Roof challenge
DESIGN OF PASSENGER CAR ROOF, USING SIEMEN NX CAD & TO CALCULATE HEAT DISTORTION AND SNOW LOAD CRITERIA
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.
Master Section- I Used these master Sections and Values to make Front Roof rail, and Rear Roof Rail
Front Roof Rail Rear Roof Rail
OBJECTIVE-To develop the Essential flanges and Reinforcement, Check for draft analysis, Creation of roof ditch area, Perform Calculations to determine the position of Bow Roofs.
- Heat Distortion Calculation
- Snow Load Calculation
SOFTWARE USED-Siemen Nx Cad
MAJOR PARTS OF ROOF
Ditch Area-Ditch Area is Joined with Body Side Outer, Windshiel glass, and Back door.Spot weld is applied to join the parts. Thickness is 0.7mm, headroom clearance, Visibility Criteria, Clearance for windshiel and Backdoor are some of the factors to be considered while designing ditch area.
Front Roof Rail-Front Roof Rail is created to support the roof which is mounting the windshield Glass, Body side outer and the inner panel.It is made from body side outer scrap and thickness of rail is 0.75mm.A draft angle of 3-5 degree is given for deep drawing operations.
Bow Roof-Here I consider the Headroom Clearance and Visibility criteria while designing bow roof.Spot welds are not applied for Joining the rail to the roof, Mastic sealant is applied.
Center Roof Rail-Here also I consider the Headroom Clearance and Visibility criteria while designing Center roof rail.Spot welds are not applied for Joining the rail to the roof, Mastic sealant is applied.
Rear Roof RaiL-It is the support which is joined with the Back door and Body side outer and inner panel. It is also made from Body side outer scrap and thickness is 0.75mm.I have taken into considerations the Rear Headroom Clearance and Rear Visibility Criteria while designing rear roof rail.Spot weld is applied.
Analysis-
Curvature study-It is done to justify positioning of bow roofs.
- Heat Distortion
- Snow Load
- Roof crush test
Heat Distortion Criteria-Heat distortion temperature is the temperature at which the metal soften and deform under a specific load. This study is done to check the ability of roof to withstand high temperature.
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
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]
l = Bow Roof Span [mm]
HEAT DISTORTION CRITERION CALCULATION
SNOW LOAD-Snow load Criteria study is done to check the ability of the roof to withstand snowfall and bounceback to its original shape without any permanent deformation once load is removed.
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)
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 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]
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 panel X curvature radius of length s in Side view
Here I get NG Condition in 3 parts, So for this I Create a local Emboss on Top of Roof to Increase strength of Roof
Draft Analysis-Draft analysis is done to Check that part is Manufacturable or not.Here It is done to check draft angle.The angle of 3 degree is taken on Front roof rail.
Roof
Rear Roof Rail
Center Roof Rail
Bow Roof
Front Roof Rail
Conclusion-Roof Designing, Front rail roof, Rear Roof rail, Bow roofs and Center Roof rail, Draft analysis, Calculation of Heat Distortion values, Snow load values Completed Successfully.