A method for precisely controlling the position and frequency of metal chip breakage

Abstract

The present application is a kind of method for accurately controlling the fracture position and frequency of metal chips.According to the monitoring results of the previous turning process, the area where chip winding disturbance occurs is determined, and the minimum micro groove depth of the workpiece surface that ensures chip breaking under the current cutting condition is calculated. Before the next turning process, micro grooves are machined in the determined chip winding disturbance area, and the final depth of the micro grooves is equal to the minimum micro groove depth. When the cutting tool cuts to the micro groove, part of the micro groove is transferred to the free surface of the chip, inducing the chip to break at the micro groove, and eliminating the chip winding disturbance phenomenon that occurred in the previous turning process. The method of the present application is suitable for solving the chip winding disturbance problem caused by continuous chips in the machining production line. Compared with the prior art, it can achieve more stable and efficient chip control, and has less impact on machining quality and tool life, and can effectively reduce the work intensity of traditional manual continuous chip processing.

Description

Technical Field

[0001] This invention relates to a method for precisely controlling the location and frequency of metal chip breakage, belonging to the fields of mechanical manufacturing processes and metal cutting. Background Technology

[0002] Chip entanglement is a common problem in metal cutting, referring to a series of major production line issues caused by continuous metal chips, including out-of-tolerance part positioning, increased scrap rates, and machine tool hardware damage. To avoid excessively long and entangled chips, manual monitoring of the cutting process or the installation of chip detection devices is often necessary. However, these measures cannot completely eliminate the risks associated with insufficient chip breaking, especially in the machining of highly ductile metals such as aluminum alloys and titanium alloys, where truly unattended operation is difficult. Furthermore, manual chip removal is time-consuming and labor-intensive, contradicting human-centered manufacturing principles and severely hindering production efficiency, causing disruptions to the production cycle.

[0003] Existing chip entanglement control technologies and methods include:

[0004] 1) Select appropriate tool geometry and cutting parameters to make the chips more curled;

[0005] 2) Set chip breaking grooves on the rake face of the cutting tool or insert to force chip deformation and breakage;

[0006] 3) High-pressure injection of cutting fluid or gas into the chips to break them apart with external force.

[0007] The aforementioned technical solutions are difficult to achieve stable control during the precision cutting of high-strength alloys such as stainless steel, high-strength steel, and titanium alloys. Therefore, they cannot fundamentally eliminate the phenomenon of chip entanglement and disturbance, and in most cases, manual monitoring is still necessary. Furthermore, the chip entanglement control effect of existing technologies has a certain degree of randomness and cannot precisely control the location and frequency of metal chip breakage. They also suffer from excessively high investment and maintenance costs.

[0008] Another method involves inducing chip fracture through prefabricated structures.

[0009] Reference 1: US Patent US7441484B1 discloses a method for promoting chip breaking, in which a workpiece is placed in a spindle fixture, and before the cutting tool moves, an indexing cutting tool is used to cut a groove along the workpiece and to cut the workpiece to the final machining depth; when the cutting tool cuts to the pre-processed position, the chip breaks actively and controllably due to the sudden change in the thickness of the newly formed chip.

[0010] Reference 2: The paper (Jiang Yan. Research on chip breaking methods in pipe threading [J]. Hydraulics, Pneumatics & Seals, 2010, 30(02): 55-57.) discloses a new laser-assisted chip control technology developed by AmeriChip, Inc. in the United States. This technology uses a laser beam to carve a narrow groove on the surface of the workpiece material. When the material is processed, it is cut away in the form of small chips instead of forming long, ribbon-like chips. When the laser beam is focused on the workpiece material, its energy melts and vaporizes the metal, while an air nozzle blows the molten material away from the groove. Lower laser power and faster movement speed result in shallower grooves; higher laser power and slower movement speed result in deeper grooves. The system can be adjusted according to the constantly changing dimensions of the workpiece material during processing, preventing over-carving.

[0011] Reference 3: Chinese Patent No. 2020103145417 discloses a method for controlling metal chip breakage during the turning of shaft parts. Before each cutting pass of the cutting tool, the surface of the workpiece is pre-treated by surface shaping and modification. When the cutting tool cuts to the pre-treated position, there is a sudden change in the thickness or material properties of the newly formed chips on the workpiece surface, thereby achieving chip breaking.

[0012] For ease of description, the above technology will be referred to as "induced chip breaking technology" in the following text.

[0013] The shortcomings of existing induced chip breaking technology are:

[0014] 1) References 1-3 do not provide a specific calculation method for the optimal depth of grooves / slots / microgrooves under the premise of ensuring smooth chip breakage; they only limit the depth range of grooves / slots / microgrooves. In fact, the shallower the groove / slot / microgroove, the more beneficial it is to the stability and smoothness of the turning process. Conversely, if the groove / slot / microgroove is too deep, the turning process will tend to transition to intermittent cutting. Intermittent cutting will generate vibration, causing changes in the relative distance between the cutting edge and the workpiece surface, resulting in increased surface roughness and the appearance of so-called "tool marks." Intermittent cutting will also accelerate tool wear, not only increasing tool consumption but also requiring more frequent tool setting operations on the machine tool, affecting machining efficiency. On the other hand, if the depth of the machined groove / slot / microgroove is greater than the optimal depth, the groove / slot / microgroove machining process will take longer and the process cost will be higher. However, if the depth of the machined groove / slot / microgroove is less than the optimal depth, it cannot guarantee that the chips will break smoothly, and the technical effect will not be achieved. In conclusion, finding and determining the optimal depth of grooves / slots / microgrooves is crucial for the technical effectiveness, implementation cost, implementation efficiency, part machining quality, and tool life of induced chip breaking.

[0015] 2) The induced chip breaking techniques mentioned in References 1-3 all require workpiece pretreatment, which is equivalent to adding an extra auxiliary process. Furthermore, the pretreatment operation is independent of the turning process and has no direct relationship with it. Therefore, pretreatment increases the total process time and is not conducive to maintaining the original machining cycle time. In addition, the implementation of these techniques requires investment in new hardware and may even require adjustments to the existing machine tool structure, resulting in high costs for practical application. For example, Reference 1 requires the addition of a cutting tool, while References 2 and 3 require the addition of lasers, motors, supports, and other hardware. In summary, existing induced chip breaking techniques are costly to implement and increase the number of processes and the total process time.

[0016] 3) The induced chip breaking techniques mentioned in references 1-3 only consider the control of the chip breaking position on the workpiece surface, failing to further consider the handling of broken chips in conjunction with induced chip breaking technology. Broken chips may affect the machined surface, machine tool sensors, and subsequent machining processes. Specifically, when using a robotic arm to load and unload workpieces, broken chips may adhere to the machined surface; if the robotic arm's clamping position overlaps with the chip adhesion position, the chips will affect the robotic arm's clamping accuracy; if subsequent processes use the surface with adhered chips as a positioning reference, it will cause a decrease in workpiece positioning accuracy; if broken chips float and adhere to the surface of the camera or tool setter, it will damage these sensors. In summary, existing induced chip breaking technologies only focus on achieving chip breaking, without considering the derivative effects of broken chips. Summary of the Invention

[0017] The technical problem solved by this invention is that existing induced chip breaking techniques suffer from numerous drawbacks, including the inability to determine the optimal chip breaking depth, high implementation costs, increased number of processes, increased total process time, and failure to consider the control of fractured chips. Therefore, this invention proposes a method for precisely controlling the location and frequency of metal chip fracture. The technical solution is as follows:

[0018] Step (a): Based on the monitoring results of the previous turning process, determine the area where chip entanglement disturbance occurs;

[0019] Step (b) involves determining the minimum microgroove depth that ensures smooth chip breakage under the current cutting conditions through theoretical calculations or knowledge base methods.

[0020] Step (c): Before the next turning operation, microgrooves are machined in the chip entanglement area determined in step (a), the final depth of which is equal to the minimum microgroove depth determined in step (b).

[0021] In step (d), when the cutting tool cuts to the microgroove, part of the microgroove is transferred to the free surface of the chip, inducing the chip to break at the microgroove. Therefore, the chip entanglement disturbance that occurred in the previous turning process will not occur in this machining.

[0022] Specifically, the method for determining the region where chip entanglement occurs in step (a) is manual identification or sensor identification. If sensor identification is used, the sensor is at least one of an optical sensor, a mechanical sensor, or an acoustic sensor.

[0023] Specifically, in step (b), the theoretical calculation method is finite element simulation or fracture mechanics solution, and the knowledge base method is a data body that combines finite element simulation, fracture mechanics solution and experimental data, containing the minimum microgroove depth information under multiple turning parameter combinations.

[0024] Specifically, the microgrooves in step (c) are machined on the outer diameter or inner hole surface of the workpiece by mechanical scribing. The direction of the microgrooves is parallel to the axis of the shaft part or symmetrically distributed around the central axis of the shaft part. The cross-sectional shape of the microgrooves is one of the following: circular arc, parabola, or broken line. By controlling the position of the mechanical scribing, the distribution of the microgrooves on the workpiece surface is controlled, and depending on the mechanical scribing method, the microgrooves can be straight lines or spirals. If the microgrooves are spirals, the pitch of the spiral is controlled, and thus the frequency of chip breakage can also be controlled.

[0025] Specifically, the mechanical scribing in step (c) can be performed either by the secondary cutting edge of the cutting tool or by another cutting tool. If performed by another cutting tool, that tool is also mounted on the machine tool post or tool head.

[0026] Specifically, the microgrooving in step (c) is formed by mechanically scribing the workpiece surface during the return stroke of the cutting tool to the origin of the process, and this process has no significant impact on the total process time.

[0027] Specifically, in step (d), the broken chips, under the influence of gravity and an artificially added external force, move along a specific trajectory and fall into the chip collection device; the specific trajectory avoids the processing area, thus not affecting subsequent workpiece positioning and clamping. The artificially added external force is the driving force of gas or liquid.

[0028] The significant innovations of the above technical solution are: 1) proposing a method for calculating the minimum microgroove depth, which makes the chip breaking process have less impact on the turning process; 2) proposing to embed the mechanical scribing of microgrooves into the turning process, so that the microgroove machining has no significant impact on the total process time; 3) proposing to control the movement trajectory of the chip after it breaks, so as to avoid the chip breaking affecting the subsequent workpiece positioning and clamping.

[0029] This invention provides a method for solving the problem of chip entanglement and disturbance caused by continuous chips in machining production lines, enabling more stable and efficient chip control. Compared with existing technologies, it has less impact on machining quality and tool life, significantly improving the quality and efficiency of turning operations while reducing the workload of traditional manual handling of continuous chips. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the prior art principle.

[0031] Figure 2 This is a schematic diagram of prior art technology for prefabricating grooves on the surface of a workpiece.

[0032] Figure 3 This is a block diagram illustrating the implementation logic of the method of the present invention.

[0033] Figure 4 This is a schematic diagram illustrating the implementation process of the method of the present invention.

[0034] Figure 5 This is a schematic diagram of the cross-section of the chip-breaking microgroove on the workpiece surface.

[0035] Figure 6 This is a schematic diagram of a finite element model.

[0036] Figure 7 This is a schematic diagram of the calculation results from the finite element model.

[0037] Figure 8 This is a schematic diagram of a fracture mechanics model.

[0038] In the figure, 1 is the cutting tool; 11 is the chuck; 12 is the machine tool spindle; 2 is the tool post; 20 is the workpiece; 21 is the chip breaker; 3 is the straight microgroove; 31 is the linear microgroove; 32 is the helical microgroove; and 4 is the turning trajectory. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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.

[0040] The terms "first," "second," "third," "fourth," etc. (if present) in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in sequences other than those illustrated or described herein.

[0041] It should be understood that in the various embodiments of the present invention, the sequence number of each process does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0042] It should be understood that in this invention, "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0043] It should be understood that in this invention, "multiple" refers to two or more. "And / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "Contains A, B, and C", "Contains A, B, and C" means that all three A, B, and C are contained; "Contains A, B, or C" means that one of A, B, and C is contained; "Contains A, B, and / or C" means that any one, two, or three of A, B, and C are contained.

[0044] It should be understood that in this invention, "B corresponding to A", "B corresponding to A", "A and B correspond", or "B and A correspond" means that B is associated with A, and B can be determined based on A. Determining B based on A does not mean determining B solely based on A; B can also be determined based on A and / or other information. Matching A and B is defined as a similarity between A and B that is greater than or equal to a preset threshold.

[0045] Depending on the context, "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection."

[0046] To facilitate understanding of the significant differences and technical effects between this application and conventional techniques, conventional techniques prior to this application, such as US Patent 7441484B1, are first introduced. Figure 1 and Figure 2 As shown.

[0047] The workpiece 20 is clamped in the chuck 11, and the spindle drives the workpiece 20 to rotate. The cutting tool 1 is controlled to move back and forth along the axial direction of the workpiece 20, mechanically etching straight microgrooves 31 and helical microgrooves 32 on the surface of the workpiece 20. Figure 2 As shown. The depth of the microgroove is 80% of the cutting depth. During subsequent turning processes, the microgroove 40 will generate intermittent chips, i.e., broken chips 21.

[0048] The shortcomings of the conventional technical means are:

[0049] 1) Limiting only the depth range of grooves / slots / microgrooves does not mean that the depth of microgrooves is the optimal choice. In fact, finding and determining the optimal depth of microgrooves is crucial for the effectiveness, cost, efficiency, part machining quality, and tool life of induced chip breaking technology.

[0050] 2) Pre-processing of the workpiece is required, which is equivalent to adding an extra auxiliary process. Furthermore, the pre-processing operation is independent of the turning process and the two are not directly related. Pre-processing will increase the total process time and is not conducive to maintaining the original processing rhythm.

[0051] 3) New hardware and adjustments to existing machine tool structures are required, resulting in high costs for technology implementation.

[0052] 4) Only the control of the chip breaking position on the workpiece surface was considered, and the disposal of broken chips was not further considered in conjunction with induced chip breaking technology.

[0053] The implementation steps of the method of the present invention are as follows: Figure 3 As shown, it includes the following steps.

[0054] Step (a): Identify the area where chip entanglement occurs based on the monitoring results of the previous turning process;

[0055] Step (b) involves determining the minimum microgroove depth that ensures smooth chip breakage under the current cutting conditions through theoretical calculations or knowledge base methods.

[0056] Step (c): Before the next turning operation, microgrooves are machined in the chip entanglement area determined in step (a), with a final depth equal to the minimum microgroove depth determined in step (b).

[0057] In step (d), when the cutting tool cuts to the microgroove, part of the microgroove is transferred to the free surface of the chip, inducing the chip to break at the microgroove. Therefore, the chip entanglement disturbance that occurred in the previous turning process will not occur in this machining.

[0058] The technical solution of the present invention will be described in detail below with reference to specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0059] Example 1.

[0060] In Example 1, the workpiece 20 is an optical shaft made of 316L stainless steel with a diameter of 56 mm. This example requires turning the outer diameter of the workpiece 20 to 55 mm, while achieving a surface roughness of Ra1.6 on the outer surface.

[0061] Based on the above requirements, a corresponding machining strategy is formulated. The left end of workpiece 20 is held on chuck 11. The outer cylindrical surface of workpiece 20 is machined in two passes. The purpose of the first pass is to quickly remove the remaining material of 0.7 mm, after which the outer diameter of the workpiece is 55.3 mm. The purpose of the second pass is to reduce the surface roughness of the part and obtain a finished outer cylindrical surface, the second pass removes the remaining material of 0.3 mm, after which the outer diameter of the workpiece is 55 mm.

[0062] To meet the surface roughness requirements, the feed rate for the first pass is 0.4 mm / revolution, and the feed rate for the second pass is 0.15 mm / revolution.

[0063] During the two passes, the spindle 12 of the machine tool maintains a constant rotation speed of 500 rpm.

[0064] Step (a): Based on the monitoring results of the previous turning process, determine the location area on the workpiece (20) surface where continuous metal chips are generated. In the previous turning process, it was found that: due to the large depth of cut in the first pass, no chip entanglement occurred, so the first pass did not require the intervention of the method of the present invention; however, the depth of cut and feed rate of the second pass were both smaller, resulting in narrower chip width and longer total length. The chips became entangled with the spindle and cutting tool, and chip removal was required for each machining operation. Therefore, the second pass required the intervention of the method of the present invention.

[0065] Step (b) involves determining, through theoretical calculation, the minimum microgroove depth Hmin that ensures smooth chip breakage under the current cutting conditions.

[0066] Step (c): Determine the distance St from which the cutting tool 1 cuts into the workpiece 20 radially; and machine microgrooves on the workpiece 20 by mechanical scribing.

[0067] In step (d), when the cutting tool cuts to the microgroove, part of the microgroove is transferred to the free surface of the chip, inducing the chip to break at the microgroove.

[0068] The specific implementation process of this embodiment is as follows: Figure 4 As stated above.

[0069] like Figure 4 As shown in the first figure, the cutting tool 1 is mounted on the tool holder 2; driven by the tool holder 2, the cutting tool 1 starts from the initial machining position and feeds along the axial direction (left side in the figure) of the workpiece 20. The initial machining position is on the right side of the right end face of the workpiece 20.

[0070] like Figure 4 As shown in the second figure, when the cutting tool 1 is fed to the leftmost position, the first pass machining has been completed.

[0071] At this point, the conventional technical process involves moving the cutting tool 1 radially away from the workpiece 20, and then controlling the cutting tool 1 to translate to the right in the same direction as the workpiece 20, at a speed of V. a The cutting tool 1 continues to move radially toward the workpiece 20 until it returns to its initial horizontal position. Then, based on the remaining machining allowance, the cutting tool 1 is controlled to move radially toward the workpiece 20. In summary, in conventional processes, after the first pass, during the return of the tool to its initial machining position, the cutting tool 1 and the workpiece 20 do not come into contact.

[0072] like Figure 4 As shown in the third figure, the method of this invention involves inserting the cutting tool 1 radially into the workpiece 20, with the cutting tool 1 moving a distance St relative to the workpiece 20. Then, the cutting tool 1 is controlled to translate to the right, with the direction of movement being the same as the axial direction of the workpiece 20, and the speed being V. b The cutting tool 1 is moved radially toward the workpiece 20 until it returns to the horizontal position it was in at the start of machining, which is located to the right of the right end face of the workpiece 20. Then, based on the remaining machining allowance, the cutting tool 1 is controlled to move radially toward the workpiece 20.

[0073] like Figure 4 As shown in the fourth figure, during the process of the lathe tool 1 translating from left to right, it mechanically scribing a straight microgroove 3 on the outer cylindrical surface of the workpiece 20. Since the relative motion trajectory between the secondary cutting edge of the lathe tool 1 and the workpiece 20 is a spatial spiral, the straight microgroove 3 is similar to the spiral microgroove 32 in the prior art.

[0074] like Figure 5 As shown in the fifth figure, during the second pass of the cutting tool 1 as it moves from right to left, the relative motion trajectory between the cutting tool 1 and the workpiece 20 is the turning trajectory 4.

[0075] The straight-cut microgrooves 3 and the turning trajectory 4 are both located on the outer surface of the workpiece 20, thus they intersect in space. Therefore, during the second machining process, at the intersection point, the originally continuous chips break, ultimately suppressing chip entanglement.

[0076] The cross-section of the directly engraved microgroove 3 is as follows Figure 5 As shown, the optimal choice is to have the machining depth of the directly engraved microgrooves 3 equal to the minimum depth Hmin required to ensure chip breakage. This is most beneficial for turning smoothness, tool life, and surface finish.

[0077] Example 2.

[0078] Example 2 discloses a method for calculating the minimum depth Hmin of a directly etched microgroove 3. Therefore, Example 2 is a supplement to step (b) of Example 1, including method b-1 and method b-2.

[0079] Method b-1 employs finite element simulation.

[0080] First, establish such as Figure 6 The finite element simulation model shown includes features of cutting tool 1 and workpiece 20. The upper surface of the latter has microgrooves. It is assumed that the depth of the microgrooves participating in the finite element simulation calculation for the first time is H1; the value of H1 is equal to the depth of cut.

[0081] Next, define the material properties of the cutting tool 1 and the workpiece 20, set the initial boundary conditions for their motion, force, and temperature fields, and divide the finite element calculation mesh; the initial boundary conditions for the motion, force, and temperature fields are the same as those for actual turning.

[0082] Subsequently, the simulation calculated the entire process of chip separation from the workpiece 20, deformation, and eventual fracture, such as... Figure 7 As shown.

[0083] Repeat the above finite element simulation calculation process. The microgroove depth in the second calculation is H2, the microgroove depth in the third calculation is H3, and so on.

[0084] H1, H2, H3…Hn, Hn+1 form a decreasing sequence. When the (n+1)th finite element simulation calculation shows a microgroove depth of Hn+1, if the microgroove cannot cause chip breakage, it indicates that the microgroove depth of Hn+1 is insufficient to induce chip breakage. Therefore, Hn is the minimum theoretical depth of the microgroove.

[0085] The relationship between the minimum theoretical depth Hn of the microtrench and the minimum depth Hmin1 of the directly etched microtrench 3 is as follows:

[0086] H min1 =C1·C2·Hn

[0087] In the formula, C1 and C2 are amplification factors.

[0088] C1 is the simulation error amplification factor, which is related to the accuracy of the finite element simulation and ranges from 1.0 to 1.2. The higher the accuracy of the finite element simulation, the smaller the C1 value; conversely, the lower the accuracy, the larger the C1 value. The evaluation method for the accuracy of the finite element simulation can be one of the following: cutting force evaluation, chip morphology evaluation, or cutting heat evaluation. For example, if the main cutting force in the finite element simulation is 20N, and the actual measured main cutting force is 23N, then the error of the finite element simulation is (23-20) / 23 = 13%, and the value of C1 is 1 + 0.2 × 13% = 1.03.

[0089] C2 is the tool wear amplification factor, which is linearly related to the degree of tool wear and ranges from 1.00 to 1.10. The more severe the tool wear, the larger the C2 value; conversely, the smaller the C2 value. The evaluation method for the degree of tool wear can be calculated by dividing the number of parts already machined by the expected total number of parts to be machined. For example, if the number of parts already machined by the tool is 500 and the expected total number of parts to be machined is 1000, then the tool wear degree is 0.5, and the corresponding C2 value is 1.05.

[0090] The finite element model calculation results are as follows Figure 7 As shown, this includes the entire process of chips separating from the workpiece 20 body, deforming, and eventually breaking.

[0091] Method b-2 employs fracture mechanics calculations.

[0092] First, establish such as Figure 8 The fracture mechanics calculation and analysis model shown includes local chip features with microgroove structures on its surface. The analysis focuses on the minimum theoretical depth H of the microgrooves that can induce chip fracture under torque M. n In the diagram, the strain of the material on the neutral layer mn is zero, meaning it is neither stretched nor compressed. The location at the bottom of the microgroove is called the fracture layer ef.

[0093] Assuming the chip deforms under bending moment M, the stress on the fracture layer has the following relationship:

[0094]

[0095] In the formula, R1 is the radius of the chip before bending moment, and R2 is the radius of the chip after bending moment.

[0096] On the neutral layer, the strain before and after applying the bending moment M is zero, and we have:

[0097] (R1+i·Hc)dθ1=(R2+i·Hc)dθ2 2)

[0098] In the formula, H C Let be the chip thickness, and i be the neutral layer coefficient, with a value between 0 and 1. i·HC This represents the average distance from the neutral layer to the bottom of the chip.

[0099] Combining the two formulas above, we have:

[0100]

[0101] According to the stress intensity factor K Ⅰ and fracture toughness K ⅠC The relative magnitudes of the cracks are used to establish a criterion for crack instability propagation and brittle fracture, namely:

[0102] K Ⅰ >K ⅠC 4)

[0103] In the formula, K Ⅰ K is the stress intensity factor, a mechanical parameter that represents the magnitude of the stress field intensity at the crack tip in a cracked body. It is determined by the applied stress, the specimen size, and the crack type. ⅠC Fracture toughness is a mechanical property index of a material. It depends on intrinsic factors such as the material's composition and microstructure, but is unrelated to extrinsic factors such as applied stress and sample size. When a cracked body is subjected to stress, brittle fracture will occur if the above conditions are met; conversely, even if a crack exists, fracture will not occur.

[0104] Stress intensity factor K Ⅰ , represented as:

[0105]

[0106] In the formula, σ is the characteristic stress, a is the crack length, and Y is a dimensionless constant related to the crack geometry. For the parabolic crack shape of this invention, Y can be calculated by the following formula: Y = 1.12 × π 0.5 =1.98.

[0107] Further consideration of the correction of the crack plastic zone

[0108]

[0109] In the formula, r p It is the radius of the crack plastic deformation zone, calculated by the following formula:

[0110]

[0111] In the formula, σ ys It is the chip yield stress.

[0112] Substituting equation 7) into equation 6) yields:

[0113]

[0114] The above equation can be simplified to obtain

[0115]

[0116] Incorporate the condition K for crack propagation Ⅰ =K ⅠC 9), Equation 8) becomes

[0117]

[0118] To satisfy the crack propagation conditions on the fracture layer, σ b Both equation 3) and equation 10) must be satisfied simultaneously. Combining equations 3) and 10), we get:

[0119]

[0120] For a specific turning embodiment, the stress intensity factor K of the workpiece material Ⅰ The value is a constant, and the chip thickness H c As can be measured in practice, the value of i can be set manually. Therefore, by solving equation 11), the minimum theoretical depth H of a series of microgrooves can be obtained. n The distribution of values. The minimum theoretical depth H of the microgroove. n The numerical value is affected by the value of variable i, but variable i has little influence on H. n The effect is non-linear, exhibiting localized density characteristics in numerical terms. Therefore, we select densely occurring H... n The value is used as the minimum theoretical depth H of the microgroove. n The final solution result.

[0121] In method b-2, the minimum theoretical depth H of the microgroove is... n2 Minimum depth H of the directly engraved micro-groove 3 min2 The relationship between them is as follows:

[0122] H min2 =C3·H n2

[0123] In the formula, C3 is the theoretical calculation error amplification factor, which is related to the plasticity of the workpiece material and ranges from 1.5 to 2. The better the plasticity of the workpiece material, the higher the value of C3. For example, stainless steel has a value of 1.3, and aluminum alloy has a value of 1.6.

[0124] Example 3.

[0125] Example 3 discloses how to accurately machine a straight-lined microgroove 3 with a minimum depth Hmin on a workpiece 20 by mechanical scribing. Therefore, Example 3 is a supplement to Examples 1 and 2.

[0126] In step (d) of Embodiment 1, it is described that "the cutting tool 1 is inserted into the workpiece 20 radially, and the moving distance of the cutting tool 1 relative to the workpiece 20 is St". The method for calculating the relative moving distance St between the cutting tool and the workpiece radially is as follows:

[0127] St=C6·H min +C4+C5

[0128] In the above formula, H min The minimum depth of the straight-cut microgroove 3 is calculated and amplified using finite element simulation or fracture mechanics calculation methods.

[0129] In the above formula, C4 is the workpiece deformation amplification factor, used to offset the effect of the workpiece's flexural deformation caused by the cutting tool's pressure on the mechanical scribing depth. C4 is equal to the radial offset distance of the workpiece in the mechanical scribing area due to flexural deformation, and its value is equal to the deflection of the workpiece at the machining position;

[0130] In the above formula, C5 is the workpiece size deviation magnification factor, which is equal to the absolute value of the size tolerance of the workpiece in the mechanical scribing area.

[0131] In the above formula, C6 is the workpiece springback error amplification factor, used to compensate for mechanical scratching errors caused by elastic deformation of the workpiece material. C6 is equal to the ratio of the elastic modulus of the workpiece material to the elastic modulus of ductile iron, that is, the degree of springback of the workpiece material is estimated based on ductile iron.

[0132] Example 4.

[0133] In the specific implementation of Example 1, it is described that: the cutting tool 1 is controlled to translate to the right, the direction of movement is the same as the axis of the workpiece 20, and the speed is V. b This embodiment illustrates how to set an appropriate V b This is used to control the frequency of chip breaking. Therefore, Example 4 is a supplement to Example 1.

[0134] The ultimate goal of controlling the chip breaking frequency is to produce single-segment chips with the expected length and quality.

[0135] Assuming that during the translational movement of cutting tool 1 to the right, the machine tool spindle speed is N. A The speed at which the cutting tool 1 moves to the right at a speed of V revolutions per minute is 100 revolutions per minute. b During the second pass of the lathe tool 1, which moves from right to left, the machine tool spindle speed is N. B The expected chip breaking frequency is f (revolutions per minute). A Then the above variables have the following relationship:

[0136]

[0137] In the formula, L is the length of the spiral line produced by the mechanical scribing of the lathe tool 1 within 1 second. Where R is the radius of the workpiece at the mechanical marking position; f B The rotational frequency f of the machine tool spindle during the second pass machining process. B =60 / N B .

[0138] By rearranging equation 12), we can obtain

[0139]

[0140] Solving equation 13) yields V. b If the machine tool spindle speed is 0 during the translational movement of tool 1 to the right, then the type of microgroove is linear.

Claims

1. A method for precisely controlling the location and frequency of metal chip fracture, characterized in that... Includes the following steps: Step A: Monitor the cutting process of the workpiece (20). Based on the monitoring results of the previous cutting process of the workpiece (20), determine the location area on the surface of the workpiece (20) where continuous metal chips are generated. Step B: Determine the minimum microgroove depth that can ensure smooth chip breakage under the current cutting conditions through theoretical calculations or knowledge base methods. The microgrooves are pre-set on the surface of the workpiece (20) in a specific manner before the turning process begins; Step C: Before the next turning operation, machine microgrooves in the area determined in step A, wherein the final depth of the microgrooves is equal to the minimum microgroove depth determined in step B. Step D: When the cutting tool (1) cuts to the microgroove on the surface of the workpiece (20), a portion of the microgroove is transferred to the free surface of the chip, inducing the chip to break at the microgroove. The method for determining the location area where continuous metal chips are generated on the surface of the workpiece (20) in step A is manual identification or sensor identification; if it is sensor identification, the sensor is at least one of optical sensor, mechanical sensor, and acoustic sensor. In step B, the theoretical calculation method is either the finite element simulation method or the fracture mechanics solution method. The knowledge base method combines finite element simulation, fracture mechanics solution and experimental data to form a data body, which contains the minimum microgroove depth information under multiple turning parameter combinations. The finite element simulation method first establishes a finite element simulation model, including the features of the cutting tool (1) and the workpiece (20). The surface of the workpiece has microgrooves. The depth of the microgrooves H1 in the first finite element simulation calculation is equal to the depth of cut in the turning process. Second, the material properties of the cutting tool (1) and the workpiece (20) are defined, and the initial boundary conditions of their motion, force, and temperature fields are set. The finite element calculation mesh is divided. The initial boundary conditions of the motion, force, and temperature fields are the same as those in the actual turning process. Third, the entire process of chip separation, deformation, and fracture from the workpiece (20) body is simulated and calculated. The above finite element simulation calculation process is repeated. The depth of the microgrooves in the second calculation process is H2, the depth of the microgrooves in the third calculation process is H3, and so on. H1, H2, H3...Hn, Hn+1 are a decreasing sequence. When the depth of the microgrooves is Hn+1 in the (n+1)th finite element simulation calculation, if the microgrooves cannot cause chip fracture at this time, then Hn is the minimum theoretical depth of the microgrooves. In the finite element simulation method, the relationship between the minimum theoretical depth Hn of the microgroove and the minimum depth Hmin of the microgroove is as follows: H min = C1∙C2∙Hn; In the formula, C1 and C2 are amplification factors; C1 is the simulation error amplification factor, which is related to the accuracy of the finite element simulation and has a value between 1.0 and 1.2; C2 is the tool wear amplification factor, which is linearly related to the degree of tool wear and has a value between 1.00 and 1.

10. The fracture mechanics solution method first establishes a fracture mechanics calculation and analysis model, including local chip characteristics, whose surface has a microgroove structure. Then, it analyzes the minimum theoretical depth H of the microgrooves that can induce chip fracture under torque M. n Solving the following equation yields the minimum theoretical depth H of a series of microgrooves. n Distribution of values: ； In the formula, R1 is the radius of the chip before bending moment, and R2 is the radius of the chip after bending moment. H C For chip thickness, i Neutral layer coefficient, i The value ranges from 0 to 1. i∙H C σ represents the average distance from the neutral layer to the bottom of the chip; ys It is the chip yield stress; Y K is a dimensionless constant related to the crack geometry. ⅠC It refers to the fracture toughness of the workpiece material; Selecting densely occurring H n The value is used as the minimum theoretical depth H of the microgroove. n The final solution result; In the fracture mechanics solution method, the minimum theoretical depth H of the microgroove is... n Minimum depth H of the microgroove min The relationship between them: H min = C3∙H n ; In the formula, C3 is the theoretical calculation error amplification factor, which is related to the workpiece material and takes a value between 1.5 and 2.

2. The method according to claim 1, characterized in that: The microgrooves in step C are machined on the outer circle or inner hole surface of the workpiece (20) by mechanical scribing. The direction of the microgrooves is parallel to the axis of the shaft part or symmetrically distributed with respect to the central axis of the shaft part. The cross-sectional shape of the microgroove is one of the following: circular arc, parabola, or broken line; the distribution of the microgroove on the workpiece surface is controlled by controlling the position of the mechanical scribing, and the groove shape of the microgroove is either a straight line or a spiral line depending on the mechanical scribing method. If the microgroove is a spiral, the pitch of the spiral can be controlled artificially, and thus the frequency of chip breakage can also be controlled artificially. The mechanical scribing process in step C is carried out by the secondary cutting edge of the cutting tool (1) or by another cutting tool; the other cutting tool is also mounted on the tool holder (2) or tool head of the machine tool. The microgrooves in step C are formed by mechanically scribing the surface of the workpiece (20) during the return stroke of the cutting tool as it returns to the initial machining position.

3. The method according to claim 1, characterized in that: The chips that break in step D are subjected to gravity and external force applied by the user, and fall into the chip collection device along a specific trajectory. The specific trajectory avoids the processing area; The source of the artificially applied external force is the driving force of gas or liquid.

4. The method according to claim 1, characterized in that: Microgroove machining is achieved through the relative motion between the cutting tool (1), the workpiece (20), and the machine tool spindle (12); The cutting tool (1) is mounted on the tool holder (2); driven by the tool holder (2), the cutting tool (1) starts from the initial machining position and feeds along the axial direction of the workpiece (20); After the cutting tool (1) completes its first pass, it cuts into the workpiece (20) radially. The distance the cutting tool (1) moves is St. Then, the cutting tool (1) is controlled to translate in the opposite direction of the first pass, with the direction of movement parallel to the axis of the workpiece (20) and the speed is... V b Until the cutting tool (1) returns to the initial machining position, the cutting tool (1) is in the horizontal position; then, according to the remaining machining allowance, the cutting tool (1) is controlled to move radially toward the workpiece (20); The cutting tool (1) is at a speed V b During the translational motion, microgrooves are mechanically etched on the outer cylindrical surface of the workpiece (20); The machining depth of the microgroove is equal to the minimum microgroove depth Hmin that can ensure chip breakage.

5. The method according to claim 4, characterized in that: The method for calculating the radial movement distance St of the cutting tool (1) along the workpiece (20) is as follows: St = H min + C4 + C5; The H min The minimum depth of the microgroove is calculated theoretically and scaled up after correction using finite element simulation or fracture mechanics calculation methods. C4 is the workpiece deformation amplification factor, used to offset the influence of the workpiece's flexural deformation caused by the extrusion force of the cutting tool on the mechanical scribing depth; the value of C4 is equal to the deflection of the workpiece at the machining position. C5 is the workpiece size deviation amplification factor, which is equal to the absolute value of the workpiece size tolerance in the mechanically scribing area.

6. The method according to claim 4, characterized in that: The control tool (1) moves to the right in the same direction as the workpiece (20) along its axis, at a speed of... V b The calculation method is as follows: ； In the formula, N A The spindle speed of the machine tool during the translational movement of the cutting tool (1) to the right. N B The spindle speed of the lathe tool (1) during the second pass is... f A The expected chip breaking frequency, R It is the radius of the workpiece at the mechanically marked position.

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