Design of backdoor

Aim:

Use the provided styling surface to come up with a back door design, use appropriate design methodologies, and provide the necessary reinforcements and embosses.

What is a back door?

A door is a hinged part which is used for entry and exit of the vehicles. Back doors are one of the type doors of the vehicle which are located next to the passenger seat which provides access to the luggage compartment. In most of the cars, these back doors are operated with the help of gas stay which in turn reduces the effort required to lift open the door. Some luxury cars have powered backdoor which in turn is driven by an electric motor. This kind of system is also called a powered trunk lid system. Hatchback or station wagons are sold as 3 door or 5 door models. In this case, the rear hatch is classified as door this is because it enters the passenger compartment. The naming is mainly used in Europe countries. In case of safety, the back door designed should meet the safety requirement for the rear collision.

Types of the back door based on working positions:

The door or opening of a cargo area may be hinged at the top, side, & bottom. If the door hinged in the bottom it is called as a tailgate.

Top-mounted:

This type of back doors is used in a station wagon, pickup truck and some of the sport utility vehicles.

SIDE MOUNTED DOORS:

As the name signifies side-mounted doors are the one which is used in the van type MPVs, SUVs, pickup truck vehicles. These side-mounted doors or barn doors are a lot easier compared to top-mounted doors.

Bottom / split type:

This bottom type or split type backdoor system are used in the car type such as estate type car, pickup trucks and some luxury SUVs.These are the most convenient type of back door in which the bottom split is used as a support or even as a table for the tour going people.

Types based on working mechanism.

Gas stays type:

Gas stay types backdoor/liftgate/tailgate is an ideal and most commonly used tailgate mechanism from lower segment car to luxury car segment. The ideal components of tailgate consist of a hinge, door, gas stay and some rubber beadings for sealing of door which is shown in the image below:

Powered lift system:

Power trunk lid system is another sophisticated way of trunk/liftgate opening mechanism which is to automatically open and close of the trunk/liftgate and release of the latch by the touch of a button. The following image shows the component as used in the powered trunk/back door lift system.

BACK DOOR ASSEMBLY:

The back door assembly of a hatchback or SUVs has the following components.

• Inner panel
• Outer panel
• Hinge reinforcement
• Gas stay reinforcement
• Wiper motor reinforcement
• Latch/striker reinforcement

Different processes used for manufacturing the Back Door:

Deep Drawing:

The metal deep drawing process is an effective method of manufacturing cups, cans, and other similar deep drawing products. The deep drawings having 2 main categories.

1. First-stage drawing: The blank shape of metal is placed on the die and in contact with the punch. When the metal specimen is a flat piece of sheet metal is used in forming and finish the product. Initially, the punch moves in a downward direction. The outer rim of the blank is subjected to pure radial drawing (drawing toward vertical axes) between the die and blank metal. The metal becomes a bend and slides over the die and is also stretched between die and punch. The metal in the vicinity of the punch head and contact with it bend and slide over the radii and stretch over the punch head.
2. Redrawing: The components drawn from the first stage again it is redrawn convert into more depth to form a cup shape in the die and punch. The second stage of drawing is called redrawing.

DESIGN OF BACKDOOR:

The Outer Panel is the styling surface of the back door design. Other components of the backdoor are designed with reference to the outer panel surface. It acts as the outer cover & deals with the aesthetics of the car.

In this design outer panel is divided into two-part.

1. Outer Upper Panel
2. Outer Lower Pane

Outer Upper Panel:

The Outer Upper Panel Extracted from a provided styling surface.

The panel is modified for the required design with the surface tools of NX CAD.

The thickness provided to the outer panel is 0.75 mm.

Hemming is provided with corner reliefs.

Outer Lower Panel:

The Outer Upper Panel Extracted from the given styling surface.

The panel is modified for the required design with the surface tools of NX CAD.

The thickness provided to the outer panel is 0.75 mm.

Hemming is provided with corner reliefs.

Outer Upper & Lower Panel:

Tooling Direction:

• Before starting to design the inner panel of the back door the tooling direction for Deep Drawing purposes should be created.
• Then the styling surface needs to be checked properly and analyzed since it might have irregularities, hence it must be fixed first.
• The back door was designed using a top-down approach.

DESIGN OF BACKDOOR INNER PANEL:

The Inner Panel Extracted from a given styling surface.

The panel is modified for the required design with the surface tools of NX CAD.

The thickness provided to the outer panel is 0.75 mm.

MASTIC SEALANT:

The mastic sealant is used to fix the inner panel and the outer panel which increases the NVH factor & stiffness of the back door.

HINGE, GAS STAY, WIPER MOTOR & LATCH & STRIKER EMBOSS:

The upper two reinforcements denotes the hinge emboss which was created using the datum plane and emboss feature in NX. It is also designed in a way that the emboss should have a flat surface for assembling the hinges using it.

The side reinforcements denotes the gas stay emboss which was created using the surface of the connecting flange.

The middle reinf. denotes the Wiper motor emboss which was created using the surface of the connecting flange.

The bottom reinf. denotes Latch and Striker emboss were designed by creating a trajectory that follows the opening and closing of the back door with respect to the axis of the hinge.

Trajectory:

The position of the hinge should be perpendicular to the latch at the time of latch and striker meets. The circle is drawn from the centre of the hinge axis to find the path of the striker and perpendicular to the path.

HEMMING:

Hemming & seaming are two similar types of metalworking processes in which a sheet metal edge is rolled over onto itself. Hemming is the process in which the edge is rolled flush to itself.

• The outer panel was designed as two different parts named as outer upper panel and outer lower panel.
• After designing the outer panel, the Hemming was created by offsetting the surface with the help of face blend & swept surface.
• The two different outer panels will be joined using Blanking

CORNER RELIEF:

During the hemming process, when giving the Corner Relief helps to control sheet metal material behavior & to prevent unwanted deformation during unbend operations & also helps to minimize the number of passes in hemming.

DESIGNING THE REINFORCEMENTS:

The thickness provided for all reinforcements is 1 mm.

1. Hinge Reinforcement
2. Gas stay Reinforcement
3. Wiper motor Reinforcement
4. Latch Reinforcement

Hinge and gas stay reinforcement:

Hinges allow 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. Hinges can be placed outside or inside the backdoor.

The hinge reinforcements are added to compensate for the weak region due to the acting load over it.

Gas Stay is a device used to support the back door in its open position. Gas stay requires no manpower & it is engaged into support position automatically as the back door opens. One end of the Gas Stay is fixed on the backdoor & another end is on the Body Side or on the Back door stationary area.

Embossing is provided at the Gas Stay mounting area to compensate for weakness & improve strength.

Wiper Motor Reinforcement:

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

Latch and Striker Reinforcement:

The Latch & Striker together form 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 & Striker area. To recoup for the same, reinforcements are added in this area.

DRAFT ANALYSIS:

• The draft analysis was performed for the tooling direction created at first and checked that the model is suitable for manufacturing.
• Then to get a complete green portion the required changes to the draft angle of the embosses were carried out by optimizing the model.
• The Draft Analysis command is used to detect that the part drafted will be easily removed or not.
• This type of draft analysis is performed based on colour ranges.
• The identifying zones on the analysed element where the deviation from the draft direction at any point, corresponds to specified values.
• The red zone which can be seen will not be done in deep drawing instead it will be a cut out seperatelly so the analysis shows the part is manufacturable.

Views of Back door design:

CONCLUSION:

The inner panel has been designed keeping in mind the tooling direction with necessary embosses and reinforcement slots in necessary places. The mastic flange is also made with necessary distance and draft analysis has been done which indicates the part can be deep drawn.