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, aluminum, plastic, or carbon fiber 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 the front and rear roof rails. 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. The longer the roof, the more the number of roof rails. Other dimensions like strength and material are governed by the factors like headroom, 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

 ASSEMBLY COMPONENTS OF ROOF:

MASTER SECTION OF FRONT ROOF RAIL:

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 degrees is provided for deep drawing operation. The visibility criteria and headroom clearance of the passengers are taken into consideration for the bottom-most flange. The windshield end and the roof ends are spots 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 localized strength improvement and it is joined directly to the roof itself with several spot welding or even with mastic sealant.

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

MASTIC POINTS:

Why does Automotive use MASTIC SEALANTS?

Engineers are constantly faced with the challenges of sealing assemblies against air, dust, and noise and making sure that these assemblies do not squeak and/or rattle.

Sealants are materials that are for one-time use only. This means, that the whole assembly is replaced or the particular area that needs to be sealed will not be taken apart and put back together as part of its requirements.

Prevents excessive absorption of adhesive or penetration of liquid or gaseous substances.

• Reduction of Direct Labor Costs
• 
  Reduction of Indirect Costs/Inventory Management
• 
  Reduction of Scrap Materials
• 
  Material Cost Reduction
• 
  Ease of Accommodation of Engineering Changes

CENTER ROOF RAIL: Center roof rail or reinforcement center is used as a cross member between the 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 the 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 rear of the rail, Why because if we use more than 0.75 mm means there is an increase in the overall weight of the car leads to low performance, need for more power, and simply weight of the car increases.

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

Thickness for automotive sheet metal components varies 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 are 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 another end is joined with the roof.

I provided Some embosses for the extra strength for the front roof rail. We give embosses for the strength of the component.

DITCH AREA: It is the extended portion of the main roof concealed by other BIW panels and not a styling surface. Headroom clearance, visibility criteria, and clearance for the windshield and back door are some of the factors to be considered while designing the ditch area.

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.

FRONT ROOF RAIL:

BOW ROOF 1:

BOW ROOF 2:

CENTER ROOF RAIL:

REAR ROOF RAIL:

HEAT DISTORTION CURVATURE STUDY:

The heat distortion study plays an important role in sheet metal usage. Heat distortion temperature is a temperature limit above which the material cannot be used for 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 an elevated temperature. To avoid bending or damage to the roof, based on heat distortion temperature, this study will predict the bow roof position on the roof to strengthen the roof. 

Curvature study on the roof:

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

First created a sketch with the required lines, Then made intersection points.

Projected the points on the surface then created 3-point arcs.

Find the Rx and Ry values.

HEAT DISTORTION CRITERIA
S NO	BOWS	Rx mm	Ry mm	R mm	t mm	I mm	1.10*10^-3	I*(1.10*10^-3)	1.73*10^-3	L mm	(1.73*10^-3)*L	1.85*10^-8	(R^2)/t mm		W	OK/NG
1	FR-BR-1	2824.14	5716.1	0.001058	0.75	475.69	0.0011	0.523259	0.00173	1927.36	3.3343328	1.85E-08	1.49268E-06	2.76146E-14	1.1775918	OK
2	BR-1 -CR	6557.37	4881.64	0.000715	0.75	334.51	0.0011	0.367961	0.00173	1927.36	3.3343328	1.85E-08	6.81059E-07	1.25996E-14	1.0222938	OK
3	CR-BR-2	10739.81	3945.47	0.000693	0.75	465.9	0.0011	0.51249	0.00173	1927.36	3.3343328	1.85E-08	6.40579E-07	1.18507E-14	1.1668228	OK
4	BR-2 -RR	14708.09	3261.03	0.000749	0.75	430.1	0.0011	0.47311	0.00173	1927.36	3.3343328	1.85E-08	7.48566E-07	1.38485E-14	1.1274428	OK

SNOW LOAD CRITERIA:

S NO	BOWS	Rx	Ry	Rx+Ry	Lx	Ly	Y	Iy	L1	L2	S	My	ALPHA	t	Iy*t^2	Alpha*S	(Rx+RY/2)^2	Q1*R1*10^-8	Qr	OK/NG
1	FR-BR-1	2853.63	4365.98	7219.61	1133.53	1816.79	559.97	1627	559.97	413.67	486.82	703781.5	0.904282	0.75	915.1875	440.2226	13030692.1	57.36404626	15.95403	OK
2	BR-1 -CR	6497.77	3786.56	10284.33	1085.63	1816.79	413.67	2295	413.67	545.51	479.59	580428.7	0.684089	0.75	1290.938	328.0822	26441860.9	86.7510317	14.88095	OK
3	CR-BR-2	11277.37	4288.57	15565.94	1060.57	1816.79	545.51	1637	545.51	345.14	445.325	693496	0.78005	0.75	920.8125	347.3759	60574622	210.4216379	4.376035	OK

Moment of Inertia (Iy):

FRONT ROOF RAIL :

BOW ROOF 1 :

CENTER ROOF RAIL :

BOW ROOF 2 :

REAR ROOF RAIL :

Views

CONCLUSION

The automotive roof is designed and the curvature study is done on the outer panel of the roof.