Challenge

Design of backdoor

PPrasad Parkhe16 Sept 2023

SHEET METAL DESIGN

While designing components top priority is for function and second is for cost effective manufacturing process selection.

This can be achieved in design by:

Keeping part simple
Lesser material yield
Consideration of minimum manufacturing stages

OBJECTIVES OF SHEET METAL DESIGN:

Function: Most low stress (and many high stress) components requiring moderate stiffness can be created from sheetmetal. Sheetmetal is particularly effective for parts that function as containers, chutes and gates, but can effectively be used for mounting brackets as well.
Attachment method: Sheetmetal parts are typically joined by welding, riveting or via fasteners.

DESIGN TIPS

Study Manufacturing process available.

Shape: Use simple shapes such as straight cuts, bends, and punched holes. Whenever possible, avoid internal cuts, curved cuts, and close-fit holes.

Simple: Complex sheetmetal parts are difficult to manufacture using tooling available. Typically, complex sheetmetal parts can be broken down into multiple simple parts.

Material specification: Choose a optimum material and thickness.

Tolerances: In modern industry parts are made using high precision CNC lasers and bending equipment. However, sheetmetal features are generally cut by aligning the layout lines by eye, so design sheetmetal parts to have large feature tolerances.

Order of operations: The order of forming operations is important for sheetmetal parts. Holes and cuts must be created prior to bending. The bending sequence can typically be performed in only one or two ways. Be familiar with the available tooling and processes and do not design parts that cannot be fabricated using the available tooling in lab.

BACKDOOR

A car backdoor consist of inner pannel, 2-3 outer pannel & reinforcements. Car backdoor is mainly made of steel or aluminium based on the budget of a car. The inner pannel consist of hinge reinforcement, gasstay reinforcement, latch and striker reinforcement & wiper motor housing.

CHARACTERISTICS

The distinguishing feature of a hatchback is a rear door that opens upwards and is hinged at roof level (as opposed to the boot/trunk lid of a sedan, which is hinged below the rear window). Most hatchbacks use a two box body style,where the cargo area and passenger areas are a single volume. The rear seats can often be folded down to increase the available cargo area.Hatchbacks may have a removable rigid parcel shelf or flexible roll-up cover to cover the cargo space behind the rear seats.

Why Inner Panel

Inner door panel is a component which is use for strengthening the door assembly and it is one of the most important components on witch all accessories are mount like hinges, glass guide channel. Back door inner panel is mounted with the the Roof. The weight of Door inner panel is near about 7to8kg depends upon its material and its thickness. The possible method is the integration method. In the integration method, the part is stamped out of a single blank. This reduces the number of tools needed; the assembly cost, and eliminates any fit ability problem. However, the design engineer is forced to work with same grade, thickness, and corrosion resistance throughout the entire part. Since the most demanding of all these conditions must be satisfied for the entire blank, this would increase the cost and weight of the part.

MATERIAL USED

Material used for exsisting inner door panel 0 . 7mm thick, EDD 513,1.6mm thick, St40e

Design Of Door Inner Panel For Reducing Cost And Weight Of Back Door Assembly

In this paper we are going to reduce weight of a back door assembly by using tailor welded blank concept for front door inner panel and using less thickness high strength material and reducing cost by replacing molded trim with hard pad in back door assembly.

a) Methods of preparing inner do or panel

(1) In current automotive stamping technology , there are two basic paths that can be followed to arrive at the final inner door panel. The first method is part disintegration or part separation. In this technique, each different section of the blank is stamped separately and then spot welded together in the shape of the final part. This method has numerous advantages such as the ability to select the specific properties, i.e. the strength, thickness, corrosion resistance, etc. of each area of the blank. This method also gives a higher yield ratio of material used.

(2) The other possible method is the integration method. In the integration method, the part is stamped out of a single blank. This reduces the number of tools needed; the assembly cost, and eliminates any fit ability problem. However, the design engineer is forced to work with same grade, thickness, and corrosion resistance throughout the entire part. Since the most demanding of all these conditions must be satisfied for the entire blank, this would increase the cost and weight of the part significantly.

(3)A solution to the problems listed above is the utilization of tailor-welded blanks. A tailor-welded blank is a blank that is comprised of two separate pieces of sheet metal that has been welded together previous to stamping. Tailor welded blanks allow the welding of the different grades, different thickness or different corrosion coatings together in order give the properties needed in different areas, without increasing the number of tools needed to form the part and eliminating the fit ability concerns. They also allow a high degree of flexibility in designing parts and large blanks can be formed from much smaller sheets .The use of tailor-welded blanks would reduce the weight of the car. Having the ability to selectively place different thickness of material would result in weight reductions. An example of this used in production is the door inner panel. The only strength requirement on a door inner is in the region where the hinges attach to the panel.

b) Design guidelines for designing door inner panel

Beads and ribs increases the cross sectionalarea of component and load taking capacity increases.By adding beads we are able to reduce spring back effect of component.

c) Material used for new door inner panel

0.7mm thick, EDD 513, 1.2mm thick, DP590

d) Design of new door inner panel for solving water leakage issue

Tailor Welded Blanks are made from individual steel sheets of different thickness, strength and coating which are joined together by laser welding. When we design inner door panel with tailor welded blank in witch some portion of a panel having different thickness and other is different. In our case some portion of door inner panel is 0.7mm thick shown below with pink color and another is 1.2mm thick shown below with sky color. There is a 0.5mm gap between these two thicknesses and this is the reason that water is leakage between door inner panel and secondary sill in shower test.

Forming Analysis

The technique of sheet metal forming analysis requires non-contact optical 3D deformation measuring system. The system analyzes, calculates and documents deformations of sheet metal parts, for example. It provides the 3D coordinates of the component's surface as well as the distribution of major and minor strain on the surface and the material thickness reduction. In the Forming Limit Diagram, the measured deformations are compared to the material characteristics. The system supports optimization processes in sheet metal forming by means of; Fast detection of critical deformation areas, Solving complex forming problems. The optical forming analysis with forming analysis system provides for precise and fast measurement of small and large components using a high scanning density. Forming analysis system operates independently of the material. It can analyze components made from flat blanks, tubes or other components manufactured by an internal high pressure forming process (Hydro forming). The Forming limit curve is used in sheet metal forming for predicting forming behavior of sheet metal. The diagram attempts to provide a graphical description of material failure tests, In order to determine whether a given region has failed, a mechanical test is performed. The mechanical test is performed by placing a circular mark on the work piece prior to deformation, and then measuring the post-deformation ellipse that is generated from the action on this circle.

Designing of Back Door using NX CAD

Why Hatchback required ?

1. Compact design:

Hatchback cars offer space and convenience over the luxurious sedan cars. They offer the convenience of driving in narrow spaces where a usual sedan or SUV may not fit. For example, driving a hatchback on a traffic-laden road is easier as compared to driving larger models of other types of cars.

2. Basic controls:

It is easier to learn driving on a hatchback car as compared to a sedan or SUV. Sedans may have complex mechanisms like additional gears or complicated control panels. This is not the case with a hatchback. These cars consist of some of the most basic models. Thus they are considered to be the best for new drivers. If you have a learning driver in your family, you can consider buying a hatchback rather than choosing other types of cars.

3. Low maintenance cost:

India serves as a huge market for hatchback cars. Models like Maruti Wagon R are manufactured in the country. This is one of the main factors that contributed to the maintenance cost being lower as compared to other types of cars. The availability of spare parts is high when it comes to Indian automobile manufacturers. This not only speeds up the repair/replacement process but also lowers the final cost.

4. Enhanced boot space:

As mentioned earlier, a hatchback car is capable of carrying a decent amount of goods/load plus passengers. To serve this purpose, you will receive a large boot space in your hatchback car. This makes it an ideal fit for families with fewer members, singles, and people who travel alone and carry load.

Nowadays, people prefer to change the fuel type of their car to CNG due to its affordability. The CNG kit mainly consists of a large cylinder filled with CNG fuel and control options. Enhanced boot space of hatchback cars serves as a perfect fit for installing the CNG kit, making this category of cars even more popular.

5. Affordability:

In India, buying a hatchback is cheaper than buying a sedan or SUV. We have numerous options like Maruti Alto, Maruti Wagon R, Tata Tiago, Hyundai Santro, and many more that cost less than 5 lakh rupees. As mentioned earlier, their maintenance cost is also low.

Thus, a hatchback is a complete package consisting of useful features and low cost. Those who wish to avail more features can always opt for premium hatchback models. The above factors make hatchback cars a popular choice in the Indian market.

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 )

INNER PANEL

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

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

Above picture shows that the inner panel for 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

Emboss

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 inclinte in angle and it should not be in 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.

Creating emboss in the outer panel direction because when collision happens from backside of the car this impact intially falls on the embossed faces then force disssipates according to the design of emboss then the remaining force hits the inner panel.For this case i designed my emboss towards outer panel direction.

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 products ability to disperse liquid more effectively, reduction 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

I left some gap for Headlamp Harness and tailgate light harness cables.

Left some gap also dissipates the force when collision happens.

To much of cutting the inner panel leads to weaken 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 two mounting Flanges for mounting the inner panel with outer stylish panel.

Two flanges is wnough strength for holding the outer and inner panels with the help of sealants.

In between inner panel and outer panel we providing sealants.

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 has 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 the aesthetic looks. Thus we cannot use bolts or welding. This has to be done with the help of the 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 panel. 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 that it has a very smooth exterior while keeping its rigid form underneath.

Surfaces do not have to be primed when using this type of sealant, and although applied thick, 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 on 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 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 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.

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,Four 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

Below picture represents that the hinge reinforcement of Back Door,I designed both LH and RH separatly.

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

Gas Stay Reinforcement

Below picture represents that the Gas stay reinforcement of Back Door,I designed both LH and RH separatly.

Why we need Reinforcement ?

We need reforcement for gas stay also,while opening and closing the backdoor gas stay plays a major role here,We using gas stay for backdoors is for smooth opening of back door .

Gas stay Reinforcement thickness be 1.2mm to 1.5mm.

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.

Above picture represents the orginal wiper motor for rear window

Here is the wiper motor places and mounted.

Orange colored part is the reinforcement for wiper motor,I given 1.5mm thickness to the wiper motor reinforcement.

HEMMING PROCESS

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. Conventional die hemming.

Hemming is the process in which the edge is rolled flush to itself, while a seam joins the edges of two materials. Normally hemming operations are used to connect parts together, to improve the appearance of a part and to reinforce part edges. In hood design, 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. Dimensions of hemming are given below.

In between the outer panel and inner panel there will be glueing after or before hemming process because to reduce NVH and also sticking the two panels.

Types of Hemming

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.

While manufacturing the hood we choose Roll hemming only.

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.

Above picture represents there is relief at the corners.

Above picture represents there is sharp corners,I avoided sharp corners by filleting.

POSITION OF LATCH

Position of latch and striker is perpendicular to the hinge then only the latch and striker mechanism works properly when the door closing 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, hinge is assembled at its position. Once it is placed, hinge axis is drawn.

To check the hinge axis as the center we draw a big circle to the 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 two hinges,Why because while closing and opening of latch and striker the opening position be similar actions.

Below some pictures of perpedicularity of latch.

DESIGNED BACK DOOR PHOTOS

Outer Panel

Inner panel

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.