Roof Design
ROOF DESIGN
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. Because the earliest automobiles were designed in an era of horse-drawn carriages, early automobile roofs used similar materials and designs.
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…
INTRODUCTION: Design of any product starts from a 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 software’s. Another important thing in the design is that, every product that is designed should be able to manufactured. so, the role of the design engineer is to design the product that can be easily manufactured and with less cost effective. This is the place where the Design for manufacturing [DFM] and Design of assembly [DFA] takes a role while developing any product. The process of
development of design carries on until the design satisfies the customer needs. Here in this project the product that we are going to develop is a car roof
CAR 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. Roof is the structure above the wind shield glass having the reinforcements to provide the strength to the overall structure and to with stand the overhead forces like snow
WHY REINFORCEMENTS: If the roof is flat, it is very weak and cannot able to with stand 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 surface of the roof with the different joining process
Different types of reinforcements that the car has are:
Front roof rail
Bow roofs
Central roof rail and Rear roof rail.
FRONT ROOF RAIL: Front roof rail is the one which joins the wind shield glass, body side outer and the inner panel also. Here the front roof rail is designed based up on the master section given
Master Section
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 canter of the roof which is connected to the B-pillar support structure. This central roof rail helps in adding the strength to the roof during the roll- over test. The thickness of the central roof rail is 1.25 mm.
Master Section
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 depending on the overall size of the roof. Presently in this project two bow roofs are added.
Master Section
JOINING PROCESS: Mastics are introduced between the roof outer panel and the reinforcements for joining. where ever the mastic is introduced there is remarkable improve of the strength Spot welding is also introduced to join the reinforcements and the outer panel.
DESIGN CONSIDERATIONS FOR A ROOF:
Visibility criteria
Head clearance
Curvature study
Heat distortion and snow load criteria
Draft analysis
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, that how to perform the crush test. IIHS gives the rating based up on this test. For this they consider two points while giving the rating
How fast the car can reform to its original shape after the roll over and
How deep is the protrusion after the roll over
CONDITIONS TO FOLLOW FOR ROOF CRUSH TEST: There are two conditions that should be followed for the roof crush test, they are
INITIAL CONDITION:
Close and lock all the doors
Close all the windows
SECOND CONDITION: Fix the body sill or chassis frame on a hard lever surface horizontally
METHOD OF APPLYING THE FORCE: The load is applied in such a way that 5 is tilted from the front end to the rear end and the load will be in 1800 mm in length and 750 mm in width. The load is applied at the position of 25 from the flatness of the roof. The load is applied on the roof for almost 120 sec and the crush speed at which the load applied is 13 mm/sec or less than that.
Snow Load Criteria:
The test is done to know how is the roof behaving when there is a snow over the roof, normally due to snow weight dent will happen. But the roof should be designed in such a way that when the snow is removed the roof should go the original shape. This is the basic requirement for snow load criteria.
Thank You,
Ravichandra Swamy.