Design of backdoor

Aim:

      To model a Backdoor of a car using NX CAD based on Engineering inputs, Design considerations that satisfy manufacturing requirements and functional requirements.

Introduction:

       A backdoor, also known as a 'tailgate', is a car's rearmost part. It is one of the BIW closure components. A door can be moved up or down while loading and unloading (Swinging commodity).

      A car’s tailgate panel consists of an inner and outer glass fibre composite panel bonded together, along with a toughened and heated window glass attached to the outer surface. A striker pin in each rear corner of the car’s tailgate engages with a spring-loaded latch plate on the body, with a single release cable operating both latches and terminating the release handle on the driver's side of the cabin's rear bulkhead.

       In this project, we will be designing the inner panel concerning the given A-surface by creating reinforcements for the latch & striker, Gas stays LH & RH, Hinge and finally hemming it with the Backdoor outer panel.

Gas Stay Powered Tailgate :

Electric Operated Tailgate :

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 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:

Hemming is a forming operation in which the edges of the sheet are folded or folded over another part to achieve a tight fit. Normally hemming operations are used to connect parts together, improve the appearance of a part and 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:

1. Conventional die hemming: In conventional die hemming, the flange is folded over the entire length with a hemming tool.
2. 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.

Teardrop Hem: In teardrop hem the bend angle is greater than 180 degrees.

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

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 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.

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 aluminium 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.

The outer panel upper and outer panel lower are joined through spot welding .So there must be no gap between the outer panel upper and outer panel lower.

Design of Back door in NX CAD: 

The door parts thickness is given below,

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

Parts Of the BackDoor

Inner Panel

Hinge Mounting Bracket ( LH & RH )

Gas Stay Bracket ( LH & RH )

Wiper Motor Support Bracket

Latch

Latch Reinforcement

Hinge reinforcement ( LH & RH )

Gas Stay Reinforcement ( LH & RH )

Given Data,

(Styling data)

Given surfaces have to be repaired according to the smoothness. After repairing the surfaces, the door is divided into two parts Door Outer Upper and Doo Lower Panel.

First, we need to create the Tooling direction for the Deep drawing operation. It shows that all the operations like embossing are done by considering this vector direction and it will help in manufacturing the part,

After that, we have to create Sealing Flange by offsetting the outer panel to a specific distance.

Then we will be creating the Back door inner panel flange by offsetting the outer surface at a distance considering the sheet thickness and thickening direction.

Then created the connecting flange to join the inner panel and sealing flange.

Then for the windshield panel mounting, the windshield panel is created and joined with the sealing flange.

Then to improve the strength of the inner panel and to reduce the weight 'Y' type emboss and other cut-outs are created. Also, for Latch and Stricker mounting cut-out is created. This cut-out is also done on another side of the inner panel to maintain the centre of gravity of the Back door.

Parts Of the BackDoor 

• Inner Panel
• Hinge Mounting Reinforcement(LH & RH).
• Gas Stay Reinforcement (LH & RH).
• Wiper Motor Reinforcement.
• Latch Reinforcement.
• Outer panel upper.
• Outer panel Lower.

INNER PANEL

The inner door panel is a component which is used for strengthening the door assembly and it is one of the most important components on which all accessories are mounts like hinges, glass guide channel and gas stay. The back door inner panel is mounted with the the Roof. The inner is mounted with the outer panel with the help of the hemming process.

• Materials used for the Inner panels are steel, Aluminum.
• For giving more strength to the inner panels by Adding extra reinforcements to strengthen the parts.

The above picture shows that the inner panel of the Back door of a car.

In the Inner panel i used embosses,Outer panel and inner panel mounting area, space for Harness, Wind Glass Mount and fillets, No sharp corners.

Embossing

Embossing is a metal forming process for producing raised or sunken designs or relief in sheet material 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.
• Emboss should be in 7 degree to 25-degree incline in angle and it should not be a 90-degree angle, why because when we do stamping in manufacturing the stamping tool fits the sheet metal hence it will not come out of that sheet metal,So this is the main reason why the emboss face is in angle.

Characteristics of the metal embossing process include:

• Its ability to form ductile metals,
• Its use in medium to high production runs,
• The ability to maintain the same metal thickness before and after embossing,
• The ability to produce unlimited patterns, depending on the roll dies, and
• The ability to reproduce product with no variation.

• Located within the embossing stand itself are two engraved and mated hardened steel rolls, geared together to maintain top-to-bottom pattern registration. The width and diameter of these rolls depends on the strip width, material thickness, pattern depth, and material tensile strength and hardness.
• In most machines, the upper roll blocks are stationary, while the bottom roll blocks are movable. The pressure with which the bottom roll is raised is referred to as the tonnage capacity. This figure also depends on the aforementioned parameters.
• Embossing machines are generally sized to give 2" of strip clearance on each side of an engraved embossing roll. Many embossing machines are custom-manufactured, so there are no industry standard widths. It is not uncommon to find embossing machines in operation producing patterns less than 6' wide all the way up to machines producing patterns 70"+ wide.
• The illustration that follows provides a two-dimensional look at a typical embossing line setup with an embossing roller in the middle. The illustration shows the metal sheet entering the roller, and then the embossed sheet leaving toward the drawing rollers. 
• Embossed metals are used in industry for two reasons: aesthetic and functional. Aesthetic applications also include appliance panels, building products, elevator panels, garage door panels, automotive trim, metal office furniture, and others.
• Functional applications are those in which a performance characteristic is enhanced. This can include a metal product's ability to disperse liquid more effectively, reduce friction and static, increase a metal panel’s stiffness and rigidity, increase a metal surface area for acoustic or heat transfer applications, and improve traction.
• The embossing process can produce a variety of patterns. Some of the most common patterns include stucco, leather grain, wood grain, weather grain, and rough-sawn cedar. Most embossers will tool to form any needed pattern, depending on the cost parameters involved.

Materials commonly used in the metal embossing process include:

• Aluminum (All Alloys)
• Aluminum (T1/T2)
• Brass
• Cold rolled steel
• Copper
• Galvanized steel
• High strength, low alloy, steel
• Hot rolled steel
• Steel (All Alloys)
• Zinc

Cable Harness Gaps

Small round and rectangular Holes for Harness cables.

To much of cutting the inner panel leads to weakening the panel.

I & O Panal Mounting Flange ( Inner and outer )

Highlighted red spot is the mounting portion of inner panel to the outer stylish part.

I provided one mounting Flange for mounting the inner panel with the outer panel by mastic.

In between inner panel and outer panel we provide sealant.

MASTIC SEALANTS

A mastic sealant is a type of liquid sealant that cures in an elastic state, thus making it flexible while holding the bond of the surfaces that have attached together. It adheres to just about any material making an all-purpose type of sealant. 

• The main purpose of the outer panel is for aesthetic looks. Thus we cannot use bolts or welding. This has to be done with the help of hemming and mastic sealants. Mastic sealants are elastic compound that behaves like the rubber. It is placed between the outer and inner panel. Initially is it in paste form, but after the hot furnace bath, it gets hardened thus joining the outer and inner panels. Mastic sealant has the tendency to increase the strength of the panel and has influence of 80mm diameter.

PROS

• One positive characteristic of mastic sealant is its smooth exterior while keeping its rigid form underneath.
• Surfaces do not have to be primed when using this type of sealant, and although applied thickly, it adheres smoothly to any surface. It is important that the area to be joined or sealed be clean and dry, just like any other sealant on the market.
• Mastic sealant may be used outdoors as well because of its waterproof quality. It can be applied to rain duct leaks outdoors, for example.
• It is also favored for areas under high or low temperatures such as heater vents or drier vents and contains ultraviolet inhibitors to make sure that it is protected from the damaging effects of the sun that will often weaken other types of sealants. That makes it a good choice for use on roofs, or any surface that is constantly exposed to sunlight. Most mastic sealants will also work well with metal because they do not corrode over time.
• it functions well in areas with mild vibration and heat, like heating ducts.

CONS

• Mastic sealant is not recommended for areas that have too much joint movement, or anything that will be moved a long length.
• It works well with constant pressure on it, but not the constant movement.
• It also works best when applied thickly and is not recommended if only a thin layer is needed such as touch-ups. Another sealant is a better choice for those types of repairs.

Sealant Space in between Inner and Outer Panel

As you see in the above picture represents the how the mounting takes place in between inner and outer panel.

Transparent panel is outer panel and charcoal color represents inner panel of the back door.

Mounting the inner panel and outer panel with the help of sealants.

I given gap between inner and outer panel about 4-5mm for sealants.Sealants can hold the outer and inner panel and also it reduces the NVH of the vehicle.

DRAFT ANALYSIS:

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

WIPER MOTOR MOUNTING

Below picture represents wiper motor mounting area,Highlighted red spot area is for wiper motor mouniting area.

Below Picture represents the wiper motor mounting area, Two holes for Mounting the wiper motor.

 

REINFORCEMENT 

Vehicle Door reinforcement structures as provided to reduce impact in collisions. In one embodiment, the structure is to include a lower reinforcement panel configured to mount to a vehicle chassis and an upper reinforcement panel welded to the lower reinforcement panel wherein the deflection of a front deformable wall of the upper reinforcement panel is configured to trigger deflection of rear deformable wall of the lower reinforcement panel.

 Latch and Stiker Reinforcement:

To reduce the impact to the occupants inside the car, additional latch and hinge reinforcement to the hood. When latch and striker are placed, there is drop in strength at that position thus reinforcement is required. Also stiffness pads are placed to reduce NVH. Hinge and latch reinforcement thickness is kept at 1.5 mm but it may vary.

Where there is movements like hinge,hood opening and closing,Doors etc,In this cases there is less strength in that particular opening and closing areas in that we need to add Reinforcement to giving the additional strength to that areas.

Hinge Reinforcement

What is HINGE ?

Hinges are simple mechanical bearing devices that are used to connect two parts and allow them to rotate relative to each other about a fixed axis. Depending on the type employed, the components can move (most commonly) within a limited arc or with 360° freedom.

Material Used for HINGE

Due to the applications in which they are applied, hinges need to be able to withstand the stress of consistent opening and closing. To fulfill this requirement, many hinges are made of stainless steel as the strength of steel materials allows the hardware to bear heavy components, and the stainless characteristics prevent rust and corrosion. The latter is important because hinges used in external applications, especially near the ocean or salt lakes, can experience fatigue and failure much quicker due to exposure to moisture and salt in the environment.

Why we need Reinforcement ?

Hinge rotates in the rotational axis in that it will loose some strength there,It means huge Back door opens with the help of small hinges only in this case hinge needs extra strength,For this we providing extra strength in the form of Reinforcement

Hinge Reinforcement thickness be 1.2mm to 1.5mm.

Gas Stay Reinforcement

What is Gas Stay or Gas Spring ?

Gas springs, or gas struts, are rods that provide support for doors, hatches, lids and covers that are horizontally hinged. They act as support in a variety of ways including, lifting, positioning and lowering; because of this versatility they are used in a wide range of applications.

Wiper Motor Reinforcement

What is Wiper Motor ?

Windshield wipers are powered by a small electric motor, usually mounted on the firewall or under the cowl (the area under the windshield's base). The motor activates linkage that moves the wiper arms back and forth. On vehicles with a rear window wiper, a separate motor powers the one in the rear.

RELIEF DATA:

Relief is provided onto the part or component in order to remove any stresses developed in a particular area i.e sharp corners that takes place during the hemming process is carried out. Thus corners are rounded or chamfered.

We leaving 2 mm from sheet metal for Roll hemming process. I have made a cutout in Outer panel lower & upper Joining area.

POSITION OF LATCH:

Position of latch and striker is perpendicular to the hinge then only the latch and striker mechanism work properly when the door closes and opening position.

For the proper opening and closing of the Door, the striker should be perpendicular to the trajectory of the Door. For this, the hinge is assembled at its position. Once it is placed, the hinge axis is drawn.

• To check the hinge axis as the center we draw a big circle to position the latch in such a way that it is perpendicular to the hood trajectory.
• In between the two hinges the striker is perpendicular to the midpoint of the two hinges, Why because while closing and opening of the latch and striker the opening position is similar actions.

CONCLUSION:

Thus,For the provided styling surface of a back door design, I used appropriate design methodologies and provided the necessary reinforcements and embosses for the BackDoor design.thus i designed a back door.