Design of backdoor

BACK-DOOR DESIGN

Objective:

Use the provided styling surface to come up with a back door design, use appropriate design methodologies and provide the necessary reinforcements and embosses.

Back Door:-

A back door is a BIW component found in all Automotive car generally used for opening and closing of the so called car luggage that is usually used for storing items inside a car. In general the opening and closing of the door is co-ordinated by the Latch and Stricker position and the Gas stay position that is mounted on the body and back door of the car. These positions play a major role in ensuring smooth opening and closing of the tail gate.

Material Selection:-

The material selection play a major role in determing the overall weight of the back door. The materials generally used are Steel and Aluminium. The Density of Steel is higher than Aluminium thus it results in adding more weight of the door. Basically the material is used based on the budget of the car, because the cost of steel very cheap than Aluminium. If aluminium is used instead of steel there is no need of many parts like Reinforcements for each mounting and the overall weight geta reduced by 6-10 kg approximately. But the draw back is Aluminium is much costlier than Steel. Hence based on the budget of the car aluminium is used. In higher end models like Benz, Audi, Porshe and BMW we can find aluminium is used instead of steel resulting in reduced weight and increased performance of the vehicle.

Another Factor to make a note is using Casted Aluminium instead of deep drawn Steel components and adding reinforcements to it is the space of the luggage commodity gets increased by a certain amount because the draft angle for Casted aluminium is much lesser (3 degree) than the deep drawn Steel inner panel (7-9 degree). Thus it reduces the space between the inner and outer panel resulting in much larger cabin space than the deep drawn steel inner panel. Thus the material selection is one of the design consideration taken. Since it reduces the space between the inner and the outer panel the rear visibility of the car is also inproved giving more space for the mirror to view.

Hence in this design the material chosen is steel since it is designed for a medium budget car and hence high cost could not be afforded to design the back door.

Design Considerations In Back Door Design:-

The following are the Design considerations taken while designing the Back Door. They are,

• Visibility Criteria
• Force Dissipation
• Latch and Stricker Positions
• Hinge Position
• Gas Stay Position
• Material Selection
• Space Availability
• Hemming and Relief Areas

All these design considerations go hand in hand with eachother because these positions are dependant on each other and if position gets altered all the positions has to be altered for effective opening and closing of the back door. The Latch and Stricker, Hinge Position and the Gas stay Positions has to be maintained in a proper way so that they play a major role in the opening and closing as well as the rear Visibility criteria of the car.

Parts of a Back Door:-

1. Outer Panel Upper
2. Outer panel Lower
3. Back Door Inner panel
4. Hinge Reinforcements
5. Gas Stay Reinforcements
6. Wiper Motor Reinforcement
7. Latch and Stricker Reinforcement

1.) 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.

We have considered a 2-part outer panel for our design, outer upper panel and outer lower panel prospectively.

I) Outer panel upper:-

II) Outer panel lower:-

2.) Back Door 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.

3.) Reinforcements :-

Reinforcements are provided to provide support and add extra material to the sheet 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. Thickness of all reinforcements is 0.15 mm.

I) LH & RH Hinge Reinforcement :-

II) Gas Stay Reinforcements :-

LH Gas Stay Reinforcement :-

RH Gas Stay Reinforcement :-

III) Wiper motor reinforecement :-

IV) Latch and Striker Reinforcement :-

Mastic Sealants:-

The highlighted region in the image is the region where both the inner and outer panel are joined at the centre with the help of Mastic Sealants. There is a gap of 5mm for the mastic sealants to melt and gets fixed at the surface of the panels.

Design Methodology:-

We start with the styling surface that is provided to us, and consider top-down approach for this assembly modeling. 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

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.

Tooling Direction

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 center 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 center 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.

Inner Panel

Trajectory circle

Reinforcement

Hemming and relief

Draft Analysis :-

In order to make sure the drawing of inner panel body is proper; we do draft analysis. We need to define the drawing direction and select the inner panel body. We take limit angle as 5 degrees. The result of the draft analysis is as follows

Conclusion

Thus the back door was designed from the given styling surface and Draft analysis is also done on the inner panel to check the manufacturing conditions. In this challenge i learned to design the Inner panel, the Outer panel, Wiper Motor reinforcement, Hinge reinforcement, Gas Gtay reinforcements, Latch and Striker reinforcement and its position.