Challenge

DESIGNING A B-PILLAR

YYash Ghate27 Dec 2021

DESIGNING A B-PILLAR

AIM: To design a B-pillar from the provided class-A surface and master-section as inputs.

ABSTRACT:

This report describes the designing/approach of designing followed in the industries. In this model we had to create a close solid body from the aesthetic surface provided and later work on the engineering features considering every standard design rules followed in the OEMs on the B-side of the model. The overview of the approach followed is mentioned below:

Check for any defects or irregularities in class-A surface.
Make a tooling axis.
Run the draft analysis beforehand in case if there are any faces which does not have drafts, those can be corrected by the class-A designer.
Understand the master-section.
Make the flange on both sides to make aesthetic model complete.
Make class-B and class-C surface.
Make a surface model by trimming surface A, B and C together.
Close the model.
Make B-side feature.
Run draft analysis on the final model and make a report.

DESCRIPTION:

MASTERSECTION: These are the guidelines provided to a design engineer which describes how a component would/must look like once it is modeled into a solid component from the class-A surface. For example, in this model we have received master-section as an input which tells us about the thickness of the component and dimensions & type of the engineering features on the component.

DESIGN RULES FOR RIBS:

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.
Thickness of ribs: 40% of wall thickness or 0.4*t where t is the wall thickness.
Height: ≤ 5 times the wall thickness i.e. 5*t
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.
Minimum thickness at the tip: 0.75
Radius: 0.25mm max
Ribs on opposite side of the wall should be offset
Ribs should be connected to other structural features where possible.
Rib root thickness should not be more than 30% of the wall thickness.

DESIGN RULES FOR DOG HOUSE:

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

NOTE: The design rules for designing 4-way locator pin is the same as that of ribs design rules.

CREATING TOOLING AXIS

In this model we will need two tooling axis. One main tooling axis and other will be for the inside surfaces of the dog house. This will be our lifter tooling axis. We used bisecting line method to make the tooling axis. As the position of the tooling axis does not matter, we have taken master section as the reference to make a point and a plane.

First bisect the two opposite lines of any master section in a positioned sketch.
Then similarly, so it for other master section.
Check if both are same line or not. If they are same, we can name any one as our tooling axis.
If they are different then we will bisect them and the resulting line will be our tooling axis.

For making lifter axis we make a simple line using point (earlier) and direction as parallel to the inside face.

CREATING CLASS-B SURFACE

We generally extract the flat surfaces but due to presences of many styling fillets on the class-A surface we had extracted the whole class-A surface at once and offset it at 2mm (we got this thickness from the master-section). But while making an offset, we faced the below problem due to which a patch of surface was missing from the offset.

This problem was rectified by following the mentioned method:

Taking extracts of all the edges.
Making the curves smooth if necessary.
Using multi section surface tool to fill the surface in the gap.
Joining all the sub elements together to get one single surface.

The resulting surface is our class-B surface.

NOTE: We should always extrapolate the surfaces as in the end we have to trim all surfaces together so they must intersect each other.

CREATING FLANGE

When we observe the master-section properly, we will find the class-A has some projection outwards which is not in the input. So we have to create these flanges on class-A on both the sides, taking master-section into consideration as it contains all the description of the flange. Once we make flanges on both sides of the surface, we can offset it and trim with class-B surface too. A simple approach is followed to make the flanges:

Extracting the respective boundary of class-A surface and then using smooth curve tool.
Sweeping this curve with the reference surface as class-A surface (make sure it is extending on both side of class-A, this will reduce our time of creating extrapolate later).
We have to put different values for draft till the flange matches the master-section.
Once this is done, we get our flange. Offset it by 2mm downwards for class-B.
Trim them with respective surface.

While making flange on one side we observed that the class-A surface and master section are not matching at one point. Here we made a flange as parallel to the master-section’s flange as possible and then made an offset (1) of that flange. Later we trimmed it with the class-A surface. On this side the offset was our original flange, so for class-B we made an offset of this surface. In the following image, the lines make “I” are the intersection of the flange and class-A surface which clearly are not in line with the master section as in it the lower line represent the same. The lower line marked “E” is a parallel curve to the flange were we want the flange to be, so we measured the distance between the two and made an offset to that distance (this is the distance for offset (1).

While making the above offset, we encountered a problem. A patch of surface was missing from the offset. We followed mentioned steps to correct it:

Make two splines at two open ends to connect two sub-elements.
Use multi section surface tool with these splines as guide curves and the edges as section with their respective surface as support to fill the gap.
Join all of them together.

CREATING CLASS-C SURFACE:

As this model has complex edges, it is difficult to make a sweep surface at that point. So we made the sweep surfaces only at the straight edges and followed various methods to make C surface. At some edges we extrapolated so they intersect each other. At some edges, we made two straight surfaces and filled the gap between them and extrapolated them. Once this is done, we have to trim all of them with each other to get class-C surface. We have extrapolate class-A with flange too, so that it intersects with class-A and we get required class-C surface after trimming.

CREATING B-PILLAR

Once we have every surface to create surface model we can follow the following steps:

Trim class-A and class-C together.
Trim the result with class-B surface.
Go to part design and close the model to get a solid model.

B-SIDE FEATURES

Once we get our solid model we can start working on B-side features. We will get the required information from the master section. On observing the master section we came to a conclusion that the features are dog house, 4-way locator pin and ribs.

DOG HOUSE

As we have to create this from the master section, we have to understand it properly. We should focus on understanding its orientation, its height, width etc. all this information is in the master section. Once we understand it properly, only then can we make dog house. The below approach was followed to make dog house:

Make the positioned sketch for the dog house from the master section. Dimension the sketch and we can see there is already a draft of 0.5deg given in the sketch so no need to give it in the model.
Extrude this sketch. Then make a positioned sketch again from the other master section, this sketch will limit our dog house from the front and back.
Extract them separately and extrude them. Trim the rear limit and the earlier extrude together and keep the front end open. The front extrude will be used later.
Make use that both the sketches represent the inner face of the dog house so that we can thicken outward (else thicken accordingly).
Split the solid model with the extruded surface at the front.
A smart way to avoid complications later is to run a draft analysis now to check if all the faces have a proper draft or not. If not then edit the respective sketch and give 0.5deg angle.
Give the fillets on inside and outside.
After this, we have to make a sink saver in the dog house.
Make the surface model for sink saver by extracting the B-surface and intersecting it with rear limit. Then make a sketch of it and extrude it (make sure the intersect is between offset B-surface at 3-6mm as this is the height according to the rules).
According to the rules, to give a width of 0.8mm offset it.
Split the model, give necessary draft and fillets.
Use Boolean operation to join it to the model.

4-WAY LOCATOR

From the master-section take the dimensions of the locator.
Pad it with appropriate thickness.
Give chamfer, draft and fillets according to the master section and design rules.
Use Boolean operation to join it to the model.

RIBS

The only detail we have about ribs is that they are 50mm apart, so we make the ribs according to the design rules which are 50mm apart. They ribs should not be greater in height than flange. And also we will consider the height from the side wall according to the rules. Once that is done we will use Boolean operations to join it to the main body.

TREE STRUCTURE: