Challenge

Design of backdoor

DDurgesh Choukiker28 Feb 2023

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

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, 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:

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

Design Intent:

The intent of his project is design the BIW back door of the vehicle by following the engineering standards and manufacturing requirements 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.

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.

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.

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 takes the reference of this tooling axis and manufactures 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, molded 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.

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.

Gas Stay Reinforcement (LH/RH):

Hinge Embosses (LH/RH):

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 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.

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.

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.

Draft Analysis:

The draft analysis command enables you to detect if the part you drafted will be easily removed. This type of analysis is performed based on color ranges identifying zones on the analyzed 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 color infers on the parts that all face along the tooling direction has positive draft angle greater than 7 degree and passed in analysis.