Design of backdoor

OBJECTIVE:-

To devlope the car backdoor by using given surface method by automative shhet metal design.

BACKDOOR:-

A backdoor is located at the rear end of the car which gives access for the boot space to store luggage,spare wheel etc.These doors cab be operated mannualy or electric powered.In most of the luxuray car is electric powered.Back door is also called as 'Hatch' or 'tailgate','trunk-lid','boot-door' is basically the 5 door in a 4-door car.Its rearmost part of the vehical which gives access to the trunk and has mounts wiper motor,tail lamps,hinges for supporting its weight in opened position,gas stay 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 backdoor varies as per the price range of the vehicle.Most of the low cost vehicle use steel as it is cheaper and use parts are stamped using moulds.These parts are usually of uniform thickness and reinforcement are added to improve local strength where needed.

REINFORCEMENT:-

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

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

Hemming:-

Hemming is a forming operation in which the edge of the sheet are folded or folded over another part in order to achive a tight fit.Normally hemming operations are used to connect parts together,to improve the apperance of the part and to reinforce part edge.

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:-

1)Conventional die hemming:-

In conventional die hemming,the flange is folded over the entire length with a hemming tool.Conventional die hemming is suitable for mass production. In die hemming, the flange is folded over the entire length with a hemming tool. Normally the actual hemming is a result of a forming operation in which the flange is formed with a hemming tool after the drawing and trimming operations have been completed. The formed flange is then hemmed in several process steps. These steps include, for example, the pre-hemming and final hemming depending on the respective opening angle of the flange. Production plants for conventional die hemming are very expensive, but the cycle times are very low.

2)Roll hemming:-

In roll hemming,the hemming roller is guided by an industrial robot to form thr flanges.Roll hemming is carried out incrementally with a hemming roller. An industrial robot guides the hemming roller and forms the flange. Roll hemming operation can also be divided into several pre-hemming and final hemming process steps. Roll hemming is very flexible to use and tool costs are significantly lower as compared to those of conventional die hemming. However, the cycle times are much higher since the hemming is realized using a hemming roller which follows a defined path.

Blanking:-

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

Punching:-

Its similar to blanking only the main differance is that,the hole is required product and the material punced out from the hole is considered as a waste.

OUTTER PANEL UPPER AND LOWER:-

Outter panel is the styling surface of the back door.Glass for rear visibility is mounted on the outter panel upper.rear light 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 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 customer.

INNER PANEL:-

Car backdoor inner panel is made of either steel or aluminium.Most of the luxuary car's inner panel are made of aluminium because of its properties.But the cost of aluminium is high.Cost of aluminium is more as compared to steel.To easily understand,the cost of aluminium for inner panel is higher than the cost of all parts of backdoor together.

Wiper motor,latch reinforcements,hinge reinforcement and gas stay reinforcement are mounted on the inner panel of the backdoor only.The embosses in the inner panel helps stiffening 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 sealant.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 sealant.There should be a gap between the extension and the outter panel is minimun 5mm for mastic sealant.

INNER PANEL DRAW DIRECTION:-

The inner panel is produced by either casting or through deep drawn method.mostly aluminium 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.

HINGE REINFORCEMENT:-

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

GAS STAY REINFORCEMENT:-

Gas stay reinforcement is used to lift the backdoor automatically.There are two types of gas stay one is semi-automated type the back door needs little force to lift after that it lift the backdoor automatically.In fully automated,it has power spindle which lift the bck door automatically.

WIPER MOTOR REINFORCEMENT:-

Wiper is ued to to wipeout the rain water falls on the backdoor window.Its 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 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 electronics devices are mounted on the inner panel only.

HEMMING:-

Hemming is the metalworking process in which a sheet meatl 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 sheet metal is rolled even more and in last roll it completely fits or covered the inner panel.There must be a 0.20mm gap between outter and inner panel in both upper and lower side.

DRAFT ANALYSIS:-

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

The draft angle for alluminium casted panel is 2 to 3 degree is enough but if its steel then the angle is more than 7 degree.

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