The gas shielded welding machine has many advantages such as easy operation, low price, strong applicability and high welding strength.
It is an essential maintenance equipment for many automobile repair companies and schools. Gas shielded welding machines have fewer failures, and common problems include wire binding and blockage in the flow of shielding gas.
This article takes the example of a 6250 MIG welding machine to present the causes and troubleshooting methods of its blocked shielding gas flow.
1. Gas protection principle
When metal welding is carried out, if the welded parts are directly exposed to air, the liquid metal at high temperatures will react with nitrogen, oxygen and hydrogen in the air, causing defects such as pores and cracks during the metal solidification process.
This can result in a decrease in strength or weakening of the welded area.
To ensure good welding strength, certain protective measures are taken during welding. For example, manual arc welding involves coating the surface of the welding rod with a layer of flux.
During welding, the flux breaks down and melts, covering the surface of the weld to isolate it from air. This method eliminates the influence of harmful gases and guarantees good welding results.
However, this method is suitable for welding thick steel sheets, but not for thin steel sheets used in automobile repairs.
In automobile repair, gas shielded welding machines are commonly used, which generally use pure carbon dioxide or a mixture of carbon dioxide and argon as the shielding gas.
The shielding gas is transmitted to the welding area via the gas supply pipeline. The activation and deactivation of the gas supply piping is controlled by a control solenoid valve, which is operated by the welding gun switch.
When the welding gun switch is pressed, the welding machine first opens the control solenoid valve to connect the gas cylinder to the welding gun gas supply pipeline, thereby removing air in the welding area and ensuring that no there are harmful gases in the welding area. before electricity is supplied for welding.
When the welding gun switch is released, the welding machine delays the closing of the control solenoid valve to allow the weld to cool down under the protection of the shielding gas, improving the welding quality and ensuring the strength of the welding.
2. Identification of abnormal shielding gas
As discussed above, the welding quality in gas shielded welding mainly depends on the shielding gas. So, how do you assess whether shielding gas is normal?
Firstly, it is necessary to develop the habit of checking before welding. Loosen the gas cylinder valve and the pressure gauge (as shown in Figure 1) connected to the valve will show the protective gas pressure in the cylinder.
By checking the pressure gauge, the amount of protective gas stored in the cylinder can be determined.
Secondly, during the welding process, if smoke increases or the metal in the weld pool boils, it indicates that the shielding gas flow is blocked, leading to insufficient shielding gas.
Finally, check the quality of the weld. If there are many pores in the weld, as shown in Figure 2, it means that there was insufficient or no shielding gas during welding.
3. Common causes of shielding gas flow blockage
Before starting work, it is necessary to check the amount of shielding gas in the gas cylinder.
If there is enough shielding gas in the cylinder, but the shielding gas still flows poorly during welding, there are several common reasons:
(1) The fuse of the welding machine blows.
To prevent damage from sudden increases in current, such as electrical surges, gas shielded welding machines are equipped with fuses.
When the fuse blows, the sound of the welding machine exhaust can still be heard, but the shielding gas does not connect and the wire feeder structure does not work. This type of failure is relatively easy to identify.
(2) Blockage of the gas supply pipeline.
This is the most common cause of poor gas flow in gas shielded welding machines. The welding machine's working environment is harsh, and dust and particles are more likely to accumulate, making it difficult to keep the welding machine clean.
To ensure smooth sliding of the welding wire, lubricating oil can be applied to the wire feed tube of the welding gun.
Over time, the build-up of dust and particles can cause blockages in the gas supply piping.
Additionally, bends and weight pressure in the pipeline can also cause blockages, leading to insufficient gas flow.
(3) Abnormal control solenoid valve (as shown in Figure 3).
When the control solenoid valve is working normally, it can turn on and off the gas supply pipeline as needed, thus ensuring welding protection and saving gas.
If the control solenoid valve is abnormal, it will not open when turned on, and the valve will remain closed, preventing shielding gas from being supplied to the welding area, resulting in a lack of shielding gas.
4. Troubleshooting insufficient gas flow in shielding gas
Once you understand the principles of gas shielding and the reasons for poor gas flow, it will not be difficult to troubleshoot poor gas flow in shielding gas. The usual method is to start checking from the gas cylinder along the gas flow direction.
A more efficient approach is to first divide the troubleshooting into segments using the control solenoid valve as the threshold and then use instrumentation to make judgments.
The inspection steps are as follows:
(1) Check the gas cylinder pressure.
Open the gas cylinder valve and check that the pressure regulator gauge shows 0 MPa. If yes, it means that the gas cylinder is empty or the pressure gauge is faulty.
Loosen the connecting thread between the pressure regulator and the gas cylinder. If the gas flow is weak, it indicates that there is no shielding gas in the gas cylinder and it needs to be replaced with a cylinder filled with shielding gas. Then test again that the gas flow is unblocked.
If the gas pressure of the gas cylinder is not 0 MPa, proceed to the next step.
(2) Check the control solenoid valve.
Remove the outlet tube from the control solenoid valve, open the gas cylinder valve and turn the flow meter control knob to ensure smooth flow of gas through the front section of the control solenoid valve.
Press the ventilation switch of the welding machine or the air supply switch of the welding gun to check whether the gas flow from the control solenoid valve outlet is normal.
If it is normal, it indicates that the front gas supply piping of the control solenoid valve is normal.
You can skip to step 6 for additional checks. If the gas flow from the control solenoid valve outlet is abnormal, proceed to the next step.
(3) Check the gas flow at the control solenoid valve inlet.
If the gas flow at the control solenoid valve inlet is normal, it indicates that there is a fault in the control solenoid valve. If the gas flow at the control solenoid valve inlet is abnormal, proceed to the next step.
(4) Check the gas flow meter (as shown in Figure 4).
Remove the gas flow meter outlet tube, open the gas cylinder valve, and adjust the flow meter control knob to change the gas supply flow from small to large and then back to small.
Check that the small steel ball that indicates the flow rate changes accordingly. If the indication changes abnormally, check whether the gas flow meter inlet is blocked or replace the gas flow meter for testing.
If the indication changes normally, proceed to the next step.
(5) Check the gas supply piping before the control solenoid valve inlet.
If the gas cylinder has sufficient gas storage, the pressure regulator and gas flow meter are normal, and the reason for low gas flow is due to a blockage in the gas supply piping between the meter outlet gas flow rate and the solenoid valve control input, you can unblock or replace the gas supply piping.
If the gas supply piping before the control solenoid valve inlet is normal, proceed to the next step.
(6) Check the air flow between the welding gun wire and the welding machine body interface with the welding gun gas distributor (see figure 5).
The shielding gas is sent from the welding machine body, flows through the welding gun wire feed pipe, and is sprayed by the gas distribution device.
Use an air gun to blow air through this section of gas supply piping to verify that the gas flow is unblocked.
If it is not unlocked, check or replace the gas distribution device and gas supply piping separately. If this section is unlocked, proceed to the next step.
(7) Check the gas supply piping inside the welding machine body after the control solenoid valve. This section of the pipeline is generally closed and rarely fails.
However, it can become bent or crushed, causing poor gas flow in the piping. It can be repaired or replaced.
5. Troubleshooting case of insufficient gas flow in shielding gas
Failure phenomenon:
During a welding process in a welding training room, a newly purchased DaiKa MIG 6250 welding machine was used for less than 4 months.
The previous work was relatively stable, but suddenly there was an increase in welding smoke, surface contamination of welded parts, boiling of the weld pool, high welds and internal porosity.
Error Diagnosis:
When testing the welding machine separately, it was found that the flow of the shielding gas was not smooth, causing the weld to lose its protection.
Because the usage time was not long, the usage rate was not high, and the body had never been disassembled, blockage was very rare.
After checking according to the above-mentioned troubleshooting steps for poor gas flow in shielding gas, all suspected components involved in the first six steps were normal.
Then, after further disassembly, the gas supply piping, circuit board and related components behind the control solenoid valve were all normal.
Continuing to check the gas supply pipeline along the gas flow direction, it was found that the gas supply pipeline behind the wire feeding mechanism on the other side of the welding machine was severely bent and deformed, as shown in Figure 6, causing the shielding gas to be unable to pass through.
After smoothing the curve of the gas pipeline, the welding machine was tested and the gas flow was unblocked, the machine operated normally and the fault was resolved.
Why did the failure occur suddenly after 4 months of purchase, rather than at the time of purchase, and where is the root cause of the failure? Common reasons for equipment failure include improper operation, environmental factors, design defects, etc.
Since there was no violation of the operating instructions of this welding machine, human error can be ruled out as the reason.
The failure occurred in the hot summer, while the machine was purchased in winter, and there is a significant temperature difference between seasons.
The gas supply pipeline is made of plastic material, which is relatively hard when the temperature is low and becomes soft when the temperature is high.
During installation, when the temperature was low, the pipeline had greater flexural strength, but as the temperature increased, the flexural strength decreased, causing the degree of deformation to become more severe.
The gas pressure inside the gas supply pipeline cannot expand the gas pipeline, and therefore the welding machine experienced weak gas flow in the shielding gas.
To prevent the recurrence of such failures, high-quality adhesive tape can be used to secure the gas supply pipe, as shown in Figure 7.
Problems solution
After fixing the air supply pipe with high-quality adhesive tape and testing the machine, the fault was completely resolved.
Fault Summary
The failure appeared to be caused by the air supply piping bending due to changes in ambient temperature, but was actually caused by the piping being too short, which is a design issue. Maintenance personnel must have basic equipment maintenance and repair skills. For common welding machine failures, don't limit yourself to conventional thinking. Be bold and innovative because there can also be problems with the design.
