Roof Design

ROOF DESIGN

OBJECTIVE :

• The objective of this project is to design car roof with essential flanges and reinforcements like ditch area , front roof rail , bow roofs, central roof rail and rear roof rail for the the given styling surface
• Perform a curvature study on the roof and perform the calculations for the heat distortion and snow load criteria to determine whether the bow roofs are at the correct positions.
• Finding moment of inertia and section modulus for Bow roofs , central roof rail . front roof rail and rear roof rail .

Perform the draft analysis for each reinforcements.

Introduction:-

Before designing the product we should keep in mind the purpose or the product and where it is going to be used,on the basis of that we make a rough sketch of the component and then with the use of 2D and 3D making CAD software we design the object and keep in mind the DFM & DFA which is DESIGN FOR MANUFACTURING & DESIGN FOR ASSEMBLY.

CAR ROOF :

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. Roof is the structure above the wind shield glass having the reinforcements to provide the strength to the overall structure and to with stand the over head forces like snow

WHY REINFORCEMENTS :

If the roof is flat it is very weak and cannot able to with stand the forces like snow , so in order to increase the strength of the roof these reinforcements like front roof rail, central roof rail, rear roof rail and the bow roofs are introduced and joined to the flat surface of the roof with the different joining process

Different types of reinforcements that the car has are :

• Front roof rail
• Bow roofs
• Central roof rail and
• Rear roof rail

Front roof rail

Front roof rail is the one which joins the wind shield glass , body side outer and the inner panel also. Here the front roof rail is designed based up on the master section.Also som embosses are provided to provide more strength to the part.

1. The bottom layer is offseted 32mm as per the provided master section,and trimmed at 80mm using offset curve on surface command and trim surface command.
2. The side walls are made using the studio surface command after trimming the upper surfaces at a distance of 10mm and 5mm shown with green and yellow lines.
3. After joining all the surfaces the the embosses and fillets are provided for strength.

Bow roof 1

Bow roof 2

The bow roofs are give to improve the torsional stiffness and load bearing capacity of the roof structure . The number of bow roof present is depends on the overall size of the roof . Presently in this project two bow roofs are added.

Centre roof rail

central roof rail helps in providing effectively support to the flat area of the roof as it is more susceptible to failure under the action of load . generally central roof rail is placed at the center of the roof which is connected to the B-pillar support structure . This central roof rail helps in adding the strength to the roof during the rool- over test. The thickness of the central roof rail is 0.75 mm .

Process for Bows

The surface has been formed according to the provided master section 6.5mm offset downwards.

To join I used bridge curves command .

Later by joining them using studio surface command and provided fillets of 5mm and mirrored the bows and in case of Centre roof rail provided some gaps also.

REAR ROOF RAIL

Rear roof rail is the one which joins the back door and the body side outer.

REAR roof rail is also made according to the provided dwg.

JOINING PROCESS :

Mastics are introduced between the roof outer panel and the reinforcements for joining . where ever the mastic are introduced there is remarkable improve of the strength

Spot welding is also introduced to join the reinforcements and the outer panel.

Manufacturing processes used:-

Techniques used in the automotive sector are sophisticated and more engaging. There has been an improvement in the technology used over decades, such as automation of the manufacturing process. The application of new technologies has resulted in faster construction, reduction in cost, and improvement inefficiency. Some of the techniques used in manufacturing include:

Injection Molding

It is a process that is useful in the formation of parts of motor vehicles by inserting molten material into a cavity. The equipment takes shape, size, and configurations of the mold after cooling. The molten material is injected into metal cavities or steel depending on the preferences in the construction material of the parts. Currently, it’s applied in the construction of plastic parts of motor vehicles. This can be molded to any required shape as the shape depends on the shape and size of material you are going to pour the hot mold into.

3D Printing

IT is a technology that involves the use of 3D printers to apply layers to products. The process is computer-controlled. It has enabled the production of finished products with complex shapes and improved accuracy. The application of this technology in the manufacturing sector has led to the creation of digital models on finished products. Most of the automotive in recent times digitalized. This helps to make their operation less complicated, comfortable, and updated; hence, technology plays a part and is very helpful.

CNC Machining

Computer numerical control machining is a technology that uses computers to control machines such as drills and lathes automatically. It involves feeding a computer numerical control machine with coded information that it uses to execute its functions without being handled manually. CNC is an automated technology and has enabled faster production of products as compared to the non-computerized machining. A computer numerical control machine is a free tool that is controlled by a computer. Its time savvy and cost efficient and more convenient. This technology has helped in the production of more beautiful and more precise productions as it is more accurate as compared to manual handling.

Sheet Metal Fabrication

This technology is automated and applied in car modification sustaining and satisfying customer needs. It is used because of its plasticity and elasticity. Sheet metal fabrication is also involved in the construction of unibody parts, car restoration, and roll cage work, thus improving the performance and safety of these components. The best producers also focus on the best ways of improving safety, whereby sheet metal can also play a role.

Hemming

This process is used to fold the sheet metal wherever there is a requirement of a closed body.

DESIGN CONSIDERATIONS FOR A ROOF :

• Visibility criteria
• Head clearance
• Curvature study
• Heat distortion and snow load criteria
• Draft analysis

ROOF CRUSH TEST :

Roof crush test is the design given by the IIHS ( insurance institute of highway safety ) . After analyzing the many accidents IIHS has then fixed some regulations , that how to perform the crush test .

IIHS gives the rating based up on this test . For this they consider two points while giving the rating

• How fast the car can reforms to its original shape after the roll over and

How deep is the protrusion after the roll over.

GOAL OF ROOF CRUSH TEST :

To minimize the protrusion into the occupant compartment , so that the seat belts and air bags can do there job in protecting the occupant

CONDITIONS TO FOLLOW FOR ROOF CRUSH TEST :

There are two conditions that should be followed for the roof crush test , they are

INITIAL CONDITION :

• Close and lock all the doors
• Close all the windows

SECOND CONDITION :

Fix the body sill or chassis frame on a hard lever surface horizontally

METHOD OF APPLYING THE FORCE :

The load is applied in such a way that 5⁰ is tilted from the front end to the rear end and the load will be in 1800 mm in length and 750 mm in width . The load is applied at the position of 25⁰ from the flatness of the roof . The load is applied on the roof for almost 120 sec and the crush speed at which the load applied is 13 mm/sec or less than that

RESULTS :

If the displacements goes above the requirements level then we have to increase the bow roof thickness or add more mastics points to increase the strength . the stronger the roof the better it can protect the occupants in the roll over crashes.

HEAT DISTORTION STUDY ON THE ROOF :

The heat distortion study plays a major role in sheet metal usage . heat distortion temperature is a temperature limit above which the material cannot be used for the structural applications . This study is used to predict the heat distortion temperature at where the material starts to soften when exposed to a fixed load at elevated temperature . In order to avoid bending or damages on the roof, based on the heat distortion temperature , this study will predict the bow roof position which helps to strengthen the roof .

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

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]

Judgement Condition : OK< 2.7> 3.1

• To calculate the Heat distortion criteria, we have to take a note of few values and note it down.
• To note down the values, first, we need to create a sketch.
• Create a line at the center of the roof part in the 0-Y axis and then draw another line with a distance of 300mm to the O-Y line.
• Now create lines at a distance of 100mm on both sides to the 300mm line.
• Extract the required points and project them on the roof surface. Now using these points create a 3 point arc or circle and note the radius of the arc in the X direction as Rx and in the Y direction as Ry.

APPLY THE VALUES IN THE FORMULA :

In order to find the heat distortion apply all the necessary values from the roof to the given formula

CALCULATIONS :

As all the values of W are satisfying the conditions hence its OK.

SNOW LOAD CRITERIA :

This test is done to know how is the roof behaving when there is a snow over . normally due to the snow weight the dent will happen. But the roof should be designed in such a way that when the snow is removal the roof should go it its original position . This is the basic requirements for snow load criteria .

Create the same cross on the centreline for this test.

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)

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 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 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]

APPLY THE VALUES IN THE FORMULA :

In order to find the snow load criteria apply all the necessary values from the roof to the give formula

CALCULATIONS :

for moment of inertia value of BOW roof 1

for moment of inertia value of Centre roof rail

for moment of inertia value of BOW roof 2

AS VALUES OF S AND Qr are not satisfying the condition of the snow load condition we will add embosses to the roof to add more strength to the roof.

Embosses are 5mm outwards with 5mm edge fillets and 25 degree draft.

DRAFT ANALYSIS :

The Draft Analysis command enables you to detect if the part you drafted will be easily removed. This type of analysis is performed based on color ranges identifying zones on the analyzed element where the deviation from the draft direction at any point, corresponds to specified values.

Minimum draft angle of 7⁰ is considered for analysis . green colour infer on the parts that all face along the tooling direction has positive draft angle greater than 7⁰ and passed in analysis.

Outer Roof Panel:

Front Roof Rail:

Bow Roof 1:

Bow Roof 2:

Center Rail:

Rear Roof Rail:

AFTER THIS ALL THE PARTS ARE THICKENED 0.75MM.