introduction to CNC machine.

BY...
ANISH RANJAN JHA
3RD YEAR
PRESENTATION ON
CNC Milling and variation in
CNC MILLING
Faculty
Dr Basil kuriachen
04-07-2017 1

contents
 Introduction
 Types of milling operation
 Three dimensional cartesian
coordinate system
 Brief introduction on the cnc milling
programing
 Varaition analysis in cnc milling.
 conclusion
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INTRODUCTION
 MILLING is the cutting operation with a
geometrically specified cutting edge in which
the tool makes the rotating and movement , and
the feed as well as the infeed movement are
generally made by the work part.
 Milling machines may be operated manually or
by CNC.
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CLASSIFICATION OF MILLING
MACHINE
 According to the position of the milling axis
towards the work part i.e. Between face
milling and peripheral milling .In case of
face milling , the milling axis is located
vertically to machining.
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Computer and numerically
controlled Machines
Numerically Controlled (NC)
NC is the operation of machining tool by a
series of coded instruction consisting of
numbers, letters of the alphabets and
symbols , which is MCU(MACHINE
CONTROL UNIT) can understand.
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 Computer numerical controlled (CNC)
when the numerical control is
performed under the supervision , it is
called computer numerical
control(CNC).A programmer enters
some information in the program but
the computer calculates all necessary
data to get the job done
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Comparision
 Both are working in the same principle
only the way of execution is different
 The new system are faster , more
powerful, and more versatile
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Three dimensional cartesian
coordinate system
 The coordinate system used in most
cases of CNC machining is a
rectangular system, the technical
name for this being the Cartesian
Coordinate System.
 When writing coordinates it is
standard practise to write them in the
order of X, Y, and Z.
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Diagrammatic representative
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Continue.....
 By now you would have
seen X, Y and Z coordinates mentioned
everywhere. They refer to the planes, or
axes of movement of a CNC machine. In
simple terms they mean:
 X axis = Left and right movement
 Y axis = Forward and backward
movement
 Z axis = Up and down vertical movement
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CONTINUE...
 We now have 3 referenced axes in 3 dimensional space.
This means our CNC machines can now cut 2 dimensional
profiles and cut them at different depths using the Z (vertical)
axis. This movement suits the majority of CNC router, milling,
laser, plasma and 3D printer machines.
 However some may want more advanced movement than
this; such as the ability to rotate around these axes. This is
where A, B and C come in:
 A axis = Rotation around the X axis
 B axis = Rotation around the Y axis
 C axis = Rotation around the Z axis
04-07-2017 12

CNC milling programing
 These additional axes are usually seen on
much higher end, more expensive CNC
machines. The addition of rotation on axes
increases the difficulty of G-Code
programming immensely as well and
usually requires specialised CAM
software.
04-07-2017 13

 G00 Positioning
 G01 Linear interpolation
 G02 Circular interpolation/Helical interpolation
CW
 G03 Circular interpolation/Helical interpolation
CCW
 G04 Dwell
 G09 Exact stop
 G20 Input in inch
 G21 Input in mm
 G22 Stored stroke check function on
 G23 Stored stroke check function off
 G27 Check reference point return
 G28 Automatic return to reference position
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 G29 Automatic return from reference
position
 G30 2nd reference position return
 G32 Thread cutting
 G40 Cutter compensation cancel
 G41 Cutter compensation left
 G42 Cutter compensation right
 G50 Scaling cancel
 G52 Local coordinate system setting
 G53 Machine coordinate system selection
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 G70 Finish maching cycle
 G71 Inside and outside diameter rough
cutting cycle
 G72 Step rough cutting cycle
 G73 Pattern repeating
 G74 Peck drilling cycle-Z axis
 G75 Grooving in X axis
 G76 Thread cutting cycle
 G80 Canned cycle cancel
 G83 Peck drilling cycle
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 G84 Tapping cycle
 G85 Boring cycle
 G87 Back drilling cycle
 G88 Back tapping cycle
 G89 Back boring cycle
 G90 Cutting cycle ‘A‘
 G92 Thread cutting cycle
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 G94 (step)cutting cycle
 G96 Constant surface speed control
 G97 Constant surface speed control
cancel
 G98 Feed per minute
 G99 Feed per rotation
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M-code
 M00 Program stop
 M01 Optional stop
 M02 End of program
 M03 Spindle on CW
 M04 Spindle on CCW
 M05 Spindle stop
 M06 Tool change
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 M08 Coolant on
 M09 Coolant off
 M30 Program end and reset
 M48 Cancel
 M49 Bypass Override
 M94 Mirror image cancel
 M95 Mirror image of X axis
 M96 Mirror image of Y axis
 M98 Subprogram call
 M99 Subprogram end
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SAFETY CONDITION
Tool offset Work offset
G00 G43 H1Z10.0;
G00 Rapid travel
G43 Tool length
dimensional
compensation.
 G00 G90 G54 X 0.0
Y0.0;
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Tool Radius compensation
04-07-2017 22
Core portion Cavity
portion

Steps to write program in the
machine
 Write the introduction.
 Check the safety first.
 Get the tool ready.
 Getting closer
 Common comand.
 Stimulations
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Codes
 Name of program say: O0002
 G90 G49 G17 G21 G40 G15 G80 G53 Z0
 T2
 M3S600
 G0 G43 H2 Z50
 G0 G54 X-20.0 Y 20.0
 G01 G98 G83 Z-10 Q1 R2 F50
 X-20 Y-20
 X20 Y20
 X20 Y-20
 G0 G40 G80 Z50
 M30
04-07-2017 25

Some useful Advantages
 Complex shape can be obtained.
 Better surface finish compair to the
other machining operation.
 100% accuracy unless the user made
an programming error.
 Manufacturing industries heavily relay
on cnc machine nowdays.
04-07-2017 26

Variational analysis for CNC milling process
Accuracy of machining process strongly depends on the ability in
driving the machine tooltip along the nominal cutting path defined by
the machine control system..
The positioning errors of the tooltip is the result of different sources
ranging from machine structure defects to control system inaccuracy,
to deformation related to static and dynamic loads. Most of the error
is usually recovered by means of machine calibration, an expensive
and time-consuming procedure, which evaluates the distance between
the actual and nominal position of the tool tip, and applies a
compensation to the machine control system.
The calibration process could be faster and the machine process
could be more accurate if the contributions to the position error of the
tool tip are minimized according to an innovative design process
where the different error sources are simulated and evaluated in order
to forecast the best structure of the produced machine.
04-07-2017 27

Major causes of errors in the machine tool system
include imperfections and misalignments of guide-ways
of the sliding stages. The assembly errors of the
alignment of each axis, the
 non-parallelism of guide-ways and the profile errors of
guide- ways affect the accuracy of. 3-axis machine tools
and became more and more relevant in multi-axis
machine tools, where the assembly error of the
alignment of each axis is more significant..
04-07-2017 28

 Huge problems may present during the
assembly process if the tolerance study
on a subcomponent was not carried out or
was ineffectual. These problems will
introduce additional reworking time and
product costs which are not compatible
with today’s industry requirements.
04-07-2017 29

The case study
. Real GX series of CNC machine
 In our work we investigate
on the GX1000 vertical
machining center to provide
a realistic simulation of
position error of the tooltip
taking into account
different contributors,
ranging from geometric
defects to dynamic load.
04-07-2017 30

Continue...
Simplified model for VSA
 the VSA and preliminary
FEM analysis are
implemented separately. We
demonstrate accurate
simplified model to transfer
all the effective
characteristic of the
machine to have better
FEM analysis
04-07-2017 31

Geometric Dimensioning and
Tolerance (GD&T)
 According to the PMI approach, a complete set of
dimensional and geometrical tolerances describes the
errors admissible on the components of the CNC
machine. Therefore it is possible to carry out a
simulation of tool tip displacements taking into
account the contributions of all the CAD components
involved in the CNC machine. Although the GD&T
model is applied to the real machine, the simplified
model illustrated in is allows a faster analysis of error
contributors. We just illustrate the tolerances applied
to the base of the CNC machine.
04-07-2017 32

Kinematic analysis
 The motion of the sliding stages along the guide-ways modifies the
interaction of geometrical defects applied to the CAD models of CNC
machine components. A reliable analysis of tooltip displacements should
take into account the different positions of the sliding stages. Actually the
software for the kinematic simulation of devices does not allow for such
analysis. Due to software limitation, it is not possible to control the axes,
to stop the tooltip at the specific point in the working volume, to run the
variation simulation analysis (VSA). To overcome this limitation, we
provide a transitory solution to keep our goal. Working volume
encompasses limitless points. Furthermore, it is not feasible and is time-
consuming procedure to take into account whole space to see in every
point how much is the tool tip deviation. working volume and its
relationship with the whole machine.
 At the end of the simulation we have a result that is
the merging of GD&T and Kinematic analysis of the
CNC machine.
04-07-2017 33

Thermal analysis
 The thermal effects in the machining process are mainly concentrated on the tools, as
demonstrated by different papers [17]. Continuous usage of a machine tool causes heat
generation at the moving elements and the heat causes expansion of the various structural
elements of the machine tool. The expansion of the structural linkage of the machine
leads to inaccuracy in the positioning of the tool. Such errors
 are called thermal errors and may constitute a significant portion of the total error in a
machine tool. Thus the overall volumetric error of a machine tool is not only dependent on
errors due to the assembly and its specific kinematic structure but also on the thermal errors.
Some of the possible heat sources are:
 Bearing
 Gear and hydraulic oil
 Drives and clutches
 Pump and motors
 Guideways
 Cutting action and swarf
 External heat sources
 In a complete description of the behaviour of CNC machine, a finite element model of the
machine should be developed to analyse the thermal deformation resulting from
machine
 The deformation of the CNC machine structure related to heating process of engines and
friction should be evaluated in order to provide and accurate model.
04-07-2017 34

Finite element analysis (FEA)
The present study develops a finite element model along with
an end milling machine structure model to analyze the tooltip
errors in the milling process of workpieces. The structure of
tool milling machine is modeled with the CTETRA
 (4) mesh element that can more accurately simulate the
geometry and structural behavior of the machine. The
workpiece is not modeled here and we just consider the worst
case configuration during milling process. This study neglects
the dynamic effect during milling and assumes that the tool and
the workpiece deform to their static equilibrium positions at any
milling instant.
we introduced the preliminary model for FEM analysis in
order to see the effect of static loads on the tooltip position. We
create the Assembly of FEM in order to have to whole part in
their position respects to the other one illustrates the a detail of
the FEM models developed for finite element analisys.
04-07-2017 35

Results
04-07-2017 36
Results of the preliminary FEM model. Most critical zone in working volume

conclusion
 In the paper the authors illustrates the analysis of tooltip
positioning error in a CNC machine. Several error sources
are analyzed to develop, during the design phase, the best
solution to reduce the tooltip position error:
 Dimensional and geometrical tolerances
 Kinematic of CNC machine
 Thermal effects
 Static and dynamic loads
The paper illustrates, with different level of the detail, the
different approaches for contributors analysis and their
integration.
Further work is requested to provide a reliable industrial tool
and the future investigation should be divides in two different
paths:
04-07-2017 37

1)Model improvement
 The FEM model requires deeper investigation to simulate the effect of loads in
the working volume of the CNC machine. According to the scientific literature,
the solution could be derived from the Finite element analysis applied to sheet
metal assemblies. Such solution is available in different CAD software suites,
and allows for the analysis of stress and deformation in sheet metal parts under
different constraints and loads. The adoption of such solution will evaluate the
role of static and dynamic loads on the tooltip position error in the whole
working volume of the CNC machine.
 The FEM model should be effectively applied for the thermal analysis of the
structure of the CNC machine. Currently the effect of heating seem to be less
relevant than other sources of error, but it could be related to our pour modeling of
heating sources.
 The kinematic model requires a deeper analysis too. The current solution,
relying on the discretization of the working volume, should be improved in order
to carry out a complete analysis of kinematic consequences in the working
volume of CNC machine.
 Finally, we should improve the integration of the results of different analysis.
Such integration is operating on GD&T and Kinematic analysis, but it should
be improved in order to
04-07-2017 38

2)Software improvement
During our work by mean of Siemens software, NX PLM and
Teamcenter visualization, we figured out some technical
limitations, which prevent us from fast and more flexible
analysis. Our main goals in such area consist of the following
improvements:
 Improve the PMI method to allow for a faster transferring
of features and Tolerances from NX environment to the
Teamcenter visualization.
 Link the JT file with the Process document to improve the
application of modification in both the environments.
 Improve the kinematic assembly operation of Teamcenter
visualization. It is necessary to control the axis motion and
stop it to the desired position in order to perform a VSA
analysis in any points of the working volume.
04-07-2017 39

reference
Variational analysis for CNC milling process/
Armin Afkhamifar, Dario Antonelli, Paolo
Chiabert*
www.sciencedirect.com
www.sci-hub.com
Google
Wikipedia
CAD/CAM engineering book
04-07-2017 40

introduction to CNC machine.

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