Roof challenge

ROOF DESIGN

Objective

• To create a Roof Design and create an Assembly by developing the essential flanges for the outer roof and creating the reinforcements.
• To check whether the design satisfies the design criterion.
• To prepare a Draft Analysis of the roof design.

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. Because the earliest automobiles were designed in an era of horse-drawn carriages, early automobile roofs used similar materials and designs.

Safety point of view vehicle roof plays very crucial role specially roll over kind of accidents, in which vehicle tips over onto its side of roof. And vehicle rollover crashes are the causes of many fatalities and several head, neck and spine trauma around the world. Therefore passenger safety is also very important parameter in front of OEM’s. It is not only a marketing strategy but also it is a obligation stipulated by international standards that are now place in several countries, as well as a governmental requirement. For this reason strength is very important criteria for designing vehicle roof.

Design Consideration

• Head Clearance
• Front and Rear Visibility Criteria
• Heat Distortion Criteria
• Snow Load Criteria
• Strength

Main Components in a Roof

• Roof Outer Panel: This is the outermost part of the roof which is visible for all the beings. There can be multiple ways to be showcased this structure as it varies on different companies.

• Front Roof Rail: The front rail roof is situated at the front part of the roof as it connects between the roof and the windshield. The bottom flange of the front roof rail depends upon the visibility crieteria and the windshield design.

• Bow Roofs: Bow roof rails are present in the roof to provide strength to the roof. When a crash happens , the passengers inside the car when rolled over are protected by the strength of the roof.

• Centre Roof Rail: The Centre roof rail is present atmost to the centre part of the roof . The lateral dimesions when designing the center roof rail is more when comparing with the bow roof. This reinforcement also provides strength to the roof.

• Rear Roof Rail: When designing the roof , it is atmost important when connecting the roof with the backdoor. At that time rear roof rail helps. The dimensions are constrained with the design of the backdoor.

DESIGN OF ROOF

SOFTWARE USED:

Simens Nx12 Cad

Main Commands Used

• Offset Surface
• Wave Geometry Linker
• Trim sheet
• Extend Sheet
• Offset curve on face
• Intersection Curve
• Bridge Curve
• Face Blend
• Edge Blend
• Sew
• Mirror Geometry
• Thicken

MASTER SECTIONS :

• Front Roof Rail

• Bow Roof Rail

• Centre Roof rail

• Rear Roof rail

OUTPUT

• Front Roof Rail:

• First Bow Roof:

• Centre Roof Rail:

• Second Bow Roof Rail:

• Rear Roof Rail :

CALCULATIONS

• Heat Distortion Criteria:

This Criteria is used to measure the variation of the surface of roof as metal softens or deforms when reaching a particular temperature under specefic load.

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]

The heat distortion calculation is presented in the table given below:

• Snow Load Criterion:

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

Note: The Qr value given over here is correct. There was a typo error in the formula given in the video.

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 front 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

The table below shows you the snow load calculation :

So the Snow load criterion doesnt satisfy the CR-BR2 area, so its better to advise the styling team to modify the radius and length of the bow roof 2 placement to a lesser value.

• DRAFT ANALYSIS

CONCLUSION

The Design and analysis of Roof design using Simens Nx 12 Cad is thus completed.