GATE MT 2019 Q10. Two blocks of same metal are to be welded. The configuration that will undergo least deformation after welding is :

The methods used for the control of distortion when welding aluminum are the same as other materials; however dependent on material thickness and structure design, we may need to give greater consideration to the following:

1. Probably the most common cause of excessive distortion is from over welding. In order to reduce distortion, we should try to keep the heating and shrinkage forces to a minimum. We should design the weldment to contain only the amount of welding necessary to fulfill its service requirements. The correct sizing of fillet welds to match the service requirement of the joint can help to reduce distortion. We should not produce fillet welds that are larger than specified on engineering drawings. We should provide welders with fillet weld gauges so they are able to measure their welds to ensure that they are not producing welds that are much larger than that specified. With butt joints we should control edge preparation, fit-up and excessive weld build-up on the surface in order to minimize the amount of weld metal deposited and thereby reduce heating and shrinkage.

2. When welding thicker material, a double-V-groove joint requires about half the weld metal of a single-V-groove joint and is an effective method of reducing distortion. Changing to a J-groove or a U-groove preparation can also assist by reducing weld metal requirements in the joint.

3. We may consider the use of intermittent fillet welds, where possible. We can often maintain adequate strength requirements and reduce the volume of welding by 70% by using intermittent fillet welds over continuous welding, if the design allows.

4. Balance welding around and position welds near to the neutral axis of the welded structure. The neutral axis is the center of gravity of the cross section of the part. Placing similarly sized welds on either side of this natural centerline can balance one shrinkage force against another. Placing the weld close to the neutral axis of the structure may reduce distortion by providing less leverage for shrinkage stresses to move the structure out of alignment.

5. Reduce the number of weld beads, if possible. Few passes with a large electrode are preferable to many passes with a small electrode. The additional applications of heat can cause more angular distortion in multipass single fillet welds and multipass single-V-groove welds.

6. Carefully select the welding process to be used. Use a process that can provide the highest welding speeds and is able to make the weld in the least amount of weld passes. Make use of automated welding, whenever possible, as these techniques are often capable of depositing accurate amounts of weld metal at extremely high speeds. Fortunately, with modern arc welding processes we are often able to use high welding speeds which can help us when fighting distortion.

7. Use welding sequences or backstep welding to minimize distortion. The backstep technique allows for the general welding progression to be in one direction but enables us to deposit each smaller section of weld in the opposite direction. This provides us the ability to use prior welds as a locking effect for successive weld deposits.

8. Whenever possible, weld from the center outward on a joint or structure. Wherever possible, alternate sides for successive passes on double-sided multi-pass welding. An even better method to control distortion is to weld both sides of a double-sided weld simultaneously.

9. Preset components so that they will move during welding to the desired shape or position after weld shrinkage. This is a method of using the shrinkage stresses to work for us during the manufacturing process. Through experimentation we can determine the correct amount of offset required to compensate for weld shrinkage. We then need only to control the size of the weld in order to produce consistently aligned welded components.

10. Consider the use of restraints such as clamps, jigs and fixtures and back-to-back assembly. Locking the weldment in place with clamps fixed to a solid base plate to hold the weldment in position and prevent movement during welding is a common method of combating distortion. Another method is to place two weldments back-to-back and clamp them tightly together. The welding is completed on both assemblies and allowed to cool before the clamps are removed. Pre-bending can be combined with this technique by inserting spacers at suitable positions between the assemblies before clamping and welding.