Roof challenge
Roof Design Challenge
Introduction
An automobile roof is the portion of the automobile which sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements. Though it just looks like a styling surface that protects from the various environmental conditions are taken into account for designing of the same.
Roof should be provided with proper reinforcement for strengthening, they can be subjected to high heat conditions or load during heavy snow conditions, to make the roof withstand these conditions various calculations are done, which ensures the safety of the passenger in the vehicle.
Objective
The main objective of this project/ challenge is to design a roof and its reinforcement from the styling surface provided, heat and snow load calculations are to be done with respect to 0Y section of the roof.
Roof Assembly
Design and Calculations
The roof and its reinforcement are designed in NX CAD from the given styling surface. Sheet thickness is considered as 0.75 mm for all components, two bow roofs are provided for strengthening of the roof.
Front Roof Rail
This is the reinforcement provided at the front, this part is joined to the BIW (Body-in-White) and windshield. Visibility criteria are taken into account for joining it with windshield. It is fixed with BIW using spot welding and the roof surface is attached with the help of mastic sealants.
A draft angle is provided for deep drawing operation.
Bow Roof 1
It is an additional reinforcement provided to increase the strength of the roof; it is fixed with roof body with mastic sealants.
Centre Rail Roof
Centre rail roof can be considered as reinforcement joining the left and right part of the roof, it is fixed to the roof by mastic sealants and to BIW by spot welding.
Bow Roof 2
It is similar to the Bow Roof 1 provided for extra/ better strengthening.
Rear Roof Rail
It is provided as reinforcement for the rear side of the roof, Backside and Bodyside panels are attached to this part. It is also attached with mastic sealants and spot welds.
Heat Distortion Study
This study is done to check how the sheet metal components perform in extreme heat conditions; sheet metals have the tendency to change their shape in extreme temperatures. To avoid any failure of sheet metal components this study is done to determine its capacity.
Bow-Roof Prediction Formula
W = [1.73x10^-3 x L] + [1.85x10^-8 x (R^2)/t] + [1.10x10^-3 x l]-2.68
Judgement Condition: OK<2.7mm<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]
Result Table
Snowed Load Criteria
- Qr = [Iyxt2] / [α x s x [(Rx + Ry)/2]2 x 10-8]
Where,
α = My x Lx2 x 10-12, My = Y(Ly-Y)
Judgement condition = Qr ≥ 3.1
250 ≤ s ≤ 380 (S varies depends on the Input)
t = Roof plate thickness [mm]
Ly= Distance between the Front and rear roof Rails on the Vehicle along 0Y [mm]
Length of Roof panel with the center point between Roof rails 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 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
Result Table
Section Inertia Analysis
Bow Roof 1
Center Rail Roof
Bow Roof 2
Conclusion
Design of roof was done and checked for heat load and snow load criteria, the design passed the heat load criteria as well as the snow load criteria.