Roof challenge
DESIGN OF CAR ROOF USING NX CAD
Objective:
The main objective of this project is to design the Roof using the engineering parameters and dimension criteria for the standard Roof design.
Introduction:
Roof is the top most region of the vehicle which covers the inner cabin, it is welded to the pillars of the vehicle, it is designed in such a way that it can resist some of the impact loads when an accident occurs, it consists of roof outer panel, front roof rail, rear roof rail, side roof rails, center roof rail, and Bow’s. the picture below shows the roof from the outer styling side.
And the picture below shows the roof from the inner side
Design methodology/approach:
Description and calculations:
Some of the important design considerations for the Roof assembly are:
- Roof outer panel:
The main features and design used for the Roof outer panel are the surface features like law extension, offset surface, trim and extend, etc. and thickening of the surface is done at the final stage.
Thickening is usually done to get the required thickness of the whole outer panel so that the surface is converted to a sheet.
- Front roof rail:
The front roof rail is the part which comes in role to place the front windshield with rubber packing, this also give some strength to the roof outer panel.
The moment of inertia (MOI) for the front roof rail is
- Rear roof rail:
This rear roof rail, acts as a supportive part for the roof, and this is the part where the back door assembly is hinged in the vehicle.
The moment of inertia (MOI) for the rear roof rail is
- Center roof rail:
The center roof rail comes colinear with the B-pillar of the vehicle, this also acts as a supportive member for the roof.
The moment of inertia (MOI) for the center roof rail is
- Bow roof 1:
The bow is placed under the roof outer panel for the extra strength of the roof at the place where it is almost a flat surface, the no of bows can be defined by the design of the roof, and even for the placement of the bow roof the bow prediction is used to evaluate if it is good or not good.
The moment of inertia (MOI) for the Bow roof rail 1 is
- Bow roof 2:
The moment of inertia (MOI) for the Bow roof rail 2 is
- Calculations:
- -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]
Values:
- Snow load Prediction formula
Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]^2 x 10-8]
Judgement condition = Qr ≥ 3.1
250 ≤ s ≤ 380
Where,
Alpha,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 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 between 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
Values:
Views of the Roof assembly:
Front view:
Left side view:
Right side view:
Isometric view:
Top view:
Conclusion:
The roof assembly is designed with all the dimension factors and design criteria using NX CAD, by this we get to know what are all the factors to be considered for the roof to be designed and even the manufacturing process of that design.