Roof Design

For the Given Roof styling, create an ASSEMBLY by developing the essential flanges for the outer roof and creating the reinforcements.

Provide appropriate dimensions and check for Draft analysis.

Do a curvature study on the roof and perform calculations to determine the position of the Bow-roofs.

Suggest and implement remedies in the design if the criterion is not full-filling

Start with the creation of a roof ditch area with a tool opening angle of 7 degrees.

Develop the reinforcements as separate parts

Bow–Roof Prediction Formula

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]

Judgment Condition

OK< 2.7

Snow Load Prediction Formula

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

Judgment condition

Qr ≥ 3.1

250 ≤ s ≤ 380

Here are some Reference images for the Master sections - These images are just to give you a brief idea about the design.

Solution:

AIM: For the given car roof styling, design and develop the essential flanges and reinforcement, namely the Ditch area, Frontal Roof rail, Rear roof rail, Centre Roof rail and Bow roofs.

Do the curvature study on the roof and perform the calculation for heat Distortion and snow load criterion to determine and justify the position of the Bow roofs.

INTRODUCTION: An automobile roof is the portion of an automobile that sits above the compartment, protecting the vehicle occupants from Sun Heat, rain wind, and other external factors.

1. Reinforcements and Design

The Ditch Area is the extended portion of the main Roof concealed by other BIW panels. The rail supports of the roof are attached to the Ditch Area using Spot welds. since it is not a styling surface and remains concealed.

2. Front Roof Rail

It is the support that is joined the windshield glass. Body side outer and the inner panels. Its thickness is usually 0.75mm. The windshield end flanges are the extract offset of the roof surface. The bottom-most flanges is decided after taking into consideration the visibility criteria. Spot weld is applied at the windshield end of the other end is joined with the roof using Mastics sealants which also contributes to increases strength.

3. Rear roof rail

It is the support that is joined to the back door and the Body side outer and the inner panels. it is usually made from body side outer scrap and therefore the thickness of the rail is 0.75mm. Similar to the Front roof rail design. We have to take into consideration the rear headroom clearance and the rear visibility criteria while designing the rear roof rail from the backdoor design and also taken into consideration od the required clearance. Spot welds are applied at the back door end of the rail and the other end is joined with the roof using Mastic sealants.

4. Bow Roof Rails

Similar to the other design, we have to take into consideration of the headroom clearance and the visibility criteria while designing the centre roof rail and bow roof rail. Here spot weld is not applied for joining these rails of the roofs. Instead mastic sealants are used are introduced at both ends since centre Roofs are fully positioned under the styling surface of the roof. For increasing the strength of the rails, Embossing is done. To reduce the weight of the material used, different styling has been followed with a thickness of 0.75mm.

5. Centre Reinforcement

Assembled Images

Front View

Top View

Side View

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 refernece 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

RX value Images:

Front roof to Bow roof1 :

Bow roof 1 to Centre Reinorcement

Centre Reinorcement to Bow roof 2

Bow roof 2 to Bow roof 3

Bow roof 3 to Back roof Rail

RY value images:

Front roof to Bow roof1 :

Bow roof 1 to Centre Reinorcement

Centre Reinorcement to Bow roof 2

Bow roof 2 to Bow roof 3

Bow roof 3 to Back roof Rail

Results are as follow:

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

RX value Images:

Front roof to Bow roof1 :

Bow roof 1 to Centre Reinorcement

Centre Reinorcement to Bow roof 2

Bow roof 2 to Bow roof 3

Bow roof 3 to Back roof Rail

RY value Images

Front roof to Bow roof1

Bow roof 1 to Centre Reinorcement

Centre Reinorcement to Bow roof 2

Bow roof 2 to Bow roof 3

Bow roof 3 to Back roof Rail

To find out the geometrical moment of Inertia , we created a intersection curve and used section inertia command.

Bow roof 1:

Centre Reinforcement:

Bow Roof 2:

Bow Roof 3:

After doing the calculation, Here are the results.

According to the judgement criteria Qr ≥ 3.1

Here one result of Qr is not fulfilling, this model will pass over to the styling team to change the curvature to improve the strength.

Draft Analysis:

Draft analysis was performed with 7 degrees value.

Front Roof Rail:

Bow roof 1:

Centre Reinforcement:

Bow Roof 2:

Bow Roof 3:

Back Roof Rail:

Outer Panel:

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.

Please find attached files for your reference.