Roof challenge
ROOF CHALLANGE
Aim:
To a given roof styling create essential flanges and reinfrocements.
Introduction:
An automobile 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. To a given roof styling, create essential flanges and reinforcements.
Obejective:
To develop the essential flanges and reinforcements with appropriate dimensions and checking draft by using draft analysis. calculating the heat distortion, snow load and section inertia on roof.
Procedure:
A dumb solid body of roof CAD model is provided for which following points to be desinged and analyzed are as follow,
* Extracting the styling surface and for the given car roof styling and desing the essential flanges and reinfrocement, namely Ditch Area, Front Roof Rail, Rear Roof Rail, Centre Roof Rail, and Bow-Roofs.
* Do a Curvature study on the roof and perfrom calculations for Heat Distortion and snow load criterion to determine and justify the position of the Bow-Roof.
* Finding a moment of interia and section Modulus for Bow Roof Rails and Centre Roof Rail.
* Perfrom a Draft Analysis of each reinfrocement.
The Automobile roof consists of the following parts.
* The Outer Panel
* Front roof Rail
* Bow Roof
* Centre Roof Rail
* Rear Roof Rail
Front Roof:
The front roof rail is created at the front side of the roof to provide strength to the roof.
Headroom clearance and the driver visibility are the two important factors to be considered While desing the front roof rail. the front roof rail is connected to the roof outer panel with the help of mastic seal.
Bow Roof:
It is used to give strength to the area between the front roof and the centre roof rail. Also it is created in the area roof rail to provide enough strength.
It can be created in any numbers depending upon the roof length but position of the bow roofs is to be justified by curvature study.
Centre Roof Rail:
It is created at the centre of the roof. it is connected to the roof by mastic seal.
Rear Roof Rail:
It is Created at the rear end of the roof. The fitment of the backdoor is to be considered while desing the rear roof rail.
Roof Images:
Heat Distortion Criteria:
Heat distortion temperature is which metal softens and deforms Under a specified load. While desing roof, this Criteria is taken into consideration. We create bow roofs When the roof is long and flat to increase its strength. The position of the bow roofs is to be justified and this justification is done by curvature study.
Bow-Roof Prediction Formula
W=(1.73x10^(-3)xL)+(1.85x10^(-8)x(R^2)/t)+(1.10x10^(-3)xl)-2.68
Judgement Condition : OK<2.7>3.1
Rx=Roof Length in X-Direction(mm)(Roof dimension in 0-Y)
Rx=Xcurvature
Ry=Ycurvature
t=Roof Plate thickness (mm)
l=Bow Roof Span (mm)
To Measure L:
To Measure Rx:
To Measure Ry:
To Measure l ( Bow Roof Span ):
Here we can see that the roof is completely satisfying the conditions of heat distraction.
Snow load Prediction Formula:
snow load is the downward force on a car's roof by the weight of accumulated snow and ice. The roof can fail if the snow load exeeds the weight the roof was desinged to shoulder. or if the roof was poorfly desinged or constructed.
So there is a formula to predict the strength of the roof.
Qr=(lyxt^2)/(axsx((Rx+Ry)/2)^2x10^8)
Note: The Qr value given over here is correct. there was a typo error in the formula given in the vedio.
Where
a=MyxLx^2x10^-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 OY(mm)
Length of Roof Panel with the 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 thebroof 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 beara divided load(mm)
S=L1/2+L2/2
Iy=Geometrical moment of interia of Roof Bow (Y cross-section)(mm4)
Rx=Laterial direction curvature radius of panel Y cross-section on Roof Bow (mm)
Roof panel curvature Radius of the length Lxin Front view
Ry=Longitudinal Direction curvature radius of the Roof panel X cross-section on Roof Bow(mm)
To Measure Ly:
To Measure Lx:
To Measure Ry:
To Measure Rx:
To Measure s:
To Measure y:
After calculating all these valvue the Qr is found out.
it is observed that the roof is satisfying the condition. so in order to strengthen the roof at these areas embosses are created on the outer roof.
Section modulus study of the selection of the roof rails:
The selection modulus of the cross-selectional shape is of siginificant. it is a direct measure of the strength of the structure.
A structure that has a larger section modulus than another will be stronger and capable of suporting greater loads.
SECTION MODULUS (S)=I/y
WHERE,
I=MOMENT OF INTERIA IN (MM^4)
Y=DISTANCE BETWEEN THE NEUTRAL AXIS AND THE EXTREME END OF THE OBJECT (MM).
FRONT ROOF RAIL:
SECTION INERTIA ANALYSIS:
I=10871.9mm^4
y=114.28mm/2=57.14mm
S=I/y=190.27mm^3
BOW ROOF 1
I=154.8MM^4
Y=74.97MM/2=37.49mm
S=I/y=4.13mm^3
CENTRE ROOF RAIL:
I=9154.3MM^4
Y=89.99MM/2=44.99MM
S=I/y=203.45MM^3
BOW ROOF 2
I=160.89MM^4
Y=75.84MM/2=37.92MM
S=I/Y=4.24MM^3
REAR ROOF RAIL:
I=3513.54MM^4
Y=91.73MM/2=45.86MM
S=I/Y=76.61MM^3
DRAFT ANALYSIS:
In NX to check wether the sheet metal part we have desinged can be deep drawn, there is an option called draft analysis. this type
Of analysis is performed based on color ranges identifying zones on the analyzed element where the deviation from the draft direction at any point, corresponds to specified values.
ROOF MODEL VIEWS:
CONCLUSION:
The Desing of Roof, Front roof rail, Rear Roof Rail, Bow Roofs and reinforcement roof center by following the Master section with the desing parameter for the given class A surface is done.
The roof was created with all required parameters with all a certain rails, and calculation the heat distortion, snow load are done and performed Draft analysis safety concerns. The results is satisactory.