Roof challenge

Objectives:

To design the Roof Reinforcement and Bow roofs for the given Roof styling using NX CAD software and to perform the calculations to determine whether the positioned Bow roofs are as per the Heat Distortion and Snow Load conditions.

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.

The roof is a styling surface part which is fixed with the BIW body through the rails and panels inside the upper roof to provide it strength and stiffness.

To design a roof with reinforcement we have a master sketch and some reference images.

Front roof rail

Bow roof

Centre roof rail

Bow roof 2

Back 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.

2. Bow roof 2

Here we designed the bow roof by offseting the outer surface and combined those surfaces with studio surface command by giving certain draft angle. Holes are created for mounting for cabin light positioning. Mastics are created at the sides to increase the stifness of the part.

3. Centre roof rail

For the centre

reinforcement follow the same procedure from the bow roof creation with bigger

dimensions.

4. rear 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:

After Completing the design part, we have done calculations to calculate the strength of the roof.

Heat Distortion Calculations:

We have a data to calculate

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]

Here we have to find out the RX and Ry values. To find that

• Create a sketh on top roof and drawn a horizontal line at the centre.
• Then offset this line below 300mm and called it as -3Y line.
• From the _3Y line offset 100 mm above and below and convert all these line into reference lines.
• Draw the vertical lines at the middle of the each reinforcements and offset it to 100 mm both sides.
• Intersection point is created where the lines are met.
• Project these points to the outer roof panel.
• Now draw the arc by connecting three points and measure the min radius value
• 

Here

• 'l' value is from one reinforcement centre to other reinforcement centre value.
• 'L' value is total length from one end to another end.
• 

According to the judgement criteria OK< 2.7> 3.1, All values are satisfied.

Snow Load Calculations:

We have a data to calculate

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)

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

Here we have to find out the RX and Ry values. To find that

• Create a sketh on top roof and drawn a horizontal line at the centre.
• Offset this line to 100mm on both sides. Convert all these line into reference lines
• Draw the verical lines at the middle of the each reinforcemnts and offset it to 100 mm both sides.
• Intersection point is created where the lines are met.
• Project these points to the outer roof panel.
• Now draw the arc by connecting three points and measure the min radius value
• the result is mentioned below:
• 
• master section are mentioned below
• 
• 
• 
• 
• 

Learning:

• Here we learned how to create a rails with the given standards by using Master Sketch.
• Learned How to calculate Heat Disorsion and Snow load criteria
• Learned how to do Draft analysis.

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

thankyou.....