Challenge

Week 8 - Challenge 1 - Base Bracket Design

CChetan Muninarayanappa27 Nov 2022

AIM :
To Create the Base Bracket Plastic component through the given Class-A surface. To begin with, the tooling axis for the given Class-A Surface should be created meeting
the requirements of the draft angle and at the end perform the Draft analysis on the model.

INTRODUCTION

Draft angle and Why it is needed?
Draft is an angular taper given at the design stage to every Plastic Component that has to be manufactured. It is given in the direction of the Mold Movement. The Draft
allows the parts to release easily from the mold without creating any damage between the surface of component and the core and cavity plates.
When a Plastic component cools down inside the mold, the natural tendency of it is to shrink and attach to the core or cavity half. The movement of mold opening causes
friction on the walls of the component as well as the core/cavity blocks. This reduces the life of the mold as well as the component itself. The component may also have
rough surface finish as well as weak structure due to this. This problem can be solved by giving draft to the component.

The general draft angles used in the industries for different purposes.
0.5 degrees on all vertical faces is strongly advised.
1 to 2 degrees works very well in most situations.
3 degrees is minimum for a shutoff (metal sliding on metal).
3 degrees is required for light texture.
5 or more degrees is required for heavy texture.

Tooling axis

The tooling axis is basically the direction that the mold pills apart. The mold is built in two separate pieces basically. You have a cavity side and you have the core side. The
core pulls apart from the cavity and that is the dyeline or the tooling direction.
The draft angle, which also plays a major role in plastic component design, is decided with reference to the main tooling axis of the component

What is Draft Analysis?
No parts can be ejected from the tool if it is having a straight 90 degree profile from its base surface. A small draft angle is provided to each and every area of the
component in order to get an easy removal of the component from the tool. Draft analysis technique is used to analyze whether our part model created in cad is
manufacturable based on the draft condition applied. Here the part should get easily removed from the panel dies (in case of Sheet metal part) or Mold (in case of plastic).
Here we are providing a direction in which components should eject inorder to get an easy removal of components from the tool. In other words it also lets us know
whether the model is having a draft angle and how much is the draft angle from the tool direction.

On what type of components we perform Draft Analysis?
Draft analysis is performed on the components where the ejection of materials happens after the material is made inside the tools. In case of Automotive Sheet Metal
manufacturing, the blank sheet after turning into automotive panels like Hood, Fender, Roof, Side Doors, Back Doors etc. need to be removed from Panel Dies. If a
considerable amount of draft angle is not provided, the removal components from the tool will be difficult. Same in the case of mold(plastic component) after getting
filled inside the core and cavity, it needs to get ejected easily with the help of ejectors.

What factors should be considered while doing the draft analysis for Plastic/Automotive Sheet Metal parts?
The major consideration of Draft Analysis is whether sufficient Draft Angle is provided on the component. Components while designing should be provided with a
considerable amount of draft angle depending on the manufacturing consideration. For Plastic components we provide a draft angle of 3degree(Draft angle of 0.5 is given
ideally to the features inside the plastic part). But for Automotive Sheet Metal Parts, it will be from 7 degrees or more.

1.) Createing Tooling Axis using bisecting method
Component :- Base Bracket

Software used:- CATIA v5

Procedure

Step-1: Continuity check on class-A surface of Base Bracket
Initially for any class-A surface , first step is to check wheather the surface has continuity without any breaks and disjoints in it.

Step-2: Creating Dummy tooling axis for referance
Next, Analyse the component clearing in all three directions and decide the best tooling direction manually and create a tentative tooling axis.

Step-3: Create cut sections of the component along xz and yz planes.
Using intersection tool in the Catia create a boundarys like cut section between components and xz, yz planes.

Step-4: Create lines alonge with the surface which may occur during manufactureing.

Step-5: Create a bisecting line for tooling axis along two line which is tangent to the surfaces of most perpendicular. Publish the actual tooling axis and the surface for the
draft anlysis.

2.) Performing Draft analysis on Fan cover
Component :- Base Bracket

Software used:- CATIA v5

Procedure for draft analysis

Step-1- Choose the Feature Draft Analysis command from the Analysis toolbar marked in red box.
Insert-> Analysis-> Draft analysis

Step-2- Enable the compass feature in the Draft Analysis Toolbar as shown below.

Step-3- Place the compass on the required position and along the desired tooling direction on the part

Step-4- Select the part on which draft analysis has to be performed. The part turns to the combination of colors present in the scale

Step-5- Analyse the part with respect to the results obtained based on the scale, to identify the parts with draft feature. Quick analysis mode was chosen for the analysis.

The above image shows the result on min of 3deg draft angle. Since the required draft value is 3 degrees as seen in the scale, the parts highlighted in green color have draft
values greater than 3 degrees i.e, the parts achieved required draft value and the part can be cleared.
Image of complete Draft analysis and color scale variant

3.) Creation of Class-B Surface

Procedure

Consider the thickness of the component as 2.5 mm. Now we need to create a B surface which will be similar to the A surface at an offset value of 2.5 mm.
First, we are creating the ribs in this operation. To create the ribs, first extract the surfaces of it from Class A surface.
Once the surfaces are extracted, untrim it and then extrapolate it by 10mm by using point propagation. Now trim these surfaces and offset it to 2.5 mm.
After creating both the ribs, create the base of the base bracket as mentioned above.for that extract the base from the class a and untrim it. then extrapolate the
base. then trim the surfaces ribs and base the final part as shown in below. Then give the fillet to the part as per the class a surface. and this is the final class b
surface.

4.) Creation of Class-C surface

Procedure

To create a Class C surface, first extract the boundaries of the Class A surface

Now using the sweep option create the surface. To perform this operation, Go to the Toolbar > Sweep > Profile type > Line > Subtype > With draft direction > Guide curve 1 -
(select the extracted boundaries) > Draft direction - (select the tooling axis) > angle and length as 3 deg and 20mm respectively and click ok.For holes extract the
boundaries and use the sweep operation to form a surface.

Atlast Join the surfaces which are formed by using sweep command to form a Class C surface.
After creation of Class A, Class B and Class C surfaces, we need to join Class A and Class C surface to form a new surface. Then trim the joined surface with Class B
surface to form the final required surface.
Now using the close surface option from part workbench to convert the surface body to part body.

Screenshots of the solid model with the proper color code of the draft angle in various orientations (Isometric, Front, Side, and Top View)

Isometric View