Roof challenge

Design of roof using nx CAD:

Objective:

• Given car roof styling design develop a roof of a car with front foot rail , Bow roof rail, center roof rail and rear roof rail by following engineering standard process.
• The roof must be subjected to draft analysis for verifying whether it meets the manufacturing requirements.

INTRODUCTION:

• An automobile roof of car to is the position of the module that sure above the passenger compartment, protecting the vehicle occupants from Sun, wind,rain and other external elements.
• It also acts a member between body studded of the car body and provide provisions for front wind sheilds , backdoor. Roof assembly of also one among the part which provides safety for rollover accidents.

DESIGNING THE REENFORCEMENTS:

1. DITCH AREA:

• The Ditch area of the roof was designed by taking the considerations provided by the styling team.
• The ditch area designed to have only 3 degrees of maximum draft angle and 0.75mm thickness.
• The ditch area is the extended portion of the main roof concealed by other BIW panels.
• The rails of the roof attatched by using for welds and matric sealants visibility criteria.

Front roof rail:

• Front roof rail is located on the front of the roof where the windshield joins with the roof.
• The visibility criteria and the head room clearance of the passenger are taken into consideration for the bottom flange.
• Over end of the rail is joined using for welding while the other end is joined with the roof using mastic sealants for increased strengths.

Front roof Rail master section image

BOW roof:

Bow roof is an additional siffening member for the roof to increase the strength and so that it can satisfy the norms. Both ends are joined together using mastic sealants to increase strength and also this will not affect the styling of the roof.

Master section of bow roof

REENFORCEMENTS center:

Centre roof rail or the reenforcements centre is located at the centre of the roof.
The cross section of this is more since it needs to provide more strength to the roof. Hence, both ends are joined together using mastic sealents.

section view

Rear roof rail: The roof rail joines with back door and the roof. Inputs from the backdoor area taken into consideration for designing the roof rail. Here one end is joined using spot welding while the other end is joined using matric sealents.

Master section of the rear roof rail

assembly of roof

Heat distortion criteria:

Heat distortion temperature is the temperature at which the metal softens and deforms under a specific load. This study is done to check the ability of the roof to withstand high temperature with dress to position of the reenforcements which contribute to increase strength.he creteria is used to check whether the deforms during high temperature eg: If the car is standing in Sun light.

• To find the check the creteriaa line is made by offset the center of the roof to 300mm in x direction.
• The above line is offseted by 100mm on both side.
• A line is made in center of two consecutive roof rails.
• Above line are offseted to 100mm on both side.
• The intersection of the line is projected in roof surface.
• An arc is draw on both sides on both X and Y direction by using local radius analysis curvature of the arc is measured

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

we find Rx and Ry values

t = Roof plate thickness [mm]

l = Bow Roof Span [mm]

Judgement Condition : OK< 2.7> 3.1

Snow load prediction:

Snow load prediction is a of study done to check the ability of roof whether it can withstand to different temperature like cold whether and also bears the atmosphere snow falls and rebounds to its original position when a snow load removed.

procedure

• determine whether the roof will bear the weight of snow
• To find the snow load, the center line is projected on the plane and offseted by 100mm on both side.
• The same procedure is followed by heat distortion
• Moment of Inertia is bowed by roof 1 and 2 of center of roof rail.
• Length measure in Y direction and individual length between the two consecutive rails a long the x direction

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]

bow roof rail

bow roof rail2

center roof rail

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

by using local radius analysis we find Rx and Ry values

Draft analysis:

While designing a component design Engineer must make sure that the component can be produced by any means of manufacturing method with least amount of time material and manpower and power.
So that can reduce the overall cost of the car.
In NX draft analysis can be done after modelling so that we can verify whether the product is manufactured by using pressing or not. One side of the surface is highlighted by green and other ride by red colour means that model can be manufactured.

bow roof rail

rear roof rail

bow roof rail2

outer roof rail

Conclusion:

1. Thus the required ditch area, Bows and reenforcements for the roof were designed
And developed from the given styling.
3. Calculation of the Heat distortion creteria and snow load predictions were also performed.