Design of backdoor

Backdoor of Vehicle:

Backdoor of a vehicle is that commodity that sits behind the rear compartment which houses the boot space and rear passenger area (if it is an SUV, MUV, etc.). Backdoor is also called as tailgate, this tailgate gives the access to load and unloads the rear space provided by opening and closing the commodity.

Functions of Backdoor:

• It serves as the rear door for luggage and passengers.
• Protects rear occupants and luggage from getting damaged.
• It is an assembly of tail lamps and wiper motor.
• Also has a rearview camera as an additional safety feature.
• Rear visibility through rear windshield glass.
• Parking sensors.

Design consideration of a backdoor:

• Hinge positions.
• gas stay positions
• latch and striker
• shape of sealing flange
• visibility criteria through the rear glass while designing the sealing flange.
• the shape of the inner panel and its thickness affects in boot space.
• position and orientation of latch-striker should be perpendicular to the hinge axis.
• reinforcements to be provided at the hinge, gas stay region.
• While designed embosses and material removal on the inner panel.
• Drain holes to be provided (as the commodity undergoes electrolytic dipping and paint process).
• The minimum radius of bending to avoid material failure during stamping operation.
• Hemming Relaxation at bends.

Materials for Backdoor:

Both aluminium and steel can be used in backdoor depending upon the material requirement and the cost of the project.

Aluminium	Steel
Parts are casted and can thickness can be varied throughout the panel	Parts are stamped and have uniform thickness throughout the panel
reinforcement is not needed and hence lighter in weight	reinforcement is needed and hence are heavier
can have a minimum radius at bends and provides more luggage area	cannot have less than 3 mm radius at bends results in less luggage area.
lighter in weight improves the performance of the car	heavier in weight reduces the performance of the car
high cost	low cost

However, in most of the commercial and budget, friendly cars have parts made of steel and there is a requirement of reinforcements such as the following:

• Hinge and gas stay reinforcement
• wiper motor reinforcement
• Latch and Striker reinforcement

The thickness of the inner panel and the outer panel is 0.75mm.

Types of Backdoor:

Side-hinged backdoor for SUV

Upper hinged Backdoor For SUV

backdoor only for luggage for SEDAN

Master Section provided:

This master section has an outer upper and lower panel.

From the above master section inner panel is designed by the following steps:

• Design of sealing flange: This Sealing flange is that section of the inner panel which enables the backdoor to sit over the rear body side of the car. It is the most important part of the inner panel as it decides how a backdoor is mounted on the rear body side of the car and also restricts any external matter to enter inside the vehicle.

• Embosses and material are removed on less curve section made on the inner panel for better stiffness and strength. Here there is a huge removal of material which reduces the weight of backdoor. Force directions are specified how the force will be diverted towards the sides of the backdoor hence by safeguards the rear occupants and luggage

• This part serves as an additional joining part to join the inner panel to the outer upper panel and it also reduces vibrations to a large extent. The 0.2mm gap is provided between the flange and outer upper panel to get joined by mastic sealants.

• Hinge and Gas Stay emboss:
• At hinge emboss, hinges will be affixed to this section so as backdoor can swing up and down about the hinge axis.

• Reinforcement:
• Now since hinges are fixed on inner panel and commodity will swing about it, there is a need of reinforcement at this region to improve its strength locally.
• 1.5mm thickness of reinforcement is added to improve the strength.

• For fixing Gas stay on the inner panel a Diabola emboss is made on curvature part, This diabola emboss is a critical emboss as it is designed on curvy region and gas stay pistons to push the backdoor over this region for opening and closing. During the complete opening, it takes the maximum load both due to the force of piston acting upward and weight of the backdoor acting downwards.
• under such loads, there is a reduction of strength on the inner panel so it needs a 1.5 mm thickness of reinforcement to improve its strength locally.

• Wiper motor reinforcement:
• Wiper motor, it is motor is which is installed on the backdoor just below the rear windshield or on the glass. This motor mounted on the inner panel so it also needs reinforcement to improve its strength locally at the mounting region. The thickness of reinforcement is just 0.75mm as the load effecting here is less as compared to hinge and gas stay region.

The positioning of Latch and Striker:

Backdoor is a swinging part so it rotates about hinge axis so the position and orientation of latch-striker are perpendicular to the hinge axis as shown below.

Overall inner panel design:

The inner panel has all above necessary reinforcements such as hinge, gas stay and wiper motor reinforcement.

• In the above inner panel design, it is made sure that the commodity has good strength and stiffness that's why embosses and material removal is more at flat regions as these regions strength is less. So by embossing and removing material gives better stiffness to the body locally and this also reduces the weight of the commodity.
• The inner emboss structure is also designed in such a way that force should get diverted outside the car body.
• Necessary drain holes are also provided at some sections to give a passage for the liquid to drain out.
• The position of Latch-striker is perpendicular to the hinge axis for perfect locking to rear body side.
• The inner panel thickness is 0.75mm.
• 3 mm is the minimum radius at each bend.
• A vertical rectangular hole is provided on latch-striker location to mount latch-striker.

Hemming:

It is the mechanical interlocking joining method to join sheet metals with the help mastic sealants. The 0.2mm is the minimum gap to be maintained between the panel for perfect sealing.

• Here we have three panels outer upper panel, outer lower panel and inner panel.
• The outer upper panel will be joined to inner panel upper section
• The outer lower panel will be joined to inner panel lower section
• Relaxation is given at every bend so that material does not create any failures at the bends.
• Maximum hemming length is 6mm and the minimum is 2mm.
• Also, the gap between the inner edge of the outer panel and the outer edge of the inner panel is 2mm.

In the above gap of 0.2mm mastic sealants will be filled to join the panel together and hence we avoid other joining method which may reduce the aesthetic look of the panel.

Draft Analysis:

This analysis shows whether the part is producible or not. The analysis report shown below indicates the green colour for the part hence this part is producible may not undergo any failure during stamping operation to imprint this design on a real commodity.

Inertia Analysis:

Inertia Analysis gives an idea about how much bending stress the commodity can resist without undergoing any failure. Here in this inertia analysis, we check for the minimum moment of inertia value as at this value the part will start breaking so this is also called as a critical moment of inertia value

• Inertia Analysis of Hinge Reinforcement

• Inertia Analysis of gas stay reinforcement

• Inertia Analysis of Wiper reinforcement

The CAD model of this project is attached in this report for a more detailed study.