Roof Design

Roof design:

• AIM: To Design the automotive car Roof using the master section and OEM's design standards.

What is a Roof?

• The roof is one of the components of the automotive vehicle.
• The roof is one of the top surfaces in automotive vehicles.
• It protects the person who sits in the vehicle from weather conditions such as sun rays, dust particles, wind, etc.

Design consideration:

• Visuality criteria
• Head clearance
• Heat Distortion
• Snow load criteria
• The minimum Draft angle should be 7 degrees.

Manufacturing and Joining Method:

• Stamping
• Mastics
• Spot welding

Types of reinforcements required in the roof:

• Front roof rail
• Bow roofs
• Central roof rail and
• Rear roof rail

Why we need reinforcements in the roof:

• Reinforcement in terms of the metal sheet means adding an extra sheet to increase the strength of the component.
• In the case of the roof, as the roof is a flat surface, and if any load is applied to it.
• It will be bent because of that load.
• So, to increase the strength of the Roof we are adding the above reinforcement types in the roof.

1. FRONT ROOF RAILS:

• To design the front roof rails, we will follow the master section. (Refer to the given pic below)

2. REAR ROOF RAIL:

• To design the Rear roof rails, we will follow the master section. (Refer to the given pic below)

3. BOW ROOF RAIL-1:

• To design the bow roof rails-1, we will follow the master section. (Refer to the given pic below)

4. CENTER ROOF RAIL:

• To design the center roof rails, we will follow the master section. (Refer to the given pic below)

5. BOW ROOF RAIL-2:

• To design the bow roof rails-2, we will follow the master section. (Refer to the given pic below)

• 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

Sr No.	Region	Rx	Ry	Rx*Ry	Rx+Ry	R	I	t	L	W	Condition	Result
1	Front roof rail to Bow roof 1	5717.1789	2814.3823	16090327.1	8531.5612	3771.953743	469.2337	0.75	2028.3134	1.696088	W<2.7	OK
2	Bow roof 1 to center roof rail	4935.5294	6341.0737	31296555.7	11276.6031	5550.706254	350.308	0.75	2028.3134	1.974309	W<2.7	OK
3	Cernter roof rail to bow roof rail 2	1344.3078	10537.3449	14165434.9	11881.6527	2384.421645	454.3255	0.75	2028.3134	1.468982	W<2.7	OK
4	Bow roof rail to back roof rail	1443.8521	14416.0215	20814602.9	15859.8736	2624.813216	359.2627	0.75	2028.3134	1.394116	W<2.7	OK

• SNOW LOAD CRITERIA:

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

Sr No.	Region	Iy	L1	L2	Ly	Lx	Rx	Ry	t	Y	S	My	α	Qr	Condition	Result
1	Front roof rail to Bow roof 1	8189.552	549.6949	415.7444	2028.3134	1130.5501	4371.6599	2350.9109	0.75	549.6949	482.7197	812789.0485	1.038861	81.30541	Qr≥3.1	OK
2	Bow roof 1 to center roof rail	8828.055	415.7444	519.7791	2028.3134	1084.408	5258.7402	4258.5441	0.75	963.0095	467.7618	1025897.776	1.206395	38.8604	Qr≥3.1	OK
3	Cernter roof rail to bow roof rail 2	1457.969	519.7791	478.4321	2028.3134	1057.3232	3234.9773	11028.1563	0.75	1479.438	499.1056	812027.031	0.907791	3.558955	Qr≥3.1	OK
4	Bow roof rail to back roof rail	9218.133	478.4321		2028.3134	1043.3406	5815.0045	16154.5299	0.75	1949.528	239.2161	153594.5304	0.167197	107.4399	Qr≥3.1	OK

• SECTIONAL INERTIA ANALYSIS:

1. BOW-ROOF RAILS-1:

2. CENTER ROOF RAILS:

3. BOW ROOF RAILS-2:

• DRAFT ANALYSIS OF ROOF AND ITS RESULT:

1. Front roof rail

2. Bow roof rail 1

3. Bow roof rail 2

4. Centre Roof rail

5. Back roof rail

6.Roof Outer Panel