Roof Design

https://drive.google.com/drive/folders/1k2ugKnEvdhxOvjcI30DPr0XeJPpyXjjS?usp=drive_link

A

Project Report

of

Roof Design

on

Nx Cad

By

Manish Kumar

Objective

To design the roof assembly from a roof part file with components such as front roof rail, rear roof rail and bow roof rail with reinforcements.

Analyse the bow roof prediction formula and snow load prediction formula of the assembly designed.

Introduction

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.

Types of Roofs

Fixed Hard Roof

It is the most common rigid roof found in the car. In modern car it is made up of plastic or steel. The fixed hardtop is your traditional car roof and is suitable for all climes and weather. It protects car occupants from the sun and wind when driving. It also offers more sense of privacy and noise-free driving. Many cars designed this way also tend to be more stable and solid than other types of roofs.

Convertibles Roofs

Convertibles are passenger cars that can be driven with or without the entire roof in place. There are different types of convertibles based on the method of conversion and the materials used.

Retractable hardtops:

A retractable hardtop — also known as "coupé convertible" or "coupé cabriolet" is a car with an automatically operated, self-storing hardtop, as opposed to the folding textile-based roof used by traditional convertible cars. These roofs are made from metal or plastic and is automatically retracted.

Detachable hardtops:

This type of hardtop is manually removed from the roof and then stored usually in the trunk. They are also made from metal or plastic.

Soft tops:

This type of convertibles has roofs that are not made from metal or plastic. They are made of textile. The earliest versions of the convertible used canvas for the roofs. More recent models use cloth materials instead. Other materials used now include latex, vinyl, polyvinyl chloride.When the roof is folded, it is called a stack.

The T-Top roof

An ‘almost convertible’ car. Actually, it was built this way because the car manufacturers were not sure the government of the day would approve convertibles. So, they made a ‘T-shaped bar’ from front to rear and made the roof on either side detachable. Of course, this type of roof is no longer in production.

Sunroofs

This type of roof is also quite popular. You might have been seeing it around. A sunroof is an operable type of roof that allows for an opening in the roof of an automobile; say a window in a roof. It can allow either light or air or both to enter the vehicle. They are either operated manually or automatically.

Types of sunroofs

Pop-up:

The pop-up sunroof usually tilts when you open it. It is the most basic and relatively cheaper type of sunroof. Some can even be removed so that they are kept properly, maybe in the trunk whenever you want to go ‘sunroof mode.’

A pop-up sunroof pops up!

Spoiler:

The spoiler is a pop-up that would slide, instead of tilting upwards. The advantage of this is that it can easily be restored to its original position by sliding.

Spoiler sunroofs are easy to slide

Panoramic sunroof:

Panoramic sunroofs are distinct. While other sunroofs basically allow air and light or both into the front seats, the panoramic sunroof would allow for both the front and rear. Of course, this means the aperture would be larger than the spoiler or pop-up, bit hey, what is the purpose of the window in the roof if it is not big enough. The sunroof allows car users to enjoy light and air without having to remove the entire roof. It also adds to the sleek design of the car and the automatically operated types just add to the awesome features of the car.

How the panoramic sunroof appears inside

Car roof Lining

The car roof lining is also known as a headliner or headlining. It is a fabric material used on the roof of an automobile. Its primary purpose is to:

· Enhance the interior beauty of the car by giving it a smooth texture.

· Absorb excess noise from outside.

· Regulates internal temperature by buffering heat and cold from outside.

Design of the Roof Assembly

The roof assembly consist of the outer roof panel, rear roof rail, centre roof rail, bow roof rail, rear roof rail.

Input Data

The skin surface of the Roof outer panel

Master section of various roof rails

Front roof rail

Rear roof rail

Bow roof rail

Centre roof rail without sun roof

Centre roof rail with sun roof

Outer Panel Improvement

The outer panel is improved as per the master section, from the front and the rear end.

Master section of roof outer panel from front end

The outer panel from the front end has a flange of length 21.5mm where the front roof rail is spot welded with the roof outer panel. A 2mm clearance is also given for proper spot welding.

Master section of roof outer panel from rear end

At the rear end the sharp bend and surface as per the vehicle design.

So, after analysing the outer panel master section the outer panel is need to improve from front end as well as from rear end.

Procedure of the outer panel improvement

From the front and side creating a surface using the law extension.

Joining it with the help with ‘through curve mesh’.

Using the law extension command creating the surfaces as per master section.

Joining all the surfaces either by edge blend or face blend.

Cutting the side of the outer panel at the rear end for different mountings.

+

The improved outer panel of the roof assembly.

Front roof rail

The front rail provides the strength to the outer panel from the front side. The design consideration taken care during front roof rail is the visibility of the car.

The master section of the front roof rail.

The commands used in the creation of roof rail

· Wave Geometry Linker

· Offset Surface

· Offset curve in surface

· Extend Sheet

· Law Extension

· Edge Blend

· Face Blend

· Emboss

· Trim

· Trim and extend

Procedure to create the front roof rail

Using the outer panel as the reference surface, offsetting the outer flange with 1.5mm.

Trimming the offsetting surface with 2mm clearance front side.

Offsetting the roof outer panel with the 32mm. Joining both the surface with law extension with 7-degree clearance.

For the rear end of the front roof rail, offsetting the roof outer panel with 6. 5mm.Cutting the surface with 10mm length.

Again, offsetting the roof surface with 4.5mm. and cutting the surface with 5mm length.

Joining all the surfaces with law extension.

Creating the emboss surface on the largest surface to increase the strength of the front roof rail.

The front roof rails

Analysis of the front roof rail

The front roof rail is analysed with joining positions with outer roof panel at different surfaces.

At the spot-welding position

There must be a contact between the spot-welding position.

There must be 2mm horizontal gap between the front roof rail and roof outer panel at front end.

At different position distance between roof outer panel and front roof rail.

At centre there must be 32mm, at mastic region 6.5mm and at rear end 4.5mm vertical gap respectively.

Different fillets of the front roof rail

The draft analysis of the front roof rail

Bow roof rail

The distribution of the bow roof rail in the outer panel depends upon the curvature of the outer panel, bow roof prediction formula and snow roof prediction formula.

The bow roof is created more along the flat surface of the roof outer panel.

The master section of the outer roof panel

So, creating one bow roof rail towards the front roof rail and 2 bow roof rails at the ends.

Master section of the bow roof rail

Taking the outer roof panel as reference, creating the bow roof rail using offset surface command, and law extension command.

The surface of the bow roof rail

Analysis of the bow roof rail

The bow roof analysis is done on the basis of the length of the bow roof length and the distance between the outer roof panel and the top surface of the bow roof rail.

The length of the bow roof rail is 74mmwhich is in the range of “65mm to 75mm”.

The mastic region between the roof outer panel and bow roof rail

Draft Analysis

Centre Roof rail

It is the surface of the roof assembly which is situated approximately in the middle of the roof outer panel. The master section of the centre roof rail is of two types.

Type 1

When sun roof is absent

Type 2

When sunroof is present

Since the vehicle has only one centre roof rail, then creating roof rail with sun roof present.

Procedure of the centre roof rail

Since centre roof rail with sun roof has two panels which are attached to each other.

The outer roof rail is offsetted twice with the distance of 7.25mm and 6.5mm respectively.

The mastic region should be at a distance of 5mm.

With the side view

Analysing of the centre roof rail with sun roof

The length of the centre roof rail is 80mm which is in the range of 80mm to 90mm.

The mastic region of the centre roof rail

Draft analysis of the centre roof rail

Bow roof rail 2

Using the same procedure as for the bow roof 1.

Analysis of the bow roof rail

Draft analysis

Bow roof rail 3

The bow roof rail 3 is created with the same procedure as the bow roof rail 1.

Analysis of the bow roof rail 3

The length of the bow roof rail 3 is 70mmwhich is in the range of 65mmto 75mm.

The distance between the bow roof rail and the roof outer panel is 6.5mm.

Draft analysis

Rear roof rail

The master section of the rear roof rail

The rear roof rail is created with taking the improved roof outer panel as the reference surface.

The image of the designed rear roof rail

Analysis of the Rear roof rail

The section view of the rear roof rail and the outer roof rail

The distance between the different surfaces of the outer roof rail and rear roof rail as mentioned in the master section

Draft analysis

Bow roof prediction Calculation

The value

Judgement Condition

OK< 2.7

Result

All the calculation are within the judgement condition.

Snow Load Calculation

Judgement Condition

Qr > 3.1

Result

All calculation with in judgement condition.

Manufacturing process

a. Cutting

Various cutting operation required for cutting of sheet metal in automobile. Laser, plasma, and shearing are the three common sheet metal cutting techniques in automotive part manufacturing.

Laser Cutting

Laser cutting is the most common automotive fabrication technique when there is a need for high-precision cutting. The process involves using a focused laser beam to melt and vaporize the sheet metal, leaving a precise and clean cut.

Plasma Cutting

This sheet metal cutting process uses plasma (high-velocity ionized gas) to cut a metal sheet. The plasma melts and blows away the metal. Plasma cutting is suitable for cutting thick materials, and you can enhance its precision and accuracy by integration with computer-controlled machines. Sheet metal plasma cutting is applicable in cutting thick sheet metal used in making the car frame and chassis.

Shearing

Shearing is another sheet metal cutting process that involves using a machine called a shearer to cut the sheet metal. The machine exerts a downward force to make a cut using the machine’s upper and lower blades. It is the basic sheet metal cutting process in automotive fabrication, but unlike the others, it is less precise and more suitable for car parts that do not require tight tolerance, like brackets and supports.

b. For forming techniques

Bending and stamping are cold-forming processes widely used in the automotive part manufacturing industry.

Bending

This involves creating angles and curves by deformation of the sheet metal using a press brake machine. The press brake machine applies force along a predetermined point on the sheet metal, bending it to the required shape/design. Bending is suitable for creating complex shapes and structural/body components such as brackets, frames, and doors in auto part fabrication.

Stamping

Also known as pressing, stamping is a set of car part fabrication techniques that involves pressing a die into a sheet metal. It comprises techniques such as blanking, punching, embossing, etc., that allow the creation of identical parts in high volumes. Stamping is a core automotive manufacturing process applicable in making auto parts such as body panels and brackets.

c. For joining sheet metal

Sheet metal joining techniques such as welding and riveting are among the oldest and most integral processes in automotive part manufacturing. Adhesive bonding is also an important application in the sheet metal industry.

Welding

Welding involves joining two or more materials using heat. The heat melts the two materials, fusing them to form the product.

Riveting

Riveting is more popular in joining dissimilar metals by creating a hole in each part, inserting a rivet in the hole, and deforming the rivet to secure the joint. Unlike welding, it is a cold joining process suitable for structural components of dissimilar materials, where strength and durability are essential.

Adhesive bonding

This involves using special materials with high adhesive properties to join two or more sheet metal parts. The adhesive material is applied on the surface of one or both parts and pressed together until curing occurs. The process is gaining popularity in the electric automotive industry because it does not contribute to weight but improves vehicle aesthetics.

Conclusion

The roof assembly with the component is within the judgement condition for the snow load and bow roof.

Challenge 4 link- https://drive.google.com/drive/folders/1k2ugKnEvdhxOvjcI30DPr0XeJPpyXjjS?usp=drive_link