Fabrication and Welding Technology
- Category:Engineering and Construction
- Document type:Assignment
Fabrication and Welding Technology
Task 1a: Formability of metals
Formability refers to the ability of the sheet metals to be formed to a desired shape without necking or cracking. The elongation of the metal as well as straining is some of the important aspects that influence the formability of metals. The ability of the metal to undergo a large amount of stain is one of the aspects that influences positively on its formability. Other factors such as the property of the metal influence the formability of the metal (Sekar, 2014). The ability of the metal to undergo plastic deformation without being damaged is also an important aspect of formability. The properties such anisotropy has a direct impact on the formability process. Planar anisotropy is the ability of the sheet metal to exhibit different behaviours in different planar directions. This characteristic is mainly common in cold rolled sheets due to the preferred orientate of the mechanical fibring. Planar anisotropy can be reduced through a process of annealing at a lower strength. Deep drawing is one of the methods that are utilized during formability. This involves the use of a punch tool pressing on the inner region of the sheet while the side material is held by a blank holder, which can be drawn towards the center (Bruschi, et al, 2014). The material with good drawbility characteristics usually behaves anastropically. During the formability process, anisotropy is concerned with the hardening behavior of the metal as well as the thinning values. The anisotropic behavior greatly influences the plastic deformation during the formability process.
During the formability process, the R-value is a term that is used to describe the forming problems which includes wrinkling and thinning failures. The metals with a bigger R-Value have the ability to resist the forces of plastic deformation (Isik, Silva, Tekkaya & Martins, 2014). Compression instability is an aspect that contributes to wrinkles and hence affecting the formability process. The geometry of the parts is also associated with the wrinkle failures during the process of formability. The thickness of the sheet is also an important property that influences formability. This is because the stress as well as the strain usually changes with the thickness of the sheet. The strain at the maximum stress is usually increased with an increase in the thickness of the sheet metal. However, it may face a gradual decrease with a further increase in the thickness of the metal. The stress values may however remain constant with an increase in thickness of the sheet during formability. The failure strain of the metal is decreased with an increase in the sheet thickness. An increase in the thickness of the metal usually results to an increase in the force that is required during the punching process (Sekar, 2014). Formability is thus dependant on the thickness of the sheet as it determines the force that may be required before the plastic deformation limit is attained. When the sheet metal is thin, lower force is required during the punching process. This therefore offers little resistance to the process of formability. Depending on the characteristics such as anisotropy and thickness of the sheet, the plastic deformation limit may be attained within a short period.
When a technique such as air bending is used, the failure strain of the sheet due to its thickness is reduced. The biaxial deformation conditions during the formability process usually result to biaxial stress. The state of stress of the metal during the formability process is an important influential factor. The shape of the component being fabricated is an important determinant of stress during the process. The forming limit diagrams are commonly used for purposes of predicting the stress that may be encountered during the process (Bruschi, et al, 2014). The force applied as well as the thickness of the metal sheet determines the stress levels during the formability process.
Task 1b: (LO1: 1.2)
Stretch forming process
This method involves stretching the sheet metal and bending it simultaneously over a die in order to ensure that large countered parts are formed. It is usually performed on a stretch press with the piece of metal sheet secured along its edge using a grip jaw. The teeth jaws are usually attached to a carriage, which is usually subjected o a hydraulic or pneumatic force for e purpose of pulling. A stretch form block, which is referred to as a form die, is the tooling that is used during the process (Isik, Silva, Tekkaya & Martins, 2014). It is also a solid form contour in which the sheet metal is pressed against. The orientation of the stretch press is usually vertical and a hydraulic ram is usually utilized during the process of lifting. The tensile force is increased when the die form is driven into the sheet. This action usually results into the plastic deformation f he sheet metal resulting to a new shape. When the horizontal stretches are used, the griping jaws usually pull the sheet horizontally along the die form. The stretch forming equipment has the ability to produce different complex shapes. Better shape control as well as surface quality is usually attained when the stretch forming equipment is used (Isik, Silva, Tekkaya & Martins, 2014). The process usually subjects the sheet metal into a plastic as well as elastic deformation. The stretch forming process is use in various industries and different types of materials can also be developed.
Stretch forming process
The stretch forming process is widely used for metal forming process in different industries (Leotoing, Guines, Zidane & Ragneau, 2013). This includes the automobile industry where the aluminum parts are produced through the process. In the aeronautic industry, stretch forming is applied in producing large wing edges. It is also applied in the process of developing the nose section and door panels for the aircrafts. The application can be attributed to the low cost involved as well as the ability to us large sheets of metal. This process has the potential of stretching different types of metals that are used in the manufacture of the aircrafts (Sekar, 2014). It also has several advantages as compared to the other technique use in the metal forming process. The advantages include the ability to minimize the internal stress, high volume output, large pars and lower costs. The process is usually carried out using two main types of equipment. This includes the longitudinal as well as the transverse equipment. The two main parts of the hydraulic stretching equipment includes the power unit and he ram.
A press brake is a machine that is used for sheet metals as well as plate materials (Leotoing, Guines, Zidane & Ragneau, 2013). There are different are different types of brake machines and this includes the mechanical, pneumatic, servo electric and hydraulic. The mechanical press brake machine adds energy to the flywheel through an electric motor. It also has a clutch that engages the fly wheel in order to power a crank mechanism. The main advantages of this type of mechanic press brake machine are high levels of accuracy and speed. Mechanical press braking was popular until the 1950s when it was gradually replaced due to technological advancement (Bruschi, et al, 2014). The pneumatic press brake utilizes air pressure in order to develop tonnage on the ram. It is however used in lower tonnage application. The hydraulic press brake machine is increasingly becoming popular in the market. It is this type of press brake that replaced the mechanical type. It mainly operates through two synchronized hydraulic cylinders on the C-frames, which moves the upper beam. It is also known for high quality products, reliability, low energy use and high levels of safety. The safety is due to the ease of stopping the motion of the ram. The electric brake machine use a servomotor for driving a ball screw in order to exert tonnage on the ram (Zhang, Lin, Min & Kang, 2016). Although it is fast and efficient, it is mainly used in lower tonnage application. The use of electric and hydraulic is increasingly becoming common as it supports the modern technological features.
As compared to the other forming processes, the press braking tool is more effective. The press brakes usually have multi-axis computer controlled back gauges. It is also equipped with optical sensors, which allows for adjustments to be made during the forming process. The sensors have the ability of sending real time data regarding the bending angle (Isik, Silva, Tekkaya & Martins, 2014). This therefore makes is more accurate and efficient as compared to the other forming processes. Press braking tooling is an aspect that determines the quality of bends. The different tools that utilized in the press brake determine its efficiency. Punch profiles are utilized in some of the press brakes. This ensures that the setup time is reduced and the clamp interference is reduced. Air bending is a three point ending that can be carried out through the use of the press-braking machine. When carrying out this process, different tools re usually utilized. A is used for pressing the material into the die which is also an important tool use during the process. Care has to be taken to ensure that the punch does not come into contact with the deepest part of the die. This technique is considered flexible ad it has the ability of creating multiple bend angles. A precise drive of the punch is required in order to avoid the incidences of springback, which may affect the process (Leotoing, Guines, Zidane & Ragneau, 2013).
Coining is also a bending technique that can be carried out through the use of a press brake machine. This process involves crushing of the sheet metal to the bottom of a die rough the use of a punch (Zhang, Lin, Min & Kang, 2016). The process requires a heavy force in order to ensure precision. The heavy force and high levels of precision play an essential role in preventing any incident of a springback. It is however important to note that this press method is quite expensive.
Coining, Source, Metal forming magazine
The punching press is usually comprised of a swan neck frame, which are mainly acts as a passage for the sheet metal to be machined. It also has a slot that can be used a height adapter during the aching process. The location of the swanneck is important in ensuring that the maximum recisin is obtained. During the metal forming process, the die can be used for forming the bead. During the bead forming process, the edge of the sheet metal is bent into the cavity of the die (Bruschi, et al, 2014). This plays an important role in providing stiffness by increasing the moment of inertia of the edges. This process is useful in improving on the appearance of the sheet and ensuring that the sharp edges are eliminated.
Bead forming with one and two dies, Source, <http://image.slidesharecdn.com/sheet-metal-forming-processes-130114203855-phpapp02/95/sheet-metalformingprocesses-16-638.jpg?cb=1358195999>
When using the standard offset press barking tooling, the offsets are usually bent too close together. The correct type and style of tooling is however critical during the process. There are two main varieties of offset tooling that is used during the process and it includes upspring and horizontal (Zhang, Lin, Min & Kang, 2016). The upspring tool is commonly utilized during the process of forming bends that are too close together. However, when in need of offsetting one material thickness, the horizontal is used.
When using the press brake, the Vee Die opening has to be determined accurately. This process requires the use of a formula in order to carry out the calculation. The following formula can be used during the calculation:
Vee Die opening = Outside radius x 0.7071 x Factor.
Where 0.7071 is sin 45 and the factor is the multiplier.
Bending is one of the most important aspect of the metal sheet forming process. During the bending process a radius is usually formed. The minimum bending radius is usually expressed in terms of the thickness of the material. The bend Radius (R) can be obtained through the following equation.
Lb = a ( R + kt )
Lb = Bend allowance
a = Bend angle
R = bend radius
t = Thickness of the sheet
k = Constant
Sheet metal bending, Source, <http://nptel.ac.in/courses/112107144/Metal%20Forming%20&%20Powder%20metallurgy/lecture6/lecture6.htm>
The punch force is responsible for generating the bend during the metal forming process (Zhang, Lin, Min & Kang, 2016). The punch force therefore varies during the process. At the begging, the punch force is usually zero. However, it increases and reaches the maximum value at the bottom of the stroke. The following equation can be used for calculating the punch force (P).
P = k.Y.L.t2 / D
Where, k = constant
L = bend length
D= Die opening
t = Thickness of the sheet
Y = Yield stress
Retrofitting CNC has been introduced in the pres brake for the purposes of ensuring that it is effective. The CNC brakes set up requires a high levels of expertise during the process of operation. Different levels of knowledge as well as experience are useful in the operation of the CNC brakes (Isik, Silva, Tekkaya & Martins, 2014). The brake set up and operations is unique and hence the need for expertise. The tonnage charts are however important during the process of operating the press brakes. It is also important for the operator to understand the tooling. Each type of bending in most cases requires a different type of tooling in order for the process to be effective.
Task 1b: (LO1: 1.3)
High-energy rate forming (HERF) is a method that involves the use of high surge in the sheet metal formation (Zhang, Lin, Min & Kang, 2016). The process usually takes place at a fast rate and hence the need for a proper selection of the materials. The desired material has to be ductile when subjected to a high deformation speed. There are different methods of HERF and this includes electro hydraulic forming, electromagnetic forming and explosive forming.
Electro Hydraulic forming
Electro hydraulic forming is a unique high energy forming process that is used for the sheet metals. The method involves the use of energy from combustion of a thin metal wire (Zhang, Lin, Min & Kang, 2016). Two electrodes connected to a wire are submerged into a liquid. A sheet metal is then secured on top of a mould with a ring clamp and vacuum created in the die cavity located under the blank. During the process, electrical energy is stored in a capacitor bank. When the electrical energy is discharged through the electrodes and the wire, it is instantly vaporized creating shockwaves that travels through the water (Bruschi, et al, 2014). The shock waves leads to formation of the sheet metal to the mold cavity. The shock wave produced when using this method is relatively low and can only be used for thinner works. The production rate of this method is relatively low and the wire needs to be replaced after each operation.
Electro Magnetic Forming
Electromagnetic forming is one of the high-energy rate process that utilizes magnetic surge to form the sheet metal parts. The process involves placing an electric coil close to a metalwork piece. A capacitor blank is charged the just like in the electro hydraulic forming process. The electric is sent through the coil to forms a magnetic field as opposed to shock waves produced in the electro hydraulic forming process (Leotoing, Guines, Zidane & Ragneau, 2013). Eddy currents are produced when the magnetic current is disrupted by the material. The eddy currents in turn produce their own magnetic field that opposes the original magnetic field that had been produced in the coil. The opposing forces push the fields apart leading to the formation of the works. Depending on the nature of the desired work, the coil can be placed inside or over the work. This method just like the electro hydraulic forming is commonly used in thin metal sheets.
Explosive forming as compared to the electro hydraulic and electromagnetic method has a long cycle time (Zhang, Lin, Min & Kang, 2016). In most case, it is used for low quantity production of large and unique parts. Mechanical properties imparted by the explosive process are similar to that of other forming processes. The amount of pressure needed to for the parts is a factor that determines the explosives used (Isik, Silva, Tekkaya & Martins, 2014). This method just like the electro hydraulic forming is utilizes shock waves generated by the explosive traveling a long a spherical front experiencing an expansion. However, the work piece does not absorb much of the shock wave generated. Reflectors are also in place for the purposes of focusing the energy surge. This therefore ensures efficiency in terms of the energy use. The energy generated is usually directed into a closed container that contains the die cavity. The parts are formed when the energy from the canned explosive forces the sheet metal to the walls of the mould. Die failure may result to safety problems which is an indication that this method is dangerous. The explosive forming method is quite different from the other two methods.
Task 2a (LO2: 2.1)
Initial blank diameter
Using the volume constancy, it can be calculated as follows
115 + 1.243
Safe drawing ration for the first draw
The blank diameter for the first draw
= + 4(116.243 x 100)
= 244.968 mm
The draw ratio for the second stage draw
244.968 x 0.2
=48.99 + 244.968
An approximate value, in tonnes, for the press capacity
P = 1.3 σt π t [D – d]
= 1.3 x 450 x 3.14 x 0.9 [1.243]
= 2.054 Tonnes
A self-secured joint does not require the use of mechanical fixing such as bolts, rivets, screws or clamping devices (Sekar, 2014). Soldering brazing and welding is also not required in the self-secured joints. There are different types of self-secured joints that can be used for commercial mechanized manufacture. This includes the grooved seam, knocked up and panned down. The joints cannot fall apart once it has been formed. However, it is also important to note that a non-thermal bonding may be required in case it has to be as or water tight. The use of non-thermal boning is not required for holding the joints together. This is a mechanism that is applied only when it has to be water or gas tight. A paned down joint is usually formed with one section folded at 90 degrees while the other is folded at 180 degrees (Sekar, 2014). A panning hammer is used for fitting the sections together. It application is mainly involve joining the sides of cylinders. This type of joint is also effective when used on squares and rectangles. The knocked up joint is more secure and stronger due to more than one folding. A self-secured joint requires a lot expertise in order for the joints to be effective.
Secured sheet metal joint, Source, Jay Gibson Fabrication
Patented sheet metal captive fasteners
The sheet metals can also be joined through the use of captive fasteners. This method is considered non-self secured due to the use of the captive sheet metal fasteners (Zhang, Lin, Min & Kang, 2016). In the market, there are a high number of patented sheet metal fasteners. This is mainly dependant on the manufacturers as well as the quality and application. Some of the most commonly used sheet metal fasteners include the rivet nuts, studs, weld studs and threaded fasteners (Leotoing, Guines, Zidane & Ragneau, 2013). The captive fasters are commonly used when the joint is put in place on a permanent basis. The patented sheet metal fasteners are effective in ensuring that the joints are able to hold firmly and stronger. Depending on the type of captive fastener used, it may stronger as compared to the self-secured joints. Most of the patented sheet metal captive fasteners are commercially available and widely used.
Task 2b (LO2: 2.2)
The bolting process requires a lot of precision in order for the joint to be successful. The joint failure is mainly attributed to the insufficient preload as well as the inaccurate tightening method. The features and characteristics of the methods used to tighten the bolt have to be considered. The tacking bolts are commonly used in order to connect the joints (Xu, Wu, Ling, Luo, Du & Sun, 2013). However, this type of bolt does not provide strength to the members. The tacking bolt is mainly an assembly aid that is aimed at enhancing the fastening process. When tightening high strength friction bolts, several methods can be utilized. Torque control tightening is a fastening method that is commonly used to control preload. Calculations are used for determining the relationship between the torque and the resulting bolt tension. This method however ignores the torsional stress with an assumption direct stress in the thread is proportional to the yield stress at the bolt. The method is also effective where vibrations may end up contributing to loosening of the bolts. The angle controlled tightening is a method that has been commonly used for high strength friction grip bolts since the World War 2 (Vimal, Vinodh & Raja, 2015). It is used with power wrenches when there is a pre-determined angle that is beyond the elastic range. However, this method has some disadvantages in terms of precision. The fasteners may also fail as it can only withstand a limited number of re-application.
Yield control tightening is a method that has the ability of ensuring that a high preload is achieved. This is through the minimization of the influence of friction as well as its scatter. The yield point of the fastener can be detected with reasonable precision when this method is used. A control method that is sensitive to the torque gradient is also used in this technique (Vimal, Vinodh & Raja, 2015). This is achieved through the use of sensors to read the torque and angles. The use of this method is however limited to the high costs of tools. The bolt stretch method is used in fastening the bolts that require high strength friction grip. A small hydraulic ram that fits over the nuts is utilized in this method. Hydraulic oil is also used during the process, which ensures that efficiency is obtained. The preload in the bolts is effectively controlled by the hydraulic pressure when this method is used. Heat tightening is a method that utilizes thermal expansion (Xu, Wu, Ling, Luo, Du & Sun, 2013). This involves the heating to the bolt that causes it to expand. The bolt is then constrained longitudinally when it attempts to cool. A direct flame can is commonly used during heating process and it may take a lot of time. It is effective for very large bolts that require high strength friction grip. The tension indicating method involves the use of special load indicating bolts and washers. Stretching of the bolt takes place s the tightening process continues. This plays an important role in eliminating the gap and preventing the rota from rotating.
Task 2c (LO2: 2.3)
The joining of the structural sections is an important aspect of that depends on various factors. The behaviour of the end plate must be known in order to ensure that the process is carried out effectively. Depending on the thickness of the plate, the behavior can be divided into three different categories. The direct relationship between the bolt and the bolt applied is termed as the thick plate behavior. Thin plate behavior is mainly associated with a maximum prying force with the prying forces as well as forces assigned to the plate forming the maximum prying force (Xu, Wu, Ling, Luo, Du & Sun, 2013). In thick and thin plates, the intermediate plate behavior is usually exhibited. The joining plate dimensions are thus dependant on various factors including the properties of the materials. The joining plate dimensions have to be calculated during process in order to ensure that accuracy is attained. The number of sections must first be determined before the dimensions are obtained. The length as well as the circumference must be calculated in order to ensure that the dimensions are obtained. In order to calculate the circumference, the following equation can be used. C = 2 x pi x r,where r is the radius of the plate being used during the joining process (Xu, Wu, Ling, Luo, Du & Sun, 2013). The depth between the flanges is an important aspect that is associated with the joining of the structural sections. The values can however be obtained directly from the tables during the calculations.
Task 3a (LO3: 3.1, M1, D1)
Oxy fuel gas cutting is a process that mainly utilizes oxygen and fuel for the purposes of cutting the metal. Pure oxygen as opposed to air is used during the cutting process. The reaction between the oxygen and fuel usually result to an exothermic reaction (Vimal, Vinodh & Raja, 2015). The exothermic reaction is useful in the process of ensuring that the metal is melted and hence leading to the cutting process. During the cutting process, the pre heat flames are used for raising the surface to ignition temperature. The pure oxygen is in turn directed towards the heated area. This is carried out in a fine and high-pressure stream in order to establish the cut. When using this method, cutting can only take place when the oxides of the metal have a lower melting point as compared to the base metal itself. It is for this reason that it is commonly used in the carbon steel during the cutting process.
Different types of cutting can be carried out when using the thermal process. This method is considered as one of the oldest method of cutting the metals. However, as a result of technological advancements, new technologies as well equipment are in place to ensure that the process is carried out effectively. This includes the use of mechanized oxy cutting that is effective in the regulation process, which ensures efficiency (Xu, Wu, Ling, Luo, Du & Sun, 2013). CNC cutting is mainly utilized when dealing with steel although this requires a lot of expertise. Cross carriage type of cutting machine is also increasingly becoming popular in the cutting process. The issue of safety is an important when using the thermal cutting machines. It is therefore important for the operators to ensure that safety aids are used during the cutting process. This method is also cost effective due to its ease of use.
Arc plasma cutting
The arc plasma cutting process mainly utilizes high velocity jets of ionized gas, which is delivered, from a constricting orifice. The plasma usually heats the work piece ensuring that the material is melted. The molten metal is blown away mechanically leading to the cutting of the material. It is however important to note that plasma cutting can be performed on any conductive metal. This means that the method can be used widely during the cutting process. Swirling of the gas can be carried out in order to ensure that plasma plume is constricted and a narrower gap is achieved with fewer bevels (Vimal, Vinodh & Raja, 2015). A second shroud gas can also be used in order to ensure that a narrower gas is achieved. A number of methods are usually used during the process to start the arch. In most cases, the arc is created by putting the torch in contact with the work piece.
When working near sensitive electronics, it is important for other means to be used for cutting when the arc plasma cutting technique is used. The arc plasma cutting method is increasingly becoming common due to the high speed, precession and low costs. Thick materials can be cut easily through the use of this method. A hot and localized cone is usually produced when the plasma cutter is used (Xu, Wu, Ling, Luo, Du & Sun, 2013). This makes it useful for the cutting the sheet metals in curved or angled shape. This method is considered as one of the most productive when it comes to cutting the sheet metals. Eye protection is required during the cutting process to avoid damage from the strong light as well as debris produced from the cutting process.
The mechanical cutting can be carried out through a high number of techniques. The mechanical shears can be used during the mechanical cutting process. It involves the use of an eccentric to power the ram and bring it down under load. Guillotine is also used as part of the mechanical cutting process (Vimal, Vinodh & Raja, 2015). This mainly utilizes vertical guided ram shears. High carbon chrome knives are commonly used as shear knives for the purposes of carrying out the cutting process. Saws have been used over the years as one of the mechanical cutting tool. The hacksaws usually cut through the use of a reciprocating motion that is driven mechanically. This method is one of the simplest in the process of cutting metals. Depending on the size of the metal, different types as well as sizes of blades can be used in the cutting process. The method is however slow and cannot be used for mass production.
Mechanical cutting can also be carried out through the use of a punching tool. This subjects the sheet metal to a punching force leading to the cutting process. This method requires a high mechanical punch force during the cutting process. The drilling tools can also be used for the purposes of cutting the metals (Vimal, Vinodh & Raja, 2015). The drill tools in most cases are powered by electricity and hence making it effective during the cutting process. The mechanical cutting tools are however not effective as compared to thermal and plasma cutting. This is because it mainly utilizes the mechanical aspects as during the process. The mechanical cutting is mainly comprised of some of the oldest methods of cutting metal.
List of References
Bruschi, S., et al, 2014. Testing and modeling of material behaviour and formability in sheet metal forming. CIRP Annals-Manufacturing Technology, 63(2), pp.727-749.
Isik, K., Silva, M.B., Tekkaya, A.E. and Martins, P.A.F., 2014. Formability limits by fracture in sheet metal forming. Journal of Materials Processing Technology, 214(8), pp.1557-1565.
Soeiro, J.M.C., Silva, C.M.A., Silva, M.B. and Martins, P.A.F., 2015. Revisiting the formability limits by fracture in sheet metal forming. Journal of Materials Processing Technology, 217, pp.184-192.
Leotoing, L., Guines, D., Zidane, I. and Ragneau, E., 2013. Cruciform shape benefits for experimental and numerical evaluation of sheet metal formability. Journal of Materials Processing Technology, 213(6), pp.856-863.
Sekar, K.V. ed., 2014. Manufacturing engineering and technology. Prentice Hall, New York.
Zhang, L., Lin, J., Min, J., Ye, Y. and Kang, L., 2016. Formability Evaluation of Sheet Metals Based on Global Strain Distribution. Journal of Materials Engineering and Performance, 25(6), pp.2296-2306.
Xu, B., Wu, X.Y., Ling, S.Q., Luo, F., Du, C.L. and Sun, X.Q., 2013. Fabrication of 3D metal micro-mold based on femtosecond laser cutting and micro-electric resistance slip welding. The International Journal of Advanced Manufacturing Technology, 66(5-8), pp.601-609.
Vimal, K.E.K., Vinodh, S. and Raja, A., 2015. Modelling, assessment and deployment of strategies for ensuring sustainable shielded metal arc welding process–a case study. Journal of Cleaner Production, 93, pp.364-377.