1 What will be the cutting time for machining the workpiece of width 1000 mm when the bull wheel is rotating at 150 rpm with the feed of 2 mm per stroke?
a) 90 sec
b) 120 sec
c) 200 sec
d) 500 sec
Explanation: Cutting time is calculated by formula,
CT = W/ (Ns*Fc) where, W is width of the work piece
Ns is the bull wheel rpm
Fc is the feed rate
Therefore,
CT = 1000/ (150*2)
= 3.34 min = 200 sec.
2. Which word best describes the roll forming?
a) Die forming
b) Coining
c) Progressive
d) Profiling
Explanation: Roll forming is a continuous process for forming sheet, strip or coiled metal stock into long shapes of essentially uniform cross-section. The material is fed through pairs of contoured forming rolls, which progressively shape the metal until the desired cross-section is produced.
3. Which of the following are the most desirable materials used in roll forming?
a) Spring steel
b) Chromium-molybdenum steel
c) Non-metals
d) Mild steels and aluminium
Explanation: Both ferrous and non-ferrous metals as well as some non-metallic material can be roll formed. Mild steel and aluminium are the most common materials used in the process. Additionally, polished, painted, coated and plated materials can also be roll formed.
4. The most common cutting method of roll forming is ____________
a) sawing
b) pre-cutting
c) parting
d) post-cutting
Explanation: The stock to be roll formed may be either pre-cut to a pre-determined length before roll forming, or post-cut afterward to a specified dimension. But the latter one is the most common. By incorporating auxiliary equipment such as pre-notching, punching, embossing, etc. the post-cut method can be a complete net-shape process, fully automated.
5. Pre-cut roll forming production speed are ______________
a) 600 to 800 feet per minute
b) up to 1000 feet per minute
c) 50 to 250 feet per minute
d) 100 to 300 feet per minute
Explanation: In the pre-cut method, material passes through the rolls at fixed speeds of 50 to 250 feet per minute or 15 to 76 meters per minute. Pre-cut roll forming is commonly used for low production when nothing is required that cannot be easily done using post-cut lines, or when multiple profile widths require expensive and or time consuming tool changeover.
6. Post-cut roll forming production speeds are ______________
a) 100 to 180 feet per minute
b) 650 to 780 feet per minute
c) 800 to 900 feet per minute
d) up to 100 feet per minute
Explanation: The post-cut method typically involves a stock uncoiler, a roll forming machine, and a runout table. Production speeds average 100 to 180 feet, or 30 to 55 meters per minute, but can be as high as 600 feet or 185 meters per minute.
7. Camber refers to deviation from a straight line the____
a) side edge before roll forming
b) vertical plane
c) horizontal plane
d) side edge after roll forming
Explanation: Depending on the length, roll forming length tolerance of plus or minus 0.020 to 0.093 of an inch, or 0.51 to 0.236 of a millimetre are possible. To determine the straightness few terms are used and camber being one of them. Camber means the deviation a side edge from a straight line measured prior to roll forming.
8. When does springback occur?
a) When the material does not stress beyond its elastic limit
b) When the material is stressed beyond its elastic limit
c) When the material is too hard
d) When the material is too soft
Explanation: Elastic limit is the point beyond which material deforms permanently under stress. Springback is the tendency to regain the initial shape. Therefore, it occurs when the material does not stress beyond its elastic limit during forming. Spring is often compensated by overforming the material and then allowing it to ‘spring back’ to the required profile.
9. The flower design is____
a) the total number of formed bends
b) a station-by-station overlay of progressive part contours
c) the part’s finished profile
d) the finished profile divided into component bends and straight sections
Explanation: The design of forming rollers is dependent on several factors such as number of forming passes, material width, roll material, flower design, etc. Flower design is a station-by station overlay of the progressive part contours starting with the flat strip width before forming and ending with the final desired section profile.
10. Which of the following is the most common material used to produce forming rolls?
a) Aluminium
b) Carbide
c) Chrome steels
d) Oil hardened tool steels
Explanation: Several types of materials are used in the manufacture of the forming rolls and oil hardened tool steel being the most common. For extended tool life, hardened high-carbon, high-chromium too steels are used. On extremely tough forming applications involving high temperatures and or abrasive materials, aluminium/bronze or carbide rolls are required.