A bonding NdFeB magnet forming tool, forming method and application thereof

Abstract

The invention discloses a forming tool, a forming method and an application of a bonded NdFeB magnet, wherein the forming tool comprises an upper punch, a middle die and a lower punch which are coaxially arranged from top to bottom in sequence and a core rod arranged in the lower punch, wherein the outer wall of the core rod, the inner wall of the middle die, the bottom surface of the upper punch and the top surface of the lower punch enclose a die cavity; the upper punch is composed of an integrally formed upper support portion and an upper punch, wherein the radius of the upper punch is 1-2 mm larger than the radius of the upper support portion, the lower punch is composed of an integrally formed lower support portion and a lower punch, wherein the radius of the lower punch is 1-2 mm larger than the radius of the lower support portion, the gap between the upper punch and the inner wall of the middle die is greater than the gap between the lower punch and the inner wall of the middle die, and the draft angle of the middle die is 89.90-89.99°. The finished bonded NdFeB magnet produced has a dimensional fluctuation of 0.15-0.25%. Density fluctuation is 0.7-0.8%, magnetic eccentricity (0.02-0.15) / 100mm.

Description

Technical Field

[0001] The invention relates to the technical field of material forming, and in particular to a forming tool, a forming method and application of a bonded NdFeB magnet. Background Art

[0002] With the development of the third generation of permanent magnetic materials, NdFeB magnets have been widely used. According to the differences in the use conditions, higher requirements are also put forward for its performance in various aspects. In some special occasions, a magnet is needed, which has extremely high requirements for magnetic eccentricity (magnetic eccentricity <0.1mm / 100mm) and uniform density under large size, and a bonded NdFeB magnet is required. The magnet has a large volume, small density fluctuation (density fluctuation <1%) during mass production, small dimensional tolerance, and the product appearance quality and high product qualification rate must be guaranteed during the molding process. Therefore, it is necessary to study a bonding NdFeB magnet molding method, which can produce large-size bonded NdFeB magnets with excellent performance and stable and reliable quality, and at the same time ensure the stability, economy and production efficiency of the products in mass production. The present invention is made under this background. Summary of the invention

[0003] The purpose of the present invention is to provide a forming tool for bonded NdFeB magnets in view of the technical defects in the prior art. Due to the special structure and special size of the forming tool, the tool has the advantage of long service life.

[0004] Another object of the present invention is to provide a method for forming a bonded NdFeB magnet. Based on the above-mentioned special-sized forming tooling and special process parameters, a bonded NdFeB magnet with a magnetic eccentricity of less than 0.1 mm / 100 mm can be processed.

[0005] Another object of the present invention is to provide an application of the molding method, wherein the finished bonded NdFeB magnet has a size fluctuation of 0.15-0.25%, a density fluctuation of 0.7-0.8%, and a magnetic eccentricity of (0.02-0.15) / 100mm.

[0006] The technical solution adopted to achieve the purpose of the present invention is:

[0007] A forming tool for bonded NdFeB magnets, comprising an upper punch, a middle die and a lower punch which are coaxially arranged in sequence from top to bottom, and a core rod arranged in the lower punch, wherein the outer wall of the core rod, the inner wall of the middle die, the bottom surface of the upper punch and the top surface of the lower punch enclose a mold cavity;

[0008] The upper punch is composed of an integrally formed upper support portion and an upper punch, the radius of the upper punch is 1-2 mm larger than the radius of the upper support portion, the lower punch is composed of an integrally formed lower support portion and a lower punch, the radius of the lower punch is 1-2 mm larger than the radius of the lower support portion, the gap between the upper punch and the inner wall of the middle die is larger than the gap between the lower punch and the inner wall of the middle die, and the draft angle of the middle die is 89.90-89.99°.

[0009] In the above technical solution, the upper punch is fixed on the top cylinder support seat of the press, the lower punch is installed on the die frame base of the press, the middle die is fixed on the die frame lifting platform of the press, and the core rod is installed on the press base nut.

[0010] In the above technical solution, the middle die and the core rod are made of KG2 tungsten steel, and the upper punch and the lower punch are made of SP60 alloy steel. In the above technical solution, the single-side clearance between the upper punch and the middle die is 0.025-0.035 mm, preferably 0.03 mm.

[0011] In the above technical solution, the single-side gap between the upper punch and the core rod is 0.005-0.015mm, the single-side gap between the lower punch and the middle die is 0.01-0.02mm, and the single-side gap between the lower punch and the middle die is 0.005-0.015mm.

[0012] In the above technical solution, the distance between the outer wall of the core rod and the inner wall of the middle mold is 0.80-0.85 times the width of the bonded NdFeB magnet ring.

[0013] Another aspect of the present invention is a molding method based on the molding tool, comprising the following steps:

[0014] Step 1, weigh the powder with a weighing accuracy of 1000g±0.5g;

[0015] Step 2, manually adding the powder into the mold cavity, and circumferentially scraping the powder so that the top of the powder is flush with the upper surface of the middle mold 2;

[0016] Step 3, using floating middle mold for compression molding: at a compression speed of 1 to 3 mm / s and a pressure value of 260 t to 360 t, top pressing stroke, floating pressing, bottom pressing stroke, holding pressure and gas protection demolding are performed in sequence in the press, wherein the holding pressure time is 10 to 20 s;

[0017] Step 4, place the formed workpiece in an electric blast drying oven for drying. During drying, first heat from room temperature 20-30°C at a rate of 1-5°C / min to 155-165°C, then keep warm for 1.5-2.5h, and then naturally cool to room temperature 20-30°C in an environment with humidity ≤70%RH.

[0018] In the above technical solution, the pressing stroke is: the upper punch moves downward into the middle die to form a closed cavity, and the entering distance is 1 / 4 of the entire pressing stroke, wherein the pressing stroke = filler height - product height.

[0019] In the above technical solution, the floating pressing is: the upper punch and the middle die move downward synchronously to perform floating pressing, and the stroke is 1 / 2 of the entire pressing stroke, wherein the pressing stroke = filler height - product height.

[0020] In the above technical solution, the bottom pressing stroke is: the upper punch continues to move downward alone, and the stroke is 1 / 2 of the entire pressing stroke, wherein the pressing stroke = filler height - product height.

[0021] Another aspect of the present invention also includes the application of the molding method in the production of bonded NdFeB magnets, wherein the finished bonded NdFeB magnets produced have a size fluctuation of 0.15-0.25%, a density fluctuation of 0.7-0.8%, and a magnetic eccentricity of (0.02-0.15) / 100mm.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] By matching the size of the molding tool and the molding process parameters, the present invention can mass-produce large-size bonded NdFeB magnets with excellent performance, stable and reliable quality, while ensuring the stability, economy and production efficiency of the products in mass production. The magnets produced have small size tolerances, density fluctuations of <1%, and good magnetic eccentricity (magnetic eccentricity <0.1mm / 100mm). BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Shown is a schematic structural diagram of the present invention.

[0025] In the figure: 1-upper punch, 2-middle die, 3-lower punch, 4-core rod, 5-lower support part, 6-gap, 7-draft angle, 8-lower punch, 9-upper punch, 10-upper support part, 11-top cylinder support seat, 12-lifting platform, 13-die frame base, 14-press base nut. DETAILED DESCRIPTION

[0026] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] Example 1

[0028] A forming tool for bonded NdFeB magnets, comprising an upper punch 1, a middle die 2 and a lower punch 3 which are coaxially arranged in sequence from top to bottom, and a core rod 4 arranged in the lower punch 3, wherein the outer wall of the core rod 4, the inner wall of the middle die 2, the bottom surface of the upper punch 1 and the top surface of the lower punch 3 enclose a mold cavity;

[0029] The upper punch 1 is composed of an integrally formed upper support portion 10 and an upper punch 9, the radius of the upper punch 9 is 1-2 mm larger than the radius of the upper support portion 10, the lower punch 3 is composed of an integrally formed lower support portion 5 and a lower punch 8, the radius of the lower punch 8 is 1-2 mm larger than the radius of the lower support portion 5, the gap 6 between the upper punch 9 and the inner wall of the middle die 2 is larger than the gap between the lower punch 12 and the inner wall of the middle die 2, and the draft angle 7 of the middle die 2 is 89.90-89.99°.

[0030] In the above technical solution, the upper punch 1, the middle die 2, the lower punch 3 and the core rod 4 are installed on the die frame of the press, and the forming operation is completed under the driving action of the press.

[0031] In the above technical solution, the upper punch 1 is fixed on the top cylinder support seat 11 of the press, the lower punch 2 is installed on the mold frame base 13 of the press, the middle mold is fixed on the mold frame lifting platform 12 of the press, and the core rod is installed on the press base nut 14.

[0032] In the above technical solution, the middle mold 2 and the core rod 4 are made of KG2 tungsten steel.

[0033] In the above technical solution, the material of the upper punch 1 and the lower punch 3 is SP60 alloy steel. In actual production, the middle die 2 and the core rod 4 are made of Chunbao KG2 tungsten steel, and the upper punch 1 and the lower punch 3 are made of Swedish SP60 alloy steel.

[0034] In the above technical solution, the single-side gap between the upper punch and the middle die is 0.025-0.035 mm, preferably 0.03 mm.

[0035] In the above technical solution, the single-side gap between the upper punch and the core rod is 0.005-0.015 mm, preferably 0.01 mm.

[0036] In the above technical solution, the single-side gap between the lower punch and the middle die is 0.01-0.02 mm (the single-side gap caused by the draft angle is a range).

[0037] In the above technical solution, the single-side gap between the lower punch and the middle die is 0.005-0.015 mm, preferably 0.01 mm.

[0038] In the above technical solution, due to the elastic aftereffect, the distance between the outer wall of the core rod and the inner wall of the middle mold is 0.80-0.85 times the width of the bonded NdFeB magnet ring.

[0039] Through the coordination of the above dimensional parameters, the product requirements are met while ensuring the consistency of mass-produced products (bonded NdFeB magnets). After verification of the production process of about 200,000 products, the process has high stability, the fluctuation of each product dimension is about 0.2%, the density fluctuation is about 0.8%, and the magnetic eccentricity of the finished product is (0.02-0.15) mm.

[0040] Example 2

[0041] A molding method based on the molding tool comprises the following steps:

[0042] Step 1: weigh the powder with a weighing accuracy of 1000g±0.5g. This can be achieved by automatic weighing equipment.

[0043] Step 2, manually add the powder into the mold cavity, scrape the powder circumferentially so that the top of the powder is flush with the upper surface of the middle mold 2; a brush can be used when scraping the powder to ensure the parallelism of the pressed product. In the press, add the material when the middle mold 2 rises.

[0044] Step 3, compression molding using a floating middle mold: at a compression speed of 1 to 3 mm / s and a pressure value of 260t to 360t, top compression stroke, floating compression, bottom compression stroke, pressure holding and gas protection demolding are performed in sequence in the press, wherein the pressure holding time is 10-20s; during the molding process, mold release agents cannot be used, and gas protection demolding must be used to prevent the product from being faulted, cracked, and edge collapsed during the demolding process.

[0045] Step 4, place the formed workpiece in an electric blast drying oven for drying. During drying, first heat from room temperature 20-30°C at a rate of 1-5°C / min to 155-165°C, then keep warm for 1.5-2.5h, and then naturally cool to room temperature 20-30°C in an environment with humidity ≤70%RH.

[0046] There are three reasons why mold release agents are not used for demoulding:

[0047] 1. The bonding NdFeB magnetic powder itself also contains epoxy resin adhesive, which can be miscible with most oily release agents, causing product contamination after curing and various appearance quality problems on the surface.

[0048] 2. The use of release agent increases the adhesion of fine powder on the side wall of the middle mold during the filling process, which is not conducive to the life of the mold.

[0049] 3. The release agent adheres to the product surface, which is not conducive to subsequent surface treatment.

[0050] In the above technical scheme, the top pressing stroke is: the upper punch moves downward into the middle die to form a closed cavity, and the entering distance is 1 / 4 of the entire pressing stroke (pressing stroke = filler height - product height); the floating pressing is: the upper punch and the middle die move downward synchronously for floating pressing, and the stroke is 1 / 2 of the pressing stroke; the bottom pressing stroke is: the upper punch continues to move downward alone, and the stroke is 1 / 2 of the pressing stroke; the core rod does not move during the entire pressing and molding process.

[0051] In the above technical solution, due to the elastic aftereffect, the size of the mold cavity is designed to shrink by 8% to 12% according to the actual size of the product.

[0052] Automatic weighing and feeding are adopted to ensure product quality and accuracy while taking into account production efficiency, with a production capacity of 500 pieces / shift; special mold design is adopted, and the mold material is selected after a large number of experiments. After more than 100,000 products have been pressed, the mold life exceeds 20,000 pieces / set, which has good economy; at the same time, the design and selection of mold gap value ensures product quality while helping to reduce powder leakage and mold jamming during the pressing process, greatly increasing the mold life, and at the same time facilitating the exhaust during the pressing process, reducing product pores and increasing product density. Designing the draft angle greatly reduces the demoulding force and reduces the wear of the mold and product side walls.

[0053] Example 3

[0054] The molding method is applied to the production of bonded NdFeB magnets, and the finished bonded NdFeB magnets produced have a size fluctuation of 0.15-0.25%, a density fluctuation of 0.7-0.8%, and a magnetic eccentricity of (0.02-0.15) / 100mm.

[0055] The reasonable molding process parameters are adopted to ensure the consistency of mass production products while ensuring the product requirements. After verification of the production process of about 200,000 products, the process has high stability, the fluctuation of each dimension of the product is about 0.2%, the density fluctuation is about 0.8%, and the magnetic eccentricity of the finished product is (0.02-0.15) mm.

[0056] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A forming tool for bonded NdFeB magnets, characterized in that: It comprises an upper punch, a middle die and a lower punch which are coaxially arranged in sequence from top to bottom, and a core rod arranged in the lower punch, wherein the outer wall of the core rod, the inner wall of the middle die, the bottom surface of the upper punch and the top surface of the lower punch enclose a mold cavity; The upper punch is composed of an upper support portion and an upper punch formed in one piece, the radius of the upper punch is 1-2 mm larger than the radius of the upper support portion, the lower punch is composed of a lower support portion and a lower punch formed in one piece, the radius of the lower punch is 1-2 mm larger than the radius of the lower support portion, the gap between the upper punch and the inner wall of the middle die is larger than the gap between the lower punch and the inner wall of the middle die, and the draft angle of the middle die is 89.90-89.99°; The upper punch is fixed on the top cylinder support seat of the press, the lower punch is installed on the die frame base of the press, the middle die is fixed on the die frame lifting platform of the press, and the core rod is installed on the press base nut; The middle die and the core rod are made of KG2 tungsten steel, and the upper punch and the lower punch are made of SP60 alloy steel; The single-side clearance between the upper punch and the middle die is 0.025-0.035mm, and the single-side clearance between the upper punch and the core rod is 0.005-0.015mm; The distance between the outer wall of the core rod and the inner wall of the middle mold is 0.80-0.85 times the width of the bonded NdFeB magnet ring; The finished bonded NdFeB magnets produced have a size fluctuation of 0.15-0.25%, a density fluctuation of 0.7-0.8%, and a magnetic eccentricity of (0.02-0.15) / 100mm.

2. A molding method based on the molding tool as claimed in claim 1, characterized in that: The following steps are involved: Step 1, weighing the powder with a weighing accuracy of 1000g±0.5g; Step 2, manually adding the powder into the mold cavity, and circumferentially scraping the powder so that the top of the powder is flush with the upper surface of the middle mold; Step 3, using floating middle mold for compression molding: at a compression speed of 1 to 3 mm / s and a pressure value of 260 t to 360 t, top pressing stroke, floating pressing, bottom pressing stroke, holding pressure and gas protection demolding are performed in sequence in the press, wherein the holding pressure time is 10 to 20 s; Step 4, placing the formed bonded NdFeB magnet in an electric hot air drying oven for drying. During drying, first heat from room temperature 20-30°C at a rate of 1-5°C / min to 155-165°C, then keep warm for 1.5-2.5h, and then naturally cool to room temperature 20-30°C in an environment with humidity ≤70%RH.

3. The molding method according to claim 2, characterized in that: The pressing stroke is: the upper punch moves downward into the middle die to form a closed cavity, and the entering distance is 1 / 4 of the entire pressing stroke, wherein the pressing stroke = filler height - bonded NdFeB magnet product height.

4. The molding method according to claim 2, characterized in that: The floating pressing is as follows: the upper punch and the middle die move downward synchronously to perform floating pressing, and the stroke is 1 / 2 of the entire pressing stroke, wherein the pressing stroke = filler height - bonded NdFeB magnet product height.

5. The molding method according to claim 2, characterized in that: The bottom pressing stroke is: the upper punch continues to move downward alone, and the stroke is 1 / 2 of the entire pressing stroke, wherein the pressing stroke = filler height - bonded NdFeB magnet product height.

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