Roof challenge
TITLE OF THE PROJECT: DESIGN OF FRONT ROOF, BOW ROOF, CENTER ROOF AND REAR ROOF.
OBJECTIVE: To design the Front Roof rail, Bow Roof rail, Center Roof rail and Rear Roof rail as per the master sketch and to pass the Bow-Roof prediction and Snow load prediction conditions. Perform the draft analysis to produce the positive draft for manufacturing feasibility.
Software used: Siemens NX.
Automotive roof: An automotive 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.
The Roof is enclosed with different roof rails as reinforcement for the top roof body namely, Front roof, Bow roof, Center roof and Rear roof.
Flanges and Reinforcement of Roof Design:
The extreme left end roof which is in Cyan color is the Front Roof followed by 1st bow roof, center roof, 2nd bow roof and Rear roof:
DRAFT ANALYSIS: The roof body must have positive draft angle, so that manufacturing feasibility is achieved. From the Below picture, the draft analysis is successful in obtaining positive draft angle. The color green on the roof part indicates Positive draft over the positive draft limit angle:
SECTION MODULUS ON THE O-Y SECTION FOR ALL THE ROOF RAILS:
FRONT ROOF SECTION:
BOW ROOF 1 SECTION:
BOW ROOF 2 SECTION:
CENTER ROOF SECTION:
REAR ROOF SECTION:
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 2.7 FOR THE BOW-ROOF DISTANCE PREDICTION.
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]
FROM THE ABOVE REPORT, THE SNOW LOAD CRITERIA IS PASSED. THE VALUE OF Qr IS GREATER THAN 3.1.
Please find below shareable google drive link of Roof Rails Design Part file:
https://drive.google.com/file/d/1UhtM1yCMwX9mC0wqH_RDYBpwftMN3aFe/view?usp=sharing
CONCLUSION: DESIGN OF ROOF AND BOW ROOF RAILS IS FEASIBLE FOR MANUFACTURING AS PER THE CRITERIA SHOWN IN THE ABOVE ANALYSIS REPORTS.