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.

DESIGN CONSIDERATION-

1. Visibility criteria

2. Head clearance

3. Curvature study

4. Hear distortion and snow load criteria

5. Draft analysis.

Components of roof-

1.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.

2.Bow roof 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.

3.Centre 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.

4.Bow roof 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.

5.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.

CALCULATION

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

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:-

Bow position	Rx	Ry	R	i	L	T	W	ok/ng
FR and 1st- bow	14322	3306	5372	347.91	2039	0.75	1.22	ok
1st and CTR	10441	3938	5719	449.98	2039	0.75	1.32	ok
CTR and 2nd- bow	6144	4824	5470	430.19	2039	0.75	1.34	ok
2nd and RR	2997	5869	3967	334.91	2039	0.75	1.23	ok

Draft analysis-

Before we give the part for manufacturing we have to some analysis ourself to check all the constraints and to check if we have any negative draft on a part .

We have a tool called draft analysis in NX Cad to check the following.

OUTER PANNEL-

Front roof rail-

Bow roof 1-

Centre roof rail-

Bow roof 2-

Rear roof rail-

We gave a limit angle of 3 degree.

When the colour is green it means it has a positive draft it means area which are more than 3 degree is shown as green. If it is shwn in yellow that means it has less then 3 degrees and if in blue or red then it means it has negative draft.

CONCLUSION

We were successfully able to design the roof with all the roof rails for better support and strength. We designed it so as to satisfy the norms and regulations by calculating the heat distortion criteria and the snow load critera. While doing this we also understood about the methodology behind designing the roof of the car and what all we take into consideration while designing so.