Roof challenge

Automobile roof design using NX 12 and optimization by calculation HEAT DISTORTION CRITERION, SNOW LOAD CRITERIA,SECTION MODULUS ANALYSIS AND DRAFT ANALYSIS

OBJECTIVE :- The main objective of this project are

• To develop the necessary flanges and reinforcement from the styling A surface.
• Check for the draft analysis in 0-Y direction
• To do a curvature study on the roof and performe calculation to determine the position of the bow-roof.

INPUT:-

FRONT ROOF RAIL MASTERSECTION

REAR ROOF RAIL MASTERSECTION

ROOF:- An automobile is a close body and must have a protection on top which is know as roof of the vehicle to keep the passengers safe from the outside elements like weather, dust, flying objects , stone chips etc for a comfortable and hassel free journey. It also protects froms rollover and a sudden impact on roof.

• Roof is not a single component it consist of different assyembly which are having various parts .
• It consists of an outer pannel , Front roof rail, Bow roof rail, Centre roof rail with reinforcement and Rear roof rail. To provide a better strength to the roof and safety to passengers inside.
• For better strength to the roof outer pannel embosses are provided to the outer pannel which enhance the aesthetic appearance as well as the strength in flat roofs like in SUVs.4

COMPONENTS OF ROOF

1. FRONT ROOF RAIL
2. BOW RAOOF RAIL 1
3. CENTER ROOF RAIL
4. CENTER REINFORCEMENT
5. BOW ROOF RAIL 2
6. REAR ROOF RAIL

FRONT ROOF RAIL :- It is the part which joins the windscreen glass to the outer body pannel, It is made from front scrap point of the roof outer and has the thickness of 0.75mm and a minimum draft of 5 degrees for deep drawing. The design also consider the upper vision point of the driver.

BOW ROOF RAIL :- These are the reinforcement which helps the roof to provide strength.These provide extra support to center bow roof and rear roof rails, these roof rails numbers depends on class vehicle. Some vehicles do not have bow roof rails it all depends on the design of the roof. Bow roof rails and roof outers are joinned with mastics because spot welding is not possible at the styling surface.

BR 1

BR 2

CENTER ROOF RAIL:- Center roof rail is placed in the between of the roof, in some cases a additional roof rail is also added to support the CRR, but this also depends on the structure of the roof and class of the vehicle.CR is joinned with the mastics to the roof as spot welding is not possible because it will pop on the styling surface of the roof.

REAR ROOF RAIL :-It is the rear most part and it attach the backdoor with the body of the outer pannel. Input of the backdoor is also taken in account to increase the headroom of the rear passengers and the view of the irvm is also considered. To attach backdoor with the rear roof rail spot welding is done and rear roof rail with the roof outer is joined with mastics.

CALCULATION TO DETERMINE BOW ROOF POSITION:-

Heat distorition criteria

Heat distortion temperature is the criteria in which the metal becames soft and deforms under specific load.The study is done to check the ability of roof to windstand high temperature with respect to the position of the reinforcement.

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> NG

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]

BOW	Rx	Ry	R	l	L	t	R^2/t	W	OK/NG
FR&BR1	4702.6	2661.7	3399.3	473.9	1989.8	0.75	15406987	1.57	OK
BR1&CR	4899	6319.3	5519	320.7	1989.8	0.75	40612481	1.86	OK
CR&BR2	4149	9235.7	5725.7	348.7	1989.8	0.75	43711520	1.95	OK
BR2&RR	3431.2	12409	5375.9	476.2	1989.8	0.75	38533734	1.99	OK

Snow Load Criteria

Snow load criteria is the study of the roof to check the ability to withstand the snow and retain its original position when the load is removed before going in permanent deformation.

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 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

Section Modulus Study

Front roof rail

Bow roof rail

Bow roof rail 2

Center roof rail

Reinforcement center

Rear roof rail

Draft Analysis

Front roof rail

Bow roof rail

Center roof rail and reinforcement

Rear roof rail

CONCLUSION

The design and analysis of automoblie roof and its component with heat distorition and snow load is done sucessfully