Introduction
Spot Welding Definition
Spot welding refers to a welding method that uses a cylindrical electrode to form a welding spot between the contact surfaces of two overlapping parts during welding.
During spot welding, pressure is first applied to ensure firm contact between the workpieces, and then an electric current is passed, causing the contact area of the workpieces to melt due to the effect of heating by resistance. After cooling, a weld point forms.
Spot welding is mainly used to weld thin plate components and stamped parts with a thickness of less than 4mm, and is especially suitable for welding automobile bodies and cabins and aircraft fuselages.
However, it cannot be used to weld containers with sealing requirements. Spot welding is a type of resistance welding, mainly used for welding thin plate structures and reinforcing bars.
Importance and applications of spot welding machines
Spot welding machine is a type of resistance welding. During welding, it uses upper and lower cylindrical electrodes to apply pressure, ensuring firm contact between the surfaces of the parts.
An electrical current then passes through, filling the electrode rod with current and applying resistance heating to melt the contact area of the workpieces. After cooling, a weld point forms.
Depending on the usage scenario and welding objects, spot welding machines are divided into medium frequency spot welding machines, precision spot welding machines and energy storage spot welding machines.
Due to its high welding efficiency and ease of automation, the application of spot welding machines is becoming more and more widespread, and now almost all industries can use spot welding equipment.
Main application fields of spot welding machine:
(1) Automotive and aviation industry. Examples include the overlay of thin sheet metal stamping parts on automobile cabins and carriages, the gluing of carriage sidewalls and roofs, thin sheet metal trailer plates with molded steel frame and cladding frame, as well as automobile components .
(2) Electronic industry. Examples include batteries, capacitor cover plates, electrical switches, electronic components, and screen printing.
(3) Household appliance industry, e.g. refrigerator casings.
(4) Irregular parts, etc.
Components of a spot welding machine
Main components of the equipment:
The whole machine includes: welding host (body), flexible welding cylinder, AC welding power supply and control system, upper and lower electrode parts, water cooling system, safety mechanism, etc.
(1) Welding host (body): adopts our company's mature welding structure to ensure that the rigidity required by the cylinder can be fully satisfied during operation.
(2) Welding cylinder: equipped with large-diameter air inlet and quick-response cylinder with built-in damper spring. The piston rod and guide rod are made of high-quality steel, quenched and tempered, with a surface hardness greater than 0.8 after chrome plating and grinding.
The piston cylinder is processed from hard aluminum to prevent the rust on the piston from affecting the quality of the gas-steel. The cylinder base is made of cast aluminum with a self-lubricating function, which reduces the cylinder's coefficient of friction. Adopts high quality sealing rings imported from Japan, has good sealing performance, durability and good fixed tracking performance.
(3) AC welding power supply and control system: adopts microcomputer control, can store 15 sets of welding programs, and can be independently adjusted to easily meet the welding requirements of products with different specifications and shapes.
The resistance welding transformer is composed of silicon steel sheets with 15,000 Gauss magnetic induction, and is internally forced water-cooled, with small vibration, better thermal conductivity, high power factor, high safety factor and large output power . It has long service life, low noise and compact and reasonable structure.
(4) Upper and lower electrode parts: adopt high-quality hardness, durable and wear-resistant tungsten copper and zirconium electrodes, and the electrodes are all internally water-cooled to reduce the durability of the electrode caused by high temperature when The electrode material is electrified, thus ensuring the useful life of the electrodes.
(5) Water cooling system: divided into four parts: transformer group water cooling, upper electrode water cooling, lower electrode water cooling and output copper block water cooling, and equipped with protection against overheating to ensure normal operation of the equipment without damage.
Types of spot welding machines
Spot welding machine can be divided into universal spot welding machines (general purpose, special purpose) according to their purpose of use;
According to the number of welding points welded at the same time, they can be divided into single-point, double-point and multi-point types;
According to the method of conduction, they can be divided into unilateral and bilateral;
According to the transmission mode of the pressure mechanism, they can be divided into pedal-driven, motor-cam type, pneumatic, hydraulic and compound (air-hydraulic) types;
According to their operating characteristics, they can be divided into non-automated and automated;
According to the installation method, they can be divided into fixed, mobile or light (suspended) spot welding machines;
According to the movement direction of the movable electrode (generally the upper electrode), they can be divided into vertical stroke (the electrode moves in a straight line) and circular stroke.
Factors to Consider When Choosing a Spot Welding Machine
Due to its convenience of operation, many sheet metal processing companies now generally choose spot welders as their main welding machines. However, there are many types of spot welders on the market, which can make choosing difficult. In this article, I will present the main factors to consider when selecting a spot welder.
The work of a spot welder is closely related to the size of the current, welding time and welding pressure. Traditional spot welders' pressing systems include foot pedals (manual), cams (electric), pneumatic (external air source), and a small amount of hydraulic (generally used in vacuum diffusion welding).
The role of pressure in spot welding is often overlooked by most people. When the melting point forms a welded joint, excessive or insufficient pressure may cause the speckled welded joint to crack. Excessive pressure can also cause shrinkage cavities. Therefore, good monitoring performance of the pressurization system is necessary, that is, it must stop at any time. A good pressure curve is the basis for a good spot welder.
Using linear bearings as a means of transmitting pressure is an ideal solution to avoid pulling the cylinder body. Closed loop control is used for current to avoid large current fluctuations.
Operation and safety tips for spot welding machines
Instructions for using a spot welder:
1. When welding, adjust the position of the electrode rod so that the electrode just presses the workpiece and the electrode arms remain parallel to each other.
2. Current adjustment switch level selection can be based on the thickness and material of the workpiece. After the power is turned on, the power indicator light should light up and the electrode pressure can be adjusted by adjusting the spring pressure nut to change its degree of compression.
3. After completing the above adjustments, the cooling water can be turned on first, and then the power can be turned on for welding preparation. The welding process is as follows: place the part between the two electrodes, step on the pedal, make contact with the upper electrode and press against the part.
When the pedal continues to be pressed, the power contact switch is turned on and the transformer starts to work, so that the secondary circuit is electrified to heat the part. When the welding time is up, release the pedal, the electrode will rise and the power will be cut off by the spring tension before returning to its original state, ending the single spot welding process.
4. Workpiece preparation and assembly: Steel parts must be cleaned of all dirt, oil, oxide scale and rust before welding. For hot-rolled steel, it is best to acid wash, sandblast or remove oxide scale with a grinding wheel. Although unwashed parts can still be spot welded, this seriously reduces electrode life and decreases production efficiency and quality. Medium to low carbon thin coated steel can be spot welded directly.
Process data:
Additionally, users can query the following process data when using a spot welder:
Welding time: When welding medium to low carbon steel, this machine can use strong specification welding (instantaneous current) or weak specification welding (long-term current). Welding with strong specifications should be used for mass production as it can improve productivity, reduce energy consumption, and minimize part deformation.
Welding current: The welding current depends on the size, thickness and contact surface of the part. Generally, the higher the metal conductivity and electrode pressure, the shorter the welding time. The required current density also increases proportionally.
Electrode pressure: The purpose of applying pressure to the workpiece with the electrode is to reduce the contact resistance in the weld and ensure the pressure required for weld formation.
Security:
1. For on-site use, a rain, moisture and sun-proof shed must be provided, and corresponding fire-fighting equipment must be installed.
2. Flammable and explosive materials such as oil, wood, oxygen cylinders, acetylene generators, etc. cannot be stored within a 10 m radius of the welding location.
3. Welding operators and auxiliary personnel must wear labor protection equipment as required by regulations. Safety measures must also be taken to avoid accidents such as electric shocks, falls from heights, gas poisoning and fires.
4. The connecting copper plate of the secondary tap must be pressed firmly, and the connecting pillar must have a washer. Before closing, check the connecting nuts, screws and other components in detail and confirm that they are intact, complete and free from looseness or damage. Protective covers are provided on all connecting pillars.
5. Before use, check and confirm that the primary and secondary line connections are correct, that the input voltage meets the specifications on the welding machine nameplate, and that you understand the applicable types and ranges of welding currents. spot welding machine welding. After turning on the power, do not touch live parts of the primary circuit. Protective covers must be installed at the junctions of the primary and secondary lines.
6. When moving the spot welder, turn off the power supply and do not move the welding machine by dragging the cable. If there is a sudden power failure during welding, the power must be cut off immediately.
7. When welding non-ferrous metals such as copper, aluminum, zinc, tin, lead, etc., it should be done in a well-ventilated area and welding personnel should wear a gas mask or respirator.
8. When multiple spot welders are used together, they must be connected to a three-phase power supply network to balance the three-phase loads. The grounding devices of multiple welding machines must be connected separately to the grounding poles and not in series.
9. Welding is strictly prohibited on pressure pipelines, containers containing flammable and explosive materials and live components that are in operation.
10. When welding preheated parts, a baffle must be installed to isolate the radiant heat emitted by the preheated part.
Installation and Maintenance:
The welder must be properly grounded before use to ensure personal safety. Before using the welder, use a 500V megohmmeter to test the insulation resistance between the high-voltage side of the welder and the chassis to ensure that it is not less than 2.5 megohms before turning on the power.
When checking and repairing, please turn off the power supply first before opening the case for inspection. The welder must be watered before welding, and it is strictly prohibited to work without water.
Cooling water should be supplied with industrial water at a temperature of 5-30°C and an inlet water pressure of 0.15-0.2 MPa. In winter, after the welder finishes working, compressed air must be used to blow the water into the pipe to prevent it from freezing and cracking.
Welding cables must not be too thin or too long and the voltage drop during welding must not exceed 5% of the initial voltage. The starting voltage must not deviate from the power supply voltage by more than ±10%. When operating the welder, wear gloves, aprons and protective glasses to avoid burns caused by sparks. The sliding parts must be kept well lubricated and metal splashes must be removed after use.
After 24 hours of using the welder, all screws must be tightened once. Pay special attention to the connection screws between the flexible copper joint and the electrode arm, which must be tightened. After use, the oxide between the electrode rod and the electrode arm must be cleaned frequently to ensure good contact.
If the AC contactor does not close tightly when the welder is in use, the mains voltage is too low. Users must first solve the power supply problem before using it when the power supply is normal. It should be noted that if there are quality problems with the main components of a newly purchased welder within half a month, a new welder or main component can be replaced.
The main part of the welder is guaranteed for one year and provides long-term maintenance services. In general, after the user notifies the factory, the service will be effective within three to seven days depending on the distance. Damage to the welder caused by user reasons is not covered by the warranty. Vulnerable parts and consumables are not covered under warranty.
The electrode contact area determines the current density, and the resistivity and thermal conductivity of the electrode material affect heat generation and dissipation. Therefore, the shape and material of the electrode have a significant impact on the formation of the weld nugget. As the electrode tip deforms and wears, the contact area increases and the resistance of the welded joint decreases.
Oxides, dirt, oil and other impurities on the surface of the part increase contact resistance. An excessively thick oxide layer can even impede the passage of current. Local conduction due to high current density can cause splashes and superficial burns.
The existence of the oxide layer will also affect the uneven heating of each welding point, causing fluctuations in welding quality. Therefore, complete cleaning of the part surface is a necessary condition to ensure high-quality joints are obtained.
Problems solution:
The welder does not work when the pedal is pressed and the power indicator light does not come on:
The. Check whether the power supply voltage is normal; check whether the control system is normal.
B. Check whether the foot switch contacts, AC contactor contacts and branch change switch are in good contact or burnt out.
The power indicator light is on, but the workpiece is not welded when pressed:
The. Check that the pedal travel is in place and that the pedal is in good contact.
B. Check that the pressure rod spring screw is adjusted correctly.
There are unexpected spatters during welding:
The. Check whether the electrode tip is very oxidized.
B. Check whether the welded part is very rusty and has poor contact.
w. Check whether the adjustment switch is set too high.
d. Check whether the electrode pressure is too small and whether the welding program is correct.
Weld recoil is severe and there is extruded material:
The. Check if the current is too high.
B. Check whether the welded part is uneven.
w. Check whether the electrode pressure is too high and whether the shape and cross-section of the electrode tip are suitable.
The strength of the welded part is insufficient:
The. Check whether the electrode pressure is too small and whether the electrode rod is fixed correctly.
B. Check whether the welding power is too small and whether the welded part is heavily rusted, causing poor contact at the welding point.
w. Check whether there is a lot of 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 has increased due to wear, resulting in decreased welding energy.
It is. Check whether there is severe oxidation on the contact surface between the electrode, the soft copper gasket and the electrode arm.
Abnormal noise from AC contactor during welding:
The. Check whether the input voltage of the AC contactor is lower than its own release voltage of 300V during welding.
B. Check whether the power cord is too thin or too long, causing excessive line voltage drop.
w. Check whether the mains voltage is too low to operate normally.
d. Check whether the main transformer is short-circuited, causing excessive current.
Welder overheating:
The. Check whether the insulation resistance between the electrode holder and the body is weak, causing local short circuit.
B. Check whether the water inlet pressure, water flow rate and water supply temperature are adequate and whether the water system is blocked by impurities, causing the electrode arm, electrode rod and electrode tip to overheat due to to insufficient cooling.
w. Check for severe oxidation on the contact surface between the soft copper gasket and the electrode arm, electrode rod and electrode tip, causing an increase in contact resistance and severe heating.
d. Check whether the cross-section of the electrode tip has increased too much due to wear, causing the welder to overload and overheat.
It is. Check whether the welding thickness and charging duration exceed the standard, causing welder overload and overheating.
Innovations and future trends in spot welding technology
With the continuous development of the national economy and the increasing consumption of steel materials, more companies are showing an upward trend in the demand for welding equipment. This trend is definitely being gradually dominated by digital integrated spot welders on the market.
In terms of production composition and technological development direction, welding equipment in China is developing toward high-efficiency, automation, intelligence, energy-saving and environmentally friendly welding.
Welding equipment belongs to a large-scale and diverse product category with a full range of specifications, which is gradually approaching international levels. The market share of high-efficiency, energy-saving, material-saving and consumption-reducing products will continue to expand. To meet market demands, it is necessary to adjust product structure and improve product quality, especially by vigorously developing inverted-type welding power supplies and automatic/semi-automatic welding machines, especially high-energy storage welding machines. efficiency and energy saving.
The research and development direction of resistance spot welding technology mainly focuses on medium and high power. Microcomputer-controlled quality monitoring, inverter resistance welding technology, intelligent and specialized systems, complete sets of flexible resistance welding equipment and resistance welding robots are important research contents and professional production guidelines.
The development of resistance welding machines specifically for welding requirements of coated materials, aluminum alloy materials and precision parts welding has become more prominent.
The development of technology and testing equipment will promote the improvement of companies' processes and technical levels.
Automated welding technology and equipment are developing at an unprecedented speed. The development of large-scale national infrastructure projects such as the West-East Gas Pipeline Project, aerospace engineering and shipbuilding engineering, as well as the rise of the domestic automobile industry, has effectively promoted the development and progress of advanced welding processes, especially welding automation technology. Welding robots and intelligent welding will also be developed appropriately in specific and widely applied fields.
The demand for complete and special welding equipment will continue to increase, the scope of application will become more extensive, and the technical performance requirements will be increasingly higher.
Equipment that caters to new, high-efficiency processes is becoming more mature and popular. Domestic complete welding equipment manufacturers should also work on the selection of enterprise quality management, various basic components and supporting components to pursue new advances in special and complete welding equipment.
Conclusion
Overall, spot welders are a very important component in the manufacturing industry, especially in connecting sheet metal parts. As presented in this comprehensive guide, there are several types of spot welders to choose from, each with its own unique features and benefits.
When selecting a spot welder, factors such as the type of material to be connected, material thickness, and production requirements must be considered. Furthermore, appropriate maintenance and safety measures must be taken to ensure the life and efficiency of the spot welder.
Through proper machine selection and proper use, spot welding can become an efficient and effective sheet metal fabrication process that achieves strong and reliable welding.
