Roof Design
PROCEDURE AND EXCECUTION.
AIM: For the given car roof styling . design and develop the essential flanges and reinforcement , namely the ditch area , frontal roof, rear roof rail, centere roof rail and Bow roofs.
Do the curvature study on the roof and perform the calculation for heat distortion and snow load criterion to determine and justify the position of the bow roofs.
INTRODUCTION:
An automobile roof is the portion of an automobile that site above the compartment, protecting the vehicle accupants from sun heat, rain wind,and other external factors.
DESIGN PROCEDURE:
impact 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 and 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 weldsm. 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 ussaly 0.75mm. The windshield and flanges are the extract offset of the roof surface. the bottom -most flanges is dicided after taking into consideration the visibility criteria. spot wield is applied at the windshield end of the other end is joined with the roof using mastics sealants which also contributes to increase strength.
REAR ROOF RAIL:
It is the support that is joined to the back door and the baby side aoter and the inner panels. it is ussaly made from body side outer scrap and therefore the thickness of the rail is 0.75mm. similar to the front roof rail designed . 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 considereation od the requred clearance. spot welds are applied at the back door end of the rail and outer 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 desgining the ventere roof rail and bow roof rail. here spot weild is not applied for joining these rails of the roofs. instead mastic sealants are used are introduction at both ends since centere roofs are fully positioned under the styling surface the roof . for increasing the strength of the rails , Embosing 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 . there purpose is to provide an attachment point for crossber and other devices designed to secure loads carried on the roof of the vehicle , it absorbs energy at hte time of the crash. its thickness is 1mm.
ANALYSIS:
1. CURVATURE STUDY:
. Heat distortion criteria
. Snow load criteria
HEAT DESTORTION 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
Ry = Y curvature
t = Roof plate thickness [mm]
l = Bow Roof Span [mm]
From the model we have the value show 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 is given below:
The radius of curvature of the hood component along the Y-axis is below:
Calculations are done and tabulated in the table as given below:
Snow Load Criteria:
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
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:
Calculations are done and tabulated in the table as shown below:
Draft Analysis: Draft analysis is a method of checking the draft angle on various faces of a part in a particular direction. it should be more than 7 degrees. draft analyzing command which lets you know if your model or design has a draft angle in a given tool direction.
If the part lies within the conditions it shows in green colour if not shown in blue or red colour.
The below figures show the draft analysis for Roof, Front Roof Rail, Rear Roof Rail, Bow Roofs and Reinforcement Center.
Results: The Design of Roof, Front roof rail, Rear Roof Rail, Bow Roofs, and reinforcement roof center by following the Master section with the design parameter for the given class A surface is done and the final model is shown in the fig. below.
