Inner through hole drill bit welding and detecting method

Abstract

The invention discloses an inner through hole drill bit welding and detecting method, and relates to the field of coal mine drilling tool machining. The method comprises the five steps of preparation before welding, gauge protection strip copper welding, PDC cutting blade silver welding, post-welding treatment and welding effect detection. The method comprises the following steps: carrying out sand blasting and ethanol cleaning pretreatment, carrying out silver soldering on a PDC (Polycrystalline Diamond Compact) cutting blade by using an oxyacetylene flame copper welding gauge protection strip, superaudio frequency induction heating equipment and a special induction coil, carrying out heat preservation and slow cooling treatment, and carrying out multi-level detection, including appearance, surface and internal defect and destructive tests. A detection result shows that the welding strength reaches more than 175 MPa. According to the invention, the welding process is optimized, the efficiency and the quality stability are improved, the reliability of the drilling tool under complex geological conditions is enhanced, the production cost is reduced, and the method is suitable for industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal mine drill production, and relates to a method for welding and detecting an internal through-hole drill bit. Background Art

[0002] The internal through-hole drill bit is an indispensable key component in coal mine drilling, and its processing quality and performance directly affect the drilling efficiency and the service life of the drill. In the prior art, the manufacturing of internal through-hole drills (especially flat-bottom type) mainly relies on the manual oxyacetylene gas welding process. This method welds the cutting piece and the drill body by flame heating. However, there are many technical defects in its actual application. First of all, it is difficult to precisely control the temperature during the heating process of oxyacetylene gas welding. Operators usually judge the heating degree by observing the flame color based on experience, and this subjective judgment method is likely to cause the temperature to be too high or uneven. When the heating temperature exceeds a certain range, the working part of the synthetic polycrystalline diamond (PDC) in the cutting piece may undergo performance degradation, thus losing the cutting and wear resistance capabilities, resulting in premature scrapping of the drill. Secondly, manual gas welding completely relies on manual operation, with high labor intensity for workers, long preheating time for the drill body, and due to uneven temperature distribution, cracks are likely to occur in the drill body during the welding process, leading to low processing efficiency. In addition, the stability of the welding quality is difficult to guarantee, and the bonding strength between the cutting piece and the drill body is insufficient. Especially when drilling in complex alternating strata or hard rock strata, problems such as tooth dropping, chip breaking, and premature wear of the outer circle of the drill body often occur, greatly shortening the service life of the drill.

[0003] The deficiencies of the prior art are also reflected in many aspects. On the one hand, manual oxyacetylene gas welding is difficult to meet the requirements of the upgrade of drill processing towards automation and industrialization. With the continuous improvement of the requirements of modern industry for high-efficiency and safe production, the limitations of traditional manual operation have become increasingly obvious. On the other hand, there are significant safety hazards during the welding process, especially for large-diameter drills, and manual flame heating increases the operation risk. In addition, due to the lack of scientific process management and advanced equipment support, the scrap rate is relatively high during the processing, bringing additional economic burdens to enterprises. Research shows that the selection and control of the welding process are important factors affecting the performance of PDC drills, and the traditional methods have significant shortcomings in terms of process optimization and quality assurance. For example, it is difficult to ensure that the temperature and time of each welding are the same during manual operation, resulting in large fluctuations in product quality and difficulty in meeting the requirements of mass production.

[0004] In recent years, the industry has attempted to introduce some improved technologies to address the above problems. For example, brazing processes such as copper brazing and silver brazing are applied in drill tool manufacturing and have received some attention because they can provide relatively high welding strength and fatigue resistance. However, these processes are still mainly manual in actual applications and do not fully utilize modern heating equipment and process control means. Induction heating technology, as an efficient heating method, has been applied in some metal processing fields. It generates heat through electromagnetic induction and has the advantages of fast heating speed and high energy utilization rate. Nevertheless, the application of this technology in the welding of internal through-hole drills is still immature, especially for the design of special induction coils for four-wing structures and the matching process flow, which is still in the stage of technical exploration. In addition, existing post-welding treatment methods mostly use natural cooling and do not fully consider the release of welding stress, which may lead to fatigue failure of drill tools during use. In terms of detection, existing technologies are usually limited to visual inspection and simple dimensional measurement, lacking systematic quality verification means, and potential defects are difficult to be detected and corrected in a timely manner.

[0005] In summary, the traditional welding process for internal through-hole drills has problems such as low efficiency, poor safety, and unstable quality, and the existing improved technologies have not formed a complete set of solutions. In view of these deficiencies, it is necessary to develop a scientific, efficient, and safe welding and detection method to optimize the welding process flow, improve the processing quality and production efficiency, and at the same time meet the performance requirements of drill tools under complex geological conditions. Summary of the Invention

[0006] In view of this, the present invention provides a method for welding and detecting internal through-hole drills to solve the problems of low efficiency and unstable quality in traditional welding processes. This method optimizes the welding process through a scientific process flow and advanced equipment, improves the processing efficiency, and verifies the welding quality through multi-level detection.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A method for welding and detecting internal through-hole drills includes the following steps:

[0009] (1) Preparation before welding:

[0010] Pre-treat the welding position of the drill body of the internal through-hole drill and the PDC cutting piece, including sandblasting and cleaning with anhydrous ethanol to remove surface oxide scales and dirt;

[0011] (2) Brazing the gauge strip:

[0012] Using brazing solder and brazing flux, preheat the gauge strip groove of the drill body with an oxyacetylene flame until it turns dark red. Then, apply the brazing flux to the welding position to remove the oxide scale. Next, melt the brazing solder in the flame and pour it into the gauge strip groove. Place the gauge strip in the groove and apply pressure while heating until it is firmly welded.

[0013] (3) Silver brazing PDC cutting inserts:

[0014] Using silver brazing solder and silver brazing flux, heat the four-wing cutting insert groove of the drill body with an ultra-audio frequency induction heating device and a special induction coil. The special induction coil is made of copper tubing, and its shape and structure are designed to be similar to the geometric characteristics of the four-wing cutting insert groove of the drill body. The distance between the induction coil and the four-wing cutting insert groove of the drill body is 10 - 15 mm to ensure that the heating area is parallel or equidistant from the cutting insert groove, and the current flow direction between adjacent turns is the same, thus improving the heating uniformity and efficiency. The number of turns and the gap with the workpiece are adjusted according to the heating efficiency. During the heating process, control the welding temperature within an appropriate range through a closed-loop temperature control system to avoid graphitization of the PDC cutting insert. Apply the silver solder paste flux to the cutting insert groove. After removing the oxide scale, place the PDC cutting insert in the groove and weld it.

[0015] (4) Post-welding treatment:

[0016] Put the welded drill bit into a heat preservation pool or furnace, cover it with a layer of perlite powder, keep it warm for a period of time, and then slowly cool it to room temperature.

[0017] (5) Welding effect detection:

[0018] Conduct visual inspection, surface defect inspection, internal defect inspection, and destructive tests on the welded PDC cutting inserts to verify whether the welding strength and quality meet the design requirements.

[0019] Furthermore, in step (1), the pretreatment of the PDC cutting insert also includes: cross-grinding the hard alloy welding surface with fine sandpaper to remove the oxide scale, and heating the ground PDC cutting insert and the sheared silver brazing sheet in a container filled with silver brazing flux until it becomes paste-like.

[0020] Furthermore, in step (2), the brazing solder is L10*, with a specification of Φ2×1000 mm and a melting temperature of 880°C to 909°C; the brazing flux is CJ30*, with a melting temperature of 650°C.

[0021] Furthermore, in step (3), the silver brazing solder is Bag61*, with a specification of Φ2×450 mm or δ0.2×25 mm and a melting temperature of 630°C to 690°C; the silver brazing flux is QJ10*, with a melting temperature of 600°C to 850°C.

[0022] Further, in step (3), the special induction coil is made of copper pipe with a diameter of more than 4 mm. The gap between the small workpiece and the induction coil is controlled within 1 - 3 mm. The manufacturing method includes: after annealing treatment, fine sand or fine salt is poured into it, and after bending and forming, the filler is removed, and a high-temperature resistant insulating material is sleeved to prevent short circuit between turns.

[0023] Further, in step (4), the post-welding treatment also includes:

[0024] Put the welded drill bit into a heat preservation pool or a heat preservation furnace, cover it with a perlite powder layer with a thickness of not less than 10 cm, and after heat preservation for 4 hours, slowly cool it to room temperature;

[0025] Clean the drill bit with hot water and a wire brush to remove the surface welding flux;

[0026] Grind the outer circle of the drill body with a hand-held grinding wheel so that the diameter protection strip exposes no more than 0.1 mm outside the circle, and remove the excess welding flux;

[0027] Perform sandblasting treatment on the drill bit to keep the surface clean.

[0028] Further, in step (5), the appearance inspection includes the following requirements and methods:

[0029] Check that the weld of the PDC cutting insert drill bit shall have no air holes, welding flux, or welding slag. The outer surface painting shall be uniform and beautiful, using the visual inspection method;

[0030] Check that the PDC cutting insert shall not be damaged, the composite insert matrix shall fit tightly with the blade groove of the drill body, the drill body and the diameter protection strip shall have no cracks, and the lower end of the diameter protection strip shall be flush with the assembly of the drill body, using the visual inspection method.

[0031] Further, in step (5), the surface defect inspection includes the following welding test requirements and methods:

[0032] The PDC cutting insert and the blade groove of the drill body shall fit tightly. The welding shall have no air holes, cracks or slag inclusion defects, and the welding shall be full and firm, measured with a vernier caliper;

[0033] The welding of the diameter protection strip and the drill body shall have no air holes, slag inclusion, or crack defects. The surrounding gap shall be welded full, and the weld shall be higher than the surface of the drill body, and the welding shall be firm, using the visual inspection method.

[0034] Further, in step (5), the surface defect inspection also includes the thread test, requiring that the internal thread surface of the drill body is smooth and shiny, without iron filings, oxidation or rust spots, using the visual inspection method.

[0035] Further, in step (5), the internal defect inspection includes the dimension test, with the requirements as follows:

[0036] The nominal diameter of the outer diameter of the drill bit and the size of the PDC cutting insert meet the design requirements, measured with a vernier caliper;

[0037] The height, cutting angle, side inclination angle, and back angle of the drill bit meet the requirements of the drawing. The height tolerance of the drill bit is ±1 mm, and it is measured using a vernier caliper and an angle gauge.

[0038] After the gauge strip is welded to the drill bit body, its dimensions meet the design requirements and are measured using a vernier caliper.

[0039] Furthermore, in step (5), internal defect inspection is performed using X-ray or γ-ray detection to check for porosity, slag inclusions, or lack of penetration defects in the weld.

[0040] Furthermore, in step (5), the destructive tests include:

[0041] Macroscopic metallographic analysis: Detect the weld metallographic structure to verify the welding quality;

[0042] Shear strength test: Test the shear strength of the welded surface of the PDC cutting piece on a material testing machine. The calculation formula is: τ = F / (π × D2 / 4), where F is the average value of the shear load and D is the diameter of the PDC cutting piece; the technical index requires that the shear strength is not less than 175 MPa.

[0043] The beneficial effects of the present invention are as follows:

[0044] 1. Improve welding efficiency and process stability

[0045] The present invention combines brazing and silver soldering processes, which are respectively used for welding the gauge strip and the PDC cutting piece, optimizing the welding process. Brazing uses oxyacetylene flame heating, and silver soldering uses an ultra-audio frequency induction heating device and a special induction coil. The two heating methods are reasonably divided according to the characteristics of different components. The special induction coil is designed according to the geometric characteristics of the four-wing cutting piece groove to ensure heating uniformity, significantly shortening the preheating time and improving the processing efficiency compared with traditional manual gas welding. At the same time, the standardized design of the process flow reduces the randomness of manual operation, improves the stability of the welding process, and reduces the defect rate caused by improper operation.

[0046] 2. Enhance welding quality and bonding strength

[0047] Before welding, the drill body and PDC cutting bits of the present invention are pretreated by sandblasting and cleaning with absolute ethanol to ensure that the welding surface is clean and free of impurities, providing a good foundation for subsequent welding. During the silver brazing process, the combination of a special induction coil and an ultra-audio-frequency induction heating device concentrates the heat on the four-wing cutting bit groove. Together with the application of a silver brazing paste flux, it ensures the fullness and firmness of the weld seam. After welding, through heat preservation and slow cooling treatment, the welding stress is effectively released, avoiding the generation of cracks in the drill body. The implementation of multi-level detection means (appearance inspection, surface defect inspection, internal defect inspection, and destructive tests) further verifies the welding quality and ensures that the bonding strength between the PDC cutting bit and the drill body meets the design requirements.

[0048] 3. Improve the applicability and reliability of the drill

[0049] The internal through-hole drill bit processed by the method of the present invention exhibits excellent performance under various geological conditions. The copper-brazed diameter protection strip enhances the wear resistance of the outer circle of the drill body, while the silver-brazed PDC cutting bit ensures the strength and stability of the cutting part. In the welding effect detection, the results of the shear strength test show that the strength of the welding surface is not less than 175 MPa, capable of withstanding the impact loads of complex alternating strata and hard rock strata. In addition, the thread test and dimension test ensure that the assembly accuracy and geometric parameters of the drill bit and drill pipe meet the requirements, thereby improving the reliability of the drill in actual use and extending its service life.

[0050] 4. Reduce production costs and safety risks

[0051] Compared with traditional manual oxyacetylene gas welding, by introducing an ultra-audio-frequency induction heating device, the present invention reduces the dependence on manual experience, lowers the labor intensity and operation risks of workers. The efficient heating of the special induction coil reduces energy waste. The post-welding sandblasting treatment and grinding process improve the surface quality and reduce the rework rate. The systematic detection process can timely detect potential defects during the production stage, avoiding late failures caused by quality problems, thereby reducing production costs and economic losses and providing technical support for the industrial production of internal through-hole drill bits.

[0052] 5. Promote industrialization and automation development

[0053] The method of the present invention combines modern heating technology with scientific technological processes, laying a foundation for the batch production of internal through-hole drill bits. The design and use of the special induction coil, as well as the standardized implementation of multi-level detection means, meet the requirements of automated production. Compared with traditional manual operations, this method has significant advantages in process repeatability and quality consistency, can meet the urgent needs of the modern coal mine drilling industry for efficient, safe, and reliable drills, and promotes the industrial upgrading of drill manufacturing technology.

[0054] Other advantages, objects and features of the present invention will be set forth in part in the following description, and in part will be obvious to those skilled in the art upon examination of the following, or may be learned from the practice of the present invention. The objects and other advantages of the present invention may be realized and obtained by the following description of the specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, wherein:

[0056] Figures 1 to 4 It is a schematic diagram of an internal through-hole PDC drill (flat-bottom type) in an embodiment of the present invention.

[0057] Figure 5 、 6 It is the metallographic inspection result of the welding quality in an embodiment of the present invention.

[0058] Reference numerals: 1 - welded assembly of internal through-hole drill body; 2 - welded assembly of cross beam; 3 - pin column; 4 - ball head pin column. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0059] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0060] Among them, the drawings are only for illustrative purposes, showing only schematic diagrams, not physical diagrams, and should not be construed as a limitation to the present invention; in order to better illustrate the embodiments of the present invention, some components in the drawings will be omitted, enlarged or reduced, which does not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0061] In the attached drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the attached drawings. This is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the attached drawings are only for illustrative purposes and should not be construed as a limitation of the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0062] Please refer to Figures 1 to 4 , which is a structural schematic diagram of an internal through-hole PDC drill (flat-bottom type), mainly composed of the following components: internal through-hole drill body assembly welding 1, crossbeam assembly welding 2, pin 3, and ball head pin 4.

[0063] Example 1: Welding and Detection of Φ96mm Four-wing Concave PDC Bit

[0064] 1. Preparation before welding

[0065] Select a Φ96mm four-wing concave internal through-hole drill bit. The drill bit body is made of 42CrMo steel and is subjected to overall quenching and tempering treatment, with HRC 25 - 30, and is equipped with 4 pieces of PDC cutting blades with a size of Φ13.44mm × 8mm. Place the four-wing cutting blade grooves and gauge strip grooves of the drill body in a sandblasting machine, and perform sandblasting treatment with 80-mesh alumina sand. The sandblasting pressure is 0.5MPa, and it lasts for 15 seconds to remove the surface oxide scale and oil stain. Subsequently, wipe the welding position with a cotton cloth soaked in anhydrous ethanol to ensure that the surface is clean and free of residues. Cross-grind the hard alloy welding surface of the PDC cutting blade with 400-mesh fine sandpaper, with each piece being ground for about 30 seconds to remove the oxide layer. Place the ground PDC cutting blade and the sheared Bag61* silver solder strip (specification Φ2 × 450mm) in a heat-resistant container containing QJ10* silver solder flux, heat it to 150°C, and stir evenly to form a paste for standby.

[0066] 2. Brazing the gauge strip

[0067] Select L10* copper solder (specification Φ2×1000mm, melting temperature 880℃-909℃) and CJ30 copper soldering flux (melting temperature 650℃). Adjust the oxyacetylene flame to a neutral flame with an inner flame length of about 10mm. Preheat the diameter-preserving strip groove of the drill body and heat it for about 2 minutes until the surface turns dark red (visual temperature about 800℃). Use a brush to evenly apply CJ30* soldering flux into the diameter-preserving strip groove. After the flux melts and removes the oxide scale, place the L10* solder under the flame to heat until it melts, and the melted solder flows into the diameter-preserving strip groove. Place the pre-cut diameter-preserving strip (made of cemented carbide, size 10mm×5mm×50mm) into the groove, apply a pressure of about 5kg with a fixture, and at the same time continue to heat with the oxyacetylene flame for about 30 seconds to ensure that the solder evenly fills the surrounding gaps and is firmly welded after cooling.

[0068] 3. Silver soldering PDC cutting inserts

[0069] Select Bag61* silver solder (specification Φ2×450mm, melting temperature 630℃-690℃) and QJ10 silver soldering flux (melting temperature 600℃-850℃). Use an ultra-audio frequency induction heating device with a power of 15kW, equipped with a special induction coil made of 4mm diameter copper tubing, with 3 turns and the gap controlled at 1-2mm. The induction coil is designed according to the four-wing cutting insert groove of the drill body, with a profile structure similar to a rectangle and parallel to the groove to ensure uniform heating. Fix the drill body on the workbench of the induction heating device, start the device, set the heating time to 20 seconds, and the closed-loop temperature control system monitors the temperature through an infrared thermometer and adjusts the power. Apply the pre-prepared silver soldering paste flux (a mixture of QJ10* and Bag61*) to the cutting insert groove with a brush. After removing the surface oxide scale, place the PDC cutting insert into the groove, keep it centered, fix it lightly with a fixture, and continue to heat for 10 seconds until the solder melts and fills the weld, then stop heating and let it cool naturally.

[0070] 4. Post-welding treatment

[0071] Immediately put the welded drill bit into a heat preservation furnace with the furnace temperature set at 200℃, covered with a 12cm thick layer of perlite powder, turn off the power after 4 hours of heat preservation, and let it cool naturally to room temperature (about 25℃). After taking out the drill bit, wash the surface with 60℃ hot water and a wire brush to remove the residual soldering flux, and the washing time is about 5 minutes. Use a hand grinder (grinding wheel grit 120 mesh) to grind the outer circle of the drill body at a speed of 2000rpm until the diameter-preserving strip exposes about 0.08mm outside the circle to remove the excess solder and burrs. Finally, place the drill bit in a sandblasting machine and blast it with 100 mesh alumina sand at a pressure of 0.4MPa for 20 seconds to keep the surface clean and smooth.

[0072] 5. Welding effect detection

[0073] Visual inspection: Inspect the weld seam with the naked eye. There are no air holes, flux residues or welding slag, and the outer surface is evenly painted; the PDC cutting disc has no chipped edges or cracks, the matrix fits tightly with the blade groove, the gauge strip is flush with the drill body, and there are no cracks.

[0074] Surface defect inspection: Measure the fitting clearance between the PDC cutting disc and the blade groove with a vernier caliper with an accuracy of 0.02 mm. It is less than 0.05 mm, there are no air holes, cracks or slag inclusions, and the weld seam is full; visually inspect that the weld seam of the gauge strip is about 0.5 mm higher than the surface of the drill body, and the surrounding gaps are evenly filled. The thread surface is smooth, without iron filings or oxidation marks.

[0075] Internal defect inspection: Measure the outer diameter of the drill bit with a vernier caliper to be 96 ± 0.1 mm and the height to be 80 ± 1 mm. Measure the cutting angle with an angle gauge to be 15° ± 1°, all of which meet the requirements of the drawing. Use an X-ray detector (voltage 120 kV, exposure time 10 seconds) to check the inside of the weld seam, and there are no air hole or slag inclusion defects.

[0076] Destructive test: Take samples for macroscopic metallographic analysis, please refer to Figure 5 、 6 ,It can be seen that the weld seam structure is uniform and there is no obvious segregation; use a universal material testing machine to conduct a shear strength test, apply a load until it is cut off, record the F value as 5500 N, and calculate τ = 5500 / (π × 13.44 2 / 4) = 188 MPa, which is higher than the requirement of 175 MPa.

[0077] Example 2: Welding and Detection of Φ113mm Four-wing Flat-bottom PDC Drill Bit

[0078] 1. Preparation before welding

[0079] Select a Φ113mm four-wing flat-bottom internal through-hole drill bit. The drill body is made of 42CrMo steel, which is subjected to overall quenching and tempering treatment, HRC25 - 30, and is equipped with 4 pieces of Φ16mm × 8mm PDC cutting discs. Place the four-wing cutting disc groove and the gauge strip groove of the drill body in a sandblasting machine, sandblast with 60-mesh alumina sand, pressure 0.6 MPa, for 20 seconds to remove the surface oxide layer and dirt. Wipe the welding part with a cotton cloth soaked in anhydrous ethanol, wipe 2 times to ensure no oil residue. Cross-grind the hard alloy welding surface of the PDC cutting disc with 320-mesh fine sandpaper, grind each piece for about 40 seconds to remove the oxide scale. Place the ground PDC cutting disc and the sheared Bag61* silver solder strip (specification δ0.2 × 25mm) in a container containing QJ10* silver solder flux, heat to 160 °C, and stir until it becomes a paste for standby.

[0080] 2. Brazing the gauge strip

[0081] Select L10 brazing solder (specification Φ2×1000mm, melting temperature 880℃-909℃) and CJ30 brazing flux (melting temperature 650℃). Adjust the oxyacetylene flame to a neutral flame with an inner flame length of about 12mm, and preheat the gauge strip groove of the drill body for about 3 minutes until it turns dark red (visual temperature is about 850℃). Apply CJ30* flux to the groove with a brush. After the flux melts and removes the oxide scale, place the L10* solder under the flame to melt, and the molten liquid flows into the gauge strip groove. Place the prefabricated gauge strip (made of cemented carbide, size 12mm×6mm×60mm) into the groove, apply a pressure of about 6kg with a fixture, and continue heating for about 40 seconds to ensure uniform filling of the solder. After cooling, it is firmly welded.

[0082] 3. Silver brazed PDC cutting insert

[0083] Select Bag61 silver brazing solder (specification δ0.2×25mm, melting temperature 630℃-690℃) and QJ10 silver brazing flux (melting temperature 600℃-850℃). Use an ultra-audio frequency induction heating device with a power of 20kW, equipped with a special induction coil, a 5mm diameter copper tube, 4 turns, a gap of 2-3mm. The induction coil is designed as a quadrilateral-shaped profiling structure to match the four-wing groove. Fix the drill body on the workbench, start the device, heat for 25 seconds, and the closed-loop temperature control system monitors and adjusts the power through an infrared thermometer. Apply the silver brazing paste flux to the cutting insert groove. After removing the oxide scale, place the PDC cutting insert into the groove, centered, apply a light pressure with a fixture, and continue heating for 15 seconds until the solder melts and fills the weld seam, then stop heating and cool.

[0084] 4. Post-welding treatment

[0085] Put the welded drill bit into the heat preservation pool, set the temperature to 250℃, cover it with a 15cm thick layer of perlite powder, keep it warm for 4 hours and then slowly cool to room temperature (about 25℃). After taking it out, clean the surface with 70℃ hot water and a wire brush, and clean for about 6 minutes to remove the flux. Use a hand grinder (grinding wheel grit 150 mesh) to grind the outer circle at a speed of 1800rpm until about 0.1mm of the gauge strip is exposed, and remove burrs and excess solder. Place the drill bit in a sandblaster, blast it with 80 mesh alumina sand at a pressure of 0.5MPa for 25 seconds to ensure a smooth surface.

[0086] 5. Welding effect inspection

[0087] Appearance inspection: Visually inspect that there are no pores, flux or welding slag in the weld seam, the paint spraying is uniform and beautiful; the PDC cutting insert is not damaged, fits tightly with the blade groove, the gauge strip has no cracks, and the assembly is flush.

[0088] Surface defect inspection: Use a vernier caliper to measure that the fitting gap of the PDC cutting disc is less than 0.06 mm, without pores, cracks or slag inclusions, and the weld seam is full; Visually inspect that the weld seam of the gauge strip is about 0.6 mm higher than the surface and the filling is uniform. The thread surface is smooth without iron filings or rust spots.

[0089] Internal defect inspection: Use a vernier caliper to measure the outer diameter of 120 ± 0.1 mm and the height of 100 ± 1 mm, and use an angle gauge to measure the cutting angle of 20° ± 1°, all of which meet the requirements. γ-ray detection (exposure time: 12 seconds) is adopted, and there are no slag inclusions or incomplete penetration defects in the weld seam.

[0090] Destructive test: Metallographic analysis shows that the weld structure is uniform; The record of the shear strength test shows that the F value is 6800 N, and calculate τ = 6800 / (π × 16² / 4) = 216 MPa, which is higher than the requirement of 175 MPa.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for welding and detecting an inner through hole drill, characterized in that: The following steps are involved: (1) Preparation before welding: Pre-treat the drill bit welding position and PDC cutting disc of the internal through-hole drill bit, including sandblasting and cleaning with anhydrous ethanol to remove surface oxide scale and dirt; (2) Brazed gauge strip: Use brazing solder and brazing flux, use oxyacetylene flame to preheat the drilled gauge groove to dark red, apply brazing flux to the welding position to remove the oxide scale, then melt the brazing solder in the gauge groove under flame heating, place the gauge in the groove and heat it under pressure until it is firmly welded; (3) Silver solder PDC cutting blade: Silver solder and silver solder flux are used, and supersonic frequency induction heating equipment and a special induction coil are used to heat the four-wing cutting blade groove of the drill. The special induction coil is made of copper tube, and its shape and structure are designed according to the geometric characteristics of the four-wing cutting blade groove of the drill. The distance between the four-wing cutting blade groove of the drill is 10-15mm, so as to ensure that the heating part is parallel or equidistant with the cutting blade groove, and the current flow direction between adjacent turns is consistent, so as to improve the heating uniformity and efficiency. The number of turns and the gap with the workpiece are adjusted according to the heating efficiency. During the heating process, the welding temperature is controlled within an appropriate range through a closed-loop temperature control system to avoid graphitization of the PDC cutting blade. The silver solder paste flux is applied to the cutting blade groove, and after the oxide scale is removed, the PDC cutting blade is placed in the groove and welded. (4) Post-weld treatment: Put the welded drill bit into a heat preservation pool or heat preservation furnace, cover it with a layer of perlite powder, keep it warm for a period of time, and then slowly cool it to room temperature; (5) Welding effect detection: The PDC cutting pieces after welding are subjected to appearance inspection, surface defect inspection, internal defect inspection and destructive test to verify whether the welding strength and quality meet the design requirements.

2. The method for welding and detecting an inner through hole drill according to claim 1, characterized in that: In step (1), the pretreatment of the PDC cutting piece also includes: cross-grinding the carbide welding surface with fine sandpaper to remove the oxide scale, and placing the ground PDC cutting piece and the sheared silver solder sheet in a container containing silver solder flux and heating them into a paste.

3. The method for welding and detecting an inner through hole drill according to claim 1, characterized in that: In step (2), the copper solder is L10*, with a specification of Φ2×1000mm and a melting temperature of 880°C to 909°C; the copper solder flux is CJ30*, with a melting temperature of 650°C.

4. The method for welding and detecting an inner through hole drill according to claim 1, characterized in that: In step (3), the silver solder is Bag61*, with a specification of Φ2×450mm or δ0.2×25mm and a melting temperature of 630°C to 690°C; the silver solder flux is QJ10*, with a melting temperature of 600°C to 850°C.

5. The method for welding and detecting an inner through hole drill according to claim 1, characterized in that: In step (3), the special induction coil is made of a copper tube with a diameter of more than 4 mm, and the gap between the small workpiece and the induction coil is controlled at 1-3 mm. The production method includes: pouring fine sand or fine salt after annealing, removing the filler after bending and forming, and covering with high temperature resistant insulating material to prevent short circuit between turns.

6. The method for welding and detecting an inner through hole drill according to claim 1, characterized in that: In step (4), the post-weld treatment further comprises: Put the welded drill bit into a heat preservation pool or heat preservation furnace, cover it with a perlite powder layer with a thickness of not less than 10 cm, keep it warm for 4 hours and slowly cool it to room temperature; Clean the drill bit with hot water and a wire brush to remove surface flux; Use a hand grinder to grind the outer circle of the drill, so that the diameter bar exposed outside the outer circle does not exceed 0.1mm, and remove excess flux; Sandblast the drill bit to keep the surface clean.

7. The method for welding and detecting an inner through hole drill according to claim 1, characterized in that: In step (5), the appearance inspection includes the following requirements and methods: Check that the weld of the PDC cutting blade drill bit must not have pores, flux, or welding slag, and the paint on the outer surface must be uniform and beautiful, using visual inspection; Check that the PDC cutting piece is not damaged, the composite piece base fits tightly with the blade groove of the drill bit body, there are no cracks on the drill bit body and the gauge strip, and the lower end of the gauge strip is flush with the drill bit body. Use visual inspection method.

8. The method for welding and detecting an inner through hole drill according to claim 1, characterized in that: In step (5), surface defect inspection includes the following welding test requirements and methods: The PDC cutting blade should fit tightly with the blade groove of the drill body. There should be no pores, cracks or slag inclusions in the welding process. The welding should be full and firm. Use a vernier caliper to measure. The welding between the gauge strip and the drill body must not have defects such as pores, slag inclusions, and cracks. The gaps around should be welded full, the weld should be higher than the surface of the drill body, and the welding should be firm. Visual inspection should be used.

9. The method for welding and detecting an inner through hole drill according to claim 1, characterized in that: In step (5), the surface defect inspection also includes a thread test, which requires that the thread surface inside the drill body is smooth and shiny, without iron chips, oxidation or rust spots, and is carried out by visual inspection.

10. The method for welding and detecting an inner through hole drill according to claim 1, characterized in that: In step (5), internal defect inspection includes dimensional testing, and the requirements are as follows: The nominal outer diameter of the drill bit and the size of the PDC cutting disc meet the design requirements and are measured using a vernier caliper; The drill bit height, cutting angle, side tilt angle, and back angle dimensions meet the requirements of the drawings. The drill bit height tolerance is ±1mm and is measured using a vernier caliper and an angle ruler. After the gauge strip is welded to the drill body, the dimensions meet the design requirements and are measured using a vernier caliper.

11. The method for welding and detecting an inner through hole drill according to claim 1, characterized in that: In step (5), internal defect inspection uses X-ray or gamma-ray detection to check for pores, slag inclusions or incomplete penetration defects inside the weld.

12. The method for welding and detecting an inner through hole drill according to claim 1, characterized in that: In step (5), the destructive test includes: Macroscopic metallographic structure analysis: detect the metallographic structure of the weld and verify the welding quality; Shear strength test: The shear strength of the PDC cutting blade welding surface is tested on a material testing machine. The calculation formula is: τ = F / (π×D2 / 4), where F is the average shear load and D is the diameter of the PDC cutting blade. The technical indicator requires that the shear strength is not less than 175MPa.

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