Modern Methods Used In Sheet Metal Forming Mechanics Essay
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Published: Mon, 5 Dec 2016
This report elaborates the recent advancements in the process of Sheet-Metal forming in automotive industry since this technique is considered as one of the most important issues in the current industry. Further more in this report brief description is explained on the most modern forming methods like Electro-magnetic forming, Super Plastic forming and Fine Blanking. Based on the understanding and analysis of each forming processes, the best one is suggested.
In the world of automotive industry a lot of metals have to be used to make the parts of an automobile. The metals found are of very rigid shapes and sizes and it cannot be directly used, to make the required sizes and shapes in the automotive industry the main metal working process used is the sheet-metal forming process. The sheet metal forming process is a process in which solid metals can be made into thin or flat pieces, and sheet-metal forming is one of the very fundamental methods in manufacturing. It can be defined as, a manufacturing process which fabricates by shaping or moulding a piece of metal into a sheet.Sheet-metal forming has a number of processes in the present world but a lot of modern processes are being preferred to the classical processes. Usually, fabrication of complicated sheet metal components requires a complex combination of various shaping processes and the final assembly involves welding, riveting and other binding methods. Henceforth a very much affordable solution for sheet metal forming is by applying efficient and modern processes like Electro-Magnetic forming, Super-plastic Forming, Fine blanking, Explosive forming, Hydro-forming, Electro-Hydraulic forming, etc.In this report the most modern processes of sheet metal forming are discussed and
III. Main Body:
1. Electro-magnetic Forming:
Electromagnetic Forming is one of the advanced methods of sheet-metal processes. It is basically called as EMF in short form. Electromagnetic forming has been in use for nearly three decades. The principle of this process is that it makes use of the electromagnetic forces to make a sheet or a part by using high speed velocity forming techniques. Electromagnetic forming works in a way, in which, a current is produced from a capacitor and it is made to pass through a coil to form a strong magnetic field around the coil. The coil is situated in the work piece, thus forming an induced eddy current around the coil the eddy current generates another magnetic field in the metal work piece (El-Azab et al. (2003)). The two magnetic fields have repulsive force with each other and cause a deformation to the work piece. This deformation is permanent due to the stress created on the work piece by the force and this is called as Electromagnetic Forming. So EMF makes the material to stretch at very high speeds.
1.1 Advantages of EMF:
EMF has many advantages, they are listed below,
- It has very high property of repeatability because of the energy output which can be adjusted as many number of times.
- There is no such contact between any tools to the work piece due to the magnetic fields.
- EMF does not need any lubricant because there is no tool acting on the whole process and hence leaving no marks created by the tool on the work piece.
- EMF is basically called as a non-contact process thus it does not have any damage on the work piece.
- Due to no physical contact extra bits and pieces will not fall out and will thus have less cleaning to do with the sheet.
- By doing this process the work piece will get a good coating.
- There is very less time consumption in this process.
- There will be no friction or physical stress on the work piece as no mechanical forming methods is used.
- This process can only make thin sheets because only a less amount of pressure is applied by the coils.
- The work piece material will have a very short time to stretch as the whole EMF is process occurs in a very short time.
1.3 In Automotive Industry:
Aluminium is the main material used to make parts for the automotive industry. There is a great demand for fuel-efficiency in present world and the weight of the automobile is another basic factor. The only possible ways of weight-reduction is by making a controlled design or by using lightweight materials. Aluminium is the best considered material as it satisfies the regarding properties, by using aluminium die-cast materials can be used to make highly complex materials form a single piece, thus it helps in attaching fewer parts more rigidly and hence a rigid body can be created by using Aluminium die-cast materials (Davies et al. (2004)). When taking aluminium in to consideration with its characteristics, increase in rigidity and passenger protection can be achieved without considering the lightness.
1.4 Uses of EMF in Automotive Industry:
- It is a non-contact process and no touching of the part is needed because the only effect affecting the part is the magnetic field and thus the automotive parts are made damage free.
- The ductility is very high.
- Anyone operating the machinery does not need any special training due to the process being noncontact.
- If there is a comparison between this method and another method, the main benefit for the EMF will be the repeatability.
- Due the method being a non-contact process and electrical, there is wear and tear of the part even though many numbers of parts is made which can look exactly the same to each other.
1.5 Limitation of EMF in Automotive Industry:
- This method being electrical, if the materials used have less electrical conductivity then there is no point in using this process.
- The aluminium part is slightly expensive and that can be one of the problems or the companies which use Electromagnetic forming.
2. Super Plastic Forming:
This process is one of the modern processes used in the automotive industry. In short form it is called as SPF which means Superplastic Forming. It mainly involves the super plasticity which means the point at which the metal ruptures due to the strain produced in the process and in which the metal can stretched and made into thin sheets. Super plastic forming process is takes place at increased temperature, where the stress-flow of the sheet metal is less. At first the metal sheets which are supposed to be used is heated at the ends and then a gas pressure is implied when the whole apparatus is inside a simple shape or a complex shape to make a required shape (Davis and Hyrn (2007)). The process involves expanding of the materials but it cannot be applied for materials that do not have super plastic properties. Normally super plastic materials can elongate up to 10 times. Whereas titanium naturally posses super plastic properties and some aluminium alloys and a few stainless steel alloys also be made to show superplastic properties. Aluminium alloys can expand about 1/4th during the forming process.It was first used widely in making parts for jets and aerospace regarded objects but as time grew automotive industry has used a lot of benefits from SPF.
In general superplastic forming uses the sheet forming processes to mainly elongate the work piece by using very high temperatures and SPF can be used to materials which accept the properties of superplasticity. This process helps to make very complex geometry of parts. It is mainly used in making aircraft wings and automotive parts as the metal aluminium is used in which it are stretched by heat. The basic materials used in the SPF are the aluminium alloy which is quiet expensive. The process basically needs nearly 900 ° C regarding the alloy used, dueto this heatthe flow of the stress involved in the sheet material is low(Gallagher (2001)). The sheet material is placed on a SPF die in which a simple or complex geometry is present and then the tooling is given high heat and a gas pressure is implied which in turns deforms to the shape of the simple or complex cavity.
There are many different types of properties of superplasticity with regards to microstructural mechanisms and deformation and the materials which undergo these types of superplasticity can be considered as a superplastic material;
- Transformation superplasticity
- Internal stress superplasticity
The following processes can be used for forming superplastic sheet materials and they are:
- Blow forming and vacuum forming
- Deep Drawing
- Superplastic forming with Diffusion Bonding
a) Blow forming and vacuum forming basically has a die cavity in which the superplastic sheet are placed, the sheet is placed in between the cavity and a gas pressure is implied to the cavity, from which the superplastic sheet takes the shape of the die cavity.
b) Thermo-forming is generally used for forming thermoplastics. In this type of forming there are two dies which in this case is male or female and they are moveable, this moveable die enables the sheet to stretch before a gas pressure is imposed on the sheet to make the required shape of the die cavity.
c) Deep Drawing with heat can be imposed on superplastic materials. Firstly deep drawing depends on the hardening of strain to get the needed formability and to prevent damage while forming the material and thus has less advantage compared to Blow forming and thermo-forming. This is because superplastic materials can only harden strain to a limit.
d)Superplastic forming (SPF) with the use of Diffusion bonding (DB) is a method which combines both qualities of SPF and DB, but DB is basically not a sheet metal process, since the temperatures used in the process of SPF and DB are similar they can be made use in unique fabricating methods for the materials. The aims of this combined process is to make a damage free forming process and to reduce the number of components and joints used in the processes.
2.2 Materials used:
The most common materials used for superplastic forming are as follows:
- Titanium alloys
- Aluminium alloys
- Bismuth-tin alloys
- Zinc-aluminium alloys
- Stainless steel
- Aluminium-lithium alloys
2.3 Advantages of SPF:
- Less weight and which increases fuel efficiency
- Performance of the design is improved with the help by its structure
- Can make very complex parts which in turn has great formability
- Low cost tooling thus resulting in low cost of the parts
- Low noise and
- Does not affect environment
2.4 Limitations of SPF:
- Low strain rate
- The time consumption of the process in which it forms the part is one important limitations of the SPF.
- The whole process’s cycle can vary, thus it is used on materials which has less volume.
3. Fine Blanking:
Fine blanking is a process in which a type of metal stamping is used to make the flatness of metal and very precise sheared edges of a metal. It is one of the modern methods used in the automotive industry for sheet-metal forming. The process is mainly made use by the automotive industry because of the quality level and the size of the materials and tools used which in turn makes it cost effective. At firstfine blanking was first discovered in Switzerland to make small gears and levers for a watch and clock company and after that grew to be more versatile and feasible for it could be made use in the automotive industry. In this process there is no chance of fracturing of the metal while shearing, for example it can make a number of holes in a metal sheet with perfect shearing and no damage with regards to the size of the metal, thickness of the metal and how far the holes are spaced. The process can generally make very complex shapes in a quick span of time without having to do too many procedures in the whole process. It is basically a bypass for processes like casting, forging and fabrication in manufacturing. The process is a combination of stamping, punching and an extrusion process. Fine blanking is less expensive than processes like forging or casting but fine blanking although being a very versatile sheet-metal forming process it cannot make 3-d shapes of any use, but some innovative thinking and designing can be put forth to make such products which can economically benefit fine blanking.
3.1 Working of Fine Blanking:
Fine blanking generally uses the materials like aluminium, copper, brass, carbon and stainless steel alloys. Fine blanking is a way of metal pressing processes but it has got extra parts to make it unique. It includes two dies (male and female), a guide plate and a V-ring which is also called as a stinger. The male die is the hardening punch which punches the material, whereas the female die is the hardening blanking die. The stinger basically is a sharp edge that surrounds the area of the material that has to be punched. Now, there will be a pressure applied to the punching die so that it cuts the metal and it pushes the cut metal into the empty die. The guide plate helps to hold the material into place firmly so that there is no movement of the material while the pressure is applied, thus the whole process acts like an extrusion rather than a traditional punching process (Hedrick (2006)). Due to the guide plate holding the material so tightly, the material’s flatness in perfect, there is no distortion or damage and there is a very minimum amount of edge burr. Burr is actually called as rough edge of a metal after a cutting, drilling or a punching process. After the punching is done while the material is held tightly by the guide plate, the slug and minute particles are pushed away to keep it clean for the net material to start the process. With a very good fine blanking process one can make many parts in a short period of time and with only one operation. The parts manufactured can be pierced fully like a hole, or partially pierced, embossed and also coined. Many gears, levers and materials have been made by the use of fine blanking.
To make a fine blanking process function exclusively to manufacture a quality product, the following points should be required:
- Fine Blanking Press
- Fine Blanking Tool
- Ductile Material
Fine blanking process has got many advantages and they are:
- By doing fine blanking we can get tremendous flatness of material that is merely never possible to acquire by any other cutting processes, thus it does not have to undergo any other flattening processes after the basic operation of fine blanking.
- Fine blanking can be used to make small holes in very thick and heavy metals and it can be used on many different metals.
- It can be used in embossing of metals or can be made use in coining and piercing.
- The process has got very good accuracy in making materials with precision, control and has good repeatability in production wise.
- Fine blanking helps to make the edges perfectly sheared,very straight and have no breakage of edges compared to other metal cutting processes.
- There is very high tolerance level in the tools of fine blanking when making holes and other parts which gives very good quality to the material.
- Many features can be put in while fine blanking in to just one operation other than having any secondary or tertiary operations.
Fine blanking although being a very versatile and feasible process, it has got a few limitations and they are listed below:
- Fine blanking can cause damage to the tools used because of the small clearance level of the whole process thus the tools are generally coated with few materials to prevent the wear and tear.
- In general the stinger or the V-ring consumes a lot of space therefore a lot of material is needed to be used to make a small part.
- In fine blanking, after the material has been cut out, burring is present in large amounts, so, often there is a need for deburring.
- Fine blanking process is a slow process which consumes a lot of time to make parts in comparison with the other similar processes.
The equipment used is slightly expensive than more conventional punching methods. Since it is a little expensive many companies who want to use fine blanking give a lot of consideration before investing in the tools
After doing research on the modern processes used in sheet-metal forming in the automotive industry for manufacturing the latest technology which is involved in this method are Electro-magnetic forming, Superplastic Forming and Fine blanking process. These processes were more efficient and cost effective while compared to traditional processes like bending, stamping, shearing and drawing, but these processes might not be the ultimate result with regards to sheet-metal process. From the three processes discussed above the most favourable process which can be recommended in the automotive industry is Superplastic forming process. The key advantages of Superplastic forming are design structure of the material used, formability of parts, fuel efficiency and low cost in tooling in comparison with the other two processes is much better. Hopefully in the future, there may be more processes which are more efficient for the production in sheet-metal processes in the automotive industry.
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