Transcript
Surface Modeling Surface modeling is a technique whereby the CAD model represents only the outside surfaces of product. It was one of the earliest methods of creating 3D models and preceded solid modelers (which represent the volume occupied by the product) by many years. They have the advantage of being able to represent very complex shapes and so are still in use today in many industries. Wildfire has the advantage of combining a solid modeler and a surface modeler into a single system. This means that you can use surface modeling techniques when needed for complex shapes and then convert the resultant model into a solid model and use solid modeling techniques for more basic engineering functions. This tutorial describes how surface and solid modeling techniques can be combined 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 the least constrained way of designing allowing you to sketch in a freeform manner 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 shape there are elements which must interface to engineered parts such as the rotary cutters. The shape of these is largely defined by their function. Wildfire is quite capable of combining geometric and freeform shapes. to draw the shape shown in Figure 1. To start use the sketch tool Note: the dotted construction circle is achieved by drawing a normal circle,
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 you will learn about in this tutorial. Also notice a STYLING menu is added to the 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 website where you found this tutorial you will find a picture called shaver which you should download and save in your working directory. This is a hand drawn sketch of the intended design (you can’t beat paper and pencil for quickly recording ideas). We are going to use this as an underlay to help us in the design process. From the STYLING menu choose TRACE SKETCH… and a dialog box will appear as shown in Figure 2. Click on the name FRONT in this dialog and an OPEN dialog will appear to allow you to find the picture you downloaded. When you open this picture it will appear attached to the front plane in the main window. In the Trace Sketch dialog click on HORIZONTAL. The picture will now be bounded by two horizontal yellow lines. Use the mouse to drag these so that they just touch the head of the shaver as shown in Figure 2. The sketch you have already drawn specifies that the overall height of the head (between these two yellow lines) should be 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 and press the FIT button and the size of the picture will change. Now the distance between the lines is 50mm. In the PROPERTIES area at the bottom of the dialog you will find more tools. Use the MOVE H & V winders to position the sketch so it matches curve you drew as shown in Figure 2. Click OK to finalise the trace.
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
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Figure 2 : A Trace Sketch Page 1 of 8
Surface Modeling Now we have the trace we can use it as we draw. We are going to start by drawing profile curves of the shaver. These need to be drawn on the tool in style to pick any datum plane FRONT plane. You can use the to make it the active plane. Use this now to make FRONT active (it will be drawn with a grid on it to show it is active. Now press and hold the right mouse button and choose ACTIVE PLANE ORIENTATION from the popup menu to change the view to look onto this plane. To start drawing curves choose bottom of the screen.
and a dashboard will appear at the
In this mode you can make changes to the shape simply by dragging the points on the curve. You can also right click and hold on the curve to add a point 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 the curve joins on to the end of the head curve you drew in Figure 1. Drag the end point now but hold the SHIFT key down as you drag and the point will lock on to nearby geometry. When you release the point it will show it is locked by a small cross. You may find this easier to do if you spin the view around to a 3D view first.
Figure 3 : Sketch Dashboard Make sure the PLANAR option is chosen then draw a curve by clicking points with the mouse. Try to follow the profile of the trace as shown in Figure 4. You will need more points where the curve is tighter but it is good practice to use as few points as you can. If it is not perfect don’t worry – you can improve it later.
Figure 6 : Locked and Normal You may have noticed that when you clicked on the endpoint of a curve a yellow line is drawn from the point. This is the tangency line – the direction in which the curve leaves the point. You can move this to by dragging its end. In this case we want the curve to be at right angles to the RIGHT plane. Select the endpoint then press and hold the right mouse button near the end of the yellow tangent curve and choose NORMAL from the pop-up menu. You will be asked to pick a plane to be normal to – pick the RIGHT plane. To help you to achieve a smooth curve there are some useful analysis
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).
icon. tools. Choose ANALYSIS > GEOMETRY > CURVATURE or the In the dialog that appears click on SAVED then pick the curve you are drawing. You may need to go to the DEFINITION pane and increase the scale to see the curvature display. Close the dialog now when you move the curve points the curvature display updates. Use this display to guide your curve design – you want a curve that increases and decreases in radius smoothly and does not oscillate between concave and convex any more than it should. You can delete the curvature analysis at any time with ANALYSIS >
Figure 5 : Edit Dashboard By D Cheshire
DELETE ALL > DELETE ALL CURVATURE or
.
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Surface Modeling
Figure 9 : Datum Plane Figure 7 : Curvature Use the techniques you have learnt create a second curve to follow the lower profile of the shaver.
The new plane should become the active plane so can immediately sketch a new planar curve as shown in Figure 10. Remember the ends of the curve should be snapped to the ends of the existing curves and that the tangencies at each end of the new curve should be set normal to the FRONT plane.
Figure 10 : Fourth Curve Now its time to put these curves together to make a surface. Surfaces are Figure 8 : Second Profile We now have 3 curves – we just need to add the curve at the end. This curve will also be planar so we need to create a plane to draw on. You can access the plane creation tools of Wildfire from within Style using . You should be familiar with how to STYLING > INTERNAL PLANE or create planes using the dialog box. Use the ENDS of the two curves and FRONT datum as a NORMAL reference.
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made with the
tool which has its own dashboard.
Figure 11 : Surface Dashboard You should be taken straight into curve selection. Start by selecting the original curve. This was drawn with straight lines and arcs so it won’t select all together but you can hold the SHIFT key whilst picking the 2
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Surface Modeling lines and 2 arcs. Now release the SHIFT key and hold the CTRL key whilst you pick the other 3 curves. When you have picked the 4 curves you will have to click on OK in the small select dialog and if you have selected correctly a surface should be created!
show 4 views which you can zoom and pan independently. You should now with a bit of practice and patience be able to edit the curve in a controlled manner. Once again make sure the ends of the curve are snapped to the profiles and the tangencies of this curve are set to be normal to the FRONT datum plane.
Figure 12 : Surface Created If a surface is not made check the information lines at the end of the screen to see if it warns of curves not connected – if it does you need to edit the curves so that the ends snap to their neighbours. Take a close look at Figure 12. You can see some small arrows on the edge of the surface. These are a visual indication that there is a constraint on these edges. In this case these were created because the two curves (on either end of the shaver) were created with normal tangencies. You will see more of these constraints and how to use them later. The surface looks OK but we can refine it even further by adding internal curves. We are going to draw a new curve but we are going to use a new type of curve – a FREE curve. These curves give you more freedom but are more difficult to get the hand of – practice! and in the dashboard choose To start drawing the new curve choose FREE. Now place points for the curve using SHIFT to snap the first and last point to the upper and lower profile curves. Try editing these points and you will find they are difficult to move because you are trying to position a point in 3D space using a 2D screen. To help you can use the split screen view set using the By D Cheshire
icon. The screen should change to
Figure 13 : Free Curve To add this to the definition of the surface click anywhere on the existing surface 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 to reflect the shape of this curve – if it doesn’t did you remember to snap the ends and make them normal to FRONT? Have you noticed that the surface is linked to the defining curves? This means that if you edit the curves they will update in real-time so you can dynamically control the shape of the surface – try it and see. Add more internal curves until you are happy with the shape. The internal curves don’t all have to go across the surface they can go along the surface as well but if they do they should be snapped to the cross where they touch. Finish the style feature by clicking the toolbar.
icon from the right hand
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Surface Modeling
Figure 14 : Finished Surface Let’s create another style feature to show some more options. This will be a 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 shown in Figure 15. This line will not be used to create the surface – it will be used as a construction line for a new plane.
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 the small select dialog and if you have selected correctly a surface should be created! Notice this surface was created with only two curves. If we wanted more control we could have drawn more curves.
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. Use this line for the plane to pass through and the FRONT datum as a NORMAL reference. Set the viewing direction onto this plane and draw the planar curve in Figure 16a making sure that the ends of this new curve are locked onto the straight line and the end tangencies are normal to the FRONT datum. Create a second curve but this time chose the COS (curve on surface) option and draw the curve in Figure 16b making sure that the ends of this new curve are locked onto the edge of the original surface and the end tangencies are normal to the FRONT datum. Notice how this new COS curve sits on the original surface. It is linked to the original surface so if that updates so will this curve. It also has implications for the creation of the surface using this curve as we will see. By D Cheshire
Figure 17 : Surface Connection Options
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Surface Modeling Figure 17 shows the new surface but also note the small arrow symbols. These indicate that there is a connection along this edge of the surface. The single arrow indicates the new surface is tangent to the original surface – because this is a COS curve. If you click on this arrow where it crosses the edge of the surface it will swap to a double arrow (and the surface shape will change) which indicates both tangency and curvature continuity. If you hold SHIFT and click on this arrow where it crosses the edge of the surface it will change to a dotted line (and the surface shape will change) which indicates only positional continuity. The dotted line on the other similarly indicates positional continuity and clicking on this will change it to be normal to the original planar curve. Figure 17 shows all the combinations for this case. If you want to change these options later you can also use the
So far we have been working on only half of the model. The other half can be mirrored into place now. Click on the style surfaces you have made – you will notice that a single pick selects both surfaces because they have been joined by the trim operation into a single ‘quilt’. This will be further explained later. To mirror the model choose EDIT > MIRROR, pick the FRONT plane and press the the model is created.
icon on the dashboard. The other half of
Now let’s fill in some of holes. The easiest to fill in is the triangular head as this is a flat planar surface and there is already a sketch plane in place. Choose EDIT > FILL and a new dashboard appears.
icon. Change the icons to match the last picture in
Figure 17 and press the creation.
icon on the dashboard to end surface
The creation of this second surface has left a part of the original surface inside the new surface which is not wanted. This can be cut away using the tool. Pick the tool then pick the original surface (the one which needs to be cut away) and OK then pick the curve at the bottom of the new surface (the COS curve) and OK again. The surface to be trimmed will highlight in green – now pick on the piece of surface you want to remove highlighted in red in Figure 18. When you press the the dashboard the piece will be removed.
Figure 19 : Fill Dashboard Choose References > Define from this dashboard and go through the normal sketching process using RIGHT as the sketching datum to sketch the outline of the head (use
).
icon on
Figure 20 : Filled Surface There is no plane in place for the second fill on the raised portion for the on/off button but it can be made very easily. Choose EDIT > FILL and start to create the required plane using . All that is needed to define the plane is to pick one of the edge curves. The plane will appear and it may seem to be oddly oriented but that doesn’t matter. Choose OK then press
Figure 18 : Surface Trimming
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in the dashboard to continue the fill process. Choose References > Define from this dashboard and go through the normal sketching process
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Surface Modeling using the new plane as the sketching datum to sketch the outline (use
).
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 a collection of individual surfaces joined at their edges. Right at the bottom of the screen you should see a list box which normally says smart. This box controls what type of geometry is picked with the mouse. Change this now to say quilts and move the mouse over the model to see the individual quilts highlight. The model is made up of 5 quilts. We need to join them into a single quilt. This process will be in several steps. Step 1: Pick the two halves of the model (use CTRL to multiple select) and choose EDIT > MERGE. When you press the the two quilts will be merged into 1.
Figure 21 : Second Fill We could use the same technique to fill the final hole but let’s show how you can combine simple modelling techniques with these complex surfaces. You should be familiar with extruding solids but you can also extrude surfaces to. Choose the extrude icon
and make sure you
from the dashboard. This will cause the select the surface icon extrude command to create a surface rather than a solid. This means that you don’t need to draw a closed sketch. Draw the sketch in Figure 22 on the FRONT plane (HINT: use
and make sure the ends are aligned
with the surface edges). Extrude the surface both ways
by say 50.
icon on the dashboard
Step 2: Pick the main body of the model and the triangular head surface (use CTRL to multiple select) and choose EDIT > MERGE. When you press 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 (use CTRL 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 (use CTRL to multiple select) and choose EDIT > MERGE. This surface needs a little more thought because the extruded surface is too long. The merge command doesn’t just connect surfaces together it will also trim off overlapping portions. The portions which will be kept are covered in a dotted mesh. If the wrong part of the surface is highlighted use one of the icons to switch it and use the press the
to check the result. When you
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 this single quilt encloses a single volume with no gaps – this is an ideal candidate to convert into a solid. Select the quilt and choose EDIT > icon on the dashboard to make a solid. Now SOLIDFY and press the it is a solid you can perform all the normal solid modelling functions that you are familiar with. Try adding some rounds and add an extrusion to locate the head to prove the point.
Figure 22 : Extruded Surface
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Surface Modeling One PRIMARY curve and one SECONDARY curve can produce surfaces in much the same way as 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 linear interpolation between them. This is also known as a ruled surface. 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 using 4 boundary curves and (optional) internal curves. Dependant on how many curves you select you can create surfaces in many different ways. Some examples are shown in Figure 24. Have a go at building these surface types yourself as a good understanding of how to make surfaces is fundamental to this type of modelling.
If one SECONDARY curve is added surfaces are produced in much the same way as the more complex form of the VARIABLE SECTION SWEEP command. Additional SECONDARY curves can be added as well.
Three PRIMARY curves create a surface which is made in much the same way as the four sided surfaces in the tutorial. This can be a very useful option. Additional SECONDARY curves can be added as well.
Figure 24 : Style Surface Creation
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