Roof Design
AIM:- To create an assembly for the given styling surafce.
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 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 reinforcements.
INTRODUCTION:-
- Along with stylish aesthetics, there is also involved a lot of engineering behind the design of the roof. The roof has an outer panel which is the styling part. Strengthening parts are present below an outer panel of a roof, which are front roof rail, Bow roof, Centre roof rail, and Rear roof rail.
- 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 Pannel is attached to the car with the help of Front and Rear roof rail and few bow roof.
NEED OF 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 are as follow :
1)Front roof rail
2)Bow roofs
3)Centre roof rail and
4)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 saection given.
REAR ROOF RAIL :-
Rear roof rail is the one which joins the back door and the body side outer.
CENTRAL ROOF RAIL : -
center roof rail is used as a cross member between Left hand and right-hand bodysides.
BOW ROOFS :-
The bow roofs are give 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.
Here, I have created two Bow Roofs.
MOMMENT OF INERTIA FOR ROOFS ARE AS FOLLOW:-
- M.I. FOR BOW ROOF FRONT
- M.I. FOR BOW ROOF REAR
- M.I. FOR CENTRE ROOF
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
HEAT DISTORTION STUDY ON THE ROOF :-
The heat distortion study plays a major role in sheet metal usage.heat distortion temperature is a temperature limit above which the material cannot be used for the 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 the roof, based on the heat distortion temperature,this study will predict the bow roof position which helps to strengthen the roof.
Bow – roof prediction Formula
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
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]
l = Bow Roof Span [mm]
Judgement Condition : OK< 2.7> 3.1
t=0.75
L=2015.9
CALCULATIONS :-
| ROOF RAILS | Rx(mm) | Ry(mm) | Rx*Ry(mm) | Rx+Ry | R(mm) | L(mm) | t(mm) | l(mm) | W | RESULT |
| FR-Bow-1 | 5650.90 | 3267.14 | 18462337.94 | 8918.05 | 4140.44 | 2015.9 | 0.75 | 558.5 | 1.5 | PASS |
| Bow-1-CR | 4767.21 | 7028.43 | 33506001.78 | 11795.64 | 5681.08 | 2015.9 | 0.75 | 236.48 | 1.4 | PASS |
| CR-Bow-2 | 4156.38 | 9687.44 | 40264681.87 | 13843.82 | 5816.99 | 2015.9 | 0.75 | 220.41 | 1.35 | PASS |
| Bow-2 -RR | 3454.46 | 13470.99 | 46534996.12 | 16925.45 | 5498.81 | 2015.9 | 0.75 | 534.42 | 1.65 | PASS |
SNOW LOAD CRITERIA :-
This test is done to know how is the roof behaving when there is a snow over.Normally due to the snow weight the dent will happen. But the roof should be designed in such a way that when the snow is remove from the roof then it should be in its original position.This is the basic requirements for snow load criteria.
Snow Load Prediction Formula
Qr = [Iy x t^2] / [α x s x [(Rx + Ry)/2]^2 x 10^-8]
Where
α = My x Lx2 x 10-12 , My = Y(Ly-Y)
Judgement condition = Qr ≥ 3.1
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 rail Front /Rear as the reference point of the front and the rear.
Lx = Distance between the Left and Right end of the roof on the Roof BOW [mm]
Width of the roof panel exposed on the surface.
Y = Distance front Front Roof Rail 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 [mm]
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 [mm]
| ROOF RAILS | Iy(mm) | Lx(mm) | Ly(mm) | L1(mm) | L2(mm) | Rx(mm) | Ry(mm) | t(mm) | Y(mm) | s | My | α | Q | RESULT |
| FR-BOW -1 | 4505.88 | 1087.1 | 1935.8 | 654.6 | 318.4 | 4121.5433 | 3323.95 | 0.75 | 654.6 | 486.5 | 838673.52 | 0.9911 | 37.93 | PASS |
| BOW-1-CRR | 5659.96 | 1066 | 1935.8 | 318.4 | 302.32 | 3822.75 | 6941.96 | 0.75 | 973 | 310.36 | 936804.4 | 1.0645 | 59.12 | PASS |
| CRR- BOW-2 | 4524.86 | 1052.2 | 1935.8 | 302.32 | 660.6 | 4177.40 | 9145.19 | 0.75 | 1275.3 | 481.46 | 842335.65 | 0.9325 | 12.77 | PASS |
CONCLUSION:-
The above table shows that all the rails has passed the requirement condition of Snow Load Criteria i.e. QR > 3.1
DARFT ANALYSIS:-
The Draft Analysis command enable us to detect if the part we drafted will be easily removed. This type of analysis is performed based on color ranges.
Minimum draft angle of 7degree is considered for analysis. Green colour infer on the parts that all face along the tooling direction has positive draft angle greater than 7degree and passed in analysis.
Here, I have given 13 degree as a draft angle.
DRAFT ANALYSIS FOR ROOFS ARE AS FOLLOW:-
- FRONT ROOF RAIL
- BOW ROOF FRONT
- CENTRE ROOF RAIL
- BOW ROOF REAR
- REAR ROOF RAIL
- OUTER ROOF RAIL
CONCLUSION:-
Hence, a roof assembly was created by developing the essential flanges for the outer roof and created reinforcements for the given roof styling,curvature study on roof assembly and calculation for the position of the bow roofs has been done and also carried out draft analysis to check feasibility of manufacturing.