Roof challenge

Aim:-

To Design a Car Roof and to do the curvature study to resist Heat distortion and snow load condition of the surface.

Introduction:-

An automobile roof or car top 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 carriage, early automobile roofs used similar materials and designs.

Different types of Car Roofs are:-

• Convertible roofs Hardtops
• Sunroofs
• T-tops
• Targa tops
• Vinyl roofs

The roof of the cars is made up of multiple parts that provide support and strength to the roof components. The actual roof sheet and the roof rails in a car the front, center and rear, While in additional roof rails are called bow roof rails. The number of bow roof rails depends on the size of the roof. Headroom, visibility criteria and target region also play a key role in roof design.

Vehicle Roof Structure:-

A roof structure for a vehicle body includes a roof opening defined by a pair of spaced apart side rails, each having a flange extending inwardly and being vertically offset below the roof surface and by front and rear header each having a flange defining a window opening. A roof panel assembly includes a root outer panel and a pair of inverted hat shaped reinforcement of the roof outer panel and include inwardly and outwardly directed legs abutting the underside of the roof outer panel. The outermost portion of the side edges of the roof outer panel are hem flanged over outwardly directed flange of the reinforcement rails so that the roof outer panel and reinforcement rails define the roof panel assembly. The roof outer panel has fore and aft end flanges which overlie the flanges of the front and rear headers and are spot welded there to. A bead of adhesive is placed on the inwardly extending flanges of the side rails and the roof panel assembly is lowered into the roof opening with the adhesive to attach the roof panel assembly to the vehicle body. The subsequent installation of the front and rear window hides the spot welds.

Different components of Car Roof:-

• Roof
• Front Roof Rail
• Center Roof Rail
• Rear Roof Rail
• Bow Roof 1
• Bow Roof 2

Roof:-

An automobile roof or car top 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.

Front roof rail:-

Front roof rails are used in the assembly of a roof in which it provide mounting provision 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 provision for the mounting the inside rear view mirror.

Centre roof rail:-

The reinforcement center is used as a cross member between bodyside LH and RH respectively. In some cases, the reinforcement center not joined with the roof in both roof and bodyside. The reinforcement center and bow roof are joined either spot weld or by mastic sealants and provision for the same are given.

Bow roof:-

It is an additional stiffening member used in the roof assembly for the localized strength improvements and it is joined directly to roof itself with several spot welding or even with the mastic sealant.

Bow roof 1:-

Bow roof 2:-

Draft Analysis:-

Parts cannot be ejected from the tool if it is at 90- degree for this reason, a small draft is to be provided for each surface for the components in order to easily remove the components from the mould without any defects, Draft is the angle in which the part is tapered to allow it to release. Most of the sheet metal part require minimum 7 degree to 10 degree however 7 degree is widely accepted in sheet metal components design.

Roof:-

Centre roof:-

Bow roof 1:-

Bow roof 2:-

Section modulus calculation:-

Section modulus is a geometric property for a given cross-section used in the design of beams or flexural members. Other geometric properties used in design include area for tension and shear, radius of gyration for compression and moment of inertia and polar monent of inertia for stiffness. Any relationship between these properties is highly dependent on the shape in question.

Formula to calculate section modulus:-

S-I/Y

where,

S- Section modulus

Y- Moment of inertia

I- Maximum distance between neutral axis and one of the extreem end of the object

Central Roof Rail & Bow roof:-

I=680.8714 MM^4

Bow roof 1:-

I=568.4818 MM^4

Bow roof 2:-

I=232.9317 MM^4

Heat distortion criteria:-

Heat distortion is the temperature at which the metal soften and deform under a specific load. This study is done to check the ability of thge roof to withstand high temperature w.r.t the positioning of the reinforcement which contribute to increased strength.

Formula to calculate heat distortation:

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

Judgement Condition : OK< 2.7> 3.1

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]

Calculation table:

CRR: Centre roof rail

1st & 2nd: bow roof 1st & 2nd

Snow load prediction:-

Snow load Prediction formula:

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

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]

Width of the roof panel 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

Calculation table:

CRR: Centre roof rail

1st & 2nd: bow roof 1st & 2nd

Complete assembled view:-

Sectional view:-

Conclusion:-

I design the car roof, as per design consideration and the curvature study to resist heat distortion and snow load condition.