Design of backdoor

Design of Back Door (Or) Tail Gate

What is Back Door?

The Tail gate or the Back door of a car is the Door at the rear end of the car, which provides access to the luggage compartment. In most of the cars, these back doors are operated with the help of gas stay which in turn reduces the effort required to lift open the door. Some luxury cars have powered backdoor which is driven by an electric motor. This kind of system is also called a powered trunk lid system. The Back door is also responsible for dissipating the force created while rear collisions, away from coming inside the car.

Design Consideration of Back door:

• Material Selection
• Manufacturing method (Depends on Material)
• Rear Visibility Area
• Weight of the part
• Hinge and Latch position

Material:

Material selection is the key parameter. All other design consideration is always depends on it.

Most commonly two type of material used in this process

• Steel
• Aluminum

Stainless steel and aluminum are two of the most popular metals used for manufacturing. Widely used for their versatility and corrosion resistance, aluminum and stainless steel are staples in the metals industry.

To know when it is better to use aluminum vs stainless steel, we must compare factors like their compositions, properties and cost.

 

WEIGHT DIFFERENCE 

Even with the possibility of corrosion, steel is harder than aluminum. Most spinnable tempers and alloys of an aluminum dent ding or scratch more easily as compared to steel.

 

Steel is strong and less likely to warp, deform or bend underweight, force or heat. Nevertheless, the strength of steel’s tradeoff is that steel is much heavier/much denser than aluminum.  Steel is typically 2.5 times denser than aluminum.

 

STRENGTH DIFFERENCE 

Aluminum is a very desirable metal because it is more malleable and elastic than steel. Aluminum can go places and create shapes that steel cannot, often forming deeper or more intricate spinnings. Especially for parts with deep and straight walls, aluminum is the material of choice.

Steel is a very tough and resilient metal but cannot generally be pushed to the same extreme dimensional limits as aluminum without cracking or ripping during the spinning process.

 

CORROSION RESISTANCE

While malleability is very important for manufacturing, aluminum’s greatest attribute is that it is corrosion resistant without any further treatment after it is spun. Aluminum doesn’t rust.With aluminum, there is no paint or coating to wear or scratch off.  

Steel or “carbon steel” in the metals world (as opposed to stainless steel) usually need to be painted or treated after spinning to protect it from rust and corrosion, especially if the steel part will be at work in a moist, damp or abrasive environment. 

COST DIFFERENCE

Cost and price are always an essential factor to consider when making any product. The price of steel and aluminum is continually fluctuating based on global supply and demand, fuel costs and the price and availability of iron and bauxite core; however steel is generally cheaper than aluminum.

The cost of raw materials has a direct impact on the price of the finished spinning. There are exceptions, but two identical spinnings (one in aluminum and one in steel) the aluminum part will almost always cost more because of the increase in the raw material price.

 

Composition

Composition of Major Stainless Steel Alloys

Alloy Grades	%C	%Mn	%P	%S	%Si	%Cr	%Ni	%Mo
SS304	0.040	1.580	0.024	0.040	0.400	18.35	8.040	0.070
SS304L	0.010	1.638	0.023	0.002	0.412	18.56	8.138	0.364
SS316	0.080	2.000	0.045	0.030	1.000	16.80	11.20	2.500
SS316L	0.020	1.390	0.024	0.080	0.480	16.80	10.22	2.080

 

 

 

 

 

 

Composition of Major Aluminum Alloys

Alloy	%Cu	%Mg	%Mn	%Si	%Zn
2024	4.4	1.5	0.6	0	0
6061	0	1	0	0.6	0
7005	0	1.4	0	0	4.5
7075	1.6	2.5	0	0	5.6
356.0	0	0.3	0	7	0

 

Manufacturing Process:

Aluminum

Aluminum is one of the most abundant elements on earth, but it’s also one of the most challenging to work with.

How to Manufacture Aluminum Car Parts?

There are many ways to manufacture metal auto parts. Some of them are very expensive, while others are cheaper. Depending on your budget and needs, you may choose one method or another.

CNC machining

CNC Machining is an automated method of manufacturing metal parts using Computer Numerical Control (CNC) technology. CNC machining allows us to create complex shapes and features in our metal parts at very high speeds.

We can also cut materials like aluminum with CNC aluminum machining. CNC machining offers several advantages over manual processes. First, we can achieve higher accuracy and repeatability. Second, we can reduce cycle time and increase productivity.

But it is an expensive way to manufacture alum auto parts. Therefore, you should only choose these for vast quality, reducing your per part cost.

 

Casting:

Aluminum castings are formed by pouring molten metal into molds that have been shaped by a pattern of the desired final product.  It is an efficient process for the production of complex, intricate, detailed parts that exactly match the specifications of the original design. A positive benefit of aluminum cast parts is the layer of aluminum oxide that forms immediately after the part is removed from the mold, which provides a wall of protection against corrosion and rust.

Three common types of molding methods are used to produce casting: die casting, permanent mold casting, and sand casting.

The Aluminum Casting Process

One typical method for casting aluminum is to pour molten aluminum into a steel mold that has been precision processed to ensure that the cast piece will have an exceptionally smooth and refined surface. This particular process is one of several methods used to produce aluminum castings, each of which is used for the creation of specific types of parts.

A variation in the casting processes is the type of mold, which can be permanently made of steel or temporarily made of a non-metallic material. Each of the types of castings has their benefits and is depended on for their reliability and product quality.

In order to discuss the aluminum casting process, it is necessary to examine each of the different distinct methods and how they are used since there isn’t just one process. Though there are manufacturers who specialize in one or several methods, many producers offer customers a choice as to which process they would prefer.

 

Permanent Mold Casting

Much of the expense of aluminum permanent mold casting is the machining and shaping of the mold, which is normally made from gray iron or steel. The mold is shaped into the geometric shape of the designed part with the specifications and shape of the part divided into two halves. In the injection process, the halves of the mold are tightly sealed such that no air or contaminants are present. The mold is heated prior to the pouring of the molten aluminum, which can be ladled, poured, or injected.

At the completion of the process, the mold is allowed to cool to allow the aluminum part to solidify. Once cooled, the part is rapidly removed from the mold to prevent the formation of defects.

Regardless of how simple the process may seem, it is a scientifically and technically engineered method for producing high volume parts.

 

 

Sand Casting

The sand casting process involves packing sand around a reusable pattern that has the shape, details, and configuration of the final product. Included in the pattern are risers that allow the molten metal to be poured into the mold and for hot aluminum to feed the casting during solidification to prevent shrinkage porosity.

Included in the pattern is a sprue that allows molten metal to be inserted into the mold. The dimensions of the pattern are slightly larger than the product to account for shrinkage during the cooling process. The sand has the weight and strength to maintain the shape of the pattern and is resistant to interacting with the molten metal.

 

Die Casting

Die casting is a process where molten aluminum is forced under pressure into the mold. The products produced are exceptionally accurate and require minimal finishing or machining. The process of die casting is rapid, which makes it ideal for mass production of high volume parts.

The two forms of die casting are hot and cold. The difference between them is related to how the molten metal is injected into the mold. In hot die casting, the hot chamber is connected to the melting pot and uses a plunger to force the molten metal through a gooseneck into the mold. In cold die casting, the melting pot is not attached to the die casting system, and the molten melt is ladled into the cold chamber where it is forced by a plunger into the mold.

 

Vacuum Die Casting

Vacuum die casting uses an airtight bell housing that has a sprue opening at the bottom and a vacuum outlet at the top. The process begins by submerging the sprue below the surface of the molten aluminum. A vacuum is created in the receiver creating a pressure differential between the die cavity and the molten aluminum in the crucible.

The pressure differential causes the molten aluminum to flow up the sprue into the die cavity, where the molten aluminum solidifies. The die is removed from the receiver, opened, and the part is ejected.

Controlling the vacuum and the pressure differential between the die cavity and molten aluminum makes it possible to control the fill rate required by part design and gating requirements. Control of the fill rate enhances the ability to determine the soundness of the finished part.

 

Having the sprue submerged below the surface of the molten aluminum ensures that the molten aluminum will be the purest alloy free from oxides and dross. Parts are clean and sound with minimal foreign materials.

 

Investment Casting

Investment casting, also known as lost wax casting, begins with wax being injected into the die to create the pattern of the finished product. The waxed patterns are attached to a sprue to form a tree ike configuration. The tree is dipped into a slurry multiple times, which forms a strong ceramic shell around the wax shape.

 

Once the ceramic has set and hardened, it is heated in an autoclave to complete the dewax burnout. To achieve desirable temperature of the shell, it is preheated before being filled with the molten aluminum, which is poured into the sprue and passes through the series of runners and gates into the molds. When the parts harden, the ceramic is knocked off leaving the tree connected parts to be cut from the tree.

 

Lost Foam Casting

The lost foam casting process is another type of investment casting where wax is replaced with polystyrene foam. The pattern is molded from polystyrene in a cluster assembly like the runner and sprues of investment casting. Polystyrene beads are injected into heated aluminum molds at low pressure with steam added to expand the polystyrene to fill the cavities.

The pattern is placed in densely packed dry sand that is vibration compacted to eliminate voids or air pockets. As the molten aluminum is poured into the sand mold, the foam is burned off, and the casting is formed.

 

Steel:

Deep drawing

It is a manufacturing process that is used extensively in the forming of sheet metal into cup or box like structures. A basic deep drawing operation could be the forming of a flat sheet into a three dimensional cup, or a box. The shape of a deep drawn part is not limited to a circle or square, more complex contours are possible. However, as the complexity goes up, the manufacturing difficulties increase rapidly. It is best to design the shape of a deep drawing to be as simple as possible. For the primary sheet metal deep drawing process the part will have a flat base and straight sides.

 

The Process

Deep drawing of sheet metal is performed with a punch and die. The punch is the desired shape of the base of the part, once drawn. The die cavity matches the punch and is a little wider to allow for its passage, as well as clearance. This setup is similar to sheet metal cutting operations. As in cutting, clearance is the lateral distance between the die edge and the punch edge. The sheet metal work piece, called a blank, is placed over the die opening. A blank holder, that surrounds the punch, applies pressure to the entire surface of the blank, (except the area under the punch), holding the sheet metal work flat against the die. The punch travels towards the blank. After contacting the work, the punch forces the sheet metal into the die cavity, forming its shape.

Equipment for sheet metal deep drawing processes would involve a double action, one for the blank holder and one for the punch. Both mechanical and hydraulic presses are used in manufacturing industry. Typically the hydraulic press can control the blank holder and punch actions separately, but the mechanical press is faster. Punch and die materials, for the deep drawing of sheet metal, are usually tool steels and iron. However, the range of materials for punch and die can span from plastics to carbides. Parts are usually drawn at speeds of 4 to 12 inches per second.

Deep Drawing Practice

Deep drawing is a sheet metal forming process that involves complex material flow and force distributions. As mentioned, the punch and die setup is somewhat similar to a sheet metal cutting operation, such as punching or blanking. Two main factors will cause the punch in deep drawing to draw the metal into the die cavity, rather than shearing it.

One major factor in deep drawing is the die corner radius and the punch corner radius. When cutting sheet metal, the punch and die edges do not have a radius. Sharp corners on the punch and die cause it to cut. A radius on an edge will change the force distribution and cause the metal to flow over the radius and into the die cavity. The other major factor causing the punch to draw the sheet metal and not cut it, is the amount of clearance. Clearance in cutting operations is relatively small, usually 3% to 8% of sheet metal thickness. In deep drawing manufacture, if the clearance is too small the sheet may be cut or pierced, (not well), despite the radius. Clearance in deep drawing manufacture is greater than sheet thickness, usually clearance values are 107% to 115% of sheet thickness.

For many calculations the sheet metal thickness is assumed to remain constant. However, there are changes in thickness in certain areas, due to the forces involved. In order to form the side walls of the part, material must flow from the blank's peripheral over the die corner radius, then straight in the direction of the punch. Material forming the straight wall is under tensile stress that will naturally cause it to thin. Deep drawing process factors are controlled to mitigate thinning, but some thinning of the sheet metal is unavoidable. Maximum thinning will most likely occur on the side wall, near the base of the part. A correctly drawn part may have up to 25% reduction in thickness in some areas.

 

Drawing Ratio

Measurement of the amount of drawing performed on a sheet metal blank can be quantified. This can be done with the drawing ratio. The higher the drawing ratio, the more extreme the amount of deep drawing. Due to the geometry, forces, metal flow and material properties of the work, there is a limit to the amount of deep drawing that can be performed on a sheet metal blank in a single operation. Drawing ratios can help determine the maximum amount of deep drawing possible.

The drawing ratio is roughly calculated as,
DR = D_b / D_p

D_b is the diameter of the blank and D_p is the diameter of the punch. For shapes that are noncircular the maximum diameter is sometimes used or occasionally drawing ratio is calculated using surface areas. The limit to the drawing ratio for an operation is usually 2 or under. Actual limits to the amount of drawing possible are also dependent upon the depth of drawing, punch radius, die radius, anisotropy of the sheet and the blank's material.

Reduction

Another way to express drawing ratio is the reduction (r). Reduction is measured using the same variables as drawing ratio. Reduction can be calculated by r = (D_b - D_p) / (D_b).

D_b and D_p being blank and punch diameters respectively. Reduction should be .5 or under. Often expressed as the percent reduction r = (D_b - D_p) / (D_b) X 100%. In this case the reduction should be 50% or under.

 

 

Redrawing Sheet Metal

If required percent reduction of sheet metal is over 50%, the part must be formed in multiple operations. Redrawing is the subsequent deep drawing of a work that has already undergone a deep drawing process. By using more than one operation, a greater magnitude of deep drawing can be accomplished.

The amount of forming of the sheet metal that can be accomplished on the first redraw is less than on the original draw. For the original drawing of the blank 50% reduction is rarely used during industrial manufacturing practice. The initial reduction is usually 35% to 45%. First redraw is commonly performed at a 20% to 30% reduction. Second redraw can typically range from 13% to 16% reduction. If a severe amount of deep drawing is to be performed and several redrawing operations are necessary, then the part should be annealed every two operations. This will recover the material for further redrawing.

Deep drawing process design must include the drawing of intermediate part shapes, in situations requiring redrawing. For every redraw to be performed there will be one intermediate part.

Intermediate shape design is important and unique tooling and setup will be required for each intermediate step. Each operation will affect the next one and analysis must be done for each step. When designing intermediate shapes, the sheet metal reduction should be considered and in most cases it can be assumed that the surface area of the blank, any intermediate shapes and the part, to be the same.

Reverse redrawing of sheet metal, or reverse drawing, is sometimes used to redraw parts. In reverse redrawing, the intermediate part is flipped over before being placed on the die for the next operation. This will cause the sheet metal to now be drawn in the opposite direction as the first draw.

 Forces in Deep Drawing Sheet Metal

Force used to accomplish a sheet metal deep drawing operation must be adequate enough to provide for the sheet's deformation, enact proper metal flow and overcome friction during the process. Magnitude of force must not be too high or applied incorrectly, or else tearing of the sheet metal may occur. The punch and the blank holder will exert separate forces and force analysis should be done for both.

Understanding the material flow during the manufacturing process is essential to understanding the forces acting on the work. Imagine placing a piece of paper flat on a round cup. This is similar to a piece of sheet metal on a round die cavity. Now, imitating the action of the punch, the paper is forced into the cup to take the cylindrical form of the cup. What happens is the paper folds or wrinkles in the process. This is not how a sheet metal work piece should act during a deep drawing operation. One reason is that metal material can flow, unlike the paper. So instead of the paper, place a piece of aluminum foil on the cup. Aluminum foil is metal but it still wrinkles when forced into the cup. The reason why aluminum foil wrinkles when forced into the cup is because of the inadequate thickness of the foil.

Imagine now, a sheet metal blank being deep drawn into a round cylindrical part. The material under the punch gets forced into the cavity, pulling material with it, to form the walls of the part. Sometimes in deep drawing an amount of sheet metal material is not drawn into the die and forms a flange around the completed part. However, during a deep drawing operation all of the material not yet drawn over the die radius and into the die cavity is often referred to as the flange. During the ongoing process material from the flange is constantly being forced into the die. The diameter of the die cavity is smaller than that of the sheet metal blank and metal is flowing from the outer peripheral inwards.

 

 

It can be illustrated that more material is being forced into smaller spaces, since the same material from the peripheral is moving into a circle of smaller diameter.

Metal flow can be observed in the figure above. As the deep drawing progresses metal from zone A is forced into zone B, metal from zone B is forced into zone C and metal from zone C is forced into the die cavity. This continues until eventually, (providing no flange in the final product), even the material in zone A is forced into the cavity. The constriction of space will cause compressive forces to act within the material. Tensile forces will also be present in the flange because of the drawing of the metal into the die.

Compressive forces on material elements in the flange can be related to the analogy of a metal beam in compression, such as the one illustrated in the following figure.

Now imagine decreasing the width of the beam. If the width becomes low enough, relative to length, the beam will tend to buckle under stress.

This is similar to the situation in the flange during a sheet metal deep drawing operation. As mentioned, the force exerted on the beam is similar to the compressive forces acting on the blank's material. Reducing the width of the beam is equivalent to reducing the thickness of the sheet metal. The buckling of the beam is manifested in the wrinkling of the sheet metal. The thicker beam has a high enough width to allow for proper metal flow. A metal beam of greater width is equivalent to a thicker sheet metal blank. It is now evident that the lower the sheet metal thickness the more likely it is to wrinkle during deep drawing. Wrinkles start in the flange. Once wrinkling starts, it will continue to propagate. Wrinkles that start in the flange are pulled into the die and will end up in the part's walls.

In order to solve the problem of sheet metal wrinkling a blank holder is used. By applying pressure to the surface of the blank, the blank holder can prevent wrinkling for many parts. The blank holder would be the equivalent to force applied over the side of the thinner beam, causing it to compress properly, rather than buckle. However, remember this is only an analogy to help understand the mechanics occurring. The actual situation is different, since forces and material flow are also occurring simultaneously in other directions.

Sheet metal thickness is an important aspect of deep drawing process design. Thickness to diameter ratio is a main factor used to quantify the geometry of a blank and can be calculated by t/D_b. Thickness is represented by t, and D_b is the diameter of the blank. For noncircular sheet metal parts the maximum diameter is sometimes used. Usually it is expressed as a percent t/D_b X 100%. Blank holders are generally effective for thickness ratios of 1% and over. Ratios of .5% to 1% are marginal and for thickness ratios less than .5% even a blank holder may not prevent wrinkling.

Die corner radius and punch corner radius are important in force distribution and material flow during the sheet metal deep drawing process.

Corner radius, for deep drawing manufacturing, should be sufficient to allow for smooth metal flow. If a radius is too small, the sheet metal can tear. Often this occurs as the material is traveling over the corner. Optimization of corner radius should be achieved, because if the radius is too large it may cause wrinkling. While low corner radius can be a source of stress, that can initiate tearing at another location in the part. However, sometimes the location of the occurrence of the tear, in the sheet metal, will be an indication of the cause.

Forces involved in the formation of the part wall are also important.

As the punch progresses, it draws material from the flange into the die cavity, increasing the length of the part wall. Metal forming the part's walls is in tension. Even though material is constantly being drawn from the flange region to supply the growing part walls, the tension forces will tend to create a thinning effect. Thinning will usually be greatest near the part's base. The decrease in thickness, occurring in the walls of a deep drawn part, is mitigated by control of process parameters. A certain level of thinning is usually unavoidable. Often, the manufacturing process of ironing is employed to finish deep drawn parts by evening the wall thickness.

Punch force and blank holder force should be determined when designing a particular sheet metal deep drawing operation. Punch force will vary throughout the operation. Commonly, the punch force will reach its maximum at about 1/3 of the stroke. Both punch force and blank holder force are dependent on punch and die geometry, punch and die radius, blank geometry, blank thickness, blank material and friction. Although it will differ, a common value for the blank holder force is about 30% to 40% of the maximum punch force. References are available to calculate these forces, based on these variables.

Blank Optimization For Deep Drawing

Sheet metal blank material, thickness and shape are major elements in deciding the nature of the metal flow and forces. All the factors involved in a deep drawing manufacturing process will have an effect on the quality of the part. Sheet metal parts can be tested for formability. Blanks are often printed with a square grid with circles in each grid box. The squares and circles distort with the sheet metal as the process occurs. After drawing, the blanks can be studied to determine blank distortion, thinning and the general direction of metal flow as a result of the deep drawing process. By examining different proportions of bi-axial straining and areas of tearing, an understanding of the blank's behavior can be created. Forming limit diagrams are often constructed to quantify the results of these experiments.

One major goal is to optimize the shape of the sheet metal blank for a certain deep drawing process. Excess material in the work can interfere with metal flow and increase forces acting within the blank while drawing. In order to optimize the shape of the sheet metal blank, the flow of material during an operation must first be known. A common deep drawing is a square box. When a square box is drawn from a square blank it is obvious that the metal does not flow evenly into the die from all directions.

Metal flows faster and easier into the die cavity from the sides of the blank than from the corners. More complex metal flow at the corners causes more impedance to material movement. Less metal is drawn from these sections as a result. Removal of material, from areas such as this, will improve metal flow and reduce forces. The optimal blank shape will vary for different parts and contours. Computer programs have been developed to predict such shapes, given the parameters.

However, it should be remembered that actual trial and error testing is a vital part of deep drawing process design and sheet metal manufacturing.

Defects In Deep Drawing Manufacturing

Defects that occur during deep drawing of sheet metal can be controlled by careful regulation of process factors. Tearing is one of the most common defects. Excessive thinning in areas of the sheet metal is also an unwanted defect. Causes of these are mostly too high or improper force distribution and material considerations. Many times the reduction ratio needs to be evaluated. Ratios for initial reduction are usually 35% to 45%, but can be lower. Redraws are always less. Reduction ratios may need to be lower, or annealing of the metal may be necessary to allow for sufficient redrawing. Usually maximum thinning of the cup wall occurs near the base. For this reason, tearing of the sheet metal is most likely to occur in this region even if the stress is originating somewhere else.

Another reason for the tearing of the sheet metal may be excessive force caused by material impediments, due to an inefficient blank shape. When tearing occurs at the corners of the wall it may indicate a problem with the blank's geometry. Surface of the blank is important also, gouges, scratches and pits can all cause propagation of cracks. Blank holder force must be sufficient. However, friction between blank holder, blank and die surfaces will act to resist the movement of the blank's material into the die. Thus, excess friction will increase the force the punch exerts to draw the sheet metal. Higher punch forces usually cause a tear in the weakest spot, predominately in the cup wall near the base. For this reason, the blank holder force must not be too high.

Die and blank holder surfaces for deep drawing sheet metal must be as smooth as possible; they should be ground and lapped to mitigate friction. Any type of friction will increase force, hence stresses in the material. Friction between the punch and work surfaces, as well as friction over corners, can be a source of failure. Lubrication is important in deep drawing of sheet metal. Lubrication will allow for easier metal flow and more uniformly distributed metal strains, due to decreasing friction. Lubrication also helps to reduce wear on tooling and machinery. Lubricants are applied to both sides of the sheet metal blank. Common lubricants used in deep drawing include oil, soap, emulsions, wax and sometimes solid lubricants.

Wrinkling is another common defect and was discussed in detail earlier. Wrinkling may often occur if the blank holder force is too low. Therefore optimization of blank holder force is necessary, since too high a force will cause excess friction. Sheet metal thickness is an essential parameter. As stated earlier, with a thickness ratio of .5% or under even a blank holder may not stop wrinkling. If corner radius is not high enough tearing may occur, but if the corner radius is excessive this may also cause wrinkling. Corner radius, like holding force, must obtain an optimum value.

Earing is a problem characteristic to deep drawing. Earing is the formation of wavy edges at the open end of the drawn cup. These are usually trimmed. The anisotropy of a particular sheet metal blank is the predominant source of earing.

Surface scratches or irregularities may appear on drawn parts. Make sure punch and die surfaces are smooth. Other causes of surface scratching could be improper clearance, or inadequate lubrication.

Draw beads

Draw beads are sometimes used to help regulate metal movement during deep drawing manufacture. Draw beads bend and unbend metal as it travels into the die cavity, thus altering its flow. Draw beads can reduce the necessary blank holder force.

 

Drawing Without A Blank holder

In some situations sheet metal deep drawing can be performed without a blank holder. This makes the manufacturing process simpler and tooling cost lower, in cases that it can be applied to. The process requires sheet metal with a high thickness ratio, to avoid wrinkling. For deep drawing without a blank holder thickness ratio should be at least 3%. A sheet metal blank is placed on a die and pushed through by a punch, similar to the standard deep drawing process. The die, when drawing without a blank holder, will have a special curve to facilitate the forming of the part in this manner.

Irregular Deep Drawings

Common non standard deep drawing part geometries include stepped, tapered and domed cups. Stepped parts can be created by partial redrawing. Domed cups are formed with a stretch forming type process. Tapered cups can be manufactured by first producing stepped cups, and then the sides are formed to create the tapered shape.

Embossing

Embossing is a sheet metal forming operation related to deep drawing. Embossing is typically used to indent the metal with a design or writing. This manufacturing process has been compared to coining. Unlike coining, embossing uses matching male and female die and the impression will affect both sides of the sheet metal.

Designing A Deep Drawing Operation

Designing a deep drawing manufacturing process will require planning, calculations and probably some in house testing. Calculate the surface area of the finished part and allow for a trimming allowance. Set the surface area of the part equal to the surface area of the sheet metal blank, then solve for D_b. Extra material can be added to the blank, (ie. +10% D_b), this will create a flange that can be trimmed off latter. This can help calculate a standard optimum blank shape for the operation.

Measure the thickness ratio = t/D_b X 100%. Thickness ratio should be over 1% or wrinkling may be a problem. Calculate percent reduction. r = (D_b - D_p) / (D_b) X 100%. If the percent reduction is over 50% plan for redrawing operations. Redrawing will require the design of intermediate shapes. When designing intermediate shapes, consider the reduction, and then set the surface areas of the blank, intermediate parts and final drawing to be equal.

Required punch and blank holder force can be calculated based on blank shape, blank thickness, punch and die shape, punch and die corner radius, sheet metal material and friction. Deep drawing process iteration through trial and error can optimize the manufacturing operation over time. Process factors such as amount of reduction, blank shape, corner radius, or blank holder force may have to be adjusted based on the results of previous processes.

 

Back door test case:

Some tests are performed on the Back door, to check the strength, quality and durability.

Design Steps:

In this case we have to consider the material used for back door is “Stainless Steel”, so according to the manufacturing procedure we will follow our design work.

 

 

Basic Data:

Part	Thickness (in mm)
Inner & Outer Panel	0.75
Reinforcement	1.5

 

Outer Panel:

It is the outer part of the rear door and is mostly responsible for aesthetics of the vehicle. We have two part (i.e) outer upper panel and outer lower panel. Outer panel is manufacture by stamping the sheet metal. Thickness for outer panel is 0.75 mm

Inner Panel:

It is the inner part of the door. All the reinforcements and components are mounted on it. It is manufactured either by casting (aluminum) or sheet metal stamping (steel). Thickness of inner panel is 0.75 mm.

Reinforcements:

• Hinge Reinforcement
• Gas Stay Reinforcement
• Latch Reinforcement
• Wiper motor Reinforcement

Reinforcements are provided to provide support and add extra material to the sheet metal part to increase its strength near component installation regions and minimize the impact of collision. Thickness of all reinforcements is 1.5 mm.

Draft Analysis:

Draft analysis tool is used to determine, whether the outcome of the design project will be producible or not.

In this case we draft analysis the Rear door inner panel along with the tooling direction at an angle of 7 deg.

Majority of the area have positive draft at the same time we could find some embosses with negative draft. But in this case it’s negligible as all the embosses can’t be deep drawn in a single stretch.

Conclusion:

• Car back door was designed using the given styling surface.
• Necessary Reinforcements are provided.
• Draft analysis performed