08. BACKDOOR DESIGN

Aim:

To design a backdoor of the car on sheet metal using the appropriate design and provided skin data by considering design parameters.

Objective:

• To design a back door of a car with an inner panel, outer panel and reinforcement for hinges, gas stay, Wiper motor and latch.
• The inner panel is subjected to the draft analysis to ensure whether it is satisfying the deep drawing requirements for the tooling direction that is created in the design.

Introduction of Backdoor:

                                             

   

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, but there are more functions that come with it which has to be considered while making a design of the same like rear visibility criteria and boost space.

This part is usually designed keeping the master section of the rear roof rail because of the sealant flange and also various other consideration, as it is also in contact with the side body of the car.

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.

Types of Back Door in a car:

• Top Mounted door
• Side mounted door
• Bottom Mounted Door

Components of Back Door:                                  

• Inner Panel
• Outer Panel Upper / Lower
• Hinge Reinforcement LH / RH
• Gas Stay Reinforcement LH / RH
• Wiper motor reinforcement
• Latch Reinforcement
• Plastic Trim

Design Intent:

The intent of his project is designing the BIW back door of the vehicle by applying the engineering standards and manufacturing requirements knowledge which satisfies the deep drawing process.

 

Deep drawing is one of the most widely used processes in sheet metal forming. Apart from its use in many other sectors, it is applied in the automotive industry for the manufacturing of car body parts. The deep drawing process is a forming process which occurs under a combination of tensile and compressive conditions. A flat sheet metal blank is formed into a hollow body open on one side or a hollow body is formed into a hollow body with a smaller cross-section. [DIN 8584]

Deep drawing processes are divided into three types:

• Deep drawing with tools
• Deep drawing with active means
• Deep drawing with active energy

In the automotive industry, deep drawing is usually carried out using rigid tools.

Design Consideration:

• Rear visibilities for safety and functionality
• Support structures like hinges and Gas stay/ Power lifter
• Rear crash regulations
• Boot space
• Mounts for wiper motor and lights
• Strength criteria
• Draft analysis

Design methodology:

Firstly, we have to check if there are any surface irregularities in the skin data, if irregularities are there, then repair if by using a bridge curve and through curve mesh and sew it. At some places you can also use 2-face blend.

Then we create a sealing flange. Generally, with the help of master sketch, we will design the panel with appropriate dimensions. But here there is no master sketch, we designed by assumption. with the help of sealing flange then we create connecting flange to create the inner panel, after that we used embosses in the inner panel to create gas stay and hinge embosses using faces in the inner panel.

Creation of Tooling Direction:

Back door is going to be manufactured by deep drawing process. In deep drawing process has a tool which is core and Die. The core part follows the single straight path the inclination angle of the core is known as 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. It is designed by using Top-down approach.

Mastic Region:

The mastic points are defined on the back door inner panel where the back door can easily deform. They help the backdoor outer panel to come back to its original shape after it gets deformed. Mastic sealants are elastic compound that believe like the rubber.

The gap between the inner panel and the outer panel over the embosses is filled with mastic sealants at curtained specified places, this helps to reducing vibrations and overall NVH (Noise, Vibrations and Harness)

Then, the sheet will bend with the helped of another die to make the flanges in “L” Shape.

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.

Inner Panel:

The inner panel is a component which is used for strengthen the door assembly and it is one of the most important components on which all accessories are mounted like hinges, glass guide channel, moulded trim, latch 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.

Outer Panel:

The outer panel of the back door is similar to the other BIW components where it is the aesthetic part of vehicle. The coating provided is of multi stage which has the property of scratch resistance, rust prevention and smooth and attractive finishes. The outer panel also has the provisions for the tail. Lamp, rear fog lamp and also has the provision for license plate mountings. Most of the hatchback cars have the provision for wiper motor. 

1.Embosses & Reinforcement:

With the distinctive cross section, embosses are created. The embossed are used to increase the strength of the backdoor. While designing we should keep in mind that it should not be over strength. So, we prefer to design big embosses rather than small embosses. These embosses are used to despite the forces sideways.

  

2.Gas Stay Reinforcement:

 

3.Hinge Embosses:

4.Latch and striker trajectory:

To define the opening and closing trajectory, the hinge and latch are positioned based on the hinge axis and trajectory. The circle drawn should be perpendicular to the latch striker to satisfy the condition. Based on the rotation trajectory the hinge axis, latch striker and predefined Gas stay are correlated for smooth kinematics of the door opening and closing.

5.Wiper Mechanism Reinforcement:

Hemming Operation:

Hemming is a mechanical joints design which is used for joining inner and outer closure panels as found indoors, hoods, bonnets and lift gates. To increase crash resistance the gap between the hemmed panels is filled with a high strength adhesive which also prevents from corrosion.

Hemming Corner Relief:

Hemming relief are cut out which are provided on the hemmed corner of the panel assembly which in turn to avoid some of the hemming defects such as wave – like or wrinkle formed surface as shown below, the back door design requires two locations where the roller type of hemming relief is required which are shown below.

Draft Analysis:

The draft analysis command shows you to detect if the part you drafted will be easily removed. This type of analysis is performed based on colour ranges identifying zones on the analysed element where the deviation from the draft direction at any point, corresponds to specified values.

Minimum draft angle of 7 degree is considered for analysis, green colour indicates on the parts that all face along the tooling direction has positive draft angle greater than 7 degree and passed in analysis. 

Screenshot Back Door Assembly:

CONCLUSION 

The backdoor is designed based on design considerations. Required reinforcement provided on inner panel. The design is checked by using draft analysis feature.