weight optimization of lathe bed using FEA

PROJECT OBJECTIVE
The bed of Lathe acts as the base on which the different fixed and
movable parts of the Lathe are mounted
Usually it is made with toughened cast iron.
Lathe machine bed undergoes various cutting forces and vibrations in
large magnitude during machining process
To retain lathe bed in safe operating environment, it must be designed
with high rigidity and damping capacity
To achieve rigidity and damping capacity, lathe beds being designed
with high mass quantity. It increases both material and manufacturing
cost

PROJECT OBJECTIVE
In current project, lathe bed will be modeled for the complete analysis
with maximum load conditions.
Then FEA simulation will be carried out to reduce the weight of the
lathe bed without deteriorating its structural rigidity and damping
capacity
This weight reduction will be achieved by adding ribs and removing
material where less deformation and stresses are induced

PROJECT PROCEDURE
Solid modeling of lathe machine bed with help of Creo (formerly Pro –
Engineer) CAD software
Importing CAD model into ANSYS APDL (FEA software)
Assigning material properties (Cast iron)
Assigning boundary conditions (constraining FEA model DOF
according to real time conditions)
Applying loads on FEA model (force)
Simulating structural analysis for finding stress and deformation
magnitudes
Simulating modal analysis for finding natural frequency ranges
(modes)

PROJECT PROCEDURE
Identifying minimum stress and deformation zones. Reducing
material form these zones by adding ribs
After incorporation of these changes, again conducting FEA
analysis on modified model
Comparison of FEA results of initial and modified models
Conclusion based on results comparison
Project document preparation

REFERENCE LITERATURE
TITLE : Design and analysis of a machine tool structure based on
structural bionics (Author : Sujeet Ganesh Kore, IJMERR )
Objective : A structural bionic design process is systematically presented for
lightweight mechanical structures. By mimicking biological excellent structural
principles, the structure of lathe bed or the stiffening ribs of a lathe bed were
redesigned for better load-bearing efficiency.
Initial lathe bed design Modified lathe bed design for light weight and higher
strength by circular shape after considering
biological structures as shown above figure

REFERENCE LITERATURE
TITLE : Modelling and Analysis of CNC Milling Machine Bed with
Composite Material (Author : Venkata Ajay Kumar, IJSRD )
Objective : The bed in machine tool plays a critical role in ensuring the precision
and accuracy in components. It is one of the most important tool structures which
tend to absorb the vibrations resulting from the cutting operation. To analyze the
bed for possible material changes that could increase stiffness, reduce weight,
improve damping characteristics and isolate natural frequency from the operating
range. This was the main motivation behind the idea to go in for a composite
model involving High Modulus Carbon Fiber Reinforced Polymer Composite
Material (HM CFRP).
Initial lathe bed design
Structural and modal analysis is carried out with
3 different materials as shown in above table. From
These results author concluded HM CFRP material
Is best in terms of less weight and higher stiffness
and damping capacity

LOAD CONDITIONS (REFERENCE LITERATURE)
TITLE: Finding Cutting Forces While Turning Operation on Lathe
Machine at Different Depth of Cut of Different Metals (Author :
B.Tulasiramarao, IJIRS)
OBJECTIVE: In this study, a lathe tool dynamometer that can measure cutting
force, feed force and also thrust/Axial force by using strain gauge accelerometer
has been Studied and used. The dynamometer used in this project is a 500kg
force 3- component system. The dynamometer is connected to a data acquisition
system. As the tool comes in contact with the work piece the various forces
developed are captured and transformed into numerical form system. In this
project various forces for four different materials have been noted down and the
materials used in this project are aluminium, brass, mid steel & nylon. The forces
on these materials with variation in depth of cut are studied. Graphs are drawn on
how these forces vary due to variation in depth of cut.
Machine tool Dynamometer

TITLE: Finding Cutting Forces While Turning Operation on Lathe
Machine at Different Depth of Cut of Different Metals (Author :
B.Tulasi ramarao, IJIRS)
OBSERVATIONS :
Machine tool dynamometer works on the principle of measuring strain or
deflection induced in machine tool during cutting operation.
Dynamometer connected to data acquisition system (Computer loaded with
relevant software). Dynamometer collects data during machining process. This
data will be analyzed and converted into forces (component wise like X, Y and Z
component forces
Cutting force, feed force and axial / thrust forces can be calculated with help of
Dynamometer
For detailed analysis of forces which are acting on machine tools, strain gauges
will connect to various locations of machine tool
LIMITATIONS : Unavailability of dynamometer and data acquisition system

TITLE: Rigidity and Dynamic Analysis of Lathe Bed (Authors : P.
Karunakar, A. Ramesh and S. Vidya Sagar ICARMMIEM)
OBJECTIVE: Lathe is the most important machine tool, It is used to perform
number of operations. The requirements of lathe are zero deflection & high rigidity
heavy type lathe beds. The main objective of this paper is to develop geometric
model of lathe structure, stress and deflection analysis of lathe bed structure by
considering the specifications of Lathe bed. Here we determine the natural
frequencies of lathe structure and observed mode shapes and also we found the
amplitudes at various critical location ie., A1 120, A2 203 by two methods(1)
Model Analysis (2) Hermonic Analysis with respect to lathe speed by finite
element approach.

TITLE: Rigidity and Dynamic Analysis of Lathe Bed (Authors : P.
Karunakar, A. Ramesh and S. Vidya Sagar ICARMMIEM)
Force acting on lathe bed
The force acting on the lathe bed can be calculated in the following way.
The specifications of the PANTHER ENGG.CO LATHE are as follows,
i) Motor HP/KW = 2/1.5
ii) Spindle speed range = 45-938 rpm
iii) Spindle hollow (D) = 42mm.
iv) Power (P) = 2πNT/60 Where,
N – Spindle speed in R.P.M, T – Torque in N-m.
From above formulae Torque can be calculated as: T = P*60/2πN N-m.
T = 1.5*1000*60/2π*45,T = 318.30 N-m.
T = 318.308*103 N-mm.
We know that Torque = F * r
F is the force,
r is the radius of hollow spindle.
r = D/2= 42/2, r = 21mm.

TITLE: Rigidity and Dynamic Analysis of Lathe Bed
(Authors : P. Karunakar, A. Ramesh and S. Vidya Sagar ICARMMIEM)
F = T/r = 318.30*103/21, F = 15157.142 N.
This is the force acting on the lathe bed. This force is divided equally and
applied on selected nodes of the lathe bed.
So the force on each node (FN) is given as
FN = 15157.142/1063, FN = 14.258 N/node.
This force is applied on the selected nodes of the lathe bed which are
selected from head stock side of the lathe bed. The load applied on the
bed can be seen in the figure.

TITLE: Rigidity and Dynamic Analysis of Lathe Bed
(Authors : P. Karunakar, A. Ramesh and S. Vidya Sagar ICARMMIEM)
OBSERVATIONS :
Maximum torque generated by electric motor is converted into force as shown in
previous slide
This force is applied near head stock region (Because head stock region
experience high magnitude forces)
We opted for this method due to availability of input data
LIMITATIONS :
We can’t capture induced stress patterns for entire lathe bed accurately
But we can get idea about maximum stresses and deformations which can
be induced during machining process
For getting complete data about forces acting on lathe machine bed we need
strain gauges and data analyzing equipment

MATERIAL OPTIMIZATION TECHNIQUES (REF. LITERATURE)
TITLE: DESIGN AND STRUCTURAL ANALYSIS OF CNC VERTICAL MILLING
MACHINE BED (Authors: B. Malleswara Swami, K.Sunil Ratna Kumar IJAET)
OBJECTIVE: In this paper, a machine bed (Manufacturer: M/s Lokesh Machine
Tools Ltd) is selected for the complete analysis for both static and dynamic
loads. Then investigation is carried out to reduce the weight of the machine bed
without deteriorating its structural rigidity and the accuracy of the machine tool
by adding ribs at the suitable locations. In this work, the 3D CAD model for the
base line and the optimized design has been created by using commercial 3D
modeling software CATIA. The 3D FE model has been generated using
HYPERMESH. The analyses were carried out using ANSYS and Design
Optimization is done with the help of Optistruct. The results were shown with
the help of graphs to analyze the effect of weight reduction on the structural
integrity of the machine bed before and after the weight reduction and
conclusions were drawn about the optimized design.

3D CAD model of milling machine
(base line design)
3D CAD model of milling machine
(optimized model)

OBSERVATIONS :
FEA is carried out with help of HYPERMESH (Optistruct) and CAD modeling is
done in CATIA
Milling machine bed is divided into 2 parts i.e., 1. Design space 2. Non-design
space
Modifications are allowed into design space and modifications are not allowed
into non-design space (critical regions which can’t be allowed to modify)
Base portion of milling machine bed is chosen as design space because of low
intensity of stresses
They are done FEA analysis with 3 different materials. They are Cast iron G15,
Cast iron G40 and Cast iron G70.
FEA analysis is carried out for finding maximum stress, maximum deflection and
natural frequencies

OBSERVATIONS :
After analyzing FEA results, material removed from locations where minimum
stresses and deformations are induced as shown in modified figure
Again FEA analysis is carried out on the modified model with 3 different
materials as already mentioned
From these results comparison, Cast iron G15 was selected as best material
due to low stress and high natural frequencies as shown in below graph
Von-mises stress comparison Weight comparison

OBSERVATIONS :
Natural frequencies comparison
of Cast iron G15
of Cast iron G 40
of Cast iron G70

OBSERVATIONS :
Deformations comparison in mm

TITLE: STRUCTURAL REDESIGNING OF A CNC LATHE BED TO IMPROVE ITS STATIC
AND DYNAMIC CHARACTERISTICS (Authors: S. Syath Abuthakeer, P.V. Mohanram,
G. Mohan Kumar ANNALS)
OBJECTIVE: In the past, the design of CNC machine tools focused on their
functional aspects and was hard to acquire any resonance with customers.
Nowadays, despite the needs of low price, capabilities withstand at higher cutting
speeds and operate at high acceleration and deceleration with high quality
machine, many customers request good-looking machine. Regarding this, our
study aims to provide various form designs of machine tool structure with the help
of structural modifications made in CNC machine tool bed. After the lightening
effect was verified by finite element simulation, scale-down models of an original
bed and vertical ribs with hollow bed models were fabricated using rapid
prototyping method and tested. The dynamic characteristics of those different
form designs of the bed were analyzed experimentally. Numerical analysis was
done and results were validated with experimental results. Results indicated that
the cross and horizontal rib with hollow bed can increase the specific stiffness by
8% with 4% weight reduction and its dynamic performances is also better with
increases in the first natural frequencies. The modified design is effective in
improving the static and dynamic structural performances of high speed machine
tools.

TITLE: STRUCTURAL REDESIGNING OF A CNC LATHE BED TO IMPROVE ITS STATIC
AND DYNAMIC CHARACTERISTICS (Authors: S. Syath Abuthakeer, P.V. Mohanram,
G. Mohan Kumar ANNALS)
FEA Results shows that the cross and horizontal rib with hollow bed can
increase the specific stiffness by 8% with 4% weight reduction and its dynamic
performances is also better with increases in the first natural frequencies.

SOLID MODELING OF LATHE BED
Make South Bend Lathe Co
Model No. SB 1007
Overall
Dimensions(L X B X H )
1550 x 724 x 559 mm
Mass 246 kg
Overall
1420 x 174.5 x 215.7
mm
Mass 90 kg
Material Gray Cast Iron

TECHNICAL SPECIFICATIONS OF LATHE MACHINE
Electric Motor 2 HP, 1750 rpm /1.5 KW
Swing Over Bed 273 mm
Maximum Weight between centers 36.2 kg
Spindle Bore 34.5 mm
Spindle speeds 55 – 2200 rpm
Number of Spindle Speeds 8
Swing Over Cross Slide 168 mm
Swing Over Saddle 235 mm

LOADS APPLIED ON LATHE BED
Self Weight Of Lathe Bed - Gravitational Force
Weight Of Head Stock - 246 – 105.8 = 140.2 kg / 1375 N (Carriage
and tailstock weights are not subtracted due to unavailability of individual
weights. It does not effect FEA results because we are not reducing
loads and as compared to lathe bed weight these weight are very less in
magnitude)
Maximum force applied at carriage which is produced by electric motor
- 15092 N ( Calculation is shown in next slide)
Maximum Weight Between Centers - 36.2 kg / 355 N

Force acting on lathe bed
The force acting on the lathe bed can be calculated in the following way.
The specifications of the South Bend Lathe Co are as follows,
i) Motor HP/KW = 2/1.5
ii) Spindle speed range = 55-2200 rpm
iii) Spindle hollow (D) = 34.5 mm.
iv) Power (P) = 2πNT/60 Where,
N – Spindle speed in R.P.M, T – Torque in N-m.
From above formulae Torque can be calculated as: T = P*60/2πN N-m.
T = 1.5*1000*60/2π*55,T = 260.33 N-m.
We know that Torque = F * r
F is the force,
r is the radius of hollow spindle.
r = D/2= 34.5/2, r = 17.25 mm = 0.01725 m
F = 260.33/0.01725 = 15091.6 N
LOADS APPLIED ON LATHE BED

FE ANALYSIS FLOW CHART
Lathe bed CAD model generation by Creo
Importing CAD model into ANSYS APDL in .IGES format
Assigning material properties and applying forces and displacement constraints
Conducting structural and modal analysis on lathe bed
Reviewing analysis results
Finding out high and concentrated stress zones, high deflection zones
and low stress and deflection zones
Adding material or modifying design at high stress zones
and removing material at low stress zones And adding ribs / stiffeners
Conducting structural and modal analysis on modified lathe bed
Results comparison

CAD MODELING OF LATHE BED
Model No. SB 1007
Overall
1550 x 724 x 559 mm
Mass 246 kg
Overall
1420 x 174.5 x 215.7
mm
Mass 105.816 kg

IMPORTING CAD MODEL INTO ANSYS APDL

DEFINING ELEMENT TYPE
Solid 285 is a lower order 3-D, 4 node mixed u-P element. The element has a
linear displacement and hydrostatic pressure behavior. The element is defined
by four nodes having four degrees of freedom at each node: 3 three
translations in the nodal X, Y and Z directions, and one hydrostatic pressure.

ASSIGNING MATERIAL PROPERTIES
Material Gray Cast Iron Grade 70
Young’s Modulus 140E9 N / m^2
Poission’s Ratio 0.3
Density 7200 kg / m^3

DESCRITIZING (MESHING) CAD MODEL
Element edge length 6 mm
Number of elements 250630
Number of nodes 58904
Mass 105.816 kg

APPLYING FORCES AND DOF ON LATHE BED
1552.5 N applied at headstock region
15092 N applied at carriage region
177.5 N applied at tailstock region
All DOF applied at lathe bed base
Gravitationalforceappliedonlathebed

STRUCTURAL ANALYSIS RESULTS(SX)
Fixed to ground
Fixed to ground

STRUCTURAL ANALYSIS RESULTS(SY)

STRUCTURAL ANALYSIS RESULTS(SZ)

STRUCTURAL ANALYSIS RESULTS(VON-MISES STRESS)

STRUCTURAL ANALYSIS RESULTS(REACTION FORCES)
Reaction forces developing at fixed support
Sum of reaction forces (in Newtons)
FX FY FZ

STRUCTURAL ANALYSIS RESULTS(UX)

STRUCTURAL ANALYSIS RESULTS(UY)
0.0277 mm
0.000932 mm

STRUCTURAL ANALYSIS RESULTS(UZ)
0.00751 mm
0.000525 mm
0.000525 mm

STRUCTURAL ANALYSIS RESULTS(USUM)
0.0286 mm (Max. deformation)
0 mm (Min. deformation)

CONCLUSION OF STRUCTURAL ANALYSIS
From this structural analysis, we found that maximum stress (15.9
Mpa) occurring on bottom curved area near headstock leg. This is
occurring because
We can compare lathe bed with fixed beam by its construction.
When we apply force at carriage region, middle portion of bed tries
to bend downwards.
Maximum internal resistance forces develop at fixed support.
These forces tries to oppose deflection. Due to this resistance
forces maximum stress is inducing near lathe bed base
This induced stress is very much low as compared to
compressive strength (970 Mpa) of Gray cast iron. But this stress is
concentrating at small curved region.
We will change lathe bed design at this location to attain uniform
stress distribution

Lathe bed side walls after carriage region experiencing less stresses
Due to this we will remove material of side walls after carriage
region by adding ribs.
Base CAD model Modified CAD model

Modified CAD model
Base CAD model
Base CAD model Modified CAD model

MODAL ANALYSIS OF LATHE BED
Mode failures of lathe bed (mode -1 to mode – 6)

MODAL ANALYSIS OF LATHE BED
Above frequencies are natural frequencies of lathe bed at which mode
failure occurs. The shape of mode failure shown in previous slide
These values are extracted from modal analysis. The natural
frequencies are useful to under stand at what frequency lathe bed will
damage structurally due to vibrations which are induced during working
condition
Also these natural frequencies range should not vary much in modified
design

CAD MODELING OF LATHE BED
Model No. SB 1007
Overall
1550 x 724 x 559 mm
Mass 246 kg
Overall
1420 x 174.5 x 215.7
mm
Mass 97.992 kg

DESCRITIZING (MESHING) CAD MODEL
Element edge length 6 mm
Number of elements 539450
Number of nodes 122798
Mass 97.992 kg

STRUCTURAL ANALYSIS RESULTS(SZ)
Compressive stress 4.57 kPa
Tensile stress 5.68 kPa

STRUCTURAL ANALYSIS RESULTS(UY)
0.029 mm
0.00101 mm

STRUCTURAL ANALYSIS RESULTS(UZ)
0.00859 mm
0.00149 mm
0.00149 mm

STRUCTURAL ANALYSIS RESULTS(USUM)
0.0302 mm (Max. deformation)
0 mm (Min. deformation)

MODAL ANALYSIS OF MODIFIED LATHE BED
Mode failures of lathe bed (mode -1 to mode – 6)

MODAL ANALYSIS OF MODIFIED LATHE BED

STRUCTURAL ANALYSIS RESULTS COMPARISON
S.No Description Base Model Modified Model
1. Max. Von-Mises stress (MPa) 15.9 13.6
2. Max. Deformation (mm) 0.0286 0.0302
3. Min. Deformation (mm) 0 0
4. Mass (kg) 105.816 97.992
5. Reaction force in Y direction (N) 15823 15902

MODAL ANALYSIS RESULTS COMPARISON
Mode.No Description Base Model Modified Model
1. Frequency (Hz) 211.24 230.40
Deformation (mm) 204.898 238.068
2. Frequency (Hz) 474.16 507.81
3. Frequency (Hz) 595.13 572.46
4. Frequency (Hz) 634.89 649.25
5. Frequency (Hz) 794.16 838.73
6. Frequency (Hz) 1031.8 938.13

CONCLUSION
In this project, we have prepared Lathe bed CAD model of M/s South
Bend Lathe Co
The weight of the lathe bed before modification is 105.816 Kg, after
modifying the design weight of the bed has reduced to 97.992 kg. This weight
reduction is equal to 7.4% base model weight
We identified concentrated stress and low stress zones in lathe bed by
conducting structural analysis. We achieved linear stress distribution at
concentrated stress zones after lathe bed design modification
We conformed that modified Lathe bed CAD model is not deviating with base
Lathe bed CAD model in terms of vibrational damping capacity by conducting
modal analysis for 6 modes (Natural Frequencies). There is no much variation
in modal analysis results
Through these structural and modal analysis results, we can conclude that
modified model is best in terms of weight, stresses and damping capacity

weight optimization of lathe bed using FEA

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