Designing the inner panel of an automotive Back Door using CATIA V5

Introduction

Back door is the rear most part of a car. It gives access to the rear storage compartment of the vehicle. It has to be strong enough to sustain the rear crash.

Back doors are made from steel/aluminum panels that swings (moves up or down during loading and unloading) with the help of a hinge mechanism. Back door is hinged with the car body. The door may be hinged at the top, side, or bottom. Hinges allow the panel to be raised. Devices such as a gas stay can keep the panel up in the open position.

Back door is securely locked to the vehicle body with the help of latch & striker mechanism, which may be locked to prevent unauthorized access from the exterior.

Back door consists of an inner panel, outer panel and some reinforcements, they are bonded together by hemming and welding processes. Embosses and reinforcements are used to increase the strength of the door.

The parts are made of steel/aluminum, based on the budget of the car. While using aluminum, we can achieve improved strength than steel, where we can avoid the reinforcements. We can vary the thickness of the part because they are casted. Therefore, we can reduce the number of parts. But aluminum is costlier than steel. While using steel parts, we cannot vary the thickness because they are stamped. Therefore, we cannot reduce the number of parts and reinforcements are needed to strengthen the part locally. Which would increase the weight of the part. Nowadays most of the car manufacturers are trying to use aluminum instead of steel. Therefore, the number of parts gets reduced, which in turn reduces the weight of the car drastically.

The car back door consists of the following parts,

• Outer panel
• Inner panel
• Hinge reinforcement
• Gas stay reinforcement
• Latch reinforcement
• Wiper motor reinforcement

Modeling of the back door involves two stages. They are,

• Modeling of the individual parts
• Assembling of the parts

Modeling of individual parts

The Class A surface (outer panel) of the back door where aesthetics is mainly concentrated is modeled initially, because these surfaces are visible outside. But here we design the inner panel of the back door and their reinforcements.

Figure 1: Inner panel

Inner panel is designed based on the outer panel, because it should provide necessary strength to the outer panel, embosses are added wherever necessary, via the deep drawing operation. A minimum draft angle of 7 degree is provided to get the smooth deep drawing operation.

Inner panel is made of 0.75 mm thick

Commands Used: offset, extract, line, multi-section surface, extrapolate, trim, fillet, boundary, healing, join, plane, sketch, connect curves, extrude, sweep, split, intersect, fill, corner, symmetry, project, thick surface

Reinforcements

The reinforcements are used to strengthen the part locally. The reinforcements used here are

• Hinge reinforcement
• Gas stay reinforcement
• Latch reinforcement
• Wiper motor reinforcement
• Side reinforcement

Reinforcements are made of 1.5 mm thick.

Figure 2: Hinge reinforcement

Hinge reinforcement is to enable swing (open and close) to the back door. It also increases the strength of the part locally. It has two parts one part is mounted with the car body and another is mounted with the back door.

Commands Used: plane, split, offset, sweep, healing, sketch, extrude, fillet, extract, thick surface

Figure 3: Gas Stay reinforcement

Gas stay reinforcement is used to fix the gas stay. Gas stay makes the motion of the door ease. It also helps by holding the door, while the door is open.

Commands Used: split, parallel, corner, offset, cylinder, trim, fill, fillet, healing, plane, multiple extract, extract, sketch, project, sweep, thick surface.

Figure 4: Latch & sticker reinforcement

Latch reinforcement is used to fix the latch and increases the strength locally. Helps the latch to assemble with the inner panel

Commands Used: plane, split, multiple extract, extract, offset, corner, thick surface.

Figure 5: wiper motor reinforcement

Wiper motor reinforcements is used to seat the wiper motor and is used to assemble the wiper motor with back door

Commands Used: plane, split, symmetry, multiple extract, corner, offset, thick surface.

Figure 6: Side reinforcement

Side reinforcement is used to improve the strength locally, which gives additional strength to the back door

Commands Used: plane, split, offset, healing, corner, parallel, cylinder, trim, fill, fillet, thick surface.

Assembly

The modelled parts are imported one after another and the constraints like fix, offset, coincidence, symmetry (mirroring the part) are used to assemble the parts, where it is to be placed.

Figure 7: Inner panel imported and fixed in assembly

Inner panel is the part imported first and then fixed.

Figure 8: Hinge reinforcement assembled with inner panel and mirrored

Hinge reinforcement is then imported and mated with the inner panel by selecting the respective planes and the offset distance is set as zero, then it is mirrored

Figure 9: Gas stay reinforcement assembled with inner panel and mirrored

Gas stay reinforcement is then imported, mated with the inner panel and it is mirrored

Figure 10: Latch and sticker reinforcement assembled with inner panel

Latch and sticker reinforcement is then imported and mated with the inner panel by selecting the respective planes and the offset distance is set as zero, then it is mirrored

Figure 11: Wiper motor reinforcement assembled with inner panel

Wiper motor reinforcement is then imported, mated with the inner panel and it is mirrored

Figure 12: Side reinforcement assembled with inner panel and mirrored

Side reinforcement is then imported, mated with the inner panel and it is mirrored

Figure.13: Fully assembled inner panel

Thus, the inner panel of backdoor and their reinforcements are modeled and assembled.