Roof challenge

OBJECTIVE: To design the Front Roof rail, Bow Roof rail, Center Roof rail and Rear Roof rail as per the master sketch and to pass the Bow-Roof prediction and Snow load prediction conditions. Perform the draft analysis to produce the positive draft for manufacturing feasibilit

Software used: Siemens NX.

Design Considerations

• Visibility criteria
• Head clearance
• Curvature study
• Heat distortion and snow load criteria
• Material thicknes

Introduction:

The external sheet metal part of any car which sits above passenger compartment is called roof panel which is mounted on and supported by roof bows. It act as a shielding part which safeguards the occupants from outside environment.

Components that were designed with the given styling roof

1. Front Roof Rail
2. 1^st Bow Roof
3. Center Reinforcement Roof Rail
4. 2^nd Bow Roof
5. Rear Roof Rail

1. Front Roof Rail:

With the help of mater sketch we designed a front roof with proper dimensions and creataed a embosses to strengthen the part and brackets are given for mounting.

Here are the images of Front roof Rail

The Flanges are created at the front outer panel to avoid sharp edges by using bridge curve and Through curves.

Bow Roofs:

Bow roof 1:

Bow Roof 2:

Centre Reinforcement:

For the center reinforcement follow the same procedure from the bow roof creation with bigger dimensions.

Back Roof Rail:

With the help of mater sketch we designed a front roof with proper dimensions and creataed a embosses to strengthen the part and brackets are given for mounting.

Here is the image of Back Roof Rail.Rear Flange is created in which backdoor hinges will position and back door will sit over it.

After doing all the reinforcements and mastics create a thickness to the part.

Assembled Images:

Front View

Top View

Side View

DRAFT ANALYSIS: The roof body must have positive draft angle, so that manufacturing feasibility is achieved. From the Below picture, the draft analysis is successful in obtaining positive draft angle. The color green on the roof part indicates Positive draft over the positive draft limit angle:

Outer Panel:

Front Roof Rail:

Bow roof 1:

Bow Roof 2:

Centre Reinforcement:

Back Roof Rail:

SECTION MODULUS ON THE O-Y SECTION FOR ALL THE ROOF RAILS:

Section Modulus for the reinforcement cross-sections which is used to anlyse strength of the cross section under particular load acting on it as well as while calculating snowload calculation.

FRONT ROOF SECTION:

BOW ROOF 1 SECTION:

BOW ROOF 2 SECTION:

CENTER ROOF SECTION:

REAR ROOF SECTION:

Curvature Study, Heat Distortion :-

This Study Shows us that, when the temperature is uniformly spread on the roof, it gives us an idea where the bow roof’s position could be placed and will give us an idea of how to maintain the overall strength of the roof. If the given requirements are not met, then the following value would be a no-good condition

RY value Images, RX value Images:

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]

According to the judgement criteria OK< 2.7

After doing the calculation, Here are the results.

Snow load Prediction formula:-

The given snow load criteria don’t meet, hence an NG condition. Thus emboss have to be given on the vehicle's roof to satisfy the load thereby adding strength and stability.

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

According to the judgement criteria Qr ≥ 3.1

After doing the calculation, Here are the results.

Conclusion:

The roof was created with all required parameters with a certain rails, and calculation the heat distortion, snow load are done and performed Draft analysisfor safety concerns. The result is satisactory.