Design of backdoor

Design of Backdoor

Objective:

To design Back door of car using the given surface by the styling team

Introduction

BACK DOOR

Back door or tail gate simply refers to the back of the car that can open and close.it covering the rear of the vehicle.It provide access to a cargo area (trunk/boot ).A tailgate hinged at the roof is a predominant characteristic of hatchbacks, estates/station wagons and lift backs .The door or opening of a cargo area may be hinged at the top, side, or bottom.

In most cars, usually this process will be done manually. One has to get down the car to open and close the tail-gate with the car key.Nowadays, automobile manufacturers providing Advanced features like the automated tail-gate. An automatic tail-gate in the car will do the process of shutting and opening the tail-gate electronically.

Functions of the Backdoor:

• It protects the occupants and luggage from getting damaged.
• It houses assembly of tail lamps, wiper motor and other components.
• It serves as entry and exit point for luggage/passengers.
• It houses windshield glass which helps in rear visibility.
• Parking sensors, rear view camera are mounted on it.

Types of Backdoor

Top mounted

These type of back doors are used in a station wagon, pickup truck and some other sports utility vehicles. Today’s modern cars use top mounted tailgating systems which are both powered and also gas stay supported. These tailgates provide greater rear visibility compared to other types.

Side mounted

It is generally used in van type MPVs, SUVs, pickup truck vehicles. These side mounted door/barn doors are a lot easier compared to top mounted ones.

These doors are generally small in size and can be easily accessed. These doors are more convenient for the goods handlers carrying lengthy objects, long pipes where one door is kept open. It also saves accidental head impacts. It is a lot easier to load /unload things in vehicles having side-mounted doors.

Bottom mounted

Bottom type or split type backdoor system is used in estate type cars, pickup trucks and some luxury SUVs. These are most convenient type of backdoor in which the bottom split is used as a support or even as a table for the touring people.

DESIGN CONSIDERATION OF back door

The design consideration of back door are ,

• Visibility Criteria
• Force Dissipation
• Latch and Striker Positions
• Hinge Position
• Gas Stay Position
• Hemming and Relief Areas
• Material selection

STAMPING PROCESS

Stamping processes to be used for a panel depend on its design. However, normally the processes used extensively are blanking, drawing, piercing, forming, notching, trimming,hemming, etc.

Blanking prepares the initial approximate form of the part in flat sheet. Drawing is generally the first operation to attain depth related form. Piercing, notching, hemming, are product design related operations.

Trimming generally removes the extra material on the periphery of the panel provided for blank holding during draw operation. Decision on trim line is very important and becomes deciding factor to obtain good draw.

1. Blanking

When required, blanking is the first step of the stamping process. Blanking is the process of cutting larger sheet or coils of metal into smaller, more manageable pieces. Blanking is usually performed when a stamped metal piece will be drawn or formed.

2.Piercing

If a part requires slots, holes, or other cutouts, piercing can be employed. Piercing, which can be performed simultaneously with blanking, punches the requisite shapes out of the metal sheet.

3.Drawing

Drawing is the actual stamping in the metal stamping process. A punch forces a section of metal through a die, providing the primary shape of the part. When the depth of the part is less than the primary opening, it is considered shallow drawing; parts with a depth greater than the opening are deep drawn.

4. Bending

Bending is a fairly self-explanatory process. The part-in-progress is placed on a specially designed die and a ram pushes against the metal, providing the required bend. Bending is performed after drawing, as attempting to punch an already bent piece of metal causes the entire part to deform.

5.Hemming

Hemming is a technology used by the automotive industry to join inner and outer closure panels together (hoods, doors, tailgates, etc.). It is the process of bending/folding the flange of the outer panel over the inner one. The accuracy of the operation affects significantly the appearance of the car’s outer surfaces and is therefore a critical factor in the final quality of a finished vehicle.

roller hemming :-The robotized hemming systems use a standard industrial robot integrated with a roller hemming head, offering a very flexible solution. This roller hemming head consists of a body, some guides and a number of rolls that are designed according to the geometry of the part in each case.

Materials Selection:

The selection of material plays a major role in determining the overall weight of the back door. The common materials used are Steel & Aluminum. The density of Steel is higher than Aluminum thus adding more weight to the door.

The material used in the manufacturing of the backdoor depends upon the budget of the car, most low cost vehicles use steel as it is cheaper compared to Aluminium.

Another aspect to be noted is that, if casting Aluminum parts are used instead of deep drawn steel parts there is no need of reinforcements and the overall weight of the car is reduced by approximately 5-10kg thus increasing the performance of the vehicle.

Also the draft angle for casting parts is around 3 degrees while for deep drawn parts is around 7-10 degrees which helps in increasing the luggage/ cabin space.

The below table gives a comparative information about Steel and Aluminium.

	Aluminium	Steel
Parts	Parts are casting process to make it	Parts are stamped
Reinforcements	Reinforcements can be neglected	Reinforcements are necessary
Thickness	Thickness can be varied	Thickness should be uniform
Weight	Lighter in weight	heavier in weight
Cost	Costly as compared to Steel	Cheap as compared to Aluminium
No. Of components	Less No. of components	More No. of components

PARTS OF BACKDOOR

• Back door outer panel (upper and lower)
• Back door inner panel
• Hinge reinforcements L & R
• Gas stay reinforcements L & R
• Latch and striker reinforcements
• Wiper motor reinforcements

BACK DOOR OUTER PANEL

In this design back door is created as two different parts back door outer panel upper and lower. This outer panel designed based on visibility criteria and proper reliefs provided at the corner for hemming operation .The thickness of outer panel is 0.75 mm .

Corner Relief:

During hemming process multiple rollers are used which causes vibrations and stress concentrations at the some locations due to which design intent of the panel shouldn’t be changed (i.e the panel should spring back to original formation after roller is removed). But most of the time that is not the case at corners so to avoid that situtaion reliefs are provided at corners.

BACK DOOR INNER PANEL

Back door outer panel designed based on hinge, gas stay, wiper motor position and reinforcement as well as visibility criteria .Suitable tooling direction is created for trouble free manufacturing process.In this design stamping operations created based on this tooling direction. Embosses are provided in this design for force dissipation. In this design appropriate clearance given in mastic areas .The inner panel thickness is 0.75 mm

Embosses:

It is provided to give extra strength to sheet metal panel and to help dissipate forces/energy towards a specific direction. Here embosses (Y/V emboss) are designed in such a way so as to direct them towards the outer end of the backdoor as shown in the image.

Mastic Area

Mastic sealants used for joining of outer panel and inner panel. It increase the strength of back door and good NVH. So accurate clearance given for mastic sealant.

Hinge mount & gas stay mount creation

Sealing Flange:

It is that section of the inner panel which enables the backdoor to sit over the rear body side of the car. Its design is important as it decides how a backdoor is mounted on the rear body side of the car and also restricts any external matter to enter inside the vehicle.

Reinforcements

Reinforcements are generally placed to increase the strength of the panel in localized areas which is relatively small compared to sheet metal parts for absorbing loads imposed thereon and dissipating such loads throughout the panel assembly to help maintain rigidity of the panel assembly. The reinforcements are usually 1-1.5mm thick as opposed to 0.75mm thick panel used in this part.

Hinge reinforcements

Hinge is a pivot mechanism which supports the total weight of the backdoor. So reinforcements are added for strength and rigidity.

Gas stay reinforcements

Gas stay is used to lift the backdoor automatically and is used to support the backdoor in its open position. It can be of Two types Semi-automated and fully automated.

Wiper Motor reinforcement

Wiper is used to wipeout the dust particles/water on the windshield glass which affects the rear visibility. It is actuated by the motor which is mounted on the inner panel. Due to vibration and heat of the motor, inner panel gets deformed which results in loss of strength & rigidity of the panel thus leading to poor NVH. So reinforcement is provided to avoid these conditions.

Latch and Striker reinforcement

In the bottom part of the panel emboss is created for placement of latch and striker assembly. There is over slamming and abusing while opening and closing of the door, thus arising the need for reinforcement to be placed.

Positioning of Latch & striker/ Latch Trajectory:

Backdoor is the swinging part which rotates about hinge axis. The position and orientation of latch striker is important for proper opening and closing of the backdoor. The positioning is done by sketching a circle with center as the axis of the hinge which passes through the striker at appropriate position with respect to inner panel.

Draft analysis

PERFORMING FEATURE DRAFT ANALYSIS

• The draft analysis was performed on each thickened surface.
• This draft analysis is done to check the manufacturing feasibility.

Gas stay reinforcements

Hinge reinforcements

Latch and Striker reinforcement

multiple views

CONCLUSION

The backdoor is designed based on design considerations .Required reinforcement provided on inner panel. The design is checked by using draft analysis feature