Design of backdoor

Car Back Door

The back door has a hinged door/tailgate at the rear of the vehicle. It may be used for loading and unloading cargo, or to get passengers in and out, in case there are seats present at the rear. The back door comprises of certain components which form the back door assembly together.

The components of back door are as follows,

Inner Panel

The inner panel, as the name suggests, is the inner part of the door. It is where most of the reinforcements and components are mounted. It is manufactured either by casting (aluminum) or sheet metal stamping (steel). Thickness of inner panel is 0.75 mm.

Outer Panel

As the name suggests, it is the outer part of the rear door and is mostly responsible for aesthetics of the vehicle. Outer and inner panels are connected by mastic sealants in center and by hemming process at edges. The outer door handle and in some cases, the number plate may also be installed on the outer panel of the back door. We have considered a 2-part outer panel for our design, outer upper panel and outer lower panel prospectively. Outer panel is manufacture by stamping sheet metal. Thickness for outer panel is 0.75 mm

Reinforcements

Reinforcements are provided to provide support and add extra to the sheet material metal part to increase its strength near component installation regions and minimize the impact of collisions. We have considered following reinforcements during our design. The reinforcements maybe manufactured by stamping.

Hinge Reinforcements Hinges

Hinges connect the door with the vehicle body and allow the door to rotate around a fixed axis for opening and closing movement. Generally, hinges are a 2-part assembly, where one part is bolted to door and other is bolted to vehicle body.

Gas Stay Mounting Reinforcement

Gas Stay

Gas stay is basically a gas spring that relies on elastic deformation of a compressed gas which is enclosed in a cylinder. It is used to reduce required effort while opening the back door. Although all the cars don’t come with gas stays, it may be required in case of a heavy back door.

Wiper Motor Mounting Reinforcement

Wiper and wiper motor mounting

As the name suggests, wiper is used to wipe off the dust and water from the rear windscreen of the vehicle.

Latch Striker Reinforcement

Design Methodology:

We start with the styling surface that is provided to us, and consider top-down approach for this assembly modelling. First, we create the assembly and then create the components in the assembly file itself. Inner and outer panel are the largest parts and all other parts depend on them so we start with them. Also, the given styling surface is part of the outer panel so we create it first. Using various commands and features we design the outer panel from the styling surface. We have 2 parts for outer panel, which are separated by a flange, hence we create outer panel upper and lower respectively. They will be spot welded with each other. It is necessary to make sure that all the surfaces are properly joint to their adjacent surface and there are no disjoints at their intersection edges to avoid further errors. Also, Inner and outer panels are connected by hemming process so we can come back to outer panel and do that that after completion of inner panel.

Outer Panel Upper Part

Outer Panel Lower Part

Now, as we know inner panel is at a particular distance from outer panel, we offset the outer panel surface and design inner panel on the same. Inner panel is important as most the mountings will be done on it. Before starting inner panel design, we need to define the tooling direction as a reference for manufacturing team. Then we design the inner panel. While designing the inner panel we need to consider various factors like the mounting point positions, mastic sealant application positions and the cut outs in sheet to make access to tail light assembly easier. As the bottom centre part of inner panel is not connected to outer panel, we need to create a surface that comes out and connects to outer panel as shown in the image. This part will be connected to outer panel using mastic sealant. Also, the hinge embosses must be taken by considering proper directions. The emboss surface must be parallel to z-axis to get proper geometry for the latch striker path curve. Then we draw a line connecting the hinges, such that it forms the hinge axis (axis around which the door rotates while opening or closing). Then we can draw a circle with centre at the hinge axis and circumference passing somewhere around the emboss endcap. So that when we get the emboss for latch striker mounting, we can take the end cap by creating a plane normal to the path (using On Curve) in the direction normal to the path of striker. Thus, after some trial and error, we can adjust the emboss and the circle dimensions properly.

Tooling Direction:

Before starting to design the inner panel of the back door the tooling direction for Deep Drawing purpose should be created.

Then the styling surface needs to be checked and analyzed since it might have irregularities, hence it must be fixed first.

Then the back door was designed using the top-down approach.

Latch Striker Path

The position of the hinge should be perpendicular to the latch when the latch and striker meets. The circle is drawn from the center of the hinge axis to find the path of the striker and positioned perpendicular to the path

Draft analysis

Conclusion

Here we have made the back door and its components with the given surface and made a draft analysis.