Roof challenge

Aim: - To Develop the Roof reinforcement from the given styling surface.

Here we are going to understand What Is the Roof and the uses of its Reinforcement?

About Roof

An automobile roof is a portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements. Under the styling surface that is seen on the outside, there are many other structures under the roof that contribute to its strength and stability. The number of such structures/supports differ with respect to the size of the vehicle. They are primary installed on flatter areas of the roof to enhance the strength. These are the Front Roof Rai, Rear Roof Rail, Centre Roof Rail, and Bow Roofs and they are joined to the roof by the Ditch Area.

Reinforcement

Ditch Area

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. Headroom Clearance, visibility criteria, clearance for Windshield and Back door are some of the factors to be considered while designing the Ditch Area. It is given a thickness of 0.75 mm.

Front Roof Rail

It is the support that is joined with the Wind Shield Glass, Body Side Outer, and the inner panels. It is usually made from Body Side Outer scrap and therefore the thickness of the rails 1.5 mm. A draft angle of 3-7 degrees is provided keeping in mind the deep-drawing operation. The Wind Shield end flange is the exact offset of the roof surface. The bottommost flange is decided after taking into consideration the visibility criteria and the Headroom Clearance of the passenger. Spot Welds are applied at the Wind Shield end of the rail and the other end is joined with the roof using Mastic Sealants which also contributes to increased 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 also usually made from Body Side Outer scrap and therefore the thickness of the rails 1.5 mm. 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. Inputs from the backdoor design are also taken to accommodate 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.

Centre Roof Rail and Bow Roofs

Similar to other Rails designs, we have to take into consideration the Headroom Clearance and the visibility criteria while designing the Centre Roof Rail and Bow Roofs. But unlike the Front and Rear Roof Rails, Spot Welds are not applied for joining these rails to the roof. Instead, Mastic sealants are introduced at both ends since Centre Roof Rail and Bow 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, a different styling has been followed with a thickness of 1.5 mm.

Given

Styling Surface

Tools Required

1 Surface Workbench Tools

2 part Workbench Tools

Sequence of operation

1. creating Ditch Area
2. Creating Bow Roof
3. Creating Central Bow Roof
4. Creating Central Bow Roof Reinforcement
5. Creating Front Roof Rail
6. Creating Rear Roof Rail
7. Calculating Heat Distortion criteria
8. calculating Snow load criteria
9. checking section Modulus
10. Checking Draft Analysis

1. Creating Ditch Area

By Using Sweep Command I created a ditch area for the rooftop on three sides

joined every sweep plates and Symmetry to the other side to make a full top roof with its ditch areas and thicken the surface to the value of 0.75mm(inside direction)

2. Creating Bow Roof

By Following stands and given the Master section of the Bow creation, I make a sketch and use the sweep command.

For Mastic creation I have taken sketch and extrude

By using connect lines b/w Bow and Ditch Area and Multi-section surface I create the connection.

joined every element and Symmetry to the other side to make a full Bow with its Mastic Areas and thicken the surface to the value of 1.5mm(Outside direction)

In the same manner, I created multiple Bow-2 also.

3. Creating Central Bow

I followed the same sequence which I used to create Bow's but for the central Bow, we didn't create the connection element for the central Bow because for the central Bow we add additional strength by providing the extra reinforcement to the central Bow for that reinforcement we creat connection element b/w the Ditch Area and the Reinforcement.

4. Creating Central Bow Reinforcement

5. Creating Front Roof Rail

By Following stands and given the Master section of the Front Roof Rail creation, I use the Off-set & sweep command.

For providing more strength I create Emboss to the Rail.

For Emboss I create the sketch and use extrude, split, sweep, and fill commands

After Creating all emboss I join together and symmetry to the other side for full Front Roof Rail and thicken the surface to the value of 1.5mm(Outside direction)

6. Creating Rear Roof Rail

By Using the sweep command and following the given master section I create the Rear Roof Rail

For Emboss I create the sketch and use extrude, split, sweep, and fill commands

After Creating all emboss I join together and symmetry to the other side for full Front Roof Rail and thicken the surface to the value of 1.5mm(Outside direction)

Roof with all element

7. Calculating Heat Distortion criteria

Heat Distortion temp is the temp at which the metal gets softens and deform under a specific load. this study is down to check the ability of the roof to withstand high temp with respect to the positioning of the reinforcement which contributes to increased strength.

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

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]

F.R - B.R_1

W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68

R = 2(Rx*Ry)/(Rx+Ry)

= 2(3,265.692*14,797.354)/(3,265.692+14,797.354)

= 5,350.54

(R^2)/t = 5,350.54^2/0.75

= 38,171,037.722

w = [1.73 x 10^(-3) x 2033.705] + [1.85 x 10^(-8) x 38,171,037.722] + [ 1.10x10^(-3) x 308.791] - 2.68

= 1.881mm

B.R_1 - C.R

W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68

R = 2(Rx*Ry)/(Rx+Ry)

= 2(3,992.478*10,534.659)/(3,992.478+10,534.659)

= 5790.458

(R^2)/t = 5790.458^2/0.75

= 44,705,871.799

w = [1.73 x 10^(-3) x 2033.705] + [1.85 x 10^(-8) x 44,705,871.799] + [ 1.10x10^(-3) x 309.176] - 2.68

= 2.005mm

C.R - B.R_2

W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68

R = 2(Rx*Ry)/(Rx+Ry)

= 2(4,971.948*6,199.832)/(4,971.948+6,199.832)

= 5518.411

(R^2)/t = 5518.411^2/0.75

= 40,603,813.286

w = [1.73 x 10^(-3) x 2033.705] + [1.85 x 10^(-8) x 40,603,813.286] + [ 1.10x10^(-3) x 309.005] - 2.68

= 1.929mm

B.R_2 - R.R

W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68

R = 2(Rx*Ry)/(Rx+Ry)

= 2(5,797.291*2,450.796)/(5,797.291+2,450.796)

= 3445.157

(R^2)/t = 3445.157^2/0.75

= 15,825,476.254

w = [1.73 x 10^(-3) x 2033.705] + [1.85 x 10^(-8) x 15,825,476.254] + [ 1.10x10^(-3) x 295.811] - 2.68

= 1.456mm

S.No	positioning	RX	RY	R	l	L	t	R^2/t	W	Status
1	F.R. - B.R_1	3,265.692	14,797.354	5,350.54	308.791	2,033.705	0.75	38,171,037.722	1.881	OK
2	B.R_1 - C.R	3,992.478	10,534.659	5790.458	309.176	2,033.705	0.75	44,705,871.799	2.005	OK
3	C.R - B.R_2	4,971.948	6,199.832	5518.411	309.005	2,033.705	0.75	40,603,813.286	1.929	OK
4	B.R_2 - R.R	5,797.291	2,450.796	3445.157	295.811	2,033.705	0.75	15,825,476.254	1.456	OK

Note F.R - FRONT ROOF RAIL

B.R_1 - BOW ROOF_1

C.R - CENTRAL ROOF RAIL

B.R_2 - BOW ROOF_2

R.R - REAR ROOF RAIL

8. calculating Snow load criteria

The snow load criteria study is down to check the ability of the roof to withstand the snowfall and bounce back to its original shapes without any permanent deformation once the load is removed.

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)

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 reference point of the front and the rear.

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

S.No	positioning	LY	Y	My = Y(Ly-Y)
1	F.R. - B.R_1	2,033.705	472.791	737,986.090
2	B.R_1 - C.R	2,033.705	509.226	776,304.343
3	C.R - B.R_2	2,033.705	509.117	776,193.668
4	B.R_2 - R.R	2,033.705	463.533	727,826.537

S.No	positioning	MY	LX	α = My x Lx2 x 10-12
1	F.R. - B.R_1	737,986.090	1,046.886	0.808
2	B.R_1 - C.R	776,304.343	1,061.934	0.875
3	C.R - B.R_2	776,193.668	1,090.266	0.922
4	B.R_2 - R.R	727,826.537	1,142.898	0.950

S.No	positioning	L1	L1/2	L2	L2/2	S=L1/2+L2/2
1	F.R. - B.R_1	472.791	236.395	509.226	254.613	491.008
2	B.R_1 - C.R	509.226	254.613	509.117	254.555	509.168
3	C.R - B.R_2	509.117	254.558	463.533	231.766	486.324
4	B.R_2 - R.R	463.533	231.766	-	-	-

S.No	positioning	IY	α	s	RX	RY	[(Rx + Ry)/2]2	t	Qr	Status
1	F.R. - B.R_1	7.3*10^4	0.808	491.008	3,965.851	16,683.193	106,595,754.528	0.75	97.096	OK
2	B.R_1 - C.R	3.8*10^5	0.875	509.168	4,274.277	11,025.477	58,520,618.115	0.75	819.838	OK
3	C.R - B.R_2	7.6*10^4	0.922	486.324	3,765.675	6,106.665	24,365,774.268	0.75	391.290	OK
4	B.R_2 - R.R	-	0.950	-	4,648.145	2,508.346	12,803,840.858	0.75		-

Note F.R - FRONT ROOF RAIL

B.R_1 - BOW ROOF_1

C.R - CENTRAL ROOF RAIL

B.R_2 - BOW ROOF_2

R.R - REAR ROOF RAIL

9. checking section Modulus

10. Checking Draft Analysis

Conclusion

Thus the required reinforcements and Ditch Area for the Roof were designed and developed from the given styling. The curvature study was done after performing calculations for the Heat Distortion and Snowload conditions with the position criterion met for all reinforcements.

Further, the Section Modulus study was conducted and Draft Analysis was done for each reinforcement successfully.