Roof challenge
Car Roof Design
Objective: Devlope and design the given car roof with proper reinforcement by following the master section to creat the roof ditch area, Front roof rail, Rear roof rail and Bow-roofs.
Introduction: A automobile roof is very essential component of a vehicle. It protects the passengers and the driver from sun, rain and many other elements.
Apart from the roof work of outside it has so many things inside to increase the strength and stabilty to keep people protected. It has also a lamp for lighting inside the car.
Some cars are also has open roof system,In those passengers use roof whenever they want or not.
Procedure:
First we have to devlope and design the roof with given master section and creat the ditch area. After that we need to design Front and rear roof rail and bow roofs. After that we need to assemble those with the roof.
After completing assembly we need to do inspection and test the strength, heat distortion and snow load capacity of that aseembly.
Ditch Area:
Ditch area is the extended part of the roof to which Roof rails and bow roofs are concealed using spot welds. For designing the part there are some factors we consider and those are Headroom clearence, Driver visibilty criteria, wind sheild clearence and Back door. The thickness we give is 0.75mm.
Front Roof Rail:
Front roof rail is joined with the wind sheild glass, Body side outer panel and inner panel. While designing a 3-5 degree draft angle we provide as per the visibility criteria and head room clearence of the driver.The wind sheild end is joined with the rail by using spot weld and the other end of the rail is joinf with roof using mastic seals as they give proper strenth to it.
Rear Roof Rail:
This is also joined with exactly considering the same criterias we followed in front roof rail. This is also joined with the back door, body outer panel and inner pannel. Head room cleareance and back side visibility everything should be considered. Here also one end of rail is spot welded with back door and other end is sealed using mastics with the inner panel.
Center Bow Roof:
This bow roof is also designed as considering the head room clearence and strengthing the roof. This roof is joined with the inner panel using mastic points. As this is the center part so we are adding extra reinforcement to increase the strenght. We add an extra layer of bow roof on it. It's inertia value is 4895mm4.
Bow Roofs:
Bow roofs are also we put for increasing the strenght of the car roof. For reducing weight and we did some styling and emoboses also. Two of them were used and each are diffenerntly designed as per the postion we are going to fix with inner panel of the roof.
Front Bow roof has an inertia value 6275mm4.
Rear side bow roof has an inertia value 3551mm4.
Complete Assembly:
Analysis:
After the assembly we do a curvature on the roof to justify the position of bow roofs. For that we normally test 3 criteria.
1. Roof Crush Test
2. Heat Distortion
3. Snow Load
1.Roof Crush test:- This test is done after manufacturing the roof with complete assembly.
2.Heat Distortion:- This test is done to know at which tempreture the material deforms under specific load. This test results shows the withstand capability of the roof and the bow roofs which was assembled.
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
where as,
L= Roof length in 0Y direction
R= Roof curvature =2(Rx * Ry)/Rx + Ry
Rx= X curvature
Ry= Y curvature
t = Roof plate thickness [mm]
l = Bow Roof Span [mm]
These are all things we need for calculation, we need to measure all those from our assembled design. The answer is must meet the condition : OK< 2.7> 3.1.
Here above all the condition is below 2.7. So this is a OK condition.
3. Snow Load:- This test is done to know the withstand capability of the roof in assembled condition while snowfall. When the snow was there for long time the roof goes slightly down and after removal of that load, wheather it's coming back to its original shape without having any permanent deformation or not.
Snow load Prediction formula:
Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]
α = My x Lx2 x 10-12 , My = Y(Ly-Y)
Where as,
Iy= Moment of inertia of bow roofs in mm4.
t= Roof thickness
Lx=Distance between the Left and Right end of the roof on the Roof BOW [mm]
Ly=Distance between the front and rear roof Rails on the Vehicle along with 0Y[mm]
s=Distance for which Roof BOW bears divided load [mm] (s = L1/2 + L2/2)
Rx=curvature radius of roof panel Y cross-section on Roof BOW [mm]
Ry=curvature radius of roof panel X cross-section on Roof BOW [mm]
The answer must meet the condition Qr ≥ 3.1.
Conclusion:
This design of roof is meeting all the conditions succesfully. So this roof design can be acceptable.