Design of backdoor

Aim: 

Designing the Backdoor by Using the provided surface to come up with a back door design and  using appropriate design methodologies and make the necessary reinforcements and embosses.

Back Door:

• A Back door is a hinged part which is used for openning and clossing the rear side when you need to access the space
• 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.
• 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.

1) Top-mounted:

        This type of back doors is used in a station wagon, pickup truck and some of the sport utility vehicles. Today’s modern cars use top-mounted tailgating systems which are both powered and also gas stay supported. These top mounted tailgates provide greater rear visibility compared to side-mounted or bar doors which have canter pillars in it. 

2) 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. These doors are generally smaller in size and can be easily accessed. These doors are more convenient for the goods handlers for long pipe and lengthy components where one door is kept open. These doors also save accidental head impacts. It is a lot easier to load and unload items in the side-mounted doors.

3) 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.

1) 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:

Power Spindle 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.Powered trunk lift system consists of a power latch, anti-pinch switch, PTG ass’y, 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.

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

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.

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.

SPOT WELDING:

Spot Welding is a form of resistance welding also known as Resistance Spot Welding (RSW). Spot Welding involves using heat produced by resistance to an electrical current to join materials together. The current heats the materials to a point where they become malleable. The use of strong pressure bonds them together.

Another form of resistance welding is Projection Welding. This process involves fusing a fastener’s embossed or coined projections to the metal base material to form a weld. As the materials never melt, they do not intermix. This means the resulting weld is more like a forging of the materials.

Spot welding is only suitable for a small selection of base materials. Low carbon steel is the most suitable material for spot welding. This is because it is more resistant to electricity and has a lower thermal conductivity than the copper electrodes used to create the required electrical current.

High carbon steels and aluminium alloys can form brittle welds that don’t last with the spot welding process. Pure aluminium can qualify for spot welding but requires higher current levels. This is because it has a lower resistance to electricity than low carbon steel.

The outter panel upper and outter panel lower are joined through the spot welding .So there must be no gap between the outter panel upper and outter panel lower.

BACK DOOR ASSEMBLY:

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

• Inner panel
• Outter panel upper
• Outter panel lower
• Reinforcement

DESIGN OF BACKDOOR OUTER PANEL:

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

In this design outer panel is divided into two parts

1. Outer Upper Panel

2. Outer Lower Panel

Outer Upper Panel:

•           The Outer Upper Panel Extracted from a styling surface.
•           The panel is altered for the required design with the surface tools CATIA V5.
•           The thickness provided for the outer panel is 0.75 mm
•           Hemming is provided with the corner relief.

Outer Lower Panel:

•            The Outer Upper Panel Extracted from a styling surface.
•            The panel is altered for the required design with the surface tools of CATIA V5.
•            The thickness provided for the outer panel is 0.75 mm.
•            Hemming is provided with the corner relief.

Outer Upper & Lower Panel:

Tooling Direction:

• Before starting to design the inner panel of the back door the tooling direction for Deep Drawing purpose should be created.

• Then the styling surface needs to be checked and analyzed since it might have irregularities, hence it must be fixed first.

• Then the back door was designed using the top-down approach.

DESIGN OF BACKDOOR INNER PANEL:

•            The Inner Panel Extracted from a styling surface.
•            The panel is altered for the required design with the surface tools of CATIA V5.
•            The thickness provided for the outer panel is 0.75 mm.

    After creating the tooling direction the design of the inner panel will begin where we will first develop an effective sealing flange by checking all the boundaries and by following the shape of the inner panel design. By creating multiple flanges and by using surface modeling techniques the concept design of the inner panel was created.

• After the concept of the inner panel is developed, then the child components like a hinge, latch, gas-stay locations, and their reinforcements must be designed. Which completes the overall design of the tailgate.

• The embosses were created in ‘V-Shape or Y-Shape’ so that if the vehicle undergoes the crash then the force dissipates over it which reduces the damage transferred to the trunk space.

MASTIC SEALANT:

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

HINGE, GAS STAY & WIPER MOTOR EMBOSS:

LATCH AND STRIKER EMBOSS:

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

HEMMING:

             Hemming and seaming are two similar 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 separate parts named as outer panel upper and outer panel lower.

• After designing the outer panel the Hemming was created by offsetting the surface with the help of face blend and swept surface.

• The two separate 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 and to prevent unwanted deformation during unbend operations and also helps to reduce the number of passes in hemming.

DESIGNING THE REINFORCEMENTS:

The thickness provided for all reinforcements is 1.5 mm.

1. HINGE REINFORCEMENT

2. GAS STAY REINFORCEMENT

3. WIPER MOTOR REINFORCEMENT

4. LATCH REINFORCEMENT

        All the reinforcements were created using the same method, first, the linked body was created separately for each with the help of extract geometry and then the required portion was trimmed out and then thickened.

Hinge reinforcement:

            Hinges enable 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, on both sides. 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 Reinforcement:

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

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

Wiper Motor Reinforcement:

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

Latch and Striker Reinforcement:

           The Latch & Striker forms 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 and Striker area. To compensate for the same, reinforcements are added in this area.

DRAFT ANALYSIS:

• The draft analysis will be 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 necessary changes to the draft angle of the embosses were carried out by optimizing the model.

• The Draft Analysis command enables us to detect that the part drafted will be easily removed or not.

• This type of analysis is performed based on color ranges identifying zones on the analyzed element where the deviation from the draft direction at any point, corresponds to specified values.