Roof Design
The Given Roof styling, create an ASSEMBLY by developing the essential flanges for the outer roof and creating the reinforcements.
Provide appropriate dimensions and check for Draft analysis.
Do a curvature study on the roof and perform calculations to determine the position of the Bow-roofs.
PROCEDURE:
Designing the roof from the given styling surface with Front and Rear roof rails.
Creating the Bow roof rails and center Bow with reinforcement.
Create a curvature study on the roof and validate the design by applying the Heat distortion criteria and Snow Load criteria.
Performing the section modulus.
Performing the draft analysis.
THEORY:
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.
The roof is a styling surface part which is fixed with the BIW body through the rails and panels inside the upper roof to provide it strength and stiffness.
Ditch area plays an important role here to fix the reinforcement on the component.
The rails and reinforcements are joined to the ditch area with a spot weld where it's not the styling part.
The required tool opening angle is minimum 3 Degrees.
Factors which are considered before creating Ditch area,
Headroom clearance
Visibility criteria
Back door assembly
Windshield assembly
APPROACH TO WORK ON THE PROJECT:
(1). Designing the roof surface usings styling part.
(2). Creating Front Roof Rail.
(3). Creating Rear Roof Rail.
(4). Creating Front Bow Roof Rail 1.
(5). Creating Rear Bow Roof Rail 2.
(6). Creating Reinforcement Roof Rail with Bow Roof Rail 3.
(7). Creating and measuring all required arcs/curves/length for calculations.
(8). Heat Distortion Calculation.
(9). Snow Load Calculation.
(10). Draft Analysis.
DESIGNING THE ROOF SURFACE USING STYLING PART
Creating 5mm of bridge curve to avoid sharp edge on the end corner of the roof stuyling surface.
Law extending the edge with 15 mm and 3 degrees of draft angle.
Law extending the edge with 21.5 mm at 75 degrees.
CREATING FRONT ROOF RAIL :
Offsetting styling surface to 32mm downwards.
Law extends 20mm length and 25 degrees according to the master section provided.
Offsetting flange of roof.
Trim the surface to 80mm.
Offset the upper roof surface by (0.75+0.75+5) and (4.7+0.75+0.75+5) cut it by 5mm and 10mm respectively.
Join the trimmed sheets by studio surface.
Provide 5mm radius face blend on the lower side of the front roof rail and 3 mm radius of face blend on upper sides.
Sketch a pattern, project and trim the front roof rail from material removal
Mirror the front roof rail and sew it to get a complete front roof rail.
CREATING REAR ROOF RAIL :
For the rear roof rail I repeated the same procedure from the above along the master section of rear roof rail.
CREATING FRONT BOW ROOF RAIL 1:
For the front bow rear roof rail 1, I repeated the same procedure from the above along the master section of bow roof rail 1.
CREATING CENTER BOW ROOF RAIL:
For the center bow rear roof rail, I repeated the same procedure from the above along the master section of center roof rail.
CREATING FRONT BOW ROOF RAIL 2:
For the front bow rear roof rail 1, I repeated the same procedure from the above along the master section of bow roof rail 2.
CURVATURE STUDY ON THE ROOF :
After getting the final body it has to be checked and justify that it passes the standards.
The tests we are done on the Roof are which satisfies the standards and the Bow roof positioning and the Final design are
1.Heat distortion
2.Snow load
Heat distortion criteria:
Heat distortion test is to check the strength of the roof. Heat distortion temperature is when the metal softens and deforms under specific loads.
To calculate the heat distortion criteria by the bow roof position formula.
We need to create a sketch, draw a line on the center of the roof on OY axis.
Draw a line from the center line by a 300mm distance.
Draw a line from 100mm distance on both sides of the 300mm line
Draw a line between the center of roof rails and draw the lines from the center line by the distance of 100mm on both sides.
At last, make an intersection on these lines from a coincident line to get points.
From that point draw a three-point arc and measure the Radius of the arc that will be our Rx and Ry values
Bow–Roof 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
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]
Judgment Condition
OK< 2>
|
FORMULA |
W |
0.00173 |
L |
+ |
1.85E-08 |
* |
R |
/ |
T |
+ |
0.0011 |
* |
I |
- |
2.68 |
OK< 2> |
||
|
FR-BOW1 |
W |
0.00173 |
2040 |
|
1.85E-08 |
|
18681630.7 |
|
0.75 |
|
0.0011 |
|
261.6542 |
|
2.68 |
W1 |
1.597833 |
OK |
|
BOW-CR3 |
W |
0.00173 |
2040 |
|
1.85E-08 |
|
30109141.8 |
|
0.75 |
|
0.0011 |
|
533.4116 |
|
2.68 |
W2 |
2.178645 |
OK |
|
CR3-BOW3 |
W |
0.00173 |
2040 |
|
1.85E-08 |
|
12152571.5 |
|
0.75 |
|
0.0011 |
|
521.0398 |
|
2.68 |
W3 |
1.722107 |
OK |
|
BOW-RR |
W |
0.00173 |
2040 |
|
1.85E-08 |
|
9623012.68 |
|
0.75 |
|
0.0011 |
|
175.2327 |
|
2.68 |
W4 |
1.279324 |
OK |
Snow load criteria:
The snow load test was used to verify that roof assembly exhibited no permanent deflection due to distributed load representing snow load.
To calculate the snow load condition, we have a snow load formula.
To measure the required values.
I created a sketch and drew a line on the OY axis from the center of the roof.
From that line draw a parallel line distance of 100mm on both sides.
Then make intersection points of these lines and draw a three-point arc.
Bow–Roof 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.
Where
α = My x Lx2 x 10-12 , My = Y(Ly-Y)
Judgement condition = Qr ≥ 3.1
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 inside view
|
ly |
|||||||
|
bow rail 1 |
44.28069585 |
||||||
|
bow rail 2 |
44.60427485 |
||||||
|
center rail |
45.40854798 |
||||||
|
front bow rail |
136.9293792 |
||||||
|
rear bow rail |
397.5009005 |
||||||
|
LY-Y |
My |
lx2 |
10^-12 |
lx2*10^12 |
ALFA |
||
|
front |
1648.4861 |
654914.0196 |
1303499.441 |
1E-12 |
1.3035E-06 |
0.853680058 |
|
|
bow1 |
800.0755 |
996648.2098 |
1182832.432 |
1E-12 |
1.18283E-06 |
1.178867825 |
|
|
center |
423.1611 |
686624.2053 |
1125380.02 |
1E-12 |
1.12538E-06 |
0.772713162 |
|
|
bow2 |
78.9622 |
155303.3287 |
1087828.974 |
1E-12 |
1.08783E-06 |
0.168943461 |
|
|
rx |
ry |
rx+ry |
rx+ry/2 |
rx+ry/2^2 |
|||
|
bow1 |
4702.03467 |
3627.047 |
8329.08167 |
4164.540835 |
17343400.37 |
||
|
bow2 |
5258.2245 |
6251.3368 |
11509.5613 |
5754.78065 |
33117500.33 |
||
|
bow3 |
2623.8952 |
6334.8925 |
8958.7877 |
4479.39385 |
20064969.26 |
||
|
bow4 |
17300.5406 |
9074.8603 |
26375.4009 |
13187.70045 |
173915443.2 |
||
|
L1 |
L1/2 |
L2 |
L2/2 |
S=(L1/2+L2/2) |
|||
|
CASE 1 |
397.282 |
198.641 |
613.326 |
306.663 |
505.304 |
||
|
CASE 2 |
613.326 |
306.663 |
936.413 |
468.2065 |
774.8695 |
||
|
CASE 3 |
936.413 |
468.2065 |
344.1989 |
172.09945 |
640.30595 |
||
|
CASE 4 |
344.1989 |
172.09945 |
0 |
0 |
172.09945 |
||
|
LY |
2045.7682 |
||||||
|
Y |
LY MOI |
y |
|||||
|
Y1 |
397.2821 |
bow rail 1 |
1645.027851 |
front roof |
61.8 |
||
|
Y2 |
1245.6927 |
bow rail 2 |
1665.523623 |
Rear Roof Rail |
100 |
||
|
Y3 |
1622.6071 |
center rail |
2014.550231 |
Front Bow Roof 1 |
37.15 |
||
|
Y4 |
1966.806 |
front bow rail |
8462.235633 |
Rear Bow Roof 2 |
37.34 |
||
|
rear bow rail |
39750.09005 |
Center |
44.365 |
||||
|
t |
0.75 |
LX |
lx^2 |
||||
|
t2 |
0.5625 |
lx 1 |
1141.709 |
1303499.441 |
|||
|
lx2 |
1087.581 |
1182832.432 |
|||||
|
L |
1950.6953 |
lx3 |
1060.8393 |
1125380.02 |
|||
|
lx4 |
1042.9904 |
1087828.974 |
|||||
|
BOW |
Ly*t2 |
/ |
A |
S |
Rx+RY/2^2 |
A*S*(RX+RY)/2^2 |
* |
10^-8 |
α x s x [(Rx + Ry)/2]2 x 10-8 |
QR<3> |
DETERMINATION |
|
FR-BOW1 |
24.90789142 |
/ |
1.059415373 |
505.304 |
17343400.37 |
9284387462 |
* |
0.00000001 |
92.84387462 |
0.268 |
failed |
|
BOW1-CR |
25.54230824 |
/ |
1.178867825 |
774.8695 |
33117500.33 |
30251800716 |
* |
0.00000001 |
302.5180072 |
0.084 |
failed |
|
CR-BOW2 |
25.0899046 |
/ |
0.772713162 |
640.30595 |
20064969.26 |
9927601735 |
* |
0.00000001 |
99.27601735 |
0.253 |
failed |
It failed in the show load criteria, Due to failed when give a emboss in the outer roof panel.
SECTION MODULUS:
Section modulus formula
S = I/y S = Section Modulus.
I = Moment of Inertia.
y = distance between the neutral axis and the extreme end of the object.
Front Roof Rail
By taking the minimum value from the two values, Unit is converted from meter to millimetre.
MOI = 8.462235633*10^3
Y =61.8
S = (I/Y)
S=136.9293792
Rear Roof Rail
MOI =3.975009005*10^4
Y =59.45
Section Modulus = (MOI/Y)
S=668.6306148
Front Bow Roof 1
MOI =1.645027851*10^3
Y =37.15
Section Modulus = (MOI/Y)
S= 44.28069585
Front Bow Roof 2
MOI = 1.665523623*10^3
Y = 37.34
Section Modulus = (MOI/Y)
S= 44.60427485
Center Bow Roof
MOI = 2.014550231*10^3
Y = 44.365
Section Modulus = (MOI/Y)
S= 45.40854798
DRAFT ANALYSIS:
ROOF
Front Roof Rail
Rear Roof Rail
Front Bow Roof 1
Front Bow Roof 2
Center Bow Roof
FINAL ROOF DESIGN:
CONCLUSION:
Above the Given Roof styling, create an ASSEMBLY by developing the essential flanges for the outer roof and creating the reinforcements.
Provide appropriate dimensions and check for Draft analysis.
Do a curvature study on the roof and perform calculations to determine the position of the Bow-roofs.