Design of backdoor

A BackDoor of a car gives access for the boot space to store luggage, spare wheel etc. These doors can be operated manually or electric powered. In most of the luxury cars, door is electrically operated.

Back Door Assembly:

• Inner panel
• outer panel
• hinge and its reinforcement
• wiper motor reinforcement
• latch & stricker and its reinforcement

Different Sheetmetal processes used for manufacturing the Back Door

Deep Drawing:

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

1. First- stage drawing: The blank shape of metal is placed on the die and it is made to contact with the punch. Initially the punch moves in downward direction. The outer rim of blank is subjected to pure radial drawing (drawing toward in vertical axes) between die and blank metal. The metal become a bend and slides over die.
2. Redrawing: The components drawn from first stage is redrawn and then it is converted into more depth to form a cup shape in the die and punch. This stage of drawing is called as redrawing.

Embossing:

Embossing is a metal forming process for producing raised or sunken designs or relief in sheet materials by means of matched male and female roller dies. Metal sheet is drawn through the male and female roller dies producing a pattern or design on the sheet. Depending on the roller dies used, different patterns can be produced on the metal sheet.

Materials commonly used in the metal embossing process include:

• Aluminum alloys
• Steel alloys
• Zinc
• Copper
• Galvanized steel
• Brass
• Cold rolled steel

Components to be designed:

Outer panel

It is the outer styling skin surface of the back door. It should have a good aesthetic view for a better markrt value. It is provided with multistage coatings which has property of scratch resistance, rust prevention etc. It is wrapped around the inner panel through hemming process.

Hemming: Hemming is a forming operation in which the edges of the sheet are folded over another part in order to achieve a tight/perfect fit. Usually, hemming operations are used to improve the appearance of a part and to reinforce part edges. In car production, hemming is used in an assembly as a secondary operation after deep drawing, trimming and flanging operations to join two sheet metal parts (outer and inner) together.

2) Inner Panel

The inner panel provides strength and helps in dissipation of forces outside the part with the help of embosses made on it. It helps in mounting of accessories like hinges, wiper motor, gas stay, latch & striker etc. The inner panel is produced by either casting or through Deep drawing process. Mostly Al is casted whereas steel inner panel are manufactured by deep drawing process. If deep drawn, there must be a tooling direction through which that panel must be deep drawn.

Also Embosses are provided to give extra strength to sheet in the inner panel and it also help to dissipate forces/energy towards a specific direction. Here embosses helps to direct the forces/energy towards the outer end of the backdoor.

Mastic Sealants: Bolting or spot welding or any other joining techniques may damage the aesthetic looks of the outer panel. Thus mastic sealants are used for joining the Inner panel elements with the outer panel. A maximum gap of 5mm is to be maintained in between parts where mastics are to be applied. These mastics are like a glue which are applied and both the parts are pressed which form a joining seals.

Reinforcements usually increase the strength of the panel in localized areas.It also helps to maintain rigidity of the panel assembly. The reinforcements are usually 1-1.5mm thick as opposed to 0.75mm thick panel is used in this design.

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.

Wiper Motor reinforcement

Wiper 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

Latch and striker assembly is over slamming and abusing while opening and closing of the door, thus arising the need for reinforcement to be placed at the bottom of the panel.

It has a proceedure to place on the panel. A circle whoce centre point is the midpoint of line joining two hinge reinforment is drawn. The trajectory of the Latcher should be tangential to the drawn circle.

All these three parts are then thickened to appropriate direction and are assembled together.

Draft Analysis:

The draft Analysis is done to view whether the part is manufacturable or not. For zero draft or negative draft, the parts are very tough to manufacture along the draft direction. It also give insights about the critical zones, so that appropriate changes in the design can be made if needed.