Roof Design

Roof Design

INTRODUCTION

The roof of a car or other vehicle is the top part of it, which protects passengers or goods from the weather. The roof also protects the passenger from any injury when the car gets crashed or is rolled over or something heavy falls on the roof.

OBJECTIVE

The mian objective of this project is to understand the design process to design the roof with all the roof rails and to understand the calculations behind it. We also get to learn about the different tools used in NX cad for designing.

METHODOLOGY

We get the model of the roof of the from the styling team. Then we will have to do all the engineering work. We create the ditch area for the roof and also the roof bows and roof rails for the roof which would we designed by us considering all the safety norms and regulations.

DESCRIPTION

DESIGN CONSIDERATION-

1. Visibility criteria

2. Head clearance

3. Curvature study

4. Hear distortion and snow load criteria

5. Draft analysis.

Assembly of roof-

Components in roof assembly

1) Roof outer

2)Front Roof rail

The front roof rail is located on the front of the roof where the wind shield joins with the roof. The visibility criteria and the head room clearance of the passenger are taken into consideration for the bottom flange. One end of the rail is joined using spot welding while the other end is joined with the roof using mastic sealants for increased strength.

3) Bow roof rail 1-

Bow roof is an additional siffening member for the roof to increase the strength and so that it can satisfy the norms. Both the ends are joined together using mastic sealants to increase strenght and also since this would not affect the styling of the roof.

4) Center roof rail -

Centre Roof rail or the reinforcement centre is located at the centre of the roof . The cross section of this is more since it needs to provide more strength to the roof. Here both are ends are joined together using mastic sealants.

5) Bow roof rail 2-

This bow roof also have the same purpose as that of the first one. This one is located between the centre bow roof and rear roof rail.

6) Rear roof rail -

This roof rail joins with the back door and the roof. Inputs from the backdoor are taken into consideration for designing this roof rail.

Here one end is joined using spot welding while the other end is joined using mastic sealants.

Draft Analysis-

CALCULATIONS

Heat Distortion Curvature Study-

This study is used to find out and predict the heat distortion temperature at where the material starts to soften when exposed to a fixed load. So in order to avoid bending or damage of the roof based on this calculation we will decide the position on the roof bows on the roof.

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

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]

Judgment Condition

OK< 2.7

Result

	L	Rx	Ry	R	t	I	W	Status
Front roof Rail	2029.2617	3099.197	2069.6456	2481.886152	0.75	391.2541	1.41294297	OK
Bow Roof 1	2029.2617	4992.7578	6114.9685	5497.174822	0.75	442.2012	2.06244436	OK
Center Roof rail	2029.2617	3351.3892	14124.281	5417.355931	0.75	420.5811	2.017173001	OK
Bow Roof 2	2029.2617	4002.584	10453.572	5788.717281	0.75	304.1651	1.991765796	OK

Snow Load Criteria-

Here we calculate the snow load Prediction, as to create safe design.

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

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 reference point of the front and the rear.

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]

Moment of Inertia -

Bow roof 1

Center roof rail

Bow roof 2

Result -

	Iy	t	My	Y	Ly	Lx	a	L1	L2	s	Rx	Ry	Rx+Ry	Dividing Equation	Dividing Equation	Qr	Status
Case 1	893.46934	0.75	662977.9369	454.7064	1912.7416	1057.9102	0.7419876637	573.3914	494.7064	534.0489	5947.1221	15748.007	21695.1291	502.5765038	466.27507	1.077854117	Not Okay
Case 2	1990.24	0.75	914444.2048	970.5448	1912.7416	1062.9209	1.03313983	494.7064	516.2962	505.5013	11838.089	10924.729	22762.818	1119.51	676.5087881	1.654834379	Not Okay
Case 3	1801.84	0.75	655685.9474	1465.2511	1912.7416	1057.9102	0.7338266587	516.2962	454.2486	485.2724	3760.5845	4149.924	7910.5085	1013.535	55.70932393	18.1932741	Okay

Manufacturing techniques-

The roof itself may be constructed of soft or rigid material. Soft-tops are made of vinyl, canvas or other textile material; hard-top convertibles have roofs made from steel, aluminium, plastic or carbon fibre composites.

It is manufactured with Sheet metal techniques.

Note- In the zip file attached there are three parts which are hidden and not in use so plesae do not consider it in the assembly.