The production of many things, even in an era when we are surrounded by incredible innovations that we take for granted today (electronics, cars, airplanes), requires a lot of time, money, and planning. Teams of designers and engineers develop parts using existing technologies for their production on equipment that can be seen in factory workshops, which turns raw materials into finished parts. When there is a need to manufacture a metal part, most manufacturers around the world start with a workpiece in the form of a rod or sheet material. Then, skilled workers use subtractive machines to remove excess material volume by turning, milling, drilling, etc., until the final shape is achieved. Next, these processed metal parts are delivered to customers around the world, where they are assembled into the final product. This traditional system of manufacturing metal parts is full of problems and compromises. This is because almost all traditional processing technologies have their own characteristics and limitations: in the geometry of the parts to be manufactured, in the time required for their production, and in the cost of converting raw materials into the desired object. Often, due to these limitations, engineers have to manufacture multiple elements separately and then weld, glue, or assemble them into a finished product. This happens simply because the designs of many parts cannot be manufactured as a single whole using conventional methods. Another significant disadvantage of traditional subtractive technologies for manufacturing parts is that a large amount of waste is generated during the processing process, which must be recycled or disposed of in landfills. It is estimated that in the aerospace industry, about 90 percent of the material purchased for the manufacture of metal parts becomes waste after cutting, turning, milling, and grinding operations necessary to obtain the final part in the required dimensions. By weight, after all processing operations, the metal material in the aircraft design accounts for about 10 percent of the originally purchased material, and the rest is sent to waste. And although most manufacturers strive to minimize costs by recycling waste, working with them is an integral part of the traditional production approach and significantly increases production costs. Unfortunately, these technological limitations hinder everyone. Designers, engineers, manufacturers, and consumers face these limitations every day. Traditional manufacturing of complex parts from smaller components often leads to suboptimal characteristics of the final product, adding unnecessary weight and changing its properties. Such a traditional approach to manufacturing metal parts of various purposes does not allow the world to create more innovative and safe products. In addition, such production technologies often limit the feasibility of manufacturing products in close proximity to their use. This is because traditional technologies require significant investments in equipment and centralized placement of production facilities, which can lead to supply chain problems that can become critical. And, as the COVID-19 pandemic has shown, it can lead to a situation where what is needed is not available at the moment when it is most needed. Undoubtedly, it's time to modernize the global system of manufacturing metal parts using additive technologies for their production.
“Additive manufacturing” or “Additive manufacturing, abbreviated as AM” - is the official industrial term (ASTM F2792). The roots of this new approach date back to the 1980s, and after decades of development, AM is finally ready to undergo revolutionary changes thanks to the technology of jet processing with a binder. Large and small companies from various industries around the world have already begun to realize the benefits of jet processing with a binder in the manufacture not only of finished metal parts but also in the more efficient production of tools and equipment for traditional subtractive technologies.
One of the many technologies of additive manufacturing, called the technology of jet processing with a binder (Binder Jetting, abbreviated as BJ) or 3D printing with a binder, is the key to more efficient production of metal parts. Jet processing with a binder allows for the high-speed production of metal parts without the use of lasers or other tools that are expensive and mostly take a significantly longer time to produce parts. Instead, jet processing with a binder uses an industrial printing head with multiple nozzles, which allows for the rapid application of a binder substance to thin layers of metal powder, sand, ceramics, or composite materials. This high-speed process is repeated layer by layer, forming the part in height until the shape of the object is created according to its digital model from a CAD design file. The process of jet printing with a binder is very similar to simple ink printing on paper, where each “sheet” represents a very thin layer of powder, usually 30-200 microns (μm) thick, and the “ink” is the binder substance (a specially designed chemical composition) that is applied by the printing head to this layer and interacts with the used metal or other powders.
The stage of final sintering is not new in the world of metal processing. In fact, it is identical to the process of producing metal parts using metal powders and binders on the markets of metal casting under pressure (MIM) and press sintering (PM) applied for over 40 years. In these processes, metal powder with a binder is either injected into a mold or stamped in a mold using a press and extracted for final sintering. These processes are reliably used in the electronics, medical, and automotive industries for over 40 years. The main difference between jet printing with a binder and MIM or PM is that metal parts manufactured using 3D printers do not require a mold, which provides greater design freedom. Today, metal parts manufactured by jet processing with a binder have better final density than after stamping or sintering, and, depending on the specific material, equal or superior density to parts manufactured by MIM.
Powder laying
The device for applying powder (spreader) first lays it out in a thin layer on the surface of the working platform in the building chamber.
Applying liquid binder
Industrial jet printing heads, moving together with the portal on which they are installed, bind particles in the necessary places by selectively applying a binder to the layer of powder. The type of binder depends on the type of powder material used.
Lowering and re-laying
After applying the binder, the working platform is lowered for laying the next layer of powder. Re-laying is an important stage in binder printing, as the powder must be applied accurately, compactly, and continuously to produce high-quality and accurate parts. Regardless of the size of the particles used, dense powder laying is an important factor for the successful application of the binder.
Repeating layers
After completing the laying of the next layer of powder on the working platform, selective application of the binder to this layer begins. This sequence of re-laying powder and applying a binder is repeated until the part is ready.
High-speed layer printing
3D printers using the capabilities of a jet printing head with multiple nozzles for applying binders can print a full layer in a very short time. This is one of the main advantages of jet printing over other methods of additive manufacturing.
Finishing printing
When the printing task is completed, the part can be removed from the building chamber. Depending on the material used as a binder, additional stages of curing and post-processing may be required. Metal parts usually require hardening and sintering.
Binder Jetting technology opens up new opportunities for the application of 3D printing, especially in mechanical engineering. This method allows for the production of parts with complex geometry, reducing their weight and solving complex engineering problems. One of the main advantages of jet processing with a binder is the high efficiency of material use. In the printing process, only the necessary amount of powder is used, and the remaining unbound powder can be recycled and used up to 16 times, which allows achieving a total material efficiency of up to 96%. Jet processing with a binder also has a significant advantage that other additive technologies can hardly offer. It allows for mass production with a speed and cost comparable to traditional production technologies. This technology is becoming a key to creating decentralized metal processing and mechanical engineering ecosystems, which allows for the production of products closer to the place of consumption, reducing logistics costs and increasing productivity. Moreover, this solution helps minimize waste of primary materials and transition to a digital model of storing primary material reserves, which increases flexibility and production efficiency. Binder Jetting offers unique opportunities for the mass production of metal parts, combining high performance, low costs, and minimization of waste. This method is becoming increasingly popular, opening up new opportunities for the development of modern production ecosystems. Today, more and more companies are using Binder Jetting technology in mass production. For example, German automakers have successfully applied this method for the production of casting molds from sand in the production of engine components for cars. The foundry industry has been using jet processing with a binder for the serial production of sand molds and cores for over 20 years, which proves the reliability and effectiveness of this technology.
To understand how jet printing with a binder allows for the implementation of the concept of mass production and why other methods of 3D printing metals do not fully cope with this task, it is necessary to delve deeper into the ecosystem of 3D printing metal parts. In general, additive manufacturing is a process of creating an object, usually directly from 3D model data, layer by layer; it is opposite to subtractive manufacturing, where parts are cut out from a larger amount of material than is required in the end. However, there are many ways to perform layer-by-layer 3D printing of metal parts, each with its advantages and disadvantages. ASTM classifies the AM process for metals - a type of 3D printing that emerged in the mid-1990s - into six categories. The most developed methods presented on the market today are material extrusion, laser powder bed fusion, binder jetting, and directed energy deposition. However, new metal AM methods are constantly being developed, categories are being combined, or completely new approaches are being created within known categories. Today, many of the most developed 3D printing methods are well-suited for the production of single prototypes or even mass production. But in general, most of them are too time-consuming. For fast and cost-effective mass production of thousands or millions of parts, 3D printing takes too much time and, therefore, is too expensive. The main reason is that in most 3D printing methods, one point (usually a nozzle or laser) is used for layer-by-layer construction of the part. Even in the case of applying several lasers in one additive installation, it still cannot compete with the speed of jet printing with a binder.
In most metal 3D printing technologies, one point is used, for example, a nozzle or laser, or (what is more expensive) several separate points. The technology of jet printing with a binder with a moving portal with printing heads with multiple nozzles is one of the few methods of additive manufacturing of metal parts that allows for fast filling of a layer, printing over the entire area. And this allows increasing the printing speed and reducing costs, which is very important when transitioning from prototyping and small-batch production to large-scale production. Jet printing technology allows for faster creation of parts using relatively affordable industrial jet printers, which quickly create all layers of the part in one pass at a lower, often room temperature, until the final sintering process. This gives advantages compared to laser processes, where the part is essentially melted and cooled during assembly, and requires additional considerations regarding subsequent processing and microstructure. While many 3D printing technologies allow for the creation of monolithic complex parts that solve complex problems (for example, reducing the weight of car parts), jet printing with a binder is one of the few technologies that can provide such solutions in mass production and make it accessible.
While each 3D printing process has its advantages, jet printing with a binder is one of the few solutions that can be used for both the production of single prototypes and parts, as well as for mass and serial production. The technology of applying a binder is also surprisingly flexible in terms of material use. In fact, with the right choice of binder and process parameters, almost any powder can be processed. Today, droplet printing with a binder allows for the production of parts from a wide range of metals, various types of sand, metal ceramics, as well as ceramics and gypsum. Industrial jet printing systems with a binder can use over 20 different metal alloys in the following categories: - Aluminum alloys - Carbides - Copper + copper alloys - Nickel alloys - Nitrides - Oxides - Metal alloys - Refractory metals - Stainless steels - Titanium alloys - Tool steels As mentioned earlier, for certain types of materials, certain types of binders and their feed/transport systems may be required. This depends on several factors, including the methods of powder feed and laying, the type of printing head capable of working with a specific chemical composition of the binder. For some materials, such as aluminum and titanium alloys, installations with an inert or controlled environment in the building chamber are required. Jet printing with a binder is best suited for the production of parts where production volumes, complex configuration, and high detail are important. The technology of Binder Jetting has its advantages in such areas as the production of: - Metal parts of AM, which: are already manufactured on 3D printers using other additive technologies, such as laser powder bed fusion or material extrusion, and which are striving for more affordable or mass production - Parts with constructively complex configurations: products with complex internal channels or cavities for transporting gases, liquids, or semi-liquids, for example, used in the oil, gas, or food industry - Heat exchanger components and electric vehicles: parts that transmit thermal energy or electricity, especially in heat exchangers and electric vehicles - Complex assembly units: combining several segments of the structure into a single monolithic part to increase performance by reducing the number of operations or to reduce the weight of the entire structure - Lightweight parts: reducing the weight of parts while maintaining the ability to withstand the necessary loads, which is not available for traditional technologies - Mass-produced products with individual design: such as medical products and prosthetics, where each design iteration can be adapted individually for a specific patient without significant costs - Parts that require a reduction in production time to accelerate the production cycle: luxury goods, belt elements, bag fittings, etc. - Parts produced using MIM technology: Binder Jetting allows for the economical production of parts produced using MIM (Metal Injection Molding) technology with their size standards, as well as larger parts
