El forjado con dado impresor o forjado con matriz de impresión la pieza a fabricar adquiere la forma de los huecos o cavidades al forjarse entre dos matrices con perfil.

Cuando se realiza esta operación algo de material fluye hacia fuera y forma una rebaba, ésta tiene un papel importante en el flujo del material en el estampado ya que es delgada, se enfría rápidamente y al ejercer una resistencia gracias a la fricción que existe entre la rebaba y la matriz, somete a grandes presiones al material en la cavidad de la matriz causando así el rellenado de la cavidad.

Las piezas a forjar pueden ser preparadas previamente con otras operaciones como:.

a) Corte o recorte de una barra estirada o extraída.

b) Operaciones de preconformado, como por ejemplo la metalurgia en polvos.

c) Fundido. Una pieza bruta preformada en un forjado anterior. La pieza en estado bruto se coloca en el dado inferior y al empezar a descender el dado superior la forma de la pieza cambia de forma progresiva.

Los procesos de preformado, como el forjado con dados convexos y cóncavos, se utilizan para distribuir el material en las diferentes zonas de la pieza bruta, parecido a cómo se conforma la masa para hacer bizcochos.

En el forjado con dado cóncavo, el material de la pieza se aleja de una región. En el forjado con dado convexo se junta en una región localizada. Seguidamente a la pieza se le da la forma aproximada de la forma final con un proceso llamado bloqueo utilizando dados bloqueadores. Finalmente es el acabado del proceso de forja en matrices de estampado en el que la pieza obtiene su geometría final. La rebaba se elimina normalmente mediante troquelado.

En el proceso verdadero de forjado con dado cerrado o sin rebabas, éstas no se forman y el material de la pieza en bruto llena completamente las cavidades del dado. Es imprescindible el control del volumen del material y el del diseño correcto de la matriz para poder conseguir un forjado con matriz cerrada que tenga las dimensiones y tolerancias deseadas. Un mal control del volumen del material puede ocasionar que coloquemos piezas brutas pequeñas y no llenen completamente las cavidades del dado o por el contrario las piezas demasiado grandes pueden producir presiones excesivas y pueden hacer que los dados fallen prematuramente o se aplasten.

Advantages and disadvantages of closed die forging

This forging process has a series of advantages and disadvantages.

-Advantages:.

-Disadvantages.

Forging force with closed die

The forging force γ required in a stamping operation can be calculated with the formula:.

Where K is a multiplicative factor. For simple shapes without burrs the value of K can range from 3 to 5, and with burrs from 5 to 8, for complex shapes with burrs the value can range from 8 to 12.

Yf is the flow stress of the material at the forging temperature, and A is the projected area also including the flash.

In hot forging operations the pressure necessary for most metals ranges from 550 MPa to 1000 MPa.

Precision forged

For economic reasons, there is currently a trend towards the highest possible precision in work operations, thus reducing the number of additional finishing operations. The operations in which the part is obtained with dimensions close to the final ones are called almost net shape forging or net shape forging. In this type of process there is little excess material in the forging that must be removed by grinding or punching.

In precision forging, special dies ensure that the final pieces obtain more precise dimensions than those obtained by forging with stamping dies, and they also require less machining. In this process, greater capacity equipment is required, since greater forces must be applied to obtain the fine details of the pieces. Since the temperatures and forces required are relatively low, aluminum and magnesium alloys are highly advisable for this type of precision forging. In addition, the dies wear less and a good surface finish is obtained; steels and titanium can also be used.

The main products produced with precision forgings are: gears, cases, connecting rods and turbine blades.

In this type of forging, special and more complicated dies are needed, a more exhaustive control of the volume and shape of the yew, precise location of the yew in the die cavity and, consequently, a greater economic investment.

However, less material is wasted and not as much final machining is required because the part is closer to achieving its final shape. Therefore, choosing between normal and precision forging requires an economic analysis, especially with regard to production volume.

The advantages of performing precision forging are:.

As a drawback we can say that:

Among the closed die forging processes we can highlight:.

To design the dies, it is essential to know the ductility and resistance of the part material, its sensitivity to temperature and deformation speed, the shape and complexity of the part and its friction characteristics. An important effect to take into account is the distortion of the dies under the large loads to which they are subjected during the forging process, especially if close dimensional tolerances are required.

The most important aspect to take into account when studying the design of dies is that the part flows in the direction with the least resistance, consequently the part must be shaped (intermediate shape) in such a way that it fills the die cavities well. The preforming of the part is of great importance, since in a well preformed or preformed part, the material must not flow easily towards the burr, the grain flow pattern must be favorable, and excessive slip must be reduced on the faces that are in contact between the die and the part to minimize wear.

To choose the shapes, great experience is required and good calculations of the cross section of the surface in each place where the forging is carried out.

Computer engineering techniques have been developed to expedite these calculations, as well as to deduce the pattern of material flow in the die cavity and defect formation. As a result of the material undergoing different degrees of deformation at different speeds and in different areas of the die cavities, the mechanical properties of each location are specific to the forging.

For most forgings or forged parts, the parting line is usually located at the maximum cross section of the part. For simple symmetrical shapes, it is normally a straight line in the center of the forged piece and for pieces with more complex shapes this line may not be in a single plane, which is why dies are usually designed in such a way that they lock during coupling to avoid natural thrusts and thus balance the forces while maintaining alignment during forging.

After sufficiently limiting lateral flow to ensure optimal filling of the die cavities, the flash material is allowed to flow through a conduit called a flash channel so that additional flash does not unnecessarily increase the forging force. A general guideline for burr clearances between dies is 3% of the maximum forging thickness. The face length is usually 2 to 5 times the thickness of the burr. Over the years, different designs of the burr channel have been studied.

Draft angles are essential on almost all forging dies, to help separate the part from the die once the forging operation is completed. When the piece cools, it contracts in longitudinal and radial directions simultaneously, so the internal exit angles become greater than the external angles. The internal angles vary from 7 to 10º and the external angles from 3 to 5º.

It is important to choose the proper transition radii at corners and bevels to ensure uniform metal flow into the die cavity and improve die life. In general, small radii should be disregarded due to their adverse effect on metal flow and their propensity to wear rapidly (as a result of thermal cycling and stress concentration). Additionally, small bevel radii can be the cause of die breakage due to fatigue. Thus, these radii should be as large as the design of the forging allows.

The dice can be assembled using inserts instead of being made in a single piece, and even more so if the shapes are complicated. This assembly method reduces the cost of manufacturing several similar dice. Inserts can be made from harder, stronger materials and can be easily replaced in the event of failure or wear in a particular area.

Tolerances must be provided in the design of the dies since machining of the forged part may be required to obtain the dimensions and final surface finish. These machining tolerances must be provided for holes, flanges and mating surfaces.

Most forging operations, especially for large pieces, are carried out at high temperatures. Common requirements for die materials are:.

a) great toughness and resistance to high temperatures.

b) ability to harden uniformly.

c) resistance to mechanical and thermal shock.

d) resistance to wear, especially abrasive wear, due to the existence of scale in hot forging.

The choice of suitable materials for the manufacture of dies depends on factors such as the composition and properties of the part, the complexity of the shape, its size, the forging temperature, the type of forging operation, the cost of the die materials and the quantity of forgings demanded. Another important factor is the transfer of heat from the hot piece to the dies with their consequent distortion.

The most common materials used to manufacture sockets are tool steels and for sockets that work at high temperatures, materials containing chromium, nickel, molybdenum and vanadium.

Dies are obtained from blocks, which are in turn forged from casting, later machined and finished to the desired shape and surface finish.

Failures may occur in the manufacture of dice due to reasons that will be described in the section: dice failure, where dice manufacturing methods are also described.

Lubricants are essential and influence friction and wear as a result of the required forces (equation 1) and the flow of metal in the die cavities. Another important aspect of the lubricant is that it can act as a thermal barrier between the hot part and the relatively cold dies, slowing the cooling rate of the part and improving metal flow. It also serves as a release agent as it prevents the forged piece from sticking to the dies.

A wide variety of lubricants can be used in forging. For hot forging, graphite, molybdenum disulfide, and sometimes glass are usually used. For cold forging the lubricants generally used are mineral oils and soaps, applied after conversion coating of the blanks. In hot forging the lubricant is usually applied directly to the dies, while in cold forging it is applied to the piece. The application method and uniformity of lubricant thickness are very important to the quality of the forged product.

Different manufacturing methods can be used to manufacture dice, singly or in combination. Among them are: forging, casting, grinding, machining, electrochemical and electrical die stamping methods. The process of obtaining the die cavities is usually punching, either cold or hot. It can also be used to make small sockets with shallow cavities. Generally the dice are heat treated to obtain greater wear resistance and hardness. If required, their contour and surface finish are improved with grinding and polishing, with programmable industrial robots or by hand.

The choice of manufacturing method depends on the operation in which the die is to be used, as well as its shape and size. Generally costs determine the process to be selected since these are important in manufacturing operations. Although the dice are small and relatively simple, they can cost hundreds of euros. However, because a large number of parts are manufactured using the same die, in general the cost per unit is usually only a small part of the manufacturing cost of the part.

Dice are usually classified as male and female or by size. Generally, small dice are those that have a surface area between 2 cm² to 1 m², while large ones have surfaces greater than 1 m².

The dies can be cast in steels, cast irons and non-ferrous alloys. The processes used range from shell molding (for small dice) to sand castings (for large dice weighing several tons).

In general, cast steels are preferred for large piece dies due to their strength and toughness and the ease of controlling their composition, properties and grain size. Depending on how they are solidified, cast dice, unlike forged or rolled metal dice, may not have directional properties; They may have the same properties on all their working surfaces; however, due to shrinkage, controlling dimensional tolerances may be difficult compared to machined dies.

Dies are generally machined from a forged block, with processes such as grinding, turning, milling, electrochemical and electrical machining. Machining can be complicated when the materials are high strength, hard, wear resistant, or those that are heat treated.

The operations can be time-consuming, which is why many non-traditional machining processes are used, especially on small or medium-sized dies since they are faster and more economical and the dies usually do not require additional finishing. Diamond dies, for fine wires, are made by making holes with a thin rotating needle coated with diamond powder and oil as a lubricant.

Socket steels are heat treated to improve hardness, wear resistance and overall strength. Poor heat treatment is one of the most common causes of die failure since it can distort them due to microstructural changes and non-uniform thermal cycles.

Proper selection of heat treatment temperatures and atmospheres, media, quenching, tempering practice, and handling are important. The sockets can be subjected to different surface treatments to improve their wear and friction characteristics. The condition and composition of the die surfaces are of particular importance.

After heat treatment, the dies are subjected to finishing operations, such as grinding, polishing... to obtain the desired finish and dimensional precision.

The grinding process can cause damage to the surface if not well controlled, due to the excess heat that can be produced, and can include residual stresses on the surface that reduce its fatigue life. Scratches on surfaces can act as a source of stress concentration. Likewise, die manufacturing processes can cause surface damage and cracks unless process parameters are thoroughly controlled.

These failures are generally due in manufacturing operations to one or more causes listed below:

a) inadequate design.

b) material defect.

c) overheating and thermal cracking.

d) inadequate heat treatment and finishing operations.

e) overweight.

f) excessive wear.

g) misuse and improper handling.

Proper design is very important. To resist the forces in manufacturing processes, a die must have adequate cross sections, clearances, and sharp corners. Bevels and radii, as well as abrupt changes in cross section, act as stress concentrators. Dies can be segmented, and prestressed during assembly to improve their strength.

The handling, assembly, installation and alignment of the sockets is of great importance. Overloading tools and sockets can cause premature failure. For example, a common cause in cold extrusion dies is a robot operator not removing the finished part before the other blank is loaded.

Materials used for sockets such as carbides and diamond, despite their hardness and resistance to abrasion, are susceptible to burring and elongation due to impact forces or thermal effects caused by internal temperature variations.

Even working fluids can negatively affect die and tool materials, for example, chlorine in lubricants, sulfur additives and coolants can damage the cobalt binder in tungsten carbide decreasing its strength and toughness.

Even if manufactured correctly, dice are subjected to high temperatures and high stresses during the process, which can cause wear and (consequently) shape changes. The wear of the dies must be taken into account since when they change their shape, the pieces produced will in turn have incorrect dimensions.

During use, dies can suffer thermal cracking, due to thermal cycling especially in die casting. To avoid this defect and eventual breakage in hot operations, the dies are usually preheated to temperatures between 1500 and 2500 °C. Worn or cracked sockets can be repaired with welding and metal depositing, which include lasers.

Sockets can be designed and manufactured with replaceable inserts when they wear or crack. The design and placement of the inserts must be carefully studied since any failure in these aspects can cause them to break. Die failures and fractures can be dangerous for manufacturing plant employees.

It is possible that the dice waiting in a drawer suddenly disintegrate, due to the state of large internal stresses of their components (residual stresses). The pieces that break are thrown away at high speed and can cause serious injuries. The dies must be surrounded by metal defenses that must be well designed and have resistance to contain the fractured pieces in case of failure.

El forjado con dado impresor o forjado con matriz de impresión la pieza a fabricar adquiere la forma de los huecos o cavidades al forjarse entre dos matrices con perfil.

Cuando se realiza esta operación algo de material fluye hacia fuera y forma una rebaba, ésta tiene un papel importante en el flujo del material en el estampado ya que es delgada, se enfría rápidamente y al ejercer una resistencia gracias a la fricción que existe entre la rebaba y la matriz, somete a grandes presiones al material en la cavidad de la matriz causando así el rellenado de la cavidad.

Las piezas a forjar pueden ser preparadas previamente con otras operaciones como:.

a) Corte o recorte de una barra estirada o extraída.

b) Operaciones de preconformado, como por ejemplo la metalurgia en polvos.

c) Fundido. Una pieza bruta preformada en un forjado anterior. La pieza en estado bruto se coloca en el dado inferior y al empezar a descender el dado superior la forma de la pieza cambia de forma progresiva.

Los procesos de preformado, como el forjado con dados convexos y cóncavos, se utilizan para distribuir el material en las diferentes zonas de la pieza bruta, parecido a cómo se conforma la masa para hacer bizcochos.

En el forjado con dado cóncavo, el material de la pieza se aleja de una región. En el forjado con dado convexo se junta en una región localizada. Seguidamente a la pieza se le da la forma aproximada de la forma final con un proceso llamado bloqueo utilizando dados bloqueadores. Finalmente es el acabado del proceso de forja en matrices de estampado en el que la pieza obtiene su geometría final. La rebaba se elimina normalmente mediante troquelado.

En el proceso verdadero de forjado con dado cerrado o sin rebabas, éstas no se forman y el material de la pieza en bruto llena completamente las cavidades del dado. Es imprescindible el control del volumen del material y el del diseño correcto de la matriz para poder conseguir un forjado con matriz cerrada que tenga las dimensiones y tolerancias deseadas. Un mal control del volumen del material puede ocasionar que coloquemos piezas brutas pequeñas y no llenen completamente las cavidades del dado o por el contrario las piezas demasiado grandes pueden producir presiones excesivas y pueden hacer que los dados fallen prematuramente o se aplasten.

Advantages and disadvantages of closed die forging

This forging process has a series of advantages and disadvantages.

-Advantages:.

-Disadvantages.

Forging force with closed die

The forging force γ required in a stamping operation can be calculated with the formula:.

Where K is a multiplicative factor. For simple shapes without burrs the value of K can range from 3 to 5, and with burrs from 5 to 8, for complex shapes with burrs the value can range from 8 to 12.

Yf is the flow stress of the material at the forging temperature, and A is the projected area also including the flash.

In hot forging operations the pressure necessary for most metals ranges from 550 MPa to 1000 MPa.

Precision forged

For economic reasons, there is currently a trend towards the highest possible precision in work operations, thus reducing the number of additional finishing operations. The operations in which the part is obtained with dimensions close to the final ones are called almost net shape forging or net shape forging. In this type of process there is little excess material in the forging that must be removed by grinding or punching.

In precision forging, special dies ensure that the final pieces obtain more precise dimensions than those obtained by forging with stamping dies, and they also require less machining. In this process, greater capacity equipment is required, since greater forces must be applied to obtain the fine details of the pieces. Since the temperatures and forces required are relatively low, aluminum and magnesium alloys are highly advisable for this type of precision forging. In addition, the dies wear less and a good surface finish is obtained; steels and titanium can also be used.

The main products produced with precision forgings are: gears, cases, connecting rods and turbine blades.

In this type of forging, special and more complicated dies are needed, a more exhaustive control of the volume and shape of the yew, precise location of the yew in the die cavity and, consequently, a greater economic investment.

However, less material is wasted and not as much final machining is required because the part is closer to achieving its final shape. Therefore, choosing between normal and precision forging requires an economic analysis, especially with regard to production volume.

The advantages of performing precision forging are:.

As a drawback we can say that:

Among the closed die forging processes we can highlight:.

To design the dies, it is essential to know the ductility and resistance of the part material, its sensitivity to temperature and deformation speed, the shape and complexity of the part and its friction characteristics. An important effect to take into account is the distortion of the dies under the large loads to which they are subjected during the forging process, especially if close dimensional tolerances are required.

The most important aspect to take into account when studying the design of dies is that the part flows in the direction with the least resistance, consequently the part must be shaped (intermediate shape) in such a way that it fills the die cavities well. The preforming of the part is of great importance, since in a well preformed or preformed part, the material must not flow easily towards the burr, the grain flow pattern must be favorable, and excessive slip must be reduced on the faces that are in contact between the die and the part to minimize wear.

To choose the shapes, great experience is required and good calculations of the cross section of the surface in each place where the forging is carried out.

Computer engineering techniques have been developed to expedite these calculations, as well as to deduce the pattern of material flow in the die cavity and defect formation. As a result of the material undergoing different degrees of deformation at different speeds and in different areas of the die cavities, the mechanical properties of each location are specific to the forging.

For most forgings or forged parts, the parting line is usually located at the maximum cross section of the part. For simple symmetrical shapes, it is normally a straight line in the center of the forged piece and for pieces with more complex shapes this line may not be in a single plane, which is why dies are usually designed in such a way that they lock during coupling to avoid natural thrusts and thus balance the forces while maintaining alignment during forging.

After sufficiently limiting lateral flow to ensure optimal filling of the die cavities, the flash material is allowed to flow through a conduit called a flash channel so that additional flash does not unnecessarily increase the forging force. A general guideline for burr clearances between dies is 3% of the maximum forging thickness. The face length is usually 2 to 5 times the thickness of the burr. Over the years, different designs of the burr channel have been studied.

Draft angles are essential on almost all forging dies, to help separate the part from the die once the forging operation is completed. When the piece cools, it contracts in longitudinal and radial directions simultaneously, so the internal exit angles become greater than the external angles. The internal angles vary from 7 to 10º and the external angles from 3 to 5º.

It is important to choose the proper transition radii at corners and bevels to ensure uniform metal flow into the die cavity and improve die life. In general, small radii should be disregarded due to their adverse effect on metal flow and their propensity to wear rapidly (as a result of thermal cycling and stress concentration). Additionally, small bevel radii can be the cause of die breakage due to fatigue. Thus, these radii should be as large as the design of the forging allows.

The dice can be assembled using inserts instead of being made in a single piece, and even more so if the shapes are complicated. This assembly method reduces the cost of manufacturing several similar dice. Inserts can be made from harder, stronger materials and can be easily replaced in the event of failure or wear in a particular area.

Tolerances must be provided in the design of the dies since machining of the forged part may be required to obtain the dimensions and final surface finish. These machining tolerances must be provided for holes, flanges and mating surfaces.

Most forging operations, especially for large pieces, are carried out at high temperatures. Common requirements for die materials are:.

a) great toughness and resistance to high temperatures.

b) ability to harden uniformly.

c) resistance to mechanical and thermal shock.

d) resistance to wear, especially abrasive wear, due to the existence of scale in hot forging.

The choice of suitable materials for the manufacture of dies depends on factors such as the composition and properties of the part, the complexity of the shape, its size, the forging temperature, the type of forging operation, the cost of the die materials and the quantity of forgings demanded. Another important factor is the transfer of heat from the hot piece to the dies with their consequent distortion.

The most common materials used to manufacture sockets are tool steels and for sockets that work at high temperatures, materials containing chromium, nickel, molybdenum and vanadium.

Dies are obtained from blocks, which are in turn forged from casting, later machined and finished to the desired shape and surface finish.

Failures may occur in the manufacture of dice due to reasons that will be described in the section: dice failure, where dice manufacturing methods are also described.

Lubricants are essential and influence friction and wear as a result of the required forces (equation 1) and the flow of metal in the die cavities. Another important aspect of the lubricant is that it can act as a thermal barrier between the hot part and the relatively cold dies, slowing the cooling rate of the part and improving metal flow. It also serves as a release agent as it prevents the forged piece from sticking to the dies.

A wide variety of lubricants can be used in forging. For hot forging, graphite, molybdenum disulfide, and sometimes glass are usually used. For cold forging the lubricants generally used are mineral oils and soaps, applied after conversion coating of the blanks. In hot forging the lubricant is usually applied directly to the dies, while in cold forging it is applied to the piece. The application method and uniformity of lubricant thickness are very important to the quality of the forged product.

Different manufacturing methods can be used to manufacture dice, singly or in combination. Among them are: forging, casting, grinding, machining, electrochemical and electrical die stamping methods. The process of obtaining the die cavities is usually punching, either cold or hot. It can also be used to make small sockets with shallow cavities. Generally the dice are heat treated to obtain greater wear resistance and hardness. If required, their contour and surface finish are improved with grinding and polishing, with programmable industrial robots or by hand.

The choice of manufacturing method depends on the operation in which the die is to be used, as well as its shape and size. Generally costs determine the process to be selected since these are important in manufacturing operations. Although the dice are small and relatively simple, they can cost hundreds of euros. However, because a large number of parts are manufactured using the same die, in general the cost per unit is usually only a small part of the manufacturing cost of the part.

Dice are usually classified as male and female or by size. Generally, small dice are those that have a surface area between 2 cm² to 1 m², while large ones have surfaces greater than 1 m².

The dies can be cast in steels, cast irons and non-ferrous alloys. The processes used range from shell molding (for small dice) to sand castings (for large dice weighing several tons).

In general, cast steels are preferred for large piece dies due to their strength and toughness and the ease of controlling their composition, properties and grain size. Depending on how they are solidified, cast dice, unlike forged or rolled metal dice, may not have directional properties; They may have the same properties on all their working surfaces; however, due to shrinkage, controlling dimensional tolerances may be difficult compared to machined dies.

Dies are generally machined from a forged block, with processes such as grinding, turning, milling, electrochemical and electrical machining. Machining can be complicated when the materials are high strength, hard, wear resistant, or those that are heat treated.

The operations can be time-consuming, which is why many non-traditional machining processes are used, especially on small or medium-sized dies since they are faster and more economical and the dies usually do not require additional finishing. Diamond dies, for fine wires, are made by making holes with a thin rotating needle coated with diamond powder and oil as a lubricant.

Socket steels are heat treated to improve hardness, wear resistance and overall strength. Poor heat treatment is one of the most common causes of die failure since it can distort them due to microstructural changes and non-uniform thermal cycles.

Proper selection of heat treatment temperatures and atmospheres, media, quenching, tempering practice, and handling are important. The sockets can be subjected to different surface treatments to improve their wear and friction characteristics. The condition and composition of the die surfaces are of particular importance.

After heat treatment, the dies are subjected to finishing operations, such as grinding, polishing... to obtain the desired finish and dimensional precision.

The grinding process can cause damage to the surface if not well controlled, due to the excess heat that can be produced, and can include residual stresses on the surface that reduce its fatigue life. Scratches on surfaces can act as a source of stress concentration. Likewise, die manufacturing processes can cause surface damage and cracks unless process parameters are thoroughly controlled.

These failures are generally due in manufacturing operations to one or more causes listed below:

a) inadequate design.

b) material defect.

c) overheating and thermal cracking.

d) inadequate heat treatment and finishing operations.

e) overweight.

f) excessive wear.

g) misuse and improper handling.

Proper design is very important. To resist the forces in manufacturing processes, a die must have adequate cross sections, clearances, and sharp corners. Bevels and radii, as well as abrupt changes in cross section, act as stress concentrators. Dies can be segmented, and prestressed during assembly to improve their strength.

The handling, assembly, installation and alignment of the sockets is of great importance. Overloading tools and sockets can cause premature failure. For example, a common cause in cold extrusion dies is a robot operator not removing the finished part before the other blank is loaded.

Materials used for sockets such as carbides and diamond, despite their hardness and resistance to abrasion, are susceptible to burring and elongation due to impact forces or thermal effects caused by internal temperature variations.

Even working fluids can negatively affect die and tool materials, for example, chlorine in lubricants, sulfur additives and coolants can damage the cobalt binder in tungsten carbide decreasing its strength and toughness.

Even if manufactured correctly, dice are subjected to high temperatures and high stresses during the process, which can cause wear and (consequently) shape changes. The wear of the dies must be taken into account since when they change their shape, the pieces produced will in turn have incorrect dimensions.

During use, dies can suffer thermal cracking, due to thermal cycling especially in die casting. To avoid this defect and eventual breakage in hot operations, the dies are usually preheated to temperatures between 1500 and 2500 °C. Worn or cracked sockets can be repaired with welding and metal depositing, which include lasers.

Sockets can be designed and manufactured with replaceable inserts when they wear or crack. The design and placement of the inserts must be carefully studied since any failure in these aspects can cause them to break. Die failures and fractures can be dangerous for manufacturing plant employees.

It is possible that the dice waiting in a drawer suddenly disintegrate, due to the state of large internal stresses of their components (residual stresses). The pieces that break are thrown away at high speed and can cause serious injuries. The dies must be surrounded by metal defenses that must be well designed and have resistance to contain the fractured pieces in case of failure.