Roof Design

Question:

For the Given Roof styling, create an 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.

Suggest and implement remedies in the design if the criterion is not full-filling

Start with the creation of a roof ditch area with a tool opening angle of 7 degrees.

Develop the reinforcements as separate parts

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

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

Here are some Reference images for the Master sections - These images are just to give you a brief idea about the design.

Front Roof Rail Master section

Master section of the Rear Roof Rail

Master section of Bow Roof

Master section of Center Reinforcement Rail

Procedure :-

AIM:

For the given car roof styling, design and develop the essential flanges and reinforcement, namely the Ditch area, Front Roof rail, Rear roof rail, Centre Roof rail and Bow Roof 1 Bow Roof 2.

Do the curvature study on the roof and perform the calculation for heat Distortion and snow load criterion to determine and justify the position of the Bow roofs.

An automobile roof is the portion of an automobile that sits above the compartment, protecting the vehicle occupants from Sun Heat, rain, wind, and other external factors.

Roof Design:-

Given tha Class A surface, we have design to roof design with the help of class A surface and given Master section.

Roof Outer Panel:-

The Ditch Area is the extended portion of the main Roof concealed by other BIW panels. The rail supports of the roof are attached to the Ditch Area using Spot welds. since it is not a styling surface and remains is concealed.

Front Roof Rail:-

It is a support, that is joined the windshield glass. Body side outer and the inner panels Its thickness is usually 0.75mm. The windshield end flanges are the extract offset of the roof surface. The bottom-most flanges is decided after taking into consideration the visibility criteria. Spot weld is applied at the windshield end of the other end is joined with the roof using Mastics sealants which also contributes to increases strength.

Rear Roof Rail:-

It is the support that is joined to the back door and the Body side outer and the inner panels. it is usually made from body side outer scrap and therefore the thickness of the rail is 0.75mm. Similar to the Front roof rail design. We have to take into consideration the rear headroom clearance and the rear visibility criteria while designing the rear roof rail from the backdoor design and also taken into consideration od the required clearance. Spot welds are applied at the back door end of the rail and the other end is joined with the roof using Mastic sealants.

Center Roof Rail:-

It is the main supporting rod for the roof. Their purpose is to provide an attachment point for crossbars and other devices designed to secure loads carried on the roof of the vehicle, it absorbs energy at the time of the crash.

Bow Roof's:-

Similar to the other design, we have to take into consideration of the headroom clearance and the visibility criteria while designing the centre roof rail and bow roof rail. Here spot weld is not applied for joining these rails of the roofs. Instead mastic sealants are used are introduced at both ends since centre Roofs are fully positioned under the styling surface of the roof. For increasing the strength of the rails, Embossing is done.

Analysis

1. Curvature study

It is done to justify the positioning of the bow roofs. There are mainly two criteria to fulfil

• Heat distortion criteria
• Snow load criteria

Heat distortion 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]

below show the figure -

we have create 5 intersection point of each between 2 rail after create point do the project the point on the Roof outer panel and join the point with the help of circle defination.

It has horizontal line Rx and vertical line Ry.

Calculations in the table as given below:-

Judgment Condition

OK< 2.7

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

we have create 5 intersection point of each between 2 rail after create point do the project the point on the Roof outer panel and join the point with the help of circle defination.

It has horizontal line Rx and vertical line Ry.

Judgment condition

Qr ≥ 3.1

250 ≤ s ≤ 380

Draft Analysis:-

Draft analysis is a method of checking the draft angle on various faces of a part in a particular direction. it should be more than 7 degrees. draft analyzing command which lets you know if your model or design has a draft angle in a given tool direction.

If the part lies within the conditions it shows in green colour if not shown in blue or red colour.

The below figures show the draft analysis for Roof, Front Roof Rail, Rear Roof Rail, Bow Roofs and Reinforcement Center.

Results:-

The Design of Roof, Front roof rail, Rear Roof Rail, Bow Roofs, and reinforcement roof center by following the Master section with the design parameter for the given class A surface is done and the final model is shown in the figure below.