Design of backdoor

DESIGN OF BACKDOOR

OBJECTIVE:

1. From the given styling surface, develop a back door using appropriate design methodologies.
2. Provide the necessary reinforcements and emboss definitions.

SOFTWARE USED: NX 12

INTRODUCTION:

In this project I have are designed a back door for a hatchback where it is hinged at roof level (as opposed to the boot/trunk lid of a sedan, which is hinged below the rear window). Similar to the hood and side doors, back door is a swinging/closure commodity in a car. It consists of an outer and inner panel. It is a very critical component because of the passenger safety requirements.

Backdoor has to be designed by keeping in mind the space required for the luggage compartment as well as to accommodate the Latch and Striker motor and Wiper motor without compromising the strength of the component.

Usually Aluminum or Steel is used to manufacture the backdoor. While Aluminum backdoor is lighter in weight and has lesser number of components (since the part is “cast”, it has varying thickness and therefore doesn’t require reinforcements), Steel backdoor is “deep drawn” with uniform thickness, added reinforcements and therefore is heavier. But the production cost of the latter is lesser and therefore a Steel backdoor is priced lower.

MAIN COMPONENT OF BACKDOOR:

1. Outer panel upper
2. Outer panel Lower
3. Inner panel
4. Latch and Striker Reinforcement
5. Hinge Reinforcement
6. Gas stay Reinforcement
7. Wiper motor reinforcement

DESIGN CONSIDERATION FOR BACK DOOR :

1. Rear Visibility
2. Boot Space and accessibility
3. Fit and Clearance
4. Support Structures like hinge and gas stays
5. Mounts for wiper motor, tail lamps, and other wiring loops

DESIGN METHEDOLOGIES:

OUTER PANEL:

The Outer Panel is the styling surface of the back door. It is the source of design of other parts of the back door, primarily the Inner Panel. It acts as the outer cover and deals with the aesthetics of the car. It's thickness is in the range of 0.65-0.75 millimeters.

INNER PANEL:

The Inner Panel provides strength to the back door. They are of 0.65-0.75 millimetres (mm) thick. It is the Inner Panel where reinforcements and embosses are provided to justify its function.

There are many cases where the Inner panel is subjected to stress due to frequent opening and slamming. These stress and depression factors are compensated by features like embosses and reinforcements.

The inner panel accommodates the Latch and Striker actuator, Wiper motor actuator, Trims mounting, Hinge and Gas Stay embosses, V-Emboss, Latch, etc and therefore the necessary cut outs are provided. Various reinforcements are also spot welded to the inner panel.

HEMMING:

Hemming is a metalworking process in which a sheet metal edge is rolled over onto itself. The outer and inner panel is joined together using Hemming operation like we do for other closure and swinging components. There is a 0.2 mm gap between the two panels and 1-2 mm clearance at the edge of the inner panel. This space is provided for the sealant to ooze out and spread properly between the panels after the Hemming process in order to achieve water tightness.

Hemming is preferred over Spot Welding given its superior aesthetic finishing. Hemming relaxations/reliefs are provided at the corners and closure areas to avoid intolerance issues arising from the rolling process.

The portion of the inner and outer panel along the Wind Shield glass is joined using Brazing. Brazing is also used to join the upper and lower outer panels if they are manufactured separately.

MASTIC SEALANTS:

To improve NVH (Noise, Vibration and Harshness) i.e to reduce these levels, Mastic Sealants are used. They also improves the strength. They are made of hard Rubber and are introduced as a paste thereby joining the inner and outer panel with a thickness of 5mm. Mastic Sealants are preferred over Spot Welding to join the inner and outer panel due to the fact that the latter reduces the aesthetics of the car, especially on the outer panel which is the styling surface.

REINFORCEMENT& EMBOSSES:

Reinforcements and embosses are added or designed to compensate for loss of strength in a region or area due to the load acting there. In back door's case load acts in the form of Hinge, Gas Stay and Latch & Striker. These load cases are determined with the help of various tests and simulations.

GAS STAY REINFORCEMENT:

Gas Stay is a device used for supporting the back door in its open position. Gas stay requires no man power and is engaged into support position automatically as the back door opens. One end of the Gas Stay is fixed on the backdoor and the other end on the Body Side or on the Back door stationary area. Embossing is provided at the Gas Stay mounting area to compensate for the functional holes punched. Various simulation tests like Bend test, Torsion test, Abuse test performed on the back door as shown above reveals that there a very weak zone developed at the Gas stay region. To compensate that, a reinforcement is added in that region.

HINGE REINFORCEMENT:

Hinges enable the opening and closing of the back door. One end of hinge is fixed on the backdoor and the other end on the Roof, on both sides. Hinges can be placed outside or inside the backdoor. Similar to Gas Stay, Hinge reinforcements are added in this region to compensate for the weak zone developed due to the load acting while opening and closing the backdoor

The position of the hinges are determined by the midpoint of axis of the Hinges called the Hinge Axis point, which should be aligned with the Latch and Striker through the trajectory of the back door opening and closing. If the Striker is exactly perpendicular to the trajectory, then the Hinges can be fixed accordingly on the inner panel. Embossing is done at the Hinge placements to compensate for the functional holes punched.

LATCH & STRIKER REINFORCEMENT:

The Latch & Striker forms the locking mechanism of the backdoor with the car. Due to regular opening, closing and over slamming of the backdoor, there is stress developed in the Latch and Striker area. Further, during a rear collision this area will be the first point of contact. To compensate for the same, reinforcements are added in this area.

WIPER MOTER REINFORCEMENT:

Wiper motor reinforcement is created to mount the wiper motor assembly.

FINAL ASSEMBLY:

DRAFT ANALYSIS:

Draft Analysis is done to analyze the draft angle. This allows us to verify whether the product will be easily removed from the tool. When designing a product they need to be angled slightly so that the tool can be pulled away from the object easily, without deformation or damage. This slight angle is called draft.

I have given the condition for draft angle with a maximum deviation of 9 degrees. Anything within that limit is shown in green, which means that the part is producible.

CONCLUSION:

Thus the Back door was designed and developed from the given styling surface with essential reinforcements and emboss definitions. Draft analysis was also done on the Inner Panel.