This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Stretch Forming”.
1. Stretch forming is a sheet metal forming operation in which shearing is taking place to deform the material.
a) True
b) False
View Answer
Explanation: Stretch forming is a type of sheet metal forming process in which the metallic sheet is intentionally stretched and bent simultaneously to produce different shapes of the stretched sheet metal. The metal sheet is generally held by jaws at the ends. And then the sheet is stretched by the help of punch.
2. For proper stretching operation, the metal sheet should be stressed above its yield strength.
a) True
b) False
View Answer
Explanation: In stretch forming, a metal sheet is stretched by the help of stretcher machines. For proper and complete stretching of sheet, the material is deformed plastically which is also called as permanent deformation. The metal sheet is stressed above its yield strength for successfully achieving the plastic deformation of the metal sheet.
3. In stretch forming, spring-back is a very complicated problem which causes trouble in operating machines during the process.
a) True
b) False
View Answer
Explanation: Spring-back is basically defined as a phenomenon in which the material tries to regain its original shape during elastic loading condition. But in stretch forming process, the stretching and bending operations take place simultaneously which causes permanent deformation of the sheet metal. So, this combined effect results in negligible spring-back in the metal part and hence causes no problem in the operating machines.
4. In stretch forming, forming limit curve (FLC) is defined as a locus of all the limit strains in different strain paths of the sheet metal.
a) True
b) False
View Answer
Explanation: In stretch metal forming process, the forming limit curve (FLC) provides quantification about the formability of sheet metal, which basically gives the details about the quality of material. The forming limit curve (FLC) is generally defined as a locus of all the limit strains in different strain paths like deep drawing and biaxial stretching, of the sheet metal.
5. Which of the following processes of metal forming is best suited for making products like aircraft wings and window frames?
a) Forging
b) Rolling
c) Drawing
d) Stretch forming
View Answer
Explanation: Stretch forming is a sheet metal forming process in which the sheet metal is clamped at the edges and stretched by using the dies or form blocks. And no any lubrication is required significantly during the process. This method is best suited for making the products like aircraft wings, window frames, automobile door panels etc.
6. High volume rate of production can be possible by stretch sheet metal forming process.
a) True
b) False
View Answer
Explanation: In stretch forming, the sheet metal is fixed with stretch gripper with the support of a tool, and then operation takes place in a hydraulic stretching unit. The process consumes too much time as the stretching process takes time to strain hardens the material. So, this process includes low volume rate of production, but the process is very versatile and have economic production.
7. Stretch forming is a process which involves tensile and bending forces during the operation.
a) True
b) False
View Answer
Explanation: In stretch forming process, stretching of a metal sheet is basically done by holding its edges and bending it on a cylindrical block, simultaneously is known as stretch forming. This process basically involves tensile and bending forces during the operation. In this process, the materials with high ductility are mostly stretched by rigid dies.
8. The stretch forming process is generally performed by using a hydraulic operated ram.
a) True
b) False
View Answer
Explanation: The stretch forming process is generally performed by using a hydraulic operated ram. In this process, first a single form block is used along with the gripping jaws, and then the metal is gripped and stretched by applying high tensile forces until it deforms plastically. And then the sheet metal is bent and rolled around a form block.
9. Tangential stretch forming and simple stretch forming are quite similar to each other.
a) True
b) False
View Answer
Explanation: Tangential stretch forming is very different from simple stretch forming. However, the purpose is same. In tangential stretch forming, the metal sheet is gripped from two opposite ends. The main difference to the simple stretch forming is that the form block and gripping jaws both are movable in this process.
10. Rubber forming is a type of forming process in which polyurethane is used as a die material.
a) True
b) False
View Answer
Explanation: Rubber forming is a type of forming process in which a polyurethane or rubber pad is commonly used as the die material instead of a rigid material. These materials are highly resistance to the abrasion and have a better fatigue life. And pressures of the order of 100 bar are typical of this process. This process is also called as Guerin process.
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