Solid Modeling: Part 1

Transcription

1 Solid Modeling: Part 1 Basics of Revolving, Extruding, and Boolean Operations Revolving Exercise: Stepped Shaft Start AutoCAD and use the solid.dwt template file to create a new drawing. Create the top half of the shaft using a polyline as shown in Figure below. Make sure the polyline is closed, place it in the center of the screen, and omit the dimensions (cont)

2 Revolving Exercise: Stepped Shaft (cont) Begin at point 1, work counterclockwise, and take advantage of polar tracking. Be sure that the polar tracking increment angle is set at 45 deg, which will help you create the 45 deg chamfer. Using one of the 3D viewing options, select a viewpoint that is to the left, above, and in front of the polyline. You should now see a view similar to the one below. Enter ZOOM and.7x then save your work. Revolving Exercise: Stepped Shaft (cont) Use the Revolve command to revolve the polyline about points 1 and 2. Points 1 and 2 define the axis of revolution. Enter ISOLINES command and a new value of 25. Enter REGEN. Select the model and display its properties. Notice that the object is a 3D solid. Close the window and turn off the grid. Use the command under the solids menu to hide hidden lines. Shade the solid with a color of your choice then render the object. Save the file using the appropriate naming convention.

3 Extruding Exercise: Casting Use PLINE to draw the outline of the casting to right. The overall dimensions are 6 by 6 units. Select a viewport to the left, in front, and above the object. Pick EXTRUDE from the Solid menu. Select the polyline, enter.75 in reply to the height of the extrusion, and 5 (for degrees) of the side taper. Remove the hidden lines. Extruding Exercise: Casting (cont) Enter the PLAN command to see the plan view of the current UCS. Using PLINE to add the slotted hole shown to the right. View the object in 3D; note the hole is still only 2D.

4 Extruding Exercise: Casting (cont) Use the EXTRUDE command to extrude the hole to a height of.75 and 0 degrees taper. Use the various Isometric view to look at the object. Use the shade and render commands to color and view the object. Use the 3D Orbit command to rotate the object in space. Save the file using the standard naming convention. Solid Modeling: Boolean Operations Boolean operations are used to combine solid objects to create more complex solid models. Most operations start with basic solid objects called primitives (cylinder, cone, sphere, wedge, block, torus)

5 Constructive Solid Modeling Creation of object is defined by a tree-like structure describing sequence of operations needed to build the object. Creation technique is regularized Boolean Algebra Use Set Theory to combine primitive solids The CSG Tree Basic Set Theory? C = A U B {c i A or c i B} C = A B {c i A and c i B} C = A - B {c i A and c i B} D = cb (i.e. complement of B) { d i B} U Recall A B = A cb U

6 Trivial Example Two Orthogonal Cylinders A U B A B A B B - A U Primitives

7 Constructive Solid Geometry Similar to actually making (machining) the object. Stock Material = Primitive Welding, Drilling, Cutting = Boolean Operations Create Features Can easily create view planes (section views) Why CSG? What is stored is a creation tree or feature tree or model tree i.e. the procedure and sequence to make the object Natural link to parametric idea Parametric means that the physical shape of the part or assembly is driven by the values assigned to the attributes of its features. Feature-based means parts and assemblies are created by defining features like extrusions, sweeps, cuts, holes, slots, rounds, and so on.

8 The CSG Tree Complex Solid Model Simple Primitive Methods for Generating Solids Extrude Projecting the section straight away from the a plane Revolve Revolving the sketched section around a centerline from the plane into the part. The section must lie completely on one side of this centerline and must be closed

9 Methods for Generating Solids (cont ) Sweep Sketching a trajectory (path) and then sketching a section to follow along it. The cross section stays perpendicular to the trajectory Blend Joining together a series of at least two planar sections at their edges with transitional surfaces Creating Features Solid Extrusion Revolved Extrusion Cut Extrusion Sweeping

10 Non Uniqueness More than one way to create an object Choice of Primitives Effects the tree Complex Models can be create many different ways Issues with CSG Solid Modeling Example: Pipe Flange Start a new drawing with the solid.dwt template. Set the snap grid to Use the PLINE Arc and Radius options to create one-quarter of the flange base. Make sure each of the 4 points shown in the figure fall on the grid. Use the mirror command two times to create the entire flange base, then use PEDIT Join option to join the four polylines into one.

11 Solid Modeling: Pipe Flange Save the file. Use the Extrude command to create the object to the right. Thickness = 0.5 and taper = 3 degrees. Use the PLAN command, press W and then Zoom All. Use the Cylinder command in the Solid toolbar to put two cylinders at the locations show to the right. R = 0.375, H = 0.5. Select a view that is left, in front, and above the object. Solid Modeling: Pipe Flange Use the Subtract command under the Solids menu to subtract the two cylinders from the flange base. Remove hidden lines. Create a plan view of the WCS and ZOOM All. Place a solid cylinder at the center of the model. Make the diameter 1.75", and make it 1.75" in height. Using the same center point, place a second cylinder inside the first. Specify a diameter of 1.5" and a height of 1.75".

12 Solid Modeling: Pipe Flange Specify a viewpoint in 3D space as you did before then Subtract the smaller cylinder from the larger cylinder. The model is currently made up of two separate solid objects. Use the UNION command to join them to form a single composite solid. From the Solids menu, select Union and chose the solids. The object is now one composite object. Enter HIDE. Your model should look similar to object on the right. Use the shade and render commands to improve the appearance of the object. Save the file using an appropriate fine name and it to jglancey@udel.edu. Assignment: Pillow block Using good drafting practice, create a solid model of the object shown below. this file to jglancey@udel.edu