While considering heat, it is worth mentioning the types of cooling systems: air cooled, liquid cooled or a combination. Air cooled units rely on internal fans and shop air blowing on the cables and electronics to cool, while liquid cooled welders use a coolant circulation system. Ideally, the welder needs to be cooled everywhere heat is generated. Starting at the weld, electrode caps bring coolant to the back side of the weld. Cables, transformer, and power modules all generate heat and therefore require cooling as well. Verify what is being cooled and how. Consider the size of the coolant tank and whether the liquid is actively cooled. It will take much longer to heat up 20 liters of coolant than it does 5 liters. The type of cooling determines the duty cycle you can expect, particularly with the higher current requirements.
|A CTR7 spot welder|
Spot welders can be broken into two main categories based upon the location of the transformer. On cable welders, the transformer is larger and located in the base. They have a smaller, lighter gun (welding tong) but require large copper cables to minimize loss of power, typically no longer than 8 feet. Trans-guns house the transformer in the gun itself. Because the transformer is located near the electrodes, it is much smaller and therefore the welding cables are smaller and longer, approximately 20 feet, offering the technician mobility without having to constantly reposition the welder. Trans-gun welders are also more forgiving of poor shop power. There is a tradeoff though, trans-guns are usually heavier than cable guns.
Another shift in the industry comes from increasing OEM program requirements. In an effort to guarantee proper repairs, programs require shops to have correct tools. Some OEMs test welders themselves and publish a list of approved equipment. Other OEMs establish minimum specifications that the welder must meet. Honda recently published a requirement that STRSWs used on 1500 MPa repair parts have a minimum welding current of 9000 Amps and 770lbf squeeze pressure. Consider the vehicles you commonly repair and programs you work with when choosing a welder.
Another major consideration is where you purchase the equipment from. What can you expect for training and support? A body shop is a harsh environment for any type of electronic equipment. What resources are available if you have problems? You need a team you can rely upon just like your customers rely upon you.
As the saying goes “the only thing constant is change”. The automotive industry and repair procedures change for the better. Make sure the equipment you rely upon is ready to keep up.