Design of backdoor

Back Door :

A door s 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. Sometry 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 compartiment. 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 same of the sport utility vehicles

Today's modem cars use top-mounted tallgating systems which are both pouvered and also gas stay supported These top mounted tailgates provide greater ear visibility compared to side-mounted or bar doors which have canter pillais in it.

Side Mounted :

As the name signifies side-mounted doors are the one which is used in the van type: MPV, 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 lury 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.

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 doorlift system.

Powered trunk lift system consists of a power latch, anti-pinch switch, PTG assy. PTG main switch. When the switch is pressed in the compartment or outside the power latch releases the latch and the entire backdoor is opened. The anti-pinch switch is located in order to avoid accidental hand insertion during the operation of the door.

BACK DOOR ASSEMBLY:

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

• Inner panel
• Outer panel
• Hinge and its reinforcement
• Wiper motor reinforcement
• Latch & stricker and its reinforcement

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 casted 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 casted 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 casted	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

• INNER PANEL:

The inner door panel is a component which is used for strengthening the door assembly and it is one of the most important components on which all accessories are mounted like hinges, glass guide channel moulded trim latch etc. The possible method is the integration method. In the integration method, the part is stamped out of a single blank. This reduces the number of tools needed, the assembly cost and eliminates any fit ability problem.

• Outer panel:

The outer panel of the back door is similar to other BIW components where it is the aesthetic part of a vehicle. The coating provided is of multi-stage which has the property of scratch resistance, rust prevention and smooth and attractive finishes. The outer panel also has the provisions for the tail lamp, rear fog lamp and also has the provision for licence plate mountings. Most of the hatchback cars have the provision for wipermotor.

• REINFORCEMENT:

The reinforcement provided is of 4 numbers which consist of hinge reinforcement gas stay reinforcement, wiper motor reinforcement and latch/striker reinforcement

• HEMMING OPERATION:

Hemming is a mechanical joint design which is used for joining inner and outer closure panels as found indoors, hoods, bonnets and lift gates. To increase crash resistance the gap between the hemmed panels is filled with a high-strength adhesive which also prevents from corrosion.

• Hemming relief

Hemming reliefs are cut-outs which are provided on the hemmed corner of the panel assembly which in turn to avoid some of the hemming defects such as wave-like OR wrinkle formed surface

• Wiper and wiper motor mounting

As the name suggests, wiper is used to wipe off the dust and water from the rear windscreen of the vehicle.

• Latch/striker rotation angle:

This rotation angle of the line denotes the line of action of backdoor when hinged to the body of the car.

LOAD CASE ANALYSIS

• Bend Test
• Torsion Test
• Abuse cases
• Dent test
• Assembly Load Cases
• Endurance test

Draft analysis :

Every part which is manufactured from press tool or other forming tools require some positive draft on the faces which are parallel to the tooling direction. If we don’t give draft (Zero Draft) or give negative drafts on these faces it will stick to the mould surface and when the mould is in motion it will destroy surface thus reducing its surface finish. Thus Draft Analysis command enables us to detect if the part we have drafted can be easily ejected or not. It also give insights about the critical zones, so that appropriate changes in the design can be made if needed.

Conclusion :

The backdoor sheet metal part body for the Hatchback car was successfully created taking into consideration all the attachments embossments, hemming, and finally with the proper draft angle so that the final component is manufacturable. The approach to design the inner panel was taken in such a way that it dissipates the force outwards in the various crash test.