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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 1 Examinations 2008/
Module Title: Manufacturing Technology
Module Code: MECH
School: Mechanical and Process Engineering
Programme Title: Bachelor of Engineering (Honours) in Mechanical Engineering
Programme Code: EMECH_8_Y EBIOM_8_Y
External Examiner(s): Prof. R. Clarke, Mr. P. Clarke, Mr. Murtagh Murphy and Dr. David Fitzpatrick
Internal Examiner(s): Mr. M. Cotterell Mr. M. Uhlemann
Instructions: Answer FOUR Questions
Duration: 2 Hours
Sitting: Winter 2008
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
Q1 An orthogonal cutting test yielded the following data:
Cutting Force Fc = 550 N Feed Force Ff = 365 N Uncut chip thickness h = 0.10mm Chip thickness h (^) c = 0.24mm Tool Rake Angle γn = 10˚ Width of cut w = 4mm
From this data, construct Merchants circle and determine:
(a) Shear angle φ (5 Marks)
(b) Shear plane force components: Fs and Fn (5 Marks) (c) Apparent shear strength of the material τs (5 Marks) (d) Rake face force components: F and N (5 Marks) (e) Coefficient of friction on the rake face μ. (5 Marks)
Q2 (a) Outline the factors governing the economics of a metal cutting process and explain why the cutting speed has an optimum value. (6 Marks) (b) Using the Taylor Tool Life Equation vcTn^ = C show that the most economical cutting conditions are attained when:
T
J
n
H n ⋅
where H = Hourly machine tool running cost J = Cost of a tool change T = Tool life (min) vc = Cutting speed (m/min) n = Tool life exponent (12 Marks)
(c) A cutting process is described by the tool life equation v (^) cT0.25^ = 240. The cost of a tool change is €8.20 while the cost of running the machine tool is €32.50 per hour. Determine the cutting speed and tool life for maximum economy. (7Marks)
Q3 (a) List FOUR factors that contribute to the accuracy of the finished workpiece when cutting a simple spur gear by FORMING. (6 Marks)
(b) Write a brief note on ONE of the following Gear Finishing process (8 Marks) Gear Shaving Gear Burnishing
(c) List FOUR advantages/disadvantages of producing screw Threads by ROLLING (6 Marks)
(d) Write a brief note on TWO methods of Thread Grinding. (5 Marks)
Q
(a) For a surface grinding operation the contact length l c can be assumed to be as follows: lc = ad s
Show then, that if a rectangular chip cross-section is assumed, that the maximum chip thickness h max for the process is given by:
s s
w d
a v
v rc
h
max =
where v s = Grinding Wheel Peripheral Speed (m/min) v w = Workpiece Feed Speed (m/min) c= Active Grit Density (grits/mm^2 ) r = Grain Aspect Ratio a = Depth of Engagement (mm) d s = Grinding Wheel Diameter (mm) (15 Marks)
(b) Estimate the number of chips formed per unit time and sketch the expected chip shape/dimensions during the surface grinding of a 20mm wide steel block. The depth of engagement is 0.05mm and the feed velocity of the table is 100mm/sec. The active grit density is 5 grits/mm^2 while the grain aspect ratio may be assumed to be 15. The wheel is 200mm diameter, 25mm wide and rotates at 3000 rev/min. (10 Marks)
Q
Write technical accounts on any TWO of the following topics:
(i) Chip morphology and the factors that influence the chip type obtained in machining (ii) Grinding wheel classification and selection (iii) Hot working vs. cold working of metals (25 Marks)
