Design of backdoor

Aim: - To Develop the back door from the given styling surface.

Introduction:-

In this project, I have been 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, the 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.

The 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, Aluminium or Steel is used to manufacture the backdoor. While the Aluminium backdoor is lighter in weight and has a lesser number of components (since the part is "cast", it has a 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 Steelbackdoor is priced lower.

Outer Panel and Inner Panel:-

The Outer Panels 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. Its thickness is in the range of 0.65-0.75 millimetres

The Inner Panel provides strength to the back door. They are 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.

Reinforcement:-

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 are joined together using Hemmingoperation as we do for other closure and swing 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.

Mastic Sealants:-

To improve NVH (Noise, Vibration and Harshness) i.e to reduce these levels, Mastic Sealants are used. They also improve strength. They are made of hard Rubber and are introduced as a paste thereby joining the inner and outer panel with a thickness. 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.

Reinforcements and Embosses:-

Reinforcements and embosses are added or designed to compensate for the loss of strength in a region or area due to the load acting there. In the back door's caseload 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 Star Reinforcement:-

Gas Stayisa device used for supporting the back door in its open position. Gas stays require no manpower and are 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 ng is provided at the Gas Stay mounting area to compensate for the functional holes punched.

Various simulation tests like the 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 for that, reinforcement is added in that region.

Hinge reinforcement:-

Hinges enable the opening and closing of the back door. One end of the 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 the 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 and 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.

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 a draft.

I have given the condition for draft angle with a maximum deviation of 6.9 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.