60864
Description
Flashcards by Brandon Alcaraz, updated more than 1 year ago
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Created by Brandon Alcaraz
over 11 years ago
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| Question | Answer |
| Name the principal groups of processes included in fusion welding. | The principal groups of processes included in fusion welding are (1) arc welding, (2) resistance welding, (3) oxyfuel welding, and (4) other. The “other” category includes EBW, LBW, thermit welding, and others. |
| What is the fundamental feature that distinguishes fusion welding from solid-state welding? | In fusion welding, melting occurs at the faying surfaces; in solid state welding, no melting occurs. |
| Define what an electrical arc is. | An electrical arc is a discharge across a gap in a circuit. In arc welding, the arc is sustained by a thermally ionized column of gas through which the current can flow. |
| Electrodes in arc welding are divided into two categories. Name and define the two types. | The two categories are consumable and nonconsumable. The consumable type, in addition to being the electrode for the process, also provides filler metal for the welding joint. The nonconsumable type is made of materials that resist melting, such as tungsten or carbon. |
| What are the two basic methods of arc shielding? | (1) Shielding gas, such as argon and helium; and (2) flux, which covers the welding operation and protects the molten pool from the atmosphere. |
| Describe the shielded metal arc-welding (SMAW) process. | SMAW is an arc-welding process that uses a consumable electrode consisting of a filler metal rod coated with chemicals that provide flux and shielding. |
| Why is the shielded metal arc-welding (SMAW) process difficult to automate? | Because the stick electrodes used in SMAW must be changed frequently, which would be difficult to do automatically. It is much easier to automate the feeding of continuous filler wire, such as in GMAW, FCAW, SAW, or GTAW. |
| Define resistance welding. | RW consists of a group of fusion welding processes that utilize a combination of heat and pressure to accomplish coalescence of the two faying surfaces. Most prominent in the group is resistance spot welding. |
| What are the desirable properties of a metal that would provide good weldability for resistance welding? | High resistivity, low electrical and thermal conductivity, and low melting point. |
| Describe the sequence of steps in the cycle of a resistance spot-welding operation. | The steps are (1) insert parts between electrodes, (2) squeeze parts between the electrodes, (3) weld, in which the current is switched on for a brief duration (0.1 to 0.4 sec), (4) hold, during which the weld nugget solidifies, and (5) open electrodes and remove parts. |
| What is a sonotrode in ultrasonic welding? | It is the actuator which is attached to one of the two parts to be welded with USW and which provides the oscillatory motion that results in coalescence of the two surfaces. It is analogous to an electrode in resistance welding. |
| Distortion (warping) is a serious problem in fusion welding, particularly arc welding. What are some of the techniques that can be taken to reduce the incidence and extent of distortion? | The following techniques can be used to reduce warping in arc welding: (1) Welding fixtures can be used to physically restrain movement of the parts during welding. (2) Heat sinks can be used to rapidly remove heat from sections of the welded parts to reduce distortion. (3) Tack welding at multiple points along the joint can create a rigid structure prior to continuous seam welding. (4) Welding conditions (speed, amount of filler metal used, etc.) can be selected to reduce warping. (5) The base parts can be preheated to reduce the level of thermal stresses experienced by the parts. (6) Stress relief heat treatment can be performed on the welded assembly, either in a furnace for small weldments, or using methods that can be used in the field for large structures. (7) Proper design of the weldment itself can reduce the degree of warping. |
| What are some of the important welding defects? | Some of the important welding defects are (1) cracks, (2) cavities, (3) solid inclusions, (4) incomplete fusion, and (5) imperfect shape or contour of weld cross section. |
| What are the three basic categories of inspection and testing techniques used for weldments? Name some typical inspections and/or tests in each category. | The three categories are: (1) visual inspection, which includes dimensional checks and inspection for warping, cracks, and other visible defects; (2) nondestructive evaluation, which includes dye-penetrant, magnetic particle, ultrasonic, and radiographic tests; and (3) destructive tests, which includes conventional mechanical and metallurgical tests adapted to weld joints. |
| What are the factors that affect weldability? | Factors affect weldability include (1) welding process, (2) metal properties such as melting point, thermal conductivity, coefficient of thermal expansion, (3) whether the base metals are similar or dissimilar - dissimilar base metals are generally more difficult to weld, (4) surface condition - surfaces should be clean and free of oxides, moisture, etc., and (5) filler metal and its composition relative to the base metals. |
| What are some of the design guidelines for weldments that are fabricated by arc welding? | The guidelines for weldments by arc welding include (1) Good fit-up of parts to be welded is important to maintain dimensional control and minimize distortion. Machining is sometimes required to achieve satisfactory fit-up. (2) The design of the assembly must provide access room to allow the welding gun to reach the welding area. (3) Whenever possible, design of the assembly should allow flat welding to be performed, as opposed to horizontal, vertical, or overhead arc welding positions. |
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