Roof challenge

Aim -

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

Report

Draft Analysis: Draft analysis is a method of checking the draft angle on various faces of a part in a particular direction. it should be more than 7 degrees. draft analyzing command which lets you know if your model or design has a draft angle in a given tool direction.

If the part lies within the conditions it shows in green colour if not shown in blue or red colour.

Roof Design

Given surface is A-class and we have to design Roof surface with the help of this A-class and the help of master section which is shown below:

There is two master section for the front end Rail roof and the next one is for the rear rail roof section :

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.

Thus following the above master section the design is done which is shown below along with the draft analysis done on the roof

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.

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.

The design of the rear roof rail and the draft analysis is shown below

Bow Roof Rails (1 and 2)

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.

The design of the Bow roof and the draft analysis is shown below

Reinforcement centre rail

It is the main supporting rod for the roof. Their purpose is to provide an attachment point for crossbars and other devices designed to secure loads carried on the roof of the vehicle, it absorbs energy at the time of the crash. Its thickness is 1mm.

The design of the Centre Bow roof and the draft analysis is shown below

Analysis

1. CURVATURE STUDY:

It is done to justify the positioning of the bow roofs. There are mainly two criteria to fulfil

• Heat distortion criteria
• Snow load criteria

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

So after intersecting points on the line, we create 4points and project them on the roof surface then join these points by using the spline option.

The horizontal line is Rx and the vertical line is our Ry.

Calculations are done and tabulated in the table as given below:

Heat Distortion Criteria
S.No	Bow	Rx (mm)	Ry (mm)	R (mm)	l (mm)	L (mm)	t (mm)	R^2/t	W (mm)	Status
1	FR & 1st	5741.21	2435.06	3419.698915	353	2022.8501	0.75	15592454.22	1.496291076	ok
2	1 st & CR	4896.36	6502.57	5586.300406	579	2022.8501	0.75	41609002.97	2.226197228	ok
3	CR & 2nd	3951.98	10711.53	5773.754351	282	2022.8501	0.75	44448319.07	1.952024576	ok
4	2nd & RR	3332.72	14244.77	5401.661998	421	2022.8501	0.75	38903936.45	2.002353497	ok

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

for calculation of snow load We have to calculate the moment of inerrtia of the Front roof Rail, Rear Roof Rail, Bow Roof 1, Bow Roof 2 and Centre Bow roof and the data is given below as show in images

Front roof Rail

Rear Roof Rail

Bow Roof 1, Bow Roof 2

Centre Bow roof

The values are calculated and the result is attached below

Snow Load Condition
S.No	Bow	Iy (mm^4)	Alpha	My	Lx (mm)	Ly (mm)	Y (mm)	L1(mm)	L2(mm)	s (mm)	Rx (mm)	Ry (mm)	t (mm)	Qr	Status
1	FR & 1st	7.50E+03	0.681427993	681427.9927	1000	2022.8501	427	427	638	532.5	2502.4	4601.19	0.75	92.11211182	ok
2	1 st & CR	517	1.020002207	1020002.207	1000	2022.8501	1066	638	341	489.5	6424.01	3781.63	0.75	2.236859799	NG
3	CR & 2nd	562.79	0.832187648	866501.0907	980	2022.8501	1407	341	535	438	11241.99	4286.92	0.75	1.440627062	NG
4	2nd & RR	558.59	0.160801765	157010.8942	1012	2022.8501	1942	535	NA		15915	4085.2	0.75		Null

Conclusioin

As the Qr is not satisfying the values we need so we need to make changes in the design to rectify the above problem

To improve the Qr we need to overall increase the cross section area of the Bow roof which will be done by

• Providing the Emboss on the Bow roof to increase the cross sectional area
• Increase the depth of the bow roof
• Increasing the overall width of the bow roof
• Adjusting the position of the bow roof
• By providing the Emboss on the outer pannel

In my design I increase the depth and overall width of the bow roof to improve the value of the moment of inertia and the results are show below

By changing the value of MOI from 500 to 1600 the Qr will change and the result is show below

Snow Load Condition
S.No	Bow	Iy (mm^4)	Alpha	My	Lx (mm)	Ly (mm)	Y (mm)	L1(mm)	L2(mm)	s (mm)	Rx (mm)	Ry (mm)	t (mm)	Qr	Status
2	1 st & CR	1600	1.020002207	1020002.207	1000	2022.8501	1066	638	341	489.5	6424.01	3781.63	0.75	6.922583517	OK

So it was proved that the cross section of the roof will play a major roll

Please find the attached assembly file of the Roof Design for your review