Controls & Transformers
Questions and Answers
Constant current is a very useful feature of today’s controls. If this feature is present and you ask for 10,000 amps. The control will deliver that amperage each weld. The control adjusts its conduction and voltage to deliver the current specified. This is considered Conduction Monitoring and may be called C-Factor.
Conduction Monitoring or C-Factor monitor the AC sine wave. Once the proper settings are arrived at and set up in the control an alarm can be set to alert for any deviation. If the control was set at 50% with a plus or minus 10% tolerance, an alarm would be triggered for any variance greater than 10%. The alert does not indicate the cause for the variance. Just that it has happened. Ther cause is usually related to some change in secondary resistance. The normal causes are cables, shunts, misplaced welds, loose connections or shunting currents. There are many other possibilities not listed.
The important question is: What is the weld quality? \Secondly, is there a substandard cable, shunt, connection, water cooling or other conductor??? The electrode overheating is not usually the cause for the alarm. Often current steppers are used to increase the current to match the current increase to the electrode face area increase/wear.
Conduction Monitors can only say something has caused a need for a change in power. The cause must be determined by investigation.
Monitoring the weld nugget quality being produced is always the most important control.
Reference: RWMA - Resistance Welding Manual 4th Edition
A reader after reading the article:
What is the switching device in an inverter?
Asked how many times does the IGBT switch per second? The mid frequency direct current controls that dominate the resistance welding market operate at 1000Hz.
The IGBT’s are very fast and efficiently switch at a rate of 1000 times per second. There is an upslope as the current rises from zero to the desired level. On efficient systems this can be as fast as 3 milliseconds. This can be seen in the following diagram. There is a similar downslope.
Conversion In Control and Transformer of Mid Frequency Inverter
This diagram is more fully explained in the article:
The MFDC wave form diagram is not clear
Reference RWMA – Resistance Welding Manual 4th Edition
Installation of equipment is a very important subject. Transformers are a key component of a resistance welder and must be installed and tested properly.
American Welding Society offers a standard on installation:
“AWS J1.2 Guide to Installation and Maintenance of Resistance Welding Machines”
This blog is not able to discuss individual machine installation and set-up. Consult your equipment supplier or local distributors for assistance.
Reference: American Welding Society
This question is in reference to a previous article:
THE MFDC WAVE FORM DIAGRAM IS NOT CLEAR
The answer is in the paragraph describing point 4. The primary receives an AC input. The transformer contains diodes which convert the AC input to a DC output.
Conversion In Control and Transformer of Mid Frequency Inverter
Reference: RWMA – Resistance Welding Manual 4th Edition
As described in another article:
Constant current is a very useful feature of today’s controls. If this feature is present and you ask for 10,000 amps. The control will deliver that amperage each weld. It won’t matter if you are near the edge of the part or half way across the part. The resistance caused by the impedance is corrected by the constant current. Every weld will receive the same desired current. If you are projection welding one part in the same position each time impedance is not an issue. Knowing that you always get the proper current is a very good feature under most situations.
Another plant variation is line voltage. See the article:
During the day as equipment comes on and off line it can cause the plant supply line voltage to vary. This will create a problem for the control to deliver the proper current output. A constant voltage control corrects for this and will maintain the desired current output. Without this feature the weld current will vary and the projection welds may vary.
PROJECTION NUT WELD
Refeerence: RWMA Resistance welding Manual 4th Edition
REFERENCES: RWMA - Resistance Welding Manusl 4th Edition
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