Roof Design

Objective

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

   Provide appropriate dimensions and check for Draft analysis.

   Do a curvature study on the roof and perform calculations to determine the position of the Bow-roofs.

   Start with the creation of a roof ditch area with a tool opening angle of 7 degrees. Develop the reinforcements as separate parts

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.

      Roof is the structure above the wind shield glass having the reinforcements to provide the strength to the overall structure and to with stand the over head forces like snow

Reinforcements 

If the roof is flat it is very weak and cannot able to with stand the forces like snow , so in order to increase the strength of the roof these reinforcements like front roof rail, central roof rail, rear roof rail and the bow roofs are introduced and joined to the flat surface of the roof

Types of Reinforcements 

• Front Roof Rail
• Bow Roofs
• Center reinforcements roof
• Rear Rail Roof

Joining process.

• Spot Welding  - using internal joining. 
• Mastic Sealants - Using instead of spot weld to avoid appreance issue on outer roof 

Roof Design Considerations.

• Visibility criteria
• Head room clearance
• Roof curvature study
• Heat distortion criteria 
• Snow Load criteria 

Roof & Assembly Orientations

Front Roof Rail

Bow Roof 1

Reinforcements & Center Roof Rail

Bow Roof 2

Rear Roof Rail

Bottom View

Iso Metric View

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 condition satisfied for this curvature.

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

This Curvature is satisfied the Snowload condition.

Draft Analysis

Roof Pannel

Front Roof Rail

Bow Roofs 

Reinforcements

Rear Rail Roof