Creating Solid Models Parametric 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, ….. Ken Youssefi Engineering 10, SJSU

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 Sketching Take the word sketch literally. A sketch should be just that, a sketch 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. Ken Youssefi Engineering 10, SJSU

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

Exiting Sketch To exit the sketch, right click and select Finish Sketch Ken Youssefi Engineering 10, SJSU

Dimensioning Sketch Select the dimension icon → select the object to dimension (line), you can also select two endpoints of a line → 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 Ken Youssefi Engineering 10, SJSU

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 Select sketch and right click, choose Edit Sketch .75 Ken Youssefi Engineering 10, SJSU

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

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

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

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. Select the geometry to move. The Select button is on by default when you open the Move tool. 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. Ken Youssefi Engineering 10, SJSU

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. 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. Center of rotation 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. Angle of rotation Sketch Ken Youssefi Engineering 10, SJSU

Sketching – Modifying Tools Select sketch geometry to mirror. Select the mirror line (centerline) about which the sketch geometry is mirrored. centerline sketch Select the geometry to copy. The Select button is on by default when you open the Copy tool. 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. Ken Youssefi Engineering 10, SJSU

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

Sketching – Modifying Tools 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. Ken Youssefi Engineering 10, SJSU

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

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. Ken Youssefi Engineering 10, SJSU

Design Intent 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. 2.125 2.50 1.25 4.00 2.50 4.00 1.75 30.0O 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. Ken Youssefi Engineering 10, SJSU

Design Intent Ken Youssefi Engineering 10, SJSU

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. Ken Youssefi Engineering 10, SJSU