Roof challenge
Car roof with Design consideration
Objective:
1. The main objective of this project is to design thr Front roof, Rear roof, Bow roof, Center reinforcement for given styling surface.
2. Perform a curvature study on stylish roof and check the calculation for Heat distortion criteria and Snow Load criteria to check wether the bow roof and center reinforcement are placed in correct position or not.
3. Finding the section of modules for Front roof rail, Bow roof , Center roof and Rear roof rail.
4. Perform the Draft analysis for each roof rail.
Introduction
On the safety point of view vehicle roof plays very crucial role specially roll over kind of accidents, in which vehicle tips over on to its side roof and vehicle rollover crashes are the causes of many fatalities and several head, neck and spine trauma around the world. Therefore passenger safety is also very important parameter in front of OEM's.
The roof of a car made with multiple parts for that provide support and strength to thr roof components. The roof pannel is attached with BIW structure with the healp of Front roof rsil and Rear roof rail. They are manily three roof rails are present as Front roof rail, Rear roof rail, center roof rail in addition to that Bow roof rails are present it mainly depends on the length of roof as one or two bow roof rails as required. The roof most important factors as strength , headroom , overall space visibility criteria.
Design consideration:
1.Head room clearence
2.Visibility criteria
3.Curvature study
4.Head distoration criteria
5.Snow load criteria
6.Material thickness
Stylish Surface roof
Component of Roof rails
Front roof rail
Front roof rails are assembled with the roof in which it provide mounting with whindshield glass, body side outer and inner panels. Front roof is usually made from body side scrap and therefore the thickness of rail is 0.75mm. A draft angle of 3-5 degree is provided keeping in mind with deep drawing operation. The bottommost flange is decided after taking into consideration the visibility criteria and headroom clearence of the passenger. Spot weld are applied at wind shield end of the rail and other end is joined with using Mastic sealent which also constributes to incresed strength. the headroom clearence area also depends on region to region. Draft analysis and section modules is done to check its manufacturing ability.
Draft analysis
Section of modules
Rear roof rail
It is the support which is joined to the backdoor and the body side outer and the inner panels. Similar to the front roof rail here also need to consider the headroom clearence, rear visibility criteria whiel designing the rear roof rail. Here also spot welds are applied at the backdoor of the rail and other side is joined with mastic sealent , embosses is done on the strenth point of view.
Draft analysis
Section of modules
Center roof rail
Center roof rail plays a major role in the roof surface ,similar to the front and rear roof rail consideration of headroom clearence, visiability criteria. But unlike as front roof and rear roof as spot weld is not done because its losse the surface design so here we use mastic sealent . For increasing strength purpose of the rails, embossing is done to reduce the weight of material.
Draft analysis
Section of modules
Bow roof rail 1
Bow roof is a additional roof as the car roof is long than bow roof will be placed, it is additional stiffening member used in roof assembly for localised strength imporvement and it is join directly to roof itself with several spot welding or mastic sealent.
Draft analysis
section of modulus
Bow roof rail 2
Simalar to the Bow roof rail 1 here also it is place in roof assembly to fix it mastic sealent is used.
Draft analysis
Section of modulus
Outer Panel
Heat distoration criteria
The heat distoration criteria plays a important role in sheet metal application, this study is used to predict the heat distoration temperature at where the material start to soften when exposed to a fixed load at elevated temperature. In order to avoid damages on roof based on heat distortion temperature this study will predict the bow roof position on the roof to strengthen the roof.
Bow roof prediction formulae:
W = [1.73*10^(-3)*L] + [1.85*10^(-8)*R^2/t] + [1.10*10^(-3)* 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]
In heat distortion criteria calculation 1section is not considered because it has sunroof it doesnot contain any material so section 1 is negleted.
Snow load criteria
This snow load criteria in more in European region, we calculated the condition in which if the roof is covered with snow, wheater it sutain the snow on roof or not.
Snow load predication formula
Qr = [Iy *t^2] / [Alpha * S *[(Rx+Ry)/2]^2 * 10^(-8)
Where,
Alpha= My * Lx^2 *10^(-12) , My= Y(Ly-Y)
Judgement condition = Qr >3.1
t = Roof plate thickness[mm]
Ly = Distance between the front and rear roof rail on the vehicle along with OY[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]
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/L2 + L2 /2
iy = Geometrical moment of inertia of roof bow (Y cross-section)[mm^4]
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 the roof bow[mm]
Roof panel X Curvature radius of length in side view.
Here similar to Heat distortion crieria 1section is not considered due to material loss , in 4section we can not get a L2 valve ,so negleted that also and 3section is not satisifed for snow load criteria so creating a emboss for strength the roof.
For snow load criteria is not satisified than we inform to stylish team to change to change curvature surface if they were not agreed than we need to create embosses to strength the roof.
Conclusion
1.As per the master sketch created the Front roof rail and rear roof rail with consideration of head room clearence and visibility criteria.
2.Draft analysis and section of modules is done.
3.The result is obtain after doing Curvature study on the roof were Bow roof and center roof rail are palced in correct position or not.
4. Embossment is done to improve the strength of the roof .