In a CNC machine we can
create a CNC Program in hundreds of ways to machine the same work piece and all
the ways we can expect the same finished part.
When you receive a 3D
model to do CNC program, check the 3D Model for the numbers of ways we can
place fixtures and number of setups required to finish the part. But, in
addition to creating the CNC program, there is many other factors need to Know
to machine the work-piece. There are many questions on your mind about how to
hold the work, which cutting tools to be selected and which machining
conditions to be used to get a perfect part on CNC machine.
Step #1: Selecting a
Machine.
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As described above we
can machine a part in hundreds ways, but it’s wise to select the machine if you
have many options in your shop floor.
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If the machining part has
a difficult angles and surface profile, an ideal 3-axis machine may take number
of setups consuming time and may be difficult to achieve the tolerance.
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A 5-Axis machine can
reduce the setup and give the best tolerance for the complicated parts.
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A simple part can’t be
machine on a 5-axis machine due to the high cost. So we need to decide wisely keeping
in mind of machining time and the labour.
Step #2: Work holding Selection for the Part.
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There are number of ways
to hold a part on the machine, it always depends on the billet you are using.
Billet may be a rectangular block, forging stock, casting block.
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If you are using a
rectangular block, you can use a machine wise on the machine table. If the
block is big for machine wise you can use the push clamps to hold the block on
machine table.
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If the stock is an
forging or a casting then you need to design the special fixture which can hold
the stock comfortable and rigid.
Step #3: Choose the
cutting Tools.
- Choosing the tools for cutting the part is an
important factor for the finishing the part. We need to choose the cutting
tools depending on the type of material we are cutting.
- For aluminium stainless steel cutting tools can
perform well, but for the hard material like titanium and steel better consideration are carbide tools.
- Before generating the programs it’s better to
check the tools available in the shop floor, instead of waiting for the tools
to be ordered.
- Always shorter tools give more accurate results
than the longer tools, so wisely use the tools in your programs depending on
the height and depth of the part.
Step #4: Gather all
Cutting Condition Data.
- After the tools have been decided, calculate
your cutting data such as speed & feed which can suit easy removal of material.
- Recommended to use the cutting data given by the
tools catalog given from tool manufacturers.
- You can experiment using the different feeds and
speeds later while optimizing the programs.
Step #5: NC-Axis
Selection on the Part.
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Decide the NC axis Point
on the part. Example: you can select a corner of the part where X, Y and Z
meet.
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Selection of NC axis must
make the machine operator to probe the part X, Y and Z easily. There is only on
machine Zero axis, But you can create a number of NC axis i.e., Work
co-ordinate offset.
- If you are using a rectangular block, you can
select the corner of the block for your NC axis XYZ=0, operator can probe the
three walls of the block to make XYZ=0 on the machine and store the value on
the machine Work offset. Usually we can use G54 which is standard..
Step #6: Creating a
CNC PROGRAM.
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An NC Program can be
created in many ways, now a day’s using software like UNIGRAPHS, Catia,
Mastercam etc. is the common way to create a NC program.
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If it’s a simple program
it can be done manually, such as program involving only drilling, reaming and
tapping cycles.
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After creating the tool
paths’ using the software’s you can generate a NC-program which as G-codes
directly within built postprocessor.
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If you have a customized
postprocessor loaded with the control of your machine, then the results are accurate.
Step #7: Checking the CNC
PROGRAM.
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There are number of ways
to check the programs, program can be simulated for errors in the software’s
used for generating the tool path.
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You can use simulator
software like Vericut, where we can build our machine and load the controls and
test our G-code. The simulation can be actual like it’s been milled on machine.
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If you want to verify
only the tool paths you can use software’s like cimco edit. You can find much
software on internet to visualize the tool paths.
Step #8: Setting up
the CNC Machine.
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Setting up your machine
for testing the program is very important. Load all the fixtures decided to
hold the part and mount the part as you designed while generating tool path.
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Load the NC-program on
the CNC machine memory or you can use the DNC software’s.
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Load the tools into the
tool magazine on the machine as per the tool numbers described in the program.
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Define the individual
tool offsets and store on the machine.
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Probe and define NC
program Zero and store G54 on the machine.
Step #9: PROGRAM PROVE
OUT.
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After all the setup.
Here we go we can test our programs.
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There are number of ways
to test the programs if you are not sure of your program go well..
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Testing the programs can
be done on the dry run option on the machine.
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Testing the programs can
be done by cutting the wood instead of metal.
Good luck, have fun learning CNC Programming...
If you have any questions and comments please let me know
