Nowadays there is a wide range of possibilities for the production of parts made of steel and other materials at industrial level. This range extends from machining to MIM (Metal Injection Moulding) through more classical techniques such as investment casting. In this article we will explain the different techniques for manufacturing metal parts.
Different technologies for the manufacture of metal parts
Broadly speaking, metal parts manufacturing technologies can be classified into the following technological areas:
- PM (Powder Metallurgy) or Powder Metallurgy.
- Forming: Forging, stamping, extrusion, rolling, etc.
- Casting, in its different aspects: Investment casting, sand casting, mold casting, vacuum casting, etc.
- Metal Injection Moulding (M.I.M.)
- 3D Printing (Additive Manufacturing)
All these technologies bring to the market different solutions and approaches to the challenge of mass production of parts.
The following is a brief description of each of them:
It is the process of compacting fine powders of the chosen material to give the required geometry. This compaction is done through hydraulic or pneumatic presses. This is followed by a sintering process in a muffle in a controlled atmosphere to avoid oxidation. The main disadvantages of this technology are its improvable precision and the fact that high densities are not achieved and, therefore, the mechanical properties obtained are very limited.
Depending on the forming system and whether the process is hot or cold, there are different variants. The main ones are:
It consists of the deformation of red-hot metal through impact and pressure.
In this case the deformation is done through pressure between 2 dies or molds.
It can be done hot or cold and consists of pushing the material through a die that has the desired shape.
In this case the objective is to reduce the thickness by using pairs of rollers.
It consists of the set of operations that, by cutting and chip removal, are used to obtain the dimensions and specifications of the parts, through different operations and abrasion and cutting tools. In the case of obtaining the part with 100% machining, there is an obvious waste of material and tools, in addition to the time required. However, it is a complementary technology (and in many cases necessary) to obtain the required finishes of a part.
It is a technology used since ancient times that consists of melting the metal at high temperatures to pour it into a mold and let it cool. The main variants of this process are the:
As its name suggests, the casting is poured into a mold made of refractory sand. It is used in large pieces since the mold is destroyed.
Investment casting or lost wax casting
It consists of the injection molding of the wax part. From this wax part, the ceramic molds are created where the chosen steel or other metal (for example, aluminum) will be cast. It is one of the main manufacturing processes in Ecrimesa Group.
Valid for low melting point metals such as aluminum, where the liquid aluminum is injected into a mold and a high clamping force is applied to the two semi-molds. It is a process suitable for the production of large series.
Metal Injection Moulding
This is another of Ecrimesa Group’s main processes. It is the injection molding of a mixture of steel powder and plastic material. In a subsequent process, the polymer is eliminated to obtain the steel part. Ideal for small parts of complex geometry that require high accuracy and surface quality.
3D Printing (Additive Manufacturing)
It is the newest process of parts manufacturing that continues with the advance of 3D printing technology so present nowadays. In Ecrimesa Group we have implemented this technology both in the manufacture of prototypes prior to the manufacture of the mold and to accelerate the MIM process through the study of prototypes of the final parts. Also, short series of parts with complex geometry are produced with Additive Manufacturing.
Investment Casting and MIM at Ecrimesa Group: advantages over other processes
Ecrimesa was the first company in the world to install a continuous furnace for the MIM process and we have more than 50 years of experience in investment casting. Today, the combination of these two technologies provides a number of advantages over manufacturing by a single technique.
- Flexibility in the range of part sizes and quantities. It is possible to make both long series of small parts (with MIM technology <1 g) and smaller quantities of larger parts (e.g. >20Kg) and high added value.
- High precision in complex three-dimensional shapes, tight dimensional tolerances and high surface quality.
- Large catalog of steels, especially in investment casting, arriving, in some cases practically à la carte and/or customized for specific customers. All this is complemented with the performance of heat treatments “in house”, which allows to widen the offer of metallurgical properties of the parts.
- In the case of the new Additive Manufacturing technologies, they are not currently in competition with the MIM process. In fact, they are complementary since there are still very few materials available on the market, with a high price.
The importance of machining
All the advantages of Investment Casting and MIM are completed with machining operations within the same manufacturing process.
Because of the versatility and material flexibility of investment casting, machining can be the ideal solution for delivering parts directly to the assembly line. These machining operations are usually quite straightforward, as the precision of the investment casting part is already quite high.
In the case of the MIM process, these machining operations are more unusual given the intrinsic precision and surface quality of the process. Even so, in very specific cases, machining operations, usually simple, are performed.
What is the best technology for manufacturing metal parts?
All technologies have advantages and disadvantages; there is no one better than another, the most important thing is to choose the one that best suits the needs required by the project, both in metallurgical and dimensional terms and even aesthetics. In some cases, the combination of several is the best option.
In Ecrimesa, we advise and accompany our customers in every step of the production, from the design of the part and the selection of the most appropriate technology for manufacturing, to machining and final heat treatments.
Ecrimesa Group has the latest machinery and qualified personnel to develop manufacturing projects of steel and aluminum parts by investment casting, MIM, machining and additive manufacturing.
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The use of MIM technology has experienced exponential growth over the last decades, establishing itself as the most important technology in the manufacturing processes of metal parts. However, it is possible to find in FDM and Binder Jetting complements to this technology, so they should not be seen only as competitive processes.
MIM (Metal Injection Moulding)
MIM (Metal Injection Moulding) technology is a metal parts manufacturing technology that combines powder metallurgy with plastic injection molding technology. The raw material used is a mixture of metal powder and polymers called feedstock. This material is fed into a mold with the desired geometry by means of an injection machine similar to the one used in the plastic injection molding process. This results in the so-called green part, which is subjected to a chemical-thermal process called desbanderization, the purpose of which is to extract the binder from the part, thus obtaining the brown part. The part is then subjected to the sintering process, so that the particles are joined together to form a high-density metal part with tight dimensional tolerances. MIM technology is suitable for manufacturing parts of complex geometry, small to medium size, and a wide variety of materials are available, such as stainless steels, low alloy steels, soft magnetic, tool steel, ceramics, etc.
FDM (Fused Deposition Modeling) printing technology, also known as ME (Material Extrusion) or FFF (Fused Filament Fabrication), is the process by which parts are manufactured layer by layer by depositing extruded material (metal powder + polymers) through a nozzle similar to those used in plastic filament printers. This technology can use filament, pellets or rods as raw material and, once the green part is printed, debanding and sintering processes are needed, as in MIM technology, to obtain the final metal part.
The manufacturing process of the Binder Jetting technology is based on the deposition of a layer of metal powder on a printing platform and the agglomeration by deposition of polymeric material through a nozzle. Subsequently, polymer curing processes are necessary in each printed layer and, once the printing is finished, the so-called de-powdering process to remove the remaining powder and obtain green parts. Finally, debanding and sintering processes are needed to obtain the metal parts. The debinding process in parts printed by Binder Jetting is less critical than usual, because the amount of binder deposited at the layer junction is minimal. This results in easy removal of the binder from the green part, but at the same time makes the printed green parts fragile and difficult to handle.
Characteristics compared between Binder Jetting, FDM and MIM
Although in many articles you can find comparative graphs of technologies where we see overlap between MIM technology and some printing technology, especially Binder Jetting, the reality is that today Additive Manufacturing and MIM are not competitive technologies but complementary. Some fundamental differences between the two technologies are defined below.
Although part developments are much faster in Additive Manufacturing compared to MIM, mainly due to mold manufacturing, post-mold part production becomes faster in MIM technology compared to printing technologies.
Differences in porosity and microstructure
Large porosity associated with printing defects may appear, especially in parts manufactured by FDM. This can lead to lower metal part densities than those obtained by MIM. In addition, the nature of the metal powder used in manufacturing can generate incorrect microstructures that require subsequent heat treatments to improve it.
Portfolio of materials
MIM technology is much more versatile in terms of the materials available for manufacturing metal parts. Keep in mind that Additive Manufacturing technologies are in the midst of development and their material portfolio is likely to increase as the technology matures. As of today, the portfolio of materials available in printing technologies is limited to stainless steels, some tool steel and few other materials.
Increased roughness in Additive Manufacturing techniques. Necessary secondary finishing improvement operations to compete with MIM. In Ecrimesa Group we guarantee sintered roughness between 0.8 and 1.6 Ra.
Possibility of manufacturing more complex parts (hollow parts, bionic geometries, counter-flanges, etc.) and larger parts in Additive Manufacturing technologies.
MIM and Additive Manufacturing technologies working in different market sectors
Although Additive Manufacturing technology is constantly developing and there may be variations, it seems that this manufacturing technology is positioning itself primarily in the medical, industrial and aeronautical sectors.
The results of a comparative study of mechanical properties (tensile test) of sintered 17-4PH specimens are shown. Tensile specimens are manufactured according to ISO 2740 Sintered metal materials (excluding hardmetal) according to the different technologies and printers described in the following table.
|Technology / Printer||Density (g/cc)||Hardness (HV10)||Ultimate tensile strength Rm (MPa)||Yield strength |
|FDM Conventional 3D printer||7,53||271||811||749||6,4|
|FDM Desktop Metal||7,57||274||852||806||3,2|
|ISO 22068 |
All the mechanical properties obtained are within the ISO 22068 “Sintered metal injection molded materials specifications” for sintered 17-4PH steel, with the MIM technology showing the best mechanical properties.
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Which is the better technology for manufacturing metal parts, MIM or Investment Casting?
Compared to investment casting, which represents one of the oldest applied metal molding processes, Metal Injection Moulding or MIM is a relatively new technology. MIM technology became known in the 1980s – however, even in the 1990s, many companies involved in the manufacture of metal parts were still using investment casting. Especially in the 1980s, there were still doubts about the metallic integrity of parts produced by MIM, which was mainly applied in the manufacture of plastics. To this day, investment casting is considered as the main precision technology, and MIM as a complementary technology that is mainly used for the manufacture of small parts.
Similarities and differences between Investment Casting and MIM
Both technologies are applied to manufacture small-sized parts that are notable for a more complex structure or design and therefore traditional industrial technologies such as forging cannot be used. There may even be parts that need both technologies, investment casting and MIM, to be manufactured correctly.
One of the main differences between investment casting and MIM is the materials to which they can be applied. In general, the investment casting process allows for a wider variety of materials, as the MIM process can only be performed with alloys of a higher melting temperature. Materials such as aluminum, for example, do not work efficiently with MIM.
When to use each technology?
In addition to the materials to be processed, the decision between microfusion and MIM depends on other basic factors:
- In addition to the materials you want to work with, the decision between investment casting and MIM depends on other basic factors: the size of the part, the complexity of the structure and the tolerances it allows, as well as the number of parts you want to manufacture. The ideal part for the MIM process has a length of less than 100 mm and is produced in batches of more than 5000 pieces.
- In general, we can say that most of the parts with a final weight of less than 15 grams (depending on the material) are produced with MIM, since this technology allows thinner structures and has a higher efficiency in the use of materials and energy. However, there are still designers who, even for smaller parts, rely more on investment casting, as it is still considered the most robust technology.
- Traditionally, at Ecrimesa Group, 90 percent of the parts weighing more than 100 grams are manufactured with investment casting, since, at that size, the cost of the fine powder used in the MIM process is too high, as well as the energy required to produce them. However, due to the experience accumulated with MIM and the quality of the materials used, more and more references weighing more than 100 grams have been manufactured in recent years. The supply of tools required for MIM (e.g. injection molding machines) has also improved, allowing the technology to be applied in more cases. In any case, using investment casting, parts weighing up to 25 kg can be produced, whereas, with MIM, the maximum weight of the final part is 250 grams.
- Finally, there are some additional criteria for deciding between investment casting and MIM. In general, it can be said that the development and production process of new parts is shorter with MIM, since there is no obligation to make several molds and prototypes before starting production, which may be necessary when working with investment casting. In addition, the final part design that starts the MIM process is closer to the final part, and machining processes are saved – typically, parts manufactured with MIM have a very high surface and finish quality.
MIM and Investment Casting at Ecrimesa Group
At Ecrimesa Group we have facilities for both investment casting and MIM, and we also have a design office, where manufacturing processes can be simulated and technical advice is offered on which technology to choose to manufacture a specific part.
We also take advantage of the synergies between the two technologies. Having internalized almost all machining processes, we can accompany and support the customer in all manufacturing steps, from the idea and design to the last steps of the final finishing, including, of course, the choice between the technologies that can be applied.
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