Week 8 - Challenge 2 - Base Bracket Design

Draft Analysis:

Drafting - Introduction :

Drafting is giving a taper to the face of the mould part. Drafting is required in the mould part to remove them from the mould flask without affecting the walls of the core and cavity. Drafting eliminates the problem of sticking mould to the walls of the core and cavity.

Draft analysis is made to eliminate the problem of sticking to walls. Draft analysis shows various faces which can cause the problem of sticking. With the draft analysis done we can proceed to design the components with the necessary draft. We use 3 degrees as the standard draft angle.

Tooling axis :

The tooling axis is the reference axis with which the mould is open. We provide draft angle to our part with respect to this axis only.

Tooling axis creation :

1. Design consideration check :

We must first check the given class A surface for any opening in between the surface. This can be done using few commands. We can boundary creation tool to check if there are any open internal boundaries and close the surface to further our design. We can also use the join surface command and check if all the surfaces are joined. If not joined properly the command prompts an error window. we can know the design consideration by these techniques.

2. Visualisation Method :

In certain cases, we can find the tooling axis by simply looking at the class A surface. For a fan cover, since the part has a frustum part we can assume the axis normal to the top surface passing through the centre point of the surface as the tooling axis.

The preference of choosing the tooling axis would be the line normal to a large flat face or through any hole element in the part.

3. Analysis of various directions :

In the analysis, we create different intersection lines and find the best direction of the tooling axis. For instance, we check the mould plate movement direction by observing the surface carefully in each direction. In the above case, if we look in the direction of x as the tooling axis, there is a hindrance of the surface which don't allow us to create the axis in that direction. By observation, we find that the z-axis will hold good for the tooling axis.

4. Bisection Method to create the tooling axis :

The bisection method is generally used to find the tooling axis for the part design. This method enables us to create bisection lines and find the centre line, if in case the tooling axis is provided in that line, the draft with reference to that tooling axis would be perfect. The steps to create the tooling axis are as follows.

• Find the hole in the Class A surface. Apply boundary creation command for the hole. Create a point in the centre of that created boundary.
• Create a plane to create new sketches with "parallel through point" enabled. Select the YZ plane as the reference plane and the point create with the boundary option as point reference.
• Perform intersection option with the plane just created and by selecting the class A surface. This will create the intersection lines along the surface.
• Now create a line with the created sketch as a reference. the lines created are those surfaces that we think might create the problem of sticking.
• Now create a new line with the "Bisection" option enabled. Choose the lines created as the reference. A new line will be created along the Z direction in our case.
• The above-created line is the tooling axis in our case.

Publication :

Publication is done for easy access of the surface and sketches.

Draft analysis :

The steps to create a draft analysis are as follows,

• Change the view mode. Select the "material" radio button in the change view mode option.
• Choose Feature Draft Analysis under Insert --> Analysis --> Feature draft analysis.
• The draft analysis window will open.
• Choose Quick analysis mode or full analysis mode as per requirements.
• Create the draft direction by clicking created compass option under the direction tab. Clicking the option will enable a compass created at the place of the default compass. Drag the compass to the tooling axis and place it over the tooling axis.
• We can reverse the direction of the draft with the reverse direction option. Once the direction is chosen click the lock direction option.
• Now moving the cursor displays a red cross near the cursor. Place the cursor over the surface to begin the analysis.

Once the analysis is done, the results will be displayed in various colours over the surface. If the simple mode is chosen it displays three variant of colours that enables us to see whether the drafts within over design consideration. We can also alter the value to show the changes in draft angle in the draft analysis window.

Choose analysis under the running point option in the Display tab of the draft analysis and place the cursor over the surface to display the angle at that point. The angle displayed are with reference to the draft direction.

Class A surface :

This surface is the base to create the part model. This surface is created from concept sketches using different software like Autodesk Alias. This class A surface is given input to Catia software for further development of feasible Product. Class A surface is followed by Class B surface creation.

Class B surface :

Class B surface is similar with the difference as class B surface becomes the surface that contains provisions like, stiffeners, Screw bosses, ribs, and other product support features. This surface is the other side of the product which will be hidden from plain sight, unlike Class A surface. This surface is created by offsetting the class A surface to the thickness of the final product we want.

Class C surface :

The surface that connects the Class A with Class B surface is called as Class C surface. In many instances, the draft is given to this surface. The Boundary option is used to define the boundary of the Class A surface. The sweep surface command is used to create a class C surface with the provision of draft in the sweep creation window. The commonly used draft angle is 3 degrees. The reference to sweep is the Tooling axis that we created earlier.

Part definition :

Now that all surfaces are created, we trim the surfaces to create a closed surface. We now use the Close surface command to create the solid part model. The draft is provided to the solid model as we created it using the class C surface.

Different views are as follows,