Roof challenge

ROOF CHALLENGE

Aim: To design a Roof with its components by following the master sections of the font roof rail and rear roof rail also to design bow roofs and center reinforcemrnt roof rails with all the design perameter mentioned in the videos.

Objective: Main objective of this project is to design roof and it's components.Then do a curvature study on the roof and perform roof bow calculations Heat distortion criteria and Snow load condition to determine the position of the Bow-roofs.

Car roof top: An automobile roof or car top is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupents from sun, wind, rain, and other external elements.

ROOF

Components:

1.Roof top

2.Front roof rail

3.Rear roof rail

4.Reinforcement roof rails 1&2

5.Bow roof rails 1,2,&3

Front roof rail : Front roof rail placed under roof at front side. It provides extra strength to the roof and acts as a bow roof. Front roof rail designed as per the design requirments such as wind shield mounting area, visibility creiteria and headroom space. Front roof rail is designed as per the Maser section.

Master section:

section

• 3mm gap is maintain betwen the Front roof rail and Roof top. In those gaps mastics are placed to roof and roof rail.
• Mastic is a rubber kind of material which joins the Roof panel and Front roof rail.
• Thickness of the sheet used for roof rail is 0.75mm
• The clearence between both at extended styling surface at dich area is 0.2mm is maintained. where these two parts are joined together by doing spot weld.

front roof rail

• Deep drawin is a sheet metal forming process. Manufacturing industries largely used due to its easy operation.
• Roof rails are produced by using deep drawing operation by giving proper draft to the sheet for easy removel of produced part from the die.
• Draft analysis: The draft analysis enables to detect if the part we drafted will be easily removed from the machine. This analysis is condected at the design stage by using some design analysis softwares. This type of analysis is performed on color ranges on the analyzed element where the deviation from the draft direction at any point.
• draft angle has given for the roof is 10-15 degrees

Draft analysis:

• Section inertia analysis of front roof rail (0Y section):

Rear Roof rail : Rear roof rail is designed as per the give master section and referance section are provided. It is placed under the roof at rear end.

Master section:

section

• Thickness of the sheet : 0.75mm
• 3mm gap is maintained for placing the mastics.
• Draft angle :10-15 degrees

Rear roof rail

Draft analysis:

Section inertia analysis (0Y section):

Bow roof 1,2&3:

• Roof is not a just single panel. It is along with the Bow roofs and Reinforcement roofs.
• Bow roofs are placed at most flat areas of roof.
• To improve the strength of the roof Bow roofs are introduced.

In this roof design three bow roofs are intorduced along with the Center roof rail. 1st Bow roof was placed at in between the front roof rail and center roof rail. 2nd &3rd Bow roofs are placed next to the Reinforcement center roof rail.

• Mastic points are created on the Bow roof rails to join the roof rails with the Roof panel.
• With 5mm(max) offset roof rails are placed under the roof.
• At mastic points the gap is filled with rubber kind of material wich provides extra strength to the roof.
• Ends of the Bow roofs are connected with body side outer by doing spot weld.
• Thickness of sheet used for manufacturing Bow roofs is 0.75mm

• In these Bow roof design some emboses are created on the roofs to provided extra strength to it.

BW-1:

Section of Bw-1

Draft analysis:

Section analysis:

BW-2:

Section of Bw-2

Draft analysis:

Section analysis:

BW-3:

Section of Bw-3

Draft analysis:

Section analysis:

Reinforced roof center:

• Reinforced roof center is placed at exact center of the roof.
• Center roof rail reinforced with another roof rail at center to strengthen the roof.
• For shorter cars with better roof curvature enaugh only one Reinforced center roof rail.But for lenghty cars multiple Bow roof rails will inturduced along with the center roof rail.

Reinforced roof center

Rf-1

Draft analysis:

Reinforced roof-2

Draft analysis:

Section analysis: For this reinforced roof center section analysis is done by considering both roof rails as a single part.

Curvature study for:

• The curvature study is done on the roof and performed Heat distortion criteria and Snow load condition calculations to determine the position of the Bow roofs.

Bow roof predection formula:

Heat distortion:

W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68

Judgement 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]

Curvature study for snow load prediction:

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)

Judgement 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]

Width of the roof panel 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

conclusion: Successfully designed the Roof & it's components as per given requirments. Bow roof prediction calculations are done to determine the Bow roof positions according to the curvature study.