Roof Design

BIW ROOF

INTRODUCTION:

An automobile roof or car top is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements. Because the earliest automobiles were designed in an era of horse-drawn carriages, early automobile roofs used similar materials and designsIn the past roof was introduced as cover for passenger compartment but later on, it also used as a luggage carrier, sunroof and in recent past years with the introduction of the solar paneled electric vehicle got a major boost in the automotive industry.

DRAFT ANALYSIS:

Draft analysis is done to check if the component does not have any negative draft. a negative draft can create a problem during the manufacturing process. Sheet metal parts must have a draft of at least 7 degrees for proper tooling.

FRONT ROOF RAIL:

BOW ROOF-1

CENTER ROOF RAIL:

BOW ROOF-1

REAR ROOF RAIL:

ROOF DESIGN AND ITS PARTS:

Here we are creating the Roof , Front And Rear Roof rails along with the three Reinforcements , By taking a pre designed styling surface as the reference.

The Front roof rail and the Rear roof rail are the components , where the front and rear sides of the Roof are attached ,while the other three reinforcements gives enough strength and stiffness to the roof. This assembly of roof include

1. Roof outer panel
2. Front Roof Rail
3. Rear Roof Rail
4. Center Reinforcement
5. Bow Roof 1
6. Bow Roof 2

For designing a car Roof , there are several Design consideration and standards a design engineer must consider in his or her designs.

ROOF OUTER:

Here I have the styling surface as reference, so I only need to create the side flange and the ditch area in the roof. As I doesn’t have any data from any other parts of the car , I am taking a given master sketch as another reference.

DRAFT ANALYSIS:

FRONT ROOF RAIL:

The same master sketch taken for creating the ditch area in the roof is taking here as the reference. I have used wave geometry linker to take the roof outer surface and offset it to needed values and them trimmed of the extra materials,in this design dart are developed to atain strenght and we assume also this as a mastics reference point by this we are reduce the cost of the part by 2 in 1 operation.

BOW ROOF-1&2:

Apart from the center reinforcement I have created two Bow roofs , one in between the Rear roof rail and the center reinforcement and the other is in between Rear roof rail and the center reinforcement. Method of creation for each Bow roof are same as the center reinforcement .

CENTER REINFORCEMENT:

As in the Front Roof rail I have used wave geometry linker to take the outer surface of the roof. Then offset it to certain values and trimmed the extra materials to create the part.

REAR ROOF RAIL:

Here I have taken the y axis as the tooling direction and after analysis there is no negative draft angles

FOLLOWING OF MASTER SECTION :

Hear i developed all parts by refference of master section provided below and i attached reffernece in clipsection view.

After designing and the assembly is complete , we should check whether the positions of the reinforcements are correct and whether they can give enough support to the roof to bear enough load .Also whether the roof can withstand high temperature with out any deformation .For that we need to do two calculation

1.Heat Distortion calculation

This is the calculation to check whether the roof can withstand high temperature with respect to the positioning of the reinforcements with out any deformation .

The Heat distortion criteria is W < 2.7

We have the equation W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68

Judgement Condition : OK< 2.7

And below i attached table

from the above i have develpoed with good curvature radius and also perfect placement distance of the bow,rear& front roof rail and reinforcement centere and there by it will wistand the heat distorsion (W) was <2.7 and finally i achived the heat distorsion.

SNOW LOAD CONDITION:

n the winder season , in some countries there will be a huge load of snow on the roof top of the car. So for the roof it is necessary to have enough strength to bear this snow load.

The snow criteria is Qr ≥ 3.1

We have the equation

Qr = [Iy x t²] / [α x s x [(Rx + Ry)/2]² x 10^-8]

Where

α = My x Lx² x 10^-12 , My = Y(Ly-Y)

Judgement condition = Qr ≥ 3.1

250 ≤ s ≤ 380

t = Roof plate thickness [mm]

Ly = Distance between the front and rear roof Rails on the Vehicle along with 0Y[mm]

Length of Roof panel with the center point between Roof rail Front /Rear as the front and rear reference point.

Lx = Distance between the Left and Right end of the roof on the Roof BOW [mm]

Width of the roof panel exposed on the surface.

Y = Distance front Front Roof Rail to Roof BOW[mm]

s = Distance for which Roof BOW bears divided load [mm]

s = L1/2 + L2/2

Iy = Geometrical moment of inertia of Roof BOW (Y cross-section )[mm4]

Rx = Lateral direction curvature radius of roof panel Y cross-section on Roof BOW [mm]

Roof panel curvature Radius of the Length Lx in Front view

Ry = Longitudinal Direction curvature radius of the Roof panel X cross-section on Roof BOW [mm]

For the Snow load calculation first of all we need to find the section inertia of the three Reinforcements which are Bow roof 1, Bow roof 2 and the Center Reinforcement

BOW ROOF MOI:

CENTER ROOF RAIL:

And snow load calculation table.

From the above that case CTR & BR-2 nearer to the value of 3.1 and by the snow load condition was not attained on specific radius curvature and to attain snow load stifnees strgent of the ROOF i deloped EMBOOS on top by this change of design i achived the snow load condition and i attached it below.

CONCLUSION:

• Roof assembly has been made by following all the engineering standards and considerations
• Heat distortion criteria is been successfully passed
• Snow load criteria has been failed in some cases and to over come that Embosses are added on the Roof outer panel