Roof Design
ROOF DESIGN
ROOF DESIGN IN SIEMENS NX SOFTWARE
OBJECTIVE OF REPORT
The objective of the Report of this project is to explain the 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 given styling surface. Perform a curvature study on the roof and perform the heat distortion and snow load criteria calculations to determine whether the bow roofs are at the correct positions. Finding a moment of inertia and section modulus for Bow roofs, central roof rail. front roof rail and rear roof rail and Perform a Draft Analysis.
ABOUT
The design of any product starts from a Necessity. The design engineer sketches the product based on the requirement. Then the 2D sketch with the proper dimensions is converted into a 3D model using advanced CAD software. Another important thing in the design is that every product that is designed should be able to manufacture. so, the role of the design engineer is to design a product that can be easily manufactured and with less cost-effective. This is the place where the Design for manufacturing [DFM] and Design of assembly [DFA] take a role while developing any product. The process of development of the design carries on until the design satisfies the customer’s needs. Here in this project, the product that we are going to develop is a car roof for various vehicles or individuals walking.
An automobile Car 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. The roof is the structure above the windshield glass having the reinforcements to provide strength to the overall structure and to withstand overhead forces like snow.
Reinforcement in Automobile Roof and Its Type
Since the Car roof is flat and it is very weak and cannot able to withstand the forces like snow and any crash case, so in order to increase the strength of the roof we use reinforcements like the 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 and Some we use emboss also to increase the strength of automobile roof.
There are some types of Reinforcement listed below-
1-Front Roof Rail- Front roof rail is the one that joins the windshield glass, the body side outer and the inner panel also. Here the front roof rail is designed based on the master section given.
2-Rare Roof Rail- It is part of an automobile roof that connects the back door and the body’s outer side, rare roof design as per mention in the master section of the challenge.
3-Central Roof Rail-central 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 central roof rail is placed at the centre of the roof which is connected to the B-pillar support structure. This central roof rail helps in adding strength to the roof during the roll-over test. The thickness of the central roof rail is 1.25 mm.
4-Bow Roof Rails-The bow roofs are given to improve the torsional stiffness and load-bearing capacity of the roof structure. The number of bow roofs presents depends on the overall size of the roof. Presently in this project, two bow roofs are added.
DATA TO BE USED FOR DESIGN
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JOINING PROCESS OF ROOF AND REINFORCEMENT
Mastics are introduced between the roof outer panel and the reinforcements for joining. where ever the mastic is introduced there is a remarkable improvement in the strength.
Spot welding is also introduced to join the reinforcements and the outer panel.
The important point at the time of designing- there are a few points which are quite very important at the time of designing the roof of the car.
1-visibility criteria
2-head clearance
3-curvature study
4-heat distortion and snow load study
5-draft analysis
Roof Crush testing- The roof crush test is the design given by the IIHS (insurance institute of highway safety). After analysing the many accidents IIHS has then fixed some regulations, that how to perform the crush test. IIHS gives the rating based on this test. For this, they consider two points while giving the rating.
The main analysing factor at the time of testing are-
How fast the car can reform to its original shape after the rollover?
how deep is the protrusion after the rollover?
Advantages of roof crash test- To minimize the protrusion into the occupant compartment, so that the seat belts and airbags can do their job in protecting the occupant.
Main Condition for Crash Test- There are two conditions that should be followed for the roof crush test, they are
First Condition-
- Close and lock all door
- Close all Window
Second Condition-
Fix the body sill or chassis frame on a hard lever surface horizontally.
The process to apply force during a crash Test The load is applied in such a way that 5 degrees is tilted from the front end to the rear end and the load will be 1800 mm in length and 750 mm in width. The load is applied at the position of 25 degrees from the flatness of the roof. The load is applied on the roof for almost 120 sec and the crushing speed at which the load is applied is 13 mm/sec or less than that.
Result- If the displacements go 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 rollover crashes.
Heat Distortion Study on design roof- the heat distortion study plays a major role in sheet metal usage. heat distortion temperature is a temperature limit above which the materials cannot be used for 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 an elevated temperature. In order to avoid bending or damage to the roof, based on the heat distortion temperature, this study will predict the bow roof position which helps to strengthen the roof.
Process Involved and Calculation
Calculation- As per Above mention Formula Put all Values From the table it can be concluded that all values of w<2.7 and also not w>3.1 so this infers that the current positioning of the bow row is good in the state as per the design and found correct.
Snow Load Study on design roof- This test is done to know how is the roof behaving when there is snow over it. normally due to the snow weight the dent will happen. But the roof could be designed in such a way that when the snow is removed roof should go it its original position. These are the basic requirements for snow load criteria.
Process Involved and Calculation
Calculation- In order to find the snow load criteria, apply all the necessary values from the roof to the given formula It is observed from the values that obtained values of QR > 3.1, So we can as per our predicted method design is correct. Since at the end between the bow roof rail first to rare roof rail for calculation of the value of s only L1 is available, and L2 is unavailable, so we didn’t calculate the last case, the in this only have to study three cases.
Section Modulus Analysis- Section moment of inertia is used to predict the amount of deformation and deflection of a part. A higher moment of inertia is preferable as it reduces the amount of deflection for a given force. The thickness of the part and the addition of flanges and embosses increase the section inertia of the part. Here the master sections of the roof and roof rails and their section analysis are given.
Roof Rail 2 Section-
Moment of inertia maximum, (MAX) Imax=4.65×10^4 (mm4)
Moment of inertia maximum, (MIN) Imin=4.24x10^4(mm4)
Roof Rail 1 Section-
Moment of inertia maximum, (MAX) Imax=4.69×10^4 (mm4)
Moment of inertia maximum, (MIN) Imin=3.58x10^4(mm4)
Centre Roof Rail Section-
Moment of inertia maximum, (MAX) Imax=5.93×10^4 (mm4)
Moment of inertia maximum, (MIN) Imin=3.26x10^3(mm4)
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 colour ranges identifying zones on the analysed element where the deviation from the draft direction at any point, corresponds to specified values.
A minimum draft angle of 7 degrees is considered for analysis. green colour infers on the parts that all face along the tooling direction has a positive draft angle greater than 7 degrees and passed in analysis.
Bow Roof Rail 2 Draft Analysis
Central Roof Rail Draft Analysis
Bow Roof Rail 1 Draft Analysis –
Front Roof Rail 2 Draft Analysis-
Rare Roof Rail 2 Draft Analysis-
Front View of roof Assembly
Conclusion- Hence the roof, front roof rail, bow roof rails, central roof rail and rear roof rail is designed by following the master sections and the moment of inertia and draft analysis are carried out to check the feasibility of manufacturing.
Thank You