Roof Design

 

                                                  ROOF DESIGN

 

AIM:

 

         Main objective of this Challenge is to create a Roof in Sheetmetal design and also design its Reinforcement like Front Roof Rail, Rear Roof Rail, Bow Roof Rail, Centre Roof Rail, are Created to increase the strength of Roof.

 

Do Curvature study on Roof and performed calculations for Heat distortion and Snow load criteria to determine the positions of Bow Roof.

 

Finding the Moment of Inertia and Section Modulus for Bow Roofs and Centre Roof Rail.

 

Also performed Draft Analysis on each part.

 

INTRODUCTION:

 

                              Automobile car roof is a vital component that serves multifaceted purposes. Beyond it fundametal role in providing shelter from external elements, it contributes significantly to the structural integrity of the vehicles, enhancing safety in case of collisions. The design and materials of Car Roof influene Aerodynamics, Impacting fuel efficiency, wind noise, and stability at higher speeds. Additionally, the Roof function as an Insulator, Regulating interior temperatures for occupant comfort. Various Styles, such as hard tops, convertibles, and sunroof, offers diverse driving experiences, while modern safety features are often integrated into the roof structure to ensure enhanced protection in different driving scenarios.

 

ROOF DESIGNING:

 

            Given Input,

    

 

 

Front Roof Design,

                        

 

 

Front Roof Rail:

 

                            The Front Roof Rail in Car refers to the structural component located along the front edge of the Roof. It is part of the Roof structure and contributes to the overall strength and safety of the Vehicles.

                                  

 

 

Rear Roof Rail:

 

                        In Rear Roof Rail we need to ensure that we need to keep the clearance and rear view criteria for designing, Backdoor will be mount here.

                              

 

Bow Roof and Centre Roof Rail:

 

                                                Bow Roof are also given to Improve the torsional Stiffness and load bearing capacity of the Roof structure. here in this project two bow roof are designed considering the overall size of the Roof.

 

Centre Roof Rail helps in providing effective support to the flat area of the roof as it is more susceptible to failure under the action of load. generally the centre roof rail is placed at the centre of roof and it is connected to the B-Pillar structure.

 

This helps in adding strength to the roof during the roll-over test.

 

 

                

 

Manufacturing Process of Roof Rail:

 

                                                               The manufacturing process of roof rails involves a series of steps beginning with design and Engineering considerations to define dimensions and material specifications. Commonly constructed from material like Aluminium or High strength steel, the selected material undergoes shaping, bending and forming process to achieve the desired cross-sectional profile and structural strength. Sections are assembled and integrated into the vehicle's body structure.

 

Here in this Roof Design various Mastic points are given to join the Inner Panel and Outer Panel through spot welding.

 

Spot welding is a type of electric resistance welding, it is also known as resistance spot welding. The process of spot welding is sheet metal are made into contact with each other, and pressure is applied on specified points. So heat is generated from the resistance and weld is formed.

 

(here image given below, it is only for the understanding which I used from the Internet)

             

 

 

Roof Crush Test:

A rectangular block measuring 30 inches wide and 72 inches long is used to apply the load on car with 1.5 times the unloaded vehicles weight with different angle inclination to rectangular block. The moving distance of roof structure must be less thean 127mm or 5inches as per FMVSS standards.

 

                       

                                                             

 

Roof Crush System:

Here Crush system is shown which is manufactured by MGA Corporation. It has an Upright assembly and attached loading head that can be fixed at varied height. Pitch angle can be Varied by +5 to -5 degrees, but the roll angle is fixed to 25 degrees. Hydraulic actuators are used to control the movement of plate.

                        

 

 

Position of Bow Roof:

Bow Roofs are designed to give strength to the roof panel.It avoid the roofs to bend due to snow load. Number of bow roofs needed are estimated with the design of the roof panel.if the length of the roof is large then we need more bow roofs, if the length of the roof is less then we need ideal number of bow roofs.

The position of bow roof depends upon the curvature of the roof panel. We added bow roof on flat region as bending is more possible here than the curved portion of the roof, along with this we have Heat distortion criteria and Snow load criteria for positioning the bow roof.

 

Heat Distortion Criteria:

                  The heat distortion test evaluates the ability of car to maintain its physical structure without deformation under elevated temperature  conditions. Car roof are exposed sunlight at day time . Distortion of the car roof can create more susceptible to damage.

To calculate heat distortion, we have a 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]

Judgment Condition

OK< 2.7

                                 

Here are the detailed procedure to measure and calculate;

 

Step-1: Open Sketch and draw a centre line which bisect the roof into two halves. This will be 0-Y Line as shown in picture 

Step-2: Draw a line offset to the 0-Y line for 300mm. this is 3-Y line as shown above picture 

Step-3: Draw two lines at the both side of 3-Y line with offset value of 100mm.

Step-4: Draw a midpoint with front roof rail and end point on 0-Y line to start point of bow roof 1 on 0-Y line. this is (C-1). section in the above picture. we need to do it for (C-2), l(C-3) and l(C-4).

Step-5: Draw a vertical line with the midpoint of l(C-1). [Similarly do it for l(C-2),l(C-3) and l(C-4).]

Step-6: Draw two lines on both the side of the l(C-1),l(C-2) and l(C-4) with 100mm as offset value.

Step-7: Draw Intersection points on the created 100mm offset horizontal and vertical lines, as shown in picture

 

Step-8: Project the points on the surface of the roof and measure the radius of Rx and Ry. you can see Rx (Vertical) and Ry (Horizontal) in the picture given.

                           

Heat Distortion Calculation:

 

  All dimension are in mm,

  All dimension are in mm

Snow Load Criteria

Unlike in India there are countries with heavy snowfall. In Alaska it was recorded a record breaking 78" in 24 hours in 1963.

 

So calculating and designing the roof of the car in such a way this snow does not cause serious damage to the car.

                          

Qr  = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10^-8]

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

I have to measure inertia to find the Qr value according to the equation, here are the pictures of Inertia value for each case,

                             

 

                               

 

                    

Snow Load Calculation:

 

All dimension are in mm,

    

 

"s" value is more here, so with guidance of my mentor I created embosses on the outer roof, here is the picture given below

                        

DRAFT ANALYSIS:

                                Draft analysis is done in each parts, to perform draft analysis firstly I need to create Tooling axis for each parts. After creating tooling axis draft analysis is performed, Minimum draft angle of 7 degree is considered so I give 7deg.(6.95) on each parts.

Here are the parts that created as per the Master Sections, clearing draft analysis.

                      

 

                          

 

                                         

 

                                

All the Parts are Designed using Master Section As a Reference.

 

Here are some different views of Roof Design,

                                     

                           

                             

 

                                                

 

                           

CONCLUSION:

 

Hence the Roof is designed and I learned and Understand the Concept and design Consideration of Roof and its Reinforcement Features.

                                                     Thankyou

         Mehtab Alam