This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Gear Hobbing”.
1. Hobbing process is also used for which of the following application?
b) Metal bending
c) Rust removal
d) Sprocket cutting
Explanation: Hobbing is a machining process widely used for cutting gears, splines and sprockets. The tool used for cutting is called as a hob.
2. Hobbing is a special type of which of the following?
Explanation: Hobbing is a special type of milling in which teeth are cut by a series of cuts made by a tool known as a hob.
3. In the process of gear cutting by hobbing, the angle between the hob’s spindle axis and the workpiece’s spindle axis is fixed.
Explanation: The angle between the hob’s spindle axis and the worpiece’s spindle axis varies depending upon the type of product being manufactured.
4. For spur gear manufacturing, angle between the hob’s spindle axis and the workpiece’s spindle axis should be equal to____
a) (helix angle of the hob)/2
b) 2*(helix angle of the hob)
c) (helix angle of the hob)
d) (helix angle of the hob)2
Explanation: As hob has helical threads, it has to be oriented making some angle with the workpiece as per the requirement and then it is fed into the workpiece. For spur gears, that angle should be equal to the helix angle of the hob.
5. For helical gears, the angle between hob’s spindle axis and workpiece’s spindle axis must be _____ as the helix angle of the helical gear.
a) increased by the same amount
b) increased by the half amount
c) decreased by the same amount
d) decreased by the half amount
Explanation: For manufacturing the helical gear, one has to consider helix angle of the gear. While hobbing the helical gear, angle between hob spindle axis and workpiece spindle axis should be increased by an angle equal to helix angle of the gear.
6. Hobbing machines are characterised by _____
a) production rate
b) largest module or PCD it can generate
c) accuracy of the machine
d) size of the machine
Explanation: Hobbing machines are characterised by the largest module or pitch diameter it can generate as they can produce anything from tiny instrument gears to 10ft diameter marine gears.
7. 5in (125 mm) capacity machine can generate gears upto_____ pitch diameter.
Explanation: The number signifies the maximum pitch diameter of a gear that can be produced by that machine. Therefore 5in capacity means the largest gear manufactured by that machine will have pitch diameter equal to 5in.
8. The gear hob is a formed tooth milling cutter with helical teeth.
Explanation: The gear hob is a formed tooth milling cutter with helical teeth arranged like the thread on a screw. These teeth are fluted to produce required cutting edges.
9. As the number of threads on the hob increases, it’s accuracy_____
c) remains same
d) can’t say
Explanation: More number of threads means more difficulties to manufacture them. Therefore, accuracy varies inversely with a number of hob threads.
10. As the number of threads on the hob increases, production rate______
c) with each thread, increases by 25%
d) can’t say
Explanation: Production rate increases with an increase in the number of threads on the hob as more number of threads means less machining time. Directly it cannot be said that production rate will increase by 25% per thread.
11. Ideally how many gear threads should be there or each hob thread?
d) 10 times the number of hob threads
Explanation: For best results, there should be about 30 gear threads for each hob thread. Therefore four-thread hob should not be used to cut fewer than 120 gear teeth.
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