METAL FORMING PROCESS
1 What are the four major drawbacks of hot working?
• As hot working is carried out at high temperatures, a rapid oxidation orscale formation takes place on the metal surface which leads to poor surface finish and loss of metal.
• Due to the loss of carbon from the surface of the steel piece being worked, the surface layer loses its strength.
• This weakening of the surface layer may give rise to fatigue crack which results in failure of the part.
• Close tolerance cannot be obtained.
• Hot working involves excessive expenditure on account of high tooling cost.
2. Explain why parts produced by Forging is preffered when compared to other machining and welding process.
2 Classify the types of extrusion.
1. Hot Extrusion
2. Cold Extrusion
3. Hot extrusion
(A)Direct extrusion,(B) Indirect extrusion,(C)Tube extrusion
3 What is the difference between a bloom and a billet?
Ans: A bloom has a square cross section with minimum size of 150x150 mm and a billetis smaller than bloom and it may have any square section from 38 mm upto the size of a bloom.
4 What is impact extrusion ?
Ans: The raw material is in slug form which have been turned from a bar or punched from
a strip. By using punch and dies, the operation is performed. The slug is placed in the die and struck from top by the punch opareting at high pressure and speed.
5 Why are a number of passes required to roll a steel bar?
Ans: To reduce the thickness and to increase the width of the bar number of passesare required.
6 How are seamless tubes produced?
Ans: Seamless tubing is a popular and economical raw stock for machining because it
saves drilling and boring of parts. The piercing machine consists of two rapered rolls, called as piercing rolls.
7 What is Sejournet process?
Ans: That extrusion process which is based both on the use of a lubricantin a viscous
condition at extrusion temperature and on a separation between the lubrication of the chamber wall and die is called Sejournet process.
8 What is skew rolling ?
Ans: The rolls are powered and the workpiece is in due to frictional force between metal and surface. The torque on the rolls is being zero.
9 Explain the term Extrusion process.
Ans: The extrusion process consists of compressing a metal inside achamber to force itout
through a small opening which is called as die. Any plastic material can be successfully extruded. A large number of extruded shapes which are commonly used are tubes, rods, structural shapes and lead covered cables. During the process, a heated cylindrical billet is placed in the container and forced out through a steel die with the help of aramor plunger.
10 What are the disadvantages of forging processes?
• Complicated shapes cannot be produced.
• Generally used for large parts.
• Because of cost of dies, process is costly.
11.Define Impact extrusion.
Ans.It is a cold working process of making required shape by striking slugs of metal by high impact. It is used for making tooth paste ,shaving cream and collapsible medicine tubes.
12.What is meant by cold spinning.It is the operation of shaping very thin metals by pressing against a form while it is rotating , It is carried out at room temperature.
13.Define Hot Spinning.
It is the process of making circular cross section or a dish or head from circular , heavy plates by spinning sheet metal.
14.What is wire drawing.
Drawing of metal through a small aperture die and wounding in the form of coil is called wire drawing. The aperture is generally below 16mm diameter.
15.What is meant by deep Drawing.
It is the process of making cup shaped parts from sheet metal blanks, where the depth of the cup is greater than that of the diameter of the cup.