Numerical control.pdf 1

NATIONAL INSTITUTE OF TECHNOLOGY
DURGAPUR
PRODUCTION ENGINEERING SESSIONAL
ME 852

INTRODUCTION TO 5 AXIS MACHINES
A WRITE-UP BY
Gaurav Joshi (10/ME/67)
Deepak Kumar (10/ME/68)
Khileshwar Prasad(10/ME/69)
Manish Kumar (10/ME/70)
Biswajit Bikash Paul (10/ME/71)
Ankur Thapa (10/ME/74)
Garima Das (10/ME/75)

UNDER THE GUIDANCE OF
Prof. Indrajit Basak and Prof.A.B Puri

CNC Machine
Numerical control (NC) is the automation of machine tools that are operated by precisely programmed
commands encoded on a storage medium, as opposed to controlled manually via hand wheels or levers, or
mechanically automated via cams alone. Most NC today is computer numerical control (CNC), in which
computers play an integral part of the control.
In modern CNC systems, end-to-end component design is highly automated using computer-aided design
(CAD) and computer-aided manufacturing (CAM) programs. The programs produce a computer file that is
interpreted to extract the commands needed to operate a particular machine via a post processor, and then
loaded into the CNC machines for production. Since any particular component might require the use of a
number of different tools – drills, saws, etc., modern machines often combine multiple tools into a single
"cell". In other installations, a number of different machines are used with an external controller and human
or robotic operators that move the component from machine to machine. In either case, the series of steps
needed to produce any part is highly automated and produces a part that closely matches the original CAD
design.

Examples of CNC Machines

CNC Mills
CNC mills use computer controls to cut different materials. They are able to translate programs consisting of
specific number and letters to move the spindle to various locations and depths. Many use G-code, which is
a standardized programming language that many CNC machines understand, while others use proprietary
languages created by their manufacturers. These proprietary languages are often simpler than G-code, not
transferable to other machines.
CNC Lathes
Lathes are machines that cut spinning pieces of metal. CNC lathes are able to make fast, precision cuts using
indexable tools and drills with complicated programs for parts that normally cannot be cut on manual lathes.
These machines often include 12 tool holders and coolant pumps to cut down on tool wear. CNC lathes have
similar control specifications to CNC mills and can often read G-code as well as the manufacturer's
proprietary programming language.
CNC Plasma Cutters
Plasma cutting involves cutting a material using a plasma torch. It is commonly used to cut steel and other
metals, but can be used on a variety of materials. In this process, an inert gas (such as compressed air) is
blown at high speed out of a nozzle; at the same time an electrical arc is formed through that gas from the
nozzle to the surface being cut, turning some of that gas to plasma. The plasma is sufficiently hot to melt the
material being cut and moves sufficiently fast to blow molten metal away from the cut.

CNC Electric Discharge Machining
Electric discharge machining (EDM), sometimes colloquially also referred to as spark machining, spark
eroding, burning, die sinking, or wire erosion, is a manufacturing process in which a desired shape is
obtained using electrical discharges (sparks). Material is removed from the workpiece by a series of rapidly
recurring current discharges between two electrodes, separated by a dielectric fluid and subject to an
electric voltage. One of the electrodes is called the tool-electrode, or simply the ‘tool’ or ‘electrode’, while
the other is called the workpiece-electrode, or ‘workpiece’.
When the distance between the two electrodes is reduced, the intensity of the electric field in the space
between the electrodes becomes greater than the strength of the dielectric (at least in some point(s)), which
breaks, allowing current to flow between the two electrodes. This phenomenon is the same as the
breakdown of a capacitor. As a result, material is removed from both the electrodes. Once the current flow
stops (or it is stopped – depending on the type of generator), new liquid dielectric is usually conveyed into
the inter-electrode volume enabling the solid particles (debris) to be carried away and the insulating
proprieties of the dielectric to be restored. Adding new liquid dielectric in the inter-electrode volume is
commonly referred to as flushing. Also, after a current flow, a difference of potential between the two
electrodes is restored to what it was before the breakdown, so that a new liquid dielectric breakdown can
occur.
CNC Wire EDM
Also known as wire cutting EDM, wire burning EDM, or traveling wire EDM, this process uses spark erosion
to machine or remove material with a traveling wire electrode from any electrically conductive material. The
wire electrode usually consists of brass or zinc-coated brass material.
CNC Sinker EDM
Sinker EDM, also called cavity type EDM or volume EDM, consists of an electrode and workpiece submerged
in an insulating liquid—often oil, but sometimes other dielectric fluids. The electrode and workpiece are
connected to a suitable power supply, which generates an electrical potential between the two parts. As the
electrode approaches the workpiece, dielectric breakdown occurs in the fluid forming a plasma channel) and
a small spark jumps.
CNC Water Jet Cutter
A water jet cutter, also known as a waterjet, is a tool capable of slicing into metal or other materials (such as
granite) by using a jet of water at high velocity and pressure, or a mixture of water and an abrasive
substance, such as sand. It is often used during fabrication or manufacture of parts for machinery and other
devices. Waterjet is the preferred method when the materials being cut are sensitive to the high
temperatures generated by other methods. It has found applications in a diverse number of industries from
mining to aerospace where it is used for operations such as cutting, shaping, carving, and reaming.

Other CNC Tools
Many other tools have CNC variants, including:
Drills
EDMs
Embroidery machines
Lathes
Milling machines
Wood routers
Sheet metal works (Turret punch)
Wire bending machines
Hot-wire foam cutters
Plasma cutters
Water jet cutters
Laser cutting
Oxy-fuel
Surface grinders
Cylindrical grinders
3D Printing
Induction hardening machines[citation needed]
submerged welding
knife cutting
glass cutting

ADVANTAGES

1. CNC machines can be used continuously 24 hours a day, 365 days a year and only need to be switched off
for occasional maintenance.
2. CNC machines are programmed with a design which can then be manufactured hundreds or even
thousands of times. Each manufactured product will be exactly the same.
3. Less skilled/trained people can operate CNCs unlike manual lathes / milling machines etc.. which need
skilled engineers.
4. CNC machines can be updated by improving the software used to drive the machines
5. Training in the use of CNCs is available through the use of ‘virtual software’. This is software that allows
the operator to practice using the CNC machine on the screen of a computer. The software is similar to a
computer game.
6. CNC machines can be programmed by advanced design software such as Pro/DESKTOP®, enabling the
manufacture of products that cannot be made by manual machines, even those used by skilled designers /
engineers.
7. Modern design software allows the designer to simulate the manufacture of his/her idea. There is no need
to make a prototype or a model. This saves time and money.
8. One person can supervise many CNC machines as once they are programmed they can usually be left to
work by themselves. Sometimes only the cutting tools need replacing occasionally.
9. A skilled engineer can make the same component many times. However, if each component is carefully
studied, each one will vary slightly. A CNC machine will manufacture each component as an exact match.

DISADVANTAGES
1. CNC machines are more expensive than manually operated machines, although costs are slowly coming
down.
2. The CNC machine operator only needs basic training and skills, enough to supervise several machines. In
years gone by, engineers needed years of training to operate centre lathes, milling machines and other
manually operated machines. This means many of the old skills are been lost.
3. Less workers are required to operate CNC machines compared to manually operated machines.
Investment in CNC machines can lead to unemployment.
4. Many countries no longer teach pupils / students how to use manually operated lathes / milling machines
etc... Pupils / students no longer develop the detailed skills required by engineers of the past. These include
mathematical and engineering skills.

Axes of CNC machine tool
In CNC machine tool, each axis of motion is equipped with a driving device to replace the handwheel of the
conventional machine tool. A axis of motion is defined as an axis where relative motion between cutting tool
and workpiece occurs. The primary axes of motion are referred to as the X, Y, and Z axes and form the
machine tool XYZ coordinate system. Figure shows the coordinate system and the axes of motion of a
typical machine tool. Conventionally machine tools are designated by the number of axes of motion they can
provide to control the tool position and orientation.

In these CNC machine tools, the tool is controlled along the three axes (X, Y, and Z) simultaneously, but the
tool orientation doesn’t change with the tool motion .
If the tool axis orientation varies with the tool motion in 3 dimension space, 3-axis machine gets converted
into multi-axis orientation machine (4-, 5-, or 6-axis). Figure shows the schematic of tool motion in a multiaxis CNC machine tool.

Interpolation
It is known that 5-axis machining produces higher metal removal rates and improved surface finish , thereby
eliminating the secondary cleanup of scallops created by 3-axis machining. However the conventional
methods of 5-axis machining utilize offline part programming approaches by which the CAD system divides
the surface into a set of line segments that approximates the surface at desired tolerance level. These line
segments are further processed by line processors to produce straight line g-codes which constitute the
commands needed to control the machine. In the CNC, the g-codes the fed to the interpolator. These offline
approaches for 5-axis CNC machining either assumes a constant tool orientation along each segment, or
assumes a linear change in successive orientation between each successive end points. The constant
orientation algorithm causes severe roughness around the end points along the surface , since the
orientation changes are abrupt at these points. The linear orientation algorithm produces a better surface.

From 3-axis to 5-axis machining
The use of 3-axis tool path is sufficient as long as the part is not very deep with respect to the cutter
diameter. If the part is very deep and has narrow cavities the usage of pure 3-axis tool paths is not sufficient
for the complete finishing process of the part. Especially, if hard material has to be milled the usage of long
cutters results in a bad surface quality and long machining times. Fig.1 shows the situation for a 3-axis tool
path. Here, the minimum tool length must be very long in order to reach all regions of the tool path
vertically.
For that reason the spindle is tilted in a way that a specific region of the part can be machined with a shorter
tool. The process of setting a constant angle to the spindle is well known as 3+2-axis machining. For complex
parts it is common that dozens of views need to be defined in order to fully cover the whole part. The
resulting tool paths must overlap leading to not only an overhead in machining time, but also difficulty in
blending perfectly the different machining views. At the same time the number of lead-in and out
movements increase dramatically which results in surface quality problems and more tool movements.
Finally, programming this way is quite difficult for the user and often the sum of all views does not cover the

whole geometry. Fig.2 shows four views for the part yet there is still a region not covered in the centre of
the part. This region would again need additional views or it must be eroded. Summarizing, it is clear that
the part can be machined with a shorter cutter but for an additional price. Many overlapping views need to
be defined which in return lead to surface quality problems due to a higher number of lead-in movements
and machine blending. The programming is time consuming, needs manual interaction and is an error-prone
process.
In order to overcome the drawbacks of 3+2-axis machining new strategies for simultaneous 5-axis
tool paths have been developed. Simultaneous 5-axis machining incorporates the 3 linear axes as well as 2
rotational axes at the same time. It solves all the problems of 3+2-axis machining. The cutter can be very
short, no overlapping views need to be generated, the probability of missing an area is much smaller and the
machining can be performed continuously without additional lead-ins and lead-outs (Fig.3).

Strategies for 5-axis tool paths
Today’s CAM systems offer a variety of 5-axis tool paths. The general problem with simultaneous 5-axis
machining is that five axes simply offer too much freedom. The two degrees of freedom for the axis tilts
result for any tool path position in an infinite number of correct tilt values which are still collision free but
completely different. Finding the optimum angles is important. As a consequence any CAM-system needs
parameters by the user in putting constraints to the tool path creation process. Fig.6 shows an example of a
simple z-level finishing cutter path around a hemisphere. Each of the three 5-axis tool paths was generated
with a different constraint. The first is generated normal to surface, the second is directing to an attraction
point on a centre line above the hemisphere and the third uses a square as leading curve. The example
shows that constraints are not only necessary but also need to be defined very well. The constraints two and
three will probably never be milled because they don’t make sense from a machining point of view.
The dependencies are the milling machine itself with its angle limitations and its physical ability to run
simultaneous 5-axis tool paths. Also the used material, the surface quality, the 5-axis strategy and available
cutter are influencing the user’s constraints. In general we can distinguish the following main types of 5-axis
strategies.
Normal to surface: The cutter follows the surface normal.
Constant angle: Any axis is part of a cone having a constant angle. The other degree of freedom
is taken from the surface normal or a leading entity (e.g. point or curve).
Guiding: The shortest distance to a guiding entity (e.g. point or curve) defines the tilt axis.
Surface specific: Constraints are given by the surface itself. Examples are rolling tool paths where
the cutter rolls along a ruled surface or strategies for tubes and impellors.

From the user’s point of view he just has to choose a strategy (depending on whatever he thinks is
suitable) and run the calculation. During the calculation process the problem may arise that a constraint
cannot be held along the whole surface. An example for this is the strategy normal to surface (Fig.7). Here
the tool path climbs from a bottom plane onto a box. The real normals are shown in the left picture.
It is clear, that it would never be machined directly because the angle difference is too big at two positions
and some points would lead to collisions with the holder. To be able to smoothly machine this tool path we
must temporarily remove the normal constraint by allowing anticipation and post compensation of angle
changes. The smoothness of a 5-axis tool path is very important for the efficiency on the machine.
Smoothing a tool path usually means locally removing its constraints. In addition the process of collision
avoidance has the same effect. The constraints cannot be held if the tool holder must avoid a collision. Since
ball cutters are usually used for machining 5-axis tool paths a slight change of the tilt angle is not a problem.

Five Axis CNC

Five axis CNC machining refers to the ability of the CNC machine to perform movement about five different
axis simultaneously. Most CNC manufacturers define their machines movement starting with the three
primary axis, X. Y and Z, with the Z axis being parallel to the tool spindle, see Figure 1. The other two axis are
given by the machines ability to rotate about the X and Y axis. Axis Rx pivots or rotates parallel and about the
X axis. Axis Ry pivots or rotates parallel to and about the Y axis. Axis Rz is represents the rotation of the
cutting tool installed into the machine spindle center.

ADVANTAGES OF 5 AXIS CNC
The benefits of five-axis machining is the machines ability to machine complex shapes in a single setup.
This reduces the machinist setup time and increases production rates . By eliminating multiple
set-ups, time and errors are reduced. Additionally, the feature-to-features accuracy is improved
because the same zero or datum reference frame is used throughout the manufacturing process. Other
advantages of five axis machining is the since simultaneous movement is allowed along the X and Y axis,
shorter and more rigid tools may be used. Also, higher spindle/cutting tool speeds may be achieved while

reducing the load on the cutting tool. Shorter and thicker cutters also reduce vibration when machining deep
pockets or contoured features with three-axis machines.

Application
Applications for five axis CNC Machining are complex three dimensional profiles. These geometric are
common for impellars, turbine blades, and plastic mold tools.

Dedicated 5-axis CNC machining centers
There are three types of machine configurations for 5-axis machining.

1. Swivel Head with Rotary Table
2. Integrated Trunnion Table
3. Traveling Column

5 Axis CNC Machine Codes
According to HAAS Automation, some of the codes are:
Group
01
01
01
01
06
06

Code
G00
G01
G02
G03
G20*
G21*

Function
Rapid positioning
Linear interpolation
Circular interpolation clockwise (CW)
Circular interpolation counterclockwise (CCW)
Inch input (in.)
Metric input (mm)

Manufacturers of 5 axis CNC machines
HURCO , TARUS, CMS north America, OKUMA , CNC TAKANG Taiwan, maximart corporation, YCM (YEONG
CHIN MACHINERY INDUSTRIES CO., LTD )

TARUS TPGM5X1083 SPECIFICATIONS

Specification
X Axis Travel

3,048 mm

(120”)

Aand

2,540 mm

(100”)

Z Axis Travel

1,117 mm (44”)

Space Between Columns

3886 mm (153”)

Worktable Size, L x W

3568 mm x 2235 mm (144” x 88”)

X, Y and Z Axis Maximum Feed-rate

30 meters per minute (1,200’ per minute)

A Axes Tip

+/- 100 degrees.

B Axis

continuous

A and B Axis Positioning Peak Torque

4,073 NM

A and B Axis Positioning Feed

30 degree per second

Milling Spindle

HSK 63A
0-20,000 RPM (3 axis and 5 axis milling)
4,000 RPM base speed
70 NM constant torque
160 NM peak torque
29 KW rated power

Linear Accuracy (X, Y and Z)

± .013 mm , ± 0.006 mm, ± 0.005 mm

CNC SYSTEM

TARUS, HEIDENHAIN iTNC, FANUC, SIEMENS, FIDIA

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