Drill bit life prolonging method based on instantaneous drilling force model

Abstract

The invention relates to a drill bit service life prolonging method based on an instantaneous drilling force model, belongs to the technical field of drilling parameter design, solves the technical problem of short service life of a machining drill bit, and comprises the steps of analyzing a drill bit failure reason and determining a main drill bit failure part; dividing the drilling process into a plurality of layers from the surface of the workpiece along the depth direction according to the hardness change of the workpiece; according to drill bit structure parameters and physical characteristics of a workpiece, the axial cutting force of a drill bit cutting edge is solved according to the infinitesimal axial acting force on the drill bit main cutting edge; drilling process stages are divided according to the drill bit from workpiece contact to the heat treatment layer and from the heat treatment layer to the normal cutting layer; and a drill bit instantaneous drilling force model is established, and drilling machining parameters of all stages in the drilling process are calculated. The drill bit service life prolonging method is used for drilling machining process parameter design.

Description

Technical Field

[0001] The invention belongs to the technical field of drilling processing parameter design, and in particular relates to a method for improving the life of a drill bit based on an instantaneous drilling force model. Background Art

[0002] With the continuous development of the automobile manufacturing industry, the performance of automobile parts has been greatly improved, which has put higher and higher requirements on the performance and processing quality of key parts. The research and development of new materials for key parts and the change of heat treatment methods meet the high performance requirements of automobile parts, but increase the difficulty of parts processing.

[0003] Take the hole processing of gearbox gear parts as an example. Figure 1 As shown in the figure, the part is made of gear 1 and shaft 2 after heat treatment and interference fit, and then hole 3 is processed. Due to the different heat treatment processes of gear 1 and shaft 2, the heat treatment layer depth and hardness of gear 1 and shaft 2 are different, such as Figure 2 As shown, it can be seen that the hardness of the parts experienced by the drill bit from contacting the workpiece to the specified position is different. At present, the selection of processing parameters is completed by combining manual experience with experimental methods, and the problem of different hardness of parts at different layer depths is not considered. Although this method can complete the processing of holes, the parameter selection cycle is long and the test cost is high. In addition, once the processing parameters are conservatively selected, the processing efficiency will be affected; and if the processing parameters are given too quickly, the tool is easy to wear, affecting the processing quality and seriously damaging the machine tool. Therefore, considering the different hardness of parts, different drilling parameters are used at different layer depths to reduce the impact of drilling force changes on the drill bit and achieve the purpose of extending the tool life. This is very important for ensuring part quality, reducing production costs and production line production efficiency.

[0004] In summary, there is no professional and systematic process method for hole processing of hot-dry parts. The selection of process parameters is subjective, and the characteristics of part materials and structures are not considered. There is a lack of necessary theoretical basis, the drill life is low, and the hole processing cost is high. Summary of the invention

[0005] In order to overcome the shortcomings of low life and high cost of machined drill bits, the present invention proposes a method for improving the life of a drill bit based on an instantaneous drilling force model.

[0006] The technical solution adopted by the present invention to solve the technical problem is:

[0007] A method for improving drill bit life based on an instantaneous drilling force model comprises the following steps:

[0008] Step 1: Drill failure cause analysis

[0009] Compare the new drill bit with the failed drill bit, analyze the cause of drill bit failure, and determine the main location of drill bit failure.

[0010] Step 2: Division of the drilling process

[0011] The drilling process is divided into several layers along the depth direction from the workpiece surface according to the change in hardness.

[0012] Step 3, Calculation of drilling force

[0013] The axial cutting force of different hardness layers is different. According to the structural parameters of the drill bit and the physical properties of the workpiece, the axial cutting force of the drill bit cutting edge is calculated according to the micro-axial force on the main cutting edge of the drill bit.

[0014] Step 4: Drilling process stages

[0015] The drilling process stages are divided according to the process from the drill bit contacting the workpiece to the heat treatment layer, and from the heat treatment layer cutting out to the normal cutting layer.

[0016] Step 5: Calculation of drilling parameters

[0017] According to the drill bit geometric dimensions, drilling processing parameters and physical properties of the workpiece, the drill bit instantaneous drilling force model is established, and the drilling processing parameters at each stage of the drilling process are calculated.

[0018] The above-mentioned drill bit life extension method further includes step 6, drilling processing. According to the drilling processing parameters of each stage of the drilling process obtained in step 5, the workpiece is subjected to drilling processing.

[0019] The above-mentioned drill bit life improvement method also includes step 7, judging whether the drilling parameter selection is reasonable by the fluctuation of the feed shaft load. If the parameter selection is unreasonable, return to step 1; if the parameter selection is reasonable, calculate whether the drill bit life improvement is obvious; if the drill bit life improvement is not obvious, return to step 1.

[0020] The above-mentioned drill bit life-extending method uses a gear with a shaft as a workpiece to be processed, and uses a drill bit to drill a hole, wherein the hole passes through the gear and the shaft.

[0021] Analyze the reasons for drill failure. Gears are heat-treated parts with high surface hardness. When the drill comes into contact with the workpiece, the cutting force and cutting heat generated are concentrated on the tip of the drill, causing the tip to wear and delaminate, leading to drill failure.

[0022] The above-mentioned drill bit life improvement method divides the workpiece surface into 4 layers along the depth direction according to its hardness, wherein the first layer is a heat treatment layer, the second layer is a normal cutting layer, the third layer is a heat treatment layer, and the fourth layer is a normal cutting layer.

[0023] The above-mentioned drill bit life extension method is divided into four layers according to the hardness from the surface of the workpiece along the depth direction, which are:

[0024] The first layer has a hardness of 62HRC, the second layer has a hardness of 58HRC, the third layer has a hardness of 65HRC, and the fourth layer has a hardness of 60HRC.

[0025] The above-mentioned method for improving the life of the drill bit, said step 3, further comprises:

[0026] Axial cutting force F of drill cutting edge f , which is calculated as follows:

[0027]

[0028] In formula (5), lu is the upper limit of the cutting layer, ld is the lower limit of the cutting layer, dF f is the axial cutting force of the cutting edge microelement.

[0029] The above-mentioned method for improving the life of the drill bit, said step 4, further comprises:

[0030] The drilling process is divided into 4 stages, which are:

[0031] Stage 1 (t0-t1): from the moment the drill contacts the gear until the main cutting edge completely enters the heat-treated layer;

[0032] Stage 2 (t1-t2): The drill cuts out from the heat-treated layer of the gear until the main cutting edge completely enters the normal cutting layer;

[0033] Stage 3 (t2-t3): The drill cuts out from the normal cutting layer of the gear until the main cutting edge enters the heat-treated layer of the shaft;

[0034] Stage 4 (t3-t4): The drill cuts out from the heat-treated layer of the shaft until the main cutting edge completely enters the normal cutting layer of the shaft.

[0035] In the above-mentioned drill bit life extension method, the drill bit axial cutting force in the four stages of the drilling process is calculated as follows:

[0036]

[0037] In formula (10), f is the feed speed, is the cutting edge bevel angle, ω is the cutting edge width, κ t is the drill bit angle, and R is the drill bit diameter.

[0038] In the above-mentioned method for improving the life of a drill bit, the step 5 further comprises:

[0039] The specific drilling parameters are as follows: the drill speed at different depths during the drilling process is {n i}(i∈[1,4]), its feed rate is {f i}(i∈[1,4]).

[0040] The step 6 further comprises:

[0041] Enter the drill speed and feed rate into the code of the processing equipment respectively.

[0042] The beneficial effects of the present invention are:

[0043] A drill life improvement method based on the instantaneous drilling force model takes into account the characteristics of heat-assembled parts. It can control the sudden change of drilling force at different depths by adjusting process parameters according to the different physical properties of part materials, reduce the risk of tool failure, ensure the production rhythm and part quality of the production line, and reduce production costs.

[0044] A drill life extension method based on the instantaneous drilling force model takes into account the characteristics of the heated parts and selects different processing parameters according to the difference in hardness of different layer depths to ensure load balance and reduce the impact of the tool tip edge, thereby extending the tool life.

[0045] A drill life improvement method based on the instantaneous drilling force model establishes the relationship between machining parameters and drilling force, and takes into account the physical properties of parts. With drilling force as a constraint, different spindle speeds and feed rates are matched according to the different physical properties of parts. The results obtained can well guide the selection of machining parameters and improve the life of the tool, and have good engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a schematic diagram of the gear structure to be processed;

[0047] Figure 2 1 is a schematic diagram comparing a new drill bit and a failed drill bit according to the first embodiment of the present invention. The left figure is a new drill bit, and the right figure is a failed drill bit;

[0048] Figure 3 This is a schematic diagram of the layer depth and hardness of a part in the first embodiment of the present invention. The first layer 7, the second layer 8, the third layer 9, and the fourth layer 10 are recorded in sequence along the depth direction, and their hardness and thickness are: 62HRC, 2.1mm; 58HRC, 12mm; 65HRC, 1.2mm; 60HRC, 18mm;

[0049] Figure 4 It is a schematic diagram of the division of drilling stages in the first embodiment of the present invention.

[0050] Figure numerals: 1. gear, 2. shaft, 3. hole, 4. cutting edge, 5. cutting tip, 6. drill failure mode, 7. first layer, 8. second layer, 9. third layer, 10. fourth layer, 11 drill bit. DETAILED DESCRIPTION

[0051] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] Embodiment 1

[0053] A drill life extension method based on an instantaneous drilling force model analyzes the reasons why the drill fails before reaching its rated life through the post-heating part hole processing process, and proposes a solution for selecting processing parameters according to the part hardness. Then, through the instantaneous drilling force model, the influence of processing parameters and part physical properties on drilling force is obtained, providing a basis for the selection of drilling parameters. Finally, according to the part hardness, the fluctuation range of the part's physical properties and drilling force is determined, and appropriate processing parameters are selected at different layer depths to achieve the purpose of extending the drill life and production line processing efficiency. The specific steps include the following:

[0054] Step 1: Drill failure cause analysis

[0055] like Figure 2 As shown in the figure, by comparing the new drill bit and the failed drill bit, it can be seen that the failure mode of the drill bit is mainly caused by delamination at the cutting edge. This is because the workpiece material is a part with a high surface hardness after heat treatment. The cutting force and cutting heat generated when the tool and the workpiece contact each other will be concentrated on the cutting edge. Once the spindle speed is too high, the cutting edge will heat up rapidly. In addition, the cutting edge of the drill bit is easily worn under the action of thermal-mechanical coupling, which repeatedly leads to delamination at the cutting edge. After delamination, the drill bit cannot be centered, and thus the position and size of the hole cannot be guaranteed, resulting in the scrapping of the part. In severe cases, the drill bit will break.

[0056] Step 2: Division of the drilling process

[0057] Processed parts such as Figure 1 As shown in the figure, it is the result of the assembly of the parts after heating. Considering that the parts after heating have high surface hardness and soft core, if the drilling parameters are selected according to the part with the highest hardness, the processing efficiency will be affected; if the drilling parameters are selected according to the average hardness, the force at the tip of the drill bit will vary greatly, the tip of the drill bit will be easily worn, the tool life will be short, and the processing efficiency will not be significantly improved.

[0058] Considering that the hole size and the depth of the heat treatment layer are fixed, in order to reduce the force variation of the drill tip within a certain range, the assembly parts are layered according to hardness, and are divided into 4 layers, namely the first layer 7, the second layer 8, the third layer 9, and the fourth layer 10. Figure 3 Therefore, the holes to be processed are drilled in 4 steps.

[0059] Step 3, Calculation of drilling force

[0060] According to the analysis in step 1), the life of the drill bit is closely related to the drilling parameters and the physical properties of the parts. The physical properties of the processed parts change with the layer depth, which has a great impact on the life of the drill bit. Therefore, it is necessary to use the drilling force as a constraint condition and change the drilling parameters according to the changes in the physical properties of the parts to reduce the impact of the changes in the drilling force on the drill bit tip and achieve the purpose of extending the tool life.

[0061] According to the principle of motion synthesis, the cutting forces Fx, Fy, and Fz generated in oblique cutting can be expressed by formula (1):

[0062]

[0063] Among them: F f is the feed force; F n is the radial force; α is the drill head rake angle; β is the drill bit back angle; s is the blade inclination angle; b is the cutting width; a c is the cutting thickness; n is the spindle speed; f is the feed speed; τ s is the shear stress; φ is the shear angle.

[0064] Considering the serious wear of the drill bit tip, Figure 3 As shown, this is because this area is mainly extruded, distributing the material to the side and then removing it through the cutting edge. For the convenience of calculation, the cutting tip and cutting edge are simplified into straight lines along the cutting width direction and divided into multiple micro-elements db. The micro-element db can be expressed by formula (2):

[0065] db=dxsinκ t (2)

[0066] Where: t The drill bit angle.

[0067] Combined with formula (1), the cutting force generated in oblique cutting can be expressed by formula (3):

[0068]

[0069] Considering that the failure of the drill bit has a great impact on its axial force, the axial force F of the drill bit on a specific microelement is f It can be expressed as formula (4).

[0070] dF f =dF z cosγ d sinκ t -dF y sinγ d cosκ t (4)

[0071] Where: γ d is the cutting angle.

[0072] In order to extend the tool life, different drilling parameters are used for different hardness layers, and then the layer depth is divided. Therefore, by integrating the micro-element axial force on a specific section of the main cutting edge, the axial cutting force of the cutting edge can be obtained, which can be expressed by formula (5).

[0073]

[0074] Among them: lu is the upper limit of the cutting layer, ld is the lower limit of the cutting layer.

[0075] Step 4: Drilling process stages

[0076] According to the processing characteristics of the parts, the relative state of the cutting edge and the workpiece material at each moment in the drilling process is determined. Figure 3 It can be seen that the hole is drilled in four processes, and the drilling process is divided into four stages, such as Figure 4 Therefore, it is necessary to describe the status and characteristics of each stage in detail and then model them separately.

[0077] Stage 1 (t0-t1): This stage starts from the moment the drill contacts the gear part until the main cutting edge completely enters the heat-treated layer. At any time t in this stage, the feed depth of the drill can be expressed by formula (6).

[0078] z(t)=f·t (6)

[0079] Where: f is the feed speed.

[0080] When t=t1, it means that the drill has completely entered the interior of the part, and the upper limit of the integral reaches the maximum value (the diameter R of the drill).

[0081] Therefore, the upper and lower limits of the integral in stage 1 can be expressed by formula (7).

[0082]

[0083] in: is the cutting edge bevel angle; ω is the cutting edge width.

[0084] Stage 2 (t1-t2): In this stage, the drill cuts out from the heat-treated layer of the gear part until the main cutting edge completely enters the normal cutting layer. There is a transition between the heat-treated layer and the normal cutting layer in the middle. To simplify the calculation difficulty, the cutting process of the heat-treated layer is not considered. The upper and lower limits of the integral of stage 2 can be expressed by formula (8).

[0085]

[0086] Stage 3 (t2-t3): In this stage, the drill cuts out from the normal cutting layer of the gear part until the main cutting edge enters the heat treatment layer of the part shaft. Considering that the heat treatment layer of the part shaft is shallow, the drill tip is not completely cut. Therefore, the same as stage 2, simplifying the drilling process, the upper and lower limits of the integral of stage 3 can be expressed by formula (9).

[0087]

[0088] Stage 4 (t3-t4): In this stage, the drill cuts out from the heat-treated layer of the part shaft until the main cutting edge completely enters the normal cutting layer of the part shaft. Therefore, the upper and lower limits of the integral of stage 4 are the same as those of stage 1 and can be expressed by formula (7).

[0089] According to the above analysis, the axial forces in the four stages can be expressed by formula (10).

[0090]

[0091] Step 5: Calculation of drilling parameters

[0092] From formula (1), it can be seen that the drilling force model is a function related to the tool geometry, drilling parameters and part physical properties. The tool geometry changes with tool wear, and its change law is complex. For the convenience of calculation, its influence on the drilling force is ignored. Therefore, by studying the relationship between drilling parameters, part physical properties and drilling force, the drilling parameters are changed to make the drilling force fluctuate within a certain range, avoiding the impact of the drilling force on the drill tip, and indirectly improving the drill life.

[0093] Depend on Figure 3 It can be seen that the hardness of the parts is different at different layer depths, which can be expressed as {H i}(i∈[1,4]). The shear stress of the part is related to the hardness, and the shear stress of different layer depths can be expressed by formula (11).

[0094]

[0095] Therefore, when the axial drilling force and shear stress are fixed, the drill speed {n i}(i∈[1,4]) and feed rate {f i}(i∈[1,4]).

[0096] The calculated drill speed and feed speed are added to the positions specified by the G code respectively. The rationality of the drilling parameter selection is judged by the fluctuation of the feed axis load. At the same time, the drill life is significantly improved.

[0097] A method for improving drill bit life based on an instantaneous drilling force model first analyzes the influence of drilling process parameters and physical properties of part materials on drill bit life in the drilling process of parts combined with drill wear. Secondly, according to the different hardness characteristics of different part layer depths, the layer depth is divided by part hardness. Finally, an instantaneous drilling force prediction model is established to obtain the influence of process parameters and physical properties of part materials on drilling force, solving the problem of relying entirely on experience in drilling parameter selection. Furthermore, under the condition that the physical properties of part materials remain unchanged, a method for selecting drilling process parameters at different layer depths is proposed to reduce the sudden change of drilling force at different layer depths, thereby achieving the purpose of improving drill bit life and indirectly improving the processing efficiency of the production line.

Claims

1. A method for improving drill bit life based on an instantaneous drilling force model, characterized in that: The following steps are involved: Step 1, drill failure cause analysis: Comparing the new drill bit with the failed drill bit, analyzing the failure cause of the drill bit (11), and determining the main failure location of the drill bit (11); Step 2, division of drilling process: The drilling process is divided into several layers along the depth direction from the workpiece surface according to the change of hardness; Step 3, calculation of drilling force: The axial cutting forces of different hardness layers are different. According to the structural parameters of the drill bit (11) and the physical properties of the workpiece, the axial cutting force of the drill bit cutting edge (4) is calculated according to the micro-element axial force on the main cutting edge of the drill bit. Step 4, drilling process stage division: The drilling process is divided into stages according to the drill bit (11) from contacting the workpiece to the heat treatment layer, and from cutting out the heat treatment layer to the normal cutting layer; Step 5, calculation of drilling parameters: According to the geometric dimensions of the drill bit (11), drilling processing parameters and physical properties of the workpiece, an instantaneous drilling force model of the drill bit (11) is established to calculate the drilling processing parameters at each stage of the drilling process.

2. The drill bit life extension method according to claim 1, characterized in that: The process also includes step 6, drilling: drilling the workpiece according to the drilling parameters of each stage of the drilling process obtained in step 5.

3. The drill bit life extension method according to claim 2, characterized in that: The method also includes step 7, judging whether the drilling parameter selection is reasonable by the fluctuation of the feed shaft load. If the parameter selection is unreasonable, returning to step 1; if the parameter selection is reasonable, counting whether the drill life is significantly improved; if the drill life is not significantly improved, returning to step 1.

4. The method for increasing the life of a drill bit according to claim 1, 2 or 3, characterized in that: A gear with a shaft is used as a workpiece to be processed, and a drill bit (11) is used to drill a hole (3), wherein the hole (3) passes through the gear (1) and the shaft (2); The cause of the failure of the drill bit (11) is analyzed; the gear (1) is a heat-treated part with a high surface hardness. When the drill bit (11) contacts the workpiece, the cutting force and cutting heat generated are concentrated on the drill bit tip (5), causing the tip (5) to wear and delaminate, resulting in the failure of the drill bit (11).

5. The method for increasing the life of a drill bit according to claim 4, characterized in that: From the workpiece surface along the depth direction, it is divided into 4 layers according to its hardness, among which the first layer (7) is the heat treatment layer, the second layer (8) is the normal cutting layer, The third layer (9) is a heat treatment layer, and the fourth layer (10) is a normal cutting layer.

6. The method for increasing the life of a drill bit according to claim 5, characterized in that: From the surface of the workpiece along the depth direction, it is divided into 4 layers according to its hardness, which are: The first layer (7) has a hardness of 62 HRC, the second layer (8) has a hardness of 58 HRC, the third layer (9) has a hardness of 65 HRC, and the fourth layer (10) has a hardness of 60 HRC.

7. The method for increasing the life of a drill bit according to claim 4, characterized in that: The step 3 further comprises: Axial cutting force F of the drill bit (11) cutting edge (4) f , which is calculated as follows: In formula (5), lu is the upper limit of the cutting layer, ld is the lower limit of the cutting layer, dF f is the micro-element axial cutting force of the cutting edge (4).

8. The method for increasing the life of a drill bit according to claim 4, characterized in that: The step 4 further comprises: The drilling process is divided into 4 stages, which are: Stage 1 (t0-t1): from the moment the drill bit (11) contacts the gear (1) until the main cutting edge completely enters the heat-treated layer; Stage 2 (t1-t2): the drill bit (11) cuts out from the heat-treated layer of the gear (1) until the main cutting edge completely enters the normal cutting layer; Stage 3 (t2-t3): the drill bit (11) cuts out from the normal cutting layer of the gear (1) until the main cutting edge enters the heat-treated layer of the shaft; Stage 4 (t3-t4): The drill bit (11) cuts out from the heat-treated layer of the shaft (2) until the main cutting edge completely enters the normal cutting layer of the shaft.

9. The drill bit life extension method according to claim 8, characterized in that: In the four stages of the drilling process, the axial cutting force of the drill bit (11) is calculated as follows: In formula (10), f is the feed speed, is the cutting edge bevel angle, ω is the cutting edge width, κ t is the drill bit angle, and R is the drill bit diameter.

10. The drill bit life extension method according to claim 4, characterized in that: The step 5 further comprises: The specific drilling parameters are as follows: the drill speed at different depths during the drilling process is {n i }(i∈[1,4]), its feed rate is {f i }(i∈[1,4]); The step 6 further comprises: inputting the rotation speed and feed speed of the drill bit (11) into the code of the processing equipment respectively.

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