STUDY OF CNC MACHINES EXPT. NO: 1 DATE : AIM: To study the basic components and details of CNC machine. BASIC COMPONENTS: An operational CNC machine consist of i) Program of instruction ii) Machine control unit iii) Machine tool. PROGRAM OF INSTRUCTION: It is the detailed step by step instruction which tell the machine tool what to do. The program can input to the system either by manual data input or by a punched t ape. MACHINE CONTROL UNIT: It is also called as the controller unit. It is considered as the brain of the machine. It reads the part program and controls the machine tool operation. It consists of two units. (1) Data processing unit (2) Control loop unit. CONTROL LOOP UNIT: The control loop unit receives the data from data processing unit and converts it into control
Transcript
STUDY OF CNC MACHINES
EXPT. NO: 1
DATE :
AIM:
To study the basic components and details of CNC machine.
BASIC COMPONENTS:
An operational CNC machine consist of
i) Program of instruction ii) Machine control unit iii) Machine tool.
PROGRAM OF INSTRUCTION:
It is the detailed step by step instruction which tell the machine tool
what to do. The program can input to the system either by manual data input or by
a punched t ape.
MACHINE CONTROL UNIT:
It is also called as the controller unit. It is considered as the brain of the
machine. It reads the part program and controls the machine tool operation. It
consists of two units. (1) Data processing unit (2) Control loop unit.
CONTROL LOOP UNIT:
The control loop unit receives the data from data processing unit and
converts it into control signals. The data usually provides the control
information such as the new required position of each axis, its direction of
motion and velocity and auxiliary control signals to relays.
MACHINE TOOL:
The machine which performs the machining operation is called machine
tool. The machine tool consists of workable and spindle as well as the
motor. It also includes the cutting tool work fixture and other auxiliary equipment
needed in the operation.
RESULT:
Thus the basic components of CNC machine have been studied
PART PROGRAMMING FUNDAMENTALS
EXPT. NO: 2
DATE :
AIM:
To know about part programming fundamentals for CNC turning.
1. CO-ORDINATE SYSTEM FOR A CNC LATHE:
Machining of the work piece by an NC programming requires a co-
ordinate system to be applied to the machine tool. As all machine tool have more
than one slide, it is important that each slide is identified individually. There
are three planes in which movements can take place:
(1.) Longitudinal
(2.) Transverse
(3.) Vertical.
Each plane is assigned a letter and is referred t o an axis (i.e.)
(1.) Axis-x
(2.) Axis-y
(3.) Axis-z
The three axis are identified by the upper case x, y and z and the
direction of movement along each axis specified as either (+) or (-). The
three axes are always at right angles and parallel to work holding surface. The z-
axis is at right angles to both x and y axis.
2. MACHINE ZERO POINT:
The manufacturers of the machine specify machine zero point. This is zero
point for the co-ordinate system and reference point in the machine on
turning the lathe. The machine zero point is generally at the center of the spindle
nose face. The main spindle axis represents the z-axis, and the face determines x-
axis.
3. WORK PIECE ZERO POINT:
The point determines the work piece co-ordinate system in relation to the
machine zero point. The work piece zero point is chosen by the programmer and
the input to the system.
4. NC PROGRAM BUILT UP:
In an NC program, the machining system operations for producing a
part on the machine tool are laid down in a form that the control system can
understand. A program is composed of several block s. A block is a collection of
NC works. An NC word is collection of address, letter and sequence of number.
BASIC COMPONENTS:
An operational CNC machine consists of (i) Program of instruction (ii) Machine
control unit (iii) Machine tool.
PROGRAM OF INSTRUCTION:
It is the detailed step by step instruction which tell the machine tool
what to do. The program can input to the system either by manual data input or by
a punched t ape.
MACHINE CONTROL UNIT:
It is also called as the controller unit. It is considered as the brain of the
machine. It reads the part program and controls the machine tool operation. It
consists of two units. (1) Data processing unit (2) Control loop unit.
CONTROL LOOP UNIT:
The control loop unit receives the data from data processing unit and
converts it into control signals. The data usually provides the control information
such as the new required position of each axis, its direction of motion and
velocity and auxiliary control signals to relays.
MACHINE TOOL:
The machine which performs the machining operation is called machine tool.
The machine tool consists of workable and spindle as well as the motor. It also
includes the cutting tool work fixture and other auxiliary equipment needed in the
operation.
CNC Systems:
Point-to-point control is the positioning of the tool from one y point to
another within a coordinate system. Most often used for positioning to a
point where a manual machining operation such as drilling or boring would
occur.
Straight-cut control has the ability move a tool, while engaged, y
straight in all axes of the machine and has the ability to do angles of
45 degrees.
Contouring control systems generate a continuously controlled y tool
path by interpolating intermediate points or coordinates. Interpolating
means the ability to generate the points that make up a path.
Cutting Data and Formulae:
Here are some of the most common terms used for expressing cutting data:
Spindle speed - Spindle speed is the rotational speed of the spindle and
tooling. This value is usually expressed in RPM. (Revolutions per
Minute).
Feed rate value - The feed rate value is the numerical value at
which a tool will traverse a work piece. It is usually expressed in
either IPM (Inches per Minute) or IPR (Inches per Revolution).
Cutting speed - Cutting speed is the rotational speed of the cutting tool
or work piece. It can be stated as either RPM or SFM. (Surface Fee Per
Minute).
Depth of Cut - Depth of cut is the distance the tool tip is engaged
into the wor piece. It is incorporated into the X, Y, and Z values
in a CNC program. Separate from the program, it can be expressed in
inches or mm
Tooling Requirements:
Tooling requirements and selection are based on part restrictions and industry
manufacturing practices. Most of these ideas are common sense thoughts. Good
CNC programmers and operators should be aware of them.
Know the material to be machined and its characteristics.
Use industry standard catalog tooling to cut costs.
Make use of technical services offered by tooling manufacturers.
Quality of the fixture should be based on the number of pieces that
will eventually be produced.
Always use the right tool for the right machining operation.
Keep spares or backups of tooling in the event resharpening is needed or tool
breakage occurs.
Keep an assortment of tooling in case one type does not perform the
job as desired.
Use high speed steel tools on easily machined materials.
Use carbide tools on difficult to cut materials.
Use cobalt or oxide coated tools for exotic alloys.
Use inserts type tooling where possible t o cut costs.
Consider using reamers, instead of boring bars, on lathe applications where
chatter and chip control may be a problem
Be aware of the flexing that occurs with long length tools. Extra passes may
be required to eliminate tapering and chattering.
Unit Systems and Input Modes:
Unit Systems are the units of measurement to be used for the CNC
program. All machines understand both English and Metric standards. When
programming in English units you are using inches. And in metric its the
millimeter (mm.). The CNC machine needs to be told which units are being
used. Some machines are automatically set-up at the factory for inches or mm.
Normally at the beginning of a CNC program you will see either; G70 to
specify inches or G71 to specify mm..
Input modes refer to the type of coordinate information that is input into
the program for the CNC machine. There are two types.
Absolute input , designated by the G90 c ode, specifies distances from the
origin or program zero point. Absolute is the most common mode.
Incremental input , designated by the G91 code, specifies distances and
directions based on the previous point as an origin. Incremental input is
sometime called point-to-point. All CNC systems can be switched from absolute to
incremental mode and back unlimited times within a program.
Other input modes such as Helical also exist
PREPARATORY FUNCTIONS (G codes)
The G-codes are the codes that position the tool and do the actual work, as
opposed to M-codes, that manages the machine; T for tool-related codes. S and F
are tool-Speed and tool-Feed, and finally D-codes for tool compensation. The
programming language of Numerical Control (NC) is sometimes informally called
G-code. But in actuality, G-codes are only a part of the NC-programming language
that controls NC and CNC machine tools.
1. G00 - Rapid move (not cutting)
2. G01 - Linear move
3. G02 - Clockwise circular motion
4. G03 - Counterclockwise circular motion
5. G04 - Dwell
6. G05 - Pause (for operator intervention)
7. G08 - Acceleration
8. G09 - Deceleration
9. G17 - x-y plane for circular interpolation
10. G18 - z-x plane for circular interpolation
11. G19 - y-z plane for circular interpolation
12. G20 - turning cycle or inch data specification
13. G21 - thread cutting cycle or metric data specification
14. G24 - face turning cycle
15. G25 - wait for input #1 to go low (Prolight Mill)
16. G26 - wait for input #1 to go high (Prolight Mill)
17. G28 - return to reference point
18. G29 - return from reference point
19. G31 - Stop on input (INROB1 is high) (Prolight Mill)
