Roof Design

Aim:- Design and development of a car assembly with its reinforcements.

Introduction:- An automobile roof is considered as an integral part of BIW( body in white) design. A car roof is responsible for protecting the passenger from rain, wind, sunlight, accidents etc. its also offers aerodynamic supports to the car when it is in motion. A roof panel assembly includes a roof outer panel with dithc area and some nessesory reinforcements rails. Roof rails arre provided to give strenght to the outer panel and also provide support to the other componets present in a ncar.

There are some different roof rail reinfocements are present in a car as shown in fig

1. front roof rail

2. rear roof rail

3. bow roofs rail

componets

Softwere used :- NX cad

Given data :- Roof skin styling surface

Parameters :- there are some parameter are following while making the model which makes the model editable at every point of the cad model development.

opening angle = morethan 7 deg

fillet radius = 3mm+ thickness

thickness = 0.75mm

flange length = 20 to 22.5 mm ( for outer panel)

Design considerations for Development of roof assembly

1. Aerodynamics: car roof should be designed to minmaze air resistance and drag, which can improve fuel efficiency and reduce wind noise. The shape of the roof, the angle, and the height all play a role in aerodynamics.

2. Headroom:- car roof shold be provide adequate headroom for passengers, particularly in the front sheats. this is espacially importent for taller person and it may be a consideration for sunroof or moonroof etc.

3. Strength and safty:- car roof should be strong enough to protect occupants in the event of a rollover accident. Roof stregth can be improved through the use of high strength materials such as steels or cobon fiber and by reinforced pillers and side rails.

4. Weight:- car roof should be designed to minimize weight while maintaning strutural intigrity. This can improve fuel efficiancy and handling.

5. Functionality:- Car roof should be designed to accommodate the intended use of the vehicle. For ex. a roof rack may be nacessary for carring sports equipments or luggage.

6. Visibility and blind area:- Visibility criteria is also an importent design consideration for a car roof, as it affects the driver s ability to see the road and surrondungs. The blinde area in a vihicle is as area around the vehicle that cannot be directly observed by the driver while at the controls,under existing circumstances. Here are some visibilty related design considerations for car roofs.

These design consideration can affects the design of the roof shape height angle materials, supports, lighting and other features. they are all importent factors to consider when designing a car roof that meets the needs and preferences of drivers passengers.

here are given master sections

Roof outer panel with front roof reinfoce:- Front roof rail is used to provide strengh to the roof panel front and it also acts aslink bw windshield glass, roof panel and headliner. Headroom clearance and visibility are two importent criteria for the driver and both of them dependes upon yhe front roof rail dimentions, hence it is omportent to select appropriate deimentions for the roof rail.

Rear roof rail:-

Roof center rail:-

Bow roof 1:-

Bowroof 2:-

Drawing/Stamping diraction:- A sheet metal part is manufactured bt the stamping process. in this process a punch and dai are used to genrate the desired shape. The stampingdiraction indicates the diration in which the punch moves. here are some sheet metal oprations shown in image given below.

Draft analysis results :- Performing Draft Analysis for all the parts and include the snapshot in the report in done.

Roof curvature study and bow roof position jusitification

before sending the CAD models to the simulation team it is important to justify the position of the bow roof and their bow roof span. It actually leads to the prevention of most of the problems that may occur in the design stage. there are two ways in whivh we can performe this study before performing the study we check the roof curvature.

above is an image of the cross ssection of the roof panel as we can see that the front portion has more curvature as compared to the rear end( to the right_). we can place bow roof in such ways that more strength is given to the rear end.

for this i have proposed the following design

To justify the bow span and bow position we have to perform certain studies. In this project we have performed two studies on bow roof positioning and roof curvature.

1. Heat distortion study:- in heat distortion study we have a mathematical formula which has to be satisfied in order to justify the bow roof positions. The following formula has been used

Bow–Roof Prediction Formula

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

Where,

L = Roof Length in X-Direction[mm](Roof dimension in 0-Y)

R = Roof curvature

R = 2(Rx*Ry)/(Rx+Ry)

Rx = X curvature

Ry = Y curvature

t = Roof plate thickness [mm]

l = Bow Roof Span [mm]

Judgment Condition

OK< 2.7

calculation is done.

Here we got W values lessthan 2.7.

2. Snow Load Prediction Formula

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

Note: The Qr value given over here is correct. There was a typo error in the formula given in the video.

Where,

α = My x Lx² x 10^-12 , My = Y(Ly-Y)

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]

The width of the roof panel is 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]

Roof panel X curvature radius of length s in Side view

Judgment condition

Qr ≥ 3.1

calculation is done.

Here we got the Qr values greater than 3.1

For better strenght i am provided some long shape embosses on outer roof surface as shown in fig.

Conclusion:- Roof panel with all the necessary reinforcements has been created and roof curvature and bow roof position justification has been provided.