Draft Analysis Tools 1 Tuula Höök, Tampere University of Technology What is new in this exercise? - Draft analysis tool - Undercut analysis tool - Drafting faces with a neutral plane - Modifications to existing models according to the casting analysis results Exercise 6.1 Open the model: exercise_6_1.prt. The model is a cup shaped part with a boss in each corner. Each boss has a base hole for a thread and two ribs. Analyze the model with an Undercut analysis tool and with a Draft analysis tool. These tools are located under the Tools menu. In both of these tools you need to set the pulling direction. The pulling direction is set by selecting one of the model faces, which is perpendicular to the pulling direction. The direction can be changed by reversing the direction or by selecting another face. 1. Draft analysis tool 2. Undercut analysis tool Draft Analysis Tools 1 Page 1
What do you see? - The holes on top of each boss have draft to a wrong direction. This is also called an undercut. With this draft direction it is impossible to get the part out of the mould. - The ribs have no draft at all. To do: Fix the model by putting drafts into it. Modify the existing features by givint them a draft angle. The existing features are extrudes, a cut-extrude and two ribs. Exercise 6.2 Open the model: exercise_6_2.prt. The model is a flat, angle shaped part with a cut under. Open the model with the Draft analysis tool. What do you see? - The sides have no draft - The cut sides have no draft To do: Fix the model by putting drafts into it. Use the Draft feature. The Draft feature is one of the Features under the Insert menu. The part exercise_6_2.prt is constructed with extrudes and cut-extrudes that are orthogonal to each other. Modifying these features by giving them a draft angle will give you a combination of features, which are very difficult to handle. It is better to draft part faces instead. Experience what happens if you draft the first extrude Draft Analysis Tools 1 Page 2
with a 2 deg angle. Before drafting the faces you need to decide in which faces the dimensions are as sketched. See instructions. Remove all fillets. Prepare fillets over again when all drafts are finished. Exercise 6.3 Open the model: exercise_6_3.prt. The model is a cup shaped part with cups to both directions under and above. The pulling direction is as seen on the figure. Use the Draft analysis and Undercut analysis tools. 1. Draft analysis tool 2. Undercut analysis tool What do you see? - With this construction it is not possible to get the part out of the mould. There is no place for a parting line. The parting line should be placed to a line where draft changes direction. - The analysis results in an image on the left side should have a continuous area of green color and a continuous area of red color. The parting line can be placed in between these areas. Draft Analysis Tools 1 Page 3
To do: Fix the model by changing the shape of the original pan shape sketch and by modifying the handle. Put a collar around the pan. Under the handle there are still some shapes, which have a draft to a wrong direction. Instructions Drafting faces with a neutral plane 1. Open the Draft feature. It is located under the Insert menu being one of the Features. 2. Decide which dimensions should be unchanged after drafting. In this example these dimensions are as shown in the figure. 3. Use the face where these dimensions are located as a Draft neutral plane. In this example the mould parting line is as shown in the figure. Parting line defines the draft dimension, which is as shown in the figure. 4. If necessary, change the feature order in the feature tree to avoid changing the part basic shapes. See figure. Draft Analysis Tools 1 Page 4
5. Make the same decisions with other outer faces. The cut needs separate considerations. 6. There are different options to put a draft to the cutextrude feature faces. The draft feature does not work very well. It causes a situation shown in the figure left. It is better to modify the original sketch of the cutextrude feature. Angle the vertical lines to the same angle as other drafted walls. 7. Draft the cut under the part by giving the cut-extrude feature dimension a draft angle. You need to arrange the sketch with which the cut-extrude is prepared to the plane in which the dimensions are as sketched. In the part exercise_6_2.prt you need to make a reference plane. See figure. 8. The last step is to fillet all corners that need a fillet. Collar around a revolved surface One option is to modify the original shape of the pan. Another option is to make a revolved boss around the pan, but that is more difficult. Draft Analysis Tools 1 Page 5
Reshaping the handle under the collar 1. Totally remove the handle under the collar with a split feature. 2. Make a rib under the collar. In this example the rib direction is taken from the handle. Now there are no drafts to the wrong directions. It is possible to add a parting line. There is a reference plane for the rib. The reference plane is guided through the top plane and a sketch, which has a same direction as the handle corner. Draft Analysis Tools 1 Page 6