Milling MCQ Quiz in मराठी - Objective Question with Answer for Milling - मोफत PDF डाउनलोड करा

Concept:

Table speed (V) per minutes is given by,

V = f × N × t

Where, f = Feed per tooth, N = Number of rpm, t = Number of teeth.

Calculation:

f = 0.1 per tooth, N = 150 rpm, t = 8 teeth.

V = f × N × t

∴  V = 0.1 × 150 × 8 = 120 mm/minute

The table speed is 120 mm/minute

Explanation:

Light duty plain milling cutters:

• These are less than 19mm wide and usually have straight teeth.
• Those over 19mm wide have a helix angle of about 25°.
• This type of cutter is used only for light milling operations since it has too many teeth to permit the chip clearance required for heavier cuts.

Concept:

Table speed (V) per minutes is given by,

V = f × N × t

Where, f = Feed per tooth, N = Number of rpm, t = Number of teeth.

Calculation:

f = 0.1 mm/tooth, N = 200 rpm, t = 8 teeth.

V = f × N × t

∴  V = 0.1 × 200 × 8 = 160 mm/minute

The table speed is 160 mm/minute

Concept:

Milling is the machine operation in which the removal of metal from the work piece takes place due to a rotating cutting tool(cutter) when the work is fed past it. The cutter has multiple cutting edges and rotates at a very fast rate.

In Straddle milling two side milling cutters are mounted with a desired distance between them so that both sides of a work piece can be milled simultaneously.

Different operations performed on milling machine:

1. Plain milling or slab milling: It is a method of producing a plain, flat, horizontal surface parallel to the axis of rotation of the cutter.
2. Face milling: It is a method of producing a flat surface at right angles to the axis of the cutter.
3. Side milling: It is the operation of production of a flat vertical surface on the side of a work-piece by using a side milling cutter.
4. Angular milling:  It is a method of producing a flat surface making an angle to the axis of the cutter.
5. Gang-milling:  It is a method of milling by means of two or more cutters simultaneously having the same or different diameters mounted on the arbor of the milling machine.
6. Form milling: It is, a method of producing a surface having an irregular outline.
7. End milling: It is a method of milling slots, flat surfaces, and profiles by end mills.
8. Profile milling: It is the operation of reproduction of an outline of a template or complex shape of a master die on a workpiece.
9. Saw milling: It is a method of producing deep slots and cutting materials into the required length by slitting saws.
10. Helical milling: It is the operation of producing helical flutes or grooves around the periphery of a cylindrical or conical workpiece.
11. Flute milling: It is a method of grooving or cutting of flutes on drills, reamers, taps, etc.
12. Thread milling: It is a method of milling threads on dies, screws, worms, etc. both internally and externally. 

Concept:

Maximum Uncut chip thickness in milling is given as, \(t_{max}=\frac{2f_m}{NZ}\sqrt{\frac{d}{D}}\)

where, fm =  table feed, N = rpm, Z = number of teeth, d =  depth of cut, D = diameter of cutter

Calculation:

Given:

D = 70 mm, d = 2 mm, fm = 20 mm/min, N = 40 rpm, Z = 30

Therefore, \(t_{max}=\frac{2~\times~20}{40~\times~30}\sqrt{\frac{2}{70}}\)

Explanation:

Milling:

• Milling operations involve using multi-point rotary cutters to remove material from a workpiece by progressive chip removal.
• There are two main types of milling operations:
  1. Face milling 
  2. Peripheral milling
• Face milling cuts flat surfaces into the workpiece and flat-bottomed cavities. The feed can be either horizontal or vertical.
• Peripheral milling cuts deep slots, threads, and gear teeth.
• The workpiece can be fed into the cutting tool in either of two ways.
• Conventional milling involves feeding the workpiece against the cutter rotation. This is the recommended method for manual milling machines.
• Climb milling (Down Milling), on the other hand, feeds the workpiece in the same direction as the cutter rotation. This is the preferred method for CNC milling.
• Milling is best applied as a secondary process to an already machined workpiece. It helps to define features and serves as a “finishing coat”. Use milling as a secondary process to add features such as holes, slots, pockets, and contours.

Additional InformationGrinding:

• Grinding is an abrasive machining process that uses a grinding wheel or grinder as the cutting tool. Grinding is a subset of cutting, as grinding is a true metal-cutting process. Grinding is very common in mineral processing plants and the cement industry.
• Grinding is used to finish workpieces that must show high surface quality and high accuracy of shape and dimension. It has some roughing applications in which grinding removes high volumes of metal very rapidly.

Turning:

• Turning is a form of machining, a material removal process, which is used to create rotational parts by cutting away unwanted material. The turning process requires a turning machine or lathe, workpiece, fixture, and cutting tool.
• The workpiece is a piece of pre-shaped material that is secured to the fixture, which itself is attached to the turning machine, and allowed to rotate at high speeds. The cutter is typically a single-point cutting tool that is also secured in the machine, although some operations make use of multi-point tools.
• The cutting tool feeds into the rotating workpiece and cuts away material in the form of small chips to create the desired shape.

Explanation:

A milling machine is a machine tool in which metal is removed by means of a revolving cutter with many teeth, each tooth having a cutting edge which removes metal from a workpiece.

The work is supported by various methods on the work table and may be fed to the cutter, longitudinally, transversely or vertically.

Some parts of the horizontal milling machine:

Arbor:

• Its one end is attached to the column and the other end is supported by an overarm
• It holds and drives different types of milling cutters

Spindle:

• It gets power from gears, belt drives to drive the motor
• It has provision to add or remove milling cutters onto the arbor

Explanation:

Characteristics of down milling:

1. In down milling, cutter rotation and table movement are in the same direction so, the force acting on the tooltip is lower; hence the tool life is higher in this case. so statement A is the characteristic of down milling.
2. There is a high effect of backlash in down milling as the direction of cutter and table movement is the same so, the cut surface remains in contact with the cutter for a longer period of time so statement D is not the characteristic of down milling.
3. Surface finish produced in down milling is better than up milling because the cutter pushes the workpiece to the downward side, which gives better stability to cutting operation, so statement B is the characteristic of down milling.
4. In down milling, the chip thickness reduces from maximum to minimum so statement C is not the characteristic of down milling.

Explanation:

Milling:

• Milling is the machine operation in which the removal of metal from the workpiece takes place due to a rotating cutting tool (cutter) when the work is fed past it.
• The cutter has multiple cutting edges and rotates at a very fast rate.

In Straddle milling, two side milling cutters are mounted with the desired distance between them so that both sides of a work piece can be milled simultaneously.

Different operations performed on a milling machine:

• Plain milling or slab milling: It is a method of producing a plain, flat, horizontal surface parallel to the axis of rotation of the cutter.

• Face milling: It is a method of producing a flat surface at right angles to the axis of the cutter.

• Side milling: It is the operation of production of a flat vertical surface on the side of a work-piece by using a side milling cutter.
• Angular milling: It is a method of producing a flat surface making an angle to the axis of the cutter.
• Gang-milling: It is a method of milling by means of two or more cutters simultaneously having the same or different diameters mounted on the arbor of the milling machine.

• Form milling: It is, a method of producing a surface having an irregular outline.

• End milling: It is a method of milling slots, flat surfaces, and profiles by end mills.
• Profile milling: It is the operation of reproduction of an outline of a template or complex shape of a master die on a workpiece.
• Saw milling: It is a method of producing deep slots and cutting materials into the required length by slitting saws.
• Helical milling: It is the operation of producing helical flutes or grooves around the periphery of a cylindrical or conical workpiece.
• Flute milling: It is a method of grooving or cutting of flutes on drills, reamers, taps, etc.
• Thread milling: It is a method of milling threads on dies, screws, worms, etc. both internally and externally. 

Explanation:-

Milling Machine:

A milling machine removes material from a workpiece by rotating a cutting tool and moving it into the workpiece

based on work required in a different types axis, The milling machines are of different types. Hence, out of this the difference between the four-axis and six-axis milling machines are as follows-