Design of Vehicle's Backdoor

Objective :-

The objective of the project is to design a backdoor of a car with its constituent elements involved. This backdoor is for hatchback type cars. Backdoor influences the boot space, crush load from rear side, trim parts, plastic parts, etc.

Back Door :-

A back door is a BIW component found in all Automotive car generally used for opening and closing of the so called car luggage that is usually used for storing items inside a car. In general the opening and closing of the door is co-ordinated by the Latch and Stricker position and the Gas stay position that is mounted on the body and back door of the car. These positions play a major role in ensuring smooth opening and closing of the tail gate.

Backdoor Requirements :-

The backdoor has many accessories like lighting, wiper motor, latch and striker motor, handle mounting, gas stay or power lifter, hinge mountings etc. These parts has to be placed in the backdoor for their functions. These parts can’t be seen from either the outside or from cabin inside. The actuating motors are responsible for the function of power lifter, latch and striker, wiper, etc.

Types of Back Doors :-

Top Mounted Back Doors

Side Mounted Back Doors

Bottom Mounted Back Doors

Design Considerations In Back Door Design :-

The following are the Design considerations taken while designing the Back Door. They are,

• Visibility Criteria
• Force Dissipation
• Latch and Stricker Positions
• Hinge Position
• Gas Stay Position
• Material Selection
• Space Availability
• Hemming and Relief Areas

All these design considerations go hand in hand with eachother because these positions are dependant on each other & if position gets altered all the positions has to be altered for effective opening & closing of the back door. The Latch & Stricker, Hinge Position and the Gas stay Positions has to be maintained in a proper way so that they play a major role in the opening and closing as well as the rear visibility criteria of the car.

Material Selection :-

The material selection play a major role in determing the overall weight of the back door. The materials generally used are Steel & Aluminium. The Density of Steel is higher than Aluminium thus it results in adding more weight of the door. Basically the material is used based on the budget of the car, because the cost of steel very cheap than Aluminium. If aluminium is used instead of steel there is no need of many parts like Reinforcements for each mounting and the overall weight geta reduced by 6-10 kg approximately. But the draw back is Aluminium is much costlier than Steel. Hence based on the budget of the car aluminium is used. In higher end models like Benz, Audi, Porshe and BMW we can find aluminium is used instead of steel resulting in reduced weight and increased performance of the vehicle. Another Factor to make a note is using Casted Aluminium instead of deep drawn Steel components and adding reinforcements to it is the space of the luggage commodity gets increased by a certain amount because the draft angle for Casted aluminium is much lesser (3 degree) than the deep drawn Steel inner panel (7-9 degree). Thus it reduces the space between the inner and outer panel resulting in much larger cabin space than the deep drawn steel inner panel. Thus the material selection is one of the design consideration taken. Since it reduces the space between the inner and the outer panel the rear visibility of the car is also inproved giving more space for the mirror to view.

Hence in this design the material chosen is steel since it is designed for a medium budget car and hence high cost could not be afforded to design the back door.

Force Dissipation :-

The major criteria in designing the back door or any BIW part is the force dissipation during an impact or a colloision. Hence studies are being done inorder to dissipate the force on the sides and avoiding it reach the inner cabin of the car so that possible damage of imapct inside the car is reduced. Hence inorder to do that the V or Y embosses are created on the inner panel so that the force gets transmitted on to the sides instead reaching it on the cabin. This is one of the main criterias in back door design.

Thus from the above image it is clear that the forces are dissipated on the sides instead of reaching inside. This is the reason to have Y or V embosses on the panel to increase the stiffness and to dissipate forces onto the sides.

DESIGN COMMODITIES

1. Backdoor outer panel – class A surface(upper and bottom)
2. Backdoor inner panel
3. Hinge mounting areas for backdoor
4. Hinge mounting areas for gas stay
5. Mounting regions for wiper motor and striker emboss
6. Force dispersion emboss
7. Fixture holes
8. Mastic sealant flange
9. Sealing flange

Latch & Stricker Positions :-

The Latch & Stricker positions play a major role in determing the opening and closing of the back door. Hence the opening and closing of the had to smooth and inorder to ensure that the the centre point of the latch and stricker has to to be at the same point and the trajectory has to be tangent to the open close circle that is drawn. This is shown in the below image. Only if the centre points and the tangent line are perfect the opening and closing of the back door is smooth and clear, or else the Hinge positions, Gas stay positions and Latch and Stricker Positions has to be altered to meet the change.

Hemming & Relief Areas :-

Hemming and Seaming are two similar metal working processes in which sheetmetal edge is rolled onto itself.Hemming is the process in which the edge is rolled flush to itself, while a seam joins the edge of two materials. The Hemming is done on the outer and the inner panel with an clearance of 0.2mm on the either sides. Since at the corners the hemming is difficult to perform, clerances has been given at the ends of panels so that it would for the hemming operstion is performed. Here is the image of the hemming relief at the corners.

Outer Panel :-

The Outer Panel is the styling surface of the back door. It is the source of design of other parts of the back door, primarily the Inner Panel. The Outer panel of the back door is similar to other BIW components where it is the aesthetic part of a vehicle. The coating provided is of multi stage which has the property of scratch resistance, rush prevention & smooth and attractive finishes. The Outer panel also has the provisions for the tail lamp, rear fog lamp & also has the provision for license plate mountings. Most of the hatch back cars have the provision for wiper motor.

Inner Panel :-

The inner Panel is a component which is used for strengthening the door. It's thickness is in the range of 0.65-0.75 millimetres. It is one of the most important components on which all accessories are mounted like Hinges, Gas Stay, Wiper Moter , Latch and Striker 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.There are many cases where the Inner panel is subjected to stress due to frequent opening and slamming. These stress and depression factors are compensated by features like embosses and reinforcements.

CONCLUSION :-

Thus the Back door was designed and developed from the given styling surface with essential Reinforcements and Emboss.