Design of backdoor

BACK DOOR DESIGN

A backdoor is located at the rear end of the car which gives access for the boot space to store luggage. Spare wheel etc. This door can be operated manually or electric powered. In most of the luxury car is electric powered.

Back Door also called as 'Hatch', or 'Tailgate', 'Trunk-lid', 'Boot-door' is basically the 5th door in a car. It's the rearmost part of the vehicle which gives access to the trunk and has mounts for wiper motor, tail lamps, hinges for supporting its weight in opened position; gas stays which help with its opening and keeping it open

The backdoor of an automobile is primarily made of steel, however recently aluminium is also used to make the panels. The fundamental advantage of aluminium over steel is that it has a lower density than steel, which reduces the overall weight of the vehicle. However, aluminium is more expensive than steel.

Types of door based on the application:

1. Top mounted door
2. Side mounted door
3. Bottom mounted door

COMPONENTS INVOLVED IN THE DESIGN OF BACK DOOR:

• Inner panel
• Outer panel
• Hinges mounting & reinforcement
• Gas stays mounting & reinforcement
• Latch striker mounting & reinforcement
• Wiper motor mounting & reinforcement

DESIGN REQUIREMENTS FOR BACK DOOR

• Rear visibility criteria
• Rear crash
• Sealing and its function
• Joining techniques (Hemming & Spot welding)
• Gap & Flushness requirement
• Functional requirements-HINGE, GASTSTAY, WIPERMOTOR
• Stress relief

MANUFACTURING PROCESS OF SHEET METAL:

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 is punched out from the raw sheet is considered as a waste

Design methodologies used in backdoor design

Embossing:

Embossing is metal forming process for producing relief in sheet metal materials using matched male and female roller dies, theoretically with no change in metal thickness by-passing sheet between rolls of the desired pattern.

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. Normally hemming operations are used to connect parts together, to improve the appearance of a part.

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 together.

Typical parts for this type of assembly are hoods, doors and back door

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 pointed or if the material used is SST or Aluminium.

Spot Welding:

Resistance Spot Welding is a pressure welding process. The sheets are pressed together locally with the help of fitted copper electrode welding guns that then have a current applied to them.

DESIGN PROCEDURE:

The input for the creation of back door is class-A surface (Outer panel) which has two surfaces upper outer panel and lower outer panel.

The outer panel needs to be modified for further use as the given input is multiple surfaces, the surfaces need to be joined and surface continuity are inspected to rework on surface with edges needs to be modified for smooth operation.

INNER PANEL:

The inner panel is designed for providing structural rigidity and load bearing capacity and to mount various components used in backdoor while the outer panel will acts as styling surface.

The inner panel design starts with sealing flange creation which will seal the gap between the panel and BIW restricting the micro-dust, water splash or rainwater entering inside the car.

Sealing Flange:

The flat surfaces of outer panel which are split from the outer panel such that the final distance between side flanges of sealing flange to be 20 to 25 mm are offset to a particular distance that the curvature is maintained and the offset surfaces are joined creating multi section surfaces.

The side flanges for sealing flange are created using the boundary curve and swept with a draft angle of 7 degrees.

The outside flange is trimmed with the outer panel offset.

A portion on the outer flange of the sealing flange is trimmed such that it is easy to accommodate the outer upper and lower panel spot welding portion.

The inner flange is trimmed with the inner portion of the outer panel offset and a blend is used to create the surface between the inner upper panel and inner lower panel.

Gas stays mounting:

In order to hold the position of back door while opening the door, gas stays are used to provide the support. This will also helps in opening the door with minimum effort. In gas stay, the pressure on either side of the piston remains equal whether it’s fully extended or fully closed. It should always be mounted “rod down” when in the fully closed position.

Hence the mounting portion for gas stay is created on the inner panel such that it satisfies the final opening and closing of back door.

Hinge Mounting:

In order to join or attach the door panel with the roof attachment in order to open and close the door properly and to hold the weight of the back door hinges are required on either side of the door to support the additional tension and weight upon the frame, owing to the door's wider width.

Wiper motor Mounting:

Windshield wipers are powered by a small electric motor in recent cars, usually mounted on the firewall or under the cowl. The motor activates linkage that moves the wiper arms back and forth at rear side the motor is located in the middle of the inner panel under the wind screen.

Striker Mounting:

Door strikers are used on automobiles to facilitate the latching and unlatching of the door to the frame of the automobile and thus the opening and closing of the automobile's door. More specifically, the door strikers are mounted to the frame of the automobile and the door includes a latch mechanism that engages the door Striker to latch and hold the door to the door striker. By operating the handle of the door, the latch mechanism will unlatch from the door striker, thereby permitting the door to open.

Embosses:

Weight reduction of the automobile body has become an increasingly important issue because of various regulations which are being continuously tightened for energy conservation and environment protection. Furthermore, people have increasingly stringent demands for the passive safety of automobiles, which requires improvement in the automobile’s structure crashworthiness. As the back door have a portion of surface which don’t have any features or components, in dynamic motion of the automobile to reduce the vibration mastic sealant is used to bind the outer and inner panel. So embosses and profiles for stress relief while impact on the rear portion are created and the region for mastic sealant also created.

Symmetry:

The back door until we worked is half portion; symmetry is performed to create the full back door with respective axis and corners are created for proper attachment with the outer panel while hemming process.

Hemming:

To perform hemming operation, flanges should be created for outer-upper and lower panel and hemming relief need to be provided at corners for the offset flange for proper fit.

Thickening:

The outer panel styling surfaces and the inner panel surfaces were designed with all features and embosses the final step is to perform thickening to the surfaces.

Outer panel:

Thickness of 0.75mm applied to the outer panel styling surfaces as per the input and regulations.

Inner panel:

Thickness of 0.75mm applied to the outer panel styling surfaces as per the input and regulations.

Reinforcements:

These are the support members, when fasteners are used on sheet metal shearing takes place to avoid these reinforcement plates will be created on the opposite side of hinges, Gas stays, Wiper motor and latch emboss by taking the reference as their surface with a thickness of 1.5mm.

Draft Analysis:

Draft analysis is performed for inner panel with respect to the tooling axis and it has cleared with a draft of 7 degrees and at the sealing flange inner wall portion it is having a negative draft.

Draft analysis is performed for outer panel with respect to the tooling axis and it has cleared with a draft of 7 degrees and at spot welding portion for the outer upper panel is having no draft and for the lower portion the spot welding portion is following negative draft.

Assembly: