DE112022004072T5 - BINDERS FOR BINDER JETTING ADDITIVE MANUFACTURING PROCESSES - Google Patents

Abstract

The present invention relates to binders for use in binder jetting metal additive manufacturing (BJAM) processes.The present invention relates to the use of resins formed from certain chemicals and their use together with a binder consisting of chemicals which regulate the rheological properties such as chemical properties, viscosity and surface tension. These are responsible for binding metal powders in a way that the molded article to be formed from metal powders does not lose its shape.

Description

Technical area

The present invention relates to binders for use in binder jetting metal additive manufacturing (BJAM) processes.

The present invention relates to the use of resins formed from certain chemicals and their use together with a binder consisting of chemicals which regulate the rheological properties such as chemical properties, viscosity and surface tension. These are responsible for binding metal powders in such a way that the molded article to be formed from metal powders does not lose its shape.

State of the art

Today, Binder Jetting Metal Additive Manufacturing (BJAM) is generally used for parts such as pumps, turbines, heat exchangers, filter systems, powertrains, some prosthetics, etc. The BJAM process is generally preferred in these fields as it provides corrosion resistance, high wear resistance and strength to the parts. It is a much faster and less expensive manufacturing process as compared to other metal additive manufacturing processes. The additive manufacturing process is defined as manufacturing an object layer by layer. Various processes and technologies are used to produce the layers. This process basically uses two raw materials. The first is a powder, the second is a binder. In the process, the binder is sprayed onto the powder in a certain layer thickness. The binders are sprayed from binder print heads (piezoelectric print heads, etc.). Energy sources such as heat, light, etc. are used to partially dry/cure the binder. The resin does the main binding work in the binder. The binder content may include other chemicals in addition to resin. The rheological properties of the binders (viscosity, surface tension, etc.) must be between the operating values of the print head. Along with the resin, which performs the main task of binding, other chemicals can also be used while adjusting the rheological properties. The BJAM process is a novel and evolving additive manufacturing process. It is only available on the market as a brand from certain companies. In addition, it was mentioned that BJAM offers opportunities for mass production in the automotive sector compared to other additive manufacturing processes. Parameters such as powder selection, type of powder material, alloying elements, particle size and powder geometry are important for producing denser and stronger samples in the BJAM process. The binders used in BJAM technology and commonly found in the literature are substances manufactured by many commercial companies in their own structure. Many companies use their binders only for their own equipment. For this reason, there is a need to provide binders that are easily accessible and offer certain opportunities for those who manufacture equipment and work in the academic field in our country. Research shows that there is still no commercial equipment using this process (BJAM) in our country. The selection of the binder is crucial to improve the overall performance of all known solid freeform manufacturing processes. As important as the selection of the binder for BJAM processes is also whether the binder composition is storage stable and safe, i.e. whether it poses a material safety issue or generates hazardous waste.

A binder composition for powder metallurgy is described in the prior art in document number EP1252952B1 described. The invention provides a method of manufacturing goods. It discloses a method for use in manufacturing the binder and the free-form solid, including metal powder, wherein the binder contains at least one carbohydrate as the active binder compound. The carbohydrate contains from 6 to about 900 carbon atoms and can be selected from a variety of categories including, but not limited to, the following: For example, monosaccharides and their glycosides, such as aldose and ketose sugars, as well as hydroxyl, methyl, acyl, carbonyl, phosphate, deoxy, amino, and other derivatives; disaccharides such as sucrose, maltose, lactose, dextrose, cellobiose, gentiobiose, and trehalose; trisaccharides such as raffinose and hybritose; polysaccharides containing basic sugars; and hydrolyzed starches whose hydrolysate contains approximately 6-900 carbon atoms, including dextrins such as limit dextrin, hydrolyzed amylose and hydrolyzed amylopectin.

A binder composition for use in three-dimensional printing is disclosed in the prior art in document US5851465A A binder composition for three-dimensional printing of components is disclosed which is stable during storage and when passing through a print head, but can gel under the conditions prevailing in a powder bed. The binder composition comprises colloidal silica, a catalyst capable of promoting gelation of the composition when the composition is below a predetermined pH, and a base capable of maintaining the pH of the composition above the predetermined value at which the composition gels. The catalyst is preferably polyethylene glycol or another polymer derived from ethylene oxide and the base is triethanolamine. The pH of the binder composition is lowered by adding an acid, for example citric acid, to the powder upon impact with a powder bed, causing the binder in the powder to gel. The binder contains a catalyst that controls immobilization in the powder. The catalyst for the binder can be polyethylene glycol or another polymer derived from ethylene oxide. This catalyst promotes gelation when the pH of the binder composition is below a predetermined value, such as 7.5 for colloidal silica. The pH is lowered below the predetermined value after printing, causing the binder in the powder to gel. In the preferred embodiment, the pH is lowered by adding an acid, preferably citric acid, to the powder. The desired pH can also be lowered by other mechanisms, such as applying gaseous CO to the powder after printing.

Binder compositions for laser sintering processes are described in the state of the art in document number US6048954 A. The development of polymer binder compositions is described which provide new binders for high-temperature inorganic particles, in particular metal and ceramic particles. These materials are used in a laser beam sintering process called SLS™, which in particular produces form-fitting, high-strength objects. The new binders can be thermally removed in post-processing processes without significant residual ash. The resulting structures consist exclusively of metallic, ceramic or metal-ceramic materials. The processes described in the invention were developed to produce novel polymer binder materials and are based in part on the use of emulsion forms of selected polymers with controlled low molecular weights and high melt flow. An important aspect of the processes is the semi-continuous addition of selected chain transfer agents to the reacting emulsion. This optimizes the coating properties of the polymer binder and enables prototype components manufactured using the SLS™ process to achieve high component strength.

Metal and ceramic parts made from powder using salt-derived binders are described in the prior art in document number US6508980B1 This involves removing the formed part from the original bed when the crystalline salt is bonded to a reduced metal or a binder, a high temperature treatment to sinter or melt the precipitated salt or metal, and curing. A binder material containing a dissolved salt is used. This facilitates the bonding of the salt grains to each other.

The binder composition for additive manufacturing is described in the prior art in the document US2021053113A1 described. In general, additive manufacturing processes, binder compositions for additive manufacturing, and products made by and/or associated with additive manufacturing processes are described. In some embodiments, a binder composition is provided for additive manufacturing of metal articles by binder jetting. The binder composition includes water, a low molecular weight polymer containing acrylic acid as a repeating unit, a crosslinking agent, and a pH modifier. The crosslinking agent comprises a polyol, a polyfunctional amine, and/or a polyfunctional thiol. A binder composition is deposited on at least a portion of the first metal powder layer. The binder composition includes water and a low molecular weight polymer containing an acrylic acid repeating unit. Herein, the binder composition has a pH greater than or equal to 4. A binder composition for the additive manufacturing of metal objects by binder jetting contains water, a low molecular weight polymer containing a repeating acrylic acid unit, a polyol, a crosslinking agent with a polyfunctional amine and/or a polyfunctional thiol and a pH modifier. The binder composition further comprises an adhesion promoter.

An adhesive for an additive manufacturing technology, a material system and a molding process of the adhesive are described in the document with the number CN114213118 A, which is considered to be state of the art It provides a binder/adhesive for additive manufacturing technology that solves the problem of inconsistency with inorganic powders when using water-based adhesives for adhesive jet printing. It is used for the rapid production of products with complex structure made of metal, ceramics and metal-ceramic composites. A water-based binder solution system is used. The binder type is optimized for jet printing. Phosphate ester surfactants are used to improve the wettability of solution systems and powders because they have good affinity for the phosphate group, metals and cermet. The mass fraction of the phosphate ester surfactant is preferably 1-5% of the polymer solution. The phosphate-based surfactant is preferably at least one of lauryl ether phosphate and potassium lauryl ether phosphate. The water-soluble high molecular weight polymer is preferably at least one of polyvinyl alcohol and hydroxyethyl cellulose. A developed binder is used to improve the wettability of solution systems and powders.

Disadvantages of the state of the art, such as the specific structuring of each binder for production, the lack of possibility for standardization and formulation development, and the lack of accessibility, make it necessary to conduct a research and development study in this field.

Object of the invention

The main objective of the present invention is to ensure that the resin in the binder is retained up to the initial sintering temperature so that the metal sample can maintain its shape during the sintering phase used in the binder jetting additive manufacturing process.

The main objective of the present invention is to ensure that the resin is retained in the binder up to the initial sintering temperature, in such a way that the durability is increased by adding glycerin, polyethylene glycol-300 and similar substances to the resin.

The aim of the present invention is to adjust the rheological properties of the binder liquid, taking into account the rheological limits of the print head (viscosity, surface tension value, pH value, etc.), so that the binder is sprayed onto the metal powder in the desired shape by means of print heads in the binder jetting additive manufacturing process.

Another object of the present invention is to ensure that the wettability of the metal powder (penetration of the liquid into the metal powder) is achieved at the best surface tension values by adjusting the print head with reference to the catalogue values while adjusting the properties such as viscosity, surface tension and pH of the binder liquid.

Another object of the invention is to achieve a viscosity and surface tension lowering and/or surface tension increasing and/or boiling point increasing effect by adding glycerin, polyethylene glycol-300 and ethyl alcohol to the resin consisting of materials such as sucrose and nickel nitrate and containing 6-20 g of binder in 100 ml.

Another object of the invention is to provide the development of a suitable binder for printheads by adapting the chemicals contained in the binder in water-, alcohol-based and UV-curable liquid structures separately and/or in combination.

• - Harz, das die aus Metallpulvern geformte Probe bis zur anfänglichen Sintertemperatur in ihrer Form hält,
• - Wasser als Trägerflüssigkeit,
• - Ethylalkohol, der die Viskosität und Oberflächenspannung verringert,
• - Polyethylenglykol-300, das die Viskosität und Oberflächenspannung erhöht,
• - Triethanolamin, das den pH-Wert reguliert,
• - Glycerin, das die Viskosität, die Oberflächenspannung und den Siedepunkt erhöht.

The binder composition used in the binder jetting additive manufacturing process includes the following:

• - Resin that keeps the sample formed from metal powders in its shape until the initial sintering temperature,
• - Water as carrier fluid,
• - Ethyl alcohol, which reduces viscosity and surface tension,
• - Polyethylene glycol-300, which increases viscosity and surface tension,
• - Triethanolamine, which regulates the pH value,
• - Glycerin, which increases viscosity, surface tension and boiling point.

• - 6 % bis 20 % Harz, in Gewichtsprozent (w/v),
• - 15 bis 35 % Wasser, in Gewichtsprozent (w/v),
• - 25 bis 45 % Ethylalkohol, in Gewichtsprozent (w/v),
• - 5 bis 35 % Polyethylenglykol-300, in Gewichtsprozent (w/v),
• - 0,5 bis 3 % Triethanolamin, in Gewichtsprozent (w/v),
• - 3 bis 35 % Glycerin, in Gewichtsprozent (w/v).

The binder composition includes:

• - 6% to 20% resin, in weight percent (w/v),
• - 15 to 35% water, in weight percent (w/v),
• - 25 to 45% ethyl alcohol, in percent by weight (w/v),
• - 5 to 35% polyethylene glycol-300, in weight percent (w/v),
• - 0.5 to 3% triethanolamine, in weight percent (w/v),
• - 3 to 35% glycerin, in weight percent (w/v).

The structural and characteristic features of the present invention will be clearly understood from the following detailed description with reference to the information given therein. Therefore, the evaluation should be made in consideration of this detailed description.

Detailed description of the invention

Additive manufacturing is a process that involves the process steps in the form of manufacturing an object layer by layer. Different processes and technologies are used to create the layers. One of these processes is Binder Jetting Additive Manufacturing (BJAM) process. The manufacturing phase of BJAM technology consists of three basic steps. In the first step of the process, the powdery raw material is spread on the build platform in the desired thickness using the powder spreading roller. In the second step, the binder material is sprayed onto the powder according to the layer shape of the part using the print head so that layers are formed by bringing the powder grains together. In the last step, the binder is dried using a hardener (heat, light, etc.) to bond the powder grains to the binder. This forms a layer of the part. The part is manufactured by forming more layers by repeating these three steps one after the other. This process basically uses two raw materials. The first is powder, the second is binder. The process involves spraying binders onto the powder, which is distributed in a layer thickness. The binders are sprayed from binder print heads (piezoelectric print heads, etc.). Energy sources such as heat, light, etc. are used to partially dry/cure the binder.

The binder consists of a chemical called resin that performs the binding work, as well as chemicals that regulate rheological properties such as viscosity and surface tension (alcohol groups, polyethylene glycol groups, etc.). The binders are sprayed onto the metal powder in the desired shape using pressure heads. The rheological properties of the binder liquid are adjusted taking into account the rheological limits of the pressure head (viscosity, surface tension value, pH, etc.), as there are many different types of pressure heads. In other words, when adjusting the properties of the binder liquid such as viscosity, surface tension and pH, the catalog values of the pressure head are used as a reference. In addition, the most important aspect to consider is to detect the surface tension values at which the wettability of the metal powder (penetration of the liquid into the metal powder) is best. The part that allows the binder to be sprayed onto the powder raw material in a specific geometry is called the pressure head. The software control and electronic communication of the print head are carried out via the electronic control boards of the device. To prevent the binder reaching the print head from spontaneously flowing through the spray channels, a pneumatic vacuum system is used.

There is a binder feeding system that ensures that the binder in the binder tank, where the binder is located in a section, is transferred to the print head along with other elements for binding. In addition to the print head and binder elements, other elements in the machine include transfer pump, filters, hoses and valves.

The resin performs the main binding work in the binder. The binder content can contain other chemicals in addition to resin. The rheological properties of the binders (viscosity, surface tension, etc.) must be between the operating values of the print head. Along with the resin, other chemicals are used that perform the main task of binding and at the same time adjust the rheological properties.

The binders that are the subject of the invention consist of resin and other chemicals that are the main chemicals for carrying out the bonding process. The binders are sprayed onto the powder from the printheads in the Binder Jetting Additive Manufacturing (BJAM) process. More than one type of printhead can be used in this process. The operating conditions of each printhead (viscosity, surface tension, etc.) are different. The binders that are the subject of the invention must be mixed with different chemicals to work with each printhead used in the process.

The two most important operating characteristics of the printheads that affect the spray function are: viscosity and surface tension. For the printheads to operate properly, the viscosity and surface tension values of the binders must be between the catalog values of the printhead.

The components of the binder are listed in Table 1:

• - Harz, das die aus Metallpulvern geformte Probe bis zur anfänglichen Sintertemperatur in Form hält, ohne sie zu verlieren,
• - Wasser, das als Trägerflüssigkeit verwendet wird und eine Auflösung des Harzes ermöglicht,
• - Ethylalkohol, der die Viskosität und Oberflächenspannung verringert,
• - Polyethylenglykol-300, das die Viskosität und Oberflächenspannung erhöht,
• - Triethanolamin, das den pH-Wert reguliert,
• - Glycerin, das die Viskosität, die Oberflächenspannung und den Siedepunkt erhöht.

The binder composition used in the binder jetting additive manufacturing process includes the following:

• - Resin that keeps the sample formed from metal powders in shape up to the initial sintering temperature without losing it,
• - Water, which is used as a carrier liquid and allows the resin to dissolve,
• - Ethyl alcohol, which reduces viscosity and surface tension,
• - Polyethylene glycol-300, which increases viscosity and surface tension,
• - Triethanolamine, which regulates the pH value,
• - Glycerin, which increases viscosity, surface tension and boiling point.

• - 6 % bis 20 % Harz, in Gewichtsprozent (w/v),
• - 15 bis 35 % Wasser, in Gewichtsprozent (w/v),
• - 25 bis 45 % Ethylalkohol, in Gewichtsprozent (w/v),
• - 5 bis 35 % Polyethylenglykol-300, in Gewichtsprozent (w/v),
• - 0,5 bis 3 % Triethanolamin, in Gewichtsprozent (w/v),
• - 3 bis 35 % Glycerin, in Gewichtsprozent (w/v).

The binder composition includes:

• - 6% to 20% resin, in weight percent (w/v),
• - 15 to 35% water, in weight percent (w/v),
• - 25 to 45% ethyl alcohol, in percent by weight (w/v),
• - 5 to 35% polyethylene glycol-300, in weight percent (w/v),
• - 0.5 to 3% triethanolamine, in weight percent (w/v),
• - 3 to 35% glycerin, in weight percent (w/v).

The resin, which carries out the main binding process, is formed from sucrose, nickel nitrate and similar substances. The resin must be dissolved in a liquid (water) (carrier liquid) and be present in an amount and proportion that will produce the required bond strength. This is the first step in the manufacture of the binder.

To reduce the viscosity and surface tension of the binder, various alcohol-based solvents (ethyl alcohol and similar) are used. Sometimes these solvents are also used to dissolve the resin (sucrose, nickel nitrate) in the binder.

In addition, various chemicals based on glycol and glycerin are used to adjust the viscosity and surface tension of the binder. Finally, the print heads work from a certain pH value (normally pH 4 and above). To achieve this, some chemicals that regulate the pH value are used (triethanolamine and similar). Triethanolamine maintains the pH value of the environment at 4 and/or higher values and allows the print heads to operate.

The chemicals contained in the binder are not limited to those in the list, but can be used in various chemicals with similar properties. However, the point to consider here is the quality of the print head. There are generally three types of print heads. They are divided into structures that can spray water-based, alcohol-based and UV-curing liquids (or inks) individually or in combination. If a water-based print head is to be used, alcohol-based chemicals cannot be used here. In short, a binder suitable for the characteristics of the print head to be used must be developed.

The above binders are designed for use in the binder jetting metal additive manufacturing process and their components and types are not limited to the chemicals listed above.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• EP 1252952 B1 [0004]
• US 5851465 A [0005]
• US6048954 [0006]
• US 6508980 B1 [0007]
• US 2021053113 A1 [0008]
• CN114213118 [0009]

Claims (6)

Binder composition for the binder jetting additive manufacturing process for use in the manufacture of a three-dimensional product from a material, characterized in that it comprises: a resin which keeps the sample formed from metal powders in shape up to the initial sintering temperature without losing it, water which is used as a carrier liquid and enables dissolution of the resin, ethyl alcohol which reduces the viscosity and surface tension, polyethylene glycol-300 which increases the viscosity and surface tension, triethanolamine which regulates the pH value and glycerin which increases the viscosity, surface tension and boiling point. Binder composition for the binder jetting additive manufacturing process according to Claim 1 , characterized in that it comprises the following: water in a proportion of 15 to 35% by weight (w/v) and ethyl alcohol in a proportion of 25 to 45% by weight (w/v). Binder composition for the binder jetting additive manufacturing process according to any one of the preceding claims, characterized in that it comprises the following: resin in a proportion of 6 to 20 weight % (w/v) formed from sucrose, nickel nitrate and similar chemicals. Binder composition for the binder jetting additive manufacturing process according to any one of the preceding claims, characterized in that it comprises: glycerin in a proportion of 3 to 35% by weight (w/v), which ensures that the metal to be processed maintains the presence of the resin up to the initial sintering temperature. Binder composition for the binder jetting additive manufacturing process according to any one of the preceding claims, characterized in that it comprises: polyethylene glycol-300 in a proportion of 5 to 35% by weight (w/v), which ensures that the metal to be processed maintains the presence of the resin up to the initial sintering temperature. Binder composition for the binder jetting additive manufacturing process according to one of the preceding claims, characterized in that it comprises the following: triethanolamine in a proportion of 0.5 to 3%, by means of which the print heads can be operated in such a way that the pH of the environment is maintained at 4 and/or higher values.