Question 1
a) A cylindrical feedstock of length = 35.4 cm and diameter = 10 cm is subjected to turning using a high speed steel tool. For this tool, n and C values in the Taylor tool life equation are 0.125 and 70 m/min, respectively.
The cost for hiring an operator and using the machine tool are $82 per hour. The tooling cost per edge of cutting is $5. Loading and unloading the part on to the machine takes about 4 min, and it takes about 2.5 minutes to change the tool. At a feed rate of 0.25 cm/rev, calculate:
(i) cutting speed for maximum production rate,
(ii) tool life [minutes], and
(iii) cost per unit and total cycle time of a produced part.
b) On a rectangular stock of aluminium alloy [tensile strength = 305 N/mm² and yield strength = 215 N/mm²] with dimensions of length = 320 mm and width = 30 mm, peripheral milling is performed on the top surface. The diameter of the carbide milling tool is 60 mm, with 8 teeth. The milling tool is centred along the workpiece width. At cutting speed of 80 m/min, chip load of 0.17 mm/tooth, and a depth of cut of 5 mm, calculate the following:
(i) the time to complete one machining one pass across the surface, and
(ii) the rate of maximum material removal during this cut.
Question 2
a) List and describe the five processes that cause wear at the interface of the tool and chip and the interface of tool and work in machining. What are the two major factors which enhance tool wear mechanisms? Explain in detail.
b) List and describe the three main processes that cause grinding wheel wear. Define Grinding Ratio and explain in detail, the relationship between grinding ratio, surface finish, and wheel speed using a plot.
Question 3
a) In an Electrochemical Machining process, the feedstock is made of an aluminium alloy (Ultimate Tensile Strength=572 MPa, Tensile Yield Strength=503 MPa). The desired time to machine a hole (Φ=10 mm) through a 20 mm-thick part is 2.1 min at a feed rate of 0.18 mm/s. What are:
(i) the efficiency of the process in %, and
(ii) the current requirement in amps to achieve this machining time target?
b) Describe in detail the process of circular sawing with the aid of a freehand sketch. What are the two major mechanisms by which circular sawing is achieved and what materials are commonly used as circular saws of each type?