Creating Solid Models Parametric Modeling Concept

1. Creating Solid ModelsParametric Modeling Concept • Parametric is a term used to describe a dimension’s ability to change the shape of model geometry if the dimension value is modified. • Feature is a term used to describe the various components of a model. For example, a part can consists of various types of features such as holes, grooves, fillets, and chamfers. • Parametric modeler are featured-based, parametric, solid modeling design program: SolidWorks, Pro-Engineer, Unigraphics (CSG and parametric), AutoCAD’s Inventor, ….. Engineering 10, SJSU

2. Sketching • Take the word sketch literally. A sketch should be just that, a sketch Sketching and Features When discussing the mind-set needed for working with parametric modelers, there are two topics that need to be expanded: Sketching and Features • When sketching it is not necessary to create geometry with accuracy. In other words the geometry need not be created with exact dimension in mind. • When dimensions are added, the sketch will change size and shape. This is the essence of parametric modeling. In short, the sketch need only be the approximate size and shape of the part being designed. When dimensions are added, they will drive the size and the shape of the geometry. Engineering 10, SJSU

3. Line Spline tool fits a curve thru selected points Circle Arc Rectangle Rounding edges Sketching – Drawing Tools 2D sketch menu Engineering 10, SJSU

4. Exiting Sketch To exit the sketch, right click and select Finish Sketch Engineering 10, SJSU

5. → specify the desired value. Over dimensioning (over-constrained) – an error message will appear if there is redundancy in dimensioning. e.g., if you dimension both lines that constitute the short side of the rectangle, the window below is activated; decide which dimension to keep – Accept to make the last dimension the driver, or Cancel to make the first dimension the driver. Short sides Dimensioning Sketch Select the dimension icon → select the object to dimension (line), you can also select two endpoints of a line Engineering 10, SJSU

6. Select sketch and right click, choose Edit Sketch Editing a Sketch Browser shows the history of the model The box was created by sketching a rectangle 1.25 x .75 and then extruded by .5 (depth) Change the height from .75 to 1.0 .75 Engineering 10, SJSU

7. Click the Update icon to have the modification take effect Editing a Sketch Double click the dimension to be changed and enter the new dimension Engineering 10, SJSU

8. 1 - It is desired to have AB always vertical. 2 - It is required to have AB = CD. Constraints Click the constraint icon (perpendicular by default) to see the constraint menu. Constraints Geometric constraints may be added to sketch to apply behavior to a specific object or to create a relationship between two objects. C B A D Engineering 10, SJSU

9. Choose Equal from the constraint menu and select both lines. Constraints Choose Vertical from the constraint menu and select the line. Engineering 10, SJSU

10. Select the geometry to move. The Select button is on by default when you open the Move tool. Sketching – Modifying Tools Original shape Creates a duplicate of a selected object at a specified distance Offset shape • Click the Offset tool. • Click the sketch geometry you want to copy. • Move the cursor in the direction you want to place the offset geometry, then click to create the new geometry. • Click to place the curve at the offset distance. • If desired, use the Dimension tool to set a specified offset distance. • Set the starting point for the move command. Once selected, you can click anywhere in the graphics window or select the Precise Input check box to enter X and Y coordinates of the base point into the Precise Input toolbar. Engineering 10, SJSU

11. Set the center point about which the geometry rotates. Once selected, you can click a point in the graphics window or select the Precise Input check box to enter X and Y coordinates of the center point into the Precise Input toolbar. • Specify the rotation angle. Enter the angle, or click the arrow and select the angle from the list. The field also shows the value dynamically as you drag the pointer in the graphics window. Center of rotation Angle of rotation Sketching – Modifying Tools • Select the geometry to rotate. Click the Select button, and then select the geometry in the graphics window. The Select button is on by default when you open the Rotate tool. Sketch Engineering 10, SJSU

12. Select the mirror line (centerline) about which the sketch geometry is mirrored. centerline • Select the geometry to copy. The Select button is on by default when you open the Copy tool. Sketching – Modifying Tools • Select sketch geometry to mirror. sketch • Set the starting reference point for the copy command. Once selected, you can click anywhere in the graphics window or select the Precise Input check box to enter X and Y coordinates of the base point into the Precise Input toolbar. Engineering 10, SJSU

13. In the graphics window, pause over a curve to preview the trim, then click to complete. • Click the Extend tool. • In the graphics window, pause the cursor over a curve to preview the extension, then click to complete. Sketching – Modifying Tools Use the Trim tool to trim curves or remove segments. • Click the Trim tool. Segment to trim Engineering 10, SJSU

14. Select the geometry to scale. • Set the start point from which the geometry will scale. • Sets the exact value by which to multiply the dimensions of the selected geometry. The field also shows the value dynamically as you drag the pointer in the graphics window. Sketching – Modifying Tools Engineering 10, SJSU

15. Design Intent • In parametric modeling, dimensions control the model. • Design intent is how your model will react when dimension values are changed. Engineering 10, SJSU

16. Design Intent The drawing shows the intent of the designer that the inclined plane (chamfer) should have a flat area measuring 2.5 inches and that it should start at a point 1.25 inches from the base of the drawing. These parameters are what the designer deemed significant for this model. 2.50 2.50 1.25 4.00 Remember that the placement of dimensions is very important because they are being used to drive the shape of the geometry. If the 2.5 in. vertical dimension increases, the 2.5 in. flat across the chamfer will be maintained, but its angle will change. Engineering 10, SJSU

17. 1.75 In the last drawing, the designer calls for a specific angle for the chamfer. In this case the angle of the chamfer should be dimensioned. 30.0O 2.50 4.00 Design Intent 2.125 In this drawing, what is important to the designer is the vertical location and horizontal dimension of the chamfer, rather than the flat of the chamfer. 2.50 1.25 4.00 Engineering 10, SJSU

18. Design Intent Engineering 10, SJSU

19. Design Notes • Keep in mind that dimensioning scheme can be changed at any time. You are not locked into a specific design. You can also design without dimensioning, rough out a sketch, and then later go back and fully define it. • Do not be concerned with dimensioning to datum or stacked tolerances in the part. Those issues can be addressed in the drawing layout. Be more concerned with your design intent. Engineering 10, SJSU