Spot strength checking process

SPOT CHECKING PROCESSES

Spot welding is a process of joining two metals by creating a high current voltage ratio at the joining area and applying force in between 3-6 KN through the electrode. We do spot welding so that metal gets perfectly fitted to other metal and it doesn't affect any functionality of that joinery parts of any automobile. But some times due to some reasons like a supply of voltage-current ratio very low, or force applied through electrode is very low, cooling water supply is off through electrode and it results in Spot gets weak. But we are not able to detect it with our naked eye that its weak or ok spot. If that not ok spot joined parts goes as it is to the customer, it must cause failure in the field of that automotive part. It may result in some big matters like a major accident. To avoid such incidence and for better results or performance of parts in the field, we must use one of those checking methods on sample basics.

There are two ways of spot-checking 

• Destructive method 
• Non-Destructive method

1. Destructive test:-

                              The destructive test of spot-checking is the checking method in which we get to destroy the product during the checking method. we cannot use that part after carrying out a test on that specific part. 

There are three types of destructive tests of spot-checking.

Chisel test:-  chisel test is a destructive test of spot-checking in which we use chisel and hammer to try to separate two joined parts by creating groove to chisel end edge and setting groove over the spot in between two metal sheets. If sheets get separated by taking material with one sheet without separating at spot area then it clear that the spot is ok, if it separated without any hole at or near spot area its not ok.  In every Bodyshop, there must be quarterly or somewhere monthly chisel test of the sample body carried out. We can guess the performance of all bodies through that one sample body.

Nugget test:-  Nugget test is also a  destructive test but in this two strip of metal i.e. same thickness and metal as of body we produce has been taken instead of the complete body, a spot with the normal way we use to do daily is taken over these two strips by setting them cross overlap way. And after that try to separate those two strips by applying force clockwise and anticlockwise way. If strips separated by taking nugget over a  sheet of another sheet then its ok spot and if separated without creating any nugget its not ok spot.

Tensile load test:- Tensile load test is also a destructive test but it's a bit similar to nugget test but instead of taking spot over strip by putting cross over each other keep strip linear to each other and over each other. Take spot and use UTM (universal testing machine) Machine for separating strips by applying tensile force after fixing strips in two jaws of the UTM machine.

2. Non-Destructive test:- 

                                              The non-Destructive test is a spot-checking method in which we can check spot strength without destroying part or body. There are also two-three methods of Non-Destructive test one of them is as below.

Ultrasonic test:- Ultrasonic test is a Non-Destructive test of spot check in which we use sound waves to find out either spot is ok or not ok. An ultrasonic machine having a probe filled with water and machine creates sound waves, if sound transfer through spot after touching probe at spot display of ultrasonic machine display not ok waves. If the sound does not transfer and com back then it shows different waves in the display. We have to learn which wave is a sign of ok and which is a sign of not ok.