1.0 TITLE: CNC Milling (Non Traditional Machining) 2.0 OBJECTIVE: 1. To develop more understanding about development and principle of CNC machine. 2. To learn various type of modern CNC machines and CNC modes of operations. 3. To understand the fundamentals of part programming in terms of the various steps needed to be taken for completing a successful CNC program. 4. To understand the different preparatory (G codes) and miscellaneous functions (M codes) as used in CNC part program. 5. To understand the advantages and disadvantages of CNC machines and their applications. 1
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1.0 TITLE: CNC Milling (Non Traditional Machining)
2.0 OBJECTIVE:
1. To develop more understanding about development and principle of CNC machine.
2. To learn various type of modern CNC machines and CNC modes of operations.
3. To understand the fundamentals of part programming in terms of the various steps
needed to be taken for completing a successful CNC program.
4. To understand the different preparatory (G codes) and miscellaneous functions (M
codes) as used in CNC part program.
5. To understand the advantages and disadvantages of CNC machines and their
applications.
1
3.0 INTRODUCTION
Numerical control (NC) refers to the automation of machine tools that are operated by
abstractly programmed commands encoded on a storage medium, as opposed to manually
controlled or mechanically automated via cams alone. The first NC machines were built in the
1940s and '50s, based on existing tools that were modified with motors that moved the
controls to follow points fed into the system on paper tape. These early servomechanisms
were rapidly augmented with analog and digital computers, creating the modern computer
numerical controlled (CNC) machine tools that have revolutionized the design process. In
modern CNC systems, end-to-end component design is highly automated using CAD/CAM
programs. The programs produce a computer file that is interpreted to extract the commands
needed to operate a particular machine, and then loaded into the CNC machines for
production. Since any particular component might require the use of a number of different
tools, modern machines often combine multiple tools into a single "cell".
Diagram 1.1: CNC milling machine
Modern CNC mills differ little in concept from the original model built at MIT in
1952. Mills typically consist of a table that moves in the Y axis, and a tool chuck that moves
in X and Z (depth). The position of the tool is driven by motors through a series of step-down
gears in order to provide highly accurate movements, or in modern designs, direct-drive
stepper motors. As the controller hardware evolved, the mills themselves also evolved. One
change has been to enclose the entire mechanism in a large box as a safety measure, often
with additional safety interlocks to ensure the operator is far enough from the working piece
F Feed function S Spindle speed functionG Preparatory function T Tool function
H Unassigned USecondary motion dimension
parallel to X*
I Distance to arc centre to X VSecondary motion dimension
parallel to Y*
J Distance to arc centre to Y WSecondary motion dimension
parallel to Z*K Distance to arc centre to Z X Primary X motion dimensionL Do not use Y Primary Y motion dimensionM Miscellaneous function Z Primary Z motion dimension
Preparatory functions
This is denoted by ‘G’. It is a pre-set function associated with the movement of
machine axes and the associated geometry. It has two digits as per ISO specifications. Some
examples are shown:
6
CODE FUNCTION
G00 rapid traverse
G01 line interpolation
G02 ciccular interpolation, clockwise
G03 circular interpolation, anti-clockwise
G04 dwell
G05 hold/delay
G06 parabolic interpolation
G33 thread cutting, constant lead
G53 deletion of zero offset
G64 change in feed rate or speed
G80 canned cycle cancelled
Miscellaneous functions
These functions operate some controls on the machine tool and affect the running of
the machine. Generally, only one M-code is supposed to be given in a single block. The ISO
standard examples are:
CODE FUNCTION
M00 program stop, spindle and coolant off
M01 optional programmable stop
M02 end of program
M03 spindle on, clockwise
M04 spindle on, anticlockwise
M09 coolant off
M10 clamp
M31 interlock by-pass
M68 unclamp piece art
4.0 APPARATUS
1. CNC centroid milling machine
7
2. Machine control unit (MCU)
3. Plastic workpiece (100x100x15)
5.0 EXPERIMENTAL PROCEDURE
A demonstration was carried on by our lecturer on:
8
1. At first, we have to check the programs to ensure that the machinery will function properly and that the output will meet specifications. We downloaded the NC program to the controller by key in the data, cabling RS232 or APT after the programming work is completed.
2. Tool layout. Before the machining was started, the tool layout must be check so that we got the desired shape of workpiece.
3. Workpiece setting. In this step, operator loaded the proper cutting tools into the tool holder and positions the workpiece that is piece of metal or plastic that is being shaped on the CNC machine tool.
4. In machining process, after operator load workpieces and cutting tools into a machine, after that the start button was pressed. Operator monitored the machine for problems, and measure the parts produced to check that they match specifications.
6.0 DATA AND RESULT
9
10
11
ADDRESS
X YA 14 14B 14 86C 30 86D 70 86E 86 86F 86 14G 70 14H 30 14