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Milling
By D Cheshire
Page 1 of 6
This tutorial introduces the concept of machining of freeform surfacesusing a 3 Axis CNC miller. A sample model of a mould half is provided foryou^ to
work^
with^ in
this^
tutorial.^
It^ can^
be^ found
at
http://www.staffs.ac.uk/~entdgc/WildfireDocs/tutorials.htm
and^ is
called
mould.prt.
This^ part
should^
be^ downloaded
to^ your
working
directory
before starting the tutorial. Machining Setup To start the tutorial, create a new file for the machining data using FILE >NEW. Select MANUFACTURING and NC ASSEMBLY as shown in Figure1 and type in a name such as mould.
Figure 1 : Creating a New Machining File The^ blank
file^ created
is^ ready
to^ store
all^ of^
the^ manufacturing
information. The first data to be inserted into the file is the actual model tobe^ machined.
This^ is
specified
by^ the
command
MFG^
MODEL
ASSEMBLE
^ REF MODEL and choosing mould.prt in the file list box. Choose DONE/RETURN and the model to be machined should appear inthe window. This is an (incomplete) half of a mould for an injection-moulded part. The cavity for the part is to be machined from a rectangularblock of material. We can assume the outside surfaces of the block arealready finished to the correct dimensions.
Figure 2 : The Mould Part to Be Machined To enable visualisation of the machining process it is beneficial (thoughnot essential) that the stock material from which this part will be machinedis defined. To do this choose MFG MODEL
^ CREATE
^ WORKPIECE
and^ type
in^ the^
name^ mould_work.
Now^ choose
PROTRUSION
EXTRUDE | SOLID | DONE and create a rectangular block of material thesame size as the mould. (Hint : Pick the top surface of the mould as thesketch plane. In sketcher pick
and pick the top surface again and
ACCEPT to make a rectangle the same size as the mould. For extrudedepth choose up to surface
and pick the bottom surface of the
mould). You should be able to work out how to do this from previousexperience of model creation. When you have done this the materialshould be shown in transparent green.
Figure 3 : Reference Model and Workpiece
Milling
By D Cheshire
Page 2 of 6
When machining it is essential that you know where to consider the origin(0,0,0) for machining to be. It is common to define one corner of the topsurface of the material as zero. This is done in Pro Engineer with acoordinate system. It would be useful to create one now. Choose INSERT> MODEL DATUM > COORDINATE SYSTEM. The coordinate systemdialog is displayed. This is an ‘intelligent’ dialog – it will try and makesense of what you select. Click on the 3 sides of the block now in the ordershown in Figure 4.
Figure 4 : Defining the Coordinate System
The yellow icon shows the location of the coordinate system. Notice thatthe Z axis is pointing up. This is MOST important as the milling tool willapproach the material down the Z axis. If the Z axis is oriented wrong thenPro Engineer will try and machine from the wrong direction. Click OK toclose the dialog and ACS0 should appear in the model tree. DEFINING THE MACHINING OPERATION We can now start the machining process. It would be good at this stage toplan the sequence of events for machining. Since the outside surface arealready finished we do not need to machine these at all. Starting with therectangular block we will first remove the mass of material in the cavity
with a large tool, leaving some material to be removed by a second finercut with a smaller tool.An operation is the term Pro Engineer uses to define the type of machinethat will be used for a sequence of cuts. Since all our machining is takingplace on a single milling machine we only need a single operation.Choose the command MACHINING from the side menu and a dialogappears in^ which
you^ define
the^ Operation.
A^ series
of^ options
are
provided. Type in an Operation Name of Milling. Press
to go to the
machine
Tool^ Dialog^
and^ type
in^ a^
machine
name^
of^ Miller,
a
Machine_Type of Mill, and Number of Axes of 3 then press OK to return toOperation Setup. Next click on
next to Machine Zero, choose SELECT
and pick on ACS0. Finally click on
next to Retract Surface and choose
ALONG Z AXIS and type a depth of 5. Close the dialog with OK.
Figure 5 : Operation and Machine Tool Setup Dialogs
DEFINING THE FIRST CUT Now we start to define the first cut into the material. Choose MACHINING ^ NC SEQUENCE
^ MACHINING | SURFACE MILL | DONE. A series of parameters is offered. Ensure that Name, Tool, Parameters and Window(don’t miss this one) are checked and then choose DONE. Type the nameas RoughCut. Enter the tool values as shown in Figure 6 and APPLY OK.
Pick 1
Pick 3 Pick 2
Milling
By D Cheshire
Page 4 of 6
Having completed the roughing toolpath we can now define a secondtoolpath^
for^ the^
finishing cut.^ Choose
NC^ SEQUENCE
^ NEW
SEQUENCE
^ MACHINING | SURFACE MILL | DONE. Again a series of parameters is offered. Ensure that Name, Comments, Tool, Parametersand Window are checked but NOT Define Cut and then choose DONE.Type the Name as
FinishCut
. Enter the values as shown in Figure 10 and
also on the settings tab choose tool number 2 APPLY then OK.
Figure 10 : Finish Tool Parameters At the MFG Params menu choose SET and enter the values as shown inFigure 11 and FILE > EXIT and DONE.
Figure 11 : Finish Manufacturing Parameters There is no need to define a new window so just choose SELECT WIND,Close the search dialog then pick on the pink profile already created.To see the result of this machining exercise choose PLAY PATH
SCREEN
PLAY and
then^ DONE.
The^ actual
tool^ paths
will then
be
calculated and displayed in red followed by a tool path simulation.
Don’t
forget to save the toolpath with DONE SEQ.The toolpath definitions are now complete and as we have seen they canbe visualised to check accuracy using the PLAY PATH option. A truesimulation of the actual machining process can be achieved by choosingMACHINING
^ NC SEQUENCE and pick an existing sequence name (ROUGH) then pick PLAY PATH
^ NC CHECK
^ RUN.
This uses
software called Vericut to simulate the machining process. A graphicalrepresentation
of^ the^
part^ should
appear
on^ the
screen after^ a
few
moments. You can use the buttons in the bottom right of the screen to playthe toolpath
. Use the solid green arrow to play the
path now.
If your options aredifferent^ to
these you^ chose
the wrong^ type
of toolpath. Quit thissequence^
and create a new one ensuring^
you choose^
the SURFACE
MILL option.
Milling
By D Cheshire
Page 5 of 6
Figure 12 : Cut Verification for Rough and Finish Cuts Having completed all of the machining steps you may want to check thewhole machining process by viewing in Vericut. To join all the stepstogether you need to create an intermediate file containing all of the toolpaths. CL DATA > OUTPUT > SELECT ONE > OPERATION then pickthe operation name MILLING > FILE > DONE and accept the name milling.ncl
for the filename. This has created a .ncl file in your working
directory. Choose DONE OUTPUT > NC CHECK > CL FILE and select thefile you just created. Choosing a final DONE will take you to Vericut whereyou can view the whole machining process. POST PROCESSING Post Processing is the act of converting the toolpaths from a standardlanguage called a cutter location file (.ncl) to the language of your specificCNC machines controller. The resultant file in Pro/Engineer is known as atape^ file
(.tap)^ which^ contains
all^ the ‘G‘^ codes
to^ control
the^ CNC
machine. The post processor is a program that performs the translationprocess.
Even^
though^
Pro/Engineer
comes
with^ some
general
post
processors you must have the correct post processor for your specificmachine controller otherwise breakages may occur.You were instructed how to create a CL file in the previous section. Thissame^ file
can^ be
used^
to^ produce
the^ CNC
instructions
via^ post
processing. To use this file choose CL DATA > POST PROCESS and thenselect the filename
milling.ncl
followed by DONE. Pro/Engineer should
now generate a list of the post processors available on your system.These^ have^ names
from^
UNCX01.
to^ UNCX01.
(milling)
and
UNCL01.1 to UNCL01.99 (lathe). As you move the cursor over thesenames a description of the post processor will be shown at the bottom ofthe main window. To use the Kryle Machining Centre at Staffordshire
University choose UNCX01.99 as the post processor. On completion aninformation window will be displayed and the file milling.tap will have beencreated in your working directory. This file should be uploaded to the CNCmachine and checked by the operator before running FILE STRUCTURE The^ machining
operation
in^ Pro/Engineer
brings^
together data^ from
several^
places.^
This^ requires
several
files^ to
be^ associated
to^ the
manufacturing process. It is important to understand the structure of thesefiles because if one of these required files is deleted by mistake the wholemanufacturing process may be lost. Figure 13 shows this file structure.Mould.mfg
Stores all manufacturing parameters
Mould.asm
Assembles model and work parts together
Mould.prt^
The part to be machined
Mould_work.prt
The model of the stock material
Mould_temp.tph
Temporary geometry of all toolpaths
Milling.ncl^
Cutter location (CL) file
Millning.tap
Post processed file which is sent to CNC machine
Cgtpro1.*^
Temporary files to interface with Vericut
*.acl, *.lst, *.mbx, *.tl
Temporary files associated with creation of .tap file
Vericut.log
Temporary log file for Vericut
Figure 13 : Manufacturing File Structure
Mould.mfg Mould.asm Mould.prt^
Mould_work.prt
Milling.tap
Turnedpart_temp.tph
Milling.ncl
To CNCmachine
