Post on 07-Feb-2023
Birla Institute of Technology and Science Pilani, Hyderabad Campus
First Semester 2019-2020
ME G532 Machine Tool Engineering
Part A-Close Book Comprehensive Examination 04.12.2019
60 minutes 15%weightage
Answers should be crisp and to the point, Vague or incomplete answers will not get ANY credit
Q1. A milling machine is required to be design with stepless drive system to provide continuous
variation of speed of the cutter. Provide a circuit diagram of a hydraulic system to achieve this
purpose. Also provide the specific application/significance/importance for each of the component
used in the circuit, pointwise. [7]
Q2. For the problem stated in Question 1, suggest at least three alternate stepless drives. Also
mention their common advantages (at least 4) and limitations (at least 3). [5]
Q3. What are the modes of deformation or deflection in a lath machine spindle? Derive the
expression for the deflection of spindle for the condition shown in Figure Q3, and find its
numerical value. Stiffness at end A and B are measured as KA=300N/mm, KB=200N/mm. All
bearings are anti-friction type. [5]
Figure Q3
Q4. (a) How a machine tool can be represented using a close loop system for dynamic analysis?
Mention the components of equivalent elastic system of the machine tool and cutting process
model. [3]
(b) Being a complex system, the dynamic analysis of a machine tool is difficult. Suggest a
proper methodology for dynamic analysis of multi- degree of freedom machine tool with
necessary steps. [4]
(c) Considering a machine tool as a single degree of freedom system, derive the expression for
limiting unreformed chip thickness. [6]
***END***
a=12cm
l=32cm c=16cm
P2=1600 N P1=1200 N
A B
Birla Institute of Technology and Science Pilani, Hyderabad Campus
First Semester 2019-2020
ME G532 Machine Tool Engineering
Part B-Open Book Comprehensive Examination 04.12.2019
120 minutes 25%weightage
Answers should be crisp and to the point, Vague or incomplete answers will not get ANY credit
Q1. The duty cycle for an intermittent application
machine tool drive is given here. Determine
the duty factor (ε) for this the process. What
will be the maximum and equivalent power required if the machine tool uses, V-belt drive, Helical gear and
Jaw clutch. The prime mover is general purpose DC motor. What will be the power required if a similar
motor of standard duty factor of 15% is used for the same machine and application? [8]
Q2. Obtain the expression and limiting values of characteristics (Xu), number of speed steps (zu) and range
ratio (Rn). The common ratio (ϕ) of the geometric progression of speed is 1.06, and 1.41, and speed steps in
the last transmission group (Pu) are three. [8]
Q3. A special purpose machine tool is designed, and at the end it is observed that the tail stock is happened to
be stiffer than the head stock. The machine tool is subject to turning operation of cylindrical block. Develop
a mathematical model for the deformation of the workpiece, staring from the free body diagram to variation
of deflection curve (yx/ymax vs x/l). [10]
Q4. On a lathe machine, turning operation is performed on a cylindrical workpiece of 40cm diameter, which
covers half of the gap available between chuck center and lathe bed surface. The chuck rotates at 20rpm,
the cutting power required is measured as 120 watt (considering only cutting forces), the axial feed is
6cm/min, and the radial feed is 2.4mm/rev. The pulling force is measured as 200N, and the maximum twist
measured under saddle is 150Nm, at this condition. The workpiece weight is 20N. The coefficient of
friction at slideways can be considered as 0.2. Compute the cutting forces. [12]
Q5. It is proposed to replace the slideways of an existing lathe machine with hydrodynamic guide ways.
Presently a flat-flat slideway with carriage length of 24cm is employed, which moves linearly with a
velocity of 12cm/min. The width of the slideway faces are 6 cm for all the three faces. The maximum
pressure experienced at tool post side is obtained as 10kPa. For the new carriage assume length and width
as 8 and 6 cm, thus three hydrodynamic wedges can be accommodated in the carriage length with slight
increase in total carriage-length. The oil viscosity is 0.430 Ns/m2. Calculate the gap created between
carriage and guideway in the provided condition. What will be the compliance value for this system? [12]
***END***
Power (Watt) 10 8 0 10 8 0 8 10 9 Duration
(min) 2 1 1 2 1 2 1 3 2
Solution
Close Book
Q1.
Q2. Stepless drives: PIV drive, CVT drive, Friction coupling cone etc.
Advantages
1. Carrying out machining operations at optimum cutting speed: Improves productivity, and tool life
2. Ease of changing the speed or feed rate without stopping the machine tool. This helps in
increasing productivity as it cuts down the non-productive time.
3. Noiseless and more smooth rotation and absence of jerks which are characteristic of geared drives.
These features explain why stepless devices are generally employed in high-speed machine tools.
4. Generally more expensive than the devices providing stepped regulation.
5. Employed in high-speed machine tools
6. Hybrid speed variation: stepless drives in stepped drives
Limitations:
1. Commonly used in small-and medium-sized machine tools than hydraulic and electrical devices.
2. Mostly friction type, and therefore, their application is restricted to power transmission of up to 15 kW:
For high values dimensions increase
3. Speed adjustment on the running machine. Extremely difficult to adjust the speed on a stationary
machine
Q3: Modes: Deflection, deformation, tool holder taper joint deflection [1M]
Derivation: [2M]
Numerical value:
Ydef=1600x120+1200(320+160)(1+160/320)/(320x200)+(1600x200-1200x160)x160/(320x320x200)
=18.667mm [2M]
Q4. Close loop figure [1M],
EES components: Machine structure, Motor, Fractional effects [1M]
CP components: Tool face, Tool flank [1M]
(b) Explanation: Nyquist Method [1M] Step 1: open loop system with figure [1M]
Step 2: estimation of A and ϕ [1M]
Step 3: Polor plot, stability evaluation using combine A and ϕ value [1M]
1 M
1 M 1 M
1 M
Components: (each 0.5M), total 3M
Motor:
Pump:
Throttle valve:
Tank
Bypass line
Pressure gauges
(c) Derivation: Considering EES, A and ϕ values [2M],
Considering CP, A and ϕ values [2M]
Combining A and ϕ values [1M]
blim, expression [1M]