Design of backdoor

Aim - Designing of back door using the provided styling surface and by using appropriate design methodologies.

About -

Backdoor of a car as the name suggests is installed at rear of the car. It provides an enclosure to the storage of a car called bootspace. These can be operated manually or automatically. Manual backdoor needs human effort to maneauver it to the opening position. It is stayed at the opening position using gas stays. Automatic doors have motors to assist opening and closing.

Fig - Backdoor of a car in open position

Manual or Gasstay supported backdoor -

Fig - gasstay supported backddor in open position

Automatic backoor - Assisted by motor for maneuverability at the click of a button. Although costlier than manual backoor.

Fig - Automatic or mototr assisted backdoor

Designing of a backdoor -

Disignig of a car's backdoor includes factoring in all requirements such as luggage volume or boot space, rear collision and visibility criteria. The thinner the backdoor, the more will be the boot space avilablein the car. Collisions at rear part i.e. backdoor of a car is another major factor to be catered carefully. Embosses are provided on the backdoor inner panel in such a away that the collision force is directed away and towards the frame of the car. embosses also help reduce the intensity of collision force thereby reducing the possibility of injury to occupants of the car.

Backdoor assembly components -

• Outer panel
• Inner panel
• Hinge and its reinforcements
• wiper motor rinforcement
• latch and striker & its reinforcement

Data taken for designing of the backdoor -

• Outer panel sheet metal thickness = 0.75 mm
• Inner panel sheet metal thickness = 0.75 mm
• Reinforcemnet thickness = 1.50 mm

CAD data of the backoor -

• Outer panel - Outer panel is a class 'A' surface which has the responsibility of improving the aesthetics of a car. It is the starting point in designing the backdoor of a car. The inner panel is proceeded with inputs from the outer panel.

Fig - Outer panel of the backoor

• Inner panel - Inner panel of a car is an output of data from the outer panel. It is on this part that embosses, mountings and their reinforcements are provided.

Fig - Inner panel of the backdoor

• Sealing flange - It is an integral part of the inner panel of the backdoor which is responsible for providing water and air tight environment to the boot space or inside space of a caar. A rubber sealant is provided on the flange which facilitates the contact between the backoor and the car body in a manner that outside environment conditions are not able to enter inside the car.

Fig - Sealing flange

• Hinge mountings and reinforcements - Hingesa are used to connect the backdoor with the roof of the car. They facilitate rotatory motion to the backdoor and also acts as support elements. Reinfrcements are provided for provided localised stregth to the sheet metal.
• Gas stay mounting - Gas stay areinstalled on the backdoor at thr gas stay mountings which are reinforced using reinforcements.
• Wiper motor mounting - Wiper motoris installed on the backdoor the bottom of the wind shield panel on the wiper motor mounting.
• Striker mounting - This facilitates accurate installation of striker so that peoper engagemnet happens between the latch and the striker.

Fig - Mountings and reinforcements

To reduce the vibrations, flanges are created on the inner panel which are joint using the mastic sealant to the outer panel of the backdoor. This also provides strength the outer panel of backoor at localised area.

Fig - Mastic flange

The installation of striker is done on the striker mounting which is an emboss of flat surface. A paricular trajectory is traced by the striker for getting in engagement with the latch.

Fig - Striker trajectory

• Hemming and hemming relief - Hemming operation is done for joining inner panel of backoor with the outer panel of the backdoor. Hemming relief are given at areas where the sheet metal is of the shape of a curvature to reduce the localised stress concentration.

Fig - Hemming

Fig - Hemming relief

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 deep drawing products. The deep drawings having two main categories.

1. First- stage drawing: The blank shape of metal is placed on the die and contact with the punch. When the metal specimen is flat piece of sheet metal used in forming and finish the product. 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 sliding over die and also stretched between die and punch. The metal in vicinity of punch head and contact with it bend and slide over radii and stretch over punch head.
2. Redrawing: The components drawn from 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 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, theoretically with no change in metal thickness or by-passing sheet or a strip of metal between rolls of the desired pattern. Metal sheet is drawn through the male and female roller dies producing a pattern or design on the metal 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

Blanking:

Blanking is a cutting operation of a flat metal sheet and the article punched out is known as blank. Blank is the required product of the operation and the metal left behind is considered as a waste.

Punching:

It is similar to blanking only the main difference is that, the hole is the required product and the material punched out from the hole is considered as a waste.

Hemming:

Hemming is a forming operation in which the edges of the sheet are folded or folded over another part in order to achieve a tight fit. Normally hemming operations are used to connect parts together, to improve the appearance of a part and to reinforce part edges.

In car part production, hemming is used in assembly as a secondary operation after deep drawing, trimming and flanging operations to join two sheet metal parts (outer and inner) together. Typical parts for this type of assembly are hoods, doors, trunk lids and fenders.

There are various types of hemming operations:

1. Conventional die hemming: In conventional die hemming, the flange is folded over the entire length with a hemming tool.
2. Roll hemming: In roll hemming, the hemming roller is guided by an industrial robot to form the flange.

Open Hem: A Hem has a full round feature and a return flange. In open hem bend angle is equal to 180 degrees.

Tear drop Hem: In tear drop hem the bend angle is greater than 180 degrees.

Closed Hem: Hems without any inside radius are called as closed hem. Closed hems are not recommended if the hem geometry is to be painted or if the material used is SST or Aluminium.

Draft Analysis - Draft analysis is done to check the feasibility of drawing operation on the sheet metal in the desired shape and size. The inimum angle for steel sheet metal is 7 degrres with the face of the tool advancing in the tooling direction vector.

Green colour shows that the the drawing operation for this design of sheet metal is feasible as the minimum drawing angle is 7 degrees with respect to the direction of tooling.