Design of backdoor

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

Introduction to backdoor :

A backdoor is located at the rear end of the car which gives access for the boot space to store luggage.,spare whhel etc.These doors can be operated mannualy or eclectric powered.In most of the luxuary car is electric powered.

Back Door also called as 'Hatch', or 'Tailgate', 'Trunk-lid', 'Boot-door' is basically the 5 door in a 4-door car. It's the rear most part of the vehicle which gives access to the trunk and has mounts for wiper motor, tail lamps, hinges for supporting its weight in opened position, gas stays which help with its opening and keeping it open, radars and cameras etc.

The material used for backdoor varies as per the price range of the vehicle. Most of the low cost vehicles use steel as it is cheaper and use parts that are stamped using moulds. These parts are usually of uniform thickness and reinforcements are added to improve local strength where needed. The premium vehicles use aluminium parts which are usually die casted and hence can have variable thickness. This removes the need of reinforcements hence keeping the weight even lower as aluminium parts are lighter in comparison. On the contrary aluminium is more expensive than steel hence its applications are limited in cheaper vehicle. Currently due to the extensive use of plastics trims and plastic parts the cost of aluminium is affordable for the manufacturers in all price brackets. Use of aluminium reduces the overall weight of the component and hence the vehicle improving its fuel efficiency.

A backdoor is usually made up of 1 inner panel and 2 or 3 outer panels joined together by hemming and spot welding wherever necessary as shown below

HEMMING:

Hemming is the metelworking process in which a sheet metal edge is rolled into itself.The outter surface of the panel is rolled 2 or 3 times over the inner panel.In first roll the panel is bent slinghtly,and in the second roll the shhet matel is rolled even more and in the last roll it completely fits or covered the inner panel.There must be a 0.2mm gap between outter and inner pannel in both upper and lower side.

SPOT WELDING:

Spot Welding is a form of resistance welding also known as Resistance Spot Welding (RSW). Spot Welding involves using heat produced by resistance to an electrical current to join materials together. The current heats the materials to a point where they become malleable. The use of strong pressure bonds them together.

DESIGN CONSIDERATION FOR BACKDOOR INNER PANEL:

1. Rear Visibility.

2. Support structures like hinges and gas stays.

3. Mounts for wiper motor, tail lamps, and other wiring loops.

4. Fit and clearances.

5. Boot space

6.Rear crash regulations and requirements.

7.Sealing and its functions.

8.Joining techniques like hemming, spot welding etc.

COMPONENTS OF BACKDOOR:

• Inner panel
• Outter panel upper
• Outter panel lower
• Hinge reinforcement LH
• Hinge reinforcement RH
• Gas stay reinforcement LH
• Gas stay reinforcement RH
• Wiper motor reinforcement
• Latch reinforcement

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.

from the above figure it is seen that the extension flange is for mastic sealent .In bottom of the panel ,there is more gap between the inner panel and outter panel,to give strength and rigidity we should give those extensions and joined using mastic sealent.

Inner panel draw direction:

The inner panel is produced by either casting or through deep drawn method. Mostly alumininum panel is only casted, steel inner panel is made by deep drawn process only. If it is deep drawn ,then there must be a tooling direction through which that direction the panel is deep drawn and is shown below

Latch Design:

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.

Latch trajectory as shown below

DRAFT ANALYSIS:

Draft analysis of inner panel is carried out through the tooling direction only. Only the green areas are acceptable and in worst cases yellow regions are accepted but the blue and red regions are never accepted.

The draft angle for aluminium casted panel is 2 to 3 degrees is enough but if it is steel then the angle is more than 7 degrees.

In this project i considered it as steel and used 7 degrees as draft angle and direction is choosen as tooling direction which is the deep drawn direction.

From the above fig. it is clear that all areas are in green color so my design is passed draft analysis. The yellow sectioned flange is done using lancing process hence can be neglected to the considered tooling direction.

OUTTER PANEL UPPER AND LOWER:

Outter panel is the styling surface of the backdoor. Glass for rear visibility is mounted on the outter panel upper.Rear lights are also mounted on the outter panel upper.

Number plate is mounted on the outter panel lower.Spot welds and other manufacturing process should done only on the inner panel because the outter panel is the styling surface which should not have any scratches or welds .Because it affects the style of the car which leads to bad impression on the customers.

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.

Wiper motor reinforcement,latch reinforcements,hinge reinforcements and gas stay reinforcements are mounted on the inner panel of the backdoor as shown below.

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