JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN
MECHANICAL ENGINEERING
FINITE ELEMENT ANALYSIS OF CNC LATHE
HEADSTOCK
1
MR. A.M.JOSHI, 2 PROF. P.M. KUBAVAT, 3MR. R.D.GONDALIYA
1M.E.[Machine
Design] Student, Department Of Mechanical Engineering, School Of
Engineering, RK Technical Campus, Rajkot ,Gujarat
2 Asst.Professor , Department Of Mechanical Engineering, School Of Engineering, RK
Technical Campus, Rajkot ,Gujarat
3 M.E.[Machine Design] Student, Department Of Mechanical Engineering, School Of
Engineering, RK Technical Campus, Rajkot ,Gujarat
ashutosh1584@yahoo.co.in, pmk0079@gmail.com,gondaliya_rd@yahoo.com
ABSTRACT: The machine tool is machine that imparts the required shape to a work piece with the desired
accuracy of removing metal from the work piece in the form of chips. Beds, columns, bases, head stock are
called “structures” in machine tool. In machine tool 70-80% of the total weight f the machine is due to structure.
In this paper FE analysis of headstock is carried out for the specific cutting condition i.e. turning operation.
Here, we prepared a headstock model in pro-E 4.0 software. Based on mathematical calculation values of
cutting forces, and thrust forces are used in FE analysis. Here, we used ANSYS WORK BENCH 11.0 software
for the FE analysis of the head stock (Machine tool structure).Through this analysis we get the result in terms of
stresses and deformation and this result are within the allowable limits.
Keywords—Machine tool structure, FE Analysis of Machine tool.
I: INTRODUCTION
The machine tool is a machine that imparts the
required shape to a work piece with the desired
accuracy of removing metal from the work piece in
the form of chips. Machine tool parts, such as beds,
bases, columns, box-type housings, carriages, tables,
etc. are known as structures of machine tool.
Function of the machine tool structure is to support
and guide the work piece and cutting tool and to
resist the cutting and feed forces encountered during
the machining operations. Thus, structure of a
machine tool forms the vital link between cutting tool
and work piece on a metal cutting machine. The
demand for higher accuracy NC lathes has increased
dramatically with respect to machining accuracy
requirements [3]. Beds, columns, bases and box type
housings are called “structures” or “frames” in
machine tool. In machine tools 70-80% of the total
weight of the machine is due to the structure. [1]
Recently, researches have been conducted in the field
of improvement of structural design of machine tools
by improving stiffness and lightening weight. The
arrangement of stiffening ribs in machine tool
structures is a key factor for structural stiffness and
material consumption. So the lightening design of
stiffening ribs is significant for machining
performance and energy saving. [4]
It is generally accepted that the precision of machine
tools is determined by their static, dynamic and
thermal characteristics. Especially, the dynamic
characteristics play an important role in high speed,
precision machine tool structures, because vibration
during the machining process results in chatter marks
on the machined surface and thus creates a noisy
environment. Higher cutting speeds can be facilitated
only by structures which have high stiffness and good
damping characteristics. The deformation of machine
tool structures under cutting forces and structural
loads are responsible for the poor quality of products
and which in turn is also aggravated by the noise and
vibration produced.
II: FUNCTION OF MACHINE TOOL STRUCTURE

To provide rigid support on which various
subassemblies can be mounted i.e. beds, bases, etc.

To provide housings for individual units or
their assemblies like speed gear box,
spindle head, etc.

To support and move the work piece and
tool relatively, i.e. table, carriage, tail stock, etc.
There are two common features, which are
fundamental to the satisfactory fulfillment of above
requirements for all structures. These are:

Proper selection of material.

High static and dynamic stiffness.[5]
Fig.1 Machine tool structure
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III: MATERIAL USED FOR MACHINETOOL
STRUCTURE
The commonly used materials for machine tool
structures are cast iron and steel. While in some
applications Granite and ‘Epoxy Concrete’, newly
developed material, is also introduced. Cast iron
structures were almost exclusively used in machine
tools till a decade or so ago, but lately welded steel
structures are finding wider application due to
advances in welding technology.
Materials for the structure are cast iron, steel
weldments, Granite and Epoxy concrete. Also Dai
Gil Lee, et al [1] has suggested that, Fiber reinforced
composite materials reduces the weight of slides up
to 34% and increases damping by 1.5-5.7 times
without sacrificing the stiffness and Positional
accuracy of 5 micrometer per 300 mm of slide
displacement.
IV: PROBLEM FORMULATION
The main objective of this study is to increase the
structural stiffness, reduce the weight and
deformation of machine tool structure like bed, head
stock etc by using FEA software.
With the use of ANSYS software FE analysis of
CNC lathe centre head stock (Model Q Plus) is
carried out for different operation.
V: CUTTING FORCE CALCULATION
As it is explained, for analysing the structure loads
and constraints are required to specify. Loads should
be calculated based on the worst condition that has to
be bear by the structure during operation. Again one
can still give some design safety by overloading the
structure. Constraints also require attention, as they
restrict and control the behaviour of component
during actual operation and during analysis, itself.
Here for our case of Q Plus cutting forces are
calculated for two operations done on the machine
tool, turning and drilling. Then calculated cutting
forces are applied to the models of components of
machine tool with constraints and results of analysis
are obtained.
During the analysis of all components of structure,
Grey Cast Iron – G.C.I-25 is specified as the material
of the structure and every time material specification
is avoided during discussion.
Cutting Force Calculation: Turning operation [6]
Cutting forces are calculated based on several
assumptions, regarding cutting conditions and values
of cutting parameters, which will generate maximum
cutting force. Assumptions are listed below:
Assumptions:

Diameter of work piece (D) - 50 mm

Material to be cut – Medium carbon steel

Cutting speed (v) – 250 m/min

Feed per revolution (s )– 0.2 mm/rev
Efficiency of transmission is taken 100% from motor
to spindle; therefore full power of motor is available
at spindle.
Cutting speed,
v = π D n /1000
So, spindle speed,
n = v x 1000 / π D
= 250 x 1000 / π x 50
= 1592 rpm
Tangential cutting force,
P = 6120 N / v
z
= 6120 x 7 / 250
= 1713.6 N
= 1714 N
Torque at spindle,
T = 975 N / n
s
= 975 x 7 / 1592
= 42.87 Nm
= 43 Nm
0
Take Approach angle: 45
Rack angle: +10
Nose radius: 0.2-0.4 mm
Now resolving the cutting forces in two components
Px and Py
Px = 0.4 to 0.45 Pz = 771.12 N
Py = 0.4 to 0.5 Pz = 856.8 N
Cutting Force Calculation: Drilling operation [6]

In case of drilling, predominant effect is of
thrust generated during operation. The thrust force is
proportional to the diameter of drill, material to be
cut and feed per revolution.

By taking 100% efficiency of transmission
of power from motor to spindle, for maximum cutting
force, power at spindle should be equal to power of
motor. But for drilling this condition is having
another constraint.
Cutting forces are calculated based on several
assumptions, regarding cutting conditions and values
of cutting parameters, which will generate maximum
cutting force. Assumptions are listed below:
Assumptions:

Diameter of Drill (D) – 20 mm

Material to be cut – medium carbon steel

Cutting speed (v) – 80 m/min

Feed per revolution (s )– 0.1 mm/rev
Cutting speed,
v = π D n/1000
So, spindle speed,
n = v x 1000 / π D
= 80 x 1000 / π x 20
= 1274 rpm
For this set of values of diameter and spindle speed,
calculate power at spindle,
2
-5
N = 1.25 D K n (0.056+1.5 S) x 10
2
-5
= 1.25 x (20) x 1.45 x1274x (0.056+1.5x0.1) x 10
= 1.90 KW, that is much less than power of motor
which is= 7 Kw
Thrust force,
0.85
T = 1.16 K D (100 x S)
h
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MECHANICAL ENGINEERING
0.85
= 1.16 x 1.45 x 20 x (100 x 0.1)
= 2381.52 N, Maximum thrust
Torque,
T = 975 N / n
= 975 x 2.37/ 1274
= 18.13 Nm
VI: FE ANALYSIS OF HEAD STOCK
Dimension of headstock:
Length X 0.355 m
Length Y 0.412 m
Length Z 0.33 m
Fig 4 Max. Shear Stresses in headstock
Fig 2 Model of Head Stock
Applying load for turning operation:
Cutting forces in turning operation P x = 771.12 N
Py= 856.8 N
Fig 5 Total Deformation in headstock
VII: CONCLUSION:
Parameters
Result
Allowable
value
Max.
Von
misses Stress
7.4136e+005 Pa
8.2e+008 Pa
Max.
Stress
4.0752e+005 Pa
8.2e+008 Pa
4.1404e-006 m
5.0e-006 m
Shear
Max.
Deformation
Fig 3 Von misses stress in headstock
As shown from the analysis that the maximum
displacement is 4.14 μm which is within the
allowable limit .So the performance of the head stock
is satisfactory for the Turning operation. Again the
stress distribution is uniform except the some cases
as shown in figure.
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REFRENCES
[1] J D Suh and D G Lee, “Composite machine tool
structures for high speed milling machines”, Advance
Institute of Science and technology, Korea..
[2] David Te-Yen Huang, Jyh-Jon Lee, “On
obtaining machine tool stiffness by CAE software”,
International Journal of Machine Tools &
Manufacture, Research 41, 1149–1163, [2001]
[3] M. Mori, H. Mizuguchi, M. Fujishima , Y. Ido , N.
Mingkai , K. Konishi, “Design optimization and
development of CNC lathe headstock to minimize
thermal deformation”, CIRP Annals - Manufacturing
Technology 58, 331–334, [2009].
[4] S. Syath Abuthakeer, P.V. Mohanram, G. Mohan
Kumar, “Structural redesigning of a cnc lathe bed to
improve its static and dynamic characteristics”,
Inernational Journal of Engineering, Tome ix [2011].
[5] N.K.Meheta “Machine Tool Design and
Numerical Control”, Tata McGraw Hill Publication,
page 122-127.
[6] CMTI machine tool design handbook, Tata
McGraw Hill publication, 26th reprint, [1975].
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