Roof challenge

Roof Design

Objective:-

To design car roof with essentials like ditch area, front roof, bow roof, reinforcements central and rear roof rail.

To perform the calculations of the heat distortion and snow load criteria determine whether the bow roofs are at the correct position.

Find the moment of inertia and draft analysis for each part.

Automobile Roof

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.

Roof Types

• Convertible roofs
• Hardtops
• Sunroofs
• T-tops
• Targa tops
• Vinyl roofs

Given Roof Reference:

Master Reference Image of Front Roof Rail Section

Master Reference Image of Rear roof rail Section

Designing of Roof with Parts

Front Roof Rail

Rear Roof Rail

Bow Roof 1

Bow Roof 2

Reinforcement Center

Roof Outer Panel

Draft analysis

In NX to check whether the sheet metal part we have designed can be deep drawn, there is an option called draft analysis. this type of analysis is performed based on colour ranges identifying zones on the analyzed elements where the deviation from the direction at any point, corresponds to specified values.

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

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]

Sr.No.	Case	Rx (mm)	Ry (mm)	R (mm)	L(mm)	t(mm)	l(mm)	W	W limit	Result
1	FB-BR1	5739.2066	2534.1423	3515.8595	1974.8537	0.75	352.3262	1.428966999	OK<2.7	Pass
2	BR1-RC	6224.7185	4965.5244	5524.2753	1974.8537	0.75	385.7865	1.913629952	OK<2.7	Pass
3	RC-BR2	4021.4090	10317.568	5787.1857	1974.8537	0.75	421.4944	2.02626486	OK<2.7	Pass
4	BR2-RB	3268.0272	14668.588	5345.1940	1974.8537	0.75	335.9170	1.810759374	OK<2.7	Pass

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)

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

Section of Inertia

Sr.No.	Rx(mm)	Ry(mm)	Lx(mm)	Ly(mm)	My(mm2)	Y(mm)	alpha	L1(mm)	L2(mm)	S(mm)	t(mm)	ly(mm4)	Qr	Qrlimit	Result
1	4536.8981	2591.4530	1113.3619	1943.1539	560490.2784	352.3262	0.6947	481.3839	467.0191	474.2015	0.75	106.2868	1.4286	Qr≥3.1	OK
2	3765.7353	6134.3549	1077.7693	1943.1539	600811.3185	385.7865	0.6978	467.0191	503.1840	485.0165	0.75	4.1640	0.0282	Qr≥3.1	NG
3	4254.3643	10808.7069	1113.3619	1943.1539	641370.958	421.4944	0.7950	502.36	491.2516	497.2178	0.75	134.9248	0.3384	Qr≥3.1	NG
4	3986.5816	16508.2869	1113.3619	1943.1539	539898.1977	335.9170	0.6692	492.0748	-	245.6258	0.75	134.9248	0.4396	Qr≥3.1	NG

Assembly Roof View

Conclusion:-

• Using the given reference styling part we have successfully designed Ditch area, Front Roof Rail, Bow Roof Rail, Reinforcement centre and Rear Roof Rail.
• And the calculation of heat distortion, snow load, draft analysis and section of inertia.