Design the Automotive Car Roof and its Enforcement.

Aim - Design the automotive car roof and its enforcements as seperate parts.

Objectives -

• Design a roof, front roof rail, rear roof rail, bow roofs and center center roof rail.
• Perform draft analysis on each parts
• Perform snow load heat conditions on roof.

Methodology -

We get the model of the roof of the from the styling team. Then we will have to do all the engineering work. We create the ditch area for the roof and also the roof bows and roof rails for the roof which would we designed by us considering all the safety norms and regulations.

Given class A surface of roof -

Components of Roof -

1.Front Roof Rail -

Master Section -

Final Part -

The front roof rail is located on the front of the roof where the wind shield joins with the roof. The visibility criteria and the head room clearance of the passenger are taken into consideration for the bottom flange. One end of the rail is joined using spot welding while the other end is joined with the roof using mastic sealants for increased strength.

2. Bow Rail 1 -

Master Section -

Final Part -

Bow roof is an additional siffening member for the roof to increase the strength and so that it can satisfy the norms. Both the ends are joined together using mastic sealants to increase strenght and also since this would not affect the styling of the roof.

3. Center Roof Rail -

Master Section -

Final Part -

Centre Roof rail or the reinforcement centre is located at the centre of the roof . The cross section of this is more since it needs to provide more strength to the roof. Here both are ends are joined together using mastic sealants.

4. Bow Roof 2 -

Master Section -

Final Part

This bow roof also have the same purpose as that of the first one. This one is located between the centre bow roof and rear roof rail.

5. Rear Roof Rail -

Master Section -

Final Part

This roof rail joins with the back door and the roof. Inputs from the backdoor are taken into consideration for designing this roof rail. Here one end is joined using spot welding while the other end is joined using mastic sealants.

Performing draft analysis -

1.Rear Roof Rail -

Rear roof rail satisfies 7 degree positive draft angle.

2.Front roof rail -

Rear roof rail unsatisfies positive draft angle and goes into 0 to 7 negative draft

3. Center roof rail -

Center roof rail satisfies the 7 degreee positive draft angle

Bow roof 1

Bow roof shows positive draft but not satisfies with minimum 7 degree draft angle.

Bow roof 2 -

Bow roof shows positive draft but at one edge it does meet the minimum draft angle criteria

5.Roof Top -

Now roof top shows positive draft on upper side but negatve draft on backside. This portion of sheet goes inside so it shows negative draft. Its curvature depend on the backdoor so its negative draft is accepted.

Heat distortion calculation -

Bow- Roof prediction Formula:

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

Judgment Condition: OK<2.7

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]

Procedure to measure Rx & Ry:

• Consider a plane above the roof at the some distance & enter the sketch workbench.
• Draw a line at -3Y at -300mm from O-Y axisis and Offset it to 100mm on Both Side of -3Y lines.
• Draw Vertical lines between every two adjacent roof rails. Make these lines as reference line

• Create Points at the intersection of the lines as Shown. Then project these points on the Roof Surface and Using 3 Point Arc to draw to measure the Radius.

Snow Load Prediction -

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

Procedure to measure Rx & Ry:

• Consider a Plane above the Roof at some distance & enter the sketch Workbench.
• Draw a line at OY and offset it to 100mm on both side of 0-y line.
• Draw Vertical lines between every two adjacent roof rails. Make these line as reference line.

• Create points at the intersection of the lines as shown. Then Project these points on the Roof Surface and using Arc Option 3-Point draw the Arc and Measure Radius.

Calculation Of Moment Of Inertia Of 3 Section Respectively

Center roof rail

For bow roof 2

For bow roof 1

As We can See from the above colum that Qr>3.1, So the results are satisfied which means the Roof won't enter the Plastic state

Final Model -