Reverse assembly and normal burning pressureless impregnation diamond bit sintering mold and process method

Abstract

The application discloses a kind of anti-assembly positive burning pressureless impregnation diamond impregnated drill bit sintering mould and process method, lower graphite mould is placed in bottom, for forming drill bit working layer end face and outside positioning datum, core mould is coaxially connected in lower graphite mould middle part, and core mould is used to form drill bit inner hole and inside positioning datum;Drill bit steel body is coaxially arranged between lower graphite mould and core mould, and its lower end is used to connect with matrix working layer;Outer steel sleeve is detachably sleeved on the outside of drill bit steel body, inner steel sleeve is detachably arranged on the inside of drill bit steel body, graphite outer sleeve is used to be sleeved on the outside of the pre-assembly body after the pre-assembly body formed by lower graphite mould, outer steel sleeve, drill bit steel body, inner steel sleeve and core mould is inverted loading, outside steel sleeve and inner steel sleeve are used to define matrix material filling cavity in inverted loading stage, and are used to be extracted after whole buckling positive burning posture, to form the space of filling copper solder, copper alloy or other impregnation material.

Description

Technical Field

[0001] This invention relates to the field of manufacturing technology for geological drilling, engineering exploration, mine coring, oil and gas drilling, and drilling tools for hard and brittle rock formations, and particularly to a sintering mold and process method for a reverse-mounted, forward-sintering, pressureless impregnation and diamond-encrusted drill bit. Background Technology

[0002] Impregnated diamond drill bits are widely used core drilling tools in geological drilling and hard rock drilling. These bits typically consist of a steel drill body and a matrix working layer connected to the end of the steel body. The matrix working layer contains uniformly distributed single-crystal diamonds or other superhard abrasive grains. During drilling, the matrix encapsulates and supports the diamonds, and through wear, it continuously develops cutting edges to grind and break up the rock. The density of the drill bit's working layer, the uniformity of diamond distribution, the bonding strength between the matrix and the steel body, and the consistency of the dimensional geometry after sintering directly affect the drill bit's lifespan, efficiency, and failure mode.

[0003] Currently, the commonly used sintering manufacturing methods for impregnated diamond drill bits mainly include hot pressing sintering, pressure impregnation sintering, and pressureless impregnation sintering. Hot pressing sintering increases the density of powder forming through external pressure, resulting in better matrix strength. However, it requires high equipment investment, involves complex mold pressure conditions, and makes it difficult to form drill bits with complex gates, reinforcing ribs, high working layers, or multi-stage gauge structures in a single pass. Furthermore, improper control of temperature, pressure, and holding time can lead to thermal damage to the diamond or fluctuations in matrix properties. Pressure impregnation sintering improves the ability of the impregnating alloy to penetrate the matrix pores, but it places high demands on mold sealing, pressurization devices, and process windows, making it unsuitable for the flexible manufacturing of drill bits in multiple specifications and small batches.

[0004] Pressureless impregnation sintering eliminates the need for external pressure on the matrix during the sintering stage, resulting in a relatively simple mold structure. This allows for the fabrication of complex impregnated diamond drill bits using graphite molds, sprue blocks, gauge blocks, and core molds, making it highly versatile in drill bit manufacturing. Current pressureless impregnation processes typically employ a direct loading and firing method: first, the lower graphite mold, core mold, and sprue forming parts are placed in position; then, diamond matrix powder is loaded into the annular mold cavity from above; subsequently, the drill bit steel body, transition layer material, and impregnation alloy are placed; finally, the furnace is heated, causing the copper-based solder or copper alloy to melt and, under gravity and capillary action, penetrate the gaps in the matrix powder and connect with the steel body.

[0005] While the aforementioned direct-firing process is mature, it has significant shortcomings when preparing impregnated diamond drill bits with high working layers, complex sprue nozzles, or those requiring support structures at the ends of the steel body. Firstly, the matrix material typically falls into the die cavity from top to bottom. In narrow grooves, at the ends of the sprue nozzles, and near the ends of the steel body, bridging, suspension, and localized material shortages are prone to occur. Simply relying on vibration or manual compaction is insufficient to ensure consistent density throughout the working layer's thickness and circumferential direction.

[0006] Secondly, the diamond and the matrix powder have different specific gravity, particle size and morphology. When the material is loaded, long-distance drop or repeated compaction can easily cause local stratification, resulting in uneven distribution of diamond in the working layer. This can lead to excessively rapid local wear or insufficient cutting edge during drilling.

[0007] Thirdly, traditional drill bit steel bodies and matrix working layers are often connected using flat end faces, shallow steps, or simple annular grooves. To improve connection strength, it is usually desirable to set protruding teeth, grooves, radial holes, axial ribs, undercut grooves, or other support structures at the ends of the steel body, allowing the matrix material to enter around the support structure and form a mechanical interlock. However, in the existing forward-mounting and forward-firing process, the more complex the support structure, the more likely it is to hinder the matrix material from entering the narrow space between the steel body end and the die, forming loose, void, or unimpregnated areas, which in turn reduces the reliability of the connection between the steel body and the working layer.

[0008] Fourth, when the working layer height of the matrix increases or the drill bit end face forms multi-stage teeth, sprues, internal and external gauges, and reinforcing ribs, the internal space of the die becomes more complex, requiring the matrix material to be uniformly filled in a deeper and narrower space. Current processes, to ensure proper loading, can only increase compaction time, reduce the initial loading height, or alter powder flowability. However, these measures often lead to low efficiency, poor forming repeatability, localized over-vibration segregation, and insufficient dimensional stability. For high-life drill bits requiring deep bonding between the steel body and the matrix, these problems are even more pronounced.

[0009] Fifth, in existing pressureless impregnation sintering processes, the impregnating alloy is typically placed between the steel body and the mold or on top of the matrix powder. If the charge density is insufficient or a porous layer exists at the interface, the molten copper alloy tends to flow preferentially along large pores or interface channels during impregnation, leading to localized insufficient impregnation, copper enrichment, porosity, or fluctuations in matrix strength. After sintering, the drill bit is prone to problems such as matrix spalling, separation of the working layer from the steel body, tooth cracks, and premature failure under impact, torque, and axial loads.

[0010] Therefore, how to make the matrix material more compact and uniformly filled in complex mold cavities without significantly increasing equipment complexity, and how to reliably set a support structure at the end of the drill bit steel body to enhance the connection between the steel body and the working layer of the matrix body, are the technical problems that need to be solved in the existing pressureless impregnation and sintering process for impregnated diamond drill bits. Summary of the Invention

[0011] The purpose of this invention is to provide a sintering mold and process method for reverse-mounted, forward-sintering, pressureless impregnation of impregnated diamond drill bits, in order to solve the problems of insufficient compaction of matrix material, easy material shortage in complex structures, difficulty in setting effective support structures at the ends of the steel body, insufficient connection strength between the steel body and the working layer, and poor consistency of the drill bit after sintering in the existing forward-mounted, forward-sintering, pressureless impregnation process.

[0012] The reverse-loading and forward-firing method of this invention refers to the process of inverting the pre-assembled body, which consists of a lower graphite mold, an outer steel sleeve, a drill bit steel body, an inner steel sleeve, and a core mold, during the loading stage. This allows the matrix material to be loaded and compacted from the working layer side of the drill bit while inverted. After the graphite outer sleeve is fitted in, the entire assembly is then snapped back into the forward orientation suitable for pressureless impregnation sintering. Subsequently, the inner and outer steel sleeves are removed, and impregnation materials such as copper solder and copper alloy are filled in for sintering, thereby producing a diamond-impregnated drill bit.

[0013] A sintering mold for a reverse-mounted, forward-sintering, pressureless impregnation and inlay diamond drill bit consists of a graphite jacket, a lower graphite mold, an outer steel sleeve, a drill bit steel body, an inner steel sleeve, and a core mold. The lower graphite mold is placed at the bottom to form the end face and outer positioning reference of the drill bit working layer. The core mold is coaxially connected to the middle of the lower graphite mold and is used to form the inner hole and inner positioning reference of the drill bit. The drill bit steel body is coaxially arranged between the lower graphite mold and the core mold, and its lower end is used to connect with the working layer of the matrix. The outer steel sleeve is detachably fitted on the outside of the drill bit steel body, and the inner steel sleeve is detachably set on the inside of the drill bit steel body. The graphite outer sleeve is used to fit on the outside of the pre-assembled body formed by the lower graphite mold, outer steel sleeve, drill bit steel body, inner steel sleeve and core mold after inverted loading. The outer steel sleeve and inner steel sleeve are used to limit the matrix material filling cavity during the inverted loading stage and are used to be pulled out after the whole body is snapped back into the upright firing position to form a space for adding copper solder, copper alloy or other impregnating materials.

[0014] Preferably, the lower graphite mold is provided with a forming cavity for forming the working layer end face of the drill bit, cutting teeth, sprue, gauge protection structure, weakening groove or reinforcing rib, and the forming cavity, together with the core mold, outer steel sleeve and inner steel sleeve, defines the filling area containing diamond matrix material.

[0015] Preferably, the graphite jacket is a hollow cylindrical or cup-shaped graphite part, and the inner cavity of the graphite jacket is positioned and fitted with the lower graphite mold and the outer side of the pre-assembled body, which is used to provide external constraint on the filled jig material and pre-assembled body after being fitted.

[0016] Preferably, at least one of the outer steel sleeve and the inner steel sleeve is provided with a guide chamfer, draft angle, release coating, pull hole or threaded pull structure so as to be pulled out axially after the whole is snapped back into the correct firing position.

[0017] Preferably, the drill bit steel body is provided with a support structure at one end near the working layer of the matrix. The support structure is an annular groove, an axial groove, a radial hole, an axial tooth, a radial rib, an undercut boss, a roughened connecting surface, or a combination thereof. The support structure is used to be covered by the matrix material when the material is inverted and to form a mechanical lock with the working layer of the matrix after sintering.

[0018] A sintering process for reverse-mounted, forward-firing, pressureless impregnation and setting of diamond drill bits includes the following steps: S1: Assemble the lower graphite mold, outer steel sleeve, drill bit steel body, inner steel sleeve, and core mold, excluding the graphite outer sleeve, to form a pre-assembled body; S2: Invert the pre-assembled assembly as a whole; S3: In the inverted state, diamond matrix material is loaded into the pre-assembly body and compacted; S4: Place the graphite jacket over the outside of the pre-assembled part; S5: Replace the mold, after it has been fitted with the graphite jacket, back into the firing position; S6: Remove the outer and inner steel sleeves; S7: Fill with impregnation material and perform pressureless impregnation sintering.

[0019] Preferably, the diamond matrix material comprises matrix framework powder and single-crystal diamond particles.

[0020] Preferably, before loading the diamond matrix material, a transition layer powder without single-crystal diamond is added in the reverse loading state to fill the annular space gap at the connection between the steel body and the upper edge of the working layer. After the filling is completed, the diamond matrix material is loaded on top of it. The transition layer powder is used to connect the drill bit steel body and the matrix working layer after pressureless impregnation and sintering.

[0021] Preferably, the space formed after removing the outer and inner steel sleeves serves as a filling space for the impregnating material or a flow channel for the molten impregnating material. The impregnating material is one of copper-based solder, brass, copper-tin alloy, copper-manganese alloy, and silver-copper alloy.

[0022] Preferably, the pressureless impregnation sintering temperature is 850°C to 1080°C, and the holding time is 10 min to 120 min. Under the influence of gravity and capillary action, the impregnating material enters the pores of the matrix material and around the end support structure of the drill bit steel body. After cooling, the working layer of the matrix and the drill bit steel body are connected as one.

[0023] Compared with the existing pressureless impregnation process for formal packaging and firing, the present invention has at least the following beneficial effects.

[0024] The present invention loads the material in an inverted state, making the falling direction, compaction direction and filling direction of the complex structure of the working layer more consistent. The powder can preferentially fill the space around the tooth groove, the end of the sprue and the steel support structure, which significantly improves the compactness and uniformity of the material loading in the working layer. The inner and outer steel sleeves play a temporary supporting, positioning and shaping role during the loading stage, which can prevent the drill bit steel body from being eccentric or shaking during the compaction process, and allow the matrix material to be filled in a restricted manner in the inner and outer diameter directions, thereby improving the roundness, coaxiality and working layer dimensional stability of the drill bit. More complex and deeper support structures can be set at the end of the drill bit steel body. When the material is loaded in reverse, the matrix material can be fully filled around the support structure. After sintering, the working layer of the matrix and the steel body not only have a metallurgical bond formed by the impregnated alloy, but also a mechanical lock formed by the support structure, which can improve the connection strength and anti-peeling ability. The inner and outer steel sleeves are removed before the firing process, so they will not become part of the final drill bit, nor will they hinder the impregnation alloy from entering the matrix material. The space formed after the steel sleeves are removed can serve as a channel for the filling and melting flow of the impregnation alloy, which is conducive to the stable impregnation of copper solder or copper alloy into the matrix from the predetermined position, thus improving the impregnation sufficiency. This invention does not require the application of external pressure during the sintering stage, can utilize pressureless impregnation sintering equipment, has strong process adaptability, and can be used to manufacture conventional impregnated diamond drill bits, high working layer impregnated diamond drill bits, drill bits with reinforcing ribs, and drill bits that require enhanced steel body connection interfaces. Attached Figure Description

[0025] Figure 1 A schematic diagram of the cross-sectional view of the reverse-mounted firing mold assembly; Figure 2 The diagram shows the assembly and flipping process of the reverse-mounted firing mold, where (a) is a diagram of filling the mold body material, (b) is a diagram of the graphite outer sleeve being placed outside the pre-assembled mold body material, (c) is a diagram of inverting and flipping back to the firing position, and (d) is a diagram of removing the outer steel sleeve and inner steel sleeve. Figure 3 This is a schematic diagram of the graphite outer casing structure; Figure 4 This is a schematic diagram of the lower graphite mold structure; Figure 5 A schematic diagram of the positioning structure between the outer and inner steel sleeves; Figure 6 A schematic diagram of the drill bit's steel body and its end support structure; Figure 7 This is a schematic diagram of the inner and outer steel sleeve extraction structure; Figure 8 This is a schematic diagram of the core mold structure.

[0026] Explanation of reference numerals in the attached diagram: 1. Graphite jacket; 2. Lower graphite mold; 3. Outer steel sleeve; 4. Drill bit steel body; 5. Inner steel sleeve; 6. Core mold. Detailed Implementation

[0027] like Figure 1 As shown, a sintering mold for a reverse-mounted, forward-sintering, pressureless impregnation and inlay diamond drill bit consists of a graphite jacket 1, a lower graphite mold 2, an outer steel sleeve 3, a drill bit steel body 4, an inner steel sleeve 5, and a core mold 6. The components are preferably arranged coaxially to ensure the coaxiality of the drill bit's inner hole, outer circle, and working layer end face after sintering. The lower graphite mold 2 is placed at the bottom and is used to form the end face of the drill bit working layer and the outer positioning reference. The core mold 6 is coaxially connected to the middle of the lower graphite mold 2 and is used to form the inner hole of the drill bit and the inner positioning reference. The drill bit steel body 4 is coaxially arranged between the lower graphite mold 2 and the core mold 6, and its lower end is used to connect with the working layer of the matrix. The outer steel sleeve 3 is detachably sleeved on the outside of the drill bit steel body 4, and the inner steel sleeve 5 is detachably arranged on the inside of the drill bit steel body 4. The lower ends of the outer steel sleeve 3 and the inner steel sleeve 5 are both connected to the lower graphite mold 2, and together they limit the matrix material filling cavity and support the drill bit steel body 4 during the inverted loading stage.

[0028] The structure of graphite jacket 1 can be found in [reference]. Figure 3 The graphite jacket 1 is preferably a hollow cylindrical or cup-shaped graphite part, the inner cavity size of which is adapted to the outer size of the pre-assembled body. After the inverted loading is completed, the graphite jacket 1 is put on the outside of the pre-assembled body. On the one hand, it is used to support and constrain the matrix material when it is snapped back into the upright firing position. On the other hand, it is used to form an external thermally stable support during the sintering process to prevent the matrix material and impregnated alloy from overflowing. The graphite jacket 1 is an external support and sintering positioning part that is put on after the inverted loading. During the loading stage, the graphite jacket 1 is not put on first so that the inverted loading can be carried out from the open end of the pre-assembled body. After the matrix material is filled and compacted, the graphite jacket 1 is put on the outside of the pre-assembled body, and then the whole is snapped back into the upright firing position. After the graphite jacket 1 cooperates with the lower graphite mold 2 and the core mold 6, it forms a stable external support space for sintering, ensuring that the filled matrix material does not fall apart or shift significantly when the inner and outer steel sleeves are pulled out and the impregnated material is added.

[0029] The lower graphite mold 2 can be a disc-shaped or cup-shaped graphite forming part. The material of the lower graphite mold 2 is preferably high-temperature resistant graphite. The upper surface of the lower graphite mold 2 is processed into a corresponding forming cavity according to the required drill bit end face structure. The forming cavity may include a cutting tooth forming groove, a sprue forming groove, an inner and outer diameter positioning groove, a matrix reinforcing rib forming groove, and a graphite sheet positioning structure for forming a drill bit end face weakening groove. The outer circle and inner hole of the lower graphite mold 2 can be respectively provided with positioning steps so as to cooperate with the graphite outer sleeve 1, the core mold 6, and the outer steel sleeve 3.

[0030] The preferred structure of the lower graphite mold 2 is as follows: Figure 4 As shown, the lower graphite mold 2 can pre-form multiple circumferentially distributed tooth grooves and sprue structures within the annular working layer area. For drill bits that require a high working layer, layered diameter protection, or reinforcing ribs, the lower graphite mold 2 can also be equipped with corresponding grooves, bosses, or positioning holes to ensure that the complex structure of the working layer is formed in one step after sintering.

[0031] The positioning and extraction relationship of the outer steel sleeve 3 and the inner steel sleeve 5 can be found in [reference]. Figure 5 and Figure 7The outer steel sleeve 3 is fitted onto the outside of the drill bit steel body 4, and the inner steel sleeve 5 is fitted onto the inside of the drill bit steel body 4. During loading, the two sleeves, together with the drill bit steel body 4, form a relatively stable annular or stepped loading boundary. The outer steel sleeve 3 and inner steel sleeve 5 are preferably made of steel, which has higher rigidity than graphite parts. This makes them less prone to deformation during vibration loading and compaction, thus improving the geometric accuracy of the filler material. The outer steel sleeve 3 and inner steel sleeve 5 are removable temporary forming sleeves, preferably with guide chamfers, slight draft angles, or segmented pull-out structures, so that they can be easily pulled out after the entire assembly is snapped back into the correct firing position.

[0032] The surfaces of the outer steel sleeve 3 and the inner steel sleeve 5 can be provided with draft angles, polished surfaces, draft coatings, or pull-out threaded holes. When it is necessary to remove the steel sleeve, it can be removed by rotation, slight tapping, thread pulling, or axial pulling with a special clamp. To avoid disturbing the filled jig material when removing the steel sleeve, the surface of the steel sleeve in contact with the jig material is preferably smooth, and a guide mating surface can be provided between the lower end of the steel sleeve and the lower graphite mold 2. The outer steel sleeve 3 and the inner steel sleeve 5 can also adopt a two-lobed, three-lobed, or segmented structure to accommodate the drill bit steel body 4 with a large support protrusion or undercut structure.

[0033] The structure of drill bit steel body 4 can be found in [reference]. Figure 6 The drill bit steel body 4 is the final steel body of the drill bit. Its upper end is used to connect with the drill rod or reamer, and its lower end is used to connect with the matrix working layer. The lower end of the drill bit steel body 4 can be provided with a support structure that enters the matrix working layer. The support structure can be a circumferentially distributed support tooth, axial reinforcing rib, annular step, radial hole, groove, undercut step or roughened connection surface, welded or machined support rib, or a combination of the above structures. When the material is inverted for loading, the support structure is directly covered by the matrix material. Under the action of gravity, vibration and tamping, the powder fully enters the area around the support structure, and after sintering, a connection interface is formed by the combined action of mechanical interlocking and metallurgical bonding. Preferably, the support structure at the lower end of the drill bit steel body 4 consists of multiple axially distributed support teeth in a circumferential direction, with a matrix material filling groove formed between each support tooth. During inverted loading, the diamond-containing matrix material is fully compacted between the support teeth; after sintering, the support teeth are embedded in the matrix working layer, allowing the drill bit to transfer the load jointly by multiple support teeth under the action of drilling torque, reducing the shear stress at a single interface.

[0034] Preferably, the lower end of the drill bit steel body 4 is provided with an annular groove and a radial through hole. When the material is loaded inverted, the matrix material is filled into the annular groove and passes through both sides of the radial through hole. After impregnation and sintering, a matrix locking structure similar to riveting is formed, which can further improve the connection strength between the steel body and the working layer.

[0035] Preferably, before loading the diamond-containing matrix material, a transition layer powder without single-crystal diamond is added in the reverse loading state to fill the upper annular space at the junction of the steel body and the working layer. After filling, the diamond-containing matrix material is loaded on top. This can mix the matrix skeleton powder, diamond particles, and a small amount of volatile liquid into a wet material with a certain degree of fluidity, thereby improving the filling performance around the complex support structure. Before sintering, the volatile liquid is removed by drying to prevent the formation of pores during sintering.

[0036] The structure of core mold 6 can be seen in Figure 8 The core mold 6 is used to form the inner hole of the drill bit and define the inner diameter forming surface. The core mold 6 can be made of graphite, heat-resistant steel or other materials that are dimensionally stable and easy to demold at sintering temperature. When the core mold 6 is made of graphite, it can withstand the sintering temperature together with the lower graphite mold 2. When the core mold 6 is made of metal, it is preferable to make it easy to remove before or after sintering by leaving a gap and a demolding structure.

[0037] The impregnation material is a copper-based alloy with a melting point lower than the temperature at which diamond suffers significant thermal damage. The impregnation temperature and holding time are controlled in conjunction with the particle size of the matrix matrix powder. Preferably, the sintering temperature is 850°C to 1080°C, and the holding time is 10 min to 120 min. For drill bits using low-temperature impregnation materials, even lower temperatures and shorter holding times can be used to reduce thermal damage to the diamond.

[0038] The reverse loading and forward firing process of this embodiment is as follows: Figure 2 As shown, a sintering process for reverse-mounted, forward-sintered, pressureless impregnation and setting of diamond drill bits specifically includes the following steps: Step 1: Parts preparation. Clean the graphite jacket 1, lower graphite mold 2, outer steel sleeve 3, drill bit steel body 4, inner steel sleeve 5, and core mold 6 to remove oil, dust, and burrs. If necessary, apply a small amount of release agent to the surfaces of the outer steel sleeve 3, inner steel sleeve 5, and core mold 6 that come into contact with the matrix material. Place the corresponding forming parts, gauge-protecting polycrystalline diamond, or other auxiliary parts in the tooth groove, sprue groove, or gauge-protecting part positioning groove of the lower graphite mold 2. Step 2: Pre-assembly. First, place the lower graphite mold 2 on the assembly platform and position the core mold 6 coaxially with the lower graphite mold 2. Then, place the drill bit steel body 4 in the annular area between the lower graphite mold 2 and the core mold 6, so that the lower end support structure of the drill bit steel body 4 faces the working layer forming cavity. Then, install the outer steel sleeve 3 and the inner steel sleeve 5, so that the outer steel sleeve 3 is located outside the drill bit steel body 4 and the inner steel sleeve 5 is located inside the drill bit steel body 4. At this time, the graphite outer sleeve 1 is not installed yet, so as to retain the open space required for inverted loading. Step 3: Invert the pre-assembled body formed by the lower graphite mold 2, outer steel sleeve 3, drill bit steel body 4, inner steel sleeve 5 and core mold 6, so that the opening of the working layer forming cavity, which was originally facing downwards, faces upwards. During the inversion process, the outer steel sleeve 3 and inner steel sleeve 5 support each other with the drill bit steel body 4, which can maintain the stability of the forming space and prevent the drill bit steel body 4 from shifting relative to the lower graphite mold 2 and core mold 6. Step 4: Loading. In the inverted state, the pre-mixed, diamond-free transition layer powder is loaded into the annular loading cavity formed by the lower graphite mold 2, outer steel sleeve 3, drill bit steel body 4, inner steel sleeve 5, and core mold 6. After filling the annular space at the connection between the steel body and the upper edge of the working layer, diamond-containing matrix material is loaded on top. The loading can be done by adding small amounts in multiple layers. After each layer is added, it is vibrated, compacted, or lightly pressed to ensure that the matrix material fully enters the cutting tooth forming groove, the end of the sprue, the concave and convex spaces of the lower support structure of the drill bit steel body 4, and the narrow areas of the inner and outer diameters. Step 5: Insert the graphite sleeve. After the matrix material is filled and compacted, insert the graphite sleeve 1 onto the outside of the pre-assembled body from above, so that the graphite sleeve 1 and the lower graphite mold 2 form a positioning fit. After the graphite sleeve 1 is inserted, the filled matrix material is constrained by the graphite sleeve 1, the lower graphite mold 2, the outer steel sleeve 3, the inner steel sleeve 5, the drill bit steel body 4, and the core mold 6. Step Six: Return to the upright firing position. After fitting the graphite jacket 1, flip the entire mold back to the upright position suitable for pressureless impregnation sintering, that is, the drill bit working layer is located at the bottom of the mold, and the impregnation material filling position is located above or to the side above it. Since the graphite jacket 1 has formed an external constraint on the assembly, the matrix material is not easy to loosen or shift during the flipping process; Step 7: Remove the steel sleeves. Pull out the inner steel sleeve 5 and the outer steel sleeve 3 axially. If necessary, a slight rotation or pulling clamp can be used. After the inner and outer steel sleeves are pulled out, predetermined impregnation material filling channels or clearance spaces are formed on the inner and outer sides of the drill bit steel body 4 and at positions adjacent to the matrix material. Step 8: Fill with impregnation material and sinter. Fill the space formed after removing the steel sleeve with copper solder, copper alloy, or other copper-based impregnation alloy. Depending on the matrix formula and steel body connection requirements, a transition layer material can also be added below or around the impregnation alloy. Then, place the integral mold into a sintering furnace for pressureless impregnation sintering. After heating to the melting temperature of the impregnation alloy, hold the temperature to allow the molten metal to penetrate into the pores of the matrix material and around the support structure of the drill bit steel body 4 under gravity and capillary action. After cooling, a dense matrix working layer is formed and connected to the drill bit steel body 4 as a whole. Step 9: Cooling and demolding. After sintering, cool to a safe temperature with the furnace or according to the predetermined cooling regime. Remove the graphite outer jacket 1, lower graphite mold 2 and core mold 6. Take out the sintered drill bit blank and perform necessary cleaning and post-processing on the end face, inner and outer diameter, connecting threads and sprue.

[0039] Working principle of the invention: This invention changes the traditional upright loading method to inverted loading, allowing the matrix material to directly enter the complex structural space from top to bottom at the working layer forming cavity. Since the drill bit working layer end face, tooth grooves, and steel support structure are all located below the loading direction in the inverted state, the powder can preferentially fill these areas prone to material shortage under the action of gravity. Then, vibration or tamping is used to further eliminate voids, thereby improving the overall compactness of the loading.

[0040] The outer steel sleeve 3 and the inner steel sleeve 5 act as temporary inner and outer forming walls during loading. Compared with graphite forming parts, the steel sleeves have higher impact resistance and deformation resistance, and can withstand the local loads generated during vibration and tamping, keeping the drill bit steel body 4 stable during the loading stage. At the same time, the steel sleeves are removed before firing, so they will not be sintered with the matrix and will not hinder the impregnation flow of molten copper alloy.

[0041] The four end support structures of the drill bit steel body are fully surrounded by the matrix material during inverted loading. During sintering, the copper solder or copper alloy melts and penetrates into the gaps between the matrix powder, entering the interface region along the micropores around the support structure. After cooling, it solidifies the matrix skeleton, diamond, and steel body connection ends into a whole. This connection method combines impregnated alloy metallurgical bonding, matrix shrinkage clamping, and mechanical interlocking of the support structure, which can improve the shear, torsion, and peel resistance between the working layer and the steel body.

[0042] In the above process, the matrix material can be a mixture of matrix skeleton powder, single-crystal diamond particles, and necessary process aids, or a wet or semi-wet mixture with a small amount of temporary binder added; the impregnation material can be copper-based solder, copper alloy, brass, copper-tin alloy, copper-manganese alloy, or other low-temperature or medium-temperature impregnation alloys suitable for impregnating diamond-set drill bit matrices. The sintering temperature and holding time can be determined according to the matrix formula, drill bit specifications, and melting characteristics of the impregnation alloy.

[0043] The "reverse loading" of this invention only applies to the loading and mold conversion stages, while "forward firing" maintains the favorable flow conditions for the impregnated alloy to enter the matrix from top to bottom or through predetermined channels during pressureless impregnation sintering. Therefore, this invention improves the compactness of the loading while retaining the advantages of pressureless impregnation sintering equipment, which is simple and suitable for forming complex structures.

[0044] The above embodiments illustrate the preferred embodiments of the present invention. Any technical solution based on the six-part mold described in the present invention, involving first reversing the loading process, then inserting the graphite jacket, returning to the upright firing position, removing the inner and outer steel sleeves, and adding impregnating material for pressureless impregnation and sintering, should fall within the protection scope of the present invention.

Claims

1. A sintering mold for reverse-mounted, forward-firing, pressureless impregnation and setting of diamond drill bits, characterized in that: It consists of a graphite jacket (1), a lower graphite mold (2), an outer steel sleeve (3), a drill bit steel body (4), an inner steel sleeve (5), and a core mold (6); The lower graphite mold (2) is placed at the bottom to form the end face and outer positioning reference of the drill bit working layer. The core mold (6) is coaxially connected to the middle of the lower graphite mold (2) and is used to form the inner hole and inner positioning reference of the drill bit. The drill bit steel body (4) is coaxially set between the lower graphite mold (2) and the core mold (6), and its lower end is used to connect with the working layer of the matrix. The outer steel sleeve (3) is detachably fitted on the outside of the drill bit steel body (4), and the inner steel sleeve (5) is detachably set. Inside the drill bit steel body (4), a graphite sleeve (1) is used to be fitted onto the outside of the pre-assembled body after the pre-assembled body formed by the lower graphite mold (2), outer steel sleeve (3), drill bit steel body (4), inner steel sleeve (5) and core mold (6) is inverted and filled; the outer steel sleeve (3) and inner steel sleeve (5) are used to limit the filling cavity of the body material during the inverted filling stage, and are used to be pulled out after the whole body is snapped back into the upright burning posture to form a space for filling copper solder, copper alloy or other impregnating materials.

2. The sintering mold for reverse-mounted, forward-firing, pressureless impregnation and setting of diamond drill bits according to claim 1, characterized in that: The lower graphite mold (2) is provided with a forming cavity for forming the working layer end face of the drill bit, cutting teeth, sprue, gauge structure, weakening groove or reinforcing rib. The forming cavity, together with the core mold (6), outer steel sleeve (3) and inner steel sleeve (5), defines the filling area containing diamond matrix material.

3. The sintering mold for reverse-mounted, forward-firing, pressureless impregnation and setting of diamond drill bits according to claim 1, characterized in that: The graphite jacket (1) is a hollow cylindrical or cup-shaped graphite part. The inner cavity of the graphite jacket (1) is positioned and matched with the lower graphite mold (2) and the outer side of the pre-assembled body, and is used to externally constrain the filled body material and pre-assembled body after being fitted in.

4. The sintering mold for reverse-mounted, forward-firing, pressureless impregnation and setting of diamond drill bits according to claim 1, characterized in that: At least one of the outer steel sleeve (3) and the inner steel sleeve (5) is provided with a guide chamfer, draft angle, release coating, pull hole or threaded pull structure so as to be pulled out axially after the whole is snapped back into the positive firing position.

5. The sintering mold for reverse-mounted, forward-firing, pressureless impregnation and setting of diamond drill bits according to claim 1, characterized in that: The drill bit steel body (4) is provided with a support structure at one end near the working layer of the matrix. The support structure is an annular groove, an axial groove, a radial hole, an axial tooth, a radial rib, an undercut boss, a roughened connecting surface or a combination thereof. The support structure is used to be covered by the matrix material when the material is inverted and to form a mechanical lock with the working layer of the matrix after sintering.

6. A method for sintering reverse-mounted, forward-firing, pressureless impregnation and setting of diamond drill bits, using the sintering mold for reverse-mounted, forward-firing, pressureless impregnation and setting of diamond drill bits as described in any one of claims 1 to 5, characterized in that: Includes the following steps: S1: Assemble the lower graphite mold (2), outer steel sleeve (3), drill bit steel body (4), inner steel sleeve (5) and core mold (6) except for the graphite outer sleeve (1) to form a pre-assembled body; S2: Invert the pre-assembled assembly as a whole; S3: In the inverted state, diamond matrix material is loaded into the pre-assembly body and compacted; S4: Place the graphite jacket (1) on the outside of the pre-assembled body; S5: Put the whole mold, after being fitted with the graphite jacket (1), back into the firing position; S6: Remove the outer steel sleeve (3) and the inner steel sleeve (5); S7: Fill with impregnation material and perform pressureless impregnation sintering.

7. The sintering process for reverse-mounted, forward-firing, pressureless impregnation and setting of diamond drill bits according to claim 6, characterized in that: The diamond matrix material includes matrix framework powder and single-crystal diamond particles.

8. The sintering process for reverse-mounted, forward-firing, pressureless impregnation and setting of diamond drill bits according to claim 6, characterized in that: Before loading the diamond matrix material, a transition layer powder without single crystal diamond is added in the reverse loading state to fill the upper edge annular space gap at the connection between the steel body and the working layer. After loading is completed, the diamond matrix material is loaded on top of it. The transition layer powder is used to connect the drill bit steel body (4) and the matrix working layer after pressureless impregnation and sintering.

9. The sintering process for reverse-mounted, forward-firing, pressureless impregnation and setting of diamond drill bits according to claim 6, characterized in that: The space formed after removing the outer steel sleeve (3) and the inner steel sleeve (5) serves as a filling space for the impregnating material or a flow channel for the molten impregnating material. The impregnating material is one of copper-based solder, brass, copper-tin alloy, copper-manganese alloy, and silver-copper alloy.

10. The sintering process for reverse-mounted, forward-firing, pressureless impregnation and setting of diamond drill bits according to claim 6, characterized in that: The pressureless impregnation sintering temperature is 850℃ to 1080℃, and the holding time is 10min to 120min. The impregnation material enters the pores of the matrix material and the surrounding area of ​​the end support structure of the drill bit steel body (4) under gravity and capillary action. After cooling, the matrix working layer is connected to the drill bit steel body (4) as one unit.

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