Roof challenge

Aim:- For the Given Roof styling, Develop the essential flanges and reinforcements, Provide appropriate dimensions and check for Draft analysis, and perform a roof curvature study on the roof to determine the position of the bow roof.

Introduction:

Automobile roofs or car tops are the portions of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements.

The roof is a styling surface part that is fixed with the BIW body through the rails and panels inside the upper roof to provide it with strength and stiffness.

The Ditch area plays an important role here to fix the reinforcement on the component.

The rails and reinforcements are joined to the ditch area with a spot weld where tit affects the aesthetic look of the car.

The required tool opening angle is a minimum of 3 degrees.

Factors which is considered before creating a ditch area are.

· Head room clearance

· Visibility criteria

· Back door assembly

· Windshield assembly.

Software used for designing is NX Cad

Styling input

· With the help of this input only we have to design all the inner parts of the roof and assembled them together.

· Input roof surface is perfectly symmetrical and we will work only on one side after completion, we will mirror the entire assembly to form a complete assembly of the roof.

Components of roof:

· Front roof rail

· Rear roof rail

· Bow roof

· Centre roof rail

· Ditch area

Front roof rail: To create the front roof rail we have a master section the help of which we will design a front roof rail.

MASTER SECTION OF FRONT ROOF RAIL

DESIGN OF FRONT ROOF RAIL

The front roof rail provides strength to the front side of the roof and it also acts as a link between windshield glass, roof panel, and headliner. The front end is joined with the spot weld and the rear side is joined with the help of mastic sealant due to which strength increase.

Rear roof rail: -

The rear roof rail is assembled at the rear side of the roof panel and provides strength to the rear part of the roof.

Master section of the rear roof rail

Rear roof rail design

The rear roof rail is again used to strengthen the roof and it acts as a link between the back and roof which is connected to the backdoor of the car. The rear roof rail is joined with the spot welding in the ditch area and one end is attached to the roof with the help of mastic sealant.

Center roof rail and bow roof rail: -

Center roof and bow roofs are the most important parts of the roof design it provides strength and stiffness to the roof from various loads it is joined with the help of mastic sealant.

Center roof rail and bow roofs

Final assembly of roof: -

Final ASSY with all the component

Curvature study on the roof: -

After preparing the assembly we must justify that the roof can pass various load tests and make sure that the bow roof position is ok or not.

Following analysis test to be done to justify the position of bow roofs.

1. Roof distortion test
2. Heat distortion test
3. Snow load criteria

Heat distortion criteria:

Heat distortion temperature is a temperature at which the metal softens and deforms under a specific load. This study is done to check the ability of the roof to withstand high temperature with respect to the position of the reinforcement which contributes to the increased strength.

To calculate the heat distortion criteria by the bow roof formula

• We need to create a sketch of the center of the roof.
• Then offset the centerline by 300 mm.
• Then offset the offset line by 100 mm on both sides.
• After that, we will be going to draw a vertical line at the center of the front roof rail and bow roof.
• Then do the offset of 100 mm in both directions.
• Then after those points have been placed at the intersection of the curve.
• Then all the points must be projected onto the surface of the roof.
• Then with the help of projected points, we will be going to make the curve on the roof.

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

Judgment Condition

OK< 2.7>3.1

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]

Here the value of w is under the OK< 2.7>3.1 so we can say that the position of the bow roof is correct and pass the heat distortion test.

Snow load criteria:

A snow load test is done to check the ability of the roof to withstand the snowfall and come back to its original shape after the load is removed without any permanent deformation.

To calculate the heat distortion criteria by the bow roof formula

• We need to create a sketch of the center of the roof.
• Then offset the offset line by 100 mm on both sides.
• After that, we will be going to draw a vertical line at the center of the front roof rail and bow roof.
• Then do the offset of 100 mm in both directions.
• Then after those points have been placed at the intersection of the curve.
• Then all the points must be projected onto the surface of the roof.
• Then with the help of projected points, we will be going to make the curve on 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)

Judgment 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]

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 inside view.

Here the value of Qr is under the Qr ≥ 3.1 so we can say that the position of the bow roof is correct and pass the snow load test.

Section inertia analysis:-

1. Front roof rail

2. Bow roof 1

3. Center roof rail

4. Bow roof 2

5. Rear roof rail

Draft analysis: -

1. Roof

2. Front roof rail

3. Bow roof 1

4. Center roof rail

5. Bow roof 2

6. Rear roof rail

Conclusion

1. The roof and its components have been designed successfully according to the master section.
2. The roof has been checked for the roof distortion criteria and found to be ok.
3. The roof was also checked for the snow load condition and was found to be ok.
4. Draft analysis has been performed on all the components and all components were found to be manufacturable.