Roof challenge

Challenge:

For the Given Roof styling, Develop the essential flanges and reinforcements, provide appropriate dimensions and check for Draft analysis, and submit your Section Inertia report on the 0-Y section.

Start with the creation of a roof ditch area the tool opening angle is only 3 degrees.

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

Tool: Sieman's nx Cad

Objective:

• Develop a roof with the styling surface which is provided by styling team with essential flanges and front and rear roof rails and bow roofs.
• Then do a calculation of heat distortion and snow load on roof as well as do a draft analysis.

• And do a section modulus on each of components of roof.

What is 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. Because the earliest automobiles were designed in an era of horse-drawn carriages early automobile roofs used similar materials and designs.

What are types of roofs in modern automotive world:

In later years, many variations on the automobile roof developed. These include:

• Convertible roofs:

• Hardtops

• Sunroofs

• T-tops

• Targa tops

• Vinyl roofs

Design considerations:

• Visibility criteria

• Head room criteria
• Heat distortion and snow load
• Material thickness

Material properties:

Material: Steel

Thickness:0.75mm

Draft angle for steel 7 degrees (minimum)

Required process to join is spot welding

What is roof crush analysis:

One of the tests used in occupant safety analysis is a roof crush test. It is used to evaluate how a car will deform during a rollover accident. A safer car does not deform as much providing the occupant a larger survival space during this kind of accident. In this test, a plate shaped impactor is pushed down on one side of the roof at constant (slow, quasi-static) speed. This load case challenges the solver because of large deformations, complex contact situations as well as local buckling. This model was computed successfully with the LS-DYNA R9.0.1 MPP implicit solver including dynamic effects. Last but not least, we want to acknowledge the CCSA for the baseline model.

Components of roof:

Front roof rail:

Front roof rail is one of the parts which joining the roof outer and wind shield then the inner panel as well and we need to consider the head room clearance of driver and visibility of driver and notably this one’s manufacturing from body side outer scrap materials, it's where all the other features such as irvm and reading lamp, sun glass holder going to get mounted.

Master section of front roof rail:

Bow roof 1:

Bow roof is one of component that providing the additional support to the roof typically we use the bow roofs as I meant before and the number of itself can be varied each of vehicle's respect to the length of roof of itself.

Center reinforcement:

As we’d looked at bow roof 1 this one is also giving extra support for the roof and center roof rail there’s a reason behind adding this, we can only see this at sunroof variants since in order to create a sunroof we’ll have to reduce the material on that particular region so that’s why we’re providing reinforcement on center roof rail by spot welding or mastics.

Center roof rail:

This one’s also a known as one of the stiffening components but not only like so it does can be also a cross member of both side of the vehicle this is also joined at both ends of body side by either spot welding or mastics.

Master section of center roof rail and reinforcements:

Bow roof 2:

This one’s also providing the support to the roof same as bow roof one and whatever I've mentioned about the bow roof 1 that everything will similar to the bow roof 2 Aswell.

Master section of the bow roof 1 and 2:

Rear roof rail:

Rear roof rail is the part which joining the back door and roof as together and inner panel as well then, I've gave some embosses to make this component as stronger.

Heat distortion calculation:

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]

In this case I am going to left the points between front roof rail and bow roof 1 because I've got the sunroof over there so, let’s do study between the other points, so that let’s begin the calculation from bow roof 1 and center roof rail.

Position no 1:

Bow roof 1 and center roof rail

Rx = 4467.95mm

Ry= 7368.15mm

L= 2033.73mm

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

Hence, R= 5563.178mm

I=359.8mm

R^2/t= 41265265.95mm

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

“W= 1.99”

Position no 2: center roof rail and bow roof 2

Rx = 49855.66mm

Ry= 2902.09mm

L= 2033.73mm

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

Hence, R= 5484.904

I=370.2mm

R^2/t= 40112229.19mm

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

“W= 1.98”

Position no 3: Bow roof 2and rear roof rail

Rx = 3380.48mm

Ry=3186.74mm

L= 2033.73mm

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

Hence, R= 3280.752mm

I =345.7mm

R^2/t= 14351111.58mm

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

“W= 1.48”

POSITION OF BOWS:	Rx(mm)	Ry(mm)	R(mm)	I(mm)	L(mm)	R^2/t(mm)	T(mm)	W	OK/NG
BRR1 AND CRR	4467.95	7368.15	5563.178	359.8	2033.73	41265265.95	0.75	1.99	OK
CRR AND BRR2	49855.66	2902.09	5484.904	370.2	2033.73	40112229.19	0.75	1.98	OK
BRR2 AND RRR	3380.48	3186.74	3280.752	345.7	2033.73	14351111.58	0.75	1.48	OK

Snow load criteria:

Snow load Prediction formula

Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]

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

Position no 1:

Front roof rail and bow roof 1

Rx= 4094.74mm

Ry= 3299.25mm

Lx = 1123.6mm

Ly = 2033.73 mm

Y= 567.92 mm

Iy= -

S = 645mm

My = 832462.81

α = My x Lx2 x 10-12 so, α = 1.05

t = 0.75 mm

Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]

Qr = -

Position no 2:

bow roof 1 and center roof rail

Rx= 3851.04mm

Ry= 5700.65mm

Lx = 1079.46 mm

Ly = 2033.73 mm

Y= 432.8 mm

Iy= 8700.68 mm^4

S = 433.5mm

My = 692882.504

α = My x Lx2 x 10-12 so, α = 0.80

t = 0.75 mm

Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]

Qr= 61.872

Position no 3:

Center roof rail and bow roof 2

Rx= 2521.83mm

Ry= 4113.36mm

Lx = 1058.6 mm

Ly = 2033.73 mm

Y= 448.9 mm

Iy= 6072.42 mm^4

S = 450 mm

My = 711430.18

α = My x Lx2 x 10-12 so, α = 0.79

t = 0.75 mm

Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]

Qr= 87.296

Position no 4:

Bow roof 2 and rear roof rail

Rx= 3915.97mm

Ry= 16810.37 mm

Lx = 1046.2mm

Ly = 2033.73 mm

Y= 370.3mm

Iy= -

S = -

My = 615968.12

α = My x Lx2 x 10-12 so, α = 0.67

t = 0.75 mm

Qr= -

POSITOIN OF THE BOWS:	Rx(mm)	Ry(mm)	Lx(mm)	Ly(mm)	Y(mm)	Iy(mm^4)	S(mm)	My	α t(mm) Qr OK/NG
BRR 1 AND CRR	3851.04	5700.65	1079.46	2033.73	432.8	8700.68	433.5	692882.504	0.80 0.75 61.872 OK
CRR AND BRR 2	2521.83	4113.36	1058.6	2033.73	448.9	6072.42	450	711430.18	0.79 0.75 87.296 OK
BRR2 AND RRR	3915.97	16810.37	1046.2	2033.73	370.3	-	-	615968.12	0.67 0.75 - NEGLIGIBLE

Geometric moment of inertia:

Bow roof: 1

Center roof rail:

Bow roof 2:

Draft analysis:

Front roof rail:

Bow roof 1:

Bow roof 2:

Center reinforcement:

Center roof rail:

Rear roof rail:

So, in this case I've take the couple of tooling directions from the top and from the side of itself because in this case we have some complicated design of embosses we can’t create it by single tool in single operation so I’ve separated the parts as two and give them couple of tools to get this produced, mostly we will look how to reduce the number of tool and tooling direction for save time and cost but in some cases we’d better have multiple tools and the tooling directions as well for quality reasons.

Assembled views of my roof:

CONCLUSSION:

I've designed my roof with required flanges and as per the requirements of oem as well then roof is not as what we are seeing from out side by working on this assignment i've learnt plenty of things about design the roof.