Design of backdoor
BACK DOOR
The door or opening of a cargo area that is hinged at the top, side or bottom is called back door. If the door is hinged at the bottom, it is usually called a tailgate.
Automotive back doors are an important part of a vehicle’s design. They are designed to provide safety and security to passengers while also being aesthetically pleasing. The design of automotive rear doors is complex and involves many factors such as aerodynamics, weight, and safety.
The structure of back doors is made up of several components such as the outer panel, inner panel, and reinforcement components. The outer panel is the visible part of the door that is painted and provides the aesthetic appeal. The inner panel is the part of the door that is not visible and provides structural support. Reinforcement components are used to provide additional strength to the door.
They can be operated manually or automatically.Manual backdoor needs human effort. But it is held in open position using gas stays. Automatic doors have motors to assist opening and closing.
DESIGN PARAMETERS
Designing of a car's backdoor includes a number of factors that needs to be accounted for.
Boot Space : The back door should be designed in such a way that the trunk volume is not affected without compromising on other parameters.
Rear Visibility : The back door must ensure rear visibility via the IRVM through the rear windshield.
Rear Collision : In the event of a collision, embossments are provided on the inner panel such that the impact is directed away and towards the frame of the car.
Accessibility of components : Since the assembly takes place after the joining of the inner & outer panels of the back door. It is neccessary to ensure the ease of assembly of other components like the tail lamps,etc.
Reinforcements : Embossments are provided for improving the the overall strength of the back door as well as reinforcements for mounting hinges, gas stays, wiper motor and the striker as it improves the strength locally.
Striker Placement : The position of the striker should be perpendicular to the latch when the latch and striker meets. To ensure this, a circle is drawn from the centre of hinge axis and a tangential line which coincides with the path of the striker is made. Then the radius of the circle is varied to get the required position corresponding to the latch position.
Clearances : A gap of 0.2 mm is provided between the inner and outer panels where hemming is carried out. Similiarly a gap of 5 mm is provided in regions where mastic is applied.
Joining Method : The outer surfaces are hemmed together and hemming glue is applied in the 0.2 mm gap. Mastics are applied in the 5 mm regions
BACK DOOR SUB ELEMENTS
Outer panel : Outer panel is the class A surface which contributes to the the aesthetics of a car. There are Upper outer panel and Lower outer panel in this case.
Inner Panel : It encompasses all the structural reinforcements, embossments for mountings, sealing flange, mastic flange, etc.
Hinge Reinforcements
Gas Stay Reinforcements
Wiper Motor Reinforcements
Striker Reinforcements
All the above mentioned reinforcements serves the purpose of increasing strength locally. Their surfaces are flat to ensure the proper mounting of said components. The size, shape and location of these components directly affects the reinforcements as well.
Sealing Flange : The sealing flange is used for applying a rubber seal to keep the boot water tight.
DRAFT ANALYSIS
A tooling axis is created in the most suitable position. Draft analysis was carried out and all the surfaces were having a positive draft of at least 7 degrees, except the hemming portions. For outer panels, the hemming surface doesn't clear draft criteria of 7 degree, but it is not a matter of concern as the surface is manufactured by bending the sides. Draft analysis of different components are given below:
Adequate hem reliefs are given to avoid stress concentration issues:
The inner panel with reinforcements at emboss loaction is shown in the figure below:
Upper and lower outer panels are given below. The hemmed edges can be seen here:
Final Assemby is as follows:
Front View:
Side View:
Back side View:
