Nc Milling

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Transcript of Nc Milling

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    NC Milling Tutorial

    This tutorial shows how to use Pro/Engineer to generate a machine tool path for an NC

    mill to manufacture a part. In this tutorial a wooden workpiece of size 7" 1.75"1.3" will have

    material cut away. The first task is to use Pro/Engineer to design the part to be manufactured.

    Figure 1 shows how the workpiece will be clamped to the mill tabletop. Be sure that

    your part to be manufactured does not have material removed near the clamps so that the cutting

    tool will not intersect with the clamps1. Figure 2 shows the cutting tool that will be used in this

    exercise.

    Figure 1: Workpiece Clamped to Mill Tabletop

    Figure 2: Cutting Tool

    1 It is possible to model the clamps in Pro/Engineer and to position them relative to the workpiece. The calculated

    cutting tool path will avoid the modeled clamps. The modeling of the clamps is beyond the scope of this tutorial.

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    Step 1: Create the Part Model

    Figure 3 shows the part to be manufactured. The exact dimensions are not important for

    this exercise, but it should be apparent that the workpiece can be clamped from the sides and the

    machining operation completed without the cutting tool intersecting the clamps. The part was

    created in Pro/Engineer and was namedpinewood.prt. Pro/Engineer will create several new files

    that will be associated with the manufacturing process and it is recommended that a new empty

    directory be created and the filepinewood.prtmoved to this directory.

    Figure 3: Part to be Machined

    Step 2: Assemble the Part and Workpiece

    Start Pro/Engineer and set your working directory

    to the location of your part file. Select File, New from

    the pull down menu. The dialog box shown in Figure 4

    will appear. Check Manufacturing and NC Part and

    give your manufacturing process a name. For this

    tutorial, the namepinewoodwas chosen.

    Select OK and the dialog box shown in Figure 5

    will appear. Select your part file (pinewood.prt for this

    example) and select Open. Your part will now appear

    on the screen as shown in Figure 6.

    Figure 4

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    Figure 5

    Figure 6

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    The next step is to create the workpiece material that the part will be machined from

    using our part as a guide. On the right hand menu, select Mfg Model, then Create, then

    Workpiece. You are now prompted to enter a name for your workpiece. The name

    pinewood_wkpiece was selected for this tutorial.

    We will now enter the Sketcher to model the workpiece. To do this, on the right hand

    menu, select Protrusion, then Solid/Done, then One Side/Done. You now are asked to

    pick the sketching plane. Pick the bottom surface of the part. We want the workpiece to envelop

    the part so make sure that the direction of the extrusion arrow is pointing upward towards the top

    of the part and select Okay. You are now prompted for the reference planes. Select Right

    and pick the front side of your pinewood vehicle. The References dialog box now appears.

    Select the left and bottom references and then press Close. You are now in the Sketcher.

    Draw a rectangular box that is the shape of your workpiece. For this exercise, the

    workpiece material is 7"1.75" and is 1.3" tall. Exit the Sketcher as is normally done by clicking

    on the check mark icon. It remains to enter the depth of the extrusion. Perform a blind extrusion

    of 1.3". All elements of the protrusion are now defined. Select OK and then Done/Return.

    The workpiece is now defined and you can rotate the view as desired to view the workpiece and

    the part as is shown in Figure 7.

    Figure 7

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    Step 3: Manufacturing Setup

    We will now specify a 3 axis milling application. Selectc Mfg Setup from the menu on

    the right. The Operation Setup dialog box appears (see Figure 8).

    Figure 8

    Click on the mill icon . The Machine Tool Setup dialog box opens as shown in

    Figure 9.

    mill icon

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    Figure 9

    Make sure that the Machine Type is mill and the Number of Axes is 3 Axis. Click OK.

    You are now back at the Operation Setup dialog box (see Figure 8).

    We will now be establishing the coordinate system that the tool path commands will be

    referenced to. Select the arrow to the right of the text Machine Zero. Click on Create on the

    right side menu and then pick on the workpiece (the block from which material will be cut).

    Next select 2 Axes and Done from the right side menu. You are now prompted to pick two

    edges. We will be placing the origin of the coordinate system at the upper left corner when

    looking down on the part. Select the two edges that pass through this point. Figure 10 shows the

    screen after selecting these two edges (your screen may appear differently depending on the

    order you picked the edges). A coordinate system is shown in the upper left corner. It remains

    to define the directions of the X, Y, and Z axes. We will specify the direction of two of these

    and the third will be defined in a right-hand sense.

    The Z axis will be pointing upward, i.e. from the bottom towards the top of the part. The

    X axis will point to the right. Figure 10 shows one of the coordinate axes colored as red. For

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    this case, this is pointing in the negative X axis direction. Select Reverse from the right side

    menu. The red arrow now points in the direction of the X axis. Select X-Axis to define the X-

    axis as being in the direction of the red arrow.

    Figure 11 shows the current status of the model. The red arrow is pointing along the

    direction of the negative Y axis. We could reverse the direction and then define the Y axis, but

    instead we will work to define the Z axis.

    Figure 11

    Select Next to change which of the coordinate axes is highlighted as red (see Figure

    12). This is the direction of the Z axis so select Z-Axis to define this axis. The coordinate

    system is now completely defined. Select OK to return to the manufacturing setup menu (see

    Figure 13).

    Figure 10

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    Figure 12

    To complete the manufacturing setup, we need to specify the

    volume of the material to be removed. We will select the entireworkpiece and then remove the part to get the volume of material to be

    removed. Select Mfg Geometry from the right side menu followed by

    Mill Volume. Next select Create. You are prompted to enter a

    name for the milling volume (the material to be removed). The name

    pinewood_mill_volwas used in this tutorial.

    You are now prompted to pick a plane that is perpendicular to

    the Z axis. Select the top surface of the workpiece. A red arrow should

    appear that points in the positive Z direction (if not select flip). Press

    Okay.

    The sketch command will now be used to create the volume of

    material to be removed. Select Sketch from the right side menu. This

    is followed by Extrude/Solid/Done and One Side/Done. Now

    pick the top surface of your workpiece. The red arrow should now point

    downward along the negative Z axis. Select Okay. You are now

    prompted to select a reference so the sketcher can orient the part. Select

    Right and then pick the front of the pinewood car. Now pick two

    edges to serve as your reference lines in the sketcher (the bottom and left edges were chosen in

    this tutorial) and then select Close. Figure 14 shows the current screen image.

    Figure 13

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    Figure 14

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    Select Sketch from the top menu (see

    Figure 15) and then Edge/Use. Now select

    the four outer edges of the workpiece and then

    Close. Now exit the sketcher by selecting the

    check box . To complete the protrusion that

    will define the mill volume, select UpTo

    Surface, and rotate the model as needed to select

    the bottom surface of the workpiece. Then select

    Done.

    We have selected our entire workpiece as

    the mill volume, but still need to trim away the

    part. Select Trim from the right side menu

    followed by Done/Return, Done/Return,Done/Return. This returns us to the main

    manufacturing menu. This completes the

    manufacturing setup process.

    Figure 15

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    Step 4: Machining Sequence

    In this step, the tool and machining parameters (tool size,

    cutting speed, etc.) and a retraction plane will be specified. Select

    Machining from the manufacture main menu, followed by NC

    Sequence. Next select Volume/Done. The sequence setup menu

    will appear as shown in Figure 16. Make sure that the Tool,

    Parameters, Retract, and Volume boxes are checked. Select

    Done.

    The Tools Setup dialog box appears as shown in Figure 17.

    Set the cutter diameter to 0.375" and the length to 1". Select Apply

    then File, Done.

    Select Set from the MGF PARAMS menu. The Parameter

    Tree dialog box appears (See Figure 18). We will have to set values

    for all the parameters that have a current value of -1. Set the

    following values:

    Cut_Feed 60

    Step_Depth 0.02

    Step_Over 0.18

    Scan_type Type_Spiral

    Spindle Speed 1000

    Clear_Dist 0.5

    The cut feed parameter is the feed rate during cutting in units of xxx.

    The step depth is the depth of cut in inches. The step over parameter has been set to slightly less

    than half the tool diameter in units of inches. The spindle speed is in units of revolutions per

    minute. The clear distance is xxx. The cut feed and spindle speed values are ignored by the

    Minitech mill. The feedrate for the Minitech mill is set at 6 seconds per inch and is not

    overridden by values set here. The spindle speed for the Minitech mill is set manually and is not

    under computer control. After setting the parameters, select File and Exit. Next selectDone.

    The Retract Surface Options dialog box appears as shown in Figure 19. We will specify

    a plane that is 0.5" above the top of the workpiece. Click on Along Z Axis and enter a value of

    0.5". The retraction plane is now displayed.

    Figure 16

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    Figure 17

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    Figure 18

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    The volume of material to be removed must now be specified. Click on Select Vol on

    the right side menu. A dialog box will be displayed that shows the mill volume that we

    previously defined (see Figure 20). Click on your mill volume name and then press Select.

    The machining sequence is now complete.

    Figure 19

    Figure 20

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    Step 5: Viewing and Outputting the Results

    To view the tool path, select Play Path from the right side menu (Machining/NC

    Sequence menu). Then press Screen Play. A VCR type dialog box appears that will allow you

    to select the display speed and play back the tool path. When done viewing the tool path, close

    the VCR dialog box and select Done Seq to return to the Machining menu.

    To output a CL data file, select CL Data from the right side menu. From the Select

    Feature submenu, select Operation. From the SEL MENU submenu, select the name of your

    operation (OP010 was used in the tutorial). Select File from the PATH submenu and make

    sure that the CL FILE and Interactive boxes are checked. Select Done. You are now

    prompted for a name for your CL file. The filenamepinewoodwas used in this tutorial. You

    should have a message printed at the top of the Pro/Engineer screen that says that the file

    pinewood.ncl.1 was created successfully.

    The last step is to convert the CL data file to a tape file that has G-code commands. Thisfeature is built into Pro/Engineer, but is not working properly at this time. The teaching assistant

    will use a separate software program (Ideas) to convert your CL file to a G-code tape file.