Design of backdoor

Backdoor Design

Aim: To design a sheet metal panel of backdoor from the provided skin data taking all the design rules into consideration.

Abstract: A backdoor of a car also known as tail gate is a commodity which normally serves the purpose of covering the car from the rear end. But there are more functions that come with it which has to be considered while making a design of the same like rear visibility criteria and boot space. This part is usually designed keeping the master section of the rear roof rail because of the sealant flange and also various other considerations, as it is also in contact with the side body of the car.

Theory: Before starting the design of backdoor, we have to decide which type of backdoor we have to design because this step includes the hinge axis. This axis is the one about which the backdoor will open and close. There are three types of backdoor:

• Top mounted
• Side mounted
• Bottom mounted

It is needless to say that the hinge axis will be at that specific position where the tail gate is mounted. This initial step helps us to determine the position of latch and striker.

REPAIRING INPUT

The first step is to organize the input skin data as upper outer surface and lower outer face. But before that we have to check for any irregularities in the surfaces and repair if and sew them together.

SEALING FLANGE

Usually we will take reference from the roof master section for the sealant flange, but as it was not available we have made entire sealing flange in this model. The space occupied by the rubber sealant is usually in the range of 15mm-25mm. 25mm is the open condition, so we made maintained that distance between inner panel and the sealing flange. Once this flange is made, we make a connecting flange on both sides of it and complete this flange to be joined with inner panel.

INNER PANEL

The shape of the inner panel is same as that of the outer panel up to the windshield surface. After that we have to make space for various components such as latch and striker motor etc. So we make a proper curved surface at the lower side so that we avoid kinks at the mirroring plane. Once the main body is ready, we have to decide the design of the following things:

• Mastic region: whether we have to design it as a big one at a single region in the centre or two small regions.
• Emboss: we have to create proper emboss either Y or V or combination of both to diverge the force.
• Latch & striker motor space: this will be mounted on one side of the inner panel, but we must make a similar cutout on both the sides keeping centre of gravity in mind.
• Material cut-outs: due to ample space, we should remove the material from few regions to reduce weight of the inner panel.

There are few mountings which we have to keep in mind and make reinforcements for the same:

• Hinges: this model is made such that the backdoor will be mounted on the roof, so the hinges mounting emboss has to be provided accordingly on the top somewhere.
• Gas stay: the backdoor will have gas stay method for opening and keeping it open. Thus this mounting emboss will be needed somewhere on the side.
• Wiper motor: the backdoor will also have a wiper whose motor is to be mounted somewhere. As only single wiper will be present, it is common to give this in the middle near windshield.
• Latch and striker: it is the one which locks and unlocks the backdoor and as the backdoor rotates on the hinge axis, this must be present on that patch only.

Once all these design is made, we move on to make the mirror of the model in order to make it complete. After mirroring the inner panel, a handle mounting space is provided. After the detailing work is done, it is thickened with the thickness of 0.75mm.

MASTIC REGION

Inner and outer panel is joined using hem, but to make this bond stronger we introduce a paste between them which becomes like a rubber after solidifying. This paste covers around 80mm dia circular region around it and is firm for the distance of about 4mm to 5mm. Thus we must have a structure which is projected from the inner panel towards the outer panel and this must be around 5mm away from the outer panel to serve its purpose.

EMBOSS: This feature helps to increase the strength and reduce witherness of the backdoor. It must be prjected toward the inner panel so that in case of rear crash, this should come in contact. Apart from increasing the strength of the panel, its shape also help to diverge the force outwards. This definitely helps to atleast reduce the net force which is directed inside the car. For diverging the force, we popularly use Y or V emboss.

LATCH & STRIKER MOTOR MOUNTING: This motor operates the opening and closing of the hood. But if we make a cut-out for this motor at only region, then it will cause imbalance in our model and the centre of gravity will shift. Hence to maintain CoG we create a similar cut-out in the other side also. In the given image, motor will be mounted on the left side (with moutning holes) and a similar cut-out is made on the other side.

REINFORCEMENTS:

HINGE REINFORCEMENT:

GAS STAY REINFORCEMENT:

WIPER MOTOR REINFORCEMENT:

LATCH & STRIKER REINFORCEMENT:

HEMMING:

Hood outer panel and inner panel are joined together using hemming process. In this process the outer panel is wrapped around inner panel from all the sides to restrict its movement. This is done using rollers. The following link is to the video of hemming process.

https://www.youtube.com/watch?v=8iOoeNe6BT8

As in this model upper and lower are separate components and the part is complex unlike hood panel, creating a hem in a single step is not possible. Hence a different approach is followed while making the hem.

1. First the outer panel is offset by a distance keeping the thickness and direction in mind.
2. The sheet is trimmed so as to get a flange of 15mm width.
3. Then a bride curve is made between outer panel and the hemming flange. This curve will act as primary curve for us.
4. Then multiple swept surfaces are created to get hem like surface.
5. Everything is sewed together to get a single outer panel.

FINAL MODEL

CONCLUSION: A backdoor with proper design rules and industry standards is created.