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MACHINING THREE-DIMENSIONALSURFACES WITH PRO/NC

PTC Technical Support- Advanced Manufacturing Technique

140 Kendrick StNeedham, MA, USA

800-477-6435


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Advanced Manufacturing Technique Machining 3D Surfaces with Pro/NC

Introduction

This document explores different methods available for machiningcomplex, three-dimensional surface geometry with Pro/NC. Depending

upon the requirements for the geometry to be machined, the tool motion,and the surface finish, it may be necessary to employ different tactics forcreating NC toolpaths.

This technique utilizes the following functionalities:

Pro/NC Surface Milling Sequence

Pro/NC Mill Surface geometry

Pro/NC Mill Window geometry

Pro/ENGINEER Surface Analysis Pro/NC multi-axis milling (optional)

Estimated time to complete technique: 3 Hours

Copyright 2002 by PTC 2 PTC Technical Support


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Setup

For this technique, three NC-Assembly models were used. All contain areference model only, without a workpiece, for the sake of clarity. Thepresence of a workpiece should have no bearing on this technique.

The reference model for the theoretical discussions in this techniquecontains several curved surfaces, which, to obtain an optimal surfacefinish, must be carefully machined with Surface Mill sequences. In thiscase, the model is the upper body portion of a computer mouse.

For the Procedure section of the technique, two different models will beused. This top half of a staple remover has a curved surface on thehandle that will serve well to illustrate Straight Cut and Cut Line types ofSurface machining.



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Additionally, for the From Surface Isolines and Projected Cuts types, themodel of a computer keyboard shown below will be used.

If a different model is to be used to follow this technique, it should includea surface that is curved in two dimensions simultaneously, with curved

boundaries, and, optionally, a gap in the middle.

Example Files

The example models used in this document can be downloaded at thefollowing location: Example Part Files

http://www.ptc.com/cs/cs_23/howto/gim8787/gim8787_files.ziphttp://www.ptc.com/cs/cs_23/howto/gim8787/gim8787_files.zip


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Fundamentals

Introduction to Surface Machining

Pro/ENGINEER provides a wealth of different methods for machining

complex surfaces. In most cases, when presented with the task ofmachining such geometry, the best question to ask is not if it can be done,but how it can be done best.

There are many ways that Pro/ENGINEER can direct the tool to moveacross any given surface, but the criteria for the toolpath to be created willdictate how to construct the NC sequence.

For instance, to rough out a surface to be milled more carefully lateron, it may be useful to specify that it cut in straight lines, with a large tool,and large step distance. On the other hand, for a final cut on a surface, itmay be necessary to cut along the geometrys contours, using a small

scallop height, and a ball-nose endmill to ensure a quality finish on theresulting part surfaces.

Pro/ENGINEER Surface Mill sequences start out with very simplegeometry by default, but can be adapted to conform to more complexshapes. The simplest type merely drapes straight-line geometry over thesurface, and cuts along those paths. More advanced cut types use theactual surface geometry or boundary geometry to influence the shape ofeach toolpath pass, ensuring a more thorough cut, along with a bettersurface finish.

With that in mind, when presented with a three-dimensional surface

to machine, a few questions should be asked before proceeding: Is this a roughing or finishing toolpath, or somewhere

in between?

What is the level of precision required?

Is the speed of machining crucial, or is this a situationwhere the tool must cut slowly and carefully?

Is there a requirement for surface finish on theresulting final part?

Armed with this information, it should be possible to better employ Surface

Milling to the maximum advantage.

Tools and Parameters

The tools for Surface Mill sequences have a great deal to say aboutthe final outcome of a toolpath. Primarily, the tools effect is the level ofprecision with which a three-dimensional surface can be milled. For



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instance, a flat endmill is not going to able to fit everywhere that a ball-nose tool will.

With surface milling, envisioning the potential ability of a tool to cutthe surface is not merely a question of fitting it in between bosses, walls,and ribs, but determining its interaction with the shape of the surface. Ifan indentation in the surface is sudden and deep, it is possible that the

tool may not fit to cut it. Even with a ball-nose tool, if the nose radius isgreater than the radius of the cross-section of the dent, it still may not beable to reach some locations.

The area left, incidentally, is the ideal kind of situation with which touse Local Milling. With a smaller tool, Local Milling can clean up the areasthat the Surface mill toolpath left out. That, however, is beyond the scopeof this document.

The parameters for the sequence are, in general, similar to mostothers. A key concept with Surface Milling is STEP_OVER and

SCALLOP_HGT. The step over distance prescribes the amount betweeneach pass of the Surface Mill toolpath. The scallop height, however,determines the same thing, but in a different way.

Scallop Height determines the maximum allowable scallop left onthe part, a function of how close one pass is to another. Based on that, itcan figure out, in reverse, what the step over should be. If that value islower than that which is entered for STEP_OVER, then it is used; ifSTEP_OVER is lower, then it is used instead. The Pro/ENGINEER Helpdocuments have an excellent explanatory graphic for this, which is locatedin the document Milling Parametersat

http://www.ptc.com/cs/help/2001/html/usascii/proe/nc/milling_.htm , nearthe entry for SCALLOP_HGT.

Scan Types, while they vary depending on the Surface Mill type,are fairly typical here. One common application is to use a closed-cutlinesurface mill sequence in conjunction with a TYPE_HELICAL scan type tomachine threads on a conical or cylindrical surface.

Types of Surface Milling

Pro/ENGINEER creates Surface Mill toolpath geometry in a varietyof ways, ranging from the simple to the complex. Surface Mill sequencesare an extremely versatile functionality, and, like other NC Sequences, it isbest to understand how they work before beginning to use them. In thiscase, since Surface Mill sequences can actually take several differentforms, there is a bit more to learn.

http://www.ptc.com/cs/help/2001/html/usascii/proe/nc/milling_.htmhttp://www.ptc.com/cs/help/2001/html/usascii/proe/nc/milling_.htm


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Straight Cut

Straight Cut surface milling (formerly a separate sequence type,#Conventional, in Pro/ENGINEER 2000i and earlier) is the simplestmethod available. The #Straight Cutselection simply creates straight-line passes in the XY plane, spaced out at a distance of STEP_OVER,and drapes them over the surfaces to be machined. STEP_OVER can be

adjusted via the scallop height, and different lace options for the toolpathcan be created, but the basis for the toolpath remains the same.

While Straight Cut toolpaths can handle more complex geometry,they are most proficient at machining more gently sloping surfaces.Figure 1 below shows a typical application of a Straight Cut toolpath on agently curving surface. The yellow lines are projected onto the millingsurfaces as the green lines, which serve as the basis for the toolpath.Figure 2 shows the actual toolpath.

Figure 1. Figure 2.

Since Straight Cut toolpaths perform so admirably for thesesituations, it is tempting to select the entirety of a part for machining.However, unless the part is composed entirely of the same type of

geometry, it may not be appropriate to do so, as Pro/ENGINEER willsimply drape those lines across everything indiscriminately, with little roomfor customization.

Straight Cut also provides a convenient means for illustrating theeffect of Scallop Height on the toolpath. Note in Figure 3 howPro/ENGINEER adjusts the spacing of both the yellow and the green lineson the model, based on how close the passes must be to obtain a given



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scallop height. This applies on all types of Surface Mill sequences, butcan be most clearly visualized here.

Figure 3.

For cuts of an essentially back-and-forth nature on a curvedsurface, #Straight Cut surface mill sequences are a good choice.

From Surface Isolines

Another type of Surface Mill toolpath is defined using #AlongSurface Isolines. While a straight cut wraps straight lines over a curved

surface, an Isoline-based toolpath takes it one step further. Not only dothe lines conform to the surface in the tool axis direction, but they arecreated such that they traverse a path along the surface that follows a lineof constant curvature, or isolineon the surface. Isolines are similar innature to the lines on a weather map that represent constant barometricpressure.



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Pro/ENGINEERs isoline Surface Mill toolpaths do not follow isolinesprecisely, as that would limit both their usefulness and their success rate.While the toolpath is greatly influenced by the isolines, there is also anelement of control by the scan type and other parameters, as well. Figure4 below illustrates how the toolpath follows the curvature of the modelclosely, but not to the point of creating a useless toolpath.

Figure 4.

Note the way that each toolpath pass curves to conform to thechanges in curvature, shown in color via #Analysis, #Surface Analysis,#Gauss Curvature. The changes in the curvature in the blue region aremost noticeably influential on the toolpath nearby.

What advantages does this behavior provide to the user? By stickingto contours where there is no drastic change in the surface beingmachined, Pro/ENGINEER creates toolpaths that cut a more consistentamount of material.

A good analogy for this is that of a hiker on a steep hill. Topographicalmaps, like the one in Figure 5 show elevation change as a function of lineson the map that represent a certain, constant elevation. By walking alongthe lines, the hiker neither climbs nor descends; by walking normal tothem, he or she is in for a bit of work. Pro/ENGINEER uses the samerationale to create a toolpath here.



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Figure 5.

Since each surface patch is treated as its own self-contained entity bythe Isolines method, its usefulness is limited for situations where a greatmany surface patches make up a large quilt. The settings for the isolinedirection allow for a vestige of control over this, and also of the directionsof the isolines themselves, but it will frequently not be possible to make atoolpath flow smoothly from one patch to another, as the Straight Cutmethod would do.

Cut Line

Cutline surface mill sequences offer the most powerful array offacilities for customizing the final toolpath. The types discussed thus farcan be thought of as having a progression in terms of the complexity ofPro/ENGINEERs consideration of the surface geometry. Straight Cutsequences do not consider the surface geometry except to determineheight or scallop; they are just straight lines. Isoline sequences consider apredetermined geometric characteristic of the surface geometry inquestion. Now, Cutline sequences can generate the toolpath based on aconfigurable selection of existing surface references, or even sketched

references.

The best explanation of how cutlines work is to think of them as theintermediate defined sketches for a Blend feature. Pro/ENGINEERattempts to fit the toolpath in such a way that at the locations of thecutlines themselves, it closely matches the prescribed geometryreferences.

One of the most common applications of Cutline surface sequencesis to ensure the toolpath follows the boundaries of the surface beingmachined. In Figure 6, below, the large top surface of the mouse bodyhas the two side boundaries curving in opposite directions. Note how the

resulting toolpath gradually transitions from one side to the other. InFigure 7, the two end boundaries are different shapes; one is an arc, theother is roughly linear. The toolpath blends smoothly between the twoshapes.



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Figure 6. Figure 7.

However, Cutline sequences are not restricted to the geometry that existsin the model. It is possible, using the #Projectedoption, to sketch a lineor curve that will be projected onto the surface that is being cut. Thetoolpath contours will then use that as a reference for their shape. InFigure 8 below, a wavy line is added as an intermediate cutline, betweenthe previously defined two cutlines. The green cutlines now blend fromthe arc, through the wavy line, to the straight line.

It should be noted that, by default, the yellow and green cut line display is

turned off. Use the config.pro option MFG_DISPLAY_MCto turn them on,

per TAN 111490.

Figure 8.

The above example is certainly an exaggerated one, but it doesillustrate the potential of using cutlines. Through using selected orsketched cutlines, it is possible to exert a great deal of influence on thefinal shape of a Surface Mill toolpath. The choice of the word influencehere is not coincidental, and it should be emphasized that the cutlines arenot the final arbiter of what the toolpath will look like. Other items, such asthe scan type, the scallop height, and check surfaces will have their say

http://www.ptc.com/cs/tan/111490.htmhttp://www.ptc.com/cs/tan/111490.htm


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about the result. And, above all else, Pro/ENGINEER will do its best tomachine the surface to the fullest extent possible.

In Figure 9, below, the green lines in Figure 8 are not preciselyadhered to. For instance, at the right-hand side of the toolpath, there is awider separation of the passes, due to the peaking curvature of theunderlying part surface. While this illustrates the potential changes that

may occur in the end result, it is still clear that the cutline has had an effecton the toolpath shape.

Figure 9.

While Cutline sequences provide the most flexibility, they also canrequire a significant amount of work to create, and furthermore, to tweakuntil the best result is obtained. With the increased control over thetoolpath comes an increased potential for error, and additional items toconsider when troubleshooting.

Projected CutsThe Projected Cuts method of Surface Machining is similar to the

Straight Cut method, but allows the additional specification of boundaryconditions for the surface or surfaces that are machined by the sequence.This is particularly useful for machining a three-dimensional surface thathas gaps and holes in it.

The boundary loops of the surfaces for the sequence can beselected, and then offset, so that the tool essentially has a fence aroundthe perimeter of the area it should be machining. The surface geometrycan be projected upward to the retract plane, where the toolpath is built,

then projected downwards onto the surfaces.Using the Projected Cuts method to machine the same surface

from the prior examples, it is possible to restrict it to machining only acertain portion, thereby controlling the shape of the toolpath. For instance,if it was desired to mill out only the center region of the surface, it ispossible to establish a boundary, offset inward, to keep the tool in themiddle of the surface, as shown in Figure 10. The toolpath that results isshown by Figure 11.



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Figure 10. Figure 11.

However, another portion of the model might be better employed todemonstrate the strengths of this functionality. The surface on the front ofthe mouse body, with the gap for the scroll wheel, illustrates the ability ofthis type of sequence to pick portions of the surface around gaps to eithermachine around, or over.

Figure 12.

Figure 12 above shows how boundary conditions can be created tomachine over the thin portions of the surface, while still avoiding thatcentral hole.

After the boundary conditions are applied, the toolpath createdtherein is very similar in nature to the Straight Cut functionality. However,



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using the Projected Cuts toolpaths avoids the need for creating a tedioussurface trim on a Mill Surface to obtain the same kind of end result.

Other Characteristics of Surface Mill Sequences

Like most other NC Sequences in Pro/ENGINEER, Surface Milling

relies on part geometry as the primary defining factor of the toolpath. Inthis case, Surface references are used, either from the part or via MillSurfaces. The choice of the surfaces to be machined is a hugelyimportant factor in the success or failure of the toolpath.

Therefore, careful consideration should be given before selectingdozens of surfaces to be machined. While Pro/ENGINEER might be ableto machine a single patch among many surfaces well, perhaps the entiregroup of surfaces results in a toolpath that places undue stress on themachine, or results in a poor surface finish.

Likewise, for troubleshooting, it is frequently useful to deselect some

of the surfaces, to determine which ones cause toolpath failure. For MillSurfaces, use a Trim to cut the area in half. Tactics such as these aresimple ways to track down the cause of the difficulty.

While it is unusual for other types of sequences, in Surface Milling,depending on the choice of the Cut Definition, there may be differentselections available in the Parameter Tree. For example, someSCAN_TYPE selections will only be available for Cutline sequences, whileSCALLOP_HGT is not available at all for Isoline sequences. If, due tochanges, the combination of parameter settings and toolpath types are in

conflict, Pro/ENGINEER will use a default setting, and issue a warning inthe Message Window.

As an alternative to some uses of the Projected Cuts toolpaths, it isalso possible to use a Mill Window with Straight Cut toolpaths. Thistechnique is very useful for a quick and dirty Surface Mill sequence thatcovers a wide area of a part. Mill Windows cannot be used with otherSurface Mill types.

One unique parameter to Surface Mill sequences is

REMAINDER_SURFACE. This parameter allows for the creation of asurface to represent the material that the Surface Mill sequence couldntmachine. Figure 13 below shows an example of a remainder surface (inyellow) on the underside of the mouse body model.



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Figure 13.

Choosing a Surface Mill Type, and Designing a Sequence

With the information already presented, it should now be possibleto make a thorough evaluation of the needs of a new toolpath, and thelimitations imposed by the geometry being machined, with an eye towardsselecting the best method possible for machining it.

Having selected Surface Mill to do a particular job, that decisionneeds to be refined further into what type of Surface Mill sequence.

For a roughing type of situation, or for machining multiplesurfaces that do not need close attention to detail, StraightCutis a good choice.

For working with large, individual patches of a surface,where the quality of the cut is a prominent concern, FromSurface Isolines works well.

When it is necessary to exercise some control over theshape of the toolpath, Cut Linesequences are a goodselection.

When attempting to machine surfaces either over their

boundary, or far within their boundary,Projected Cutswillwork well.



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Procedure

The steps outlined here represent a thorough cross-section of possible SurfaceMill examples, and represent merely a starting point for further exploration of thefunctionality. The detailed instructions describe only the minimum procedures

required to further the discussion of these techniques. It is not only possible, butencouragedthat these examples be experimented with further to gain a betterunderstanding of Surface Milling.

1 Initial Steps

1.1 Retrieve the Manufacturing Model

Retrieve the example manufacturing model staple_remover.mfg.*Themodel initially contains the reference part, an operation, and a workcell; itis assumed that no discussion is necessary of Pro/NC fundamentals. Thismodel will be used to discuss the two most popular techniques for surface

milling, Straight Cut and Cut Line.

1.2 Examine the surface in question

As was shown in the Fundamentals discussion, much can be learnedabout the eventual outcome of a Surface Mill sequence by using Surface

Analysis functions in Pro/ENGINEEER. While it is not necessary to dothis, it is informative. Figure 14 below shows the reference part, with thesurface highlighted in red.

Figure 14.

It is this surface that this technique will primarily concern itself with.

*The model staple_remover.mfg is found in the zipfile gim8787_files.zip

http://www.ptc.com/cs/cs_23/howto/gim8787/gim8787_files.ziphttp://www.ptc.com/cs/cs_23/howto/gim8787/gim8787_files.zip


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1.2.1 Gauss Curvature analysis

Select #Analysis, #Surface Analysis. The Surface Analysisdialog will appear. From the Typepop-up menu, select #GaussCurvature. Select the arrow under Surface, and pick the surfacethat is to be machined, then #Done Sel. The surfaces curvaturewill be illustrated using vivid colors to represent different degrees of

curvature, as shown in Figure 15 below.

Figure 15.

The specifics of the curvature results are not important here,usually, but it is useful to observe where the shape of the surface

changes most dramatically, in case it is necessary to plan thetoolpath accordingly.

1.2.2 Normals analysis.

Select #Normalsfrom the Typemenu. The Surfacepicker shouldautomatically be chosen, then select the same surface as before,and #Done Sel. The surface should have green arrows upon it, asshown in Figure 16 below.



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Figure 16.

Each arrow represents the direction normal to the surface at thegiven point. Use the Spacingsliders to adjust the number ofarrows, and select #Compute again to adjust the display. This isparticularly useful for 4 or 5-axis Surface milling, as it provides aglimpse as to how the tool will be oriented if it is constrained to benormal to the surface.

2 Create a Surface Mill sequence (Straight Cut)

Now that some insight has been gained into what the nature of thegeometry to be machined is, the creation of a new Surface Mill sequencecan be undertaken.

2.1 Create the sequence

Select #Machining, #NC Sequence, #Surface Mill, #Done(For thoseused to Pro/ENGINEER 2000i, the former #Conventionaland #Contourare combined under #Surface Millnow).

2.2 Define the attributes

By default, every checkbox that is necessary to be defined will be checkedat the outset of sequence creation. If the sequence is to be defined with a

Mill Window rather than a set of surfaces, select #Windowhere. Makeany other desired changes here, then select #Done.

2.3 Create the tool

Typically, first up is the Tools Setup dialog. The dialog behaves nodifferent here than it does elsewhere in Pro/NC, but as previouslydiscussed, the tool selection can have a profound effect on what is and



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isnt machined. For the purposes of this example, add a .25CornerRadius to the default tool, and select #Apply, then #OK.

2.4 Define the parameters

Pick #Setto enter the Param Tree. At a minimum, four parameters willneed to be set.

CUT_FEED 12

STEP_OVER .05

SPINDLE_SPEED 1500

CLEAR_DIST .1

Others can be specified, if need be, but at a minimum, these willsuccessfully create a toolpath. Behavior with other specific parameterswill be discussed later. In general, it is assumed herein that typical MillingNC Sequence parameters are familiar, except where they are explicitlydiscussed in detail.

2.5 Specify a retract plane

Since this is the first sequence in the model, a Retract plane must bespecified. Select #Along Z Axisand enter 2, then select #OK.

2.6 Specify the surfaces to be machined

To start off, it is simplest to select #Model, in order to select surfaces

directly from the model. Select the surface shown earlier in Figure 14,then pick #Done Sel,#Done, and #Done/Return.

2.7 Define the type of cut

Next, the Cut Definition dialog will appear. Leave it set to #Straight Cutfor this example, and select #OK.

2.8 Play the sequence

Having returned to the main menu of the NC Sequence, select #PlayPath, #Compute CL, #Screen Play. Figures 17 and 18 show the straight

cut lines being projected onto the surface, and the resulting toolpath,respectively.



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While the toolpath successfully machines the surface, there are someways it could be improved.

2.9 Alter the CUT_ANGLE

First of all, it may not be desirable to have the tool making its passes onthe long axis of the surface, since it has the more dramatic curvature to it.There are two different ways to remedy this. One is to set the parameterCUT_ANGLE to 90. The other method is to go back to the Cut Definitiondialog. Select #Seq Setup, #Define Cutto return there, and note theoptions under Cut Angle Reference. Its possible to change the CutAnglehere numerically, or to specify an edge or surface for it to measurethat angle from. Either way, its easiest to just enter the value in this case.

Figure 19.

The result is a toolpath that is somewhat safer, as each pass moves in adirection that is mostly free of obstruction.



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2.10 Exchange STEP_OVER for SCALLOP_HGT

Change STEP_OVER to .25and enter a value of .001for theSCALLOP_HGT. Play the toolpath with #Play Path, #Compute CL,#Screen Play, and note, as shown in Figure 20 below, how the toolpathpasses are adjusted.

Figure 20.

Using scallop height instead of a step over does not make a noticeabledifference, except at the extreme ends of the surface, where the slope ismore pronounced. Return the Step Over and Scallop Height settings totheir original values for the next step.

2.11 Change to a Mill Window

Sometimes it is preferable to be able to enclose surfaces within a sketchin order to machine them. Perhaps in addition to the main surfaces, therounded edges surrounding it also must be machined. Rather thanpicking all those surfaces, they can be easily added to the sequence via aMill Window.

Select #Seq Setup, #Window, #Create Wind, and enter a name such asmill_window_1. Pick #Sketch, and Pro/ENGINEER will automatically

orient the model to sketch a Mill Window (on the Retract plane). Sketch

with the #Use Edge button, selecting the perimeter of the surface,with the rounds included inside.



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Before selecting #OKout of the Machine Window dialog, select the #ToolSideelement, and #Define. Set the window to allow the tool to machinepast its edges, by picking #Pastand #Done. Select #OK to finish theWindow, and use #Play Path, #Compute CL, #Screen Playto view theresult.

Figure 21.

The cuts are projected onto the model as shown in Figure 21, above.Now the toolpath machines across and over the boundaries of the surface,to make sure that nothing is left over. Clearly, a very different result canbe obtained with a seemingly minor change.

2.12 Change to a Mill Surface

In addition to simply selecting the surfaces as they exist upon the model, itis possible to use Mill Surfaces to replace them, augment them, ortruncate them, as necessary.

Select #Seq Setup, #Surfaces, then #Mill Surfaceand #Done. Select#Create Srf, and entermill_surf_1as the name. A Mill Surface is acollection of Surface-type features that, collectively, make up geometrythat can be selected for machining.

Select #Add, to start off with, and then, for the type, #Copy. Add thesame surface from the handle of the staple remover. Its possible to use#Extrude, #Revolve, and other familiar tools to create geometry outright,but it is important not to lose sight of Pro/NCs chief advantage: close tiesto the original model geometry. Select #Done Sel, #Done, and #OKtocomplete the copy.



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Next, the surface will be trimmed down to exclude parts that are notwanted. Select #Trim, and #Extrude, then #Done. Select #One Side,#Done, datum plane FRONT, #Flipthen #Okayfor the direction, and

datum plane TOPfor the #Top reference.

Sketch a rectangle enclosing the center portion of the surface, as shownin Figure 22 below.

Figure 22.

Finish the sketch, select #Side 1to keep, #Done, then #Thru Alland#Donefor the depth. Select #OKto complete the Trim, and#Done/Returnto complete the Mill Surface.

After that, Pro/ENGINEER will provide an additional opportunity to filterout which surfaces from the Mill Surface are to be machined. Select #Flipor #Okayfor the side, then #Select Alland #Done/Returnto select allelements of the mill surface.

#OKout of the Cut Definition dialog to finish the changes. When the pathis played again, the sequence will be similar, but will only machine thecenter region.



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2.13 Finish the NC Sequence

Select #Done Seq to complete the NC Sequence when satisfied with theresult.

3 Create a Surface Mill Sequence (Cut Line)

Since this surface has something of a bowl shape to it, it may be desirableto mill it using concentric passes that follow the contour of the bowl.

3.1 Create the sequence

Select #Machining, #NC Sequence, #New Sequence, #Surface Mill,#Doneto create a new sequence.


Check #Tool, so as to define a different, smaller tool to use for thissequence. Select #Doneto proceed.

3.3 Define the tool

Create a new tool, with a diameter of .25and a corner radius of .125.Select #Apply, then #OKto continue.


Select #Use Prev, #1: Surface Milling to retrieve the same set ofparameters from the first sequence. Select #Setand modify STEP_OVERto .0625. Close the Parameter Tree and select #Doneto continue.

3.5 Specify a surface to be machined

Select #Model, #Done, then select the large curved part surface from theprior sequence. Select #Done Sel, #Done, and #Done/Returntoproceed.

3.6 Define the type of cut

Select #Cut Line in the Cut Definition dialog. The dialog box will changenoticeably, to provide a wealth of additional options. Towards the bottomis a list of the cut lines that define the sequence. Before adding one,select the #Closed Loopsradio button. Then, select the +button to adda Cut Line.

By default, the cut line addition will be done using the #Bndry Chainoption, but they can be done with #Tangent Chainor #One By One,depending on which is most convenient. Here, since there are twoboundaries, Pro/ENGINEER prompts to clarify which one to consider first.Select #Nextto toggle to the outer boundary, then #Accept and #Donetoselect it. Select #OKto complete the first cutline.



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Use the same technique to select the inner, circular boundary. The resultshould be as depicted in Figure 23 below.

Figure 23.

The selected cutlines are highlighted in purple.

3.7 Return to the parameter tree

Select the Parameter Tree button from the Pro/ENGINEER main windowto quickly return there. Note that under SCAN_TYPE, the optionsTYPE_SPIRALand TYPE_HELICALare now there. Neither is necessaryhere, so no changes need to be made, but it does serve to illustrate thedifferences in capabilities with cut types.

3.8 Play the toolpath

Select #Play Path, #Compute CL, #Screen Playto compute and displaythe toolpath. The toolpath created makes concentric passes, blending theshape of each, from the squished-arrowhead outer shape, to the circularinner shape. The result is shown in Figures 24 and 25.



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Toolpaths such as this are useful for making precise final cuts, wheresurface quality is a primary concern. However, it is not required that thecutlines be closed.

3.9 Alter the cutline scheme

Its possible to use open cutlines on this sequence as well. Perhaps it isnot desirable to have the tool follow the straight portion on the top soclosely. Instead of allowing that part of the geometry a say in how thetoolpath is created, the cutlines can be altered to produce a toolpath thatonly blends the two ends of the surface.

Select #Seq Setup, #Define Cut. Delete the two existing cutlines with thebutton, and select the #Open Endsradio button. Select the +button toadd a cutline, and use #One By Oneto select the leftmost edge segmentonly. Do this again for the rightmost edge. The result should appear

similar to Figure 26 below.

Figure 26.



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The selected edges should again be highlighted in purple. Select #OKtoproceed.


Select #Play Path, #Compute CL, #Screen Playto display the toolpath.The result should be similar to Figure 27 below.

Figure 27.

While the toolpath still follows the contour of the surface boundaries, itnow only follows two significant ones, allowing for a toolpath that issimpler, but still closely tied to the actual shape of the part.

Select #Done Seqto complete the sequence.

4 Create a Surface Mill Sequence (From Surface Isolines)

For the Surface Isoline and Projected Cuts toolpaths, a differentmanufacturing model will be used, to better illustrate the strengths of bothtechniques.

4.1 Retrieve the Manufacturing Model

Retrieve the model keyboard_upper.mfg.* This model contains areference part, operation, and workcell, and is ready for new sequences tobe designed with it.

4.2 Visualize the surface curvature (optional)

Select #Analysis, #Surface Analysis, and #Gauss Curvature. Selectthe surface shown in Figure 28 below, and others, to examine thecurvature of the part to be machined.

*The model keyboard_upper.mfg is found in the zipfile gim8787_files.zip

http://cham-2/Shelf/king/seaman/rleeds/james/websweep/General/gim8787/surfmill_exercise_parts.ziphttp://www.ptc.com/cs/cs_23/howto/gim8787/gim8787_files.ziphttp://www.ptc.com/cs/cs_23/howto/gim8787/gim8787_files.ziphttp://cham-2/Shelf/king/seaman/rleeds/james/websweep/General/gim8787/surfmill_exercise_parts.zip


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Figure 28.

Note that the change in colors does not necessarily imply acommensurately drastic change in curvature. For the Isoline-basedtoolpath, the palm rest of the keyboard will be the focus of the sequence.

4.3 Create a new Surface Mill sequence

Select #Machining, #NC Sequence, #Surface Mill, #Doneto create anew Surface Mill sequence.


As this is a new model, both the #Tooland #Retractselections will beadded to the list under the SEQ SETUP menu. Select #Doneto continue.

4.5 Define the tool

Create a tool with .25cutter diameter, and a corner radius of .125.Select #Applyand #OK to continue.


Add a minimal set of parameters to the sequence, as shown in thefollowing listing.

CUT_FEED 12

STEP_OVER .05

SPINDLE_SPEED 1500

CLEAR_DIST .1

Again, a familiarity is assumed with typical parameters and reasonablesettings for them, except where explicitly discussed here. Exit theParameter Tree and select #Doneto proceed.



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4.7 Define the retract plane

Select #Along Z Axis, enter 3, and pick #OKto continue.

4.8 Select the surface

Select #Model, then, when prompted, select the broad surface that formsthe bulk of the palm rest on the keyboard model, as shown in purple inFigure 29 below.

Figure 29.

After selecting it, pick #Done Sel, #Done,and#Done/Returnto move on.

4.9 Define the cut type

In the Cut Definition dialog, select the #From Surface Isolines radiobutton to switch to an Isolines toolpath. Highlight the lone surface in the

list, Surface id= #### and use the #Directionbutton to toggle

the isoline direction such that it is parallel with the long axis of the model.

The intent is to create a cut that smoothly machines the surface, followinglines of constant curvature, which, judging from the Gauss Curvatureanalysis, can best be fit in the direction chosen.


Select #Play Path,#Compute CL,#Screen Playto view the resultingtoolpath. The tool should automatically make a curved motion on eachsuccessive pass, following the curvature of the palm rest on the keyboardpart. The result is shown in Figures 30 and 31 below.



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Figure 30.

Figure 31.

The toolpath has clearly had good success with fitting each pass onto thesurface in such a way that it follows the curvature of the part model. Itdoes not do so perfectly, of course, but given the direction specified andthe slope of the surface in both directions, its evident that the result will doa respectable job of machining the surface. This could certainly be done

with cut lines, but the advantage here is that it is done automatically, andis certain to adjust well to any changes in the design.

4.11 Add surfaces

While the strength of the Isoline toolpath is its ability to automatically adaptto surface contours, its weakness is its inability to smoothly machinemultiple surface patches at once. Return to the #Seq Setupmenu, andselect #Surfaces, then #Done, then#Model. Add the remainder of thesurfaces that make up the palm rest, then pick #Done Sel, #Done, and#Done/Returnto continue.

4.12 Configure the direction for each surface

The Cut Definition dialog will appear automatically, but now will have amuch longer list of surfaces to configure the direction for. Use the

#Directionbutton to select the correct direction (same as before, thelong axis of the part) for each of them, and select #OKto proceed.



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4.13 Play the toolpath.

Select #Play Path, #Compute CL, #Screen Playto view the result. Thetoolpath still machines the surfaces taking into account the curvature ofthem, but it does this on a patch-by-patch basis. The result is shown inFigure 32 below.

Figure 32.

This is, of course, not conducive to a good surface finish, and is the majordrawback to this type of Surface Mill sequence. A Cut Line sequence,using the upper and lower boundaries of the entire set of surfaces as cutlines, would work well in its stead.

Select #Done Seqto complete the sequence.

5 Create a Surface Mill toolpath (Projected Cuts)


Select #Machining, #NC Sequence, #New Sequence, #Surface Mill,#Doneto create a new Surface Mill sequence in the same manufacturingmodel.


Accept the default list of attributes, including the previously defined tooland retract plane, by selecting #Done.

5.3 Read the parameters from the previous sequence

Use #Use Prevto read the parameters from the previous Surface Millsequence, then select #Done.



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5.4 Select the model surfaces to be machined

Select #Model, then select the surfaces of the part that make up theprimary body of the part, surrounding the cutouts for the arrow and pageup/down keys. The appropriate selections are highlighted in purple inFigure 33, below.

Figure 33.

5.5 Define the Surface Mill type

Select #Projected Cutsfrom the top portion of the Cut Definition dialog.This will display the Projected Toolpath section of the Cut Definitiondialog.

The Projected Cuts toolpath will be employed here to ensure that, despiteall the gaps in the surface, Pro/ENGINEER will fully machine the area inbetween, and use the shape to generate the best toolpath possible, giventhe limitations. Theres a huge amount of functionality for definingcontours, and this is only a simple example of how to use it.

Use the +button to add a boundary condition to the Projected Cutdefinition. Check both #Def Contrsand #Def Offsets, then select #Done.Select using #Select All, or select an individual boundary to add anddefine. Pick #Leftor #Rightto offset the boundary, and pick #Offsettodefine the offset value. In this case, though, since the surface abuts anedge of the part, select #Onfor the side. Select #Nextor #Prevto move

onto other contours selected. The end result is shown in Figure 34,below. Changes can be easily made to these definitions using the dialog.Select #Doneto finish the definition.



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Figure 34.


Select #Play Path, #Compute CL, #Screen Playto display the toolpath

onscreen. The toolpath should machine the geometry as shown in Figure35 below.

Figure 35.

Note that if an offset is added so that the cuts are projected off of the part(hanging over an edge, for example), the toolpath created will plunge to anextreme depth, which is likely not desirable.

Select #Done Seqto complete the toolpath.



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6 Create a multi-axis Surface Mill toolpath (optional)

6.1 Create a new operation and workcell

Create a new operation in keyboard_upper.mfg, referencing a new, 5-axis workcell. No specific settings beyond the defaults are required.


Select #Machining, #NC Sequence, #Surface Mill, #4 Axis, #Done, tocreate a new 4-axis Surface Mill sequence.

6.3 Define the attributes of the sequence

An additional selection, #4 Axis Planewill be checked for definition here.Select #Doneto proceed.

6.4 Define the tool

Define a tool with .5cutter diameter and .25corner radius for use with

this sequence.

6.5 Read the parameters

Select #Use Prevand retrieve the parameters from an earlier sequence,for use here. As always, they are minimal settings that can beexperimented with further.

6.6 Select the retract plane

Pick #Along Z Axisand enter 4.

6.7 Select the surfacesSelect #Model, then select each surface of the palm-rest portion of thekeyboard model. Select #Done Sel, #Done, and #Done/Returnwhensatisfied.

6.8 Select a 4-axis plane

Just as with a 4-axis Trajectory Mill toolpath, a plane must be selected forthe tool to remain parallel to. Select the RIGHTdatum plane in this model.

6.9 Define the cut type

#Projected Cutsis not available with 4-axis Surface Mill sequences, but#Straight Cut, #Cut Line, and #From SurfaceIsolines are. Theirbehavior is similar to that for 3-axis toolpaths, but care should be taken toensure that the toolpath moves at an angle appropriate to its rotary axis oraxes. Experiment with all of them here.



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Select #Play Path, #Compute CL, #Screen Play, and note that the toolnow is capable of rotating to stay perpendicular to the surface, much likethe #Normalsanalysis showed earlier. Figure 36 below shows the endresult for a 4-axis toolpath.

Figure 36.

6.11 Other capabilities of multi-axis machining.

Five-axis Surface Mill toolpaths behave similarly, but without the restrictionof the #4 Axis Plane.

In both cases, the #Axis Defselection in the #Seq Setupmenu providesaccess to one of the more powerful abilities of multi-axis Surface Milling.

Axis Definition allows the direct specification of the tool orientation atcertain junctures of the toolpath. This can be done by creating points and

axes on the surface, or by specifying an axis or curve to pivot around.

This is not required, but does provide the opportunity to model the toolpathsuch that it more accurately reflects the milling machines range of motion.The end result would be a toolpath that is certain to be within thepostprocessors axis limits, and therefore those of the machine.

These axis definitions do have the potential to render the toolpathimpossible to create; 5-axis motion in a 4-axis toolpath is forbidden, ofcourse.



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Review

Surface Milling is best understood as its own little toolbox, consisting offour different techniques for milling Surface geometry in a Pro/ENGINEERmodel. Each different type of Surface Mill toolpath has strengths andweaknesses, and therefore is best applied in different situations.

Type ApplicationRoughing

FinishMilling

FollowingSurfaceContours

MillingMultipleSurfaces

CustomizingToolpathShape

MultipleAxisMilling

SpiralMilling

WorksAroundGaps

MillWindow

Straight Cut X X

From Surface Isolines X X X

Cut Line X

Projected Cuts X X

= works well X = not available

blank = possible, but not the best solution

Figure 37.

The above table in Figure 37 lists the four types of Surface Mill toolpaths,and a review of different applications of them. These are merely

recommendations, as persistent work with one tool may yield a workablesolution even in a less-than-optimal situation. Nevertheless, the bestresults will always be obtained by working to the strengths of each tool.

With a thorough knowledge of the pros and cons of each type of SurfaceMill, experience with manipulating Mill Surfaces to lead Pro/ENGINEER tothe right geometry, and understanding of how best to tweak the end result,Surface Milling should now be a powerful ally in the effort to machine apart.



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Additional Information

PTC Knowledge Base documents:

Frequently Asked Questions: Pro/MANUFACTURING - Milling

http://www.ptc.com/cs/cs_23/faq/mil_faq.htm#b

Milling Parameters

http://www.ptc.com/cs/help/2001/html/usascii/proe/nc/milling_.htm

Closed Cutline Surface Milling On an Undercut Surface Using a SideMill Tool.

http://www.ptc.com/cs/cs_23/howto/mil401/mil401.htm

Creating An Open Cutline Surface Milling NC Sequence


Using Axis Def to Control the Tool Axis in a 5 Axis Cut Line SurfaceMilling Sequence


External references:

(While the following links may be interesting and informative, theinformation therein is suggested for background information, and does notnecessarily reflect on Pro/ENGINEER functionality in specific.)

5-Axis Freeform Surface Milling using Piecewise Ruled SurfaceApproximation

A paper by the Computer Science department of the University ofUtah, that discusses in detail the mathematical aspects of solvingthe problem of Surface Milling for particular type of 5-axis model.Not for the faint of heart.

http://www.cs.utah.edu/gdc/publications/papers/elber97b.pdf

http://www.ptc.com/cs/cs_23/faq/mil_faq.htmhttp://www.ptc.com/cs/help/2001/html/usascii/proe/nc/milling_.htmhttp://www.ptc.com/cs/cs_23/howto/mil401/mil401.htmhttp://www.ptc.com/cs/cs_23/howto/mil456/mil456.htmhttp://www.ptc.com/cs/cs_23/howto/mil753/mil753.htmhttp://www.cs.utah.edu/gdc/publications/papers/elber97b.pdfhttp://www.cs.utah.edu/gdc/publications/papers/elber97b.pdfhttp://www.ptc.com/cs/cs_23/howto/mil753/mil753.htmhttp://www.ptc.com/cs/cs_23/howto/mil456/mil456.htmhttp://www.ptc.com/cs/cs_23/howto/mil401/mil401.htmhttp://www.ptc.com/cs/help/2001/html/usascii/proe/nc/milling_.htmhttp://www.ptc.com/cs/cs_23/faq/mil_faq.htm


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Glossary

Mill Surface A collection of surface geometry features, includingextruded, revolved, and flat surfaces, trim features, and merge features,all combined to provide a convenient and accurate reference for an NCsequence

Mill Window A two-dimensional, sketched shape which acts as aboundary for a Surface Mill toolpath.

Cut Line The term cut line refers to several similar things, but indifferent contexts. The lines shown in green and yellow in the figures inthis document, representing cut geometry being constructed andprojected, are frequently referred to as cut lines. More common, however,is the use with actual Cut Line type toolpaths. Cut Lines, in this context,represent sketched or selected references for the toolpath that influencethe way the toolpath is constructed (leading to the first type of cut line)

Mill Curve Mill Curve is another descriptor for the green and yellowcurves draped upon the model surfaces.

Isoline An isoline, here, is a line of constant curvature on the model.Tracing a path along an isoline means that the curvature of the surface willnever change along that path.

Scallop Height The height of the hypothetical amount of material left inbetween passes on a surface. Specifying a maximum scallop height canallow Pro/ENGINEER to examine the surface geometry, and calculate inreverse the necessary value of the step over to achieve that scallopheight.

Lace Option controls the shape of the connection between passes.



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3.3: Cutter Diameter [.25], Corner Radius [.125], #Apply, #OK

3.4: #Use Prev, #1: Surface Milling, #Set, STEP_OVER [.0625],#Done

3.5: #Model, #Done, [select surface], #Done Sel, #Done, #Done/Return

3.6: #Cut Line, #Closed Loops, +, #Next, #Accept, #Done, #OK, +,

#Accept, #Done, #OK, #OK

3.8: #Play Path, #Compute CL, #Screen Play

3.9: #Seq Setup, #Define Cut, [delete entities withbutton], #OpenEnds, +, #One By One, [select leftmost edge], #Done Sel, #Done, #OK,+, #One By One, [select rightmost edge], #Done Sel, #Done, #OK, #OK

3.10:#Play Path, #Compute CL, #Screen Play, #Done Seq

Create a Surface Mill Sequence (From Surface Isolines)

4.1:#File, #Open, [keyboard_upper.mfg], #OK

4.2: #Analysis, #Surface Analysis, #Gauss Curvature, [select surface]4.3: #Machining, #NC Sequence, #Surface Mill, #Done

4.4: #Done

4.5:Cutter Diam [.25], Corner Radius [.125], #Apply, #OK

4.6: #Set, CUT_FEED [12], STEP_OVER [.05], SPINDLE_SPEED

[1500], CLEAR_DIST [.1], [exit parameter tree], #Done

4.7: #Along Z Axis, [3], #OK

4.8: #Model, [select surface], #Done Sel, #Done, #Done/Return

4.9: #From Surface Isolines, [select surface], #Direction, #OK

4.10: #Play Path, #Compute CL, #Screen Play

4.11: #Seq Setup, #Surfaces, #Done, #Model, [select surfaces], #DoneSel, #Done/Return

4.12:[select surfaces], #Direction, #OK, [repeat as necessary]

4.13:#Play Path, #Compute CL, #Screen Play, #Done Seq

Create a Surface Mill Sequence (Project Cuts)

5.1: #Machining, #NC Sequence, #New Sequence, #Surface Mill,

#Done5.2: #Done

5.3: #Use Prev, [select sequence],#Done

5.4: #Model, [select surfaces], #Done Sel, #Done, #Done/Return

5.5: #Projected Cuts, +, #Def Contrs, #Done, #Select All, #On, #Next,#On, #Done, #OK



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5.6: #Play Path, #Compute CL, #Screen Play, #Done Seq

Create a multi-axis Surface Mill toolpath

6.1: #Mfg Setup, #Operation, #New, #Workcell, #New, #5 Axis, #OK,[select coordinate system], #OK

6.2: #Machining, #NC Sequence, #Surface Mill, #4 Axis, #Done

6.3: #Done

6.4:Cutter Diam [.25], Corner Radius [.125], #Apply, #OK

6.5: #Use Prev, [select sequence], #Done

6.6: #Along Z Axis, [4], #OK

6.7: #Model, [select surfaces], #Done Sel, #Done, #Done/Return

6.8:[RIGHT]

6.9: #Straight Cut

6.10: #Play Path, #Compute CL, #Screen Play, #Done Seq



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Quick Reference Card

A Quick Reference card for Surface Milling, encapsulating many of the keypoints of this document, is available at the following location:

Surface Milling Quick Reference Card
http://www.ptc.com/cs/cs_23/howto/gim8787/gim8787_qrc.pdfhttp://www.ptc.com/cs/cs_23/howto/gim8787/gim8787_qrc.pdf

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