Design of backdoor

Car back door design

Aim: to design car back door from given styling surface data under given design rules and regulations.

Car back door and components:

 The back door is 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 these are seats present at the rear. The back door comprises of certain components which form the door assembly together.

The component of the back door is as follow,

• 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 0.75mm.

 

• 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 panel are connected by mastic sealants in center and by hemming process at edges. The outer door handle and in some cases, the number plates 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 inner panel prospectively. Outer panel is manufactured by stamping sheet metal thickness for outer panel is 0.75mm.

 

Reinforcements

Reinforcements are provided to provide support and add extra material to the sheet metal part to increase its strength near components installation regions and minimize the impact of collision. We have considered following reinforcements during our design. The reinforcements maybe manufactured by stamping. Thickness of all reinforcements is 1.5mm

 

 LH and RH Hinge Reinforcements

 LH Gas Stay Mounting Reinforcement

 RH Gas Stay Mounting Reinforcement

Wiper Motor Mounting Reinforcement

Latch Striker Reinforcement

• Gas stay

Gas stay is basically a gas spring that relies on elastic deformation of a compressed gas which in 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.

 

 Car Back Door Gas Stays

• Wiper and wiper motor mounting

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

 Car Back Door Wiper

• Hinges

Hinges connected the door with the vehicle body and allow the door to rotated 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.

 

 Car Back Door Hinges

Design Methodology:

We start with the styling surface that is provided to us and consider top-down approach for this assembly modeling. Frist, we create the assembly and then create the components in the assembly file itself. Inner and outer panel are largest part 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 command and features we deign the outer panel form the styling surface. We have 2 parts for outer panel upper and lower respectively. They will be sport welded with each other. It is necessary to make surface that all the surfaces are properly joint to their adjacent surface and there are no disjoints at their intersection edges to avoid further errors.

 

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 surface and deign inner panel on the same. Inner panel is important as most the mounting will be done on it before starting inner panel design, we need to define tooling direction as a reference for manufacturing team. Then we design the inner panel

 

 Tooling Direction

 

While design 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 make access to tail light assembly easier. As the bottom create a surface that comes out and connected 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.

 

Latch striker Path

 

 Inner Panel

As the inner and outer panel are connected by hemming process, we can complete the hemming after completion of inner panel. Now as major parts are designed, we can move to reinforcements. It is fairly easy to design reinforcements as shown in image below and detailed images above as we can use the inner panel surface using wave geometry linker into the corresponding reinforcement parts.

 

 Rinforcements

Important features used while designing:

• Wave geometry linker- with this can create, associative or linked copies of any entity of a part into other parts. The changes made to the original entity will be reflected in the copy of that entity.
• Extract Body – it is used to create an associative body by extracting faces, entire body or region of faces.
• Bridge curve – it helps to create a tangent blend curve between two objects. The objects may be edges or sketch curves.
• Sew – it combines sheet bodies together by sewing their common edges. There shouldn’t be any gaps larger then specified tolerance.
• Unsew – this command is used to separate the existing sheet body or solid body into multiple bodies.
• Trim body – it is used to trim one or more bodies using a face or plane. You can also specify the bodies to retain and the bodies to discard.
• Offset surface – it allows you to offset one or more existing surfaces.
• Offset curve in face – this command will allow you to offset particular edges or curves on selected faces.
• Trim sheet – it is used to trim one or more bodies using a face or plane. You can also specify the bodies to retain and the bodies to discard.
• Through curves – it will allow you to create a body through multiple sections, where it’s shape changes to pass through each section.
• Law Extension – this command extends a curve or edge to create a sheet body at desired angle length by changing the rules under angle law and length law.
• Trim and extend – it helps you to trim and extend intersecting surface and make corner at their intersection.
• Face bland – it creates fillets between faces.
• Edge bland – it creates fillets on edges.
• Extend sheet – it will allow you to existing surface to required distance.
• Emboss – emboss command create an embossing by modifying a body with faces created by projecting a curve/section along a direction. You can modify the emboss using option like endcap location and draft angle.
• Mirror geometry – as name suggests, it allows you to mirror geometries about selected plane or surface.
• Thicken – it is used to convert a surface to solid body by providing thickness.
• Extrude – it helps you to create a feature from a sketch. You are also able to create thin feature using a sketch or curve under this command.

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

 

Draft Analysis result 

Portion that required different manufacturing methos, or are not in the direction of drawing may not be considered in draft analysis results.

Conclusion: car back door was design using the given styling surface, and under provided design regulations.