Roof challenge

REPORT ON ROOF DESIGN

BY: SURAJ KENDRE

INTRODUCTION:

• Roof of an automobile is that commodity which sits above the passenger compartment. Roof houses the vehicle as shielding part which safeguards the occupants from sunlight, heat, rain, wind, dust, etc.
• In the past roof was introduced as cover for passenger compartment but later on, it also used as a luggage carrier, sunroof and in recent past years with the introduction of the solar panelled electric vehicle got a major boost in the automotive industry.
• Since the roof has numerous functions so the roof has to be stronger enough to withstand the damage experienced by it.
• Roof has the following functions:

  Ø Protects from external damage

  Ø Prevents passenger and vehicle from accidents

  Ø Luggage carrier

  Ø Design of the roof also affects in giving aerodynamic shape to vehicle.

  Ø Sunroof

  Ø Solar panelled roof in EV

  • Material Used For Roof: Aluminium,Steel,Composite Plastics etc
  • Types Of Roof:

  1.Convertible roofs

  2.Hardtops

  3.Sunroofs

  4.T-tops

  5.Vinyl roofs

OBJECTIVE:

• The main objective of this project is to come up with a design idea for the ROOF from Styling surface that satisfies-

1.The Design requirements for the roof & its components

2.Functional requirements

3.Rollover Test Regulation & Requirements

4.Bow Roof Position Justification

5.Joining techniques like Mastic, Welding

DATA FOR ROOF DESIGN:

ROOF DESIGN:

• First thing to consider while designing the roof is the opening angle, of the flanges such that there is no negative draft.
• If the roof rail is flat it is weak and if it is tilted or curved then it has more strength.
• As the roof is large so to increase the strength of the roof where it appears flat due to its long distance Roof Bow are given to increase the strength of the roof.
• Since the roof has numerous functions so the roof has to be stronger enough to withstand the damage experienced by it. To have good strength and stiffness, the Roof consists of components:

1.Front roof rail &Rear roof rail

2.CTR Bow roof

3.Bow roof.

• The Rear roof rail has joints with the backdoor, bodyside outer where as the Front roof rail has joints with windshield glass, bodyside outer and inner panels.
• From the ergonomics team we get to know where the front driver is sitting, hence there should be minimum head clearance.
• There should be clearance of 5-10mm b/w headliner and BIW.
• There should be clearance of 85mm b/w rear roof rail plus headliner and the passenger.
• Mastics are applied between roof and the roof rail and bow roof. When the mastic gooses out it joins the roof rail, bow roof with the Roof.
• As we have curvature in front and more flat in the back side of the roof, it is sufficient to have reinforcement centre alone in front and both the roof bows behind.
• If the roof was small with better curvature we use only one centre reinforcement roof rail which also acts as the roof bow.
• Number of bow roof increases if the car size becomes longer and taller. More taller car means more flat region means more Bow roofs.
• If the styling surface does not with stand the Heat Distortion criteria and snow load condition or the strength of the roof is less then in styling surface modify the radius of curvature of the roof and send it to the styling team if they accept it then proceed.
• So as to propose a value of that curvature radius will have to do trial error for the values of Rx and Ry.
• Always gradually increase the curvature radius not drastically.
• If the styling team does not accept the change in radius of curvature of the surface then embossing is done on the roof of different shapes so as to increase the strength of the roof.
• Always place Roof Bows on the flat region and not on the curvature region.
• Also there is a bracket placed on the reinforcement centre so as to mount the room lamp in the car.

MASTIC:

• Mastics are like paste when heated get hardened and join the components.
• It is used between inner and outer panel. When it will get into the hot bath inside the furnace it will get harden and join the outer panel to the inner panel.
• Gap between Roof and Roof Bow Rails should be 2.7mm and it will be field by mastic sealants.
• Mastic sealants are used to join two panels where the spot welding is avoided such as the styling surface and its reinforcement so as to keep aesthetic look of the car.

• Mastic points for Mastic sealants are added to improve the NVH of a vehicle.

• Every mastic sealant have the tendency of improving the strength locally around 80mm diameter.

ROOF CRUSH TEST:

• Important test for roof is the Rollover that is roof crush test.
• The standards and the test is carried out by the Institute of Highway Safety.
• The ratings are given on the basis of how fast the car reforms to the original shape and how deep the protrusion after collision is.
• This test is carried out with body on frame only.

Ø Following are the criteria considered during the test:

1.Close and lock all the doors

2.Close the windows.

3.Fix the body sill or chassis frame on a hard level surface horizontally.

4.Crush speed should be 13mm/sec or less.

5.The displacement of the load application device should be 125mm or less when a load of 1.5 times the unloading vehicle weight is applied.

6.Time for test completion should be within 120sec.