Roof challenge

ROOF DESIGN:

OBJECTIVE:

• The objective of this project is to design car roof with essential flanges and reinforcements like ditch area , front roof rail, bow roofs, central roof rail and rear roof rail for the given styling surface.
• Perform a curvature study on the roof and perform the calculations for the heat distortion and snow load criteria to determine whether the bow roofs are at the correct positions.
• Finding moment of inertia and section modulus for bow roofs , central roof rail, front roof rail and rear roof rail.
• Perform the draft analysis for each reinforcement.

SOFTWARE USED:

NX-CAD

INTRODUCTION:

Design the product starts from an requirement . The design engineer sketches the product based on the requirement. Then the 2D sketch with the proper dimensions is converted into the 3D model using the advanced CAD softwares . The another important thing in the design is that every product that is designed should be able to manufactured .  

CAR ROOF:

• An automobile roof 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.
• Roof is the structure above the wind shield glass having the reinforcement to provide the strength to the overall structure and to with stand the over head forces like snow.

Why Reinforcements:

• If the roof is flat it is very weak and cannot be able to withstand the forces like snow. so in order to increase the strength of the roof these reinforcements like front roof rail, central roof rail, rear roof rail and the bow roofs are introduced and joined to the flat surfaces of the roof with the differenr joining process.

Different types of reinforcement used in this design:

• Front roof rail
• Bow roofs
• Central roof rail
• Rear roof rail

FRONT ROOF RAIL:

Front roof rail rail is one which joins the wind shield glass , body side outer and the inner panel. Here the front roof rail is designed based upon the master section.

Master section of front roof rail:

 

Design of Front roof rail

Rear Roof Rail:

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

Master section of Rear roof rail:

Design of Rear roof rail

Central Roof Rail:

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 centre of the roof which is connected to B-pillar support structure. This roof rail helps in adding the strength to the roof during the rool over test. 

Master Section of centre Roof:

Design of Centre roof:

Bow Roofs:

The bow roofs are given 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.

Master Section of Bow Roof:

Design of

Bow roof 1

Design of Bow Roof 2

Joining Process :

Mastics are introduced between the roof outer panel and the reinforcements for joining , whereever the mastic are introduced there is remarkable improve of the strength. 

Spot welding is also used to join the reinforcements and the outer panel.

Roof Crush Test:

• Roof crush test is the design given by the IIHS (insurance institute of highway safety). After analysing the many accidents IIHS has then fixed some regulations.

Goal of Roof Crush Test:

To minimze the protrusion into the occupant compartment, so that the seat belts and air bags can do there job in protecting the occupant

Conditions to follow for Roof Crush Test:

Initial Condition:

• Close and lock all the doors
• Close all the windows

Second Condition:

• Fix the body sill or chasis frame on a hard lever surface horizontally.

Method of Applying The Force:

The load is applied in such a way that 5degree is tilted from the front end to the rear end and the load will be in 1800mm in length and 750mm in width.The load is applied at the position of 25degree from the flatness of the roof. The load is applied on the roof for almost 120sec and the crush speed at which the load applied is 13mm/sec or less than that,

HEAT DISTORTION:

Bow roof Prediction Formula:

W = [1.73*10^(-3)*L]+[1.85*10^(-8)*(R^2)/t]+[1.10*10^(-3)*1]-2.68

Where 

L = Roof length in X- direction 

R = Roof curvature 

   R = 2(Rx*Ry)/(Rx+Ry)

Rx = X curvature

Ry = Y curvature

t = Roof plate thickness

l = Bow roof span

JUdgement Condition : OK<2.7>3.1

Calculations:

Snow Load Criteria:

This test is done to know how is the roof behaving when there is snow over , normally due to the snow weight the dent will happen. Bit the roof should be designed in such a way that when the snow is removal the roof should go to its original position.

calculations:

DRAFT ANALYSIS :

Front roof Rail:

Rear Roof Rail:

Centre Roof Rail:

Bow Roof 1:

Bow Roof 2:

Images of the Design :

CONCLUSION:

Hence the roof front roof rail, bow roofs, rear roof rail, centre roof rail is designed by following the given master sections and draft analysis and the calculations of the roof are carried out to check feasibility manufacturing.