Roof Design

Roof:- Roof is a component of a vehicle which above the passenger compartment and it's protect passenger from sun rays, rain water, dust and other external particles and cover the whole vehicle from upper side and in the roof there are some distributed parts which get connect to roof for their strength and support to vehicle.

Aim:- In this module need to create roof and their support types and calculate their heat distortion and snow loan with formulas and also need to draft analys each component which we give minimun 7 degree for sheet metal.

Types of car roof:-

1. Naked roof
2. Sun roof 
3. Moon roof 
4. Panoramic roof
5. Convertible roof

(1) Naked roof:- It that roof which don't have any kind glass or acrelic sheet, It's closed from every at the top of car and we can understand how it looks a like from the bottom of picture. And in india most of cheapest car for middle class family and mid range cars are made naked roof.

(2) Sun roof:- In the sunroof cars having glass metal on the roof which slides open and pos up to let light and air flow into the car and we can understand how it looks a like in the below picture.

(3) Moon roof:- In the moon roof it's clear glass which slide on the roof to fully open it and a person can easily see outside throught this moon roof and see how it's looks a like in below picture.

(4) Convertible roof:- In this roof whole roof which get folded and goes to the rear chamber which has been created for that folded roof and it can be both, Manually and electronically.

Design consideration of roof:-

1. Head clearance
2. Visibility criteria
3. Safety criteria
4. Heat distortion
5. Snow load criteria
6. Curvature design

Manufacturing and joining process:-

(1) For manufacturing roof and their reinforcements are made with sheet metals and for that there are different machine to cut the sheet metal like laser machine, puching/blanking machine and for make the hole or create empty space in sheet metal deep drawing also getting used.

(2) For joining process at some criteria used welding/spot welding process is used and for that two sheet metal must be not having gap between each other like below picture and for joing process also used mastic sealent, It is having sealent which used between two sheet metal which must have 5mm game for use this and it's also we can understand below picture.

Roof load and crash test:-

After making of roof design and checking all the design parameter there need to do load test and crash test on the roof, For that need to make car demo which only has chasis and connect it with roof and their all reinforcement and then it got press by big hydraulic press machine from top corner side and after that if it is capable to get this load without any major deformation with certain criteria it's roof design is safe. and see below picture of load test.

• Types of parts which is used in assembly of roof:-

1. Front roof rail
2. Bow roof 1
3. Center roof rail
4. Bow roof 2
5. Rear roof rail

(1) Front roof rail:- In this rail it get attached to outer roof at front with help of welding and mastic sealent and it's also have visibility criteria cause it's getting connect near front wind shield.

(2) Bow roof:- Bow roof is get attached after the front roof rail for give strength to roof and sustain the load which occurs of direct on roof and in our i've made two bow roof and it's depend of roof size that how many bow roof have to attached.

(3) Center roof rail:- Center roof rail is got attached between center of outer roof and it having major role for rainforcementof roof and for their curvature design.

(4) Rear roof rail:- It's used same as front roof rail for sustain roof strength and got attched rear side of car.

• These are join with the outer roof with help of welding process and mastic sealent and these all are having different master sections to create design and below picture shown how it get assembled.

Heat distortion:- When the temperature is affect on body or sheet metal then the sheet metal get disformation and change their shape which cannot see with naked eyes and then it's get affect on joiniing area that's called heat distortion' For that check the ability of roof under the high temperature to increase their strength and for that having some formula and calculation which has below side.

Heat distortion 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,

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]

And it's having judgement condition OK< 2.7

Conclusion:-

Step:-

• For finding these value need to create line distance 300mm from 0y and then create two symetric line distance 100mm.
• Then need to create between line front roof rail to bow roof, bow roof 1 to center roof, center roof to bow roof 2 and bow roof to rear roof and then also create symetric line of that line to 100mm.
• That's how we can get value of Rx and Ry for calculation.
• And calculation there having 4 cases and each case need to calculate the data by upper formula and other formula value details are shown upper side.

Table of calculation:-

Case	Rx	Ry	R	t	L	l	W	Result
1	200.3	201.9790	201.136	0.75	2032.0493	408.0596	1.28	OK
2	200.3976	200.0521	200.225	0.75	2032.0493	419.7295	1.29	OK
3	200.5506	200.1604	200.355	0.75	2032.0493	413.3132	1.29	OK
4	200.7655	200.5633	200.6643	0.75	2032.0493	319.9697	1.18	OK

Judgement condition OK< 2.7

Snow load prediction:- In the foreign country there is having snow fall like water rain india but cause of snow fall on the roof snow got placed after fall and it's having loan for that loan calculation get used 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.

Where,

α = My x Lx² x 10^-12 , My = Y(Ly-Y)

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]

        The width of the roof panel is 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

also it's having judgement condition 

Qr ≥ 3.1

250 ≤ s ≤ 380

Conclusion:-

Step:-

• It's having same step as heat distortion but some different changes where we need to create line on 0y and then create symetric to 100mm
• and for x value need to create between center line to front roof rail to bow roof 1, bow roof 1 to center roof, center rood to bow roof 2 and bow roof 2 to rear roof rail but some difference that we need to create from there center part and also create symetric line to 100mm
• then for Y value for first case 1 distance from front roof center line to bow roof center line then, For second case Y value calculate distance from front roof rail center to center roof rail that's how calculate each case value from front roof rail center.
• And for other calculation we can find from formula which gives at upper side

• For calculation we also need to find moment of inertia which shown as below

Case 1:-

Case 2:-

Case 3:-

Table of calculation:-

Case	Rx	Ry	Iy	t	a	My	Lx	Ly	s	Qr
1	200.0129	202.0553	415.4492	0.75	0.9148	708.923 x 10^3	1135.965	1922.2658	496.8623	1272.149
2	200.0224	200.0603	501.531	0.75	1.0863	922.846 x 10^3	1084.9089	1922.2658	493.9493	1313.978
3	200.0182	200.1399	421.2721	0.75	0.73	653.667 x 10^3	1057.4484	1922.2658	467.79	1733.475

Judgement condition:-

Qr ≥ 3.1

250 ≤ s ≤ 380

Draft analysis:- Here are picture of all parts which got draft analysis with criteria  of 7 degree for sheet metal.

outer roof:-

Front roof rail:-

Bow roof 1:-

center roof rail:-

Bow roof 2:-

Rear roof rail:-

Colnclusion:- This is how roof and their parts ( outer roof, front roof rail, bow roof 1, center roof rail, bow roof 2 and rear roof rail) are designed with heat distortion and snow load prediction calculation has done and also with draft analysis.

Note:- I cannot make STEP file beacuse of NX student version so i have attached STL file.