Draft Analysis Tools 2 Tuula Höök, Tampere University of Technology What is new in this exercise? - Using draft analysis tool to different directions - Making a reference plane to a non-flat surface - Putting draft to two directions by cutting a face with a sketched line - Outlining a moving core and making draft to the core pulling direction Exercise 7.1 Open the model: exercise_7_1.prt and make a draft analysis. The model is a tube with a pulling direction as shown in the figure. In this case there are no flat surfaces for setting the pulling direction. One of the planes is used instead. With this pulling direction the tube inner shapes need one or two moving cores. The core pulling direction is shown in the next figure. Core surfaces need a separate analysis. What will you see? - The outer surfaces need no draft at all. When analyzed to the core pulling direction, they show as surfaces with a zero draft, but there is no need to put a draft into this faces. Why? - The core surfaces also show without a draft. These surfaces need draft. Why? To which direction should the draft be designed? Draft Analysis Tools 2 Page 1
To do: Use the draft analysis tool. Based on the results, fix the model by putting drafts into it. Make the draft analysis to both directions. Fix all faces that have no draft to the pulling direction or the faces where the draft is to a wrong direction. Exercise 7.2 Open the model: exercise_7_2.prt. The model is a hook shaped part, a ladle. Open it with a draft analysis tool. Try two options: 1. The parting surface takes the direction of the handle. Before you are able to set the pulling direction, there is a need to make a reference plane. See instructions in the end of this exercise paper. 2. The parting surface takes the direction of the ladle upper edge. You can set the pulling direction from the face starting from the upper edge. 1. The first option with undercut 2. The second option with a very high core What will you see? - With the first option the ladle tip has undercut. It is impossible to get the part out of the mould. - With the second option the situation gets better, but then there will be very deep shapes and a high core in the mould. - There is a small area of zero draft face in the handle Draft Analysis Tools 2 Page 2
To do: Fix the model by reshaping the ladle, tilting the handle more or a combination of these. Check with the draft analysis tool. Put extra draft if necessary. Decide where to put the parting surface. Will it go through the handle or on the ladle upper edge? Exercise 7.3 Open the model: exercise_7_3.prt. The model is a technical part. It is a combination of a flat and tube shapes. Open the model with a draft analysis tool. The pulling direction is set from the flat face, which has an arrow shaped hole. What will you see? - There are faces, which have no draft at all - There are undercuts, that need a moving core to the mould To do: This part is a technical design. The customer technical designers insist to have the basic dimensions and shapes. Changing them to remove the undercut is not an option. Also he has decided to put fillet to both edges of the round and flat shapes. The customer is willing to change these flat surfaces to make core pulling possible. You need to realize these customer wishes: - Customer insists you to fillet both edges of the flat and round section. The other of this section edges would be the best place for the mould parting line, but because both edges need to be filleted, the parting line will be put in the middle of the face circulating the flat section. Cut the faces circulating the flat part and put a draft to positive and negative direction to the separated faces. But do not fillet the edges yet. See instructions for drafting. - Separate the moving core faces and put them a draft to the core pulling direction. See instructions. Draft Analysis Tools 2 Page 3
- Put a draft to a right direction to the tube inner surfaces. The inner shapes will be made with a core pin from both sides. - Put a draft to a right direction into the arrow shaped opening surfaces. Notice that this shape will be made with one core, which is machined with wire EDM -method. There is no need to put draft into two directions. Decide in which side the core will be and model the draft based on this decision. - Fillet the edges of the flat section if you wish. See from the finished model how the filleting has been done. Instructions Example of making a reference plane to a non-flat surface 1. Sketch a line to one of the model planes, which is orthogonal to the desired reference plane. In the model exercise_7_2.prt use the front plane. 2. Make a reference plane to a 90 deg angle with the sketch plane. Guide the plane with the sketched line. In this case the sketch plane was the front plane. Result: Draft Analysis Tools 2 Page 4
Cutting an annular surface with a plane guided split line and making a draft to two directions 1. Make sure that there is a plane, which intersects the surfaces to be cut. In the model exercise_7_3.prt, that plane is the Front plane. If there is no such plane you need to make a reference plane to the right place and right angle. 3. Insert the model an Intersection Split Line. The Split Line feature is one of the Curve features under the Insert menu. With the Split Line feature active select Intersection and then the plane, which intersects the faces to be cut. Select all these faces. Select OK and the split line is finished. 2. Insert a Draft feature. Draft feature is one of the features under the Insert menu. Use first a very large draft angle, if you are not sure, which direction the draft takes. See the result and change direction if needed. You can use either the split line as a parting line or select a neutral plane according to which the draft is directed. Select all faces from one side of the split line. Select OK. 3. Insert another Draft feature and draft the faces from the other side of the split line. 4. Check with the draft analysis tool. The result should be like seen in the figure below. Result: Draft Analysis Tools 2 Page 5
Cutting a surface with a sketch guided split line to make a draft for a moving core 1. Sketch the core outline. Use the dimensions and shapes you wish. 2. Make a Projected Split Line. Split Line is one of the Curve features under the Insert menu. With the feature active, select Projection and then use the sketched core outline as a parting line. Select faces to split. You can split both upper and above faces at the same time. 3. Make sure that there is a flat surface orthogonal to the pulling direction of the core, in the outermost core shapes. See figure. If there is no ready surface, make a reference plane. This surface will be used as a reference to the pulling direction. It is also the surface where the draft angle starts. 4. Make a Draft feature to the model. Draft feature is one of the features under the Insert menu. Take the pulling direction from a flat surface in the outermost core shapes. In this example there is a reference plane instead of a surface. Select Step Draft with Perpendicular Steps and select the sketched split line borders as a parting line. With a step draft tool you can draft faces to a wrong direction- from edges to the centre. See if the draft takes the same direction in every piece of the parting line. If not, you can change the direction by selecting the border line and changing the direction separately. Draft Analysis Tools 2 Page 6
5. Make another draft feature into some other face if necessary. In this example to the other side of the flat feature. Result: Draft Analysis Tools 2 Page 7