Roof challenge

AIM-

OBJECTIVE:

•The objective of this project is to design car roof with essential flanges and reinforcements like ditch area, front roof rail, bow roofs, central roof rail and rear roof rail for the the given styling surface

• Perform a curvature study on the roof and perform the calculations for the heat distortion and snow load criteria to determine whether the bow roofs are at the correct positions.

• Finding moment of inertia and section modulus for Bow roofs, central roof rail. front roof rail and rear roof rail

• Perform the draft analysis for each reinforcernents

SOFTWARE USED:

NX-CAD

INTRODUCTION:

Design of any product starts from an requirement. The design engineer sketches the product based on the the requirement Then the 2D sketch with the proper dimensions is converted into the 3D-model using the advanced CAD software's. The another important thing in the design is that, every product that is designed should be able to manufactured so the role of the design engineer is to design the product that can be easily manufactured and with less cost effective. This is the place where the Design for manufacturing (DFM] and Design of amb (c) takes a role while developing any product. The process of development of design caries on uni me dgn sab the customer needs

CAR ROOF:

An automobile roof or car top is the portion of an automobile tat sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements. Roof is the structure above the wind shield glass having the reinforcements to provide the strength to the overall structure and to with stand the over head forces like snow

WHY REINFORCEMENTS:

if the root is flat it is very weak and cannot able to with stand the forces like snow, so in order to increase the strength of the roof these reinforcements like front roof rail, central roof rail, rear roof rail and the bow roofs are introduced and joined to the flat surface of the roof with the different joining process

Different types of reinforcements that the car has are:

• Front roof rail
• Bow roofs
• Central roof rail and
• Rear roof rail

1.Front Roof Rail

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.

BOW ROOF1

Bow roof 1

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 thus would not affect the styling of the roof.

,,

3.Centre Roof Rail

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

BOW ROOF2

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

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 sealant

calculation

HEAT DISTORTION STUDY ON THE ROOF:

The heat distortion study plays a major role in sheet metal usage. heat distortion temperature is a temperature limit above which the material cannot be used for the structural applications. This study is used to predict the heat distortion temperature at where the material starts to soften when exposed to a fixed load at elevated temperature In order to avoid bending or damages on the roof, based on the heat distortion temperature, this study will predict the bow roof position which helps to strengthen the roof.

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

HEAT DISTORTION CRITERIA CALCULATION TABLE

S.NO.	BOW	RX	RY	R	l(mm)	L(mm)	t(mm)	R2/t(mm)	W	OK/NG
1	FR-BR-1	14312.636	3312.424	5379.785	446.4545	2117.7213	0.75	38589448.8	2.2143	ok
2	BR-1 -CR	10479.039	3988.51	5777.862	388.9132	2117.7213	0.75	44511585.7	2.244	ok
3	CR-BR-2	6252.859	4948.235	5524.570	439.360	2117.7213	0.75	40694498.3	2.206	ok
4	BR-2- RR	2855.003	5693.777	3803.0527	350.280	2117.7213	0.75	19284279.7	1.7377	ok

SNOW LOAD CRITERIA:

This test is done to know how is the roof behaving when there is a snow over. normally due to the snow weight the dent will happen. But the roof should be designed in such a way that when the snow is removal the roof should go it its original position. This is the basic requirements for snow load criteria.

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

SNOW LOAD PREDICTION CALCULATION TABLE

ROOF RAIL	IY	LX	LY	L1	L2	RX	RY	T	Y	S	α	Q	RESULT
FR	1344.4698	1085.2718	2117.7213	446.5	517	14312.636	3312.424	.75	477.1133	481.75	0.928	2.17	FAIL
CRR	2744.1508	1101.9496	2117.7213	517	434	10479.039	3988.51	.75	996.0392	475.5	1.3562	4.58	PASS
BOW ROOF2	1183.4827	1140.0695	2117.7213	434	542	6252.859	4948.235	.75	1429.0996	488	1.27	3.4	PASS

MOMENT OF INERTIA I_Y

_CALCULATION

_{BOW ROOF 1}

_{MOMENT OF INERTIA}

I_MAX -4.1239X10⁴

I_MIN -1.344X10³

CENTER BOW ROOF

MOMENT OF INERTIA -

I_MAX -5.5554X10⁴

I_MIN -2.7441X10³

BOW ROOF2

MOMENT OF INERTIA -

I_MAX -3.07955X10⁴

I_MIN -1.1834X10³

DRAFT ANALYSIS:

The Draft Analysis command enables you to detect if the part you drafted will be easily removed. This type of analysis is performed based on color ranges identifying zones on the analyzed element where the deviation from the draft direction at any point, corresponds to specified values.

Minimum draft angle of 7° is considered for analysis. green colour infer on the parts that all face along the tooling direction has positive draft angle greater than 70 and passed in analysis

FRONT ROOF RAIL

BOW ROOF1

CENTER ROOF RAIL

BOW ROOF 2

REAR ROOF

TOP VIEW

ISOMETRIC VIEW

CONCLUSION:

Hence the roof, front roof rail, bow roof rails, central roof rail and the rear roof rail is designed by following the master sections and the moment of inertia, section modulus and draft analysis are carried out to check feasibility manufacturing.