Design of backdoor

• TABLE OF CONTENT:
• OBJECTIVES & INTRODUCTION
• DESIGN CONSIDERATIONS
• MANUFACTURING PROCESS
• DESIGNING USING THE SIEMENS NX TOOL
• DRAFT ANALYSIS
• CONCLUSION

OBJECTIVE & INTRODUCTION

OBJECTIVE: Using the provided styling surface to come up with a back door design and  using appropriate design methodologies and make the necessary reinforcements and embosses

BACK DOOR: It is a hinged board or door at the rear of the vehicle that can be moved up or down during loading and unloading.

Back Door is also referred to as 'Hatch' or 'Tailgate' or 'Trunk-lid' or 'Boot-door'. It is the rearmost part of the vehicle which gives access to the trunk and has mounts for tail lamps, hinges, wiper motor, gas stay etc.…

Functions of the Backdoor:

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

Types of Backdoor based on working positions. :

1. Top mounted

These types of back doors are used in station wagons, pickup trucks, 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.

1. Side mounted

It is generally used in van-type MPVs, SUVs, and 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, and 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.

1. Bottom mounted

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

1. Split type

Types of Backdoor 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 a tailgate consist of a hinge, door, gas stay and some rubber beadings for sealing of door which is shown in the image below

Powered lift system:

            The power trunk lid system is another sophisticated way of trunk/liftgate opening mechanism which is to automatically opens and closes the trunk/liftgate and releases the latch with the touch of a button. The following image shows the component used in the powered trunk/back door lift system.

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 help in increasing the luggage/ cabin space.

	Aluminium	Steel
Parts	Parts are casted	Parts are stamped
Reinforcements	Reinforcements can be neglected	Reinforcements are necessary
Thickness	Thickness can be varied	The 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

   DESIGN CONSIDERATIONS

• Rear visibility
• Boot space & accessibility
• Sealing Flange
• Support structures like hinges and gas stays.
• Mounts for wiper motor, tail lamps, and other wiring loops
• Rear crash regulations
• Joining techniques such as hemming, spot welding, etc.
• Gap and flush requirements

  MANUFACTURING PROCESS

The manufacturing of the Fender majorly involves these operations.

1. Embossing
2. Bending
3. Cutting and Blanking
4. Hemming

                                                                             

1. Embossing

Embossing is a metal forming process for producing raised or sunken designs or relief in sheet material using matched male and female roller dies, theoretically with no change in metal thickness, or by passing a sheet or a strip of metal between rolls of the desired pattern.

2. Bending

Metal bending is a process by which metal can be deformed when applying force to the subject, which causes it to bend at an angle and form the anticipated shape, which often results in it being in a 'V' or a 'U' shape. This is done through the application of force on a workpiece. The force on the workpiece can be mechanical, pneumatic, or hydraulic.

3.  Cutting and Blanking 

Cutting processes are those in which a piece of sheet metal is separated by applying a great enough shearing force to cause the material to fail. Blanking is a steel manufacturing process in which a flat, geometric shape is created by feeding a coil of sheet metal into a press and die in this process, the blank is punched out from the large metal sheet.

   

4. Hemming

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

Assembly:

In this assembly Top down approach was followed wherein from the given styling surface the inner panel was created using various tools/commands in NX. After that, parts were modeled as per the requirements one by one.

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

• Outer panel
• Inner panel
• Hinge reinforcement
• Gas stay reinforcement
• Wiper motor reinforcement

 

    OUTER PANEL

• It is the outer styling skin surface of the back door. It is provided with multistage coatings which have the property of scratch resistance, rust prevention, etc. It is wrapped around the inner panel through the hemming process.

 

          CORNER RELIEF

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

  SEALING FLANGE

It is that section of the inner panel that 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.

      

       INNER PANEL

The inner panel is one of the most important components of the backdoor assembly. It provides strength and helps in the dissipation of forces outside the part with the help of embosses made on it. It helps in mounting accessories like hinges, wiper motor, gas stay, latch & striker, etc.

The inner panel is produced by either casting or through the Deep drawing process.

Mostly aluminum part is cast steel inner panel manufactured by a deep drawing process. If deep drawn, there must be a tooling direction through which that panel must be deep drawn.

MASTIC SEALANT

As we know the outer panel gives the aesthetic look to the vehicle, so we can’t use bolting or spot welding, or any other joining technique which damages the aesthetic look of the 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.

TOOLING AXIS & + LATCH AND STRIKER TRAJECTORY CREATION

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

            REINFORCEMENT

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 the 0.75mm thick panel used in this part.

• Hinge reinforcements

The hinge is a pivot mechanism that 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 wipe out 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, the 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.

       DRAFT ANALYSIS :  

The Draft Analysis command enables you to detect if the part you drafted will be easily removed. 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.

A minimum draft angle of 70 is considered for analysis. green color infer on the parts that all face along the tooling direction has a positive draft angle greater than 7deg  and or 10 deg passed in the analysis