A high-strength rivet nut machining method

Abstract

The application discloses a high-strength pull-rivet nut machining method in the technical field of pull-rivet nut production, and comprises the following steps: step 1, wire drawing; step 2, cold upsetting; step 3, tooth extrusion; step 4, high-frequency quenching and tempering: the product is heated on a high-frequency heating device, is heated and advanced on one side of a track type induction coil, and then is quenched in a quenching area; only the thread area of the pull-rivet nut is quenched, and the pull-rivet deformation area is not allowed to be quenched; the quenched pull-rivet nut is tempered; step 5, surface treatment; and step 6, optical full inspection. The application solves the problems of great process difficulty and low machining efficiency in the prior art due to the small size of the parts, the realization of local tempering and the influence on the thread strength.

Description

Technical Field

[0001] This invention relates to the field of rivet nut manufacturing technology, and in particular to a method for processing rivet nuts. Background Technology

[0002] Rivet nuts are suitable for unidirectional connections of thin plates and profiles. They are simple to manufacture and low in cost, and are widely used in the assembly of products in industries such as automotive, aerospace, instrumentation, and home decoration. Because rivet nuts require riveting deformation during application, the strength of the parts cannot be too high, so the overall performance level of the product is usually relatively low. However, in recent years, the market demand for high-strength rivet nuts has been increasing. These nuts need to ensure effective riveting while possessing a strength rating of 10 or even 12, which presents new challenges to product structural design and heat treatment methods.

[0003] There are two main types of processing methods for high-strength rivet nuts on the market: 1. By adjusting the product structure, while ensuring that the riveting deformation zone remains unchanged, the wall thickness of the threaded area and the thread engagement length are increased to improve the product's load-bearing capacity; 2. The product is first subjected to overall tempering treatment to improve its strength to the required level, and then the riveting deformation zone is locally annealed.

[0004] Existing technical pain points: Product structure adjustments are usually constrained by the application environment. Based on considerations of application space size, lightweighting, and cost, customers are generally reluctant to accept them; the scheme of first heat treatment and then local tempering makes the product processing steps more complicated. Due to the small size of the parts, it is very difficult to achieve local tempering without affecting the thread strength. Moreover, tempering requires processing one piece at a time, which is inefficient and costly. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for processing high-strength rivet nuts, solving the problem that the processing methods in the prior art cannot meet the requirements.

[0006] The objective of this invention is achieved as follows: a method for processing high-strength rivet nuts, comprising the following steps:

[0007] Step 1) Wire drawing: The raw material is drawn and modified into finished wires with the wire diameter required for cold heading of the product;

[0008] Step 2) Cold heading: The finished wire is cold-headed using a multi-station cold heading machine to obtain rivet nuts;

[0009] Step 3) Threading: Place the rivet nut into the tapping machine for threading processing;

[0010] Step 4) High-frequency quenching and tempering: The product is heated on a high-frequency heating device, and the track-type induction coil is heated and advanced at the same time. Then, quenching is carried out in the quenching zone. Only the threaded area of ​​the rivet nut is quenched, and the deformation area of ​​the rivet is not allowed to be quenched. The quenched rivet nut is then tempered.

[0011] Step 5) Surface treatment: Apply a surface protection treatment to the heat-treated rivet nuts, such as electroplating zinc / zinc-nickel alloy or other surface treatments with equivalent anti-corrosion effect.

[0012] Step 6) Optical full inspection: The finished rivet nuts are screened using an optical full inspection machine.

[0013] Furthermore, during heating in step 4), the output power of the high-frequency power supply is controlled to heat the product to between 860 and 910°C.

[0014] Furthermore, the track-type induction coil described in step 4) includes a pair of insulating support plates. A conveyor belt is provided below the insulating support plates. The induction coil is positioned between the insulating support plates and the conveyor belt. The flange of the rivet nut rests on the insulating support plates, and the lower end of the rivet nut abuts against the conveyor belt. The rivet nut moves forward along the insulating support plates under the action of the conveyor belt. The induction coil is a flat elliptical multi-turn coil. The length of the coil's long axis is controlled according to the heating requirements, and the width of the short axis is smaller than the diameter of the product flange but larger than the diameter of the rivet nut rod. During movement, the advancing speed of the rivet nut on the track-type induction coil is controlled to ensure that it is heated evenly and fully.

[0015] Furthermore, in step 4), the temperature of the quenching medium is 40–70°C.

[0016] Furthermore, in step 4), the tempering temperature is controlled at 200–500°C and the holding time is 0.5–2 hours, according to the required product performance level.

[0017] Furthermore, in step 4), the quenching zone is equipped with a pair of feeding belts above the quenching pool. The rivet nut can move forward along the feeding belts, and during the movement, the quenching pool quenches the threaded area of ​​the rivet nut.

[0018] Compared with the prior art, the beneficial effects of this invention are as follows: This invention enables the rivet nut structure to achieve the characteristics of high strength in the threaded area and high plasticity in the deformation area without special design. In particular, the induction coil structure is designed as a flat elliptical multi-turn coil, which is perfectly matched with the conveyor belt, allowing the rivet nuts to be processed continuously and automatically. The design of matching the long axis dimension of the induction coil with the feeding speed allows for the adjustment of the product heating time. Adjusting the high-frequency power supply ensures that the product is fully heated to above the austenitic transformation temperature of steel and maintained for a certain period of time. Then, rapid local (threaded area) quenching causes the threaded area to undergo martensitic phase transformation, significantly improving hardness. The subsequent mesh belt furnace tempering temperature and time are adjusted based on the required product performance level. High-strength grades use low-temperature tempering to obtain tempered martensite structure, while medium- and high-strength grades use medium-temperature tempering to obtain bainitic structure, enabling the rivet nuts to meet the requirements and achieve mass production. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0020] Figure 1 This is a flowchart of the present invention.

[0021] Figure 2 This is a schematic diagram of the high-frequency heating device in this invention.

[0022] Figure 3 This is a schematic diagram of the transmission system and track-type induction coil structure in this invention.

[0023] Figure 4 This is a schematic diagram of the quenching system structure in this invention.

[0024] Figure 5 This is a schematic diagram of the rivet nut structure in this invention.

[0025] Among them, 100 is a high-frequency power control system, 200 is a feeding system, 300 is a conveying system, 301 is an insulating support plate, 302 is a conveyor belt, 303 is a drive motor, 400 is a track-type induction coil, 500 is a quenching system, 600 is a tempering system, 700 is a receiving hopper, 800 is a rivet nut, 801 is a deformation zone, and 802 is a threaded zone. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] like Figure 1-5 The high-strength rivet nut processing method shown includes the following steps:

[0028] Step 1) Wire drawing: The raw material is drawn and modified into finished wires with the wire diameter required for cold heading of the product;

[0029] Step 2) Cold heading: The finished wire is cold-headed using a multi-station cold heading machine to obtain rivet nuts 800;

[0030] Step 3) Threading: Place the rivet nut 800 into the tapping machine for threading processing;

[0031] Step 4) High-frequency quenching and tempering: The product is heated on a high-frequency heating device, and the track-type induction coil 400 is heated and advanced at the same time. Then, quenching is carried out in the quenching zone. Only the threaded area 802 of the rivet nut 800 is quenched, and the rivet deformation area 801 is not allowed to be quenched. The quenched rivet nut 800 is then tempered.

[0032] Step 5) Surface treatment: The heat-treated rivet nut 800 is subjected to surface protection treatment, which can be electroplating zinc / zinc-nickel alloy or other surface treatments with equivalent anti-corrosion effect.

[0033] Step 6) Optical full inspection: Screen the finished rivet nuts 800 using an optical full inspection machine.

[0034] Specifically, the high-frequency heating device includes:

[0035] A high-frequency power supply control system 100 is used to supply power to the induction coil;

[0036] The feeding system 200 is used to feed the rivet nuts 800 one by one onto the conveyor system 300;

[0037] The transmission system 300 is used to drive the rivet nut 800 to move;

[0038] The track-type induction coil 400 is used in conjunction with the transmission system 300 to heat the threaded area 802 of the rivet nut 800;

[0039] The quenching system 500 is used to quench the threaded area 802 of the rivet nut 800;

[0040] Tempering system 600 is used to temper the quenched rivet nuts 800;

[0041] The receiving hopper 700 is used to receive the tempered rivet nuts 800.

[0042] Furthermore, during heating in step 4), the output power of the high-frequency power supply is controlled to heat the product to between 860 and 910°C.

[0043] It should be noted that this design, by adjusting the power of the high-frequency power supply, fully heats the product to above the austenitic transformation temperature AC1 of steel and maintains it for a certain period of time, so that the alloy material is completely austenitized, thus ensuring effective quenching in the subsequent process.

[0044] Furthermore, the track-type induction coil 400 described in step 4) includes a pair of insulating support plates 301. A conveyor belt 302 is provided below the insulating support plates 301. The induction coil is disposed between the insulating support plates 301 and the conveyor belt 302. The flange of the rivet nut 800 rests on the insulating support plate 301, and the lower end of the rivet nut 800 abuts against the conveyor belt 302. The rivet nut 800 moves forward along the insulating support plate 301 under the action of the conveyor belt 302. The induction coil is a flat elliptical multi-turn coil. The length of the long axis of the coil is controlled according to the heating requirements, and the width of the short axis is smaller than the diameter of the product flange and larger than the diameter of the rivet nut 800 rod. During movement, the advancing speed of the rivet nut 800 on the track-type induction coil 400 is controlled to ensure that it is heated evenly and fully.

[0045] Specifically, the conveyor belt 302 is driven by the drive motor 303. During the forward movement of the rivet nut 800, the induction coil continuously heats and keeps the rivet nut 800 warm. The deformation area 801 and the threaded area 802 of the rivet nut 800 are located within the heating range of the induction coil.

[0046] It should be noted that the induction coil structure is designed as a flat elliptical multi-turn coil, which is perfectly matched with the conveyor belt 302, enabling the rivet nut 800 to be continuously and automatically processed; the design of matching the long axis dimension of the induction coil with the feeding speed realizes the adjustment of the product heating time.

[0047] Furthermore, in step 4), the temperature of the quenching medium is 40–70°C.

[0048] Specifically, the quenching medium is L-AN15 oil, L-AN22 oil, or L-AN46 oil. These media have advantages such as good cooling performance, high flash point, suitable viscosity, no corrosion, and low price.

[0049] Furthermore, in step 4), the tempering temperature is controlled at 200–500°C and the holding time is 0.5–2 hours, according to the required product performance level.

[0050] Specifically, the tempering system 600 adopts a mesh belt tempering furnace.

[0051] It should be noted that the specific tempering process is determined based on the final performance requirements of the product (performance grade, tensile strength, hardness, and grain size, etc.). In practice, the hardness requirement is mainly used as the benchmark for process adjustment. The higher the hardness requirement, the lower the tempering temperature, and vice versa. High-strength grade rivet nuts are tempered at a low temperature (800) to obtain a tempered martensitic structure, while medium- and high-strength grades are tempered at a medium temperature to obtain a bainitic structure.

[0052] Furthermore, in step 4), the quenching zone is provided with a pair of feeding belts above the quenching pool. The rivet nut 800 can move forward along the feeding belts. During the movement, the quenching pool quenches the threaded area 802 of the rivet nut 800.

[0053] It should be noted that rapid local quenching (threaded area 802) causes the 802 microstructure in the threaded area to undergo a martensitic phase transformation, which significantly improves the hardness.

[0054] In summary, this invention mainly achieves localized strengthening and softening of the product through an online high-frequency quenching and tempering scheme, meeting the requirements of high strength in the threaded area 802 and high plasticity in the deformation area 801 of the rivet nut 800. After cold heading, the entire nut is directly heated by high frequency. The nut is conveyed to the induction coil by the feeding system. The deformation area 801 and the threaded area 802 of the nut are located inside the coil and are conveyed from left to right by the conveyor belt 302. The conveying process is the heating process. The heating power and conveying speed are set according to the requirements to ensure that the product is fully heated to above the austenite transformation temperature (recommended above 860℃) and held at that temperature. Then, the threaded area 802 is quenched in the quenching zone, allowing the threaded area 802 to cool rapidly and transform into martensite. The deformation area 801 is not quenched and cools more slowly, so the product still maintains a soft structure. The quenching zone has a martensitic structure, which is a metastable phase with high internal stress. It needs to be tempered in a tempering furnace. According to the performance grade requirements of the final product, the tempering temperature and tempering time are adjusted accordingly to obtain products of grade 10 and above.

[0055] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for processing high-strength rivet nuts, characterized in that, Includes the following steps: Step 1) Wire drawing: The raw material is drawn and modified into finished wires with the wire diameter required for cold heading of the product; Step 2) Cold heading: The finished wire is cold-headed using a multi-station cold heading machine to obtain rivet nuts (800). Step 3) Threading: Place the rivet nut (800) into the tapping machine for threading processing; Step 4) High-frequency quenching and tempering: The product is heated on a high-frequency heating device, and the track-type induction coil (400) is heated and advanced at the same time. Then, quenching is performed in the quenching zone. Only the threaded area (802) of the rivet nut (800) is quenched, and the rivet deformation area (801) is not allowed to be quenched. The quenched rivet nut (800) is then tempered. The track-type induction coil (400) includes a pair of insulating support plates (301). A conveyor belt (302) is provided below the insulating support plates (301). The induction coil is set between the insulating support plates (301) and the conveyor belt. Between (302), the flange of the rivet nut (800) rests on the insulating support plate (301), and the lower end of the rivet nut (800) abuts against the conveyor belt (302). Under the action of the conveyor belt (302), the rivet nut (800) moves forward along the insulating support plate (301). The induction coil is a flat elliptical multi-turn coil. The length of the long axis of the coil is controlled according to the heating requirements, and the width of the short axis is smaller than the diameter of the product flange and larger than the diameter of the rivet nut (800). During the movement, the pushing speed of the rivet nut (800) on the track-type induction coil (400) is controlled so that it is heated evenly and fully. Step 5) Surface treatment: The heat-treated rivet nut (800) is subjected to surface protection treatment by electroplating zinc / zinc-nickel alloy surface treatment; Step 6) Optical full inspection: The finished rivet nuts (800) are screened by an optical full inspection machine.

2. The method for processing a high-strength rivet nut according to claim 1, characterized in that, During heating in step 4), control the output power of the high-frequency power supply to heat the product to between 860 and 910°C.

3. The method for processing a high-strength rivet nut according to claim 2, characterized in that, In step 4), the temperature of the quenching medium is 40–70°C.

4. The method for processing a high-strength rivet nut according to claim 3, characterized in that, In step 4), the tempering temperature is controlled at 200-500℃ and the holding time is 0.5-2 hours, according to the required product performance level.

5. A method for processing high-strength rivet nuts according to claim 4, characterized in that, In step 4), the quenching zone is equipped with a pair of feeding belts above the quenching pool. The rivet nut (800) can move forward along the feeding belt. During the movement, the quenching pool quenches the threaded area (802) of the rivet nut (800).

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