Roof Design

AIM:

To create an ASSEMBLY by developing the essential flanges for the outer roof and creating the reinforcements

ROOF:

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.

DESIGN CONSIDERATION IN ROOF:

• Visibility criteria
• Head room clearance
• Bow roof rail and center roof rail position
• Heat distortion and snow load calculation
• Draft analysis

INPUT DATA:

Class A:

Front Roof Rail Master section :

Master section of the Rear Roof Rail :

Master section of Bow Roof :

Master section of Center Reinforcement Rail:

OUTER ROOF:

• The roof and flange is created as per the master section
• The sharp edges are got fillet

FRONT ROOF RAIL:

• The front roof rail is created as per master section
• For strengthening purpose dart and emboss are given the cutout are given for weight reduction purpose
• This front roof rail is used to connect the outer roof and wind shield

REAR ROOF RAIL:

• The rear roof rail is created as per the master section
• For strengthening purpose dart and emboss are given the cutout are given for weight reduction purpose
• This rear roof rail is used to connect the outer roof

CENTRE ROOF RAIL:

• This centre roof rail is created as per the master section given
• Mastic cutouts are made to place the mastic and the centre roof rail and outer roof will be stick together
• The corner of the centre roof rail and the outer roof flage will be spot welded
• This centre roof rail is not exactly in the center of the roof it was offseted to some distance to strengthen the rear side beacause the rear side is flat compare to front side

BOW ROOF RAIL 1:

• This bow roof rail 1 is created as per the master section given
• Mastic cutouts are made to place the mastic and the bow roof rail 1 and outer roof will be stick together
• The corner of the bow roof rail 1 and the outer roof flage will be spot welded
• This is used to add some strength to the roof rear area
• Fillets are used to clear the sharp edges

BOW ROOF RAIL 2:

• This bow roof rail 2 is created as per the master section given
• Mastic cutouts are made to place the mastic and the bow roof rail 2 and outer roof will be stick together
• The corner of the bow roof rail 2 and the outer roof flage will be spot welded
• This is used to add some strength to the roof front area
• Fillets are used to clear the sharp edges

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

• This points are created by offsetting 300mm from the centre of the roof

CALCULATION:

SECTION	L	Rx	Ry	R	t	l	W< 2.7	RESULT
Case 1	2084.4220	5701.9100	2877.6015	3824.885	0.75	462.2586	1.7061	PASS
Case 2	2084.4220	4768.97	7010.4611	5676.450	0.75	431.1277	2.099	PASS
Case 3	2084.4220	3810.88	11443.144	5717.5870	0.75	429.4718	2.108	PASS
Case 4	2084.4220	3205.1477	15081.1865	5286.727	0.75	260.6717	1.8063	PASS

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

• This points are created in the mid of the roof

CALCULATION:

SECTION	Iy	t	Ly	Y	Lx	My	α	L1	L2	s	Rx	Ry	Qr ≥3.1	RESULT
Case 1	1.986509768x103	0.75	2029.0614	570.5371	1132.236	832142.2244	1.0667	570.5371	511.1022	540.819	4388.6290	2815.8812	14.927	PASS
Case 2	2.544123607x103	0.75	2029.0614	1079.3513	1076.4922	1025070.831	1.1878	511.1022	509.893	510.4976	4330.731	12150.054	3.475	PASS
Case 3	1.99588565x103	0.75	2029.0614	1586.5408	1054.3571	702076.986	0.7804	509.8935	397.4434	453.666	4330.7318	12150.0544	4.6699	PASS

DRAFT ANALYSIS:

OUTER ROOF:

• The draft analysis is clearing the top area the rear flange of the roof will be cleared in side core axis

FRONT ROOF RAIL

REAR ROOF RAIL

CENTRE ROOF RAIL

BOW ROOF RAIL 1

BOW ROOF RAIL 2

OVERALL VIEW