Different Machining Processes MCQ Quiz in తెలుగు - Objective Question with Answer for Different Machining Processes - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

Concept:

A grinding wheel consists of the abrasive that does the cutting, and the bond that holds the abrasive particles together.

A standard marking system is used to specify and identify grinding wheels.

The following is the sequence of arrangement:

Abrasive type – Grain size – Grade of bond – Structure – Bond type

The number ‘46’ specifies the average grit size in inch mesh. For a very large size grit, this number may be as small as 6 whereas for a very fine grit the designated number may be as high as 600.

• Abrasive type: ‘A’ for aluminium oxide, ‘C’ for silicon carbide
• Grain size: They are indicated by a number ranging from 10 (coarse) up to 600 (very fine)
• Grade of bond: The grades range from ‘A’ indicating light or ‘soft’ bond to ‘Z’ indicating a firm or ‘hard’ bond
• Structure: This structure is indicated by a number from 1 to 12. The higher numbers indicate a progressively more open structure
• Bond type: V – Vitrified, S – Silicate, B – Resinoid, R – Rubber, E – Shellac, O – Oxychloride

Concept:

A grinding wheel consists of the abrasive that does the cutting, and the bond that holds the abrasive particles together.

A standard marking system is used to specify and identify grinding wheels.

The following is the sequence of arrangement:

Abrasive type – Grain size – Grade of bond – Structure – Bond type

The number ‘46’ specifies the average grit size in inch mesh. For a very large size grit, this number may be as small as 6 whereas for a very fine grit the designated number may be as high as 600. 

• Abrasive type: ‘A’ for aluminium oxide, ‘C’ for silicon carbide
• Grain size: They are indicated by a number ranging from 10 (coarse) up to 600 (very fine)
• Grade of bond: The grades range from ‘A’ indicating light or ‘soft’ bond to ‘Z’ indicating a firm or ‘hard’ bond
• Structure: This structure is indicated by a number from 1 to 12. The higher numbers indicate a progressively more open structure
• Bond type: V – Vitrified, S – Silicate, B – Resinoid, R – Rubber, E – Shellac, O – Oxychloride

Explanation:

Feed rate in slab milling operation is given by, 

f_m = f_t × N × Z 

Where f_t is the feed per tooth.

N = Spindle rotational speed (in rpm)

Explanation:-

The degree of concentration shows the content ratio of Diamond/CBN abrasive grains (abrasive grain ratio) in the abrasive layer.

• 4.4 cc/cm³ = Degree of concentration of 100" is defined, generally used in the range of 20 to 200.
• In the case of electrodeposition, which has only one abrasive grain layer, there is no degree of concentration standard.

Important Points

Explanation:

Centreless Grinding:

Centerless grinding is a high production process for continuously grinding.

Cylindrical surfaces in which the workpiece is supported not by central (hence the term centreless) or chucks but by a blade.

Typical parts made by centerless grinding are roller bearings, piston pins, engine values, camshaft, and similar components. This continuous production process requires little operator skill. 

• In through-feed grinding, the workpiece is supported on a work rest blade and is ground between two wheels.
• Grinding is done by the large wheel, while the smaller wheel regulates the axial movement of the workpiece.
• The regulating wheel, which is rubber bonded, is filled and runs at a speed of only about (1/20)^th of the grinding wheel speed.

Explanation:

Drilling:

• Drilling is a cutting process in which a hole is originated by means of a multi-point, fluted, end cutting tool.
• As the drill is rotated and advanced into the work-piece, the material is removed in the form of chips that move along the fluted shank of the twist drill.
• The point angle is the angle between the cutting edges (lips).

• The point angle varies according to the hardness of the material to be drilled.

• The point angle is located at the head of the twist drill.
• For hard materials such as stainless steel, the point angle should be large and e.g. 130° or 135°.
• For soft materials, point angles of 60° are used i.e. for drilling wood and fibre.
• With a large point angle, more of the cutting edge engages in the workpiece when drilling.

Explanation:

• Grinding is the process of removing metal by the application of abrasives which are bonded to form a rotating wheel. When the moving abrasive particles contact the workpiece, they act as tiny cutting tools, each particle cutting a tiny chip from the workpiece.
• It is a common error to believe that grinding abrasive wheels remove material by a rubbing action; actually, the process is as much a cutting action as drilling, milling, and lathe turning.

Material removal rate (MRR) = Table speed (V) × width (w) × depth of cut (d)

Calculation:

Given:

V = 300 mm/s, w = 15 mm, d = 10 μm = 0.01 mm

MRR = 300 × 15 × 0.01 = 45 mm³/s

Explanation:

For machining, a tool material needs to be much harder than the work material, not only to maintain the form but also to avoid excessive wear.

The hardness of some common materials in the Knoop scale is shown in the table.

Since Silicon carbide, Aluminium oxide and Cubic boron carbide are of the same hardness as Tungsten carbide, so the use of these materials may lead to wear and blunting of the tool.

Explanation:

Plain milling cutters:
Plain milling cutters are cylindrical, having teeth on the periphery only. They are used to produce flat surfaces, by feeding the table longitudinally. The cutter teeth may be straight or helical according to the size of the cutter. Wider plain cutters are used for slab milling which is known as slab milling cutters.

In slab milling cutters the sides are relieved or dished to prevent the sides of the cutter from rubbing or binding.

Grain size or Grit size:

• It indicates the size of abrasive particles. i.e. Size of abrasives = 1/ Grain Size Number (GSN)
• When the GSN > 600, size of the abrasive particles becomes very very small and it cannot act like a cutting tool, therefore MRR is less.
• When GSN < 600, actual size of abrasive is increasing, the chip size is increasing and MRR is increasing.
• As the GSN is reducing or size of abrasive is increasing, the MRR is increasing first and then reducing.
• The grain size is selected based on the surface finish required on the workpiece i.e. for rough grinding, course or medium grain size is selected and for finished grinding fine or very fine grain size will be selected.
• 10 - 24 = coarse, 30 - 60 = Medium, 80 - 180 = Fine, 220 - 600 = very fine