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MMA welding machines
Arc welding with a coated electrode is one of the most popular welding processes among users and various industries. This type of welding has many advantages and disadvantages, which will be discussed below.
Arc welding with coated electrode:
MMA, or SMAW, or Stick welding process is one of the arc welding processes that uses a manual electrode with a protective coating. The electrodes are coated with sealants, which helps in the better flow of the molten, and helps protect the boiling pool area from the surrounding destructive gases. This welding process is also known as stick welding. Due to its relatively cheap equipment, simplicity of operation and high adaptability, this process has become one of the most widely used and popular arc welding processes in the world.
In general, electrodes are divided into 3 categories:
In selecting the appropriate electrode, factors such as the base metal material, welding position and welding properties should be taken into account. As mentioned earlier, manual welding electrodes are covered with special coatings that create a stable arc, prevent the penetration of destructive elements into the weld pool, enhance weld quality, and create welding slag to protect it after freezing. Also, after the welding process is over and the weld is cooling, a thin coating is created on the weld that protects it from harmful surrounding gases until it cools, which is also called slag or welding mud.
In any case, what is very influential in the quality of welding is the degree of skillfulness of the welding operator during the welding process and their familiarity with different modes and settings of the welding machine.
Electrodes are generally divided into 3 categories:
- Fast melting
- Medium freezing
- Fast freezing. Each type is selected depending on the desired welding conditions and welding environment.
One of the important things to be careful about in choosing the right electrode is the compatibility of the electrode core material with the base metals. In some cases, electrodes with a central core material can be used in vicinity of each other, but in some cases, this causes irreparable damage. For example, carbon steel electrodes can be used for welding stainless steel, and vice versa. In contrast, in welding aluminum metal, an electrode with the same core must be used.
Machines suitable for manual metal arc (MMA) welding
Every welding process requires equipment and devices designed and built for that particular welding process. In this text, different types of welding machines are examined, and a suitable machine for manual welding process or MMA is described.
Types of manual metal arc welding machines
As you know, a current passing from the negative pole to the positive pole can be in form of alternating current (AC) or direct current (DC), with the direction of the current in the former being two-way and that in the latter being one-way. Stick welding machines have several parts including: power supply, cooling system, current-carrying cables, positive and negative clamps to create an arc, etc.
- Constant current (CC) welding machines or rectifiers:
- Constant voltage (CV) welding machines or inverters:
Generators are known as power generators that generate electricity by an internal combustion engine.
Transformers are electrical converters. The electric current passes through the primary winding and yields different current intensities and voltages in the secondary winding.
These machines are very suitable for manual metal arc (MMA) welding and tungsten inert gas (TIG) welding processes due to the constant current intensity during welding. This is because the length of the arc also changes as the welder's hand changes position. To perform high quality welding, we need a constant DC current, which these welding machines provide.
In this type of welding machines, a very high current intensity of about a thousand amps can be created by making a slight change in the amount of voltage. Unlike constant current welding machines, in this type of welding machine, the current is changed drastically by changing the length of the arc. These devices are used for Metal Inert Gas (MIG) and Metal Active Gas (MAG) welding processes that automatically feed the filler metal or the filler.
What are MMA welding machines?
As mentioned earlier, direct current (DC) and alternating current (AC) welding machines can be used for MMA welding process. The right choice of the device depends on factors such as the type of electrode and the thickness of the base metal. In this process, constant voltage welding machines are not used because the movement of the welder's hand and changes in welding distances cause changes in the length of the electric arc. The advantage of AC current is the very slight voltage drop across the welding cables, which results in a very negligible amount of arc deflection. However, the advantage of DC current is excellent arc stability. It is also very suitable for low current welding which requires a short arc length.
DC arc welding machines are used for welding thin sheets and metals. It should be noted that some welding machines produced by some reputable manufacturers can provide both direct and alternating currents. The use or non-use of either flow modes provided by these machines depends on the welding conditions and the needs of the welder.
For optimal use of MMA manual welding machines, it is better to follow the catalog and instructions of the machine manufacturer. Otherwise, the current intensity of 40 × A can be considered per each millimeter of electrode diameter. Also, the appropriate voltage for each millimeter of arc length is considered to be 3.6 × V.
There are a few things to keep in mind when working with shielded metal arc welding (SMAW) machines:
- Imbalance of current intensity suitable for welding:
- Imbalance in the length of the electric arc:
- Local movements of the welder's hand:
If the selected current intensity is more than the required level, the electrode consumption will increase, the edges of the welding pool will fall, and the welding endurance will decrease. If current intensity is less than required, the weld pool will not be fully formed, and there will not be adequate penetration.
Increasing the length of the arc leads to increased amount of spraying of the weld around and on the surface of the base metal, and the easy penetration of destructive agents in the air into the pool, thereby worsening the quality of the weld.
Reducing the arc length, on the other hand, reduces the space between the electrode and the base metal, so the amount of heat generated is greatly reduced and the weld pool is not formed adequately. The result is that the molten electrode is placed on the surface of the base metal and the penetration will not be done well, so the weld will not have the necessary strength.
If the welder's hand speed is too high, the welding pollen will have defects such as low width and penetration depth, and the melting will not be done well and the penetration will be reduced. Finally, it increases the porosity of the weld and decreases the quality of the weld, in terms of both appearance and strength.
The low speed of the welder, on the other hand, will have consequences including large and wide welding pollen as well as high consumption of the electrode. In addition, if the thickness of the base parts is small, the part may be damaged and the fall of the welding melt could be observed.
To choose a manual welding machine, technical points as well as specifications of the welding and working parts should be taken into account:
It is very important to prepare the final products' work plans containing sufficient technical specifications, as well as the type and specifications of the welding used. Therefore, care must be taken in selecting and purchasing the right welding machine. To buy a stick welding machine, all you have to do is send the technical information along with your written request to the welding machine manufacturing companies. After reviewing the request, a list of offered products will be sent by the manufacturer. This list includes an introduction to the proposed devices along with their technical specifications. You can customize the details and features according to your needs and expectations.
After the final agreements regarding the technical information of the manual welding machine are made, it is possible to review and continue the purchase process to the commercial unit. Due to the large number of manual welding machines produced, it is possible to purchase from local retailers, without the need to contact the manufacturer. However, if you want to purchase directly from the manufacturer, the following tips can be helpful.
- Specify the production rate, the number of working days per week, the number of working shifts per day, and the working hours.
- Describe the environmental conditions of the workplace, including humidity, temperature changes, dust levels, and proximity to other production equipment.
- The environment in which welding machines are used should not be impregnated with flammable materials.
- Based on your needs and your knowledge of the environment, you can specify the type of cables and the type of connection to the clamps. They can have protective coatings.
- Specify whether the cables should be replaceable or connected directly to the device?
- Consider the ability to easily replace pliers and tool posts.
- Note that the tool post and the welding pliers should be powerful enough to prevent sparks in the workplace during welding in addition to holding the welding wire properly and connecting it to the parts correctly.
- Select your device according to the input current. The input current can be AC and DC. For this purpose, you can use rectifier welding machines or inverters.
- Consider your required output current range.
- If you need to fine-tune the output current, use manual or digital welding machines.
- Check the accessories with the welding machine.
- Specify whether or not the device is portable.
- Note that the amount of output current is directly related to the amount of welding and the thickness of the parts.
- Specify how long the manual welding machine should be able to operate continuously.
- If you need to adjust the power supply remotely, consult the manufacturer.
- The Arc-Force feature can prevent the electrode from sticking to the part during welding. If you need this feature, you can talk to the manufacturer.
- Ask the manufacturer about the electrical circuit of the device, the type of cable connections, and the manual of the device manufacturer.
This company is one of the manufacturers of welding machines and their accessories located in France. The video below shows one of the company's manual arc welding machines.
Lincoln electric Company:
This company is one of the manufacturers of various welding machines. The video below shows how to set up and use an arc welding machine with a Stick-MMA manual electrode.