Roof challenge

Aim: To design a car roof with essential Front roof rail, Bow roofs, Center roof rail and Rear roof rail for the given master section and finally perform curvature study on each sections and draft analysis.

Given data:

Fig: Master section of Front roof rail

Fig: Master section of Rear roof rail

Introduction: 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.

To provide durability, Strength and Support to the the roof outer panel it is generally provided with other structures. They are Front roof rail, Bow roofs, Center roof rail and Rear roof rail.

1) Front Roof Rail:

The First rail provided which connects the Wind shield. A draft angle of 3 deg is provided so as to make the manufacturing process (deep drawing) easy.

Fig 1.1 Cross section of Front roof rail

2) Bow roof 1 & 2:

Situated below the styling surface and increases the strength of the roof. Cutouts are provided to minimise the overall weight of the rail.

Fig 2.1 CS of Bow roof_1 Fig 2.2 CS of Bow roof_2

3) Center roof rail:

Fig 3.1 Cross section of center roof rail

4) Rear roof rail:

Fig 4.1 Cross section of rear roof rail

5) Sectional Views:

Fig 5.1 Split view of rails

Fig 5.2 Top view

Fig 5.3 Isometric view

Curvature Study:

a.Heat distortion criteria: Heat distortion criteria is the one at which the metal softens and deforms under a specific load. It is necessary study done to check the ability of the roof to withstand high temperature under specific conditions.

W=1.73*10-3*L+1.85*10-8*R2/t+1.10*10-3*l-2.68

Where,

L=Roof length in x direction

R=Roof curvature=2(Rx*Ry) / (Rx+Ry)

Rx= X curvature

Ry= Y curvature

t= Roof plate thickness (mm)

l= Bow roof span (mm)

S.No	BOW	Rx (mm)	Ry (mm)	R (mm)	L (mm)	i (mm)	t (mm)	W	Result
1	FR & Bow 1	5732.99	2649.64	3624.24	2030	603.7	0.75	1.819	Pass
2	BOW 1 & CR	6739.49	5632.14	5632.14	2030	369.1	0.75	2.02	Pass
3	CR & BOW 2	10879.63	5762.72	5762.72	2030	446.3	0.75	2.14	Pass
4	BOW 2 & RR	15059.19	5291.19	5291.19	2030	446.8	0.75	2.01	Pass

b.Snow load criteria: Snow load criteria is done to check the ability of the roof to withstand snowfall and retain its original shape without any deformations once the snow load is removed.

Qr = Iy*t2 / α*s*[(Rx+Ry) / 2]2*10-8

Where,

α= My*Lx2*10-12, My=Y(Ly-Y)

t= Roof plate thickness (mm)

Ly= Distance between the left and right end of roof (mm)

Y= distance from front roof rail center to bow roof (mm)

s= distance for which bow roof bears divided load (mm)

Rx= lateral direction curvature radius of roof panel Y cross section on bow roof (mm)

Ry= longitudinal direction of curvature radius of roof panel X cross section on bow roof (mm)

S.No	BOW	Iy (mm4)	α	Rx (mm)	Ry (mm)	S (mm)	t (mm)	Qr	Result
1	FR & Bow 1	2815	1.13	4431.25	2547.38	186.18	0.75	61.77	Pass
2	Bow 1 & CR	27140	0.835	3807.92	6774.13	223.97	0.75	292.64	Pass
3	CR & Bow 2	2807	0.86	4294.13	11352.41	224.39	0.75	13.36	Pass
4	Bow 2 & RR	126000	0.813	3877.83	17095.22	302.59	0.75	262.9	Pass

Draft analysis:

Conclusion: All the given design aspects were taken into consideration for completing the final design & since the design satisfy the Heat distortion and Snow load condition it can be taken for further manufacturability.