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CNC Machining Centres

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stuart bain

on 15 April 2014

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Transcript of CNC Machining Centres

The CNC machine must be programmed to the specifications on the machine drawing, by either using specific coding or by CAD/CAM
The correct type and size of material to be used must be chosen. This may be composed of any type of material, such as metals, plastics, composites or wood.
The material is then secured in the machine by means of either a vice, fixture or jig, or multiples thereof. This may be done automatically in high volume production machining.
and finally,
clean the machine, remove all swarf and check that all tooling remains in a satisfactory condition.
There are numerous employment opportunities careers that develop from the use and the design of CNC Machines, these include:
Machine Fitter
CNC Operator
When working with lathe there are lots of moving parts which can get caught in loose material like hair and clothing. So learning and respecting the proper safety regulations is important.
The CNC Machine has many parts similar to a conventional machine, such as Spindle, Machine Bed, and Cutting Tools, plus a few more such as - Computer, Keyboard, The three main Axis on the machine are called the X,Y and Z axis although some machines have more than three.

Computers are crucial to the operation of a machining centre. Software needs to be especially written and designed by a skilled engineer in order that the machine functions correctly.
Thank You for
The relevant tooling required for the operations must be loaded and set to the datums, (this is the same tooling that may be used on manual machines).
Prove the program by producing a test piece, inspect the component to ensure conformity.
Run the program to produce the required amount of components and complete the batch or run.
Objectives, (The learner shall):

a) Develop an understanding of CNC machinery and the processes involved in their operation.
b) Describe the methods of inputting data and proving a program
c) Describe basic CNC operations.
What are the advantages of CNC machines over conventional milling machines ?
CNC machines produce standardized, precision components accurately and repeatedly thus eliminating waste and saving time.
What is CNC?
stands for

Software Engineer
What are the disadvantages of CNC machinery?
2) What does the abbreviation CNC stand for?
a/ Computer numbered control
b/ Control numerical computer
c/ Computer numerically controlled
d/ Can not compute
8) What types of materials can be machined on a CNC machining centre?
a/ Wood
b/ Metal
c/ Plastics
d/ All of the above
5) What coding is used to input a program?
a/ C and Y codes
b/ G and I codes
c/ G and M codes
d/ N and O codes
9) What are the advantages of CNC machines?
a/ Increased output
b/ Decreased output
c/ Slower production
d/ Precision
10) What are the disadvantages of CNC machines?
a/ Programming is speeded up
b/ Machining is faster
c/ Programming is time consuming
d/ Expensive layout
11) What is the role of the Software engineer?
a/ To repair the machine
b/ To manufacture components
c/ To develop software for the machine
d/ To compose witty ditties
4) What are the three main axis of the CNC Machining centre called ?
a/ X, Yand Z
b/ A, B and C
c/ S, H and Y
d/ G, H and I
3) Name two methods of holding the material in the machine?
1) What subject knowledge is essential for programming the CNC?
a/ Geography
b/ Mathematics
c/ Science
d/ English
6) What are the G-codes responsible for?
a/ Performing tricks
b/ Performing actions
c/ Performing arts
d/ Preformed ideas
7) What are the functions of the M-codes ?
a/ Multiple movements
b/ Miscellaneous coding
c/ Miscellaneous computing
d/ Multiple coding
Rapid move (transport the tool through space to the place where it is needed for cutting; do this as quickly as possible.
Controlled feed move in a straight line or arc.
Series of controlled feed moves that would result in a hole being bored, a workpiece cut (routed) to a specific dimension, or a profile (contour) shape added to the edge of a workpiece.
Switch between coordinate systems.
M- Codes
Miscellaneous function Action code, auxiliary command; descriptions vary. Many M-codes call for machine functions, which is why people often say that the "M" stands for "machine", although it was not intended to.
12) What does the S stand for in coding?
a/ Sound
b/ Speed
c/ Special
d/ Someone
It may also prevent machine damage in the event of tool breakage or a programming mistake.
This is especially important because it allows safe "lights-out machining", in which the operators set up the job and start it running during the day, then go home for the night, leaving the machines running and cutting parts during the night.
Individuals working with CNC machining centres need to know how to construct codes and programs together on the computer to properly operate the machine.
Good knowledge and understanding of mathematics is essential.
The programs used in CNC machining centres are formed from specific codes. These are mainly known as G-codes and M-codes.
13) What is meant by "Modal"?, Is it:
a/ Codes are constant
b/ Speed changes occur
c/ Operator warning system
d/ Codes remain in effect until cancelled
14) What is the function of the Load Monitor?
a/ Provide data to the operator
b/ Warn the operator of possible damage
c/ Warn the operator of dull / blunt tooling
d/ All of the above
Examples of M-codes are:
M00 - Compulsory Stop
M01 - Optional Stop
M03 - Spindle On Clockwise
M04 - Spindle on Anti-clockwise
M07 - Coolant on
M30 - End of Program
Examples of G-codes are:
G00 - Rapid traverse
G01 - Controlled Traverse (Straight Line)
G02 - Controlled Traverse (Arc Clockwise)
G03 - Controlled Traverse (Arc Anti-clockwise)
G20 - Imperial Units
G41 - Tool Offset Left(Cutter compensation)
G71 - Metric Units
G90 - Absolute units
15) What is the function of G00?
a/ Increases speed
b/ Increases feed
c/ Rapid movement
d/ Decrease feed
16) What does the M00 function do?
a/ Compulsory Stop
b/ Emergency Stop
c/ Controlled Feed
d/ Tool call
17) What letter designates a Tool call?
a/ B
b/ T
c/ S
d/ F
18) How accurate is a CNC machine?
a/ 1"
b/ 0.01"
c/ 0.01 mm
d/ 1.0 mm
19) Who is responsible for the health and safety of the operator?
a/ The operator
b/ The programmer
c/ The software engineer
d/ You
20) What is the safe point that the operator can rapid the tool to?
a/ 50.0 mm
b/ 5.0 mm
c/ 10.0 mm
d/ Any of the above
The CNC machining centre can perform the same basic operations as a conventional milling machine, such as facing, milling, boring, etc, as well as more complex maneouvres and operations but to a more accurate degree.
For more complex components, CNC machines with more than three axis are recommended, these machines are especially useful as they are capable of machining the components at complex angles.

Outline and explain the benefits involved with CNC machinery and to develop learners knowledge of programming.

Describe the different roles involved with CNC machines.
Programming can be very time consuming and is not always suitable for small batches or one-off work pieces. Machines can be very expensive
There are specific steps to follow before commencing with the machining of a workpiece on a CNC, firstly-
These machines are referred to as multi-axis machines and are normally denoted by the number of axis that are in operation, i.e. 4, 5 or 7-axis.
These are especially difficult to master, as the operator or programmer is required to think past a number of operations in order to produce a more complex component.
Service Engineer
The role of the service engineer is multi-faceted as they are required to repair the mechanical aspects of the machine, and also the hydraulics, pneumatics, electronics and the software.
Individually these codes are simple to understand, however when combined into programs they become more complex making it harder to understand and create.
It takes exceptional skills to produce elaborate machined parts.
G-codes are also called preparatory codes, and are any word in a CNC program that begins with the letter G. Generally it is a code telling the machine tool what type of action to perform, such as:
Many codes are "modal", meaning that they stay in effect until they are cancelled or replaced by a contradictory code. For example, once rapid linear movement(G00) had been selected, it stays in effect until the end of the program.
It is common practice to bring the tool in rapidly to a "safe" point that is close to the part - normally 3-5 mm away - and then start feeding the tool. How close that "safe" distance is, depends on the preference of the programmer/setter or operator and the maximum material condition for the raw stock.
If the program is wrong, there is a high probability that the machine will crash, or ram the tool into the part under high power. This can be costly, especially in newer machining centers.

Fortunately, most CAD/CAM software ships with CNC simulators that will display the movement of the tool as the program executes. Many modern CNC machines also allow programmers to execute the program in a simulation mode and observe the operating parameters of the machine at a particular execution point. This enables programmers to discover errors before losing material or tools to an incorrect program.
Load Monitors:
Many newer machines have a load monitors built in and it is common practice to use with CNC machinery. The load monitor will stop the machine if the spindle or feed loads exceed a preset value that is set during the set-up operation. The jobs of the load monitor are various:
It will warn of a tool that is becoming dull and needs to be replaced or sharpened. Thus an operator who is busy tending multiple machines will be given a warning by the machine,
Direct numerical control (DNC), also known as distributed numerical control (also DNC), is a common manufacturing term for networking CNC machine tools. On some CNC machine controllers, the available memory is too small to contain the machining program (for example machining complex surfaces), so in this case the program is stored in a separate computer and sent directly to the machine, one block at a time.
Machining Centres
The machining datum or origin points should be selected at this stage in order that sufficient material is removed to clean all faces.
In high volume production, machines may have more than one station, these are especially useful as they are capable of machining multiple components at the same time.
It is possible to intersperse the program with optional stops (M01 code) which allow the program to be tested. These remain in the program but are skipped during normal running of the machine.
Each of the three axis on the machine are also capable of being rotated and thus designated a seperate letter code, there are also additional axis which rotate or operate in an angular motion to the main axis.
21) What are the two methods of milling?
a/ conventional and climb
b/ climb and scramble
c/ conventional and rotate
d/ climb and rotate
22) What is the preffered method to start pocketing?
a/ Ramping
b/ Plunging
c/ Planking
d/ Planing
23) How would you support a round piece of material in the vice?
a/ With the vice alone
b/ With the aid of a V-block
c/ With the aid of a g-clamp
d/ Withthe aid of two vices
24) What is the purpose of DMC?
a/ To network computers
b/ To store larger programs outside the machine
c/ To enable complex programming
d/ All of the above
by: Stuart Bain
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