Design of backdoor

Report On Car Back Door Design

Aim- To design the Back door of the car using the appropriate design methodologies, providing the necessary Reinforcements and embosses in the inner panel for strength.

Design Considerations for a Back Door-

• Rear Visibility for Functionality and Safety.
• Boot Space and Accessibility.
• Type of Backdoor Opening (For individual vehicle requirement).
• Fixing and Support Structures like Hinges and Gas stays.
• Mounts for Wiper Motor, Back Lights/Tail Lamps and Other Wiring loops.
• Fit and Clearance (For Assembly and Aesthetically looks).
• Strength Of Backdoor (Require in collision).

Back Door - The Back door of a car is a component which hinges at the back of the car to cover the boot space or luggage area, it has back lights/ Tail lamps and Braking lights which is termed as "Third brake light" mounts on it, rear windshield fixes between inner and outer panel, in some back door spare wheel can be mounted on it, sometimes car registration number plate mounts on it and it gives a complete closed design to the car.

Image of a Car's Back door (Open)

Image of a Car's Back door (closed)

Spare wheel mounted on Back door

Things Relate to a backdoor-

Trunk-

The trunk (North American English) or boot (British English) of a Car is the vehicle's main storage or cargo compartment, often a hatch at the rear of the vehicle. It's also called a tailgate.

In (Indian English) the storage area is known as a dickey (also spelled dicky or diggy), in (South-East Asia) a compartment.

The trunk or luggage compartment is most often located at the rear of the vehicle. Early designs included an exterior rack mounted on the rear of the vehicle to which it was possible to attach a real luggage trunk. Later designs integrated the storage area into the vehicle's body and evolved to provide a streamlined appearance. The main storage compartment is normally provided at the end of the vehicle opposite to which the engine is located.

Increased variability-

• To give the space more flexibility, many cars have foldable rear seats, which can increase the size of the trunk when needed.

Back Door Openings -

There are different openings of a car back door, some of them shown in images below-

Side Opening Of a car Back door

Windshield Opening in a Car Back door

For practicality purpose-(Windshield Opening in a Car Back door)

Split Back Door

• Back door Lock-

The locking of the trunk may be achieved together with the passenger compartment.

Some cars include a function to remotely open the trunk. This may be achieved through a variety of means:

• release of the latch whereby the doorseals push the decklid away from the lock, the trunk is then open, and the lid may not have revealed the opening.
• release of the latch whereby a spring pushes the decklid away from the lock and open, the trunk is then open, and the lid reveals the opening.
• release of the latch and actuation of a drive, whether hydraulic (BMW 7 Series) or electric (BMW X6), which pushes the decklid away from the lock; the trunk is then open, and the lid reveals the opening. This may then be electrically closed again.

Images of Car Back door Lock (Latch)

Latch arrests the striker to lock the backdoor of a Car

Image of a striker

• Gas stay/Spring-

A gas spring is a type of spring that, unlike a typical mechanical spring that relies on elastic deformation, uses compressed gas contained within an enclosed cylinder sealed by a sliding piston to pneumatically store potential energy and withstand external force applied parallel to the direction of the piston shaft.

Common applications include automobiles (where they are incorporated into the design of struts that support the weight of the hatchback tailgate while they are open)

Image of a gas stay

• Hinge-

A hinge is a mechanical bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation: all other translations or rotations being prevented, and thus a hinge has one degree of freedom.

Image of a Back door Hinge

• Rear Wiper Motor-

Rear-window wipers are typically found on hatchbacks, station wagons / estates, sport utility vehicles, minivans, and other vehicles with more vertically-oriented rear windows that tend to accumulate dust. So a motor is required to move the wipers.

Image of a wiper & motor

Manufacturing Processes Used to make Backdoor-

• Deep drawing-

Deep drawing is a sheet metal forming process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. It is thus a shape transformation process with material retention. The process is considered "deep" drawing when the depth of the drawn part exceeds its diameter. This is achieved by redrawing the part through a series of dies. The flange region (sheet metal in the die shoulder area) experiences a radial drawing stress and a tangential compressive stress due to the material retention property. These compressive stresses (hoop stresses) result in flange wrinkles (wrinkles of the first order). Wrinkles can be prevented by using a blank holder, the function of which is to facilitate controlled material flow into the die radius.

• Punching-

Sheet metal punching is a cutting process in which material is removed from a piece of sheet metal by applying a great enough shearing force. CNC Punching can be used to produce holes and cutouts of various shapes and sizes.

• Embossing-

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

• Metal sheet is drawn through the male and female roller dies producing a pattern or design on the metal sheet. Depending on the roller dies used, different patterns can be produced on the metal sheet.
• Emboss should be in 7 degree to 25 degree inclinte in angle and it should not be in 90 degree angle,why because when we do stamping in manufacturing the stamping tool fits the sheet metal hence it will not come out of that sheet metal,So this is the main reason why the emboss face is in angle.

• Tailor Welded Blanks-

Tailor Welded Blanks are made from individual sheets of steel of different thickness, strength and coating which are joined together by laser welding. This manufacturing process allows for flexible part design and ensures the right material is used in the right place.

The production and use of these customized pieces in the steel and auto industries has reduced production costs, allowed automakers to build lighter and therefore more fuel efficient vehicles, and greatly improved the crash performance of cars. ... These new tailor welded blanks also had tremendous benefits for automakers.

• Laser beam welding-

Laser beam welding is a fusion welding process in which two metal pieces are joined together by the use of laser. The laser beam provides a concentrated heat source, focused to the cavity between the two metal pieces to be joined.

Image of Back door Lazer brazing

• Lancing-

Lancing is a piercing operation in which the work piece is sheared and bent with one strike of the die. A key part of this process is that there is not reduction of material, only a modification in its geometry. This operation is used to make tabs, vents etc.

• Hemming-

Hemming is a forming operation in which the edges of the sheet are folded or folded over another part in order to achieve a tight fit. Hemming is a technology used in the automotive industry to join inner and outer closure panels together (hoods, doors, tailgates, etc.). It is the process of bending/folding the flange of the outer panel over the inner one. The accuracy of the operation significantly affects the appearance of the car’s outer surfaces and is therefore a critical factor in the final quality of a finished vehicle.

• Roll hemming - In roller hemming process, a robot guides a small roller across the flange to fold a sheet onto itself or onto another sheet. The process is oriented to low volume automotive applications, providing a distinct advantage in manufacturing closures and subassemblies with developed flanges.

• Mastic Sealant-

A mastic sealant is a type of liquid sealant that cures in an elastic state, thus making it flexible while holding the bond of the surfaces that has attached together. It adheres to just about any material making an all-purpose type of sealant.

• The main purpose of the outer panel is for the aesthetic looks. Thus we cannot use bolts or welding. This has to be done with the help of the hemming and mastic sealants. Mastic sealants are elastic compound that behaves like the rubber. It is placed between the outer and inner panel. Initially is it in paste form, but after the hot furnace bath it gets hardened thus joining the outer and inner panel. Mastic sealant has the tendency to increase the strength of the panel and has influence of 80mm diameter.

• Corner Relief-

Relief is provided onto the part or component in order to remove any stresses developed in a particular area i.e sharp corners that takes place during the hemming process is carried out. Thus corners are rounded or chamfered.

Some Tests that are performed on the Back door to check the strength, quality and durability.

Components to create-

1. Outer Upper panel
2. Outer Lower panel
3. Inner panel with Embosses and Cut-outs
4. Hinge reinforcements
5. Gas stay reinforcements
6. Wiper Motor reinforcement
7. Latch reinforcement

• Outer Upper panel -

• Outer Lower panel -

Hemming is done on the both Outer Panel with the Corner Relief

Image of complete Outer panel-

• Inner panel-

Tooling Direction-

The back door is going to be manufactured by deep drawing process. In Deep Drawing process have a tool which is core and Die. The core part follows the single Straight path the inclination angle of the core is known as a tooling direction. The tooling direction/axis is created so, that the Manufacturing team take the reference of this tooling axis and manufacture the part accordingly.

Force Distribution-

When the car hits at the rear end, the impact force should dissipate outside for safety. For that we give Y/V emboss which helps to direct the force to the outer end.

Significance of ‘Y’ / ‘V’ Embosses-

As an evident from the test simulations, the design and direction of the embosses should guide the dissipating forces away from the passengers to the outside of the vehicle and thereby reducing the impact force drastically in case of a collision. Embosses also create strength on that region.

Inner Panel with embosses

Force Direction

Hinge Emboss

The backdoor is a swinging commodity, which swings with the help of hinges. This can be done by tentatively positioning the hinges and on the hinge axis, we take a center point. again we take another center point(approx) on the latch hole. Taking these two points as a reference we draw a circle. This circle is the striker trajectory and it has to be perpendicular. This can be achieved by moving the hinge axis back and forth or by rotating the latch area.

To create hinge mounting emboss

1. A plane was taken because mounting area should be flat or should not have any radius of curvature.
2. A sketch was drawn on that plane.
3. The emboss command was used to make the hinge emboss feature by using plane as an end cap of hinge emboss.
4. And holes were created for the nut and bolts for assembly of hinge.

Latch Emboss

Latch and striker trajectory

For Latch Position a circle was drawn from the axis of hinges to find out the trajectory

Gas stay Emboss

Wiper Motor Emboss

Mastic Flange

It is a connecting flange between outer panel and inner panel. The manufacturing process called "Lancing" produces this type of flange.

1. The inner panel sheet will sheared in the specific created design.
2. Then, the sheet will bend with the help of another die to make the flange in "L" shape.
3. So, this flange will have the same or shorter size than the sheared size of the sheet.
4. Thus, the flange will have somehow same design and the length will completely depend on the Cut-out, if we need more length of flange, then we need to cut more sheet.

Mastic flange with corner relief and darts for supporting strength

Mastic Sealant gap of 5 mm between Outer and inner Panel

Material removed for passing wiring required for back lights and light weight design

Reinforcements-

Reinforcements are used to support and provide stiffness and strength to other components of BIW(Body In White).

• Hinge Reinforcement- The hinge reinforcement is provided in order to give the strength of the inner panel. This is one of the part which carry the load and require strength.

• Gas-Stay Reinforcement- A gas-stay reinforcement is a required because the gas stay will carry the load of the backdoor in open position.

• Wiper-Motor Reinforcement- The Wiper-Motor Reinforcement is provided for incresing the strength of the wiper motor location.

• Latch Reinforcement- The latch reinforcement is required because the latch will fall over the striker with good amount of force, so here strength is mostly required to bear the force.

Draft Analysis

Draft Analysis is done to analyze the draft angle. This allows us to verify whether the product will be easily removed from the tool.

When designing a product it needs to be slightly angled so that the tool can be pulled away from the part easily, without deformation or damage. This slight angle is called draft.

Minimum Draft of 7 Degrees provided for easy manufacturing of sheet metal

Different View of Backdoor Assembly

Front View

Side View with Tooling Direction

Back View

Isometric View

Conclusion

The Back door was designed in "Siemens NX Student Version" with all the possible known required design guidelines for back door design and manufacturing.