A multi-blade ball-end mill and a manufacturing method thereof

Abstract

The application discloses a multi-blade ball head end mill and a manufacturing method thereof. The end mill comprises a rod-shaped body, one end of the rod-shaped body is provided with a cutting part, and the other end is provided with a handle part. The cutting part comprises a bottom blade and a peripheral blade. The bottom blade comprises a bottom blade cutting edge, a chip space and a bottom blade center. The bottom blade center comprises a bottom blade center edge and a tooth gap width. The center structure of the bottom blade center corresponding to the tooth gap width is in a Z shape. The shape of the bottom blade center edge is a circular arc curve shape. In one aspect, by adjusting the shape of the center structure of the bottom blade center, the bottom blade center can be more evenly worn under the premise of ensuring the chip space of the dense-tooth ball head end mill, and the tool damage probability is reduced. In another aspect, by changing the shape of the bottom blade center edge, the strength of the bottom blade center can be increased under the condition of ensuring the tooth gap width of the tool.

Description

Technical Field

[0001] This invention relates to the field of cutting tool technology, and in particular to a multi-flute ball end mill and its manufacturing method. Background Technology

[0002] Ball end mills are widely used in the machining of critical components in industries such as aerospace, automotive, and shipbuilding. These critical components primarily utilize difficult-to-machine materials such as titanium alloys, high-temperature alloys, and high-strength steels, which possess characteristics like high strength, low density, and high hot hardness. To machine these difficult-to-machine materials, the method of increasing the cutting edge (i.e., designing a close-tooth structure) is typically used to increase tool life. However, close-tooth ball end mills still have the following problems:

[0003] 1. Increasing the number of teeth will reduce the chip space of the tool. The bottom edge of the ball end, which has the worst chip removal and heat dissipation effect, will heat up faster. At the same time, the chips are not easy to remove, so the chip space of the bottom edge can only be increased.

[0004] 2. The number of teeth on the ball end mill can be increased, but due to the limited chip space, it is difficult to increase the number of teeth at the center of the bottom edge, which makes the center of the bottom edge prone to breakage and leads to tool failure.

[0005] A type of multi-flute ball end mill in the prior art, such as Figure 1 , Figure 2 As shown, this type of multi-flute ball end mill typically includes a bottom cutting edge 101, a peripheral cutting edge 102, and a shank 103. The bottom cutting edge 101 includes a bottom cutting edge 104, a chip flute 105, and a bottom cutting edge center 106. The bottom cutting edge center 106 includes a bottom cutting edge center 107 and a backlash width w. To ensure the roundness of the ball end mill's bottom cutting edge profile, the central structure of the bottom cutting edge center in this type of multi-flute ball end mill in the prior art is in a straight line shape (e.g., ...). Figure 2 (As shown), but this shape is prone to breakage when machining difficult-to-machine materials such as titanium alloys and high-temperature alloys. Additionally, the bottom cutting edge center cutting edge 107 of this type of multi-flute ball end mill...

[0006] It is a straight line segment. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a multi-flute ball end mill and its manufacturing method. On the one hand, by adjusting the shape of the central structure of the bottom cutting edge, the wear of the bottom cutting edge center can be made more uniform while ensuring the chip space of the close-tooth ball end mill, thus reducing the probability of tool breakage. On the other hand, by changing the shape of the bottom cutting edge center, the strength of the bottom cutting edge center can be increased while ensuring the tool tooth backlash width.

[0008] The technical solution adopted by the present invention to solve its technical problem is: a multi-flute ball end mill, comprising a rod-shaped body, one end of which is a cutting part and the other end is a shank part; the cutting part includes a bottom cutting edge and a peripheral cutting edge; the bottom cutting edge includes a bottom cutting edge, a chip groove and a bottom cutting edge center; the bottom cutting edge center includes a bottom cutting edge center edge and a tooth clearance width; the central structure of the bottom cutting edge center corresponding to the tooth clearance width is Z-shaped.

[0009] The central structure at the center of the bottom edge corresponds to a Z-shaped gap, the gap comprising a depth h and a length l; the depth h and the length l satisfy the following formula:

[0010] 1%A ≤ h ≤ 20%A;

[0011] 5A≤l≤35A;

[0012] Where A is the maximum machinable accuracy value of the preset multi-blade ball end mill.

[0013] The bottom edge center edge is shaped like an arc curve, with a maximum radius of R and a vertical distance H from the starting point of the arc curve to the center of the bottom edge. The value of R is in the range of 0.1mm≤R≤0.6mm, and the value of H is in the range of 10%w≤H≤40%w, where w is the tooth gap width.

[0014] A method for manufacturing a multi-flute ball end mill involves designing the center structure of the bottom cutting edge, corresponding to the backlash width, into a Z-shape, and using the backlash depth h and backlash length l to control the shape of the Z-shaped bottom cutting edge center; wherein, the backlash depth h and backlash length l refer to the depth and length of the backlash formed by the center structure of the bottom cutting edge center corresponding to the Z-shaped gap; the method includes the following steps:

[0015] Assume that the multi-bladed ball end mill can achieve a machining accuracy of ±A;

[0016] The initial selection range for the gap depth h is 1%A ≤ h ≤ 100%A, and the range for the gap length l is 1A ≤ l ≤ 50A.

[0017] The parameter for the gap length l is the median value, and the parameter for the gap depth h is the two endpoints of its value range and multiple points between the two endpoints. Based on the parameters of gap depth h and gap length l, a bottom edge structure model is established using modeling software. Let the maximum strain value at the center of the bottom edge be X when face milling with a conventional ball end mill. Then, under the same machining parameters, the maximum strain value at the center of the bottom edge is obtained by finite element simulation. The law of the maximum strain value changing with the gap depth h is obtained, and the upper and lower boundary points of the maximum strain value at the center of the bottom edge corresponding to the gap depth h are determined as the value range of the gap depth h.

[0018] The parameter for the gap depth h is the median value, and the parameter for the gap length l is the two endpoints of its value range and multiple points between the two endpoints. Based on the parameters of gap depth h and gap length l, a bottom edge structure model is established using modeling software. Let the maximum strain value at the center of the bottom edge be X when face milling with a conventional ball end mill. Then, under the same machining parameters, the maximum strain value at the center of the bottom edge is obtained by finite element simulation. The law of the maximum strain value changing with the gap length l is obtained, and the upper and lower boundary points of the maximum strain value at the center of the bottom edge corresponding to the gap length l are determined as the value range of the gap length l.

[0019] The above preliminary selection of optimal values ​​for the gap depth h and gap length l was based on finite element simulation.

[0020] Furthermore, when determining the range of values ​​for the gap depth h and the gap length l, the gap length l is set to 50%A, and the gap depth h is set to 30%A, 40%A, 50%A, 60%A, or 70%A; when determining the range of values ​​for the gap length l, the gap depth h is set to 25A, and the gap length l is set to 5A, 15A, 25A, 35A, or 45A.

[0021] The shape of the center edge of the bottom edge is designed as an arc curve. The shape of the arc curve is mainly controlled by the maximum radius R of the arc curve and the vertical distance H from the starting point of the arc curve to the center of the bottom edge. It includes the following steps:

[0022] The initial maximum radius R is selected to be within the range of 0.1mm ≤ R ≤ 1.0mm, and the distance H is selected to be within the range of 10%w ≤ H ≤ 50%w; where w is the tooth gap width.

[0023] The maximum radius R is the median value, and the distance H is the two endpoints of its range and multiple points between the two endpoints. Based on the maximum radius R of the arc curve and the vertical distance H from the starting point of the arc curve to the center of the bottom edge, a bottom edge structure model is established using modeling software. Let the maximum strain value of the bottom edge center be X when using a conventional ball end mill for face milling. Then, under the same machining parameters, the maximum strain value of the bottom edge center is obtained by finite element simulation. The law of the maximum strain value changing with R is obtained, and the upper and lower boundary points of the maximum strain value of the bottom edge center corresponding to the maximum radius R of the arc curve are determined as the range of the maximum radius R.

[0024] The distance H is the median value, and the maximum radius R is the range of its two endpoints and multiple points between them. Based on the maximum radius R of the arc curve and the vertical distance H from the starting point of the arc curve to the center of the bottom edge, a bottom edge structure model is established using modeling software. Let X be the maximum strain value at the center of the bottom edge when using a conventional ball end mill for face milling. Then, under the same machining parameters, the maximum strain value at the center of the bottom edge is obtained by finite element simulation. The law of the maximum strain value changing with R is obtained. The upper and lower boundary points of the maximum strain value at the center of the bottom edge corresponding to the vertical distance H from the starting point of the arc curve to the center of the bottom edge are determined as the range of the vertical distance H from the starting point of the arc curve to the center of the bottom edge.

[0025] Furthermore, when determining the range of values ​​for the maximum radius R, the maximum radius R is set to 0.5, and the distance H is set to 10%w, 20%w, 30%w, 40%w, or 50%w; when determining the range of values ​​for the vertical distance H from the starting point of the arc curve to the center of the bottom edge, the distance H is set to 10%A, and the maximum radius R is set to 0.1, 0.25, 0.5, 0.75, or 1.0.

[0026] A method for manufacturing a multi-flute ball end mill involves using a Z-shaped opening as the central structure of the bottom cutting edge, and controlling the shape of the Z-shaped bottom cutting edge through two dimensions: the clearance depth h and the clearance length l. The clearance depth h and clearance length l refer to the depth and length of the clearance formed by the central structure of the bottom cutting edge corresponding to the Z-shape. Furthermore, the backlash width w of the bottom cutting edge remains constant. The central cutting edge of the multi-flute ball end mill is designed as an arc curve, and its shape is controlled by the maximum radius R of the arc curve and the vertical distance H from the starting point of the arc curve to the center of the bottom cutting edge.

[0027] A method for manufacturing a multi-flute ball end mill, comprising:

[0028] ① Using an orthogonal experimental method, with the gap depth h, gap length l, maximum radius R of the arc curve, and vertical distance H from the starting point of the arc curve to the center of the bottom edge as factors, the set factors are divided into 5 levels, establishing L16(4 5 Orthogonal arrays;

[0029] ②Based on the orthogonal table of different structural parameters obtained above, a bottom edge structure model of a multi-blade ball end mill is established using UG modeling software;

[0030] ③ Import the obtained multi-flute ball end mill bottom edge structure model into the finite element simulation software, establish the contact relationship between the tool and the workpiece according to the machining method, set the cutting process parameters and perform numerical simulation to obtain the maximum strain value at the bottom edge center;

[0031] ④ Taking the maximum strain value at the bottom edge center as the optimization object, range and variance analysis were performed on the above-obtained results of the maximum strain value at the bottom edge center to obtain the influence law and significance of different factors on the maximum strain value at the bottom edge center; the bottom edge geometric parameters of the multi-flute ball end mill with a smaller maximum strain value at the bottom edge center are better.

[0032] ⑤ Based on the combination of merit values ​​of h, l, R and H obtained above, a multi-flute ball end mill was manufactured. Face milling experiments were conducted with a conventional ball end mill of the same specification under the same machining parameters to prove the effectiveness of the tool design.

[0033] The value range of the gap depth h is 1%A≤h≤20%A, and the value range of the gap length l is 5A≤l≤35A; the value range of the maximum radius R of the arc curve is 0.1mm≤R≤0.6mm, and the value range of the vertical distance H from the starting point of the arc curve to the center of the bottom cutting edge is 10%w≤H≤40%w; where A is the preset machinable accuracy value of the multi-blade ball end mill, and w is the tooth backlash width.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. While ensuring the chip space of the fine-tooth ball end mill, adjust the shape of the bottom cutting edge center according to the workpiece machining dimensional accuracy requirements. Change the bottom cutting edge center of the existing ball end mill from a straight line to a Z-shaped line to make the wear of the bottom cutting edge center more uniform and reduce the probability of tool breakage.

[0036] 2. While ensuring the backlash width of the cutting tool, change the shape of the center cutting edge of the bottom edge from the conventional straight shape to an arc shape, so as to appropriately increase the thickness of the center cutting edge of the bottom edge, while avoiding stress concentration and increasing the strength of the center cutting edge of the bottom edge.

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments; however, the multi-blade ball end mill and its manufacturing method of the present invention are not limited to the embodiments. Attached Figure Description

[0038] Figure 1 This is a three-dimensional structural diagram of a multi-flute ball end mill in the prior art;

[0039] Figure 2 This is a schematic diagram of the bottom cutting edge center of a multi-flute ball end mill in the prior art;

[0040] Figure 3 This is a three-dimensional structural schematic diagram of an embodiment of the present invention;

[0041] Figure 4 This is a schematic diagram of the bottom edge of an embodiment of the present invention;

[0042] Figure 5 This is a schematic diagram of the center of the bottom edge in an embodiment of the present invention;

[0043] Figure 6 This is a left view of the center of the bottom edge in an embodiment of the present invention;

[0044] Figure 7 This is a diagram showing the stress analysis location of the center of the Z-shaped bottom edge according to an embodiment of the present invention;

[0045] Figure 8 This is a schematic diagram showing the maximum stress value at the center of the bottom cutting edge of a conventional ball end mill;

[0046] Figure 9 This is a schematic diagram of the stress curve at the center of the Z-shaped bottom edge according to an embodiment of the present invention;

[0047] Figure 10 This is a schematic diagram of the center edge of the arc-shaped bottom edge according to an embodiment of the present invention;

[0048] Figure 11 This is a schematic diagram of a 6-flute ball end mill used in the experiment;

[0049] Figure 12 This is a schematic diagram of the wear at the center of a conventional straight-line bottom cutting edge;

[0050] Figure 13 This is a schematic diagram of the wear at the center of the bottom edge in an embodiment of the present invention. Detailed Implementation

[0051] Example

[0052] See Figures 3 to 7 , Figure 10 As shown, a multi-blade ball end mill of the present invention includes a rod-shaped body 1, one end of which is a cutting part 2 and the other end is a shank 3; the cutting part 2 includes a bottom cutting edge 4 and a peripheral cutting edge 5; the bottom cutting edge 4 includes a bottom cutting edge 41, a chip groove 42 and a bottom cutting edge center 6; the bottom cutting edge center 6 includes a bottom cutting edge center 7 and a backlash width w; the central structure 61 of the bottom cutting edge center corresponding to the backlash width is Z-shaped.

[0053] In this embodiment, the 6-center structure 61 at the center of the bottom edge corresponds to a Z-shaped gap 8, the gap 8 including a gap depth h and a gap length l; the gap depth h and the gap length l satisfy the following formula:

[0054] 1%A ≤ h ≤ 20%A;

[0055] 5A≤l≤35A;

[0056] Where A is the maximum machinable accuracy value of the preset multi-blade ball end mill.

[0057] In this embodiment, the shape of the bottom edge center blade 7 is an arc curve, the maximum radius of the arc curve is R, and the vertical distance from the starting point of the arc curve to the center of the bottom edge is H. The initial selection range of R is 0.1mm≤R≤1.0mm, and the range of H is 10%w≤H≤50%w, where w is the tooth gap width.

[0058] The present invention discloses a method for manufacturing a multi-flute ball end mill, wherein the center structure 61 of the bottom cutting edge center 6 corresponding to the tooth backlash width is designed as a Z-shape, and the shape of the bottom cutting edge center of the Z-shape is controlled by the backlash depth h and the backlash length l; wherein, the backlash depth h and the backlash length l refer to the depth and length of the center structure 61 of the bottom cutting edge center corresponding to the Z-shaped gap 8; the method includes the following steps:

[0059] Assume that the multi-bladed ball end mill can achieve a machining accuracy of ±A;

[0060] The initial selection range for the gap depth h is 1%A ≤ h ≤ 100%A, and the range for the gap length l is 1A ≤ l ≤ 50A.

[0061] The parameter for the gap length l is the median value, and the parameter for the gap depth h is the two endpoints of its value range and multiple points between the two endpoints. Based on the parameters of gap depth h and gap length l, a bottom edge structure model is established using modeling software. Let the maximum strain value at the center of the bottom edge be X when face milling with a conventional ball end mill. Then, under the same machining parameters, the maximum strain value at the center of the bottom edge is obtained by finite element simulation. The law of the maximum strain value changing with the gap depth h is obtained, and the upper and lower boundary points of the maximum strain value at the center of the bottom edge corresponding to the gap depth h are determined as the value range of the gap depth h.

[0062] The parameter for the gap depth h is the median value, and the parameter for the gap length l is the two endpoints of its value range and multiple points between the two endpoints. Based on the parameters of gap depth h and gap length l, a bottom edge structure model is established using modeling software. Let the maximum strain value at the center of the bottom edge be X when face milling with a conventional ball end mill. Then, under the same machining parameters, the maximum strain value at the center of the bottom edge is obtained by finite element simulation. The law of the maximum strain value changing with the gap length l is obtained, and the upper and lower boundary points of the maximum strain value at the center of the bottom edge corresponding to the gap length l are determined as the value range of the gap length l.

[0063] The above preliminary selection of optimal values ​​for the gap depth h and gap length l was based on finite element simulation.

[0064] The shape of the center edge of the bottom edge is designed as an arc curve. The shape of the arc curve is mainly controlled by the maximum radius R of the arc curve and the vertical distance H from the starting point of the arc curve to the center of the bottom edge. It includes the following steps:

[0065] The initial maximum radius R is selected to be within the range of 0.1mm ≤ R ≤ 1.0mm, and the distance H is selected to be within the range of 10%w ≤ H ≤ 50%w; where w is the tooth gap width.

[0066] The maximum radius R is the median value, and the distance H is the two endpoints of its range and multiple points between the two endpoints. Based on the maximum radius R of the arc curve and the vertical distance H from the starting point of the arc curve to the center of the bottom edge, a bottom edge structure model is established using modeling software. Let the maximum strain value of the bottom edge center be X when using a conventional ball end mill for face milling. Then, under the same machining parameters, the maximum strain value of the bottom edge center is obtained by finite element simulation. The law of the maximum strain value changing with R is obtained, and the upper and lower boundary points of the maximum strain value of the bottom edge center corresponding to the maximum radius R of the arc curve are determined as the range of the maximum radius R.

[0067] The distance H is the median value, and the maximum radius R is the range of its two endpoints and multiple points between them. Based on the maximum radius R of the arc curve and the vertical distance H from the starting point of the arc curve to the center of the bottom edge, a bottom edge structure model is established using modeling software. Let X be the maximum strain value at the center of the bottom edge when using a conventional ball end mill for face milling. Then, under the same machining parameters, the maximum strain value at the center of the bottom edge is obtained by finite element simulation. The law of the maximum strain value changing with R is obtained. The upper and lower boundary points of the maximum strain value at the center of the bottom edge corresponding to the vertical distance H from the starting point of the arc curve to the center of the bottom edge are determined as the range of the vertical distance H from the starting point of the arc curve to the center of the bottom edge.

[0068] The following example of a six-flute ball end mill with R9.5 carbide is used to further illustrate a multi-flute ball end mill and its manufacturing method according to the present invention.

[0069] To ensure uniform wear at the center of the bottom cutting edge, this invention modifies the center of the bottom cutting edge into a Z-shape. However, since the Z-shaped bottom cutting edge center will generate a gap 8, the gap depth h and gap length l will reduce the machining accuracy of the workpiece. Therefore, the gap depth h and gap length l of the Z-shaped bottom cutting edge center need to be adjusted according to the actual machining requirements.

[0070] Assume the multi-flute ball end mill can achieve a machining accuracy of ±A. Conventional ball end mill machining results in part dimensional inaccuracies due to tool breakage. To determine the range of values ​​for the clearance depth h and clearance length l, finite element simulation is used. Assuming the maximum stress at the center of the bottom cutting edge during face milling with a conventional ball end mill is X, then under the same machining parameters, the maximum stress at the center of the Z-shaped bottom cutting edge must not exceed 0.8X.

[0071] The initial selection range for h is 1%A ≤ h ≤ 100%A, and the range for l is 1A ≤ l ≤ 50A. Since the gap depth h and gap length l are independent variables, a single-factor simulation method is used. The specific values ​​for h and l are shown in Tables 1 and 2.

[0072] Table 1. Values ​​of void depth h

[0073]

[0074] Table 2 Values ​​of gap length l

[0075]

[0076] The boundary point where the maximum stress value at the center of the bottom edge does not exceed 0.8X is taken as the range of values ​​for the gap depth h and the gap length l.

[0077] Taking a carbide R9.5 six-flute ball end mill as an example, the tool machining accuracy requirement is ±0.03mm. The values ​​of clearance depth h and clearance length l are shown in Table 3. The maximum stress value at the center of the bottom cutting edge of a conventional ball end mill is as follows: Figure 8 As shown.

[0078] Table 3 Values ​​of clearance depth h for R9.5 six-flute ball end mills

[0079]

[0080] The maximum stress at the center of the bottom cutting edge of a conventional ball end mill is 724 MPa, therefore the maximum stress at the center of the bottom cutting edge should not exceed 579 MPa. The stress variation at the center of the bottom cutting edge in a "Z"-shaped cut is as follows: Figure 9 As shown.

[0081] Depend on Figure 9 It can be seen that the tolerance range of h for a carbide R9.5 six-flute ball end mill is 0.006mm-0.27mm.

[0082] To ensure consistent heat dissipation and chip clearance at the bottom edge of the tool, the backlash width w at the center of the bottom edge must remain constant. Therefore, the center edge of the bottom edge is modified to an arc curve shape, with a maximum radius of R and a vertical distance H from the starting point of the arc curve to the center of the bottom edge.

[0083] The starting point of the arc curve bottom edge center is designed below the "Z" shape to ensure a smooth connection between the arc curve and the straight line, reduce the "sharp point" that appears in conventional straight lines, reduce stress concentration, make the bottom edge center of the tool uniformly stressed, and improve the service life of the bottom edge center.

[0084] The range of values ​​for R and H directly affects the stress distribution and chip space of the tool. If R and H are too small, the effect of reducing stress concentration at the bottom edge center is insufficient; if R and H are too large, the chip space at the bottom edge center of the tool will be reduced.

[0085] Based on the ball end mill grinding process, the initial selection range for R is 0.1mm ≤ R ≤ 1.0mm, and the range for H is 10%w ≤ H ≤ 50%w. Since R and H are independent variables, a single-factor simulation is used. The specific values ​​for R and H are shown in Tables 4 and 5.

[0086] Table 4. Values ​​of R

[0087]

[0088] The values ​​of H in Table 5

[0089]

[0090] The boundary point where the maximum stress value at the center of the bottom edge does not exceed 0.8X is taken as the range of values ​​for the maximum radius R of the arc curve and the vertical distance H from the starting point of the arc curve to the center of the bottom edge.

[0091] To verify the effectiveness of the new bottom cutting edge center, a comparative experiment was conducted using a 6-flute ball end mill. The experimental parameters were: cutting speed Vc = 45 m / min, feed per tooth fz = 0.05 mm / min, depth of cut Ap = 2 mm, and width of cut Ae = 0.8 mm.

[0092] The center of the tool bottom edge wore out after 60 minutes of cutting. Figure 11 , 12 As shown in Figure 13. From Figure 11 , Figure 12 , Figure 13 It can be seen that the service life of the center of the arc-curved bottom edge is significantly improved.

[0093] The present invention provides a multi-flute ball end mill and its manufacturing method. Compared with the prior art, the beneficial effects of the present invention are:

[0094] 1. While ensuring the chip space of the fine-tooth ball end mill, adjust the shape of the bottom cutting edge center according to the workpiece machining dimensional accuracy requirements. Change the bottom cutting edge center of the existing ball end mill from a straight line to a Z-shaped line to make the wear of the bottom cutting edge center more uniform and reduce the probability of tool breakage.

[0095] 2. While ensuring the backlash width of the cutting tool, change the shape of the center cutting edge of the bottom edge from the conventional straight shape to an arc shape, so as to appropriately increase the thickness of the center cutting edge of the bottom edge, while avoiding stress concentration and increasing the strength of the center cutting edge of the bottom edge.

[0096] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, should fall within the protection scope of the present invention.

Claims

1. A multi-fluted ballnose endmill comprising a bar body, one end of the bar body being provided as a cutting portion and the other end being provided as a shank portion; the cutting portion comprising a floor and a peripheral edge; the floor comprising a floor cutting edge, a flute, and a floor center; the floor center comprising a floor center edge and a gash width; characterized in that: The center structure of the bottom edge center corresponding to the tooth gap width is in a Z shape, and the center structure of the bottom edge center corresponds to the Z shape to form a gap.

2. The multi-fluted ball-end mill of claim 1, wherein: The gap includes a gap depth h and a gap length l; the gap depth h and the gap length l satisfy the following formula: 1% A≤h≤20% A; 5A≤l≤35A; Wherein, A is the highest machinable precision value of the preset multi-edge ball head end mill.

3. The multi-fluted ball-end mill of any of claims 1 or 2, wherein: The shape of the bottom edge center is a circular arc curve, the maximum radius of the circular arc curve is R, and the distance from the starting point of the circular arc curve to the vertical direction of the bottom edge center is H, wherein the value range of R is 0.1mm≤R≤0.6mm, and the value range of H is 10% w≤H≤40% w, w is the tooth gap width.

4. A method of manufacturing a multi-fluted ball end mill, wherein a center structure of a bottom edge center corresponding to a tooth gap width is designed in a Z shape, and a gap depth h and a gap length l are used to control the shape of the Z-shaped bottom edge center; wherein, The gap depth h and the gap length l refer to the depth and length of the gap formed by the center structure of the bottom edge center corresponding to the Z shape; it includes the following steps: The machinable precision of the multi-edge ball head end mill is ±A; The value range of the initial selected gap depth h is 1% A≤h≤100% A, and the value range of the gap length l is 1A≤l≤50A; The value parameter of the gap length l is the median value, and the value parameter of the gap depth h is the two endpoints of the value range and multiple points between the two endpoints. Based on the parameters of the gap depth h and the gap length l, a bottom edge structure model is established using modeling software. Assuming that the maximum strain value of the bottom edge center of the conventional ball head end mill when face milling is X, the maximum strain value of the bottom edge center is obtained under the same machining parameters by using finite element simulation, the law of the maximum strain value changing with the gap depth h is obtained, and the upper and lower boundary points of the gap depth h corresponding to the maximum strain value of the bottom edge center not exceeding 0.8X are determined as the value range of the gap depth h. The value parameter of the gap length l is the median value, and the value parameter of the gap depth h is the two endpoints of the value range and multiple points between the two endpoints. Based on the parameters of the gap depth h and the gap length l, a bottom edge structure model is established using modeling software. Assuming that the maximum strain value of the bottom edge center of the conventional ball head end mill when face milling is X, the maximum strain value of the bottom edge center is obtained under the same machining parameters by using finite element simulation, the law of the maximum strain value changing with the gap length l is obtained, and the upper and lower boundary points of the gap length l corresponding to the maximum strain value of the bottom edge center not exceeding 0.8X are determined as the value range of the gap length l. The above, the best value of the initial selected gap depth h and the gap length l is selected by finite element simulation.

5. The method of claim 4, wherein: Further, when determining the value range of the gap depth h and the gap length l, the value of the gap length l is 50% A, and the value of the gap depth h is 30% A, 40% A, 50% A, 60% A, and 70% A. When determining the value range of the gap length l, the value of the gap depth h is 25A, and the value of the gap length l is 5A, 15A, 25A, 35A, and 45A.

6. The method of claim 4, wherein: The shape of the bottom edge center is designed as a circular arc curve, and the circular arc curve shape is mainly controlled by the maximum radius R of the circular arc curve and the distance H from the starting point of the circular arc curve to the vertical direction of the bottom edge center; it includes the following steps: The value range of the maximum radius R is 0.1mm≤R≤1.0mm, and the value range of the distance H is 10%w≤H≤50%w; w is the tooth gap width; The value parameter of the maximum radius R is the median value, the value parameter of the distance H is the two endpoints of the value range and a plurality of points between the two endpoints, based on the parameters of the maximum radius R of the circular arc curve and the vertical distance H of the starting point of the circular arc curve from the center of the bottom edge, a bottom edge structure model is established using modeling software, it is assumed that the maximum strain value of the center of the bottom edge when milling with a conventional ball head end mill is X, then under the same machining parameters, the maximum strain value of the center of the bottom edge is obtained by finite element simulation, the law of the maximum strain value changing with R is obtained, and the upper and lower boundary points of the maximum radius R corresponding to the bottom edge center maximum strain value not exceeding 0.8X are determined as the value range of the maximum radius R; The value parameter of the distance H is the median value, the value parameter of the maximum radius R is the two endpoints of the value range and a plurality of points between the two endpoints, based on the parameters of the maximum radius R of the circular arc curve and the vertical distance H of the starting point of the circular arc curve from the center of the bottom edge, a bottom edge structure model is established using modeling software, it is assumed that the maximum strain value of the center of the bottom edge when milling with a conventional ball head end mill is X, then under the same machining parameters, the maximum strain value of the center of the bottom edge is obtained by finite element simulation, the law of the maximum strain value changing with R is obtained, and the upper and lower boundary points of the maximum radius R corresponding to the bottom edge center maximum strain value not exceeding 0.8X are determined as the value range of the maximum radius R.

7. The method of claim 6, wherein: Further, when determining the value range of the maximum radius R, the maximum radius R is 0.5, and the distance H is 10%w, 20%w, 30%w, 40%w, 50%w; when determining the value range of the vertical distance H of the starting point of the circular arc curve from the center of the bottom edge, the distance H is 10%A, and the maximum radius R is 0.1, 0.25, 0.5, 0.75, 1.

0.

8. A method for manufacturing a multi-fluted ball-end mill, which uses a Z-shaped opening as a center structure of a center of a bottom blade, and controls a shape of the Z-shaped bottom blade by two dimensions of a gap depth h and a gap length l; wherein, The gap depth h and the gap length l refer to the depth and length of the gap formed by the center structure of the center of the bottom edge; and the tooth gap width w of the center of the tool bottom edge is kept unchanged, the bottom edge center edge of the multi-fluted ball head end mill is designed as a circular arc curve shape, and the circular arc curve shape is controlled by the maximum radius R of the circular arc curve and the vertical distance H of the starting point of the circular arc curve from the center of the bottom edge.

9. A manufacturing method of a multi-fluted ball head end mill, comprising: 5 )orthogonal table with the factors of the depth of the gap h, the length of the gap l, the maximum radius of the circular curve R and the distance H from the center of the bottom blade to the vertical direction of the starting point of the circular curve, which are divided into 5 levels;​ ②According to the above obtained orthogonal table of different structure parameters, a multi-fluted ball head end mill bottom edge structure model is established by using UG modeling software; ③The above obtained multi-fluted ball head end mill bottom edge structure model is imported into a finite element simulation software, the contact relationship between the tool and the workpiece is established according to the machining method, the cutting process parameters are set for numerical simulation, and the maximum strain value of the center of the bottom edge is obtained; IV. Taking the maximum strain value of the bottom edge center as the optimization object, the maximum strain value of the bottom edge center obtained above is subjected to range and variance analysis to obtain the influence law and significant degree of different factors on the maximum strain value of the bottom edge center; the multi-edge ball head end mill with smaller maximum strain value of the bottom edge center has better bottom edge geometric structure parameters; V. According to the optimal value combination of h, l, R and H obtained above, a multi-edge ball head end mill is manufactured, and face milling experiments are carried out under the same machining parameters and conventional same-specification ball head end mills to prove the effectiveness of the cutter design.

10. The method of claim 9, wherein: The value range of the gap depth h is 1% A≤h≤20% A, the value range of the gap length l is 5A≤l≤35A, the value range of the maximum radius R of the circular arc curve is 0.1mm≤R≤0.6mm, and the value range of the vertical distance H of the circular arc curve starting point from the center of the bottom edge is 10% w≤H≤40% w; wherein A is a preset machinable precision value of the multi-edge ball head end mill, and w is a backlash width.

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