Roof challenge

Roof Challenge

Objective:-

1. For the Given Roof styling, create an ASSEMBLY by developing the essential flanges for the outer roof and creating the reinforcements.

2. To make the necessary flanges and ditch area around the upper roof panel.

3. To do the Heat Distortion calculations and Snow load factor calculations to justify the design and placements of the bow roofs.

4. Perform Draft analysis of every part to check weather the designed part is produce-able or not with the necessary minimum opening angle of 7 degrees.

Introduction:-

An auto mobile roof or car top is the portion of an auto mobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements.

Car roof is the important composition parts of Integral auto mobile, and the fastness of car roof is directly connected to the quality of car performance; The processing technology of roof directly has influence on the anti-seismic performance of soundproof effect and the car of car inside; Therefore,, when processing roof, often adopt many roof cant rail actings in conjunction to guarantee the integral firmness of roof; Prevent the distortion of car body;

In later years, many variations on the auto-mobile roof developed. These include:

1. Convertible roofs

2. Roof modules

3. Roof modules

4. Hardtops

5. Sunroofs

6. T-tops

7. Targa tops

8. Vinyl roofs

Roof is designed by following some criteria-

1. Visibility criteria as safety and functionality

2. Head clearance for ease and comfort

3. Draft analysis fro easy manufacturing and tooling

4. Safety parameters for users

5. Heat distortion

6. Snow load criteria

Master Sections:-

For every part we were provided with a master section which was followed accordingly to maintain the driver visibility criteria and roof aesthetics

Front Roof Rail:-

Front roof rail is designed by taking the reference of the styling surface by offsetting it according to the design. Necessary reinforcements and embossing are provided to further increase the strength of the part.

Rear Roof Rail:-

Rear rail roof is situated at the above of the backdoor and is the widest rail in this assembly with the highest Moment Of Inertia and rigidity. Embosses are given to further increase the strength and stiffness.

Center Roof Rail:-

It is situated at the centre of this assembly giving the strength at the central portion of the roof further they are also connected to the Body frame with the help of spot welds.

Bow Roofs:-

Bow roofs are situated in between of either side of the central roof as per the design requirements. Bow roofs are generally connected to the outer panel with the help of mastic sealants because spot welds are not created as they will hamper the overall look of the outer panel.

Flanges are provided with the space for pasting the mastic sealants.

Bow Roof 1 Bow Roof 2

Curvature study on the roof and Calculations

1.Heat Distortion and Bow roof prediction:-

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

To calculate the necessary variables in the formula following conditions are used in the roof

According to the given above formula the calculations have been done and the results have been arranged in a tabular form

As from the above table clearly the bow roof has satisfied the heat distortion criteria and now we can ho ahead with he snow load calculations

2 .Snow Load Prediction:-

In the winter season in the European region there is a lot of snow fall and it by the time it cluster upon the cars roof as a big thick layer and due this it exert a dead load in the roof which deforms the shape of the roof so to retain the shape of the roof after removal of the snow enough strength is provided to the roof.

Snow Load Prediction Formula

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)

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

Sectional Analysis for Moment Of Inertia Calculations

Bow roof 1

Bow Roof 2

Front Roof Rail

Rear Roof rail

Central Roof Rail

We can see that in this criteria the bow roof design has failed in two cases which it not at all desirable so as to retain the strength special emboss in provided in the outer panel of the roof to compensate the strength and it also increase the Moment of inertia of the section of the roof.

Roof Before Modifications

Roof After Modifications

Draft Analysis:

The following attached images are snapped after performing the daft analysis of the roof parts to ensure the parts are able to be manufactured.

Summary:-

So the above is the presented report of the roof design challenge with the necessary calculations and modifications.

Report Prepared By:

Rishabh Soni