Roof Design

CAR ROOF DESIGN

AIM:

For the roof styling, develop the essential flanges and reinforcements, provide appropriate dimensions and check for draft analysis and to perform roof curvature study using NX CAD.

Introduction:

ROOF:

An Automobile roof or car top is the portion of an automobile that site above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements. The roof itself may be constructed of soft or rigid material. Soft tops are made of vinyl, canvas or other textile material. Hard top convertiable have roofs made from steel, aluminium, plastic or corbon fibre composites.

SUNROOF:

A sunroof is a movable panel that opens to uncover a window in an automobile roof, allowing light and fresh air to enter the passenger compartment. Sunroofs can be manually operated or motor driven, and are available in many shapes, size, styles.

VINYL ROOFS:

Vinyle roofs started out early in automotive history,going as far back as the 190s. They started as a necessity because, well cars needed roofs to keep the rain off of the occupants. Vinyl was used to replicate the appearance of a movabe top, similar to one on a horse carriage.

The roof is a styling part which is fixed with biw body through the rails and panels inside the upper roof to provide the strength and stiffness.

Ditch area plays an important role here to fix the reinforcement of the component. The rails and reinforcement are joined to the ditch area with spot weld where is not a styling point.

Factors considered the before creat ditch area,

• HEADROOM CLEARANCE
• VISIBILITY CRITERIA
• WINDSHIELD FASSEMBLY
• BACKDOOR ASSEMBLY
• CURVATURE STUDY
• HEAT DISTORTION AND SNOW LOAD CRITERIA
• DRAFT ANALYSIS.

ROOF COMPONENTS;

1. Front roof rail
2. Bow roofs
3. Center roof rail
4. Rear roof rail
5. Roof outer panel

1.FRONT ROOF RAIL;

Front roof rail is one which joins the windshield glass and side body outer also joined the inner panel.

2. BOW ROOFS

The Bow roofs are given to the tortional stiffness and load bearing capacity of the roof structure. The number of bow roofs present is depends on the overall size of the roof.

3. CENTER ROOF RAIL

The center roof rail is one of the reinforcement of roof surface. It joins with body side outer and B-piller.

4.REAR ROOF RAIL

Rear roof rail is the one which joins the backdoor and body side outer.

5.ROOF OUTER PANEL

JOINING PROCESS

Mastics are introduced between the roof outer panel and the reinforcement for joining. Where ever the mastic are introduced there is remarkable improove the strength.

Spot welding is also introduced to join with the reinforcement and the outer panel.

ROOF CRUSH TEST

• Therefore, passenger safety is also a very important parameter in front of OEMs. For this reason, strength is a very important criteria for designing a vehicle roof.
• The strength of the roof structure to occupants the protection in real world crashes, requiring the maximum moving distances of the roof structure should be less than 127mm when induced load is 1.5 times the vehicle weight.
• For the test, the passenger car shall be rigidly placed or positioned on horizontal surface with the doors locked and the window closed.
• This test can be conducted on either side of the roof structure, the front left or the front right side but not on both sides in one single test and still meet the requirments of the test.
• The rigid plate shall not move 0.5inches/sec and the force applied on the plate shall not exceed the lesser of 1.5 times the unloaded vehicle weight (UVW) expressed kilograms multiplied by 9.8 or 5000lbs
• Also the direction of the forces shall be downward and perpendicular to the lower surface of the rigid plate and such that moves in a straight line without rotation. The duration of the test shall not exceed 120 seconds. The longitudinal axis of the plate is pitched forward 5 degree angle as viewed from the side of the passenger car.
• Roll over accidents of a car are the most occuring accidents that we see in our daily lives. The passenger experience major injuries like neck, head and spine injuiries. So to reduce the injuries of a passenger from major fatalities it is important to provide safety in the car. Though safety is provided by seat belt and airbags during accidents. The roof of the car must have high strength to resist the crush force to avail the passenger some space for survival.
• Therfore, in this project , we have carried out of roof crush test using Federal motor safety standards (FMVSS216) in LS dyna software. We have used hyper mesh software to mesh the model and to apply boundary conditions to it. And the rigid plate is used to crush the car roof as specified by FMVSS216 standards.
• The rigid plate is oriented on the car roof structure to the baseline model to check the crossworthiness of new material.
• The outcome of test results of the new material's strength to weight ratio(SWR)was compared to baseline model and the new material is proposed for the roof (B-piller) which is found to be more crashworthy.

Why Reinforcements?

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

ROOF CALCULATION

a. BOW ROOF PREDICTION CONDITION

HEAT DISTORTION CALCULATION

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]

TABULATION FOR HEAT DISTORTION CALCULATION:

Roof rail span from	L(mm)	Rx(mm)	Ry(mm)	R	t(mm)	I(mm)	W	Result
FRNT-BOW 1	2030.3	5731.0	2676.5	3648.89	0.75	333.04	1.37	OK
BOW1-BOW2	2030.3	4978.0	6180.0	5514.25	0.75	415.48	2.03	OK
BOW2-BOW3	2030.3	3982.8	10553.8	5783.15	0.75	436.78	2.13	OK
BOW3-REAR ROOF	2030.3	3313.7	14368.2	5385.38	0.75	294.43	1.87	OK

PROCEDURE TO MEASURE THE PARAMETERS :

1. On plane parallel to the top plane draw sketch in which 0y line is offset by 300mm.
2. Draw lines perpendicular to 0y line passing through point exact midpoint of the two adjacent parts. (e.g. midpoint between front rail and bow roof 1)
3. Offset these reference lines on both sides by 100mm.
4. Mark intersection points of reference line and 100mm offset lines.
5. These reference points are projected on the roof outer panel surface to creat curves.
6. Take all necessary measurments required to calculate w value as per mentioned formula.

b. SNOW LOAD PREDICTION CONDTION

Qr = [Iy x t²] / [α x s x [(Rx + Ry)/2]² x 10^-8]

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 from 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

TABULATION FOR SNOW LOAD CONDITION

ROOF RAIL SPAN FROM	Iy(mm4)	L1(mm)	L2(mm)	Lx(mm)	Ly(mm)	t(mm)	Rx(mm)	Ry(mm)	y(mm)	s	α	Qr	RESULT
FRONT-BOW1	351.27	547	590	1035	2030	0.75	4452.16	3140.80	547	568.5	0.8689	277	OK
BOW1-CENTER ROOF	458.24	590	438	1087	2030	0.75	3763.76	6505.97	590	514	1.0038	458.5	OK
CENTER -BOW2	386.97	438	340	1059	2030	0.75	4273.63	11783.52	438	389	0.7820	310	OK
BOW2-REAR ROOF		340		1045	2030	0.75	4054.35	17035.00	340		0.6274

SECTION MODULUS

BOW ROOF 1

BOW ROOF 2

CENTER ROOF RAIL;

DRAFT ANALYSIS

CAR ROOF MANUFACTURING TEQNIQUES

1. BLANKING
2. STRETCH FORMING
3. TRIMMING AND PUNCHING
4. DEBBURING
5. WELDING
6. GRINDING
7. PAINTING
8. POLISHING
9. WAXING
10. COATING

BLANKING

Blanking is a steel manufacturing process in which a flat, geometric shape (or "blank") is created by feeding a coil of sheet metal into a press and die. In this process the blank is punched out from large metal sheet.

STRETCH FORMING;

Stretch forming is a metal forming process in which a piece of sheet metal is stretched and bent simultaneously over a die in order form large contoured parts.

TRIMMING AND PUNCHING

DEBURRING

WELDING

GRINDING

PAINTING

POLISHING

WAXING

COATING

CONCLUSION

.Using all input data we have succesfully designed in ditch area and essential flanges, front roof rail, bow roof rail. center roof rail,rear roof rail as per the requirments.

2. As per the heat distortion criteria is come to know all bow roof position are ok.

3. As per the Snow load criteria is come to know there is improvement required.

4. All roof rail draft analysis are found in ok.