Roof Design
OBJECTIVE:
Design a roof using the provided skin data and also position the bow roof rails in accordance with heat distortion and snow weight formula also to find the section modulus of the roof and roof rail and check the draft of the designed parts.
GIVEN STYLING SURFACE
ROOF:
An automobile roof or or car top is the portion of an automobile that located above the passengers compartment for protecting the vehicle occupants from the sun light, wind, rain, snow and other external elements.
To design a roof we need to provide bow roof rails, center reinforcement rail for strengthen the roof. This should also protect the car and passengers when the car is crashed or rolled over.
The reinforcements designed for this roof are-
1) Front roof rail
2) Bow roof rail 1
3) Center roof rail
4) Bow roof rail 2
5) Rear roof rail
OBJECTIVE
For the given roof styling, developing the essential flanges and reinforcements. Then providing the appreciate dimensions and check for draft analysis, and finding the section inertia report on the 0-y section.
perform the calculation of heat distortion and snow load conditions.
DESIGN PARAMETERS
For designing roof we have to create multiple number of roof rail for increasing the strength of the roof. Bow roofs are primarily fixed in flatter region to enhance the strength. front roof and rear roof rails are fixed to the ditch area using spot welding operation. The bow roofs and center reinforcement roof rails are fixed to the roof using mastics sealants.
Following criterias are taken into account for roof rail design.
- Visibility criteria'
- Head clearance
- Curvature study
- Heat distortion and Snow load criteria
- Draft analysis
MASTER SECTION
These are the cross sectional data for 3D model. These master sections are widely used in OEMs and in automotive industry to convey the functional requirement of product to the design engineer. It gives the parameters like length, width, height, angle etc.. should be considered while designing a particular or the component.
FRONT ROOF RAIL
The front roof rail is used as the reinforcement to the roof surface to increase the strength and also used to mount the brackets for some features such as room lamp and rear view mirror. the width of the front roof rail is decided based on the visibility criteria. The depth of the front roof rail is decided in such a way that there should be enough head room clearance between the head of the driver and the end surface of the roof rail to avoid the claustrophobic effect to the person.
CENTER ROOF RAIL
Center roof rail imparts strength for the center portion of outer roof panel which is supported by B pillar at both ends.
BOW ROOF RAILS
These are used between center roof rail and front roof rail & rear roof rail to impart additional support. The number of bow roof rail depends on the length of the roof panel.
REAR ROOF RAIL
It is the reinforcement provided at rear side of the roof panel. back door and body side panels are attached with this part provision for back door opening is also provided on rear roof rail.
DRAFT ANALYSIS
1) Draft analysis of front roof rail
2) Draft analysis of center roof rail
3) Draft analysis of Bow roof rails
4) Draft analysis of rear roof rail
Final Assembly
Heat load calculation
The heat distortion study plays an important role in Sheet metal application. Heat distortion is temperature limit above which material cannot be used for structural application. this study is useful to find where the material start to soften when exposed to a fixed load at elevated temperature. In order to avoid bending, damage of the roof based on the heat distortion temperature. This study will helps to locate the position of the bow roof rails to give enough strength.
Bow roof prediction formula
W=[1.73*10^(-3)*L]+[1.85*10^(-8)*(R^2)/t]+[1.10*10^(-3)*I]-2.68
where,
L= Roof length in X direction [mm](Roof dimension in 0-Y)
Roof curvature
R= Roof curvature
= 2(Rx*Ry)/(Rx+Ry)
Rx= X curvature
Ry= Y curvature
t= Roof plate thickness [mm]
I= Bow roof span [mm]
Judgement condition= w<2.7
Snow load calculation
Snow load criteria study is used to check the durability of the roof to withstand the snow fall on the roof and reflex it in original shape without any permanent deformation after load being removed.
Qr= (Iy*t2)/(α*S*((Rx+Ry)/2)2*10^-8)
Where
α= My*Lx2*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 the roof panel with center point between roof rail front / Rear as the reference point of the front and rear.
Lx= Distance between the left and right end of the roof on the bow roof [mm]
width of the roof panel exposed on the surface.
Y= Distance between the front roof rail to bow roof [mm]
S= Distance for which roof bow bears divided load [mm]
= L1/2+L2/2
Iy= geometric moment of inertia of bow roof (Y cross section)(mm4)
Rx= Lateral direction curvature radius of the roof panel Y cross section on bow roof [mm]
Roof panel curvature radius of the length Lx in front view.
Ry= Longitudinal direction curvature radius of roof panel X cross section on roof bow [mm]
CALCULATION
CONCLUSION
Design of roof was successfully completed using Siemen NX as per the given master sections. The position of bow roof are as per the given standards . Draft analysis and section analysis ensure the manufacturability of every components.