Roof challenge

                                                                      DESIGN OF ROOF BY USING

OBJECTIVE :-

• Designing a roof by by using the given styling surface
• creating bow roof's, front an rear roof rails and centre roof rail by taking the given master sections as a reference
• checking draft analysis and section modulus

IMPORTANT TERMS :-

Roof :- It is a top portion of a car which covers the vehicle from sunlight. Roof is not a single part.

                                          

It is a combination of many parts like

Front roof rail :-

             It is the one which joint with the wind sheel glass, front roof rail an body side outer

Rear roof rail :-

              It is the one which joint with the back door an body side outer

Centre roof rail :-

            It is the one which attached to the outer surface panel of a roof 

Bow roof's :-

       These are also attached to the outer panel of the roof to increase the strength of roof

                                           

Design concept sheet :- It is a sheet which have all the information of what at roof is going to have.

                                    

like,

• To which region we are going to present the thish roof
• It's material
• Where it's going to produce
• What is the thickness

Bow roof position types :-

• Heat dissipation :-

                    when the roof tends to high amount of heat due to sunlight then there is a possibility of expanding of roof. So, to avoid that expansion we place a bow roof's in such a way that the roof should not expand

• Snow load criteria :-

                     It is a condition where the roof is filled with snow in winter seasons. This snow have a weight which leads to deformation of roof.

Based on these conditions two conitions we decide the bow roof positions

DESIGN OF ROOF :-

Front roof rail :-

                  

              When we have have a styling surface we have an edge point of front roof rail which is called as styling point. For deep drawing operation we have to open it for 3 degrees . If it is less then that we can't draw the part. At this we give a flange length of 21.5mm because in this portion rubber accupies 5mm, an another mounting is 8mm then remaining place will accupie by wun sheel glass with rubber. Thickness of win sheel glass is 3.7 to 4.7 mm,below the wind sheel glass we have rubber which is pasted on it. thish paste have a thickness of 4-5mm.

By considering all this design rules and following the master sections we create a frront roof rail.

         

                                                                               Front roof rail

Rear roof rail :-

      It is also same as front roof rail but the only difference is the distance between the styling point to the en point of rear roof rail will increase.some times it depends on the opening angle of rear hood.

                         

Centre roof :-

      It is one of the part in roof which is placed at centre of the roof to give strength to the roof. It is designed by following the engineering rules 

like,

     Thickness = 0.85mm -1.25mm

     Width       = 90mm

Bow roof's :-

      These are also a part of Roof which are placed in between centre roof and rail roofs. generally we place two bow roof's for the car but in some heavy vehicles it would be 3 or more. it depends on the size of the vehicle. These bow roof's also follows engineering rules

like,

       Thickness = 0.85mm - 1.25mm

        width      = 70mm 

                                           

Heat distortion criteria :-

              Heat distortion is a condition of expansion of roof top panel due to high temperature climatic conditions. To ensure this heat distortion we attach bow roof's for the roof outer panel. After that we need to check whether the bow roof's will resist the heat distortion or not by doing some calculations. like,

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            

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)

 Hence, the obtain values are

S.No	BOW's	Rx	Ry	R	l	L	t	R^2/t	W	OK/NG
1	FRONT & 1st	3268.478	14666.358	5345.65	416.95	2091.794	0.75	38101298.56	2.10	OK
2	1st & CNTR	4057.199	10179.653	5801.96	490.185	2091.794	0.75	44883653.12	2.308	OK
3	CNTR & 2nd	4987.529	6136.41	5502.64	345.854	2091.794	0.75	40372062.62	2.066	OK
4	2nd & REAR	5735.599	2610.44	3587.91	349.406	2091.794	0.75	17164130.89	1.64	OK

Snow load criteria :- 

        Snow load is a condition where the outer panel of roof will bend due to the snow which is fall on to the foor in winter season. It's mainly occurs in forigen countries. To avoid this snow load impact we place bowroofs and checks the panel after attaching the bow roofs by using the formulae.

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 reference point of the front and the rear.

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

section modulus for reinforcements :-

 

Hence the obtain values are 

S.NO.	BOW's	Iy	α	Lx	Ly	y	s	Rx	Ry	t	Qr	determination (Qr)
1	FRONT & 1st	2.04935*10^8	0.854	523.573	2034.691	511.377	517.081	3987.233	16505.123	0.75	3.15
2	1st & CNTR	3.291*10^8	0.893	531.618	2034.691	522.785	475.5695	4235.752	9904.745	0.75	3.68
3	CNTR & 2nd	2.0393*10^8	0.8188	545.45	2034.691	428.354	453.0175	3762.095	6042.954	0.75	5.402
4	2nd & REAR		0.966	569.827	2034.691	477.735		4489.723	2660.198	0.75

 Draft alanysis :-

Roof outer panel :-

 

Front roof rail :-

 

Bow roof's :-

                

Centre roof :-

 

Rear rail roof :-