Roof Design

ROOD 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. Design of any product starts from an requirement . The design engineer sketches the product based on the the requirement . Then the 2D sketch with the proper dimensions is converted into the 3D model using the advanced CAD software's . The another important thing in the design is that , every product that is designed should be able to manufactured . so the role of the design engineer is to design the product that can be easily manufactured and with less cost effective . This is the place where the Design for manufacturing [DFM] and Design of assembly [DFA] takes a role while developing any product . The process of development of design carries on until the design satisfies the customer needs .Here in this project the product that we are going to develop is a car roof.

OBJECTIVE

• The objective of this project is to design car roof with essential flanges and reinforcements like ditch area , front roof rail , bow roofs, central roof rail and rear roof rail for the the given styling surface
  
• Perform a curvature study on the roof and perform the calculations for the heat distortion and snow load criteria to determine whether the bow roofs are at the correct positions.
  
• Finding moment of inertia and section modulus for Bow roofs , central roof rail . front roof rail and rear roof rail .
  
• Perform the draft analysis for each reinforcements.

CAR ROOF 

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. Roof is the structure above the wind shield glass having the reinforcements to provide the strength to the overall structure and to with stand the over head forces like snow.

REINFORCEMENT 

If the roof is flat it is very weak and cannot able to with stand the forces like snow , so in order to increase the strength of the roof these reinforcements like front roof rail, central roof rail, rear roof rail and the bow roofs are introduced and joined to the flat surface of the roof with the different joining process.

DIFFERENT TYPES OF REINFORECEMNT OF HAT CAR HAS ARE:

1. FRONT RAIL ROOF 

2.BOW ROOF 1&2 

3.CENTER RAIL ROOF 

4.RARE RAIL ROOF  and 

5.CENTER RAIL ROOF WITH SUN ROOF.

1. FRONT RAIL ROOF 

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 & 2

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.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.

3.CENTER RAIL ROOF 

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. RARE RAIL ROOF 

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.

5. CENTER RAIL ROOF WITH SUN LIGHT:

We then also make the ditch area around the roof.

Ditch area the extended portion of the main roof concealed by other BIW panels.

                                                                 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

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]

Result:

Bow position	Rx	Ry	R	l	L	t	R2/2	W	OK/NG
FR and 1st	5626.39	3067.66	3970.5	448.56	2033.7	1.5	21019825.94	1.53	OK
1st and CTR	4854.3	6624.76	5602.99	365.81	2033.7	1.5	41858066.77	1.63	OK
CTR and 2nd	4065.16	10593.91	5875.67	463.2	2033.7	1.5	46031333.73	1.77	OK
2nd and RR	3424.34	14478.23	5538.68	352.33	2033.7	1.5	40902692.46	1.6	OK

Snow Load Criteria-

We predict the snow load in this of the roof bows and then place and change the design of the load accordingly to satisfy the condition.

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

Judgment condition

Qr ≥ 3.1

250 ≤ s ≤ 380

Here are some Reference images for the Master sections - These images are just to give you a brief idea about the design.

Result-

Bow position	Iy	α	Lx	Ly	Y	S	Rx	Ry	t	Qr	Determination
FR and 1st	161.19	1.05	1119.69	2033.7	569.65	447.74	4105.6	15113.26	1.5	0.84	NG
1st and CTR	267.05	1.21	1081.72	2033.7	979.65	464.47	3794.03	10543.14	1.5	2.09	NG
CTR and 2nd	161.3	0.91	1059.39	2033.7	1488.08	447.71	4231.18	6602.02	1.5	3.03	NG

SECTION ANALYSYS:

 MOMENT OF INERTIA :

front rail roof:

Bow roof :

Center roof rail:

Rare rail roof :

DRAFT ANALYSYS:

BOW ROOF:

                                                                                                      

CENTER ROOF :

FRONT ROOF :

                                               

RARE ROOF :

                                                

ROOF:

                              

ROOF IMAGES :

TOP VIEW:

 SIDE VIEE:

ISOMETRIC VIEW:

CONCLUSION:

Hence the roof , front rail roof ,bow roof 1&2 , center rail roof, center rail roof with sun roof and rare roof rail is designed by the following master section ,moment of inertia and draft analysys. are carried to chechk the fesiability manufacture.