Roof Design

ROOF DESIGN

Roof is not a single element, it consists of Front roof rail, Rear Roof Rail, Bow      RoofRail, Center Roof Rail. These Bow Roofs are placed in the most Flat area of the Panel. Rear Roof Rail joins with the Back door and Body side outer. Front Roof Rail joins with the Wind shield glass and body side. Here are some reinforcement used in the Roof.

FRONT ROOF RAIL:

This will be a supporting room lamp for some cars. We need to consider the

Visibility criteria line for designing Front roof rail.

REAR ROOF RAIL:

Here we need to keep Head room clearance and rear view criteria for designing. Back door will be mounted here.

BOW ROOF AND CENTER ROOF RAIL

The bow roofs are given to improve the torsional stiffness and load bearing capacity of the roof structure .The number of bow roof present depends on the overall size of the roof . Presently I have added two bow roofs.

Centre roof rail helps in providing effective support to the flat area of the roof as it is more susceptible to failure under the action of load. generally the center roof rail is placed at the center of the roof and is connected to the B-pillar structure.This helps in adding the strength to the roof during the rool- over test. 

MANUFACTURING PROCESS:

Outside plate can be manufactured with the following process, first the open straight snips plate: first select applicable cold coiling specification, cold coiling is opened flat. Then according to production material specification it will be opened after flat and be cut into the iron plate of corresponding size. Finally the iron plate after shear is cleaned into iron filings. Then its trimmed and punched. Then its flanged and punched. Finally, after punching completed it is carried out to the operation of side folding.

Bar shaped assembly and ring-shaped component are processed by blanking, stamps out iron plate the outline blank of many roof cant rails, a ring-shaped component and a bar shaped assembly. 

SPOT WELD: 

Spot welding is a type of electric resistance welding. It is also known as resistance spot welding. The process of spot welding is sheet metals are made into contact with each other and pressure is applied on specified points. So heat is generated from the resistance and weld is formed. 

ROOF CRUSH TEST:

 A rectangular block measuring 30 inches wide and 72 inches long is used to apply the load on car roof with 1.5 times the unloaded vehicle weight with different angle inclination to rectangular block. The moving distance of roof structure must be less than 127mm or 5 inches as per FMVSS standards.

ROOF CRUSH SYSTEM:

Here Crush test system is shown which is manufactured by MGA Corporation. It has an upright assembly and attached loading head that can be fixed at varied heights. Pitch angle can be varied by +5 to -5 degrees. But the roll angle is fixed to 25 Degree. Hydraulic actuators are used to control the movement of plate. 

POSITIONING OF BOW ROOF:

Bow roofs are designed to give strength to the roof panel. It avoids the roof to bend due to snow load. Number of bow roofs needed are estimated with the design of the roof panel. if the length of the roof is large we need more bow roof and if the roof panel is lesser in length we need ideal number of bow roofs.

The positioning of Bow Roofs depends on the curvature of the roof panel. We add bow roof on flat region as bending is more possible here than the curved portion of the roof. Along with this we have Heat distortion criteria and Snow load Criteria for positioning the Bow roof.

HEAT DISTORTION CRITERIA:

The heat distortion test evaluates the ability of car roof to maintain its physical structure without deformation under elevated temperature conditions. Car roofs are exposed to sunlight at day time. Distortion of the car roof can create more susceptible to damage.

            W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8)  x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68            

FRONT ROOF RAIL -  BOW ROOF RAIL 1

Rx=5721.94   , Ry=2134.34   ,   L=1944.08   , I=257.79

                 W=1.34

BOW ROOF RAIL 1 -  CENTER ROOF RAIL

Rx=5158.35   , Ry=5438.80  ,   L=2029.12   , I=479.86

                W=2.04

CENTER ROOF RAIL -  BOW ROOF RAIL 2

Rx=3985.57   , Ry=10535.34 ,   L=2029.12   , I=549.70

              W=2.2

BOW ROOF RAIL2  -   REAR ROOF RAIL

Rx=3272.93  , Ry=14630.10  ,   L=2029.12   , I=253.99

                W=1.8

Judgment Condition

OK< 2.7

This study on Heat distortion criteria is used to predict the heat distortion temperature at where the material starts to soften when exposed to a fixed load at elevated temperature .By this way we can avoid bending or damages on the roof, based on the heat distortion temperature. Here we will predict the bow roof position which helps to strengthen the roof.

SNOW LOAD CRITERIA :

Unlike in India there are countries with heavy snowfall. In Alaska it was recorded a record-breaking 78" in 24 hours in 1963. So calculating and designing the roof of the car in such a way this snow does not cause serious damage to the car.

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

REAR ROOF RAIL INERTIA

BOW ROOF RAIL 2

CENTER ROOF RAIL 

BOW ROOF RAIL 1

FRONT ROOF RAIL

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)

Judgement condition = Qr ≥ 3.1

                250 ≤ s ≤ 380

BOW ROOR RAIL 1

       L1=359.75     ,    L2=554.92      ,  Lx=1147.62   ,  Y=359.75     ,   Ly=1944.08    ,  a=0.750    , S=457.33   ,  t=0.75

                  Qr=57.18mm4

CENTER ROOF RAIL

 L1=554.92   ,    L2=628.38     ,  Lx=1093.81   ,  Y=915.62    ,   Ly=1944.08    ,  a=1.126    , S=591.59 ,  t=0.75

                  Qr=158.04mm4

BOW ROOF RAIL 2

L1=628.38   ,    L2=419.01     ,  Lx=1061.56   ,  Y=1540.71    ,   Ly=1944.08    ,  a=0.700    , S=523.69 ,  t=0.75

                  Qr=273.00mm4

ANALYSIS

Three types of analysis were carried out to get a successful design of the BIW roof of a car which satisfies the Manufacturing Standards.

DRAFT ANALYSIS

The Draft Analysis command enables you to detect if the part you drafted will be easily removed. This type of analysis is performed based on color ranges identifying zones on the analyzed element where the deviation from the draft direction at any point, corresponds to specified values.

BOW ROOF RAIL 1

BOW ROOF RAIL 2

CENTER ROOF RAIL

FRONT ROOF RAIL

REAR ROOF RAIL

CONCLUSION

For the Given Roof styling, the essential flanges and reinforcements were developed and checked for Draft analysis. The curvature study and Section Modulus on the roof was carried out and to determine the position of the Bow-roof the Heat Distortion and Snow Load Criteria calculations were also performed.

Draft Analysis has been carried out provided 7 degree in order to check the maufacture feasibilty of the components.