Design of backdoor

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

INTRODUCTION

An automobile back door or Tailgate is the panel that covers the boot (or trunk) of an automobile. It enables access to the main luggage compartment. A hinge allows the boot lid to be raised, while devices such as springs or gas cylinders hold it up in the open position The Backdoor is an assembly of many parts such as inner panel, outer panel upper, outer panel lower and Reinforcement. Inner panel is attached to the outer panel using mastic sealant.

Total no. of parts in Backdoor are:

• Back door outer panel (upper)

• Back door outer panel (lower)

• Back door inner panel

• Hinge reinforcements
• Gas stay reinforcements
• Latch and striker reinforcements
• Wiper motor reinforcements

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 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 1.5 mm.

• 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 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.

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.

ASSY VIEW

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.

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 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 t and error, we can adjust the emboss the circle dimensions properly.

fig. TRAJECTORY CIRCLE FOR LATCH STRICKER PATH

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 surfaces using Wave Geometry Linker into the corresponding reinforcement parts.

FIG NO. -REINFORCEMENTS

IMPORTANT FEATURES USED IN DESIGN

• Wave Geometry Linker - With this you can create, associative or linked copies of any entity of a part into other parts. It may be a surface, edge, curve, body, sketch etc. 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 than specified tolerance.

• Unsew - This command is used to separate the existing sheet body or solid body into multiple bodies.

• Projected Curve - It is used to project an existing curve/curves on a selected plane or surface by selecting a direction for projection.

• 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 br 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 off a portion of a sheet body using curves, faces, edges or planes.

• 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 surfaces and make corner at their intersection.

• Face Blend - It creates fillets between faces.

Edge Blend - It creates fillets on edges. • Extend Sheet - It will allow you to extend an existing surface to required distance.

• Emboss Emboss command creates an embossing by modifying a body with

faces created by projecting a curve/section along a direction. You cr modify the emboss using options 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 tosolid 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.

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.

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Analysis Result

Portions that require different manufacturing method, or are not in the direction of drawing may not be considered in draft analysis results.

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