Design of backdoor

CAR BACK DOOR DESIGN

Aim:

To design the Back door (Tailgate) of a car from the styling surface provided using NX CAD. The ultimate aim is to design the Back Door by following Industrial Standards.

Back Door:

A back door is a BIW component found in all Automotive cars generally used for opening and closing the so-called car luggage that is usually used for storing items inside a car. In general, the opening and closing of the door are coordinated 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 the smooth opening and closing of the tailgate.

Parts of a Tail Gate:

• Outer Panel
• Outer panel Lower
• Inner panel
• Hinge Reinforcements
• Latch and Stricker Reinforcement
• Wiper Motor Reinforcement
• Gas Stay Reinforcements

All these parts are assembled together to obtain the back door of a car.

Types of Back Doors:

There are three types of back doors based on the position of the Hinge axis. They are

• Top Mounted

• Side Mounted

• Bottom Mounted.

In our design, we follow the Top Mounted Design where the Hinges are mounted on the top.

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 each other because these positions are dependent on each other and if the position gets altered all the positions have to be altered for the effective opening and closing of the back door. The Latch and Stricker, Hinge Position, and Gas stay Positions have 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.

Material Selection:

The material selection plays a major role in determining 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 to the door. Basically, the material is used based on the car's budget, because steel cost is very cheap than Aluminium. If aluminum is used instead of steel there is no need for many parts like Reinforcements for each mounting and the overall weight gets reduced by 6-10 kg approximately. But the drawback is Aluminium is much costlier than Steel. Hence based on the budget of the car aluminum is used. In higher-end models like Benz, Audi, Porshe, and BMW we can find aluminum is used instead of steel resulting in reduced weight and increased performance of the vehicle.

Another factor to make a note of is using Casted Aluminium instead of deep drawn Steel components and adding reinforcements to it the space of the luggage commodity gets increased by a certain amount because the draft angle for Casted aluminum is much lesser (3 degrees) 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 considerations taken. Since it reduces the space between the inner and the outer panel the rear visibility of the car is also improved giving more room 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.

Different Sheetmetal processes used for manufacturing the Back Door

Deep Drawing:

The metal deep-drawing process is an effective method of manufacturing cups, cans, and other similar deep-drawing products. The deep drawings have two main categories.

1. First-stage drawing: The blank shape of metal is placed on the die and in contact with the punch. When the metal specimen is a flat piece of sheet metal used in forming and finishing the product. Initially, the punch moves in a downward direction. The outer rim of the blank is subjected to pure radial drawing (drawing toward vertical axes) between the die and blank metal. The metal becomes bent and slides over the die and also stretched between the die and the punch. The metal in the vicinity of the punch head and contact with it bend and slide over radii and stretch over the punch head.
2. Redrawing: The components drawn from the first stage again it is redrawn and converted into more depth to form a cup shape in the die and punch. The second stage of drawing is called redrawing.

Embossing:

Embossing is a metal forming process for producing raised or sunken designs or relief in sheet materials by means of matched male and female roller dies, theoretically with no change in metal thickness or by-passing sheet or a strip of metal between rolls of the desired pattern. The metal sheet is drawn through the male and female roller dies producing a pattern or design on the metal sheet. Depending on the roller dies used, different patterns can be produced on the metal sheet.

Materials commonly used in the metal embossing process include:

• Aluminum alloys
• Steel alloys
• Zinc
• Copper
• Galvanized steel
• Brass
• Cold rolled steel

Hemming and Relief Areas:

Hemming and Seaming are two similar metalworking processes in which sheet metal edge is rolled onto itself. Hemming is the process in which the edge is rolled flush to itself, while a seam joins the edge of two materials.

methodologies

The Hemming is done on the outer and the inner panel with a clearance of 0.2mm on either side. Since at the corners, the hemming is difficult to perform, clearances have been given at the ends of panels so that it would the hemming operation is performed. Here is the image of the hemming relief at the corners.

Parts of the Back Door Assembly:

1) Outer Panel

2) Inner Panel

3) Reinforcements

Reinforcements:

Reinforcements are generally used to increase the strength of the mountings so that there are no unnecessary dents or noise occurs at the time of motion. This not only adds strength to the part but also increases the overall stiffness of the part so that the part is completely stable. The Reinforcements used are

1) Latch and Stricket Reinforcement

2) Wiper Motor Reinforcement

3) Hinge Reinforcement

4) Gas Stay Reinforcements

The Following Image shows the reinforcement that is used on different areas of the inner panel. They are usually spot welded on the inner panel.

Back Door Assembly:

Thus the top-down approach is followed to design the back door assembly. At first from the given styling surface the inner panel was created by Offsetting the outer Panel and then individual parts were designed accordingly by using the Inner panel Surfaces. The Reinforcement and other commodities were designed by using the inner surface as the reference thus following the top-down approach. The following image shows the assembly model of the Back Door.

Mastic Sealants:

The highlighted region in the image is the region where both the inner and outer panels are joined at the center 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.

DRAFT ANALYSIS:

Draft analysis of the inner panel is carried out through the tooling direction only. Only the green areas are acceptable.

Conclusion:

Thus the designing of the Back Door or Tail Gate is done as per Industrial standards and Manufacturing Techniques.