Design of backdoor

BACK DOOR DESIGN

AIM:

To create a Back Door Design using Siemens NX cad.

OBJECTIVE:

• To design a back door of a car with an inner panel, outer panel and reinforcement for hinges, gas stay, Wiper motor and latch.
• The inner panel is subjected to the draft analysis to ensure whether it is satisfying the deep drawing requirements for the tooling direction that is created in the design.

INTRODUCTION:

• The backdoor or tailgate is the rearmost part of the automobile which opens upwards, downwards, and sideways to give access to the luggage space or seating.
• In most automobiles, the backdoor opens upwards. It is hinged to the roof and a gas stay support fixed at the body side outer for keeping the backdoor in the open position.

TYPES OF BACK DOOR:

• 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.

• Side Mounted

       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.

• Bottom Mounted  

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

Material 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.

Fig. above shows possible no. of parts in aluminium backdoor.

Fig. above shows possible no. of parts in Steel backdoor.

                 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

Design Consideration:  

• Visibility Criteria
• Latch and Stricker Position
• Hinge Position
• Gas Stay Position 
• Space Avalibility
• Drain Holes
• Hemming and Relief area's

 Component Of Back Door:

            The Components of Back Door as follows,

• Outer Upper Panel.
• Outer Lower Panel.
• Inner Panel.
• Gas Stay Reinforcement LH And RH.
• Hinge Reinforcement LH and RH.
• Striker Reinforcement.
• Wiper Reinforcement.

                                                                                                                       

Types of mechanisms for Rear Door:

 Gas stays: 

 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.

Design Methodology:

• Firstly we have to check if there are any surface irregularities in the skin data, if irregularities are there, then repair if by using a bridge curve and through curve nesh and sew it.
• Then we create a sealing flange. Generally with the help of master sketch, we will design the panel with appropriate dimensions. But here there is no master sketch, we designed by assumption.

STYLING CLASS A SURFACE:

                           

• Once the model is opened, we get a Class A Surface of the back door.
• Try joining the Upper surface of the car, if the surface sews together, we get the outer surface and if the surface didn’t join then we need to create the surface by using studio surface tool
• Create the fillet areas, Tail Lamp areas as those areas will be vulnerable and are unable to join together.

CREATION OF TOOLING AXIS:

                                                                 

• Draw a line from left and right extremities almost parallel to the path of the surface along the unsymmetrical axis.
• Using the Derived lines tool, create a bsecting line as shown below:

BACK DOOR INNER PANNEL:

                                          

The inner panel is a component which is used for strengthen the door assembly and it is one of the most important components on which all accessories are mounted like hinges, glass guide channel, molded 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.

BACK DOOR OUTER PANNEL:

                                                   

The outer panel of the back door is similar to the other BIW components where it is the aesthetic part of 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 license plate mountings. Most of the hatchback cars have the provision for wiper motor.

EMBOSSES AND REINFORCEMENTS:

                                                                                  

With the distinctive cross section, embosses are created. The embossed are used to increase the strength of the backdoor. While designing we should keep in mind that it should not be over strength. So we prefer to design big embosses rather than small embosses. These embosses are used to despite the forces sideways.

REINFORCEMENTS:

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 0.75mm thick panel used in this part.

HINGE REINFORCEMENTS LH&RH:

                                                                                   

                                                                                                                

Hinge is a pivot mechanism which supports the total weight of the backdoor. So reinforcements are added for strength and rigidity.

GAS STAY REINFORCEMENTS LH&RH:

                                                            

                                                         

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 MOUNTED:

                                                        

                                         

Wiper is used to wipeout 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, 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:

    

In the bottom part of the panel emboss is created for placemnet of latch and striker assembly. There is over slamming and abusing while opening and closing of the door, thus arising the need for reinforcement to be placed.

Positioning of Latch & striker/ Latch Trajectory:

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

HEMMING OPERATION:

                                               

Hemming is a mechanical joints 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 CORNER RELEIF:

                                                                    

• Hemming relief are cut out 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 as shown below,
• The back door design requires two locations where the roller type of hemming relief is required which are shown belief.

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:

Thus the back door was designed and developed from the given styling surfaces with essential reinforcements and emboss. To satisfy the manufacturing requirements draft analysis was also done on the inner panel.

        NOTE : https://drive.google.com/file/d/14quCzMJ6gkZaZz2GDyAhk8701PKmhWKH/view?usp=sharing

                   https://drive.google.com/drive/folders/1rgFgJzaXoXvAxOdMbKaxUcZBpQJEWwJ7?usp=sharing

•    It is greater than 20mb,so i will paste the link.