Roof challenge
AIM :
To create the roof with essential reinforcement and flanges.
INTRODUCTION :
- An automobile roof is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupant from the external elements. Roof should be provided with proper reinforcements. Vehicle roof can be subjected to high heat conditions or load during snowy conditions. To make the roof to withstand these conditions various calculations are done. The roof also ensures the safety of the passengers in the vehicle.
- The roof is an assembly have many parts like front roof rail, bow roof, bow roof center and reinforcement center. The number of bow roofs is based on the length of the car and when in small cars the bow roof center is avoided. The roof is attached to the body of the car using mastic sealants provided between bow roofs and the front and rear rails. Roof is connected to A-pillar, B-pillar and C-pillar to cover the front and rear door. Roof is supported by reinforcement bow-roof with front and back roof rail.
Types of roof reinforcements are :
- Front roof rail reinforcement (FR)
- Center roof rail reinforcement (CR)
- Bow roof 1 rail reinforcement (BR1)
- Bow roof 2 rail reinforcement (BR2)
- Rear rail enforcement (RR)
DITCH AREA :
- It is the extended portion of the main roof concealed by other BIW panels and not a styling surface. Headroom clearance, visibility criteria, clearance for windshield and back door are some of the factors to be considered while designing the ditch area.
FRONT ROOF RAIL :
- It is the support that is joined with the windshield glass, bodyside outer and inner panels. It is usually made from from body side outer scarp and therefore the thickness of the rail is 0.65m . A draft angle of 3 - 5 degrees is provided for deep drwaing operation. The visibility criteria and the headroom clearance of the passenger are taken into consideration for the bottom most flange. windshield end and the roof end are spot welded and the other end of the front roof rail is joined with the roof using mastic sealants for increased strength.
REAR ROOF RAIL :
- It is the support that is joined to the backdoor, the bodyside outer and the inner panels. Inputs from the backdoor design is also taken to accommodate the required clearance along with headroom clearance and the rear visibility criteria while designing the rear roof rail. spot welds are applied at the backdoor end of the rail and the other end is joined with the roof using mastic sealants.
CENTER ROOF RAIL AND BOW ROOFS :
- Unlike the front and rear roof rails spot welds are not applied for joining these rails of the roof. Mastic sealants are introduced at both the ends instead of spot welds since center roof rail and row roofs are fully positioned under the styling surface of the roof.
BOW ROOF 1 :
BOW ROOF 2 :
DRAFT ANALYSIS :
The roof body must have positive draft angle, so that manufacturing feasibility is achieved. The draft analysis is successful in obtaining positive draft angle.
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]
From the above W values,
The judgement condition is met which is less than for the bow roof distance prediction.
SNOW PREDICTION FORMULA :
Qr = [Iy x t ] / [α x s x [(Rx + Ry)/2] x 10 ]
Where,
α = My x Lx x 10 , 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 crosssection )[mm4]
Rx = Lateral direction curvature radius of roof panel Y crosssection 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]
From the above criteria,
The snow load criteria is passed. The value of Qr is greater than 3.1
SECTION MODULUS ON THE O-Y SECTION FOR ALL THE ROOF RAILS :
FRONT ROOF SECTION :
BOW ROOF SECTION 1 :
BOW ROOF SECTION 2 :
CENTER ROOF SECTION :
REAR ROOF SECTION :
ROOF IMAGES :
CONCLUSION :
Thus the essential flanges and reinforcements are created . The roof was created with all the required parameters with a certain rails and calculation the heat distortion, snow load are done and performed draft analysis for safety concerns.