4. Say if the following sentences are true or false.

1. There is always a welding pool in solid-phase welding processes.

2. Total energy input in all welding processes is greater than needed to produce a weld.

3. Reactions of metals with the atmosphere or other nearby metals are favorable to the properties of a welded joint.

4. Fluxes and inert atmospheres play a protective role and prevent oxidation.

5. The heat-affected zone is a region with unaltered properties.

6. Residual stress is present in all welded structures.

Additional texts for reading and discussion Cold Forging

The cold forming process is similar to the cold heading process, however, the process uses vertical presses instead of horizontal cold heading machines. The cold forming process is also volume specific and the process uses dies and punches to convert a specific "slug" or blank of a given volume into a finished intricately shaped part of the exact same volume. The cold forming process generally compliments the cold heading process by adding more intricate shapes to the cold headed blank.

Cold forging is a reliable and cost efficient process. The main advantages are the following:

• savings in material and final machining,

• high productivity,

• excellent dimensional accuracy and surface quality of cold extruded parts,

• improvement of mechanical properties of extruded parts,

• favorable crystal grain flow increases toughness.

Cold forging encompasses many processes: bending, cold drawing, cold heading, coining, extrusion, punching, thread rolling and more to yield a diverse range of part shapes.

The main groups of produced cold forged parts are:

• Parts for starter motors (pinion, barrel, solenoid body, plunger, core…)

• Parts for alternators (claw pole…)

• Parts for switches, valves and other applications

• Parts for car seats

• Anti vibration parts, spiders, inner racks

• Parts for flywheel magnetos and other motorbike parts

• Hollow parts with stems and shafts

• Different gears and other parts etc.

Hot forging

Hot forging, also referred to as drop forging, is a process that can be used to produce a wide variety of parts in most metals. Generally, forging is the process of forming and shaping metals through the use of hammering, pressing or rolling. Forgings are produced in sizes ranging from a few millimeters maximum dimension up to 3 m or more in some cases.

The principles and practices of hot forging have been established since the last century, but improvements have obviously been made in equipment, lubricants and the ability to process the more difficult to forge materials since that time.

Hot forging is a plastic deformation of metal at a temperature and strain rate such that recrystallization occurs simultaneously with deformation, thus avoiding strain hardening. For this to occur, high workpiece temperature (matching the metal's recrystallization temperature) must be attained throughout the process.

A form of hot forging is isothermal forging, where materials and dies are heated to the same temperature. In nearly all cases, isothermal forging is conducted on super alloys in a vacuum or highly controlled atmosphere to prevent oxidation.

Because the metal is hot, it is easy to move it around, allowing for more elaborate shapes than cold forging. Hot forging is common for harder metals such as steel that would be difficult to shape when cold. The process begins with a cast ingot, which is heated to its plastic deformation temperature, then forged between dies to the desired shape and size. During this forging process, the cast, coarse grain structure is broken up and replaced by finer grains, achieved through the size reduction of the ingot.

Depending on the metal and the degree to which it was heated, the forging process itself might suffice to temper, or strengthen, the material. Usually, the product is additionally heat treated after it is hot forged.