Roof Design

Objective:

1. To design the Automotive Roof based on the given styling surface and to analyze the prepared model to check the manufacturability and the feasibility of the design.
2. To perform the section modulus study for the master sections and create for the Front roof rail, Rear roof rail, Bow roofs and center roof rail.
3. To create the Ditch area and to perform the draft analysis.

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.

The roof itself may be constructed of soft or rigid material. Soft-tops are made of vinyl, canvas or other textile material; hard-top convertibles have roofs made from steel, aluminium, plastic or carbon fibre composites.Your vehicle can also become ruined in an accident. Though a defect may seem insignificant at first, it can lead to serious consequences. Whether your roof was dented due to downfall or roughed up in a collision, it is urgently necessary to find a replacement for it. The roof panel is attached to the BIW of the car with the help of front and rear roof rail. This attachment is done with the help of sealants. Bow roofs 1 & 2 are attached depending upon the length of the roof along with the central roof rail. Longer the roof, more the number of roof rail. Other dimensions like strength and material is governed by the factors like head room, overall space, visibility, ergonomics and the rules and regulations of the states where it is sold.

DESIGN CONSIDERATIONS:

1. Visibility criteria
2. Head clearance
3. Curvature study
4. Heat Distortion and Snow load criteria
5. Material thickness

   FRONT ROOF RAIL:

   It is the support that is joined with the windshield glass, body side outer and inner panels. It is usually made from bodyside outer scrap and therefore the thickness of the rail is 0.75mm. A draft angle of 3-5 degree is provided for deep drawing operation. The visibility criteria and head room clearance of the passengers are taken into consideration for the bottom most flange. Windshield end and the roof end are spot welded and the other end of the front roof rail is joined with the roof using mastic sealants for increased strength.

   BOW ROOF 1: Bow roof center 1 is an additional stiffening member used in the roof assembly for the localised strength improvement and it is join directly to roof itself with several spot welding or even with mastic sealent

BOW ROOF 2: It is similar to that of bow roof 1 which serves the same purpose as the previous but with a limited extend and hence it is used with a smaller cross.

CENTER ROOF RAIL: Center roof rail or reinforcement center is used as a cross member between bodyside left hand and right hand respectively. In some cases, the reinforcement center is not joined with the roof and in some other cases, it is made to join in both roof and bodyside. The reinforcement center and Bow roof are joined either spot weld or by mastic sealants.

REAR ROOF RAIL:

Back Door and the Rear Roof rail got attached here with the help of masting sealants.

I maintained 0.75 mm thickness for the rearof rail,Why because if we use more than 0.75 mm means there is increase in overall weight of the car leads to low performance,need more power,simply weight of the car increases.

This 0.75mm is the perfect and stardard thickness for the automotive sheet metal components.

Thickness for automotive sheetmetal components vary from 0.65 mm to 0.75 mm.

It is the support that is joined to the backdoor, the bodyside outer and the inner panels. Inputs from the backdoor design is also taken to accommodate the required clearance along with headroom clearance and rear visibility criteria while designing the rear roof rail. Spot welds are applied at the backdoor end of the rail and other end is joined with the roof.

DRAFT ANALYSIS:

Draft analysis is a method of checking the draft angle on various faces of a part with a particular direction.

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

HEAT DISTORTION CURVATURE STUDY:

Curvature study on the roof:

Bow – roof prediction Formula is given as

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

Where

L = Roof Length in X – Direction (mm) (Roof dimension in o-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)

Judgement condition: ok < 2.7mm < NG

AS per calulation value comes below 2.7 so judgement should be ok.

SNOW LOAD CRITERIA:

case	IY	A	L1	L2	LX	LY	Y	S	RX	RY	RX+RY	RX+RY/2	T	QR
1( F ToB1)	1872	1.064386	614.96	365.771	1131.9	1965.9	614.96	490.3655	4269.31	3027.26	7296.57	3648.285	0.75	3.39
2( B1 to Center)	2250	3.734037	365.77	569.49	1087.78	1965.9	978.97	467.63	3800.17	6686.78	10486.95	5243.475	0.75	3.27
3 ( Centre to 2)	1870	0.80809	509.49	485.9435	1064.3	1965.9	1485.735	497.7168	4274.54	11076.18	15350.72	7675.36	0.75	4.439401

As the al cultion all value should be greater than 3.01, so judgment will be oK ( This roof will with stand the snow Load)