Roof Design

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

Objective :

To develop the Outer, Inner Roof panel along with the reinforcement such as Front Roof Rail, Rear Roof Rail, Central Roof Rail, Bow Roofs and calculate the Heat Distrubution and Snow Load capacity of the Roof.

Tool Used :

Law Extension

Datum plane

Trim sheet

Sketch tools

Through curve mesh

Offset surface

Offset curve on face

Mirror Geometry

Draft Analsys

Section moment of Inertia

Description : 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. It also joins the vehicle body with the lower parts such as A, B and C pillars. To provide extra protection to the roof, reinforcement are provided in form of rails and bows which also has provsions to mount different attchments.

Steps Followed :

Front Roof Rail

• With the help of given master section the First the outer roof flange is developed by using law extension and offset surface to the required dimension.
• After the outer flange is developed the edge fillet is provided to the sharp edges.
• The outer roof surface is offset to 32 mm downwords to form inner part of the front roof rail with other flanges as per given master section

After creating Front Roof draft analsys is perormed to check if it is clearing draft. The result is as follows.

Above 7 degree draft is shown in green and below 7 degree is Red and upto & is yellow.

Rear Roof Rail :

• The given outer panel is again offset in downword direction to form flange first as per given master section.
• After the Rear outer flange is developed the outer surface is again offset to to the required to form rear inner flange.
• After the lower portion is created the rear roof rail is mirrore to get the whole part which is then thicken to 0.75mm.
• At last draft analsys is performed to check the draft given to the part is proper. The result is shown below.

Central Roof Rail :

• For central roof rail the given master section is followed which shows width to be arounf 80-90mm.
• Again same process is followed and the outer surface is offset as per the dimensions given in master section to develop the central roof rail.
• The draft analsys shows proper draft values.

Bow roof :

Again same process is followed as above and draft analsys is checked for the Bow roof1 and Bow roof 2.

Heat Distribution calculation : As per the given formula for Heat Distribution

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]

As per the obtained,all the values of W is found to be greater than 2.7 which does not satisfy the condition of W<2.7 , So, several measures can be applied to improve W of the roof such as

• changing the position of central rail.
• External emboss can be provided on the roof to provide extra stregth.
• Increasing the thickness of bow roof.

Snow Load prediction :

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

Qr value found is greater than 3.1 so the roof satify snow load condition.