Roof Design
AUTOMOTIVE ROOF DESIGN USING CATIA
OBJECTIVE:
- Main objective of the project is to create the Roof Sheetmetal design and also designing Front roof rail, rear roof rail, bow roof front, bow roof rear, center roof rail and Reinforcement are creating to build the strong roof.
- Do curvature study on Roof and performance calculations for Heat distortion and Snow load criteria to determine the position of the Bow roofs.
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
Different types of reinforcements that the car roof has:
- 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
REAR ROOF RAIL:
Rear roof rail is the one which joins the back door and the body side outer
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 center 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.
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.
JOINING PROCESS:
Mastics are introduced between the roof outer panel and the reinforcements for joining. Where ever the mastic are 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 analyzing 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 reforms to its original shape after the roll over and
- How deep is the protrusion after the roll over
GOAL OF ROOF CRUSH TEST:
To minimize the protrusion into the occupant compartment, so that the seat belts and air bags can do their job in protecting the occupant
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 50 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 250 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
DESIGN SPECIFICATION FOR THE AUTOMOTIVE ROOF COMPONENT:
STYLING SURFACE FOR ROOF:
given master sections
design of frontal ditch area and rear ditch area
ditch area is creating with help of the dump solid of class A surface
FRONT ROOF RAIL:
REAR ROOF RAIL:
BOW ROOF RAIL:
CENTER ROOF RAIL
draft analysis
Ditch Area
Front Roof Rail
Rear Roof Rail
Centre Roof Rail
Bow Roof 1
Bow Roof 2
CURVATURE STUDY ON THE ROOF:
- Heat Distortion
- Snow Load
HEAT DISTORTION:
The heat distortion study the plays an important role in Sheetmetal application. Heat distortion is temperature limit above which material cannot be used for structural application. This study is useful to fin the where the material starts to soften when exposed to a fixed load at elevated temperature. In order to avoid the bending, damage to the roof based on the heat distortion temperature. This study will provide the which position of the bow roof give enough strengthen to roof.
Bow Roof Prediction Formula:
HEAT DISTORTION CRITERIA:
W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/2] + [1.10 x 10^(-3) x I]-2.68
Judgement Condition: OK<2.7>3.1
Where,
L= Roof Length in X- direction [mm](Roof Dimension in 0-Y)
R = Roof curvature
R = 2(RX*RY)/(RX+RY)
RX = X Curvature
RY = Y Curvature
t = Roof plate thickness [mm]
I = Bow roof span [mm]
Thickness for the Roof(t): 0.75 mm
ROOF LENGTH (L):
- To calculate the Heat distortion criteria, we have to take note of few values and note it down.
- To note down, first, we need to create a sketch.
- Create a line at the center of the roof part in the 0-Y axis and then draw another line with a distance of 300mm.
- Now create the line with a distance of 100 on both sides at the line which is at 300mm.
- Now create the line between the rails in the X direction and create 2 lines with a distance of 100mm on both sides.
- Now create a point coinciding with both the lines.
project the points to the roof and create the arc using 3 points by creating two lines intersecting with each othe
Measure the radius of the arc in the Y direction as Ry and X direction as Rx
Rx Value:
Ry Value:
FINAL RESULTS OF HEAT DISTORTION:
We have the necessary values for finding the heat distortion value(W):
W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/2] + [1.10 x 10^(-3) x I]-2.68
Apply the all the values,
From the above table we, conclude that all the values are of W< 2.7 and also W> 3.1. So, that all bow roofs areas are placed at the right place.
SNOW LOAD:
Snow load criteria study is used to check the durability of the roof to withstand the snow fall on the roof and reflex it is original shape without any permanent deformation after load being removed.
SNOW LOAD CRITERIA:
Qr = [IY x t2] / [α x s x [(RX + RY)/2]2 x 10-8]
Where,
α = My x LX2 x10-12, My = Y(Ly–Y)
Judgement condition = Qr > 3.1
250 < s < 380
t = Roof plate thickness[mm]
LY = Distance between the front and rear roof rails on the vehicle along with 0Y[MM],
Length of roof panel with the center point between roof rails front/ rear as the front and rear reference point.
LX= Distance between the left and right end of the roof on the roof bow[mm],
With of the roof panel exposed on the surface.
Y = Distance between Front roof rails to roof bow [mm],
s = Distance for which roof bow bears divided load [mm],
s = L1/2 + L2/2
Iy = Geometrical moment of inertia of roof bow (Y cross – section) [mm4],
RX = Lateral direction curvature radius of roof panel Y cross section on roof bow [mm4],
Roof panel curvature radius of the length LX in front view.
RY = Longitudinal direction curvature radius of the roof panel X cross section on roof bow[mm4]
- To calculate the Snow Load criteria, we have to take note of few values and note it down.
- To note down, first, we need to create a sketch.
- Create a line at the center of the roof part in the 0-Y axis.
- Now create the line with a distance of 100 on both sides.
- Now create the line between the rails in the X direction and create 2 lines with a distance of 100mm on both sides.
- Now create a point coinciding with both the lines.
project the points to the roof and create the arc using 3 points by creating two lines intersecting with each other.
- Measure the radius of the arc in the Y direction as Ry and X direction as Rx
Rx Value:
Ry Value:
Moment of inertia
Moment of inertia is defined as the quantity expressed by the body resisting angular acceleration which is the sum of the product of the mass of every particle with its square of a distance from the axis of rotation. Section moment of inertia is used to predict the amount of deformation and deflection of a part. Higher the moment of inertia lesser the amount of deflection
bow roof 1. Iy(min) =7168 mm4
value for bow roof 2 Iy(min) = 7205 mm4
value for Center roof. Iy(min) = 14210 mm4
By Following the Procedure and using the formula, We got the Qr value of Above 3.1. And thus our Result is PASS. You can look at the table below for more details.
final roof assembly
