Powder injection molding device for molding dental articles

Abstract

The invention relates to a powder injection molding device for molding a dental article, said device comprising: A) an injection unit (16) comprising a barrel (18), a nozzle (24) and a conveying means arranged in the barrel for conveying a raw material in a direction towards the nozzle; and B) a mold (10) enclosing a mold cavity (14) fluidly connected to the injection unit via a mold gate (30), said mold cavity extending along a longitudinal axis A from a proximal cavity region (36) to a distal cavity region (40) leading therein from the mold gate, characterized in that the mold comprises a mold block (11) and a mold piston (32) together delimiting the mold cavity (14), the mold piston (32) is slidably arranged in the mold block (11) and is movable with respect to the mold block (11) along a longitudinal axis A.

Description

[0001] The present invention relates to a powder injection molding (PIM) device for molding dental products and to a process for preparing dental products, in particular dental implants or dental implant abutments, using the PIM device.

[0002] Ceramic dental implants or implant abutments are usually produced by pressing a ceramic powder dispersed in a binder onto a so-called green body, from which the binder is then removed in a debinding (or "debindering") step to form a brown body, which is then sintered and in some cases hot isostatically pressed (HIP), and which is usually subsequently ground.

[0003] In order to provide the article to be produced with complex structural features, such as an external thread of a dental implant (for screwing it into the bone and obtaining the primary stability after implantation) or an internal thread (for connecting an abutment to the dental implant), the sintered body is then subjected to a machining step.

[0004] In order to avoid laborious post-processing steps such as HIP and grinding and to reduce the effort of machining the final geometry from the sintered body, proposals have been made in the past to produce implants or implant abutments by injection molding technology.

[0005] For example, EP-A-1570804 discloses a dental implant comprising an outer body made of ceramic or metal and an inner body made of metal or ceramic, wherein the metal body is produced by metal injection molding (MIM) and the ceramic body is produced by ceramic injection molding (CIM).

[0006] Furthermore, DE-A-19530981 discloses a post system for an implant structure, the post being formed by injection molding a composition comprising polyoxymethylene and zirconium dioxide powder.

[0007] US 6280193 relates to a dental implant comprising zirconium oxide, the implant having an external thread that can be screwed into bone tissue and an internal tapping obtained by molding.

[0008] US 2012 / 0301849 further discloses a zirconia dental implant manufactured by injecting a zirconia paste into a mold to obtain a green compact and sintering the green compact into the zirconia dental implant.

[0009] Although complex structures can theoretically be achieved using CIM or MIM (both fall within the definition of powder injection molding / PIM), it has been found that conventional PIM techniques result in relatively poor process stability. In particular, implants or implant abutments produced using conventional CIM or MIM are prone to surface defects due to the high viscosity of the raw materials and the resulting imperfect filling of the mold cavity.

[0010] In order to improve the flow behavior of the raw material, the mold can be preheated, thereby prolonging the hardening of the raw material and thus of the window for injection.

[0011] To achieve stable PIM (which allows for improved filling of the mold cavity without increasing cycle time), EP 3826791 teaches a process in which the step of injecting heated feedstock into the mold cavity of a mold is performed while applying vibrational energy to the feedstock. Although the process according to EP 3826791 can achieve reduced surface porosity and volume defects, and thus improved bending strength, it still suffers from the remaining problem of pressure drop experienced by the feedstock along its path through the mold cavity during filling. This is particularly disadvantageous when using feedstocks with relatively high viscosity and / or low pressure transitions for molding.

[0012] This problem is further exacerbated if the article being molded is relatively long, as is the case with dental implants or dental implant abutments. When molding such articles, the raw material must travel along the entire axial length of the mold cavity, i.e., from the proximal cavity region, which leads to the mold gate, to the distal cavity region (i.e., the region of the cavity furthest from the mold gate). In particular, pressure drops in this distal cavity region can lead to a decrease in raw material density and, after cooling, defects in the corresponding portion of the article. In the case of dental implants, these defects correspond to the coronal portion of the implant. This is particularly disadvantageous for dental implants in two-part dental implant systems, as the coronal portion is the portion with the most delicate structure, namely, the internal threads of the blind hole adapted to receive and securely attach the abutment of the dental implant system.

[0013] Therefore, the present invention aims to provide a powder injection molding apparatus that allows for improved filling of a mold cavity. Specifically, the apparatus should allow for a substantially uniform density of the raw material across the entire volume of the mold cavity. More specifically, the apparatus should allow for improved density of the raw material in the distal cavity region of the mold cavity. Ultimately, the apparatus should allow for the reduction or even avoidance of defects in the molded dental article, particularly in the portion corresponding to the distal cavity region of the mold cavity.

[0014] This problem is solved by a device according to claim 1. Preferred features are defined in the dependent claims.

[0015] According to claim 1 , the powder injection molding device is designed for molding dental products, particularly dental implants or dental implant abutments. The term "powder injection molding" encompasses ceramic injection molding (CIM) or metal injection molding (MIM). In particular, the device of the present invention is designed for CIM.

[0016] As claimed in claim 1, the device of the present invention comprises:

[0017] A) an injection unit comprising a barrel, a nozzle and a conveying device arranged in the barrel for conveying the raw material in a direction towards the nozzle, and

[0018] B) A mold enclosing a mold cavity fluidly connected to the injection unit via a mold gate, the mold cavity extending along a longitudinal axis A from a proximal cavity region into which the mold gate opens to a distal cavity region.

[0019] The invention is characterized in that the mold comprises a mold block and a mold piston which together delimit a mold cavity, the mold piston being slidably arranged in the mold block and movable along a longitudinal axis A relative to the mold block.

[0020] In the context of the present invention, it has been discovered that by using the apparatus defined in claim 1, complete filling of the mold cavity can be achieved, and thus accurate reproduction of structural details in the molded article can be achieved. Surprisingly, the tendency to form cracks or pores has also been found to be much lower than with previously described PIM techniques. By reducing these surface and volume defects, higher bending strength and, therefore, higher performance of the produced article can ultimately be achieved. This will be explained in further detail below in the context of the specific methods and concepts of PIM using the apparatus of the present invention.

[0021] Specifically, the present invention allows for the precise reproduction of very fine or complex mold cavity configurations, even when molding high-viscosity raw materials (e.g., raw materials with a flow rate of less than 0.15 ml / s). In terms of quality control for dental products, the present invention allows for reduced geometric tolerances, thereby achieving higher molding quality. In particular, the present invention allows for a workflow that results in less deviation and improved dimensional stability of the molded product.

[0022] As mentioned above, the present invention allows the use of raw materials with a flow rate lower than 0.15 ml / s without compromising the forming quality. Specifically, the "flow rate" used in this article refers to the flow rate at 160°C and a cylinder pressure of 4.9·10 6 The flow rate is measured based on ISO 1133 at Pa. More specifically, the mentioned flow rate is measured by using a flow tester CFT-500D (Shimadzu Corporation, Tokyo, Japan) having a die size defined by a diameter of 1 mm and a length of 2 mm.

[0023] As will be explained in more detail in the context of a method for producing a dental article, the device allows for improved filling via two basic processes, which can be performed individually or in combination with one another.

[0024] According to a first process, the apparatus is set to an initial stage mode M1 before filling, wherein the mold piston is set so that the mold cavity has a volume Then, the first portion of the raw material is injected from the injection unit through the mold gate until pressure is reached in the mold cavity. The first part is filled into the mold cavity with a pressure that is high enough to reproduce even very complex or delicate structures within the mold in the molded product. In particular, the internal threads of blind holes in dental implants can be accurately reproduced.

[0025] After filling with this first portion of raw material, filling continues with the second portion of raw material while simultaneously moving the piston away from the mold gate in the direction of longitudinal axis A, thereby increasing the volume within the mold cavity. Consequently, the already formed blind hole structure continuously moves away from the mold gate, allowing the remaining structure within the mold cavity to continue forming while the raw material is continuously injected under high pressure. This avoids the problem of insufficient raw material density in the distal cavity region.

[0026] In the context of this embodiment of the invention, the term "high pressure" generally relates to pressures between 500 bar and 2500 bar. In the specific context of molding dental implants, "high pressure" generally refers to pressures between 500 bar and 1000 bar.

[0027] According to the second process, an embodiment of the apparatus is used in which the mold piston includes a sleeve, a core pin, and a ram element. This embodiment will be described in detail below. In this second process, the apparatus is first set to an initial stage mode M2, in which the core pin and sleeve are set to their final position, which corresponds to the position of the blind hole in the dental article to be molded.

[0028] The raw material is then injected from the injection unit through the mold gate to fill the mold cavity. After filling, the ejector element moves relative to the core pin and sleeve along the longitudinal axis A to reduce the volume of the mold cavity until the ejector element reaches its final position.

[0029] The raw material is then solidified by cooling to obtain the final shape of the dental article, and the dental article is demolded.

[0030] Taking into account the compaction caused by the pressing force of the thrust element, a lower density of the raw material in the distal cavity region, which may occur due to a pressure drop of the raw material during filling, can be compensated after filling.

[0031] Ultimately, the present invention, particularly by reducing the free-spraying behavior of the raw materials during molding and its impact on the final product, allows for the production of molded dental products with reduced surface porosity and an improved distribution of volumetric defects (e.g., flow lines, voids, and decomposition). Consequently, even when the molding process requires complex geometries, the flexural strength of the molded dental products is improved.

[0032] According to a preferred embodiment of the apparatus according to the present invention, the injection unit and / or the mold include a heating element for heating the raw material. This allows the injection window to be extended for the duration required to completely fill the mold cavity. In particular, the heating element is designed to ensure that the raw material temperature before injection, i.e., at the nozzle of the transfer channel and / or at the mold gate, is in the range of 160°C to 200°C. Preferably, the heating element associated with the mold is designed to maintain the mold at a temperature in the range of room temperature to 60°C.

[0033] According to another preferred embodiment of the device, the mold piston is arranged in the mold block such that the volume of the mold cavity increases or decreases during its movement along the longitudinal axis A. This allows improving filling by either of the two basic concepts discussed above or by a combination of concepts.

[0034] In view of the first concept (in which, after filling the first portion of the raw material in the initial stage mode, the filling is continued with the second portion of the raw material while the piston is moved in the direction away from the mold gate of the longitudinal axis A), the mold piston is preferably arranged in the mold block so that the volume of the mold cavity increases during its movement in the direction away from the mold gate.

[0035] According to a particularly preferred embodiment, the mold piston includes a guide region extending in the longitudinal direction and in the form of a cylinder. The housing surface of this guide region fits into a guide tube arranged in the mold block, i.e., the form and dimensions of the cylinder correspond to those of the guide tube. This ensures uniaxial movement of the mold piston and, therefore, precise positioning of the corresponding structure in the distal cavity region. Furthermore, the arrangement of the mold piston in the mold block according to this embodiment ensures that no raw material can enter the guide tube. Consequently, there is no need to remove unwanted protrusions from the molded article during post-processing.

[0036] According to another preferred embodiment of the device, the end region of the mold piston that extends into the mold cavity has a form corresponding to a blind hole arranged in the dental article to be molded (specifically, a blind hole extending in the longitudinal direction of the dental article). This is particularly true for devices for molding dental implants, which typically include a blind hole with an internal thread suitable for receiving and securely attaching an abutment of a dental implant system.

[0037] In this respect, it is particularly preferred that the end region comprises a front end portion, at least a portion of which has the shape of an external thread corresponding to the internal thread in a blind hole of the dental article to be formed, and more particularly to the internal thread of a blind hole of a dental implant.

[0038] As described above, the apparatus of the present invention allows accurate replication of blind holes even when using relatively high viscosity raw materials.

[0039] According to another preferred embodiment, the end region further includes a shaft portion, which is arranged adjacent to the front end in the longitudinal direction of the mold piston, pointing away from the mold cavity. At least a portion of the shaft portion has a non-circular cylindrical shape that corresponds to a corresponding opening in the blind hole of the dental article to be molded. More specifically, the shaft portion has the shape of a polygonal shaft, such as a quadrangular (or square) or hexagonal shaft. In this context, the term "ribbed" also encompasses shafts with rounded corners. The correspondingly shaped opening allows for rotational fixation of an abutment received in the blind hole.

[0040] In this regard, it is further preferred that the mold piston include a sleeve and a core pin, the core pin being circumferentially surrounded by the sleeve and rotatable relative to the sleeve, the core pin forming the front end of the mold piston, and the sleeve forming the shaft portion of the mold piston. As will be explained in detail in conjunction with the accompanying drawings, this arrangement allows for simple demolding by rotating the core pin to unscrew it from the molded dental article and axially moving the core pin and sleeve away from the mold cavity. After separation of the mold components, the molded article can then be removed from the mold cavity.

[0041] In view of the second basic process discussed above, it is particularly preferred that the mold piston further include a thrust element arranged coaxially with the sleeve and circumferentially surrounding the sleeve, wherein the thrust element is axially movable relative to the sleeve. In this regard, it is further preferred that the thrust element include a pressing surface that lies in a plane that is at least approximately perpendicular to the longitudinal axis A of the mold cavity.

[0042] As described above, the device allows for improved filling via two basic processes that can be performed individually or in combination with one another to prepare dental articles.

[0043] Therefore, in addition to the above-mentioned apparatus, the present invention also relates to a process for producing dental articles (particularly dental implants or dental implant abutments) using the powder injection molding apparatus.

[0044] According to a first aspect, the process of the present invention comprises the following steps:

[0045] a) The apparatus is set to an initial stage mode M1, wherein the mold piston (32) is set so that the mold cavity (14) has a volume ;

[0046] b) by injecting a first portion of the raw material from the injection unit (16) through the mold gate (30) until the volume of the mold cavity is Reaching pressure , filling a first portion of the raw material into the mold cavity (14);

[0047] c) continuing to fill with a second portion of the raw material while simultaneously moving the mold piston (32) in a direction of the longitudinal axis A away from the mold gate (30), thereby increasing the volume of the mold cavity (14);

[0048] d) solidifying the raw material by cooling after filling to obtain the final shape of the dental article; and

[0049] e) demolding the molded dental article.

[0050] As described above and explained in more detail in conjunction with the accompanying figures, this allows structures that will ultimately be located in the distal cavity region of the mold cavity to be formed immediately adjacent to the mold gate at relatively high pressure. Following their formation, these structures are continuously moved away from the mold gate, allowing the remaining structures of the mold cavity to be continuously formed under the constant high pressure of the raw material. This avoids the problem of insufficient raw material density in the distal cavity region.

[0051] According to a second aspect, the process of the present invention comprises the following steps:

[0052] α) setting the device to an initial stage mode M2, wherein the core pin (56) and the sleeve (54) are set to their final positions (corresponding to the position of the internal thread and the opening of the blind hole in the dental article to be formed);

[0053] β) filling the mold cavity (14) with the raw material by injecting the raw material from the injection unit (16) through the mold gate (30);

[0054] γ) after filling, moving the ejector element (58) relative to the core pin (56) and the sleeve (54) along the longitudinal axis A to reduce the volume of the mold cavity (14) until the ejector element reaches its final position;

[0055] δ) solidifying the raw material by cooling to obtain the final shape of the dental article; and

[0056] ε) demolding the dental article.

[0057] With regard to this second aspect, it is further preferred that the demolding step (ε) comprises the following sub-steps: rotating the core pin to unscrew it from the molded dental article, and axially moving the core pin and the sleeve in a direction away from the mold cavity. Thus, a demolded article can be obtained that represents all the structures of the final article and does not require further processing of the article.

[0058] As stated above, the present invention encompasses the processes of the first and second aspects both individually and in combination with each other.

[0059] According to a preferred embodiment applicable to both aspects, the process includes a further step of heating the raw material, as described above. Preferably, the raw material is heated in the injection unit, more specifically in the barrel of the injection unit, where the raw material is conveyed from the barrel's feed zone toward the nozzle and, optionally under further heating, is transferred from the nozzle through a transfer channel and mold gate into the mold cavity. In particular, heating of the raw material in the injection unit and / or transfer channel is primarily achieved using conventional heating devices. Specifically, the raw material is conveyed in the barrel by means of a conveying screw, and plasticization or melting can be achieved through friction generated by the screw's rotation, optionally in combination with additional heating elements. This plasticization or melting results in a temperature-dependent decrease in the raw material's viscosity. Preferably, the temperature regime is such that the raw material temperature prior to injection (i.e., at the nozzle of the transfer channel) is in the range of 160°C to 200°C.

[0060] Typically, the temperature at which the mold is maintained depends on the specific raw material being used and is selected to allow good flowability of the raw material during injection into the mold cavity. Preferably, the mold is maintained at a temperature ranging from room temperature to 60°C. According to this preferred embodiment, there is no need to cool the mold before the product is demolded, which allows the process of the present invention to be applied on a large scale and with high production volumes.

[0061] The holding pressure applied during the holding phase (i.e., the phase after filling) is preferably between 300 bar and 1200 bar, more preferably between 400 bar and 1000 bar, and most preferably between 600 bar and 900 bar. However, it will be appreciated that the optimal holding pressure may vary depending on the specific raw materials used.

[0062] Example

[0063] The present invention is further described by the following embodiments and accompanying drawings, in which:

[0064] Figure 1 shows a graph associated with a typical PIM process cycle and indicating pressure measured at the injection screw over time, the graph representing the main injection phase of the cycle;

[0065] Figure 2 A powder injection molding apparatus is schematically shown, wherein the mold has a double expansion configuration according to the present invention;

[0066] Figure 3 A perspective view showing a portion of a PIM apparatus according to the present invention, wherein a mold piston is arranged in a first position (A) and a second position (B); and

[0067] Figure 4 A longitudinal section of a portion of another embodiment of the invention is shown, wherein the mold piston and its components are shown in a filling position and a pressing position.

[0068] like Figure 1 As shown in FIG, a typical PIM process cycle includes the subsequent main steps of injection, cooling, and mold resetting. During the injection step, injection pressure is applied by the injection unit. Specifically, the pressure is generated by the main hydraulic pressure that pushes the rear end of the injection screw in the injection unit. During this step, the injection pressure increases rapidly, especially when the raw material hits the mold gate 30 (see, for example, Figure 2 ).

[0069] The cooling step can be subdivided into the packing phase (or holding phase), the discharge phase, and the seal cooling phase. During the packing or holding phase, the pressure established by the injection screw reaches its maximum value and then gradually decreases as the material begins to cool. The transition from the packing phase to the discharge phase is marked by a sudden pressure drop (starting from the point at which the injection screw is allowed to move back). The pressure drop continues during the seal cooling phase, which begins at the point at which the sealing point is reached (this is the point at which the mold gate is sealed). At the end of the cycle, the mold is reset, and the pressure is again set to the value at the beginning of the injection step.

[0070] like Figure 2 As shown, the powder injection molding apparatus includes a mold 10 including a mold block 11 , which includes two mold block parts, namely, a first mold block part 11 a and a second mold block part 11 b , which are clamped together by a clamping unit 12 and surround a mold cavity 14 .

[0071] The first mold block 11a has a first contact surface facing the second mold block 11b in the assembled state, and the second mold block 11b has a second contact surface facing the first mold block 11a in the assembled state. The first and second contact surfaces form a parting surface 13 between the first and second mold block parts 11a and 11b in the assembled state of the mold.

[0072] The clamping unit 12 is designed to hold the first mold block part 11a and the second mold block part 11b in contact with each other under the action of a clamping force. The clamping unit 12 includes a fixed part 12b and a movable part 12a, wherein the movable part 12a is movable relative to the fixed part 12b.

[0073] The device also includes an injection unit 16 comprising a barrel 18 arranged on the side of the fixed part 12b opposite the mold, a hopper 20 for feeding the raw material into a feed zone 22 of the barrel, a nozzle 24, and a screw (not shown) arranged axially in the barrel and designed to convey the raw material in a direction from the feed zone 22 toward the nozzle 24, thereby passing through the compression zone and the metering zone (not shown) of the barrel. In order to heat the raw material on its way from the barrel to the nozzle 24, a heating element 26 is provided surrounding the barrel 18.

[0074] The nozzle 24 opens into a transfer channel 28 arranged in the mold 10 and opens into the mold cavity 14 via a mold gate 30. The mold cavity extends along the longitudinal axis A from a proximal cavity region into which the mold gate opens to a distal cavity region. Thus, the mold cavity (14) is fluidically connected to the injection unit (16) via the mold gate 30. The term "fluidically connected" as used in this context means that the mold cavity and the injection unit are connected in such a way that raw material can flow from the injection unit into the mold cavity.

[0075] Also like Figure 3 , in addition to the mold block 11, the mold 10 includes a mold piston 32 which, together with the mold block 11, delimits the mold cavity 14. The mold piston 32 is slidably arranged in the mold block 11, in particular in a guide tube 34 in the mold block, and is movable along the longitudinal axis A relative to the mold block 11.

[0076] Figure 3 The mold shown is designed for molding a dental implant of a two-part dental implant system. In the proximal cavity region 36, the inner wall of the mold cavity 14 contains internal threads 38 that correspond to the external threads of the anchoring component of the dental implant to be molded. In the distal cavity region 40, the mold cavity 14 widens so that its shape corresponds to the cup shape of the mounting component of the dental implant.

[0077] The mold piston 32 comprises an end region 42 entering the mold cavity 14 and a guide region 44 in the form of a cylinder, the shell surface of which fits into the guide tube 34 arranged in the mold block 11. In the embodiment shown, the guide region 42 of the mold piston 32 and the guide tube 34 of the mold block 11 are in the form of circular cylinders.

[0078] The end region 42 has a form corresponding to a blind hole arranged in the dental implant to be formed and extending in the longitudinal direction of the dental implant. Specifically, the end region includes a front end 46 and a shaft portion 48, which is arranged adjacent to the front end 46 in the longitudinal direction of the mold piston 32, pointing away from the mold cavity 14. The front end 46 includes an external thread 50 that corresponds to the internal thread in the blind hole of the dental implant to be formed. The shaft portion 48 has the shape of a quadrangular shaft 52 that corresponds to a corresponding opening in the blind hole of the dental implant, thereby rotationally securing the abutment to be mounted on the dental implant.

[0079] This embodiment allows to perform a PIM process which allows to achieve dental implants with reduced surface porosity and increased flexural strength. Figure 3 The consecutive cases A and B shown in FIG.

[0080] Figure 3 A relates to a situation in which the apparatus is first set to an initial stage mode M1 in which the mold piston 32 is set so that the front end portion 42 is arranged in close proximity to the mold gate 30. In the embodiment shown, a portion of the guide area 44 also enters the mold cavity 14. In this initial stage mode M1, the mold cavity 14 has a volume .

[0081] While the mold piston 32 is maintained in this initial stage mode M1, the mold is heated by injecting a first portion of the raw material from an injection unit (not shown) through the mold gate 30 until pressure is reached in the mold cavity 14. , the first portion of the raw material is filled into the mold cavity 14. Since the front end 46 is arranged in close proximity to the mold gate 30, there is only a small pressure drop and high pressure in the area of ​​the external thread 50 of the front end 46. This allows the grooves of the thread to be accurately formed.

[0082] Once the pressure is reached , continue filling with the second portion of the raw material. In this step, the mold piston 32 is simultaneously moved in the direction of the longitudinal axis A away from the mold gate 30 (as indicated by the arrow), thereby increasing the volume of the mold cavity 14. The movement continues until the mold piston 32 reaches its final position, the corresponding situation is Figure 3 This is shown in B. In this case, the entire volume of the mold cavity 14 corresponding to the dental implant to be formed is ultimately filled.

[0083] Then, the raw material is solidified by cooling to obtain the final shape of the dental implant, and the molded dental implant is demolded.

[0084] Another embodiment of the apparatus and process of the present invention is Figure 4 The two continuous cases in the molding process are shown in Figure 4A and B are shown.

[0085] and Figure 3 Compared to the device shown in Figure 4 The die piston 32 of the embodiment shown in FIG includes an outer sleeve 54 and an inner core pin 56, which is circumferentially surrounded by the sleeve and rotatable about the sleeve. The front end of the core pin 56 forms the front end 46, and the front end of the sleeve 54 forms the shaft 48 of the die piston 32.

[0086] The mold piston 32 further comprises a thrust element 58 arranged coaxially with and circumferentially surrounding the sleeve 54. The thrust element 58 is axially movable relative to the sleeve 54 and comprises a pressing surface 60 lying in a plane perpendicular to the longitudinal axis A of the mold cavity 14.

[0087] This embodiment of the device allows further processes to be performed which can be compared to the above Figure 3 The process combination is described in the context of .

[0088] According to the process, the device is set to the initial stage mode M2 ​​(such as Figure 4 A), wherein the inner core pin 56 and outer sleeve 54 are positioned in their final positions, which correspond to the position of the blind hole of the dental implant to be molded. Specifically, the external threads of the front end portion and the angular shaft portion are arranged in positions within the mold cavity corresponding to the internal threads and opening of the blind hole of the dental implant.

[0089] The thrust element 58 is in this position (ie in the initial stage mode M2 ​​) held at a distance D from its final position 62 , which corresponds to the coronal end of the dental implant to be formed.

[0090] Then, the first portion of the raw material is injected from the injection unit through the mold gate ( Figure 4 ), a first portion of the raw material is filled into the mold cavity 14.

[0091] After filling, the ejector element 58 is then moved relative to the core pin 56 and the sleeve 54 along the longitudinal axis A to reduce the volume of the mold cavity until the ejector element reaches its final position 62; this occurs at Figure 4 This is shown in B. According to this embodiment of the invention, the pressure in the holding phase can therefore be kept constant or even increased.

[0092] The raw material is then cooled to solidify, achieving the final shape of the dental article, and demolded. Demolding involves rotating the core pin to unscrew it from the molded dental article, and axially moving the core pin and sleeve away from the mold cavity. Finally, the mold components are separated, allowing the molded article to be removed from the mold cavity.

[0093] Taking into account the pressure of the push element, it is possible to compensate for the lower density of the material in the distal cavity area that may occur due to the pressure drop of the material during filling after filling. This also allows to reduce surface porosity and volume defects and ultimately achieve an increase in the bending strength of the article.

[0094] As mentioned above, Figure 3 and Figure 4 The processes shown in can be combined with each other. Figure 4 The mold piston shown can be used according to Figure 3 In the process. Figure 3 In the process step shown in B, the mold piston moves along the longitudinal axis A until the core pin and the sleeve reach their final position, and the ejector element moves further to Figure 4 The pre-compression position is shown at A. After filling has taken place, the pusher element is then moved to its final position, as described above, in order to further compact the material in the distal cavity region.

[0095] Reference Signs List

[0096] 10 Mold

[0097] 11 mold blocks

[0098] 11a, 11b The first and second parts of the mold block

[0099] 12 clamping units

[0100] 12a, 12b movable and fixed parts of the clamping unit

[0101] 14 mold cavities

[0102] 16 injection units

[0103] 18 barrels

[0104] 20 hoppers

[0105] 22 Feeding area

[0106] 24 nozzles

[0107] 26 heating elements

[0108] 28 transmission channels

[0109] 30 mold gate

[0110] 32 mold piston

[0111] 34 guide tube

[0112] 36 Proximal cavity area

[0113] 38 internal thread

[0114] 40 distal cavity area

[0115] 42 End area of ​​the die piston

[0116] 44 Guide area of ​​mold piston

[0117] 46 front end

[0118] 48 shaft

[0119] 50 External thread at the front end

[0120] 52 quadrangular axis

[0121] 54 sleeve

[0122] 56-core pin

[0123] 58 thrust element

[0124] 60 presses on the surface

[0125] 62 Final position of the thrust element / coronal end of the dental implant to be formed

Claims

1. A powder injection molding device for molding dental products, the powder injection molding device comprising: A) an injection unit (16) comprising a barrel (18), a nozzle (24) and a conveying member arranged in the barrel for conveying raw material in a direction towards the nozzle, and B) a mold (10) enclosing a mold cavity (14) fluidically connected to the injection unit via a mold gate (30), the mold cavity extending along a longitudinal axis A from a proximal cavity region (36) into which the mold gate opens to a distal cavity region (40), The mold comprises a mold block (11) and a mold piston (32), wherein the mold block and the mold piston together define the mold cavity (14), and the mold piston (32) is slidably arranged in the mold block (11) and is movable along the longitudinal axis A relative to the mold block (11).

2. The powder injection molding device according to claim 1, characterized in that: The mold piston (32) is arranged in the mold block (11) such that during movement of the mold piston along the longitudinal axis A, the volume of the mold cavity (14) increases or decreases.

3. The powder injection molding device according to any one of the preceding claims, characterized in that The mold piston (32) is arranged in the mold block (11) such that the volume of the mold cavity (14) increases during movement of the mold piston in a direction away from the mold gate (30).

4. The powder injection molding device according to any one of the preceding claims, characterized in that The mold piston (32) comprises a guide region (44) extending in the longitudinal direction and in the form of a cylinder, the shell surface of which is fitted into a guide tube (34) arranged in the mold block (11).

5. The powder injection molding device according to any one of the preceding claims, characterized in that The end region (42) of the mold piston (32) that projects into the mold cavity (14) has a form that corresponds to a blind hole arranged in the dental article to be molded.

6. The powder injection molding device according to claim 5, characterized in that: The end region (42) includes a front end (46), at least a portion of which has the shape of an external thread (50), which corresponds to the internal thread in the blind hole of the dental product to be formed.

7. The powder injection molding device according to claim 5 or 6, characterized in that: The end region (42) further comprises a shaft portion (48), which is arranged adjacent to the front end portion (46) in a longitudinal direction of the mold piston (32) pointing away from the mold cavity (14), wherein at least a portion of the shaft portion has the shape of a non-circular cylinder, in particular the shape of a polygonal axis, corresponding to a corresponding opening in the blind hole of the dental article to be molded.

8. The powder injection molding device according to claim 7, characterized in that: The mold piston (32) includes a sleeve (54) and a core pin (56), the core pin being circumferentially surrounded by the sleeve and being rotatable about the sleeve, the core pin forming the front end portion (46), and the sleeve (54) forming the shaft portion (48) of the mold piston (32).

9. The powder injection molding device according to claim 8, characterized in that: The mold piston (32) further comprises a thrust element (58) which is arranged coaxially with the sleeve (54) and circumferentially surrounds the sleeve, and is axially movable relative to the sleeve.

10. The powder injection molding device according to any one of the preceding claims, characterized in that The injection unit and / or the mold comprises a heating element (26) for heating the raw material.

11. A process for preparing a dental product using a powder injection molding apparatus, wherein the powder injection molding apparatus is the powder injection molding apparatus according to any one of claims 1 to 9, and the dental product is particularly a dental implant or a dental implant abutment.

12. The process according to claim 11, comprising the steps of: a) The apparatus is set to an initial stage mode M1, wherein the mold piston (32) is set so that the mold cavity (14) has a volume ; b) by injecting a first portion of the raw material from the injection unit (16) through the mold gate (30) until the volume of the mold cavity is Reaching pressure , filling a first portion of the raw material into the mold cavity (14); c) continuing to fill with a second portion of the raw material while simultaneously moving the mold piston (32) in a direction of the longitudinal axis A away from the mold gate (30), thereby increasing the volume of the mold cavity (14); d) solidifying the raw material by cooling to obtain the final shape of the dental article; and e) demolding the molded dental article.

13. The process according to claim 11 or 12, wherein the process uses the powder injection molding apparatus according to claim 9, and the process comprises the following steps: α) setting the device to an initial stage mode M2, wherein the core pin (56) and the sleeve (54) are set to their final positions; β) filling the raw material into the mold cavity (14) by injecting the raw material from the injection unit (16) through the mold gate (30); γ) after filling, moving an ejector element (58) along the longitudinal axis A relative to the core pin (56) and the sleeve (54) to reduce the volume of the mold cavity (14) until the ejector element reaches its final position; δ) solidifying the raw material by cooling to obtain the final shape of the dental article; and ε) demolding the dental article.

14. The process according to claim 13, wherein The demolding step (ε) includes the following sub-steps: rotating the core pin (56) to unscrew the core pin from the molded dental product, and axially moving the core pin (56) and the sleeve (54) in a direction away from the mold cavity (14).

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