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 :

•  Main objective of the project is to create the Roof Sheetmetal design in NX cad, and also designing Front roof rail, rear roof rail, bow   roof front, bow roof rear, center roof rail and Reinforcement are creating to build the strong roof.
  
  
• Do curvature study on Roof and performance calculations for Heat distortion and Snow load criteria to determine the position of the Bow roofs.
  
  
• Finding the moment of inertia and section modulus for Bow-roofs and center roof rail.
  
  
• And, also finding the Draft Analysis of each part.

SOFTWARE USED :

CATIA V5

INTRODUCTION :

An automobile roof is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements.

Under the styling surface that is seen on the outside, there are many other structures under the roof which contribute to its strength and stability. The number of such structures/supports differ with respect to the size of the vehicle. They are primarily installed on flatter areas of the roof to enhance the strength. These are the Front Roof Rail, Rear Roof Rail, Centre Roof Rail and Bow Roofs and they are joined to the roof by the Ditch Area.

Reinforcements and Design

Ditch Area

The Ditch Area is the extended portion of the main Roof concealed by other BiW panels. The rail supports of the roof are attached to the Ditch Area using Spot welds, since it is not a styling surface and remains concealed. Headroom Clearance, visibility criteria, clearance for Wind shield and Back door are some of the factors to be considered while designing the Ditch Area. It is given a thickness of 0.7 mm.

Front Roof Rail :

It is the support which is joined with the Wind Shield Glass, Body Side Outer and the inner panels. It is usually made from Body Side Outer scrap and therefore the thickness of the rail is 0.65 mm. A draft angle of 3-5 degrees is provided keeping in mind the deep drawing operation. The Wind Shield end flange is the exact offset of the roof surface. The bottommost flange is decided after taking into consideration the visibility criteria and the Headroom Clearance of the passenger. Spot Welds are applied at Wind Shield end of the rail and the other end is joined with the roof using Mastic Sealants which also contributes to increased strength.

Rear Roof Rail :

It is the support which is joined to the Back Door and the Body Side Outer and the inner panels. It is also usually made from Body Side Outer scrap and therefore the thickness of the rail is 0.65 mm. Similar to the Front Roof Rail design, we have to take into consideration the rear Headroom Clearance and the rear visibility criteria while designing the Rear Roof Rail. Inputs from the backdoor design is also taken to accommodate the required clearance. Spot Welds are applied at the Back doorend of the rail and the other end is joined with the roof using Mastic Sealants.

Centre Roof Rail and Bow Roofs :

Similar to other Rails design, we have to take into consideration the Headroom Clearance and the visibility criteria while designing the Centre Roof Rail and Bow Roofs.  But unlike the Front and Rear Roof Rails, Spot Welds are not applied for joining these rails to the roof. Instead Mastic sealants are introduced at both the ends since Centre Roof Rail and Bow Roofs are fully positioned under the Styling surface of the Roof. For increasing the strength of the rails, embossing is done. To reduce the weight of the material used, a different styling has been followed with a thickness of 0.65 mm.

Bow Roof 1 :

Bow Roof 2 :

Assembly top views :

Ditch Area and Roof Rails:

Assembly split view :

Assembly top view :

Analysis

1. Curvature Study

It is done to justify the positioning of the Bow Roofs. There are mainly three criterion to fulfill

1. Roof Crush test

2. Heat Distortion Criteria

3. Snow Load Criteria

Roof Crush Testing is done only after the part or prototype is manufactured in physical conditions.

 

Why do we need to calculate heat distortion criteria?

This is nothing but the curvature study and bow roof position justification.

At certain temperature material  start softening when exposed to fixed load at elevated temperature above this temperature material not stable it can be deformed or loses its strength and this is unsafe to the passenger. 

In order to know whether the material or roof is in a safer zone according to the position of the bow roof (Whether its position is right or wrong) we need to perform some formulae criteria as shown above.

Heat Distortion Criteria

SRNO	Comp	Rx	Ry	R	I	L	Lx	W	OK/NG
1.	FRR & 1BR	1757.193	2514.184	2068.61	325.615	2030.797	1143.856	1.4396	OK
2.	1BR & RRC	5074.615	5990.342	5494.586	395.168	2030.797	1090.771	1.5314	OK
3.	RRC & 2BR	3933.59	12016.3	5926.962	345.308	2030.797	1062.936	1.5796	OK
4.	2BR & RRR	3251.691	14151.02	5288.227	383.553	2030.797	1048.647	1.6043	OK

SNOWED CRITERIA

Why do we need to calculate snowed criteria?

In North INDIA there is continuous snowfall and it causes a door jam in the car to optimise this problem. We need to justify the snowed criteria theoretically.

To know whether the bow roof position is correct or not according to snowed load condition.

L- Length of roof in the X-Direction

SR. NO.	Comp	ly	Lx	Ly	Y	My	Alfa	s	Rx	Ry	Qr	Det.
1.	FRR & 1BR	771.5	1143.856	1731.336	455.2415	580931.1743	0.76	477.7237	1757.193	2514.184	104.822	OK
	1BR & RRC	1613	1090.771	1731.336	500.206	615818.6128	0.7327	475.5935	5074.615	5990.342	34.026	OK
3.	RRC & 2BR	546.3	1062.936	1731.336	450.981	577415.7783	0.6514	468.6440	3933.59	12016.3	6.3309	OK
4.	2BR & RRR		1048.647	1731.336	486.307	605466.3179	0.6658		3251.691	14151.02		NG

NOTE: Green region snows this value to satisfy the condition and the red value shows its NG.

Section Modulus Study :

Section modulus is a geometric property for a given cross-section used in the design of beams or flexural members. There are two types of section moduli, the Elastic Section Modulus and the Plastic Section Modulus. For general design, the Elastic Section Modulus is used, applying up to the Yield Point for most metals and other common materials.

Section modulus is calculated using the formula

S=Iy">S=IyS=Iy

Where,

S = Section Modulus

I = Moment of Inertia

Y = distance between the neutral axis and the extreme end of the object 

Front Roof Rail

Rear Roof Rail

Centre Roof Rail

Bow Roof 1

Bow Roof 2

Draft Analysis :

Draft Analysis is done to analyze the draft angle. This allows us to verify whether the product will be easily removed from the tool.

When designing a product they need to be angled slightly so that the tool can be pulled away from the object easily, without deformation or damage. This slight angle is called draft.

Ditch Area

Front Roof Rail

Rear Roof Rail

Centre Roof Rail

Bow Roof 1

Bow Roof 2

Conclusion

Thus the required reinforcements and Ditch Area for the Roof were designed and developed from the given styling. The curvature study was done after performing calculations for the Heat Distortion and Snow load conditions with the position criterion met for all reinforcements.

Further the Section Modulus study was conducted and Draft Analysis were done for each reinforcement succesfully.