Roof challenge
Roof Challenge
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 compositesYour
vehicle can also become ruined in an occident. 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 ore 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
Material Properties:
Density : 7890 kgim3
Young's modulus : 210000Mpa
Poisson's ration : 0.3
Yield stress : 210 Mpa
Metal Roof Mass :11.2kgs
Thickness : 0.75mrn
Joining process : Metal roof with spotweld connections.
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 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.
MASTIC POINTS:
Why Automotive uses MASTIC SEALANTS?
Engineers are constantly faced with the challenges of sealing assemblies against air, dust, noise, and making sure
that these assemblies do not squeak and I or rattle.
Sealants are materials that are for one time use only. Meaning, 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
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:
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 elevated temperature.
In order to avoid bending or damages on 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:
Bow - roof prediction Formula is given as
W=1.73x10A-3 x L+1.85x10A-8 x (RA2)it +1.10x10A-3 x I- 2.68
Where
L = Roof Length in X - Direction (mm) (Roof dimension in 0-Y)
R = Roof curvature
R = 2(Rx Ry) J (Rx + Ry)
Rx = X curvature
Ry = ' curvature
t = Roof plate thickness (mm)
I = Bow Roof Span (mm)
Judgement condition: ok < 2.7mm < Ne
S.No Positions Rx Ry R I (mm) L (mm) t (mm) R^2/t W OK/NG
1 FRR & BR1 3566.25mm 3997.85mm 3769.73mm 380mm 2065.14mm 0.75mm 27316039 1.19 OK
2 BW1 & CRR 4186.16mm 4569.40mm 4369.42mm 330mm 2065.14mm 0.75 25455774 1.65 OK
3 CRR & BR2 3987.72mm 3790.30mm 3886.50mm 351mm 2065.14mm 0.75 20139843 1.95 OK
4 BR2 & RRF 3397.52mm 3182.42mm 3286.45mm 359mm 2065.14mm 0.75 14401004 1.84 OK
For considering above calculations our design is safe according to heat distortion criteria for Bow Roof
