The pressure and heat in the welding increase synchronously, and the quality of the solder joint is more reliable.

3, expand process control

4, enhance diagnosis and monitoring

5, simplify the design of the welding tongs, improve flexibility

6, reduce maintenance rate and improve running time

7, reduce production costs (gas consumption, spare parts)

8, automatically adjust the electrode cap zero after a welding cycle

9. Check/adjust the welding tongs after changing the gun. Correct the welding tongs zero position after the welding tongs are displaced when the servo control is disconnected.



Reducing production beats is reflected in:

1. Minimize the jump path between solder joints and obstacles.

2. The electrode opening can be shortened at will to reduce the time for closing the welding tongs.

3. The pressurization can be controlled faster and better after the welding start signal is sent.

4. The welding tongs can be opened faster after the welding completion signal is issued.

5. Change the welding pressure faster.

6, reduce electrode replacement and grinding

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