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Resistance welding machine
In the metal industry for welding two metal pieces, different welding machines are used, one of the most important and widely used is spot or resistance welding machines. These types of machines are divided into two main categories: resistance spot welding machines and roller resistance welding machines or welded joints (pulleys), which we will describe in this section. Let's discuss their advantages and disadvantages and their application in various industries.
Resistance welding is a process in which an electric current is passed through the point where two metals collide with each other, while the resistance of the parts generates heat in the joint area. After heating the parts, the welding process is formed and completed by creating pressure caused by the jaws (electrodes) of the welding machine. The resulting boil is called nugget welding.
Resistance welding is based on three principles:
- The amount of current that passes through the work.
- The pressure that the electrodes transfer to the workpiece.
- The amount of time that an electric current enters.
Resistance weldings form very quickly. However, each process has its own time cycle.
Resistance welding operations are usually performed automatically. Pressure is applied by mechanical, hydraulic, or pneumatic systems. With the start of welding, the flow control is completely automatic, and this feature is taken from the programs created by the programmers in the machine control systems. Flow duration varies depending on the material and physical properties of the components. Due to this, quality welding does not depend on the skill of the welding operator, but rather on the precision of equipment adjustment and adherence to welding programs.
Heat and electric current in resistance welding:
The welding heat is proportional to twice the welding current. It means, if the flow rate is doubled, the heat generated is quadrupled. The welding heat is also proportional to the total current time, so if the current is doubled, the time can be significantly reduced. The amount of welding heat is directly related to the strength of the parts and is related to the type of material being welded and the pressure applied. Heat loss should be minimal. Welding rubber shortening is an advantage. The mechanical pressure that compresses the parts helps to modify the structure of the weld.
Heat is also generated in contact between the welding electrodes and the work. It should be noted that the amount of heat generated between the electrodes and components is less than the heat generated by the resistance between the workpieces. The opposite should not happen because it reduces the life of the electrodes and the welding process does not work properly. In most resistance welding processes, the electrodes are cooled with water to minimize the heat generated between the electrode and the work.
Resistance welding process
If we look at the surface of metals microscopically, we find that there are ups and downs on their surface. These irregularities are due to the production process and the physical and chemical properties of the metal. When two metals are placed on top of each other, only the long surface appendages of the metals are in contact with each other. After applying current to the components, the electric current will try to pass through the nearest surfaces. Assuming pressure is applied at a specific point, the protrusions of the metal surface will come into contact with each other, and after the oxide layer on its surface separates, the current flow and the strength of the parts will cause them to melt and merge. After the current is cut off and the electrodes cool, the pressure point will cool and a connection will be made.
Metals in resistance welding:
Many common metals can be welded by many resistance welding processes. It is noteworthy that in resistance welding, there may be problems in the welding process of thick parts. Some metals require heat treatment after welding. According to the table below, some metals can be welded to each other with this method.
Types of resistance welding processes:
- Flash Welding
- High frequency
- Percussion welding
- Projection welding
- Resistance seam welding
- Resistance spot welding
- Upset welding
Resistance welding applications:
Resistance welding is used in long-term production and the same conditions in production.
The automotive industry is the main user of resistance welding processes, followed by the home appliance industry is one of the most widely used resistance welding industries. This type of welding is also used in the steel industry to make pipes, tubes, and smaller structural sections. One of the advantages of this method is the production of a large volume of products at high speeds and does not require fillers. Wounds are created with reproducibility and high quality.
Weldability is controlled by three factors:
- thermal conductivity
- melting point
Metals with high flow resistance and low thermal conductivity and relatively low melting temperatures are easily weldable. Ferrous metals are all in this group. Welding metals that have lower strength but higher thermal conductivity will be more difficult. This includes light metals, aluminum and magnesium. Precious metals are the third group, they are difficult to weld due to their very high thermal conductivity. The fourth group is refractory metals that have a very high melting point and are more difficult to weld. Click for more information.
Advantages and disadvantages of welding:
- Welding speed is less than one second and is suitable for industries such as transportation and automotive.
- For sheets less than 0.25 inches thick, it performs very well.
- No need to use fillers and consumables.
- In this process, the voltage consumption is low, which will cause security in the process.
- The welding process is clean and free of contamination.
- The connection formed is reliable.
- This process can be robotically controlled and executed.
- Fatigue and low tensile strength
- It is not tolerable
- High wear on the electrode
- Its equipment is more expensive than other electric arc atmosphere processes
- If the capacity of the power lines does not match the ability of the machine, it can cause many problems.
- The welds created by the resistance welding process are not capable of non-destructive testing.
- They have low tensile strength.
resistance spot welding machines (RSW):
What is RSW welding?
A process in which two surfaces of a sheet are welded together by electric heat and the simultaneous pressure of two sheets is applied to each other at a point. Due to the electrical resistance, the two sheets approach the degree of melting point due to the passage of electric current, and that part merges with each other. This welding is called resistance welding and the machines that perform this operation are called resistance welding machines. It should be noted that the use of resistance welding machines is more than 100 years old and in this time process, the machine has undergone many changes in terms of quality and structure. It is worth noting that welding requires two parameters: pressure and heat. Pressure is supplied through the jaws of the machine or rollers, and heat is supplied through electrical resistance.resistance spot welding equipment consists of electrical circuit, control circuit, mechanical system, electric current generation system.
- electrical circuit:
- Control circuit:
- Mechanical system:
- Electric current generation system:
Includes step-down transformers, switches and secondary circuits
It is a circuit that controls the flow time and current intensity. In other words, if this circuit does not exist, the cut-off time may exceed the allowable limit, and instead of two metal plates being welded to each other, they will melt at the same point and no welding will take place.
Includes machine frame, clamps (fixtures), copper electrodes, pneumatic pressure inlet jack and pliers (jaws)
Converters are considered as the manufacturer of high amp current system for welder.
Welding steps of the resistance spot welding machine:
- The electrodes used in welding are closer to the metal surface. At this stage, pressure and force are applied to the surface.
- Electric current connects to metal parts through copper electrodes, causing them to melt.
- The electric current is cut off, but the electrodes between which the sheet is placed continue to push. This pressure lasts for one or two seconds as the molten and cooled area cools and solidifies. The important point here is that the duration of the electric current varies. This period depends on the thickness of the metal, the pressure of the electrodes, the diameter and cross section of the electrodes, and the amount of current passing through.
Sheet thickness and usage of spot welding machine:
This type of welding is used in many industries due to the lack of filler (welding wire) and also the ease of doing it and its cheapness. Through this type of welding process, metal sheets, steel, alloy, stainless steel, aluminum can be welded, which are used in various industries such as automotive, cabinet making, elevator making, and shelf making. With spot welding machines you will be able to weld sheets with a thickness range of 0.5 to 3 mm. One of the advantages of this type of welding is that it automates it from manual to automatic mode. By doing so, you can have CNC spot welding machines or spot welding robots.
Advantages of welding with spot welding machine:
- Do not spray welding
- It is cost-effective due to the lack of filler use and high power consumption
- High boiling speed
- Clean welding without welding waste
- Ability to automate it
- No need for a skilled operator
- Possibility of welding sheets with relatively different materials
- Low vapors without too much smoke
- Easy maintenance
Limitations of welding with spot welding machines:
It should be clearly stated that the following are not considered as inherent disadvantages of the machine, but refer to their limitations in certain circumstances. When we say defects, it means that there is a defect in the nature of the system that needs to be addressed, while some may consider a category as a defect and a problem, while others may not consider it as a defect. For example, some people believe that a resistance welding robot is very expensive and consider it a defect, and some do not consider it a defect and consider it as a cost for mass production and precision, or some believe that the appearance of spot resistance welding is It is not beautiful, but some believe that it is not a defect, but the nature of the resistance welding that creates that shape. But in short, the following are considered as limitations in some working conditions:
- Usable electrodes must have access to both sides of metal parts
- These welds are only suitable for thicknesses up to 3 mm
- Inability to move the electrodes in any direction
- The size and shape of the electrode must sometimes change with the material
- The welding connection takes place only at the point where the electrode is concentrated and it is not possible to weld or move the electrode.
- If the electrical current of the machine is low, the parts will not be welded together properly
- If the pressure between the two jaws is not enough, the parts will not be welded together properly.
- The appearance of welding is not relatively beautiful.
- For welding with zinc plating or alloy, the electrodes must be shaved or cleaned.
- Electrodes with high electrical resistance are used to weld copper parts.
- Generally it is not recommended for welding zinc alloys or zinc coated or aluminum.
A few tips about spot welding:
- If the material of two pieces are sheet steel or steel with low carbon content, the weld will not have high strength.
- For welding two pieces made of galvanized steel coated with zinc, we have to use more current. On the other hand, if the steel material is uncoated, less current is required.
- Zinc alloys reduce the quality of resistance welding.
- If we want to weld two metals or two sheets made of aluminum to each other through resistance welding, the head of the electrode, which is made of copper, must be replaced with the head of the electrode, which is made of nickel and titanium alloy, because the point Aluminum welding is low. Aluminum wears the surface of copper electrodes easily and quickly. The fact is that welding aluminum through resistance welding will not be an easy task and requires special experience and knowledge.
- Copper and copper alloys can be joined by spot welding. But any welding of copper and its alloys is difficult to do because the material of the electrodes is the same as the material of the part we want to weld. For this purpose, for resistance welding of copper, electrodes can be used that have high electrical resistance and their melting temperature is higher than copper. For example, you can use molybdenum and tungsten electrodes whose temperature is more than 1080 degrees Celsius.
Resistance seam welding machines or pulley (roller)
Welding seam or welding pulley (RSEW):
The welding seam process is similar to spot welding, except that instead of electrodes, a copper roller is used as the electrode. The use of these rollers increases the welding speed and welding the seams. One of the important advantages of this type of welding is the high integration of welding and its speed. This is possible by rotating the rollers between which there is a sheet or piece. Unlike spot welding, this welding model can use welding wire filler, which is placed between the grooves of the discs and the parts, and with the heat generated, it can be mixed with the part.
Uses of resistance welding machines:
This welding is used for straight paths and is mostly used for welding pipes, tubes, cans and metal plates, belts. In fact, this type of machine is used in various industries such as automotive industries - for welding brake shoes, home appliances industry, electrical industries such as control cabinets, transformers, elevators, store shelves.
Advantages of resistance welding or RSEW seam welding machines:
- High speed in welding
- Very durable and strong against spot soldering and welding
- Cheap and affordable
- Welding process No splashing and its cleanliness
- Fast fixed and non-consumable electrodes No need for filler-No need for shielding gas
- No steam and smoke
- Possibility of automation and connection to robots and CNC
- Possibility of single use and cases and several welds together
Limitations of resistance or RSEW seam welding machines:
- One of the limitations is the instability of this type of weld compared to other welds such as CO2 welding
- They are not suitable for welds whose parts have a complex shape or irregular curves, or the inner and outer corners and angles of the parts cannot be welded.
- Cannot be used for metal sheets with a thickness of more than 3 mm
- It is not possible to do butt welding
- It has good strength and stiffness and does not break or bend due to pressure
- Have high temperature resistance
- Have a suitable electrical conductivity
- Have a high thermal conductivity
Characteristics of roller electrodes (disc)
Buying a resistance welding machine
If you want to buy a resistance welding machine, it is very important to pay attention to technical and non-technical points. Some technical points include information about the parts and sheets that should be sent to the manufacturer along with product drawings and the technical points of the machine you need. After sending the technical information of the product, including dimensions, material, type of welding, etc., along with a written request to the manufacturer of the resistance welding machine, the received information will be examined and the suggestions provided by the manufacturer of resistance welding machines will be carefully studied. And action will be taken to change the items in question. After reviewing and reaching technical agreements for the machine in question, business tips will be reviewed. Presenting the wants and needs accurately and without any shortcomings can be an important help in choosing and purchasing a resistance welding machine.
Here are some tips that can help you make an optimal and safe purchase:
- First, consider the variety of your products in terms of material, dimensions, and thickness
- Examine the working environment of the machine. Humidity, dust, improper temperature, and incorrect location can impair the performance of the resistance welding machine and increase the rate of wear.
- Depending on the type of activity, production rate, and process you are considering, consider the type of resistance welding machine and search for suitable companies and send the necessary information to them.
- Compare and match the amount of budget you have planned for purchasing the machine with the type of resistance welding machine you consider for your work process. Because some resistance welding machines with smaller dimensions and less energy consumption can meet your needs and you do not need to buy complex machines.
- Specify the number of working days per week, the number of working shifts per day, and the number of hours per shift for the manufacturer of resistance welding machines.
- Improper selection of a resistance welding machine can cause the part to disintegrate, melt and deform the weld area.
- When ordering a resistance welding machine, make sure that there is a cooling system.
- Consider the minimum and maximum current output provided by the resistance welding machine.
- Some resistance welding machines can weld almost all metals, but it is important to consider whether such a machine can meet your work needs or not. If your work needs are less than the capacity of the machine, the cost you spend on it will not be economical.
- Request the necessary technical specifications from the manufacturer of resistance welding machines along with a guide for selecting the appropriate current rate.
- A variety of different tools (electrodes, etc.) and multifunction can offer you to create welds with different characteristics.
- Some resistance welding machines have the ability to move the welding jaws horizontally.
- Determine the throat depth of the machine in proportion to the activity and dimensions of the work.
- The amount of pressure applied by the electrodes to the part can be controlled and determined in three ways: hydraulic, pneumatic, and mechanical.
- Side electrode holder can be requested from the manufacturer of the resistance welding machine. The side electrode holder allows the electrodes to be replaced in the shortest possible time.
- In some welding point machines, several electrodes can be used simultaneously with different currents for different parts and in sequence. High production rate and simultaneous welding of several different types of metals are the advantages of such welding machines.
- More time can be spent on the use of resistance seam welding machines. Because welding machines have the ability to perform welding operations in consecutive cycles and for longer. The amount of output current depends on the type of part, thickness, welding speed, and step (distance) between two welds.
- The resistance spot welding machine often easily welds thicknesses between 0.5 mm and 3 mm.
- The portability or stability of the machine is one of the points that can be checked according to your needs.
- Whether the machine is single-phase or three-phase will be checked depending on the amount of current required.
- The presence or absence of a workbench with a resistance welding machine can be checked according to your wishes and needs.
- If you need an automatic resistance welding process, you can use a robotic system to create various and accurate welds.
- The choice of the type of robot and its brand will be determined depending on the type and complexity of the work. When buying a robot, be sure to pay attention to the degree of freedom and ability of the machine.
- Attention in choosing the right PLC and in accordance with the work system is very important for ease of programming and working with it.
- To use robotic resistance welding, resistance welding machines that can be mounted and adapted to the robotic system must be used.
- Resistance welding is very suitable for galvanized steels, titanium, stainless steel, low carbon steel, and copper.
- Resistance welding machines can weld cold rolled sheets, wire fences, and steel sheets well.
- In spot welding, all-carbon and high-carbon steel are hard to weld and prone to cracking, but low-carbon steels are easily welded.
- For welding aluminum with resistance welding machines, two points must be considered: first, the surface of the part must be very clean and free of any oxides and dirt, and second, that precise regulation of the output current is important to prevent melting and spillage of aluminum.
- If there is a need to weld sensitive alloys such as gold, silver, and platinum, the manufacturer of the resistance welding machine should be notified.
- It is better to send the technical information and brand of high-consumption parts, wires, hydraulic and pneumatic pipes and cylinders, workers, rails, brand and model of electric motors, bearings, keyboards, etc. to the manufacturer.
- Ask the manufacturer of the electrical circuit of the machine, the hydraulic circuit, the list of parts, the connection of the cables, the maintenance manual of the machine and its predicted errors.
- Enter the necessary agreements regarding after-sales services such as transportation, installation, training, replacement and repair warranty, etc. by the manufacturer in writing and have them signed by both parties.
- Consider safety tips in the construction and use of resistance welding machines.
This company is one of the leading manufacturers in the field of numerical control systems and automation equipment that can meet all the needs of industry owners. In this video, you can see the industrial robots made by this company that are doing the point welding process on the car body. Accuracy, speed, high performance range and performance reliability are the features of Fanook robots.
Cemsa company specializes in the production of resistance welding machines. The products of this company include Projection resistance welding machines (designed and manufactured according to the buyer's order), welding point resistance welding machine, resistance seam welding machine and Butt / Flash resistance welding machine. The video below shows one of the company's welding machines.