Week 11 - Final project

OBJECTIVE: objective for this project is to make half of the door trim panel in catia-V5 from the provided Class-A surface of the same.

ABSTRACT:  This report contains a brief theory on design rules and the approach followed to achieve the final plastic product. Draft analysis report on all the class-A surface apart from the procedure to make the class-B and class-C surface is also mentioned.

APPROACH:

Our basic approach to make a plastic model from class-A surface should be:

1. Run draft analysis
2. Make tooling axis
3. Make B surface
4. Make C surface
5. Trim all together and make it solid.

CLASS-A SURFACE

In automotive industry various teams works on various components, a car for example is not entirely designed by a single designer. There are many teams among which the task of making various components is distributed. And this is followed for every department of the industry. In this project we are given class-A surface which is designed in other software like Autodesk Alias, by a class-A designer. This is aesthetic surface and a lot of time, effort and good experience are demanded for making this continuous and a good flowing surface model. This is the major reason why, when we get this as input we are not allowed as a plastic designer to make any improvements in the class-A surface. Rather, it should be brought to the attention of the seniors which later is conveyed to the concerned team and take care of.

TOOLING AXIS

Tooling axis is the axis along which the core and cavity opens and closes. It is very important to define the tooling axis in the first step while designing a component as it is the main component which helps us to run draft analysis on class-A at initial stage to see if we can move ahead. Also for later stage, tooling axis is the direction along which class-C surface and the draft to the components is given.

In this model we have a tooling axis in the perpendicular direction to the entire door trim that is y-direction in the model. It is very evident that switch bezel will require a side core, so another tooling direction is made specifically for switch bezel. Apart from these two tooling axes we also have a side core tooling axis for dog house. 

DRAFT ANALYSIS

Our first step before starting the model should always be to check is the surface has enough draft that it will not create any problems while ejecting from the mold. This seems like a big task as we have to foresee something that will come at very later stage. But this is done by a small process called draft analysis. This analysis tells us whether our component will be safely ejected in the tooling axis we have provided. Some components require side core where there are under undercuts, holes or projections on the side walls, so for this we need a different tooling axis and a different analysis is required to check those areas.

DRAFT ANALYSIS REPORT ON CLASS-A SURFACE

As we can see from our analysis that map holder need improvements. On industrial level in such case we cannot proceed with this class-A, but for the project we are making this model anyway. We expect this component to fail the analysis later too.

DESIGNING PLASTIC COMPONENT

As the entire door panel is divided into various components, we will make this plastic component in the same way. Following steps have been carried out to make the plastic component for every component:

The first step for every component was same. The given input was not a single unit but has numerous patches. These patches were joined together using join command. Thus after performing this operation we got our single class-A surface.

Once we get class-A, we have to proceed to make class-B surface. Creating class-B by extracting every flat surface will be a complex process in such component. So we directly offset it by 2.5mm.

For making class-C surface we have used sweep command ‘with draft direction’ by giving 3deg draft angle and tooling axis as direction. But at many places this did not work so we have to sweep ‘with reference surface’ at 90deg. Once that was done, the C surface was joined together using join command.

DESIGNING B-SIDE FEATURES

DOG HOUSE: Primary function of the dog house is to avoid sink marks. But it also helps in other things like if the mating part is to be at a greater distance then we cannot make the height of the screw boss of that greater height, thus we make dog house and mount screw boss on it. Hence it helps in solving the problem of screw boss and also it helps to have perpendicular screw boss.

GENERAL DESIGN GUIDELINES FOR DOG HOUSE DESIGN:

1. Minimum height: Less than 6mm causes steel condition.
2. 3:1 ratio of steel width to height. But 2:1 is preferred.
3. Minimum width: 3:1 ratio of steel width to height. But 2:1 is preferred.
4. Draft: minimum 1.5deg.
5. Sink saver: height= 40% of nominal thickness. Width= 3.0mm-6.0mm.
6. Optimal radius:25m

SCREW BOSS: They are used for the purpose of mating two parts. They have hole in them which accepts the threaded part of the fasteners such as screws.

GENERAL DESIGN GUIDELINES FOR SCREW BOSS DESIGN:

1. Draft: 5 deg on each walls.
2. Wall thickness: 40% of the nominal wall thickness i.e. 0.4*t where t is the wall thickness which is 2.5mm in this case.
3. Height/diameter: 3:1 steel but 2:1 is preferred.
4. Radius of the fillet: minimum 0.25mm.
5. Boss gussets (rib like structure giving strength to the screw boss) must meet ribs guidelines.
6. Avoid merging the screw-boss into wide wall.

RIBS/GUSSETS: They increase the stiffness and strength without increasing overall wall thickness of the model which is not desired. They also facilitate:

1. Locating and arresting components of an assembly
2. Providing alignment in mating parts
3. Acting as stopper or guides for mechanisms.

DESIGN RULES FOR RIBS:

1. Draft: 0.5 deg per side (minimum), but this value should not be high enough that it will cause failure for other consideration. For example, more draft will result in less thickness at the top surface.
2. Thickness of ribs: 40% of wall thickness or 0.4*t where t is the wall thickness.
3. Height: ≤ 5 times the wall thickness i.e. 5*t
4. Spacing (for more than 1 rib): 3:1- steel height/width ratio (maximum). h/w =3or2(preferred) where h is the height of the rib and w is the space between two ribs.
5. Minimum thickness at the tip: 0.75
6. Radius: 0.25mm max
7. Ribs on opposite side of the wall should be offset
8. Ribs should be connected to other structural features where possible.
9. Rib root thickness should not be more than 30% of the wall thickness.