Roof challenge

REPORT ON ROOF DESIGN

OBJECTIVE:

• For the given roof styling, develop the essential flanges and reinforcements by providing appropriate dimensions for different reinforcements like ditch area, front roof rail, bow roofs, central roof rail and rear roof rail.
• Perform the draft analysis for each reinforcements.
• Perform a curvature study on the roof and perform the calculations for the heat distortion and snow load criteria.
• Finding moment of inertia and section modulus for the Front roof rail, Rear roof rail, Bow Roof Rail, and Rear Roof Rail.

DESIGN CONSIDERATIONS:

1. Visibility criteria
2. Head clearance
3. Curvature study
4. Hear distortion and Snow load criteria
5. Draft analysis

SOFTWARE USED : NX-CAD

CAR ROOF:

An automobile roof or car top is the portion of an automobile which is situated above the passenger compartment. It protects 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 withstand the overhead forces like snow.

REINFORCEMENTS:

Definition:

Requirements:

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 reinforcements that the car has are:

• Front roof rail
• Bow roofs
• Central roof rail and
• Rear roof rail

Front roof rail design

Front roof Rail master section reference image

Rear Roof Rail

Rear roof rail master section reference image

FRONT ROOF RAIL:

Reference image of the front roof rail

Front roof rails are used in the assembly of a roof in which it provides mounting provisions to windshield glasses and the changes in the front roof rail influences the frontal visibility of the passenger. The major design factor considered is the headroom clearance. The front roof rail also provides provisions for mounting the inside rear-view mirror.

BOW ROOF-1:

Reference image of bow roof

Bow-roof center is an additional stiffening member used in the roof assembly for the localised strength improvement and it is joined directly to roof itself with several spot welding or even with the mastic sealant.

CENTER ROOF RAIL (REINFORCEMENT CENTER):

Reference image of reinforcement center

The reinforcement center is used as a cross member between body side LH & RH respectively. In some cases, the reinforcement center is not joined with the roof and in some other cases, it is made to join in both rook and body side. The reinforcement center and bow roof are joined either spot weld or by mastic sealants and provisions for the same are given.

BOW ROOF-2:

The bow roof center 2 is similar to that of bow roof center which serves the same purpose as the previous.

REAR ROOF RAIL:

Reference image of the rear roof rail

The rear roof rail is the one of the important component of roof assembly which is used for the back door mounting similar to front roof rail important design consideration include rear passenger head clearance rear visibility of the vehicle.

DESIGN OF ROOF ASSEMBLY:

3. Curvature study

BOW–ROOF PREDICTION FORMULA :

W = [1.73 x 10^-3 x L] + [1.85 x 10^-8 x (R²)/t] + [1.10x10^-3 x l] - 2.68

Judgment Condition

*OK< 2.7*

Where

L = Roof Length in X-Direction[mm](Roof dimension in 0-Y)

R = Roof curvature

R = 2(R_x*R_y)/(R_x+R_y)

R_x = X curvature

R_y = Y curvature

t = Roof plate thickness [mm]

l = Bow Roof Span [mm]

SNOW LOAD PREDICTION FORMULA:

Q_r = [I_y x t² ] / [α x s x [(Rx + Ry)/2]² x 10^-8 ]*

Where

α = M_y x L_x² x 10^-12 , M_y = Y(L_y-Y)

Judgment condition

*Q_r ≥ 3.1*

250 ≤ s ≤ 380

t = Roof plate thickness [mm]

L_y = 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.

L_x = 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

I_y = Geometrical moment of inertia of Roof BOW (Y cross-section )[mm4]

R_x = Lateral direction curvature radius of roof panel Y cross-section on

Roof BOW [mm]

Roof panel curvature Radius of the Length L_x in Front view

R_y = 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

Now since these snow load values does not satisfy the condition. So to make the roof stronger, one must create embossses on the roof for strengthening purpose.

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.

Minimum draft angle of 5° is considered for analysis. green colour infer on the parts that all face along the tooling direction has positive draft angle greater than 5° and passed in analysis

DRAFT ANALYSIS FOR FRONT ROOF RAIL:

DRAFT ANALYSIS FOR REAR ROOF RAIL:

DRAFT ANALYSIS FOR BOW ROOF RAIL 1:

DRAFT ANALYSIS FOR BOW ROOF RAIL 2:

DRAFT ANALYSIS FOR CENTER ROOF RAIL:

DRAFT ANALYSIS FOR CENTER ROOF REINFORCEMENT PLATE:

SECTION INTERTIA FOR CENTER ROOF RAIL:

SECTION INTERTIA FOR BOW ROOF RAILS:

CONCLUSION:

In this way, the roof, front roof rail, bow roof rails, central roof rail and the rear roof rail is designed by following the master sections and heat distortion criteria as well as snow load criteria and draft analysis are calculated to check feasibility manufacturing of the given designed parts.