Design of backdoor

OBJECTIVE :

• From the given styling surface , develop a back door using appropriate design methodologies .
• The objective of this project is to design a BIW Back Door of a car with an Inner Panel , Outer Panel , and Reinforcements for the Hinges , Gas stay , Wiper Motor , and Latch by following the engineering standards . 
• The Inner Panel must be subjected to Draft Analysis for verifying whether it satisfies the Deep Drawing requirements for the tooling direction created in the design .

Software Used : Siemens NX CAD ( Unigraphics )

Introduction : Back door of the car is also known as Tailgate . The Back Door of a car is the rearmost part of the vehicle which gives access to the trunk space of the vehicle . The rear door also supports the reinforcements and added weights of the Wiper Motor , Gas Stay , Tail Lamp , and Latch and Striker . The Backdoor / tallgate is one of the closure commodities in BIW sheet metal design . The backdoor has a lot of components inside and is designed to incorporate them easily . It affects the rear visibility and luggage area.

Back door consists of one inner panel and two outer panel. The material used for door manufacturing depends on the budget and performance of the vehicle . Mostly Aluminium and Steel will be used whereas low budget vehicles use Steel which makes the manufacturing process easy and cost efficient since it follows the Stamping of Moulds .

Types of doors based on working position ,

1. Top Mounted Door

2. Side mounted Door

3. Bottom Door 

DESIGN CONSIDERATION OF A BACKDOOR :

• Functional Requirement of Hinge and gas stay
• Rear visibility criteria
• Luggage volume
• Crash Analysis
• Bend Test , Dent Test , Torsion Test & Endurance Test
• Rear Crash Regulation
• Gap and flushness Requirements

Assembly of Back door :  the major problem in back door is material selection . mostly in past days steel is used , but it makes a very problems the steel parts have heavy weight , so it reduces the fuel economy , insted of steel presently in high end cars aluminium is used , the main objective of aluminium it have less desnser material and its sutaible for complex shapes. 

Back Door Assembly : It consists of following parts:-

• Backdoor Inner panel
• Backdoor Outer panel
•  Outer Panel Upper 
•  Outer Panel Lower
• Hinge Reinforcement (LH & RH)
• wiper motor reinforcement  
• Latch & Stricker Reinforcement
• Gas Stay Reinforcement (RH & LH)

Different types of Sheetmetal operations are done in the Back Door:

DESIGN INTENT:  The intent of the project is to design a Body In White Back Door of the vehicle considering the engineering standards and manufacturing requirements which satisfies the Deep Drawing Process .

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 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 components drawn 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 -Bottom 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 .

Materials commonly used in the metal embossing process include :

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

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 Hemming : In tear drop hem the bend angle is greater than 180 degrees .
• Closed Hemming : 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.Blanking : Blanking 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 .

5.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 .

inputs for designing of backdoor

Outer Panel - 0.75 mm

Inner Panel - 0.75 mm

Reinforcements - 1.5 mm

DESIGN METHODOLOGY :

DESIGN OF BACKDOOR OUTER PANEL : The Outer Panel is the styling surface of the back door . Other components of the backdoor are designed with reference to the outer panel . It acts as the outer cover and deals with the aesthetics of the car.

In this design outer pannel is divided into two parts

1. Outer Upper panel
2. Outer Lower panel

OUTER Upper PANEL :

1. The Outer Upper Panel Extracted from a styling surface.
2. The panel is altered for the required design with the surface tools of NX CAD
3. The thickness provided for the outer panel is 0.75 mm
4. Hemming is provided with the corner relief .

Outer Lower Panel :

1. The Outer Upper Panel Extracted from a styling surface .
2. The panel is altered for the required design with the surface tools of NX CAD
3. The thickness provided for the outer panel is 0.75 mm
4. Hemming is provided with the corner relief .

Tooling Direction :

1. Before starting to design the inner panel of the back door the tooling direction for Deep Drawing purpose should be created .
2. Then the styling surface needs to be checked and analyzed since it might have irregularities , hence it must be fixed first .
3. Then the back door was designed using the top - down approach.

DESIGN OF BACKDOOR INNER PANEL :

1. The Inner Panel Extracted from a styling surface .
2. The panel is altered for the required design with the surface tools of NX CAD
3. The thickness provided for the outer panel is 0.75 mm
4. After creating the tooling direction the design of the inner panel will begin where we will first develop an effective sealing flange by checking all the boundaries and by following the shape of the inner panel design .
5. By creating multiple flanges and by using surface modeling techniques the concept design of the inner panel was created .
6. After the concept of the inner panel is developed , then the child components like a hinge , latch , gas - stay locations , and their reinforcements must be designed . Which completes the overall design of the tailgate .
7. The embosses were created in ' V - Shape or Y - Shape ' so that if the vehicle undergoes the crash then the force dissipates over it which reduces the damage transferred to the trunk space .

MASTIC SEALANT : The mastic sealant is used to fix the inner panel with the outer panel which increases the NVH factor and stiffness of the back door. Mastic Sealant 4 to 5 mm gap for mastic sealant.

HINGE , GAS STAY & WIPER MOTOR EMBOSS :

1. The Orange circle denotes the hinge emboss which was created using the datum plane and emboss feature in NX .It was also designed in a way that the emboss should have a flat surface for assembling the hinges using it .
2. The violet circle denotes the gas stay emboss which was created using the surface of the connecting flange .
3. The yellow circle denotes the Wiper motor emboss which was created using the surface of the connecting flange .
   
   

LATCH AND STRIKER EMBOSS : The Latch and Striker emboss were designed by creating a trajectory that follows the opening and closing of the back door with respect to the hinge axis .

STRIKER POSITION :: Latch & Striker Emboss The position of the hinge should be perpendicular to the latch when the latchi and striker meets .

The circle is drawn from the center of the hinge axis to find the path of the striker and positioned perpendicular to the path .

HEMMING :Hemming and seaming are two similar metalworking processes in which a sheet metal edge is rolled over onto itself . Hemming is the process in which the edge is rolled flush to itself .

1. The outer panel was designed as two separate parts named as outer panel upper and outer panel lower .
2. After designing the outer panel the Hemming was created by offsetting surface with the help of face blend and swept surface .
3. The two separate outer panels will be joined using Blanking. 

Corner Relief CORNER RELIEF : During the hemming process , when giving the Corner Relief helps to control sheet metal material behavior and to prevent unwanted deformation during unbend operations and also helps to reduce the number of passes in hemming .

DESIGNING THE REINFORCEMENTS : The thickness provided for all reinforcements is 1.5 mm

Reinforcement

1. HINGE REINFORCEMENT

2. GAS STAY REINFORCEMENT

3. WIPER MOTOR REINFORCEMENT

4. LATCH REINFORCEMENT 

All the reinforcements were created using the same method , first , the linked . body was created separately for each with the help of extract geometry and then the required portion was trimmed out and then thickened.

Hinge reinforcement: Hinges enable the opening and closing of the back door . One end of the hinge is fixed on the backdoor and the other end on the Roof , on both sides . Hinges can be placed outside or inside the backdoor . The hinge reinforcements are added to compensate for the weak region due to the acting load over it .

Gas Stay Reinforcement : Gas Stay is a device used for supporting the back door in its open position . Gas stay requires no manpower and is engaged into support position automatically as the back door opens . One end of the Gas Stay is fixed on the backdoor and the other end on the Body Side or on the Back door stationary area . Embossing is provided at the Gas Stay mounting area to compensate for weakness and improve strength .

Wiper Motor Reinforcement :

Wiper motor reinforcement is created to mount the wiper motor assembly .

Latch and Striker Reinforcement :

The Latch & Striker forms the locking mechanism of the backdoor with the car . Due to regular opening , closing , and over slamming of the backdoor , there is stress developed in the Latch and Striker area . To compensate for the same , reinforcements are added . this area.

Important features used while designing :

• Wave Geometry Linker - With this you can create , associative or linked copies of any entity of a part into other parts . It may be a surface , edge , curve , body , sketch etc. The changes made to the original entity will be reflected in the copy of that entity .
• Extract Body - It is used to create an associative body by extracting faces , entire body or region of faces .
• Bridge Curve - It helps to create a tangent blend curve between two objects . The objects may be edges or sketch curves .
• Sew - It combines sheet bodies together by sewing their common edges . There shouldn't be any gaps larger than specified tolerance .
• Unsew - This command is used to separate the existing sheet body or solid body into multiple bodies .
• Projected Curve - It is used to project an existing curve / curves on a selected plane or surface by selecting a direction for projection .
• Trim Body - It is used to trim one or more bodies using a face or plane. You can also specify the bodies to retain and the bodies to discard.
• Offset Surface - It allows you to offset one or more existing surfaces.
• Offset Curve in Face - This command will allow you to offset particular edges or curves on selected faces .
• Face Blend - It creates fillets between faces .
• Edge Blend - It creates fillets on edges .
• Trim Sheet - It is used to trim off a portion of a sheet body using curves , faces , edges or planes ..
• Through Curves - It will allow you to create a body Through multiple sections , where it's shape changes to pass through each section .
• Law Extension - This command extends a curve or edge to create a sheet body at desired angle length by changing the rules under angle law and length law .
• Trim and Extend - It helps you to trim and extend intersecting surfaces and make corner at their intersection .
• Extend Sheet - It will allow you to extend an existing surface to required distance .
• Emboss - Emboss command creates an embossing by modifying a body with faces created by projecting a curve / section along a direction . You can modify the emboss using options like endcap location and draft angle .
• Mirror Geometry - As name suggests , it allows you to mirror geometries about selected plane or surface .
• Thicken - It is used to convert a surface to solid body by providing thickness .
• Extrude - It helps you to create a feature from a sketch . You are also able to create thin feature using a sketch or curve under this command .

Draft Analysis for Back door : 

1. The draft analysis will be performed for the tooling direction created at first and checked that the model is suitable for manufacturing .
2. Then to get a complete green portion the necessary changes to the draft angle of the embosses were carried out by optimizing the model .
3. The Draft Analysis command enables us to detect that the part drafted will be easily removed or not .
4. This type of analysis is performed based on color ranges identifying zones on the analyzed element where the deviation from the draft direction at any point , corresponds to specified values .

CONCLUSION: The back door outer and inner panel were designed with the help of the styling surface along the tooling direction.and Draft analysis was performed on the inner panel and All the reinforcements were designed and placed at appropriate positions .