Roof Design

Roof Design Challenge

Aim:

To design a roof and create an assembly by developing the essential flanges for the outer roof and create the various reinforcements by following the given master sections and design parameters.

Objective:

• To design a outer roof and its essential flanges,
• To create the various reinforcements (Front roof, Rear roof, Bow roof, Central roof),
• To study the curvature of roof reinforcements
• To calculate the Heat Distortion Criteria of the roof.
• To calculate the snow load calculations
• To perform the draft analysis.

Introduction: Roof

Car's Roof is the top portion and it is protects the pasengers from the direct sun light, wind, rain and other weather conditions.The car's roof also protects the passengers from when the car gets crashed, rollover and any heavy objects falls on the roof.

Roof Reinforcements:

The various roof reinforcements are,

• Front roof rail
• Rear roof rail
• Bow Roof Rail
• Centre Roof rail

Design Consideration:

• Head clearance

• Visibility criteria

• Curvature study

• Hear distortion and snow load criteria

• Draft analysis.

Manufacturing Techniques & Design Parameters:

Outer Roof:

First we are going to make the roof outer panel's flanges by the given master sections.The flat roof is very weak and unsafe for the pasengers, so making the essential flanges and reinforcements.

The sheet metal manufacturing process for tooling directions and the draft angle should be considerd as main creteria.The draft angle should be more than 7 dgree. To avoid the sharp corners and make the appropriate blens to the sharp edges. The thickness of the roof is 0.75mm.

Joining Roof Assembly:

1. Spot welding

2. Mastic Points

Front Roof Rail:

Front roof rail is the supportive frame for the roof and given the strength to the front roof. Here the manufacturing process is the visible creteria and driver head clearence should be considered.

Bow Roof Rail:

Centre Roof Rail:

Rear Roof Rail:

For Sheet metal manufacturing process, the designers should be considered the tooling direction and draft angle as well as the sharp edges blending radious 3+thickness.

Curvature Study:

The curvature study is the analysis, helps us to determine and placing the positioning of the bow roof rails.

• Heat Distortion Criteria
• Snow load Criteria

Heat Distortion Criteria:

Here I design a two bow roof rails, one roof rail, centre roof rail, rear roof rail and calculate the heat distortion make sure the placing and positioning the bow roof rails.

Step by Step curvature Procedure

1. First create a sketch by front plane zero axis. Then draw 0Y line for refernce centre axis.
2. Then offset the 0Y line to 300 mm offset distance in Y-axis taht represnted as -3Y.
3. After that offset the -3Yline to 100 mm offset distance in symetric to both sides of -3Y line.
4. Now we have three horizontal lines and twelve vertical lines,then mark the intersection points of the line with three horizontal lines and as well as horizontal line we take the intersection of the vertical lines with that line mark the intersection arc points between to the each section

• After that project these points which is required to draw a 3D arc represented by Rx and Ry(curvature radius)

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

Judgement Condition: OK< 2.7

Where

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

R = Roof curvature

R = 2(R_x 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]

Here all the above sections meet the judggment conditions and the result also pass the judgment(OK< 2.7)

Snow load Prediction:

This snow load prediction is to perfrom the load calculation to the cold region where snow accurs. The bow roofs and central roof withstand the load due to accumulate the snow over the roof.The roof design should be pass through the snow load calculations.

Snow Load Prediction Formula

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

Where,

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

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

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

Moment of Innertia (Section Modulus) Iy

Front Roof to Bow Roof 1

Bow roof 1 to Centre Roof

Centre Roof to Bow Roof 2

Snow Load Curvature study

Lx, Ly, Y

s = Distance for which Roof BOW bears divided load [mm]

s = L1/2 + L2/2, Here each section the L1 and L2 value is change.

Curvature Radius for snow load study

Snow load calculation

Here the first two section the snow load with stand capacity passed the creteria.But the third condtion is not passed, so the bow roof rail between centre roof and rear roof rail is to be need to modify its design or shift the position of the roof and then we analysis the snow load after modify.

Draft Analysis

The Draft Analysis is used to detect the part to be drafted and analys the after machining. Draft analysis is performed based on color ranges identifying zones,

0 to 5 - Yellow

Above 5 - Green

0 to -5 - Blue

< -5 - Red

Outer roof Draft analysis

Front Roof Analysis

Bow Roof Analysis

Centre Roof Analysis

Rear Roof Analysis

The Minimum draft angle is considered to 7⁰ for analysis. The green colour infered on the parts that all body and single face along the tooling direction has positive draft angle greater than 7⁰ which is passed the analysis.

Final Assembly

Conclusion

In this roof design learned the design considerations and the various reinforcments such as roof outer, front roof rail, bow roof rails , central roof rail and the rear roof rail is designed by the given master sections.

In Curvature study, the Heat Distortion is satisfied in all section. But the Snow Load criteria passed only the first two section,and the third section(centre roof rail to bow roof rail 2) in not satisfied the judgment condtions..

In this above study for the third section to pass the snow load criteria chnage some design condieration following,

1. Shifting the position of the Bow roof rails,
2. Increase the cross section of Bow roof
3. Addittion the bow roof rails between the section those not satisfied the judgment.
4. Create the emboss on the outer roof.

Any one of the above mentioned statements might be satisfied the snow load judgment condtion to pass the third section.