Roof Design

AIM :

For the given roof styling, develop the essesntial flanges and reinforcements, provide appropriate dimensions and check for draft analysis and to perform roof curvature study using NX-CAD.

Introduction of roof :

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.

Class A Styling Input :

• After the file is opened, the roof part is not joined together but as the individual surfaces.
• It is also seen as the surface is perfectly symmetrical in shape which helps us to work on the half of the portion and reflect it which creates the whole roof. We work on the half of the surface and mirror to complete the rest.

Components of roof:

• Front roof rail
• Bow roof rail 1
• Centre roof rail
• Bow roof rail 2
• rear roof rail
• Ditch area

Ditch area:

Ditch area is a extended portion of the maim roof concellled by other BIW pannels.The rails support of the roof are attached to the ditch area using spot weld.

FRONT ROOF RAIL :

It is created using Given reference master section :

FRONT ROOF RAIL :

• It is a additional part, which will act as a reinforcement for the roof front.
• While designing this part, we have to consider the visibility criteria and also space nesscary for mounting windshield glass, rubber around glass, rubber paste, sealant.
• This part made from body side outer scrap materials.
• Minimum thickness required are 0.75mm.
• This part may having emboss to provide strength.

outlook design :

front roof ditch area :

draft analysis :

It is seen that the features designed clears the minimum draft angle which denoted in 'green'.

BOW ROOF 1 :

• The bow roof, which is placed under the roof to provide strength to the roof.
• Number of roof placed depends upon the length of car, there may be more than one bow roof placed under roof.
• It have a mastic point, which is used to make attached to the roof without any spot weld. This mastic seal influence over 60 to 80mm around it.
• Bow roof can be placed by two methods. One method of placing bow roof between front and rear roof rail and reinforcement center or it is placed on most flatten surface in roof.
• This flatten surface can be find by two methods depends on heat and snow condition

master section of bow roof rail :

outlook design :

draft analysis :

It is seen that the features designed clears the minimum draft angle which denoted in 'green'.

moment of inertia (I) on bow roof rail 1 :

CENTER ROOF RAIL :

Center roof rail will be at the centre of the roof to provide strength and stability to the roof. Here the centre roof rail is joint with the roofthrough mastic sealent

master section on center roof rail :

outlook design :

draft analysis :

It is seen that the features designed clears the minimum draft angle which denoted in 'green'.

moment of inertia (I) on center roof rail :

BOW ROOF RAIL 2 :

• The bow roof, which is placed under the roof to provide strength to the roof.
• Number of roof placed depends upon the length of car, there may be more than one bow roof placed under roof.
• It have a mastic point, which is used to make attached to the roof without any spot weld. This mastic seal influence over 60 to 80mm around it.
• Bow roof can be placed by two methods. One method of placing bow roof between front and rear roof rail and reinforcement center or it is placed on most flatten surface in roof.
• This flatten surface can be find by two methods depends on heat and snow condition

master section :

outlook design :

draft analysis :

It is seen that the features designed clears the minimum draft angle which denoted in 'green'.

moment of inertia (I) on bow roof rail 2 :

REAR ROOF RAIL :

Rear roof rail is again used to strengthen the roof and it acts as a link between back glass and roof which connected to the backdoorof the car.Spot welds are applied at back doorend of the rail and the other end is joined with roof using mastic sealent

It is created using Given reference master section.

It is seen that the features designed clears the minimum draft angle which denoted in 'green'.

Curvature study on the Roof:

After getting the final body it has to be checked and justify that it passes the standards.

Analysis:

It is done to justify the position of the bow roofs.

1.Roof crash test.

2.Snow load test.

3.Heat distortion criteria.

Heat distortion criteria:

Heat distortion temperature is a temperature at which the metal softens and deform 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 contribute to the increase strength.

• To calculate the heat distortion criteria by the bow roof position formula,
• We need to create a sketch , draw a line on the center of the roof on OY axis (mid horizontal axis)
• Next draw a line from the center line by a 300mm distance
• After that draw a line from 100mm distance on both sides of the 300mm line
• Then draw a line between the center of roof rails and draw the lines from the center line by the distance of 100mm on both sides.
• Atlast make an intersection on these lines from a coincident line to get points

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

HEAT DISTORTION CALCULATION :

Rx & Ry using ( -3 y ) line

tabulation of heat distortion calulation :

SNOW LOAD CALCULATION :

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

250 ≤ s ≤ 380

Rx & Ry using ( 0 y ) line

tabulation of snow load calculation :

Conclusion:

heat distortion and snow load calculations,

both calculations satisfied on the judjement conditions.

i have giving part files.

it's not working please use the goggle drive link.

https://drive.google.com/drive/folders/1d_E-74Q9rjd_MIDlOwa9lLamV8TOdMkQ?usp=share_link