Roof Design
Design Procedure:
Import the file. File>open>browse file and select the given product(product name .igs) as shown in the figure below:.
Roof Design
Given surface is A-class and we have to design Roof surface with the help of this A-class and the help of master section which is shown below:
There is two master section for the front end Rail roof and the next one is for the rear rail roof section :
Reinforcements and Design
The Ditch Area is the extended portion of the main Roof concealed by other BIW panels. The rail supports of the roof are attached to the Ditch Area using Spot welds. since it is not a styling surface and remains concealed.
Front Roof Rail
It is the support that is joined the windshield glass. Body side outer and the inner panels. Its thickness is usually 0.75mm. The windshield end flanges are the extract offset of the roof surface. The bottom-most flanges is decided after taking into consideration the visibility criteria. Spot weld is applied at the windshield end of the other end is joined with the roof using Mastics sealants which also contributes to increases strength.
Rear roof rail
It is the support that is joined to the back door and the Body side outer and the inner panels. it is usually made from body side outer scrap and therefore the thickness of the rail is 0.75mm. Similar to the Front roof rail design. We have to take into consideration the rear headroom clearance and the rear visibility criteria while designing the rear roof rail from the backdoor design and also taken into consideration od the required clearance. Spot welds are applied at the back door end of the rail and the other end is joined with the roof using Mastic sealants.
Bow Roof Rails
Similar to the other design, we have to take into consideration of the headroom clearance and the visibility criteria while designing the centre roof rail and bow roof rail. Here spot weld is not applied for joining these rails of the roofs. Instead mastic sealants are used are introduced at both ends since centre Roofs are fully positioned under the styling surface of the roof. For increasing the strength of the rails, Embossing is done. To reduce the weight of the material used, different styling has been followed with a thickness of 0.75mm.
Reinforcement centre rail
It is the main supporting rod for the roof. Their purpose is to provide an attachment point for crossbars and other devices designed to secure loads carried on the roof of the vehicle, it absorbs energy at the time of the crash. Its thickness is 1mm.
Analysis
1. CURVATURE STUDY:
It is done to justify the positioning of the bow roofs. There are mainly two criteria to fulfil
- Heat distortion criteria
- Snow load criteria
Heat distortion formula :
From the model we have the value shown in fig:
So after intersecting points on the line, we create 4points and project them on the roof surface then join these points by using the spline option.
The horizontal line is Rx and the vertical line is our Ry.
The radius of curvature for the hood component along the x-axis
The radius of curvature for the hood component along the y-axis
Calculations are done and tabulated in the table as given below:
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
Ry = Y curvature
t = Roof plate thickness [mm]
l = Bow Roof Span [mm]
Judgment Condition
OK< 2.7
| HEAT DISTORTION CRITERIA |
| S/NO | BOW | Rx(mm) | Ry(mm) | R(mm) | I(mm) | L(mm) | t(mm) | W(mm) | Status |
| 01 | Fr&1St | 2275.7377 | 5736.64 | 3258.73 | 294 | 2066.3 | 0.75 | 1.480 | OK |
| 02 | 1St&CTR | 5723.9730 | 5089.3052 | 5388.010 | 446.8 | 2066.3 | 0.75 | 2.102 | OK |
| 03 | CTR&2ND | 10311.7066 | 4032.3621 | 5797.592 | 451.6 | 2066.3 | 0.75 | 2.220 | OK |
| 04 | 2ND&RR | 14778.411 | 3251.4665 | 5330.209 | 403.8 | 2066.3 | 0.75 | 2.039 | OK |
Snow Load Criteria:
After creating all the lines we intersect points and project these points on the hood by using the spline curve option this will look like given below figure:
For the Geometrical Moment of inertia, we need a section at each rail, and shown in the figure below:
BOW ROOF RAIL-01
BOW ROOF RAIL-02
CENTER ROOF RAIL
Calculations are done and tabulated in the table as shown below:
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 center 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
Judgment condition
Qr ≥ 3.1
250 ≤ s ≤ 380
SNOW LOAD CONDITION
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DRAFT ANALYSIS
DRAFT ANALYSIS OF FRONT ROOF RAIL
DRAFT ANALYSIS OF CENTER ROOF RAIL
DRAFT ANALYSIS OF BOW ROOF RAILS
4.DRAFT ANALYSIS OF REAR ROOF RAIL
Design of roof was succsessfully completed using SIEMENS NX as per the given master sections.The position of bow roof rails are as per the given standards.Draft analysis & section analysis ensure the manufacturability of every components.