During the last decades, MIM or “Metal Injection Moulding” has been confirmed as a very competitive technology for the manufacture of small steel parts of high precision and complexity, which would be very costly to produce by other processes.
Explanation of the MIM process for metal fabrication
- The feedstock is a material composed of very fine steel powder and a polymer that acts as a binder.
- This material can be injected into a metal mold as if it were a plastic, obtaining the “green piece“, which has the same shape as the piece we want to achieve, but is 20% larger in all its dimensions, since it still retains the plastic component.
- By attacking the green part with a catalyst, a phase called “debanding”, we cause the sublimation of the polymer, which is expelled in the form of gas. We call this intermediate state, in which the part maintains its initial dimensions but is porous and has very low mechanical strength, the “brown part”.
- During the last phase of the process, the temperature is raised (always below the melting temperature of the steel) in a protective atmosphere, activating sintering by mass attraction. The part decreases in size as its density increases, reaching values above 97% for the final dimensions of the “MIM part“, which often coincides with the finished part.
- Depending on technical requirements, MIM parts can be subjected to any type of subsequent treatments (thermal, surface, straightening, machining, polishing, welding, etc.).
- In 1993, ECRIMESA was the first company in history to develop this process in a continuous furnace, having at present 3 fully operational lines. Thanks to a wide range of automatic injectors with robotic handling systems that include artificial vision systems, high levels of productivity and quality are achieved.
Advantages and Disadvantages of MIM. Comparison with other technologies
- Generally speaking, any part that can be manufactured by plastic injection molding could be produced in steel by MIM, but there are some limitations or rules to keep in mind:
- Although at ECRIMESA there are parts in production up to 350 gr (“record” of the technology, still in force worldwide), MIM is a recommended process for parts under 100 gr and especially competitive below 40 gr. The weight reduction increases the precision of dimensional tolerances and reduces raw material consumption, which has a great influence on the total cost.
- The maximum allowable radius is recommended for all edges, especially internal edges, since sharp edges can be sources of potential cracks.
- Section changes should be gradual, facilitating the flow of material during injection and avoiding isolated masses.
- A flat face will facilitate the palletizing of the part inside the MIM furnace. The more stable this support is, the smaller the deformations will be and the more precise the dimensional tolerances will be.
Advantages and Disadvantages of MIM: Comparison with other technologies
- MIM is essentially a manufacturing technology for precision steel parts, with complex three-dimensional shapes, fine details, good aesthetics, demanding mechanical requirements and high consumption.
- It is colloquially known as “the enemy of machining“, because the tight geometric tolerances (±0.5%), low roughness (between Ra0.8 and Ra1.2) and high finishing quality (possibility of including threads, knurling, logos, etc. in the mold) greatly reduce the need for second operations to obtain a finished part ready for the corresponding assembly line.
- When the shape of the part in question allows it to be manufactured by traditional powder metallurgy (single shaft pressing + sintering), MIM may often appear uncompetitive. However, these types of parts are much more porous and fragile, so it is common for the application to force a switch to higher strength components such as MIM parts.
To learn more about MIM materials:
The most important factors in setting a cost for a MIM part are:
The MIM process does not have such an important variety of materials as other metal forming technologies. In the case of the Ecrimesa Group they are materials with commercial catalytic debanding.
The list of materials we can offer are:
The type of material has an important influence on the cost of the parts for two main reasons:
- Price of the material, which is more expensive in stainless steels (316L-174PH) than in carbon steels (42CrMo4-FN08), around 30%. In relation to the price of the materials, they are 10-15 times more expensive than the material coming from bar or ingot to melt.
- Sintering process, that must be at a slower rate in stainless steels, and in hydrogen atmosphere compared to carbon steels that are normally sintered in nitrogen atmosphere and with a sintering rate 30-40 % higher.
2.- Size and configuration of the part
The size is important, as it influences the weight mentioned above, as well as the sintering capacity, since the parts are processed in molybdenum trays of size 200*200 and the greater the number of parts that can be processed per box, the better the cost of this process, both in continuous furnace and in batch furnace.
According to our records, the optimum sizes of MIM parts are between 0.5 grms and 40 grms, although we have parts above 150 grms that, due to their configuration and the machining savings obtained, are profitable compared to other technologies.
On the other hand, and no less important, is the design of the part in order to adapt it to the limitations of the technology, to avoid secondary operations such as machining and to reduce its costs.
It is very important that the parts are not designed with sharp edges, and that they have as many radii as possible to facilitate the injection of the material, to avoid segregation during injection and to prevent cracks from appearing after the sintering process.
Likewise, they must have space for the placement of the injection point and homogeneous walls for a correct injection of the material (since it must be taken into account that steel powder will be injected with the difficulty that this entails since it is not an easy material to inject).
Designing the part with adequate areas for the part, to settle during the debanding/sintering process, also has a very important influence on the cost, since in case of not having flat support faces it forces to use special sintering supports, reducing the load on the furnaces and therefore not maximizing the cost advantage.
Finally, for carbon or low alloy steel parts that require heat treatments, it is of special importance to establish adequate placements for the performance of these heat treatments in order to avoid deformations during the heat treatments, or cracks generated by the heat treatment on the part. The Ecrimesa Group has its own facilities for heat treatments and adapts them to the requirements of the parts in order to maximize the cost and quality of the part.
Making a comparison between MIM and Microfusion of a potential part:
For an annual consumption of 45,000 pieces/year the cost study would be:
|PIECE||1 €||0,94 €|
|MACHINING TOOL||1.800 €||NO|
|MOLD||6.500 €||16.000 €|
Estimating the amortization of the tooling on the first 45,000 pieces, the result would be:
|1,72 €||1,29 €|
To learn more about this technology at Ecrimesa Group:
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.
Click here to the link:
At Ecrimesa we have studied the advantages of the Desktop Metal Studio System printer. We have elaborated a small summary, downloadable in this blog. Focusing on innovation, performance, economy and quality, we explain the particularities of this technology in comparison with the others existing in the market.
Producing thousands of different parts for customers in industries as diverse as automotive, defense, aerospace, textile and food around the world requires compliance with the highest existing standards.
However, this is not enough. It is necessary to be at the forefront of technology development. At Ecrimesa, we make use of the different technologies that lead the market, at the same time that we carry out constant studies with the purpose of breaking the paradigms of the market and to offer functional alternatives to the more and more demanding parameters.
To this end, we present you the Metal Studio Desktop System and invite you to download the detailed document it at the bottom of our blog. But before doing so, we would like to mention the key aspects that allow us to give more context to our work.
In an industry of sustained growth and demanding technical standards, the innovation factor is part of our essence. Therefore, we focus on the creation of new parts and modification of old designs. For this, it is necessary to have the latest technologies, which allow us to quickly give shape to new designs.
The study in question allows us to understand why the Desktop Metal Studio System is precisely the right one to constantly innovate.
By performance we mean the speed with which results are achieved through the Desktop Metal Studio System, without losing quality. In addition to this, we can create a wide variety of prototypes in a short time.
Comparatively low costs are maintained through Desktop Metal Studio System. Immediately, since the use of the technology saves production costs. And in the long term, through the creation of high quality prototypes, it is possible to plan the respective investments of each customer.
All of the above would be meaningless if the results did not meet the highest quality standards. The Desktop Metal Studio System rightly focuses on design to constantly improve quality. As you will read in the document, this technology brings the highest quality results in our industry.
We invite you to discover the Desktop Metal Studio System by downloading our document:
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.
Learn more about our technologies and installations:
Additive Manufacturing: comparison between studio system desktop metal, conventional filament and binder jetting printers
At Ecrimesa Group we have carried out in recent years an extensive benchmarking work on solutions and suppliers of 3D printers to implement 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.
In this study process, case studies have been carried out with Desktop metal’s Studio System printer and Binder Jetting.
These are our conclusions.
STUDIO SYSTEM DESKTOP METAL PRINTER
For a more precise evaluation of the quality that can be obtained with Desktop Metal’s Studio System printer, prototypes are printed in 17-4PH material with 3 different qualities and processed up to sintering to elaborate the analysis on metal parts.
|A||250 μm||0,05 mm|
|B||400 μm||0,15 mm|
|C||400 μm||0,3 mm|
Prototype A marks the most optimal surface quality that can be obtained with the machine, with 250µm nozzle and 0.05mm layer height, while prototype C reflects the least optimal quality of the machine, printed with standard 400µm nozzle and 0.3mm layer height. Prototype B reflects an intermediate quality between A and C. It is the most optimal quality that the standard 400µm nozzle can print.
The properties obtained after debanding and sintering are shown in the table below. The higher the surface quality (smaller nozzle diameter and layer height) the better density and structure we obtain. The larger the nozzle and layer height, the greater the printing defects resulting in low densities after sintering.
|PROTOTYPE||NOZZLE||LAYER HEIGHT||DENSITY||% C||HARDNESS|
|A||250 μm||0,05 mm||7,64 g/cc||0,03||288 HV10|
|B||400 μm||0,15 mm||7,60 g/cc||0,03||291 HV10|
|C||400 μm||0,3 mm||7,46 g/cc||0,04||192 HV10|
If the deformation of the prototypes is evaluated, we obtain the opposite effect. The deformation increases the smaller the nozzle and the layer height, obtaining prototypes that require subsequent straightening processes to achieveacceptable tolerances.
|A||250 μm||0,05 mm||0,17 mm|
|B||400 μm||0,15 mm||0,05 mm|
|C||400 μm||0,3 mm||0,01 mm|
It is important to find a balance between the surface quality obtained and the deformation of the sintered prototype.
Finally, a relationship is established between surface quality, printing time and price for each prototype studied.
|PROTOTYPE||NOZZLE||LAYER HEIGHT||DEFORMATION / OVAL||COST|
|A||250 μm||0,05 mm||0,17 mm||10,17 €|
|B||400 μm||0,15 mm||0,05 mm||9,83 €|
|C||400 μm||0,3 mm||0,01 mm||9,60 €|
CONVENTIONAL FILAMENT PRINTER
Ecrimesa Group has acquired in its facilities a conventional filament printer that, like Desktop Metal’s Studio System, uses FDM printing technology but differs in that the raw material is given in the form of filament instead of bars. The manufacturing technology is also defined in this case as FFF (Fused Filament Fabrication). The advantage of this printer over the Studio System is that it is a printer with open material, i.e., it is capable of printing filaments from different suppliers, including filaments developed for specific applications and uses. For this reason, Mimecrisa has been committed to the development of filaments in collaboration with the CDTI and a technology center (stainless steels, low alloy carbon steels, superalloys, etc), for more than two years for printing prototypes and processing within its facilities, in addition to being able to use commercial filaments that already exist in the market.
BINDER JETTING AT ECRIMESA GROUP
According to the evaluation carried out in Ecrimesa Group on the prototypes printed by Binder Jetting technology, it can be concluded that the final properties of the parts printed by this technology are the most similar to the MIM technology, if we compare the Additive Manufacturing techniques based on sintering. However, the investment required for the implementation of Binder Jetting technology is much higher than in the case of FDM technology. This is why we contemplate the subcontracting of Binder Jetting work whenever the project requires it, waiting for the technology to mature and settle before incorporating the purchase of the machinery to the group.
The following point lists some design recommendations to take into account before printing parts using Binder Jetting technology (source: www.digitalmetal.tech):
- Maximum length: preferably <50 mm in the longest side, but permissible up to the dimensions of the print box to scale. Tamaño mínimo: 1 x 1 x 3 mm.
- Minimum size: 1 x 1 x 3 mm.
- Corner R: 35 µm.
- Chamfer: 35 µm steps in Z direction.
- Resolution: 35 µm.
- Wall thickness: Preferably > 300 µm, up to 150 µm depending on area and design.
- Holes: > 200 µm.
- Surface quality: Ra 6 µm (without secondary operations).
CASE STUDIES BINDER JETTING PROTOTYPES
The sintering process is one of the most critical fundamental stages of the Binder Jetting technology. The sintering cycle must be optimized for each material to obtain metal parts with the right density, carbon and deformation. Sintering in unsuitable sintering cycles can result in problems of defects, deformations, wrong shrinkage factors, incorrect properties, etc. In this sense, Ecrimesa Group has a Know-How in the sintering process consolidated during years of experience. So much so that all the sintering tests of Binder Jetting prototypes carried out in Ecrimesa Group have better results of density, carbon and deformation than the prototypes received already sintered by the suppliers of printing machines.
|MATERIAL: 316L||MATERIAL: 316L||MATERIAL: 316L|
|PROVIDER||7,72-77 g/cc||0,011||0,01 mm|
|MIMECRISA||7,72-77 g/cc||0,003||0,01 mm|
|MATERIAL: 316L||MATERIAL: 316L||MATERIAL: 316L|
|PROVIDER||7,90-92 g/cc||0,011||0,20 mm|
|MIMECRISA||7,87-89 g/cc||0,007||0,14 mm|
|MATERIAL: 17-4PH||MATERIAL: 17-4PH||MATERIAL: 17-4PH|
|PROVEEDOR||7,63-65 g/cc||0,010||0,15 mm|
|MATERIAL: 316L||MATERIAL: 316L||MATERIAL: 316L|
|MIMECRISA||7,85 g/cc||0,004||0,01 mm|
At Ecrimesa Group we use Additive Manufacturing for:
- Manufacture of prototypes prior mold manufacturing with properties as close as possible to those obtained with MIM technology.
- Possibility of offering the customer design studies with prototypes prior to mold manufacturing.
- Acceleration of the MIM process by means of studies on prototypes (sintering positioning, sintering supports, study of deformations, defects, etc).
- Manufacture of short series of parts with complex geometry, whose investment in MIM molds is not appropriate due to geometric limitations or its cost.
If you are interested in knowing more about this process:
Even though the investment casting is an industrially fully developed process, its limits have been pushed during the last years towards producing larger and more complex pieces compared to the last decades. The following image shows the market positioning and development tendency of investment casting:
On the one hand, larger production volumes are being outsourced more and more to Asian countries, mostly because of the reduced prices for manual labour that still plays a very important role in the process. To cater to this necessity, Ecrimesa Group closed contracts more than 15 years ago with Asian providers and uses infrastructure in China in order to offer our clients this option if it benefits their projects. On the other hand, the area of application has expanded towards more complex pieces and smaller production volumes. Technological progress in both the materials and the machines has been crucial for this development, as well as simulation technologies that allow predicting the behavior of the pieces in the production process during th design phase and thus avoid problems in the production. As the size and complexity of the pieces has been evolving, the flexibility of production has increased in order to allow smaller series of complex parts. Ecrimesa Group offer projects of 20.000 pieces a week as well as smaller series of just 50 parts per year.
With these quipments, projects with pieces of more than 20 kgs with high metallurgic and dimensional requirements have been realized, for example for the energetic sector or oil and gas extraction, in stainless steel, certified according to AD2000 Merkblatt W0.
As well as aluminium parts.
Another relevant sector for investment casting is the automotive sector, where tha superficial and dimensional qualities reached through this technology allow for delivering fully-finished parts. This saves costs compared to other technologies and is applicable in a wide range of materials. In this manner, we develop projects for injection systems, in stainless steel:
EGR systems in stainless steel:
PowerTrain systems in carbon or low-alloy steel with heat treatment:
Locking systems for cabrios in carbon and stainless steel:
These are all fully-finished pieces, including machining, heat treatment and, if necessary, small assembling labors that allow the client to integrate the products seamlessly into their production processes, and with volumes of up to 1,000,000 parts per year. With our machining and heat treatment plants, we offer complete services to our clients for this type of projects, for stainless, carbon, or low-alloy steels. Currently, the machining sector is very important ofr our technology as well, as we can offer tailor-made solutions for designers in order to maximize the profit and efficiency of their facilities.
Other industrial examples for the appliaction of investment casting are machinges for the food industry. The high superficial quality reached through investment casting and the materials comply with the sanitary standards of the sector:
And lastly, a promising sector in the last year has been the defense sector, both military and civil, with diverse alloys.
Ecrimesa Group has the know how of more than 50 years and 9,000 projects developed for diverse industrial sectors, making us the perfect partner for any projects our clients might want to realize.
What is additive manufacturing?
Additive manufacturing, also known as 3D printing or rapid prototyping, is the fabrication of metal parts by using a 3D model and applying several layers of material to it.
Fabricating metal parts through additive manufacturing has become one of the most interesting technologies of the sector throughout the last decade – one the one hand, because it offers the possibility of prototyping for process and case studies, on the other hand through the option of fabricating complex geometric pieces directly. Additive manufacturing is the speerhead of an industrial revolution in different sectors, especially in aviation, heavy industries and the health sector, but also in automotion and the energy economy.
There are two groups of fabrication technologies for metal parts in additive manufacturing : fusion-based technologies, where the final part is produced by directly melting the primary material, and technologies that rely on sintering, where a green part is produced first, while the final product is obtained through de-binding and sintering. The following image shows the classification of additive manufacturing technologies according to ISO / ASTM 52900.
Depending on the pre-defined objectives, either FDM (Fused Deposition Modeling) or Binder Jetting technologies are selected to implement additive manufacturing.
Definition of FDM and Binder Jetting technologies
FDM and Binder Jetting are forms of additive manufacturing the most resemble the MIM process in terms of the specifics of the process and the final products.
When fabricating metal parts through FDM, powdered materials (metal and polymeres) are applied layer by layer through a jet. This technology can use filaments, pellets, or bars as primary material. After creating obtaining the green shape, de-binding and sintering are necessary to obtain the final product.
In Binder Jetting, layers of metal powder are applied to a printing model and mixed with polymeric materials which are applied through a jet. These polymeric glues have to dry and harden after each layer. After finishing the printing, a so-called “de-powder” process is necessary to remove the excess material and obtain the green part. Then, de-binding and sintering are necessary to obtain the final product. The de-binding process is less critical than usual in the Binder Jetting process as very little gluing material has to be applied between the layers. This makes it easier to remove the binders, but in turn also amkes the green shape more fragile and complicated to handle.
The heightened economic interest in additive manufacturing has resulted in the development of a very competitive market for 3D printers. At Ecrimesa Group, we have conducted an extensive benchmarking process over the last few years in order to evaluate providers of 3D printers and implement the technology in our facilities. After the comparative study based on characteristics such as the resilience of the green shape, surface quality, porosity, deformation and the costs of the printer, we selected the Studio System printer by Desktop Metal in order to implement additive manufacturing in the company. This enables us to explore new markets and create more added value for our customers.
STUDIO SYSTEM PRINTER BY DESKTOP METAL
|Main characteristics Studio System Desktop Metal|
|Primary material||Bars (cartridges)|
|Available materials at Mimecrisa||17-4PH, 316L, 4140|
Flowchart foe the fabrication of prototypes with the printer Desktop Metal:
How to use additive manufacturing in the fabrication of metal parts
The design of the pieces has to be adapted to the technology used for their fabrication. As with traditional technologies, additive manufacturing too has certain limits that have to be respected when designing the piece. This is why Desktop Metal has developed a set of ground rules for the design that have to be applied when developing the metal parts. These rules are recommendations – if the limits shown in the following table are not respected, problems might arise in different steps of production.
The Studio System printer is equipped with two printing heads for different printing qualities: a standard jet with a diameter of 400µm and a high definition jet with a diameter of 250µm. The design recommentations in the following table are sorted per jet.
|Standard jet 400µm||High definition jet 250µm|
|Maximum size of the parts||X 240mm Y 150mm Z 155mm||X 60mm Y 60mm Z 60mm|
|Minimum size||X 6mm Y 6mm Z 6mm||X 3mm Y 3mm Z 3mm|
|Minimum wall thickness||1mm||0.6mm|
|Maximum wall thickness||10mm||10mm|
|Minimum drill size||1.5mm||0.75mm|
|Minimum pin diameter||3mm||1.5mm|
|Minimum overhang angle||40º||40º|
|Thickness of layers||0.15-0.3 mm||0.05-0.15 mm|
|Minimum elevation||X/Y W 0.45mm H 0.50mm |
Z W 0.25mm H 0.50mm
|X/Y W 0.30mm H 0.30mm |
Z W 0.15mm H 0.30mm
|Min engraving size||X/Y W 0.45mm H 0.50mm|
Z W 0.25mm H 0.50mm
|X/Y W 0.30mm H 0.30mm|
Z W 0.15mm H 0.30mm
|Empty space between components||0.3mm||0.2mm|
In terms of the dimensional tolerances that can be reached with the printer, Desktop Metal guarantees the following values for the standard printing profile. The characterisation of the other printing profiles has yet to be determined.
|Diameter of pivot point||D||<65 mm||± 0.5 mm|
|Length||L||>65 mm||± 0.8% L mm|
|Distance between pivot points||S||>65 mm||± 0.8% S mm|
The obtained tolerances depend directly on the printing, de-binding and sintering processes. Dimensions of less than 65mm result in dimensional tolerances of ±0.5mm, bigger dimensions result in dimensional tolerances of ±0.8% of the measured height. These tolerances can be guaranteed when sticking to the design rules described here.
The surface finish is one of the most important aspects of additive manufacturing. As it is one of the main limits of the technology, further processes are necessary in many cases to obtain the desired surface quality. The roughness of the printed objects depends on the size of the jet as well as the thickness of the printed layers.
Business development strategy for additive manufacturing
These are the main goals of Ecrimesa Group in the implementation of additive manufacturing:
- Manufacturing of prototypes prior to the production of the mould with characteristics as close as possible to MIM-fabricated pieces
- Possibility of design studies with the client prior to the production of the mould
- Increase the speed of the MIM process through studies on prototypes (positioning during sintering, deformation studies, defects, etc.)
- Production of short series of metal parts with complex geometry that would be too costly to fabricate by MIM or whose form is too complex to produce by MIM
Metal Injection Moulding (MIM) is a suitable technology to fabricate small or medium-sized pieces with complex geometry. A variety of materials can be used (stainless steels, low-alloy steels, soft magnetic, tooling steel or ceramic materials). MIM combines the technique and versatility of plastic injection with sintering in order to fabricate metal pieces with high density and narrow geometric tolerances.
The following image shows the MIM process.
First steps. Fabrication of the mold: The molds employed in the MIM process are made of highly resilient steel, of complex geometry and more challenging than the molds used for plastic injection. When fabricating the hollow form, it is important to fator in the contraction of the material that will be injected, which means the hollow form has to be bigger than the actual desired piece. It is vital to stick to the design rules of the technology in this step in order to obtain a stable and immaculate product.
The number of hollow forms in the mold depends on the geometry and dimensions of the esired piece and can vary between one and ten hollow forms in total. The usual number of hollow forms lies between two and four, production time can vary between 15 and 60 seconds.
Feedstock or primary material: The primary material consists of a metal powder with a particle size of maximum 32 micrometers (at least 80% of the material must be smaller than 22 micrmeters), mixed with binders, and normally comes in the shape of pellets. The binders are made of thermoplastic, waxes, polymeres and other substances.
The characterization and control of the feedstock is crucial in order to calibrate the parameters of the following processes, especially the injection and sintering, and obtain the desired tolerances and repeatability.
Injection: Now, the feedstock is injected into the mold. The most important parameters in this step are precision, the flow volume and temperatures (of the injection head and the mold). The parameters of the injection have to be adapted to the geometry of the desired piece. The manufacturer’s know-how is vital for obtaining intact parts without internal defects. The piece obtained in this production step is called the “green part”. During the extraction from the hollow form, the material normally contracts for the first time (0.7 – 0.9% when using carbon or low-alloy steels, about 0.4% when using stainless steels).
De-binding: The binder that was necessary for the injection process now has to be removed. This de-binding can take place in several different ways: 100% thermical, water-based, with solvents or through a catalytic reaction. At Ecrimesa Group, we use catalytic feedstock, because it offers several advantages compared to other methods – especially the speed of the process. The catalytic reaction is produced under controlled conditions with N2 and nitric acid with a temperature of 120ºC. During this proces,s the main component of the binder, POM, passes from a solid to a gaseous state and leaves the green form in a very fragile state, called the “brown” state.
The de-binding process can be carried out in vaccum batch furnaces or continuous furnaces. The advantages of using continuous furnaces are that manual handling is avoided and the brown state can be transferred directly to sintering. During this process, the piece is especially unstable and very susceptible to deformation and other damages, which makes the absence pf manual handling an important factor for the reliability of the process. Ecrimesa Group have both types of facilities at our disposal.
During this phase, a small part of “secondary” binders remains in the brown state, keeping it in its shape. These secondary binders are removed an the begining of the sintering process.
Sintering: The sintering is the last steps of the process, during which the desired density is aquired by interdiffusion of the metal particles due to thermal reactions and fase (H2 or N2, depending on the type of alloy). The pieces can be sintered in vacuum batch furnaces (especially suitable for small production volumes or special materials) or in continuous furnaces (more suitable for bigger production volumes). At Ecrimesa Group, we have 3 continuous furnaces and vacuum batch furnaces at our disposal. The positioning of the parts during the de-binding and sintering can alter the dimensional results, which is why the phase of definition and industrialisation is very important to obtain a robust and reliable process.
During the sintering, the second and definite cotraction occurs, resulting in the final dimensions defined before the beginning of the process. With carbon and low-alloy steels, the contraction factor between mold and final piece amounts to 1.2165, and 1.205 between the green form and the final piece. With stainless steels, the contraction factor is 1.166 between mold and final piece, and 1.160 between green part and final product.
Last steps and termination: After sintering, the product might require further operation of machining in ordr to meet the requirements of the client. Ecrimesa Group owns a modern facilty for heat treatment, allowing us to offer completely finished products. The machining can be processed in-house as well, for instance when pickling or polishing should be needed.
Our ample experience of more than fifty years in this area enables us to find synergies between the MIM and investment casting process.
Investment casting is among the oldest industrial manufacturing processes still being applied today. Its history can be traced back to 4,000 BC. At this time, bee wax and other animal greases were used instead of synthetic waxes employed today. Samples of sculptures crafted with investment casting have been found in Europe, Asia, Africa, and South America. It took until the 20th century to develop the technology industrially – 400 patents were registered between 1900 and 1940, especially in the defense and health sectors.
Many materials are suitable for investment casting: stainless steel, alumnium, carbon steels, brass or glass. The process is based on inverting the desired material in a hollow mould inside the breaking material. This hollow mould is an exact copy of the desired final piece. Due to certain characteristics of the breaking material, the superficial quality of the piece is very high, reducing the need for secondary operations.
The first step consists in fabricating a metallic mould (mostly made of aluminium or steel), into which wax is injected in the form of the desired final piece. In order to maximize the yield, this form is then melted together with other identical units, allowing to continue working with conjunctions of units. The configuration of these conjunctions is crucial to control the process and cost across the whole production.
The conjunctions are then coated with several ceramic shells until they have reached the necessary resilience for the following process steps. The integrity of the process depends on the employed materials as well as the temperature and air moisture in the work rooms and the drying process of each ceramic shell.
As soon as the desired ceramic structure is reached, the wax is removed with an autoclav, using the correct pressure and temperature settings and taking care that the ceramic shell is not damaged – creating the ceramic hollow mould. The desired final material is injected into the hollow mould and, after it has hardened, the ceramic shell is removed by vibration and shaking processes. Eventually, the single units are separated and the necessary end operations effectuated to correspond to the clients’ wishes.
The main advantages of investment casting are:
- Freedom of design: Produce complex pieces, even wit complex inner structures.
- Cost advantage: Produce pieces with precise finish and tailor-made design, lowering the weight of the pieces.
- Repeatability: By repeating the production units, homogeneous quality can be safeguarded.
- Versatility: Produce an ample variety of alloys.
- Flexibility: With investment casting, you can produce very small volumes of a few hundred pieces as well as higher unit numbers up to several millions.
Maybe, you can count among the disadvantages of investment casting that you need to produce a mould for each final piece, as well as high working efforts. Compared to other, faster technologies such as MIM, investment casting takes more time. These factors, as well as the limits of the pieces’ sizes that the technological equipment of the manufacturer can impose, make it necessary to examine in detail which tecnology is apt for producing a certain piece.
The Ecrimesa Group is looking back at more than fifty years of experience in the realm of investment casting. With more than 2,000 projects in our portfolio, we have a rich experience in producing carbon and stainless steels.
We have our own office for any adjustments of the design and the fabrication of prototypical moulds, enabling us to offer our clients complete consulting services in order to adapt their design perfectly to the process of investment casting. Our designers and metallurgic engineers use simulation softwares like Magma Soft and Inspire Cast.
We use 3D printing for rapid prototyping without having to produce the mould directly, which is very beneficial at the beginning of the process, when the customers’ vision of the desired piece is not complete yet and different samples have to be examined before making the final decision on the mould. This avoids the necessity of producing a mould for each sample, avoiding extra costs.
We have our own metallurgic laboratory with more than eight technicians, where me conduct continuous controls if the melting process and heat treatments. Moreover, we can conduct X-Ray scans, digital tomography, corrosion controls and material examinations.
In 2005, we incorporated a machining plant into our company group in order to offer our clients fully finished pieces. Internalizing all machining processes enables us to offer more versatility in the design phase as well as the finished yields.
Following this philosophy, we also have our own facilities for heat treatments, with 4 lines for hardening and tempering, including stanradized carbon control, 3 lines for hardening and a line for aluminium T6 treatments, all of them CQi-9 certified. With us, the customers receive everything out of one hand, from the design and planning up to the final piece – always with maximum quality.