This examination paper contains FOUR (4) questions and comprises FOUR (4) printed pages.
2.
Answer ALL FOUR (4) questions.
3.
This is an OPEN-BOOK EXAMINATION.
4.
All questions DO NOT carry equal marks.
PAGE 2
ME4261/ME4261E
QUESTION 1
(a)
Clearly state if the following statements are true or false. Give the correct answer if it is found to be false. (i)
It is acceptable to use n-2-1 locating principle for locating large parts.
(ii)
Fixed renewable bush is used when multiple machining is done on the same axis
(iii)
Self-adjusting locators are used to locate parts with holes that are less accurately machined.
(iv)
To prevent defacing of surfaces while clamping, it is advisable to use metal sheets at the contact of parts and clamping elements.
(v)
Fool proofing pins can be used to locate parts and provide easy loading and unloading.
(vi)
Equalizing clamps are used to clamp parts, which are symmetrical.
(vii)
For drilling a hole on mild steel the gap between the part and the jig plate must be at least 1.5 x diameter of the hole
(viii)
Toggle clamps provide ample clearance to enable easy loading and unloading of parts.
(ix)
Tenons are placed below the base plate to locate the fixture on the machine table.
(x)
During mass production cam activated clamps are used to secure parts. (13 marks)
PAGE 3
ME4261/ME4261E
QUESTION 2
A batch of 10,000 pieces of a part to be machined is given in Figure 1. Using neat sketches propose jig(s) / fixture(s) to machine the following: Operation 1: To machine the slot of width 12mm using a horizontal machining centre. Operation 2: To machine surface A using a lathe. Operation 3: To machine two holes of diameter 12 mm using a drilling machine. All dimensions are in mm. All other operations are completed. Assume the missing dimensions. In your proposed solutions clearly indicate the supporting, locating and clamping methods. (37 marks)
Figure 1
PAGE 4
ME4261/ME4261E
QUESTION 3
A tool with the side cutting edge angle = +30o, cutting edge inclination s
λ =
+5o, normal
rake angle = + 10o, normal relief angle = +5o, end cutting edge angle e = +30o, is n
n
placed on a lathe machine for rough turning of a workpiece of diameter D = 30 mm at the feedrate f = 0.9 mm/rev, with the tool height set at 1 mm above the workpiece rotation axis, and with the tool orientation setting angles G = 0°, H = 0° and L= 18°, respectively. Calculate the values of the working angles for the tool when is in cutting: (a)
What is the value for the working rake angle ;
(b)
What is the value for the working relief angle ne ;
(c)
What is the value for the working inclination angle ;
(d)
What is the value for the working side cutting edge angle ;
(e)
What is the value for the working end cutting angle .
ne
e
se
ee
(25 marks)
QUESTION 4
Design a single-point tungsten carbide cutting tool for rough turning of a steel workpiece ( u 1.1 10 9 N/m 2). If the workpiece diameter is D 160 mm, the feed rate is f 0.15 mm/rev, the height of tool cutting edge is set to be 5 mm below the workpiece rotation axis, and tool orientation setting angles G 15 , H 0 and L 0 , (a)
show the cutting elements of the tool ; (5 marks)
(b)
determine the optimum values for the tool angles , , n
n
,
and in tool-in s
e
hand system, assuming that the differences between the rake angles and relief angles measured within different reference planes can be ignored. (20 marks) (Note: 1 psi = 6.894 103 N/m2 and 1 ipr = 25.4 mm/rev)
