ASSIGMENT NO.: 5 Q1. Explain the reasons for the large difference between the specific energies involved in machining when compared to grinding? Answer: Specific energies in grinding as compared to machining are much higher because: Due to the presence of wear flats (causing high friction) Due to the large negative rake angles (typically found in abrasives) and hence, the chips formed during grinding must undergo plastic deformation, and therefore require more energy The chips produced during grinding are small in comparison to machining. Therefore, there is more surface area for frictional losses per volume of material removed when compared with machining Rubbing of grains or portion of non-active grains may also be a contributing factor Q2. Calculate the chip dimensions for the following surface grinding operation: Wheel diameter, 10 in.; Depth of cut, 0.001 in.; Work feed, 125 ft/min.; Spindle rpm, 3000 rpm; Higher than average abrasive density. Answer: Wheel diameter (D) = 10 inch Depth of cut (d) = 0.001 inch Work feed (v) = 125 ft/min = 1500 inch/min Spindle rpm (N) = 3000 rpm Tangential Velocity (V) = πDN = 3.14X10X3000 = 94248 inch/min Contact Length = Chip Length (l) = (DXd) 1/2 = (10X0.001) 1/2 = 0.1 inch As the abrasive density is higher than the average, therefore C = 750/inch 2 (100/inch 2 ≤ C≤1000/inch 2 ) and r = 15 (10 ≤ r≤20) Grain depth of cut = Chip Thickness (t) = ((4v/VCr) X (d/D) 1/2 ) 1/2 = 2.38 X 10 -4 inch Q3. Assume that a surface grinding operation is being carried out using the following conditions: D = 200mm, d = 0.1 mm, v = 40 m/min, and V = 2000 m/min. These conditions are then changed to the following D=150 mm, d = 0.1 mm, v = 30 m/min, and V = 2500 m/min. How different is the temperature rise from the rise that occurs with the initial conditions?

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ASSIGMENT NO.: 5

Q1. Explain the reasons for the large difference between the specific energies involved in machining when compared to grinding?Answer: Specific energies in grinding as compared to machining are much higher because: Due to the presence of wear flats (causing high friction) Due to the large negative rake angles (typically found in abrasives) and hence, the chips formed during grinding must undergo plastic deformation, and therefore require more energy The chips produced during grinding are small in comparison to machining. Therefore, there is more surface area for frictional losses per volume of material removed when compared with machining Rubbing of grains or portion of non-active grains may also be a contributing factor

Q2. Calculate the chip dimensions for the following surface grinding operation: Wheel diameter, 10 in.; Depth of cut, 0.001 in.; Work feed, 125 ft/min.; Spindle rpm, 3000 rpm; Higher than average abrasive density.Answer: Wheel diameter (D) = 10 inchDepth of cut (d) = 0.001 inch Work feed (v) = 125 ft/min = 1500 inch/minSpindle rpm (N) = 3000 rpm

Tangential Velocity (V) = DN = 3.14X10X3000 = 94248 inch/minContact Length = Chip Length (l) = (DXd)1/2 = (10X0.001)1/2 = 0.1 inch

As the abrasive density is higher than the average, thereforeC = 750/inch2 (100/inch2 C1000/inch2)and r = 15(10 r20)Grain depth of cut = Chip Thickness (t) = ((4v/VCr) X (d/D)1/2)1/2 = 2.38 X 10-4 inch Q3. Assume that a surface grinding operation is being carried out using the following conditions: D = 200mm, d = 0.1 mm, v = 40 m/min, and V = 2000 m/min. These conditions are then changed to the following D=150 mm, d = 0.1 mm, v = 30 m/min, and V = 2500 m/min. How different is the temperature rise from the rise that occurs with the initial conditions?Answer: The temperature difference on the surface due to grinding is given by, T = D1/4 X d3/4 X (V/v)1/2Therefore, T1 = (200)1/4 X (0.1)3/4 X (2000/40)1/2 = 3.76X0.178X7.07 = 4.73 T (approximately)T2 = (150)1/4 X (0.1)3/4 X (2500/30)1/2 = 3.49X0.178X9.13 = 5.7 T (approximately)Difference = T2 T1 = 5.7 4.73 = 0.97 T2 > T1 due to the substantially larger value of (V/v) 1/2 in the second case, as compared to the first case.Q4. What are the main advantages of electrical discharge machining and where would you utilize the process?Answer: The main advantages of electro-discharge machining (EDM) are: It can create very complex forms in extremely hard material with fine surface finishes It can even be used to disintegrate broken tools It can machine parts that are very thin or fragile as no force is imparted onto the work piece

This process can be utilized where: Complex shapes that would otherwise be difficult to produce with conventional cutting tools Very small work pieces where conventional cutting tools may damage the part from excess cutting tool pressure There is no direct contact between tool and work piece and therefore delicate sections and weak materials can be machined without any distortion

Q5: Which of the advanced machining processes would cause thermal damage? What is the consequence of such damage to the work piece?Answer: The advanced machining processes which cause thermal damage are those that involve high levels of heat, which are: EDM and laser cutting. The thermal effects of these machining processes lead to the development of Heat Affected Zone (HAZ) on the work piece, which affect the hardness and ductility of the work pieces material. Moreover, it can also lead to fatigue failure due to the development of small cracks caused by the modification in internal stresses.