Design of backdoor

DESIGN OF BACKDOOR

OBJECTIVE : To design a backdoor (Inner panel, outer panel and reinforcements) for an automotive (car) from the given skin data as per designing concederation and standard.

Backdoor : Backdoor is the part of a vehicle which is mounted on the rear side. Backdoor provides us the boot space for the baggage. Backdoor prevents our baggage from air and water by creating air tight contact between backdoor and rear body of the vehicle by the help of dynamic rubber sealent. Sometimes backdoor also known as Hatch, Tailgate,Trunk-lid, Boot-door , dickey etc. It has striker mounting as well as wiper motor mounts, tail lamps, and hinges to support the weight of the trunk when it is open, gas stays to help open and close the trunk, radars, cameras, and other features.

In most of the car the backdoor are operated with the help of gas stay which reduce the effort during opening and closing of the backdoor. In some luxury cars have power operated backdoor which operates by an electric motor. In the other hand backdoor is also important for the safety purpose ,during the rear collision of the vehicle it prevents us from accedents.

A backdoor is not a single component , it is the assembly of different parts and reinforcement ,which are inner panel, outer panel (Upper and Lower), Hinge reinforcement , gas stay reinforcement , wiper motor reinforcement and latch & striker reinforcement etc.

Automotive parts in backdoor area

Bootspace in backdoor area

Backdoor area during rear collision

Types of backdoor based on mounting position : On the basis of mounting position the backdoor of an automotive vehicle can be classified as follow :

1.Top mounted backdoors

2.Side mounted backdoors

3.Bottom mounted type backdoors

(1) Top Mounted Backdoor : In modern car top mounted backdoor is widely using type of backdoor. Mainly this type of backdoor is used in a station wagon , pickup trunk and some of the sports utility vehicle. Top mounted backdoor are available in both types powered and gas stay supported. One advantage of top mounted backdoor is that ,this type of backdoor provides greater rear visibility compared to side mounted or backdoor which have center pillars in it.

Top mounted backdoor

(2) Side Mounted Backdoor : The side mounted doors are mounted in one side of car body. Side mounted doors are generally used in the van type MPVs, SUVs, pickup truck vehicles. These side mounted doors or barn doors are a lot easier compare to top mounted doors. These doors are generally smaller in size and can be easily accessed. These doors are more convenient for the goods handlers for long pipe and lengthy components where one door is kept open. These door also save accidental head impacts. It is a lot easier to load and unload items in the side mounted doors.

Side mounted backdoor

(3) Bottom Mounted Backdoor : The bottom mounted type backdoor system are used in the car type such as car, pickup truck and some luxuary SUVs. These are the most convenient type of back door in which the bottom split is used as a support . This type of backdoor also provides more space for baggage and lenthy components. Automotive with bottom mounted backdoor is good for picnic and touring purpose.

Bottom mounted backdoor

Types of backdoor based on working mechanism : On the basis of working mechanism backdoor can be classified into two types as follow :

1) Gas stay type

2) Powered Lifting type

1) Gas stay type : Gas Stay type backdoor 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.

Gas stay type backdoor mechanism

2) Powered Lifting Type : Power trunk lift system is another way of trunk or backdoor opening mechanism which is to automatically open and close of the trunk and release of the latch by the touch of a bottom. Powered trunk Lift system consists of a power latch, anti pinch switch, PTG assly. When the switch is pressed in the compartment or outside the power latch releases the latch and the entire backdoor is opened.

Power lifting type backdoor mechanism

Design Consideration in Backdoor : Design consideration are these things or concepts which brings the attention of a designer during designing of any parts related to it's functionality , safety , life duration etc. For designing of backdoor some important design consideration are as follow :

1) Rear Visibility Criteria

2) Crush Requirements during rear collision

3) Bootspace area

4) Functionality ( Opening and closing ) of the door

5) Hinge and gas stay placement

6) Latch and striker placement

7) Wiper motor placement

8) Reinforcements and sealing criteria

1) Rear Visibility Criteriya : Visibility criteria is one off the important criteria for back door designing. The driver should be able to see from his seat to the rear side of the car. In our design the visibility criteria is already followed by styling team . We have design the backdoor as per given skin data.

2) Crush Requirements during rear collision : During the rear collision of the vehicle the backdoor should distribute the force direction in such a way that the effect of the force to the passengers inside the vehicle should be minimum. The force direction should be outward or body side of the vehicle. Also during closing of the backdoor the effect of the force on the backdoor should be minimum.

3) Bootspace area : Backdoor provides us the bootspace are for our baggage. Human desired is to have more space for luggage and baggage. So, for that it is also a important design consideration during designing of a backdoor.

4) Functionality Consideration : A backdoor designer should also consider the functionality of the backdoor means opening and closing process. Mechanism using for opening and closing of the backdoor, is it gas stay type or powered operated type or any new mechanism.

5) Placement of other component : During designing of the backdoor we have also consider the appropriate position of the all parts of door mechanism. These parts are hinge reinforcement ,gas stay reinforcement, latch and striker reinforcement , wiper motor reinforcement and proper position of dynamic rubber sealent etc.

Different Test for Backdoor : Some important test for backdoor are as follow :

• Dent Test
• Bend test
• Torsion test
• Abuse case test
• Endurance test
• Assembly load case

All components of Backdoor assembly :

Backdoor assembly consist of following components :

1) Backdoor inner panel

2) Backdoor outer panel upper

3) Backdoor outer panel lower

4) Hinge reinforcement RH

5) Hinge reinforcement LH

6) Gas stay reinforcement RH

7) Gas stay reinforcement LH

8) Wiper motor reinforcement

9) Latch and striker reinforcement

1) Backdoor inner panel : The inner Panel is a component which is used for strengthening the door and it is one of the most important components on which all other parts are mounted like as reinforcement for hinges, gas stay,wiper motor and latch and striker etc. The inner panel made by deep drawing process so, minimum draft of 7 degree is provided to the all parts. Sealing flange is provided in the inner panel in which dynamic rubber sealent is expand during the closing of backdoor and it provides us the air tight and water tight contact between backdoor and body of the vehicle. Some embosses are also created in the inner panel to improve it's strength. In the mid portion of back door rear wind shield will mount for that purpose we created a wind shield flange. Two mastic flanges are also created in the inner panel. By the help of mastic flanges the inner panel will get joints will the outer panel by mastic sealent glue.

Draft Analysis for Inner Panel

2) Backdoor Outer Panel ( Upper and Lower) : An outer panel is the outermost sheet metal of the roof in which there are aerodynamic cut-outs for the tail lamp and rear fog lamp. The outer panel (lower) also has the provision for lisence plate mounting .Backdoor outer panel provides a covering to the inner pannel , reinforcement and other components. Backdoor outer panel is made in two parts outer panel upper and outer panel lower. Both outer and inner pannel join together by the help of spot welding which is a type of resistance welding. Backdoor inner pannel joins with outer panel by the help of mastic sealent and hemming process. Since the outer panel is the aesthetic part of the vehicle so, the coating provided is of multi stage which has the property of scratch resistance , rush prevention and smooth and attractive finishes.

Outer Panel Upper Draft Analysis for outer panel (upper)

Outer Panel Lower Draft analysis for outer panel (lower)

3) Hinge Reinforcement : Most off the weight of backdoor is supported by hinges , so the force acted on that portion will also be more due to which more stresses will induced in that portion. So we have need to strengthing and provide extra support in that portion to withstand the effect of the forces. For that purpose we provides the reinforcement for both the hinges LH & RH. All reinforcements joints with the inner panel by the help of spot welding.

4) Gas Stay Reinforcement : During the open condition of the backdoor gas stay supports the weight of the backdoor. So, during opening-closing process and also in completely opened position the gas stay has to support the weight of the backdoor in huge fraction. So, stresses induced in that portion will also be more, that's why we have need to provide the extra support in the form of reinforcements to withstand the effect of force. Two gas stay reinforcement are providede there , Gas stay reinforcement LH and RH.

5) Wiper Motor Reinforcement : A dedicated space near the window is left for wiper motor assembly. A cavity is placed preferably in the middle of the panel to accommodate all the necessary wiper motor components. The holes or cavities are placed strategically to accommodate wiring looms, tail lamp mount, and other accessories. Embosses help stiffening the panel and act like local reinforcements. For mounting of the wiper motor also we provides a reinforcement which gives the extra support in that region and helps to withstand the effects of forces .

6) Latch and Striker Reinforcement : At the bottom of the latch and striker assembly. Generally a key operated or automatic remotely controllable locking mechanism is used to keep the door closed and open. When we close the backdoor it hit in the portion of locking mechanism, and large forces are induced in that portion . To reduce the effect of these forces we provides a reinforcement there which helps to withstand the effect of forces and protect the door panel.

Parts thickness used in this design:

Outer panel: 0.75mm

Inner panel: 0.75mm

All Reinforcement: 0.75mm

Trajectory for Latch and striker :

The radius between the hinge axis point and center of slot is used to trace the trajectory of the circle which can be used to locate the slot position on latch and striker reinforcement mounting.

Various Manufacturing Processes Used For Backdoor : For the manufacturing of backdoor various process used are as follow :

1) Blanking

2) Deep drawing

3) Bending

4) Lancing

5) Punching

6) Hemming

7) Joining techniques :

Spot Welding

Mastic Sealant joining

Conclusion:

The sheet metal design principles are taken into consideration while designing the whole back door assembly using NX CAD successfully.