Roof Design

INTRODUCTION

The roof of a car or other vehicle is the top part of it, which protects passengers or goods from the weather. The roof also protects the passenger from any injury when the car gets crashed or is rolled over or something heavy falls on the roof.

OBJECTIVE:

1.Main objective of the project is to create the Roof Sheetmetal design in NX cad, and also designing Front roof rail, rear roof rail, bow roof front, bow roof rear, center roof rail and Reinforcement are creating to build the strong roof.

2.Do curvature study on Roof and performance calculations for Heat distortion and Snow load criteria to determine the position of the Bow roofs.

3.Finding the moment of inertia and section modulus for Bow-roofs and center roof rail.

4.And, also finding the Draft Analysis of each part.

INTRODUCTION:

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. When it is seeing from outside of the car, it is just closing the top portion. But in design point of view, it is hard to create the design. Because of you have to create no of support rails for enough strength to withstand the load. Bow roofs are primarily fixed in flatter region to enhance strength. Front roof and rear roof rails are fixed to the ditch area using spot weld operation. But front, rear bow roof and center roof rails are fixed to roof using mastic sealants. We don’t want so much gap between roof rails and bow roof area. So, we reducing the NVH issues.

DESIGN CONSIDERATION

1. Visibility criteria

2. Head clearance

3. Curvature study

4. Hear distortion and snow load criteria

5. Draft analysis.

Components of roof

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 ROOF 1 and 2:--

The bow roofs are give to improve the torsional stiffness and load bearing capacity of the roof structure . The number of bow roof present is depends on the overall size of the roof . Presently in this project two bow roofs are added.

• CENTER ROOF

Central roof rail helps in providing effectively support to the flat area of the roof as it is more susceptible to failure under the action of load . generally central roof rail is placed at the center of the roof which is connected to the B-pillar support structure.This central roof rail helps in adding the strength to the roof during the rool- over test.

REAR ROOF RAIL :

Rear roof rail is the one which joins the back door and the body side outer

DRAFT ANALYSIS

FRONT ROOF

BOW ROOF 1

BOW ROOF 2

OUTER PANEL

Calculating the Heat Distortion criteria:--

• To calculate the Heat distortion criteria, we have to take a note of few values and note it down.
• To note down the values, first, we need to create a sketch.
• Create a line at the center of the roof part in the 0-Y axis and then draw another line with a distance of 300mm to the O-Y line.
• Now create lines at a distance of 100mm on both sides to the 300mm line.
• Create a new sketch in which we need to Project the Roof Rails curves lines between the bow roofs and rails coming at the Edge. These lines need to be created in X-direction.
• Using these Edge line create lines at a distance of 100mm on both sides.
• Now To find Rx and Ry we have to take the intersection points and meassure them
• so project the points on the surface and use Arc/Circle Command to meassure the curvature
• Now since we got all the values for calculating the Heat Distortion, substitute these values to the below equation.

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

Bow position	Rx	Ry	R	l	L	T	R2/2	W	OK/NG
FR and 1st	5687.43	2854.31	3674.63	335.41	2020.02	0.75	6751452.81	1.579	OK
1st and CTR	4867.53	6611.71	5521.14	428.29	2020.02	0.75	15241493.44	1.567	OK
CTR and 2nd	3977.89	10724.13	5871.67	429.34	2020.02	0.75	17238254.29	1.605	OK
2nd and RR	3317.65	14723.54	5438.68	316.98	2020.02	0.75	14789620.07	1.436	OK

SNOW LOAD:

Snow load criteria study is used to check the durability of the roof to withstand the snow fall on the roof and reflex it is original shape without any permanent deformation after load being removed.

SNOW LOAD CRITERIA:

Qr = [IY x t2] / [α x s x [(RX + RY)/2]2 x 10-8]

Where,

α = My x LX2 x10-12, 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 rails 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],

With of the roof panel exposed on the surface.

Y = Distance between Front roof rails 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 [mm4],

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[mm4],

Roof panel X curvature radius of length s in side view.

Roof Rails	Iy(mm)	Lx(mm)	Ly(mm)	L1(mm)	L2(mm)	Rx(mm)	Ry(mm)	t(mm)	Y(mm)	S	My	α	Qr	Result
FR-BOW_1	734.94	1179.33	2032.02	413.76	463.64	4343.02	2588.83	0.75	413.076	438.706	669571.25	0.69814	6.67130	OK
BOW_1-CR	1035.86	1132.02	2032.02	463.64	464.73	3578.18	6018.92	0.75	463.64	463.54	718894.74	0.75402	4.97254	OK
CR-BOW_2	756.25	1102.82	2032.02	464.73	440.82	4270.64	11015.21	0.75	464.73	458.72	748052.11	0.79274	1.58848	NG

CONCLUSION

I was successfully able to design the roof with all the roof rails for better support and strength and designed it so as to satisfy the norms and regulations by calculating the heat distortion criteria and the snow load critera. While doing this i was also able to understand about the methodology behind designing the roof of the car and what all we take into consideration while designing so.