Project 3: Roof Modeling

Roof Design Challenge

AIM:

For the Given Roof styling surface, develop the essential flanges, bow roofs and reinforcements, provide appropriate dimensions and check for the draft analysis. Do a curvature study on the roof and perform calculations to determine the position of the Bow-roof.

ROOF:

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. It consists of outer roof, front and rear rail roof, and bow rail roof.

Types of Car roof:

Convertible:

Convertible, cabriolet or spyder car roof have a foldable structue. It is Passenger car that can be driven with or without roof.

Hardtop:

A hardtop is a rigid form of automobile roof. The hardtop roof can be either fixed, detachable for separate storing or retractable within the vehicle itself. This model mostly used for off road vehicle like a jeep.

Sunroof:

An automotive sunroof is a movable panel that can be opened to uncover car from top. Which allows light and fresh air into the passenger compartme. It is available in three form half sunroof, fully open sunroof and mood view.

ROOF FORMING PROCESS :

In sheet metal forming, the final shape of a part is made from a flat metal sheet. The desired shape is achieved through plastic deformation, without undergoing any machining like milling. Sheet metal forming is used in almost every sector of industrial production, like the automotive industry, the aircraft industry, the home appliance industry, the food industry etc.

SPOT WELDING:

Spot welding (also known as resistance spot welding) is a resistance welding process. This welding process is used primarily for welding two or more metal sheets together by applying pressure and heat from an electric current to the weld area.

DESIGN CONSIDERATION:

• Visibility criteria.
• Head clearance.
• Heat distortion and snow load condition.
• Draft angle.
• Minimum bend radius.

Draft Analysis

It must be done for the smooth manufacturing process in particular direction i.e. normal to the surface. In this method, the draft angle will be checked. It must by more than 7 degree for the sheet metal. One should try to avoid the negative draft during the design stage. As one can see on the right side colour pattern green, yellow, blue and red. If the part have positive draft, it will present green colour otherwise blue or red. In the proceding, the draft analysis was performed for all the parts of the roof.

Note: In some portion, we can not avoid the negative draft. So bending operation used for the manufacturing process, because deep drawing can not be done at the negative draft area.

HEAT DISTORATION CRITERIA :

Thermal deformation is the phenomenon observed in solids, liquids, and gases. In this process, an object or body deformed on the application of heat (temperature). Thermal expansion defines the tendency of an object to change its dimension either in length, density, area, or volume due to heat. By using this analysis one can undersatand about the positioning of the bow roof. For all the region the values of w were evaluated and presented in the below table.

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]

SNOW LOAD PREDICTION :

This analysis is used to understand the positioing of the bow roof due to the snow load accumulating on the roof top.

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)

t = Roof plate thickness [mm]

Ly = Distance between the front and rear roof Rails on the Vehicle along with 0Y[mm] or 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] or 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]

Ry = Longitudinal Direction curvature radius of the Roof panel X cross-section on Roof BOW [mm]

Judgment condition

Qr ≥ 3.1

250 ≤ s ≤ 380

Geometrical moment of inertia of bow rails

Bow rail one

Bow rail 2

Conclusion

The roof design was done by considering all the parameters. All the bow rails were provided on the proper location that can be confirmed by considering the snow load and heat distortion criteria. Further the draft analysis were done for all the parts and all the relevent images were added in the report.