PM 12 Patterns

7/28/2019 PM 12 Patterns

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PowerMILL 12. Patterns

Issue PMILL 6.0 175

12. Patterns

Introduction.Patterns are specific 2D or 3D wireframe entities mainly used as the basis for toolpath

creation. A Pattern is either projected onto the model or traced in situ using Pattern

Finishing. Other useful applications include controlling the shape of3D Offset Finishing

strategies, and as the medium for taking wireframes in and out of the PS-Sketcher

(PowerSHAPE wireframe constructor). Unlike Boundaries, Patterns can contain open

segments.

Select Delete Al l and Reset Forms. Right click Patterns from the explorerand select Toolbar.

Select the Create pattern icon and this generates an empty Patternnamed 1, into which the user can insert geometry.

When created the Pattern is automatically numbered and made

Active as shown in the Explorer (left).

A Pattern can be created using the following options:

Automatic Pattern generation (Open the Pattern Maker form).

Insert file into active pattern (picture or dgk file).

Insert boundary into active pattern.

Insert active toolpath into active pattern.

Insert selected model into active pattern (Selected Model).

Insert a sketch into active pattern.

Insert a sketch from PS-Sketcher.


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12. Patterns PowerMILL

176 Issue PMILL 6.0

Patterns applied to 3D Offset machining

A Pattern can be used as the specified shape to be offset across the machining area of a 3D

Offset Finishing strategy allowing tailoring of the toolpath. The following exercise involves

the creation of a Selected Surface Boundary on part of the model and a Pattern is then

created along the one of the edges to be use in conjunction with 3D Offset Finishing.

Open the example, model speaker.dgk and select an Iso3 view. Define a6 Ball Nose called bn6. Define a block to Min/Max limits and resetthe Safe Heights andTool

Start Point. Select the 3 surfaces shown shaded in the following diagram.

Create a Selected SurfacesBoundary to a Tolerance of0.02.


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Issue PMILL 6.0 177

From the Pattern toolbar click the Create Pattern icon followed by

the Insert Boundary into active pattern icon .

Undraw both the model and Boundary to visually isolate the Pattern.

Only the leading edge of the Pattern is required.

The remaining parts are to be removed.

Select the single Pattern, segment by dragging a box around it. Right click on Pattern 1 in the Explorerand select Edit Split Selected

(The Pattern is now divided into many small, individual segments). Select and delete the top and side segments of the profile to leave the

bottom, leading edge.

On closer inspection it is evident that the

remaining Pattern still consists of many small

segments.

It is now necessary to Merge all of these back

into one.

Drag a window around the Pattern to select it. From the pattern 1 in the Explorerselect Edit -> Merge.

PowerMILL confirms that it has merged the Pattern

into one segment.

Select OK on the form and redraw the model.


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Select a 3D OffsetFinishing strategy and enter data into the form exactlyas shown below.

At the moment the toolpath contains

a lot of movement in fresh air. To

reduce the amount of lift moves the

Links need to be forced to be OnSurface.


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Issue PMILL 6.0 179

Select the Lead and Links icon . Select the Links tab and put the short links On surface andApply.

The toolpath follows the contour of

the Pattern across the Boundary

limits.

IfUse Pattern had not been ticked

the 3D Offset strategy would have

followed the shape of the Boundary

segment as shown left.


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Automat ic Pattern Generation

The Automatic Pattern Generation icon opens the Pattern Maker form. This provides a

series of 6 specialized options allowing the user to create 4 different types ofOffsetPatterns

between 2 open segments, an OffsetPattern inside a closed segment, as well as a

Trochoidal Pattern across a segment.

Delete all and Reset forms. Open the Example model speaker_core.dgk. Calculate the Block to model limits. Define a diameter 6mm Ball Nose tool named bn6. Reset Safe Heights and Start Point. Select an Iso2 to display the model in the orientation shown below.

Be careful not to select any other surrounding surfaces not required for this exercise.Hold down the Shift key formulti select and the Ctrl key to deselect surfaces.

In the Patterns toolbar select the icon CreatePattern followed by

select Insert model into active pattern . With the above surfaces still selected create a Selected Surface

Boundary with the box labeled Roll Over, ticked. Undraw the model and Boundary leaving a view of the new Pattern on its

own in the graphics window.

The edges of the surfaces are captured and a Pattern is

created.

The Pattern must be Split into small geometric segments to

enable the deletion of the unwanted sections while retaining

the 2 sides (arrowed).


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Issue PMILL 6.0 181

Select the Pattern by Dragging a window over it, right click over Pattern 1in the explorer, and in the menu select Edit -> Split Selected.

Delete the top and bottom straight segments to leave the two sidesections.

The two remaining profiles still consist of many small

segments are now Merged to form two.

Right mouse click on the Pattern in the exploreror in the graphics area to

open the local menu andselect Edit -> Merge.

A form will appear, similar to this one, informing

the user that the Pattern has been merged as two

separate open curves.

Select OK to close the dialogue.

The next step will be to ensure that the direction of each segment is the same. This isimportant when using Automatic pattern Generation later in the exercise.

Drag a window around both segments in the graphics area, right click overthe Pattern in the Explorer, and select Instrument (displays segmentdirections).

It is now noticeable that the two segments are

travelling in opposite directions.

This segment will be reversed.

Select the segment (arrowed) above with the mouse, right click over thePattern, and select Edit -> Reverse Selected.


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The segments now travel in the same direction and as a result are now

suitable for use with Automatic Pattern Generation.

Select them both again and select Instrument again (Switch off displaysegment directions).

Select both of the above Pattern segments.

From the Pattern toolbarselect the icon CreatePattern followed by

theAutomatic pat tern generat ion icon .

The form allows you to create various styles of

automatic Pattern.

As shown in the above diagram select the option for Create pattern alongcurves, two way and input a Stepovervalue of1.

Apply andAccept the form.

The new Pattern has been generated between the two

selected segments of the original, de-activatedPattern.

Select a Pattern Finish ing strategy.


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Issue PMILL 6.0 183

Enter the settings in the form exactly as shown (including Keep Inside -

Boundary 1) thenApply and Cancel the form. Undraw the model and Pattern1 to view the toolpath.

The Pattern Finishing, toolpath is created and limited to the inside of

the Selected Surface Boundary created earlier.

The Short Links are set to Safe Z at present but would benefit from

being changed to On Surface to reduce the machining time.

Open the Leads and Links form and select the Links tab. Set the Short Links to be On Surface. Apply andAccept the form.


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184 Issue PMILL 6.0

The amount of lifts has

been dramatically reduced.

Below is a diagram of an alternative toolpath running along the shut off face in a one-way,

Climb Milling direction. It starts at the bottom and works its way up the shut off face. This

strategy is more typical of a High Speed Machining application. By Utilising the same 2 Pattern, segments used in the previous example

apply theAutomat ic Pattern Generator to create the alternative PatternFinishing strategy described in the above pargraph.

Use these two straight

segments to produce this

toolpath shown with the

Links undrawn.


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Issue PMILL 6.0 185

Trochoidal Pattern GeneratorThe Trochoidal Pattern option within the Automatic Pattern Maker form is a technique

for machining slots especially in High Speed Machining applications. The Trochoidal

Pattern consists of a continuous spiral of advancing loops which have the effect of restricting

the tool contact area to only a part of its circumference.

This method creates the need to use a tool diameter that is smaller than the slot to bemachined. The CNC controller then performs spiral movements to mimic the full width tool.

Since the tool is no longer cutting at full width the problem of overheating is effectively

removed. (particularly important for coated solid carbide cutters used in High Speed

Machining).

Delete Al l, Reset Forms, and Import the Examples modeldashboard.dgk.

This slot to be machined using the

Trochoidal Pattern method.

Define the Block to Min/Max limits.

Create a new Pattern and use insert file into active pattern toinput the file \PowerMILL_DATA\Patterns\trochoidal_pattern.pic .

Before the slot can be produced a Helically drilled hole of diameter 8mm will be machined to

create clearance for a slot drill to plunge down to the full slot depth. This can be achieved

using Feature Sets. (Covered in more detail in the next chapter.)

Define a Ball Nose cutter of6mm diameter. Right click over Feature Sets in the Explorerand select Create Feature

Set to open the Feature Form.

Select the curved Pattern (1st click) and end point (2nd click).


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Fill in the Feature Form exactly as shown below (Create tab selected).

A new Feature will be

created that represents thehole ready for the helical

drilling.

Apply and Close the form. Select the Toolpath Strategies icon on the Main toolbar. Select the Drilling icon then OK to open the Drilling form.

Before the toolpath can be calculated, the

HoleFeature must first be selected.

Click on the Select button.


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Issue PMILL 6.0 187

Click on the Diameter 8.5 on the left of theform.

Click the Select Button and Close theform.

Fill in the form with thevalues shown thenApplyand Close the form.

It is noticeable on animation that the tool is Climb Milling in an

anti-clockwise direction. The 8.5mm Diameter hole has now

provided the clearance necessary for a smaller tool to plunge into the

slot prior to the Trochoidal milling operation.

Note: Feature Sets are not gouge checked to a Surface model so care must be taken when

creating them with regard to both size and position.


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188 Issue PMILL 6.0

Create an End Mill of diameter 6mm called em6. Deactivate Pattern 1 (trochoid_curve), but keep it displayed. (Toggle the

lightbulb; the Pattern will be displayed green). Create another empty Pattern (2). Select the curved Pattern (1) with the mouse then click on theAutomat ic

pattern generation icon .

Fill in the form as shown thenApply andAccept.

Note: The Radius must not be a value greater than half the Width. A fine Stepover is

required when applying to High Speed Machining of hardened steel.

If the Radius value used in the Pattern Maker form were 2.5

the resultant Pattern would appear as shown to the left.


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Issue PMILL 6.0 189

Select the Toolpath Strategies icon on the Main toolbar then select thePattern Finish ing strategy to open up the following form

Fill in the form exactly as shown.

Apply and Cancel the form.

The 6mm end mill tool will plunge into the

previously created 8.5mm clearance hole.

The Trochoidal toolpath defaults to a Climb

Mill direction and is ideally suited to High Speed

Machining applications.

Activate toolpath 1 (drilling) in the Explorer.


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Open the Block form.

Fill in the form exactly as shown to createa Block definition locally along the backhalf the slot width.

Accept the form.

Position the Block in the graphics area in preparation for toggling intoViewmill.

Select the RaiseViewMILL Toolbaricon.

Select the Toggle ViewMILL Window icon.

Check both the Helical and Trochoidal toolpaths in turn with ViewMILL.

Helical drill toolpath. Trochoidal mill toolpath.

Documents

PM 12 Patterns