Roof challenge
Roof Design
Automobile roof: -
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.
Roof Assembly Contain Four Reinforcement That are Front rail, 1st Bow Rial, Centre Reinforcement, 2nd Bow rail, Rear rail
After Designing All those parts, we have to Check Wither position of bow roof, Front And rear roof Rail is correct or not by calculating heat distortion and for some specific region need to check snow load condition.
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
Were
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]
Calculattions: -
|
Sr no |
BOWs |
Rx |
Ry |
R |
l |
L |
t |
W |
OK/NG |
|
1 |
Front&1st Bow |
5558.7992 |
1857.8612 |
2784.9400 |
399.1529 |
2033.70 |
0.75 |
1.46 |
Ok |
|
2 |
1st Bow &Centre |
4814.9455 |
5327.0295 |
5058.0595 |
463.6104 |
2033.70 |
0.75 |
1.97 |
Ok |
|
3 |
Center&2nd Bow |
3834.8292 |
10035.3934 |
5549.1567 |
463.6735 |
2033.70 |
0.75 |
2.10 |
Ok |
|
4 |
2nd Bow& rear |
3094.2280 |
15747.8926 |
5172.1959 |
367.2894 |
2033.70 |
0.75 |
1.90 |
Ok |
All the value of ‘W’ is Less than 2.7 So it is Conform that our positions are right
Let’s Find Snow Load Predication
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.
Were
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 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 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
Calculattions: -
|
Sr.no |
Bows |
α |
Lx |
Ly |
Y |
s |
Rx |
Ry |
t |
Qr |
Determination (Qr) |
|
1 |
Front&1st Bow |
0.900463 |
1109.3052 |
2030.5814 |
468.4250 |
508.4606 |
2978.5644 |
1522.27641 |
0.75 |
49.25 |
Ok |
|
2 |
1st Bow &Centre |
1.0433 |
1086.6853 |
2030.5814 |
508.4250 |
508.4250 |
3106.5744 |
4263.8241 |
0.75 |
15.63 |
Ok |
|
3 |
Center&2nd Bow |
0.8671 |
1058.5262 |
2030.5814 |
508.4250 |
508.4250 |
8727.8388 |
4211.7039 |
0.75 |
6.189 |
Ok |
|
4 |
2nd Bow& rear |
0.8422 |
1043.2489 |
2030.5814 |
508.4250 |
508.4250 |
3413.7339 |
14145.2053 |
0.75 |
3.46 |
Ok |
Draft Analysis: -
To Check Deep Drawing Angle, We Run Draft Analysis. We set angle at 50 and start the analysis
If the colour of part is become Green then our Draft is positive
If the colour of part is become yellow, Blue, Red the it is negative draft but sometime at critical condition yellow colour is also positive draft as
Front Rail Draft analysis -
1st Bow Rail Analysis-
Centre Reinforcement Rail Draft:-
2nd Bow rail draft :-
Rear Rail Draft: -
Outer Panel Draft: -
Section Modulus study with outer panel: -
At front rail with outer panel of hood: -
At 1st Bow rail with outer panel of hood: -
At Centre reinforcement rail with outer panel of hood: -
At 2st Bow rail with outer panel of hood: -
At rear rail with outer panel of hood: -
Designed Roof
Conclusion: -
Before sending part for simulation, we have to Calculate Heat distortion criteria and Snow load calculation to Check our correct position is ok/not and our positions are correct
With Draft analysis we got to know that our deep drawing angle is Correct