1

1 UNIT – 3 B

Course Objectives :
• To acquire knowledge on CNC part programming.

UNIT – IV
Introduction to Part Programming: Introduction, Principle of operation of NC and CNC,
General Programming Features of CNC systems, Programming of CNC Machine Tools,
CNC Turning - Gear Blank, Casting, Manufacturing Operations, Tool Motion
Parameters, Virtual Machining.

Course Outcomes : At the end of the course students will be able to

• Appreciate the importance of CNC machines to write the part programming for
different components.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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2 UNIT – 3 B
4.1 Introduction to Part Programming
What is Part Programming?
Introduction to Part Programming
• Definition:
Part programming refers to the process of creating a set of instructions or code that directs a CNC machine on how to move and operate in order
to manufacture a specific part. This code controls the movement of the cutting tool along various axes, the speed at which it operates, and the
sequence of operations required to complete the part.
Importance of Part Programming:
• Precision & Accuracy:
A well-written part program ensures that the CNC machine produces highly accurate and repeatable parts. This is critical in industries such as
aerospace, automotive, and medical device manufacturing, where tolerances are very tight.
• Automation:
Part programming allows for automated production, reducing human intervention, increasing production speed, and lowering the risk of errors.
• Flexibility:
A CNC machine can be reprogrammed quickly to produce different parts, offering flexibility in manufacturing different products on the same
machine with minimal downtime.
Types of Part Programming:
1. Manual Part Programming:
o The machine operator writes the code manually, typically using G-codes and M-codes.
o Advantages: Full control over the machining process.
o Challenges: Time-consuming, requires high skill level, and prone to human error.
2. Computer-Aided Part Programming (CAP):
o Programming is done using CAM (Computer-Aided Manufacturing) software which generates the code automatically.
o Advantages: Faster, less prone to errors, easy to modify.
o Examples of CAM Software: Fusion 360, Mastercam, Siemens NX.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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4.1 Introduction to Part Programming
Process of Part Programming:
Introduction to Part Programming

• Geometric Modeling:
o Define the geometry of the part to be machined, either manually
or using CAD software.
• Tool Path Generation:
o Create paths for the cutting tool based on the part geometry and
the desired operations (e.g., milling, turning, drilling).
• Coding (G-codes and M-codes):
o Generate the CNC code that defines the specific machine
instructions, including cutting paths, feed rates, spindle speeds,
tool changes, and coolant on/off commands.
Key Terms in Part Programming:
• G-codes: These control the movement of the CNC machine,
specifying positioning, linear or circular cutting motions, and more.
• M-codes: These control the auxiliary functions such as tool changes,
coolant activation, and spindle on/off.
• Feed Rate: The speed at which the cutting tool moves relative to the
workpiece.
• Spindle Speed: The rotational speed of the spindle holding the cutting
tool.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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4 UNIT – 3 B
4.1 Introduction to Part Programming
Manual vs Computer-Aided Part Programming
Introduction to Part Programming

Aspect Manual Part Programming Computer-Aided Part Programming (CAP)

Using specialized software to generate CNC programs
Definition Writing CNC program manually using G and M codes.
automatically.
More user-friendly with graphical interfaces and
Ease of Use Requires in-depth knowledge of CNC codes and formats.
automation tools.
Complexity Suitable for simple parts and operations. Capable of handling complex geometries and toolpaths.
Faster program generation due to automation and
Time Efficiency Time-consuming, especially for intricate designs.
templates.
Error Rate Higher chances of human errors. Reduced errors with built-in validation tools.
Learning Curve Steep learning curve; requires CNC expertise. Easier for beginners due to visual aids and user guidance.
Flexibility Flexible for minor, quick edits directly in the program. Editing requires changes in the software interface.
Visualization No visualization; relies on operator's interpretation. Provides simulation and 3D visualization of toolpaths.
Cost Low initial cost (just a CNC machine and operator). Higher due to software and hardware investment.
Integrates well with CAD/CAM systems for seamless
Integration Standalone; limited integration with other systems.
workflow.
Application Best for low-volume production or simple tasks. Ideal for high-volume production and complex parts.
Reusable templates ensure consistency across similar
Repeatability Manual reprogramming needed for similar parts.
parts.
Advanced algorithms optimize toolpaths and machining
Optimization Limited scope for optimization; trial-and-error process.
parameters.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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5 UNIT – 3 B
4.2 Principle of Operation of NC and CNC
Numerical Control (NC):
Definition:
Principle of Operation of NC and

Numerical Control (NC) is a method of controlling machine tools using a sequence of numbers, letters, and symbols. It’s a form
of automated control where pre-programmed commands determine the motion of the cutting tool and workpiece.
Principle of Operation of NC Machines:
• Manual Input of Data:
o In NC systems, the machine operator manually inputs the data using punched tapes, cards, or hardwired controllers.
o The part program is created manually using codes, and the data is fed into the NC machine via a physical medium such as a
punched tape or paper.
• Basic Workflow:
CNC

o Punched Tape Preparation:

A part program is prepared and punched into a tape with holes representing codes (G-codes, M-codes) controlling the
machine's movements.
o Tape Reader:
The punched tape is read by the NC machine's tape reader, which decodes the information and sends it to the control
system.
o Machine Operation:
The control system processes the input and moves the machine tool according to the programmed instructions.
• Limitation of NC:
o No Feedback:
NC machines lack feedback systems, meaning the machine does not adjust automatically if there’s an error or deviation.
o Program Storage:
Data is stored on physical media (e.g., punched tapes), making program storage and editing cumbersome.
Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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6 UNIT – 3 B
4.2 Principle of Operation of NC and CNC
Computer Numerical Control (CNC):
Definition:
Principle of Operation of NC and

CNC stands for Computer Numerical Control. It represents the evolution of NC by incorporating computers into the control
process, making the entire machining process more flexible, efficient, and automated.
Principle of Operation of CNC Machines:
• Direct Control by a Computer:
o CNC systems use a computer as the control unit to interpret a program written in G-code and M-code, automatically
controlling the machine tools' movements.
• Basic Workflow:
o Part Program Creation:
CNC

The part program is created using CAM software or written manually using G-codes and M-codes on a computer.
o Program Input:
The program is fed directly into the CNC machine’s controller using digital media (USB, direct transfer from CAM, or
network).
o Control System:
The CNC controller processes the program, controls the machine's toolpath, speed, and other parameters, and uses real-
time feedback to make adjustments.
o Feedback Loop:
CNC machines often incorporate feedback systems (e.g., encoders) to ensure that the actual movements of the machine
match the programmed instructions, adjusting for any discrepancies.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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7 UNIT – 3 B
4.2 Principle of Operation of NC and CNC
Key Components of CNC Machines:
Principle of Operation of NC and

• CNC Controller:
The "brain" of the machine that interprets the part program and sends commands to the motors and actuators.
• Feedback Devices (Encoders):
These devices provide real-time position and velocity feedback to the CNC controller, ensuring accuracy and precision.
Advantages of CNC Over NC:
• Flexibility:
Programs can be stored and reused digitally. Adjustments can be made easily without physically altering the data medium.
• Precision and Accuracy:
CNC systems are highly accurate due to feedback mechanisms, ensuring minimal errors in machining.
CNC

• Automation and Productivity:

CNC machines can run unattended and produce parts continuously, improving efficiency and reducing the need for manual
intervention.
• Complex Machining:
CNC can handle more complex geometries and multiple operations in a single setup, which is challenging for NC machines.
Comparison Between NC and CNC:
Feature NC Machines CNC Machines
Control Unit Hardwired, Punched Tape Computer-Based Control
Feedback System None Closed-Loop Feedback (Encoders)
Data Storage Punched Tape, Physical Medium Digital, Stored Electronically
Flexibility Limited High, with easy program modifications
Program Editing Difficult (manually edit tape) Easy (via computer)
Automation Low High
Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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8 UNIT – 3 B
4.3 General Programming Features of CNC Systems
Introduction to CNC Programming:
General Programming Features of

• Definition:
CNC programming involves creating a set of instructions for a computer to control the motion and operation of a machine
tool. These instructions are usually written in G-code and M-code, which are industry-standard languages for controlling CNC
machines.
Main Features of CNC Programming:
1. G-Codes:
CNC Systems

o Definition:
G-codes are the most common commands in CNC programming, used to control the movements of the machine tool.
Each G-code starts with the letter "G" followed by a number that signifies a specific action.
o Common G-Codes:
▪ G00: Rapid positioning (non-cutting move)

▪ G01: Linear interpolation (cutting move in a straight line)

▪ G02: Circular interpolation (clockwise arc)

▪ G03: Circular interpolation (counterclockwise arc)

▪ G90: Absolute positioning mode

▪ G91: Incremental positioning mode

o Usage Example:
G01 X10 Y5 F100;
This command instructs the machine to move in a straight line to the coordinates X=10, Y=5 at a feed rate of 100 units
per minute.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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9 UNIT – 3 B
4.3 General Programming Features of CNC Systems
Main Features of CNC Programming:
General Programming Features of

2. M-Codes:
o Definition: M-codes control miscellaneous functions of the machine such as starting and stopping the spindle, coolant
control, and tool changes.
o Common M-Codes: o Usage Example:
▪ M03: Start spindle (clockwise) M03 S1500;
▪ M05: Stop spindle This command starts the spindle rotating at 1500 RPM.
CNC Systems

▪ M06: Tool change

▪ M08: Coolant on

▪ M09: Coolant off

3. Coordinate Systems:
o Machine Coordinate System (MCS):
Refers to the fixed origin (usually the machine's home position) and coordinates defined relative to it.
o Work Coordinate System (WCS):
Allows the operator to define the origin relative to the workpiece for easier part programming.
o Absolute vs. Incremental Positioning:
▪ Absolute (G90): All tool movements are based on a fixed origin.

▪ Incremental (G91): Tool movements are made relative to the current position.

o Example of Absolute Positioning (G90): o Example of Incremental Positioning (G91):

G90 G01 X50 Y25 F200; G91 G01 X10 Y5 F200;
Move the tool to X=50, Y=25 based on the Move the tool 10 units in the X direction and 5
absolute origin. units in the Y direction from its current position.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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10 UNIT – 3 B
4.3 General Programming Features of CNC Systems
Main Features of CNC Programming:
General Programming Features of

4. Modal Commands:
o Definition: Modal commands remain active until another command overrides them. For example, when you set a cutting mode (G01), it
remains active until a different command (e.g., G00 for rapid movement) is issued.
o Example: G01 X30 Y10;
X40 Y20; // G01 is still active, so the tool will continue cutting
5. Interpolation:
CNC Systems

o Linear Interpolation (G01): Tool moves in a straight line from one point to another.
o Circular Interpolation (G02, G03): Tool moves in an arc, either clockwise (G02) or counterclockwise (G03).
o Example of Circular Interpolation: G02 X50 Y50 I10 J10;
Move the tool along a clockwise arc to X=50, Y=50, with the center of the arc offset 10 units in both the X and Y directions (I and J).
6. Feed Rate and Spindle Speed:
o Feed Rate (F): The speed at which the cutting tool moves relative to the workpiece, usually measured in millimeters per minute
(mm/min) or inches per minute (ipm).
o Spindle Speed (S): The rotational speed of the spindle, which holds the cutting tool, usually measured in revolutions per minute (RPM).
o Example: G01 X30 Y10 F150; // Feed rate of 150 mm/min
M03 S2000; // Spindle speed of 2000 RPM
7. Tool Offsets and Compensation:
o Tool Length Offset (TLO): Accounts for the length of different tools to ensure accurate cutting depths and positions.
o Tool Radius Compensation: Adjusts the tool path to account for the tool's radius when cutting complex geometries, using codes like G41
(left compensation) and G42 (right compensation).
o Example: G41 D01; // Activate tool radius compensation (left)

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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4.3 General Programming Features of CNC Systems
Additional Programming Features:
General Programming Features of

▪ Subroutines and Loops:

CNC systems allow for the use of subroutines to repeat a block of code multiple times, which is useful for repetitive
machining tasks.
Example: M98 P100 L5; // Call subroutine P100, repeat 5 times
▪ Probing and Tool Measurement:
CNC machines can be equipped with probing systems to automatically measure the workpiece and tools, helping to
CNC Systems

improve accuracy and reduce setup times.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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12 UNIT – 3 B
4.4 Programming of CNC Machine Tools
Programming of CNC Machine Tools
• What is CNC Machine Tool Programming?
CNC machine tool programming refers to the process of creating instructions (usually in G-code and M-code) that control the machine's
tool movements, speeds, feed rates, and other functions necessary to manufacture a part. The CNC controller reads these instructions
and executes them to perform the desired machining operations.
Steps in CNC Machine Tool Programming:
1. Define the Part Geometry:
o Input Design Information:
The first step in programming is to define the geometry of the part, typically done using Computer-Aided Design (CAD) software. This
design is then used as a reference for creating the toolpaths in CNC programming.
o CAM Integration:
The CAD model is often imported into Computer-Aided Manufacturing (CAM) software, where the toolpaths for the CNC machine are
generated based on the part’s geometry.
2. Choose the Machining Operations:
o Machining Process Selection:
Select the appropriate machining processes required for producing the part. These include:
▪ Turning: Removing material by rotating the workpiece while the tool moves linearly.

▪ Milling: Cutting using a rotating tool along multiple axes.

▪ Drilling: Creating holes in the workpiece.

▪ Grinding: Finishing operations for fine surface finishes.

o Example Operation:
▪ Turning: Used for cylindrical parts.

▪ Milling: Used for complex shapes or flat surfaces.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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13 UNIT – 3 B
4.4 Programming of CNC Machine Tools
Programming of CNC Machine Tools
Steps in CNC Machine Tool Programming:
3. Select the Tools:
o Tool Selection Based on Material and Operation:
▪ The tools used for cutting, such as drills, end mills, and turning tools, must be selected based on the material of the workpiece and

the type of operation.

▪ For example, HSS (High-Speed Steel) or carbide tools are often used in turning and milling.

o Tool Library in CAM Software:

CAM software typically has a tool library where you can select tools with predefined dimensions and parameters.
4. Generate the Toolpath:
o Defining Tool Movements:
The toolpath defines the movement of the cutting tool in relation to the workpiece. The path should be optimized for:
▪ Efficiency: Minimize cutting time.

▪ Precision: Ensure accurate machining.

▪ Tool Life: Maximize tool life by choosing appropriate feed rates and speeds.

o CAM Software:
In most cases, the toolpaths are automatically generated by CAM software based on the part geometry, material, and tool selection.
5. Set Feed Rates and Spindle Speeds:
o Feed Rate (F): The speed at which the tool advances through the material. It is usually specified in mm/min or inches/min. The appropriate
feed rate depends on the material being cut, tool diameter, and the operation type.
o Spindle Speed (S): The rotational speed of the spindle, measured in RPM. The spindle speed is determined based on the cutting tool and
the material's machinability.
o Example: For steel, a lower spindle speed and feed rate are generally required compared to aluminum due to differences in machinability.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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14 UNIT – 3 B
4.4 Programming of CNC Machine Tools
Programming of CNC Machine Tools
Steps in CNC Machine Tool Programming:
6. Generate the G-Code and M-Code:
o Post-Processing in CAM Software:
After setting all parameters, the CAM software generates the CNC program in the form of G-codes and M-codes, which
are machine-readable instructions. The generated program can then be transferred to the CNC machine.
o Example G-code Block:
G00 X0 Y0; // Rapid move to the start position
G01 X50 Y50 F100; // Linear cutting move to X=50, Y=50 at a feed rate of 100 mm/min
M03 S1500; // Start spindle at 1500 RPM
G02 X100 Y100 I25 J25; // Circular arc move to X=100, Y=100 with an arc center at I=25, J=25
M05; // Stop spindle
7. Simulation and Verification:
o Simulate Toolpath:
Before running the program on a physical machine, the toolpath can be simulated in CAM software. This step helps verify
that:
▪ There are no collisions between the tool and workpiece.

▪ The cutting strategy is efficient.

▪ The tool movement follows the intended design.

o Adjustments:
Any errors or inefficiencies found during simulation can be corrected by adjusting the toolpath, feed rate, or spindle
speed.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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15 UNIT – 3 B
4.4 Programming of CNC Machine Tools
Steps in CNC Machine Tool Programming:
Programming of CNC Machine Tools

8. Transfer the Program to the CNC Machine:

o Upload Program:
The G-code program is transferred to the CNC machine’s controller either via a direct network connection, USB, or
another storage device.
o Program Editing:
Minor edits to the program (such as changes to tool offsets or feed rates) can be made directly on the CNC machine
before starting the operation.
9. Setup the Workpiece and Tools on the Machine:
o Mount the Workpiece:
Securely mount the workpiece on the CNC machine’s table or chuck to ensure it remains fixed during machining.
o Install the Tools:
Load the appropriate tools into the machine’s tool holder, ensuring the correct tool offsets are set in the CNC controller.
10. Execute the Program:
o Run the Program:
Once all the preparations are completed, the program is executed, and the CNC machine performs the machining
operations as per the G-code instructions.
o Monitor the Process:
While CNC machines can run autonomously, operators typically monitor the process to ensure that there are no issues
(e.g., tool wear, unexpected vibrations, etc.).
Key Points in CNC Programming:
• Safety First: Always simulate the toolpath and verify the program to prevent crashes and tool damage.
• Efficiency: Optimize tool paths, feed rates, and speeds to minimize machining time without sacrificing quality.
• Accuracy: Use proper tool offsets, compensation, and coordinate systems to achieve the desired precision.
Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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16 UNIT – 3 B
4.5 CNC Turning – Gear Blank, Casting, Manufacturing Operations
CNC turning is a subtractive manufacturing process in which a rotating workpiece is shaped using a stationary cutting tool. The
CNC Turning – Gear Blank, Casting,

cutting tool moves in a linear direction while the workpiece rotates to produce cylindrical parts with precise dimensions.
Common Applications: CNC turning is used to produce components like shafts, bushings, bolts, and gear blanks.
Gear Blank Production via CNC Turning:
Manufacturing Operations

1.What is a Gear Blank?

•Definition: A gear blank is a pre-machined cylindrical piece of material from which gears are produced. It serves as the
foundation for subsequent gear cutting and finishing operations. Gear blanks are typically made from materials like steel,
aluminum, or cast iron, depending on the gear's final application.
2.Process of CNC Turning for Gear Blanks:
Step 1: Mounting the Blank on a Lathe Chuck: The gear blank is securely clamped on the CNC lathe’s chuck, allowing it to
rotate at high speeds during machining.
•Step 2: Rough Turning the Outer Diameter: The first operation is to rough-turn the outer diameter of the gear blank to bring it
closer to the final dimensions, leaving a small allowance for finishing.
•Step 3: Facing the End Faces: A facing operation is performed to machine the end faces of the blank, ensuring they are flat
and perpendicular to the axis of rotation.
•Step 4: Precision Turning of the Outer Diameter: A finishing pass is made on the outer diameter to achieve the required
tolerance and surface finish. This ensures the blank is ready for gear cutting operations.
•Step 5: Bore Turning (If Needed): If the gear design includes a central bore, CNC turning is used to precisely machine the
internal diameter of the gear blank.
3. Advantages of CNC Turning in Gear Blank Production:
•Precision: CNC turning ensures high dimensional accuracy for the gear blank, which is critical for proper gear engagement in
final assemblies.
•Efficiency: CNC machines can produce gear blanks quickly and consistently, reducing manual intervention and cycle time.
•Flexibility: CNC machines can be programmed to handle various sizes and shapes of gear blanks, allowing manufacturers to
switch between different jobs with minimal setup.
Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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17 UNIT – 3 B
4.5 CNC Turning – Gear Blank, Casting, Manufacturing Operations
CNC Turning – Gear Blank, Casting,

CNC Machining of Castings:

1. What is a Casting? Casting is a process where molten metal is poured into a mold to create a desired shape. Once cooled and
solidified, the casting is ready for secondary machining operations, like turning, to achieve the final specifications.
Manufacturing Operations

2. CNC Turning Operations for Castings:

o Step 1: Mounting the Casting on the Lathe:
The casting is securely mounted on the CNC lathe’s chuck. Due to the rough surface of castings, extra care is needed
to ensure stability and precision during turning.
o Step 2: Rough Turning to Remove Excess Material:
Castings often have excess material, or “flash,” which is removed during rough turning. This operation ensures that the
casting is brought closer to the desired dimensions.
o Step 3: Finishing Operations:
Once the rough turning is completed, precision turning is carried out to achieve the final dimensions and surface finish.
Features such as bores, shoulders, and grooves are machined during this stage.
o Step 4: Secondary Operations (If Needed):
Depending on the casting's complexity, additional operations like drilling, tapping, or boring may be performed to
achieve the final design.
3. Advantages of CNC Turning in Castings:
o Precision in Complex Shapes:
CNC turning allows for precision machining of castings, which often have intricate shapes and features.
o Material Efficiency: CNC turning of castings removes only the necessary amount of material, minimizing waste and
reducing the cost of raw materials.
o Surface Finish: The machining process helps improve the surface finish of cast parts, removing the rough texture left by
the casting process.
Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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18 UNIT – 3 B
4.5 CNC Turning – Gear Blank, Casting, Manufacturing Operations
Manufacturing Operations in CNC Turning:
CNC Turning – Gear Blank, Casting,

1. Facing:
A turning operation used to create a flat surface on the end of the workpiece (gear blank or casting).
Manufacturing Operations

To ensure the surface is perpendicular to the rotational axis and meets dimensional requirements.
2. Turning (Rough and Finish):
Rough Turning: Removes large amounts of material to shape the workpiece.
Finish Turning: Follows rough turning to produce the final dimensions and surface finish.
3. Boring:
An internal machining process where the internal diameter of the workpiece (such as a gear blank) is increased and precisely
sized.
Boring is used to machine holes in castings or pre-machined gear blanks.
4. Grooving:
Grooving involves cutting a narrow channel on the surface of the workpiece.
Often used for creating retaining grooves or to prepare parts for snap rings or o-rings.
5. Threading:
Threading involves cutting threads (internal or external) on a cylindrical workpiece.
Threads are machined into gear blanks or other components to allow for fastening.
6. Knurling:
Knurling is a surface-finishing process that adds a textured pattern to the workpiece. Knurling is often applied to improve grip
on cylindrical components like knobs or handles.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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4.6 Tool Motion Parameters in CNC
• What are Tool Motion Parameters? Tool motion parameters in CNC machining define how the cutting tool interacts with the
workpiece. These parameters are critical for determining the quality, precision, and efficiency of the machining process.
Tool Motion Parameters in CNC

• Key Tool Motion Parameters: The main parameters include feed rate, spindle speed, depth of cut, and cutting speed. Proper
selection and adjustment of these parameters ensure optimal machining performance, minimizing tool wear and achieving
desired surface finish and accuracy.
I. Feed Rate (F):
1. Definition: Feed rate refers to the speed at which the cutting tool moves along the workpiece. It is usually measured in
millimeters per minute (mm/min) or inches per minute (IPM).
2. Influence on Machining:
o A higher feed rate removes material more quickly but can result in a rougher surface finish.
o A lower feed rate produces a finer finish but can increase machining time.
3. Formula:
o Feed rate = Spindle speed × Number of cutting edges × Feed per tooth
o Example: If a milling cutter has 4 edges, the spindle speed is 1000 RPM, and the feed per tooth is 0.1 mm, the feed
rate would be: Feed rate = 1000 × 4 × 0.1 = 400 mm/min
4. Factors Affecting Feed Rate:
o Material: Softer materials like aluminum allow higher feed rates, while harder materials like steel require slower
feed rates.
o Tooling: Carbide tools can handle higher feed rates compared to high-speed steel (HSS) tools.
o Operation: Roughing operations typically use higher feed rates, while finishing operations require lower feed rates
for better surface quality.
Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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4.6 Tool Motion Parameters in CNC
II. Spindle Speed (S):
Tool Motion Parameters in CNC

1. Definition: Spindle speed is the rotational speed of the machine's spindle, typically measured in revolutions per minute (RPM). It directly
affects the cutting tool’s speed as it interacts with the material.
2. Influence on Machining:
o High spindle speed is suitable for softer materials or operations requiring finer finishes.
o Low spindle speed is often used for harder materials or when roughing large amounts of material.
3. Formula for Spindle Speed (for turning and milling):
o Spindle speed = (Cutting speed × 1000) / (π × Diameter of the workpiece or tool)
o Example: If the cutting speed for aluminum is 300 m/min and the workpiece diameter is 50 mm:
Spindle speed = (300 × 1000) / (π × 50) ≈ 1910 RPM
4. Factors Affecting Spindle Speed:
o Material Machinability: Different materials have recommended cutting speeds. For instance, aluminum has a higher cutting speed
compared to steel.
o Tool Life: Excessively high spindle speeds can result in rapid tool wear and increased heat, reducing tool life.
o Surface Finish: High spindle speeds generally result in better surface finishes but may require slower feed rates for precision.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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4.6 Tool Motion Parameters in CNC
III. Depth of Cut (DoC):
1. Definition: Depth of cut refers to the thickness of material removed in one pass of the cutting tool. It is typically measured in millimeters or
Tool Motion Parameters in CNC

inches.
2. Influence on Machining:
o High depth of cut allows for faster material removal but increases cutting forces, heat, and the likelihood of tool wear.
o Low depth of cut reduces the cutting force but increases the number of passes required to complete the job.
3. Types of Depth of Cut:
o Axial Depth of Cut: Measured along the length of the workpiece (e.g., in turning operations).
o Radial Depth of Cut: Measured along the diameter of the workpiece or width of the cut (e.g., in milling operations).
4. Factors Affecting Depth of Cut:
o Material Toughness: Harder materials usually require shallower depths of cut to avoid excessive tool wear.
o Tooling Strength: More rigid tooling and machine setups can handle deeper cuts.
o Operation Type: Roughing operations often use deeper cuts, while finishing operations require shallower cuts for precision and surface
quality.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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4.6 Tool Motion Parameters in CNC
IV. Cutting Speed (Vc):
Tool Motion Parameters in CNC

1. Definition: Cutting speed is the speed at which the cutting edge of the tool moves relative to the surface of the workpiece. It is typically
measured in meters per minute (m/min) or feet per minute (ft/min).
2. Importance: Cutting speed is crucial for determining spindle speed and tool life. Proper selection of cutting speed ensures efficient material
removal without causing excessive heat or wear.
3. Formula for Cutting Speed:
• Cutting Speed (Vc) = (π × Diameter of workpiece or tool × Spindle speed) / 1000
• Example: If the spindle speed is 1200 RPM and the tool diameter is 20 mm:
Cutting Speed = (π × 20 × 1200) / 1000 ≈ 75.4 m/min
4. Factors Affecting Cutting Speed:
o Material Type: Materials like aluminum allow for higher cutting speeds compared to tougher materials like titanium or stainless steel.
o Tool Material: Carbide tools can withstand higher cutting speeds than high-speed steel (HSS).
o Heat Generation: Excessive cutting speed generates heat, potentially reducing tool life and causing thermal damage to the workpiece.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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4.6 Tool Motion Parameters in CNC
V. Tool Motion Strategies:
Tool Motion Parameters in CNC

1. Linear Interpolation (G01):

o Definition: Linear interpolation moves the tool in a straight line between two points. This is the most common tool motion in CNC
programming.
o Application: Used for cutting straight edges or moving the tool to different positions.
2. Circular Interpolation (G02/G03):
o Definition: Circular interpolation moves the tool along a circular arc, either clockwise (G02) or counterclockwise (G03).
o Application: Used for machining arcs, circles, or other curved profiles.
3. Rapid Positioning (G00):
o Definition: Rapid positioning moves the tool quickly between two points without performing any cutting. It is used to reposition the tool
for the next operation.
o Application: Used to minimize non-productive time in machining.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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4.6 Tool Motion Parameters in CNC
Optimizing Tool Motion Parameters:
Tool Motion Parameters in CNC

1. Balancing Speed and Precision:

o Trade-Off:
High feed rates and spindle speeds increase material removal rates but may reduce precision. Conversely, lower speeds improve
accuracy and surface finish.
o Solution:
For roughing operations, prioritize speed with higher feed rates and spindle speeds. For finishing operations, reduce both to enhance
precision and surface quality.
2. Tool Wear Consideration:
o Effect of Parameters on Tool Life:
Excessive spindle speeds, feed rates, and depths of cut can accelerate tool wear due to increased heat and cutting forces.
o Optimized Parameters:
Use recommended cutting speeds and adjust feed rates based on tool wear indicators. Implement cooling systems to reduce heat
generation.
3. Toolpath Optimization:
o Efficient Movements:
CNC programming tools like CAM software can optimize toolpaths to reduce non-productive movements (e.g., rapid repositioning) and
ensure efficient material removal.
o Minimizing Retracts:
Reducing the number of unnecessary tool retractions can save time and increase machining efficiency.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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4.7 Virtual Machining
1. Introduction to Virtual Machining:
•Definition:
•Virtual Machining refers to the simulation of machining processes in a virtual environment using computer software. It allows the user to
simulate the behavior of CNC machines, tools, and workpieces without physically performing the machining operation.
•Purpose:
•The main objective of virtual machining is to visualize and optimize the machining process, identify potential errors, and enhance overall
efficiency before actual manufacturing.
Virtual Machining

2. Components of Virtual Machining:

a) CAD (Computer-Aided Design):
•Role: CAD software is used to create 3D models of the part or workpiece to be machined. It provides the geometric data for the
virtual machining environment.
•Example Software: SolidWorks, CATIA, Autodesk Inventor.
b) CAM (Computer-Aided Manufacturing):
•Role: CAM software generates the toolpaths based on the 3D CAD model. It converts the design into machine instructions (G-
code) that are used to control CNC machines.
•Example Software: Fusion 360, Mastercam, Siemens NX CAM.
c) CNC Machine Simulation:
•Role: CNC machine simulation in virtual machining allows users to replicate the entire machining process, including tool
movements, material removal, and machine operations, within the virtual environment.
•Simulation Software: VERICUT, NCSimul, CAMWorks.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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4.7 Virtual Machining
3. Key Features of Virtual Machining:
1. Toolpath Simulation:
o Definition: Simulates the exact movement of the cutting tool relative to the workpiece, showing the material removal process.
o Purpose: Identifies potential issues like tool collisions, inefficient toolpaths, and machining errors before real machining.
2. Machine Kinematics:
Definition: Models the physical movement of the CNC machine components (spindles, turrets, tables, etc.).
Virtual Machining

o Purpose: Ensures the programmed toolpaths are compatible with the machine’s capabilities, preventing over-travel or machine
crashes.
3. Material Removal Simulation:
o Definition: Visualizes the gradual removal of material from the workpiece in real-time, allowing users to track the machining process
and the final part geometry.
o Purpose: Helps in verifying the final part dimensions and surface finish before actual production.
4. Collision Detection:
o Definition: The simulation software checks for possible collisions between the tool, workpiece, fixtures, and machine components.
o Purpose: Prevents damage to the machine or tools and reduces costly downtime by ensuring safe operations.
5. Time and Cost Estimation:
o Definition: Virtual machining can estimate the total machining time and cost by simulating the entire process.
o Purpose: Provides insights into cycle time, tool life, and material costs, helping in accurate project planning

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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4.7 Virtual Machining
4. Applications of Virtual Machining:
1. Prototype Validation:
o Application: Virtual machining is used to validate the design and machining strategies for new prototypes, eliminating the need for
physical prototypes and reducing development time.
o Example: Automotive and aerospace industries use virtual machining to ensure the manufacturability of complex components like
engine parts and airfoils.
Virtual Machining

2. Process Optimization:
o Application: Virtual machining helps optimize toolpaths, cutting parameters, and machine setups to improve productivity and
minimize machining time.
o Example: Manufacturers can simulate different cutting strategies and select the most efficient process for high-volume production
runs.
3. Training and Education:
o Application: Virtual machining environments provide a safe and cost-effective platform for training CNC operators, allowing them to
practice and experiment with different machining operations.
o Example: Educational institutes and vocational training centers use virtual machining tools to teach students the fundamentals of
CNC machining without risking expensive equipment.
4. Failure Analysis and Troubleshooting:
o Application: Virtual machining can be used to analyze machining failures, such as surface defects, tool breakage, or part
inaccuracies, by simulating the process retrospectively.
o Example: If a part is found defective after machining, the virtual environment can help identify the root cause (e.g., incorrect
toolpath, machine vibration).

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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4.7 Virtual Machining
5. Benefits of Virtual Machining:
1. Cost Savings:
o Benefit: Virtual machining reduces the cost associated with machining errors, tool collisions, and material waste. It eliminates the
need for trial-and-error machining and minimizes setup time.
o Example: A manufacturer can simulate the entire process and optimize it before committing to actual material usage, thus saving
on both materials and labor.
2. Increased Productivity:
Virtual Machining

o Benefit: By identifying potential problems beforehand, virtual machining allows for more efficient real-world operations, reducing
downtime and machine idling.
o Example: Optimized toolpaths and cutting parameters derived from virtual machining can significantly reduce cycle times in mass
production.
3. Improved Accuracy and Quality:
o Benefit: Virtual machining helps refine tool motion and material removal strategies, improving dimensional accuracy and surface
finish of the final product.
o Example: Surface finish requirements in high-precision industries like medical device manufacturing can be achieved more
consistently with virtual machining.
4. Risk Mitigation:
o Benefit: Simulation of machining operations allows operators to foresee and mitigate risks like tool breakage, machine crashes, or
overcutting, ensuring safer operations.
o Example: In the aerospace industry, where precision is critical, virtual machining can prevent costly errors during the production of
safety-critical parts.
5. Shortened Time-to-Market:
o Benefit: The ability to simulate and optimize the machining process without physically creating parts shortens development cycles,
allowing manufacturers to bring products to market faster.
o Example: Virtual machining in the electronics industry helps reduce the lead time for producing complex components like casings
and connectors.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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4.7 Virtual Machining
6. Limitations of Virtual Machining:
1. Software and Hardware Costs:
o Limitation: High-end virtual machining software and hardware can be expensive to acquire and maintain, limiting accessibility for
smaller manufacturers.
2. Learning Curve:
o Limitation: Operating and fully utilizing virtual machining software requires significant training and expertise in both CNC
Virtual Machining

programming and simulation technologies.

3. Accuracy of Simulation:
o Limitation: The accuracy of the simulation is highly dependent on the accuracy of the CAD/CAM models, tool data, and machine
configurations input into the software. Errors in these inputs can lead to incorrect simulations

7. Future Trends in Virtual Machining:

1. Integration with AI and Machine Learning:
o Trend: Future virtual machining systems are expected to integrate AI algorithms for predictive analysis and process optimization,
enabling self-learning machining strategies.
2. Virtual Reality (VR) and Augmented Reality (AR):
o Trend: VR and AR technologies will allow users to interact with virtual machining simulations in an immersive 3D environment,
enhancing operator training and process planning.
3. Cloud-Based Simulation:
o Trend: Cloud-based virtual machining platforms will enable remote access and collaboration, making simulation tools more
accessible to smaller enterprises and distributed teams.

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3B
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Any Questions

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3A
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THANK YOU

Naresh Kumar Reddy. P., Asst. Professor., Dept. of Mechanical Engineering, BVRIT-Narsapur. 1-Dec-24 U-3A