Roof Design
NOTE - ZIP FILE OF ROOF PARTS IS COMPRESSED TO A VALUE OF GREATER SIZE THAN UPLOADED VALUE SIZE . SO I HAVE ATTACHED A GOOGLE DRIVE LINK IN NOTEPAD. PLEASE CONSIDER IT .
AIM - The objective of this project is to design car roof with essential flanges and reinforcements like front roof rail, central roof rail, rear roof rail and bow roof rail for the given styling surface and to 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.
ROOF - A car roof is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind and rain. Roof is the structure having the reinforcements to provide the strength to the overall structure and to with stand the overhead forces like snow etc.
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REINFORCEMENTS -
<!-- [if !supportLists]-->1. <!--[endif]-->FRONT ROOF RAIL – It is the one which joins the wind shield glass, outer side body and the inner panel also. It is designed according to the master section, where min 7 degrees of draft is applied and thickness of the roof is 0.75 mm. Embosses can be created to increase the strength of the roof .
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<!-- [if !supportLists]-->2. <!--[endif]-->REAR ROOF RAIL – It is the one which joins the back door and the outer side body. It is designed according to the master section, where min 7 degrees of draft is applied and thickness of the roof is 0.75 mm.Embosses can be created to increase the strength of the roof .
<!-- [if !supportLists]-->3. <!--[endif]-->CENTRAL ROOF RAIL – It helps in providing support to the flat area of the roof as it is more susceptible to failure under the action of load. Generally it is placed at the center of the roof which is connected to the B-pillar support structure and thickness of the roof is 0.75 mm.
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<!-- [if !supportLists]-->4. <!--[endif]-->BOW ROOF RAIL – It is to improve the torsional stiffness and load bearing capacity of the roof structure. Presently in this project two bow roofs are added and thickness of the roof is 0.75 mm.
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JOINING PROCESS – Mastics are introduced between the roof outer panel and the reinforcements for joining, which indeed improves the strength of the roof. Spot welding is also used to join.
DESIGN CONSIDERATIONS FOR A ROOF –
1. Visibility Criteria
2. Head Clearance
3. Heat distortion and Snow load criteria
4. Draft Analysis
SECTION ANALYSIS –
CENTRAL ROOF RAIL –
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BOW ROOF RAIL 2 –
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BOW ROOF RAIL 1 –
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HEAT DISTORTION STUDY ON THE ROOF – This 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)/t] + [1.10x10^ (-3) x l] - 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 and Ry = Y curvature
t = Roof plate thickness [mm]
l = Bow Roof Span [mm]
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Substitute the values in the formula to get desired result for heat distortion.
CALCULATIONS –
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JUDGEMENT CONDITION – All the W values should be less than 2.7
From the above table it can be concluded that all values are of w<2>
SNOW LOAD CRITERIA -
This test is done to know how the roof is behaving when there is a snow over on the roof. 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 removal the roof should go it its original position. This is the basic requirements for snow load criteria.
SNOW LOAD PREDICTION FORMULA –
Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]
Note: The Qr value given over here is correct. There was a typo error in the formula given in the video.
Where,
α = My x Lx2 x 10-12, My = Y(Ly-Y)
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 centre point between Roof rail 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]
The width of the roof panel is 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 panel X curvature radius of length s in Side view
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Substitute the values in the formula to get desired result for heat distortion.
CALCULATIONS –
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JUDGEMENT CONDITION – All the Qr values should be greater than equals to 2.7 (Qr ≥ 3.1)
From the above table it can be concluded that all values are of Qr ≥ 3.1, so thus infers that current positioning of bow row are good in state as per design and found ok.
DRAFT ANALYSIS - It helps to analyze if the part drafted will be easily removed from the cavity. This type of analysis is performed based on color ranges identifying zones on the analyzed element where the deviation from the draft direction at any point, corresponds to specified values. Minimum draft angle of 7 degrees is considered for analysis. Green color infer on the parts that all face along the tooling direction has positive draft angle greater than 7 degrees.
FRONT ROOF RAIL –
REAR ROOF RAIL –<!--[endif]-->
BOW ROOF RAIL 1 –
BOW ROOF RAIL 2 –<!--[endif]-->
CENTRAL ROOF RAIL – <!--[endif]-->
CONCLUSION –
Hence ,The roof, front roof rail, bow roof rails, central roof rail and the rear roof rail is designed according to the master section . Section analysis and draft analysis are carried out to check feasibility manufacturing.