Design of backdoor

DESIGN OF BACK DOOR OF CAR

Aim – Design of back door by use of NX cad

OBJECTIVE: To develop the car backdoor by using the given surface method by automotive sheet metal design.

Introduction

BACKDOOR: A backdoor is located at the rear end of the car which gives access to the boot space to store luggage. Spare wheel etc. These doors can be operated manually or electric powered. A most luxury 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 rearmost part of the vehicle which gives access to the trunk and has mounts for wiper motor or, tail lamps, hinges for supporting its weight in the opened position, gas stays which help with its opening and keeping it open, radars and cameras, etc.

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.

The material used for the backdoor varies as per the price range of the vehicle. Most of the low-cost vehicles use steel as it is cheaper and uses parts that are stamped using molds. These parts are usually of uniform thickness and reinforcements are added to improve local strength where needed. The premium vehicles use aluminum 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 aluminum is affordable for the manufacturers in all price brackets. The use of aluminium reduces the overall weight of the component and hence the vehicle improves its fuel efficiency.

REINFORCEMENTS:

As mentioned for local strengthening reinforcements are usually provided. Instead of making the whole panel off a thicker sheet, a thinner sheet with thicker local reinforcements wherever needed is preferred. The reinforcements are usually 1-1.5mm thick whereas the panel itself is 0.55- 1 mm thick.

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.

TYPES OF DOOR OPENING:

• Top mounted door

Side-mounted door

Bottom mounted Door

In this project, I designed Top mounted door, so here we discuss mainly top-mounted doors only.

1.Deep Drawing:

The metal deep drawing process is an effective method of manufacturing of cups, cans and other similar deep drawing products. The deep drawings having two main categories.First- stage drawing: The blank shape of metal is placed on the die in and contact with the punch. When the metal specimen is flat piece of sheet metal used in forming and finish the product. Initially the punch moves in downward direction. The outer rim of blank is subjected to pure radial drawing(drawing toward in vertical axes) between die and blank metal. The metal become a bend and sliding over die and also stretched between die and punch. The metal in vicinity of punch head and contact with it bend and slide over radii and stretch over punch head.Redrawing: The componentsdrawn from first stage again it is redrawn convert into more depth to form a cup shape in the die and punch. The second stage of drawing is called as redrawing.

2.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. 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.

3.Hemming: Hemming is a forming operation in which the edges of the sheet are folded or folded over another part in order to achieve a tight fit. Normally hemming operations are used to connect parts together, to improve the appearance of a part and to reinforce part edges.In car part production, hemming is used in assembly as a secondary operation after deep drawing, trimming and flanging operations to join two sheet metal parts (outer and inner) together. Typical parts for this type of assembly are hoods, doors, trunk lids and fenders.

There are various types of hemming operations:

Conventional die hemming: In conventional die hemming, the flange is folded over the entire length with a hemming tool.

Roll hemming: In roll hemming, the hemming roller is guided by an industrial robot to form the flange.

Open Hem: A Hem has a full round feature and a return flange. In open hem bend angle is equal to 180 degrees.

Tear drop Hem: In tear drop hem the bend angle is greater than 180 degrees.

Closed Hem: Hems without any inside radius are called as closed hem. Closed hems are not recommended if the hem geometry is to be painted or if the material used is SST or Aluminium

4.PUNCHING & Blanking:

Blanking It is a cutting operation of a flat metal sheet and the article punched out is known as blank. Blank is the required product of the operation and the metal left behind is considered as a waste

Punching It is similar to blanking only the main difference is that, the hole is the required product and the material punched out from the hole is considered as a waste

COMPONENTS OF BACKDOOR:

• Inner panel
• Outer panel upper
• Outer panel lower
• Hinge reinforcement LH
• Hinge reinforcement RH
• Gas stay reinforcement LH
• Gas stay reinforcement RH
• Wiper motor reinforcement
• Latch reinforcement
• Plastic trim

Backdoor parts thickness value used in this design:

1. Outer panel - 0.75 mm
2. Inner panel - 0.75 mm
3. Reinforcements - 1.5 mm

INNER PANEL:

Car backdoor inner panel is made of either steel or aluminum. Most of the luluxuryar's inner panel are made of aluminium because of is properties.But the cost of alaluminums high.

	STEEL	ALUMINIUM
PARTS	Parts are stamped	Parts are casted
REINFORCEMENTS	Necessary	Can be neglected
THICKNESS	Constant	Can be Varied
COMPONENTS	More	Lessin number
WEIGHT	More	Lighter
COST	less in cost as compared to Aluminium	More as compared to Steel

Cost of aluminium is more as compared to steel .TO easiy understand , the cost of aluminium for inner panel is higher than the cost of all parts of backdoor together.

Bechmark between companies who are using steel and aluminum inner panel

Wiper motor, latch reinforcements, hinge reinforcements and gas stay reinforcements are mounted on the inner panel of the backdoor only. The embosses in the inner panel help stiffen the inner panel and act as a local reinforcement. Another purpose of giving emboss is to distribute impact forces towards hinges. from the above figure it is seen that the extension 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.And there should be a gap between the extension and the outer panel is a minimum of 5mm for mastic sealant.And there should be a gap between the extension and the outer panel is a minimum of 5mm for mastic sealant.

Inner panel Tooling direction:

The inner panel is produced by either casting or through deep the drawn method. Mostly aluminum 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.

DRAFT ANALYSIS:

Draft analysis of in the ner panel is carried out through the tooling direction 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 the aluminium casted panel is 2 to 3 degrees 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 the draft angle and direction chosen 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.

OUTER PANEL UPPER AND LOWER:

The outer panel is the styling surface of the backdoor. Glass for rear visibility is mounted on the outfitter panel upper. Rear lights are so mounted on the outer panel upper. The number plate is mounted on the oouteroutter panel lower. Spot welding another manufacturing pre-process should do only on the inner panel becausouteroutter panel is the styling surface which should not have any scratches or welds. Because it affects the style of the car which leads to a bad impression on the customers.

HINGE REINFORCEMENT:

The hinges support the weight of the whole backdoor. Hence, reinforcements must be provided there too. The emboss is designed in such a way that the hinges should operate freely. The hinge is connected to the rear roof of the car

GAS STAY REINFORCEMENT

Gas stay is used to lift the backdoor automatically. There are two types of gas stay one is semi-automated and another one is fully automated. In semi-automated type the back boor needs little force to lift after that it lifts the backdoor automatically. In fully automated it has a power spindle which lifts the backdoor automatically.

WIPER MOTOR REINFORCEMENT:

Wiper is used to to wipeout the rain water falls on the backdoor window.It is actuated by the motor which is mounted on the inner panel.Due to the vibration and heat created by the motor .the inner panel where the motor is mounted gets deform and the parts attached to the motor starts to vibrate which leads to poor NVH.So we have to provide the reinforcement where the wiper motor is placed.

LATCH REINFORCEMENT:

At bottom of the panel , reinforcement and emboss are given to accomodate the latch and striker assembly.Generally key operated or automatic remotly controllable mechanism is used to keep the door open or closed.The actuators , recivers and other electronic devices are mounted on the inner panel only.

PLASTIC TRIM:

Plastic trim is the part which covers the ugly part of inner panel.There are holes given in the inner panel of the backdoor in which the plastic trim is mounted.

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.

Another form of resistance welding is Projection Welding. This process involves fusing a fastener’s embossed or coined projections to the metal base material to form a weld. As the materials never melt, they do not intermix. This means the resulting weld is more like a forging of the materials.

Spot welding is only suitable for a small selection of base materials. Low carbon steel is the most suitable material for spot welding. This is because it is more resistant to electricity and has a lower thermal conductivity than the copper electrodes used to create the required electrical current.

High carbon steels and aluminum alloys can form brittle welds that don’t last with the spot welding process. Pure aluminium can qualify for spot welding but requires higher current levels. This is because it has a lower resistance to electricity than low carbon steel.

CONCLUSION:-

The back door outer and inner panels were designed with the help of the styling surface along the tooling direction.

Draft analysis was performed on the inner panel and all the reinforcements were designed and placed at appropriate positions.