Baixe Surface Modeling: Creating Complex Shapes using Style Features and Curves in Wildfire CAD e outras Notas de estudo em PDF para Engenharia Mecânica, somente na Docsity!
Surface Modeling
By D Cheshire
Page 1 of 8
Surface modeling is a technique whereby the CAD model represents onlythe outside surfaces of product. It was one of the earliest methods ofcreating 3D models and preceded solid modelers (which represent thevolume occupied by the product) by many years. They have the advantageof being able to represent very complex shapes and so are still in usetoday in many industries. Wildfire has the advantage of combining a solidmodeler and a surface modeler into a single system. This means that youcan use surface modeling techniques when needed for complex shapesand then convert the resultant model into a solid model and use solidmodeling techniques for more basic engineering functions.This tutorial describes how surface and solid modeling techniques can becombined in the design of a complex shaped product – an electric shaver.The^ tutorial^ assumes^ you
are^ already
familiar^ with
the^ techniques
associated with solid modeling covered in earlier tutorials. Style Features Style features are one way of creating surfaces in Wildfire. They are theleast constrained way of designing allowing you to sketch in a freeformmanner without worrying about dimensions.Start^ ProEngineer,
Create^ a^
new^ part^ called
shaver^ using
the
mmns_part_solid option. Even though the shaver is a very free form shapethere are elements which must interface to engineered parts such as therotary cutters. The shape of these is largely defined by their function.Wildfire is quite capable of combining geometric and freeform shapes.To start use the sketch tool
to draw the shape shown in Figure 1. Note: the dotted construction circle is achieved by drawing a normal circle,selecting it with the
tool and then pressing and holding the right mouse button and choosing construction from the pop-up menu.
Figure 1 : Cutter Sketch
Now let’s get straight into style. Choose INSERT > STYLE… or the icon. A new set of icons appears down the right of the screen which youwill learn about in this tutorial. Also notice a STYLING menu is added tothe main menu which has some more options for which there are no icons.Since^ style^ features
are^ intended
for^ the^ early
stages^ of^ the
design
process there are some nice features to support this. On the websitewhere you found this tutorial you will find a picture called shaver which youshould download and save in your working directory. This is a hand drawnsketch of the intended design (you can’t beat paper and pencil for quicklyrecording ideas). We are going to use this as an underlay to help us in thedesign process.From the STYLING menu choose TRACE SKETCH… and a dialog boxwill appear as shown in Figure 2. Click on the name FRONT in this dialogand an OPEN dialog will appear to allow you to find the picture youdownloaded. When you open this picture it will appear attached to the frontplane^ in^ the
main^ window.
In^ the^ Trace
Sketch^ dialog
click^ on
HORIZONTAL. The picture will now be bounded by two horizontal yellowlines. Use the mouse to drag these so that they just touch the head of theshaver as shown in Figure 2. The sketch you have already drawn specifiesthat the overall height of the head (between these two yellow lines) shouldbe 50mm. In the dialog box you will see a FIT area with a value of 200.This is the current distance between the lines. Change this value to 50 andpress the FIT button and the size of the picture will change. Now thedistance between the lines is 50mm. In the PROPERTIES area at thebottom of the dialog you will find more tools. Use the MOVE H & V windersto position the sketch so it matches curve you drew as shown in Figure 2.Click OK to finalise the trace.
Figure 2 : A Trace Sketch
Surface Modeling
By D Cheshire
Page 2 of 8
Now we have the trace we can use it as we draw. We are going to start bydrawing profile curves of the shaver. These need to be drawn on theFRONT plane. You can use the
tool in style to pick any datum plane to make it the active plane. Use this now to make FRONT active (it will bedrawn with a grid on it to show it is active. Now press and hold the rightmouse button and choose ACTIVE PLANE ORIENTATION from the pop-up menu to change the view to look onto this plane.To start drawing curves choose
and a dashboard will appear at the bottom of the screen.
Figure 3 : Sketch Dashboard Make sure the PLANAR option is chosen then draw a curve by clickingpoints with the mouse. Try to follow the profile of the trace as shown inFigure 4. You will need more points where the curve is tighter but it is goodpractice to use as few points as you can. If it is not perfect don’t worry –you can improve it later.
Figure 4 : First Profile To improve the shape you can now choose
from the side menu (you
don’t have to press the
to end curve input first if you don’t want to). The^ curve^ input
dashboard^ will
be^ replaced with^ the^ edit
dashboard
(Figure 5).
Figure 5 : Edit Dashboard
In this mode you can make changes to the shape simply by dragging thepoints on the curve. You can also right click and hold on the curve to add apoint or right click and hold on a point delete it.One thing that must be done at this stage is to ensure that the end of thecurve joins on to the end of the head curve you drew in Figure 1. Drag theend point now but hold the SHIFT key down as you drag and the point willlock on to nearby geometry. When you release the point it will show it islocked by a small cross. You may find this easier to do if you spin the viewaround to a 3D view first.
Figure 6 : Locked and Normal You may have noticed that when you clicked on the endpoint of a curve ayellow line is drawn from the point. This is the tangency line – the directionin which the curve leaves the point. You can move this to by dragging itsend. In this case we want the curve to be at right angles to the RIGHTplane. Select the endpoint then press and hold the right mouse buttonnear the end of the yellow tangent curve and choose NORMAL from thepop-up menu. You will be asked to pick a plane to be normal to – pick theRIGHT plane.To help you to achieve a smooth curve there are some useful analysistools. Choose ANALYSIS > GEOMETRY > CURVATURE or the
icon.
In the dialog that appears click on SAVED then pick the curve you aredrawing. You may need to go to the DEFINITION pane and increase thescale to see the curvature display. Close the dialog now when you movethe curve points the curvature display updates. Use this display to guideyour curve design – you want a curve that increases and decreases inradius smoothly and does not oscillate between concave and convex anymore than it should.You can delete the curvature analysis at any time with ANALYSIS >DELETE ALL > DELETE ALL CURVATURE or
Surface Modeling
By D Cheshire
Page 4 of 8
lines and 2 arcs. Now release the SHIFT key and hold the CTRL key whilstyou pick the other 3 curves. When you have picked the 4 curves you willhave to click on OK in the small select dialog and if you have selectedcorrectly a surface should be created!
Figure 12 : Surface Created If a surface is not made check the information lines at the end of thescreen to see if it warns of curves not connected – if it does you need toedit the curves so that the ends snap to their neighbours.Take a close look at Figure 12. You can see some small arrows on theedge of the surface. These are a visual indication that there is a constrainton these edges. In this case these were created because the two curves(on either end of the shaver) were created with normal tangencies. Youwill see more of these constraints and how to use them later.The surface looks OK but we can refine it even further by adding internalcurves. We are going to draw a new curve but we are going to use a newtype of curve – a FREE curve. These curves give you more freedom butare more difficult to get the hand of – practice!To start drawing the new curve choose
and in the dashboard choose FREE. Now place points for the curve using SHIFT to snap the first andlast point to the upper and lower profile curves. Try editing these pointsand you will find they are difficult to move because you are trying toposition a point in 3D space using a 2D screen. To help you can use thesplit screen view set using the
icon. The screen should change to
show 4 views which you can zoom and pan independently. You shouldnow with a bit of practice and patience be able to edit the curve in acontrolled manner. Once again make sure the ends of the curve aresnapped to the profiles and the tangencies of this curve are set to benormal to the FRONT datum plane.
Figure 13 : Free Curve To add this to the definition of the surface click anywhere on the existingsurface^ then^
right^ click^ and
choose^ EDIT
DEFINITION.
The^ surface
definition dashboard will appear. Now click on the INTERNAL arrow and pick the new curve and press OK. The surface should update toreflect the shape of this curve – if it doesn’t did you remember to snap theends and make them normal to FRONT?Have you noticed that the surface is linked to the defining curves? Thismeans that if you edit the curves they will update in real-time so you candynamically control the shape of the surface – try it and see.Add more internal curves until you are happy with the shape. The internalcurves don’t all have to go across the surface they can go along thesurface as well but if they do they should be snapped to the cross wherethey touch.Finish the style feature by clicking the
icon from the right hand toolbar.
Surface Modeling
By D Cheshire
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Figure 14 : Finished Surface Let’s create another style feature to show some more options. This will bea raised section for the button. Choose INSERT > STYLE… or the icon then set the active plane to be front and draw a straight line as shownin Figure 15. This line will not be used to create the surface – it will beused as a construction line for a new plane.
Figure 15 : Construction Line Create the new plane now using STYLING > INTERNAL PLANE or
You should be familiar with how to create planes using the dialog box. Usethis line^ for^ the plane
to^ pass^ through and
the^ FRONT datum as a
NORMAL reference. Set the viewing direction onto this plane and draw theplanar curve in Figure 16a making sure that the ends of this new curve arelocked onto the straight line and the end tangencies are normal to theFRONT datum. Create a second curve but this time chose the COS (curveon surface) option and draw the curve in Figure 16b making sure that theends of this new curve are locked onto the edge of the original surface andthe end tangencies are normal to the FRONT datum. Notice how this newCOS curve sits on the original surface. It is linked to the original surface soif that updates so will this curve. It also has implications for the creation ofthe surface using this curve as we will see.
Figure 16 : New Curves Now put these curves together to make a surface. Choose the
tool
and select these two new curves (not the straight line). Click on OK in thesmall select dialog and if you have selected correctly a surface should becreated!^ Notice this
surface was created with only two curves.
If we
wanted more control we could have drawn more curves.
Figure 17 : Surface Connection Options
Surface Modeling
By D Cheshire
Page 7 of 8
using^ the^ new
plane^ as^ the
sketching^ datum
to^ sketch^ the
outline
(use^ ).
Figure 21 : Second Fill We could use the same technique to fill the final hole but let’s show howyou^ can^ combine
simple^ modelling
techniques^
with^ these^ complex
surfaces. You should be familiar with extruding solids but you can alsoextrude surfaces to. Choose the extrude icon
and make sure you
select the surface icon
from the dashboard. This will cause the extrude command to create a surface rather than a solid. This means thatyou don’t need to draw a closed sketch. Draw the sketch in Figure 22 onthe FRONT plane (HINT: use
and make sure the ends are aligned with the surface edges). Extrude the surface both ways
by say 50. Figure 22 : Extruded Surface
This extruded surface is clearly not finished yet in fact none of the fills are.At the moment the model is made up of a number of ‘quilts’. Quilt is acollection of individual surfaces joined at their edges. Right at the bottomof the screen you should see a list box which normally says smart. Thisbox controls what type of geometry is picked with the mouse. Change thisnow to say quilts and move the mouse over the model to see the individualquilts highlight. The model is made up of 5 quilts. We need to join theminto a single quilt. This process will be in several steps.Step 1: Pick the two halves of the model (use CTRL to multiple select) andchoose EDIT > MERGE. When you press the
icon on the dashboard
the two quilts will be merged into 1.Step 2: Pick the main body of the model and the triangular head surface(use CTRL to multiple select) and choose EDIT > MERGE. When youpress the^
icon on the dashboard the two quilts will be merged into 1. Step 3: Pick the main body of the model and the button fill surface (useCTRL to multiple select) and choose EDIT > MERGE. When you press the^ icon on the dashboard the two quilts will be merged into 1.Step 4: Pick the main body of the model and the extruded surface (useCTRL to multiple select) and choose EDIT > MERGE. This surface needsa little more thought because the extruded surface is too long. The mergecommand^ doesn’t
just^ connect
surfaces^ together
it^ will^ also^
trim^ off
overlapping portions. The portions which will be kept are covered in adotted mesh. If the wrong part of the surface is highlighted use one of the^ icons to switch it and use the
to check the result. When you press the^
icon on the dashboard the two quilts will be merged into 1. Now all of the surfaces are connected together into a single quilt and thissingle quilt encloses a single volume with no gaps – this is an idealcandidate to convert into a solid. Select the quilt and choose EDIT >SOLIDFY and press the
icon on the dashboard to make a solid. Now it is a solid you can perform all the normal solid modelling functions thatyou are familiar with. Try adding some rounds and add an extrusion tolocate the head to prove the point.
Surface Modeling
By D Cheshire
Page 8 of 8
Figure 23 : The Final Solid
Review So what should you have learnt?^ •^ How to use trace pictures.^ •^ How to create style surfaces.^ •^ To understand curve/surface continuity^ •^ How to merge surfaces.^ •^ How to make solids from surfaces.Any problems with these? Then you should go back through the tutorial –perhaps several times – until you can complete it without any help. Further Work You have seen how the style feature can be used to create surfaces using4 boundary curves and (optional) internal curves. Dependant on how manycurves you select you can create surfaces in many different ways. Someexamples are shown in Figure 24. Have a go at building these surfacetypes^ yourself
as a^ good^ understanding of
how^ to^ make surfaces is
fundamental to this type of modelling.
One^ PRIMARY
curve^ and^
one SECONDARY curve can producesurfaces in much the same wayas^ the^ simplest
form^ of^ the VARIABLE^ SECTION
SWEEP
command.Additional^ SECONDARY
curves can be added as well. Two^ PRIMARY
curves^ create
a surface which is made by linearinterpolation between them. Thisis also known as a ruled surface.If^ one^ SECONDARY
curve^ is added surfaces are produced inmuch the same way as the morecomplex^ form of the
VARIABLE
SECTION SWEEP command.Additional^ SECONDARY
curves can be added as well. Three PRIMARY curves create asurface which is
made in much the same way as the four sidedsurfaces in the tutorial. This canbe a very useful option.Additional^ SECONDARY
curves can be added as well. Figure 24 : Style Surface Creation
