CN111859753A - Method and system for predicting distribution of cutting force and temperature field with negative rake angle - Google Patents
Method and system for predicting distribution of cutting force and temperature field with negative rake angle Download PDFInfo
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Abstract
The invention discloses a method and a system for predicting distribution of a cutting force and a temperature field with a negative rake angle. Based on the plastic slip characteristics of the material, the invention constructs a corrected slip line field model considering the dead zone form, the thickness of the pre-shearing zone and the main deformation zone, introduces a dimensionless cutting force ratio and a chip thickness ratio, and establishes a slip line field geometric iteration solving method, thereby obtaining a cutting geometry which is more accurate and reliable. The method solves the intensities of the heat source of the main deformation area, the heat source of the second deformation area and the heat source of the dead area respectively, and then substitutes the intensities into the established mirror image heat source model to realize the prediction of the temperature field of the cutter, the workpiece and the cutting chips.
Description
Technical Field
The invention relates to the field of efficient and high-precision metal cutting machining, in particular to a method and a system for predicting distribution of a cutting force and a temperature field with a negative rake angle.
Background
Numerous cutting processes show that compared with positive rake cutting, the negative rake cutting design can greatly reduce the impact load when the cutter is cut, and can obtain better part surface quality. Through research, the advantages are greatly benefited by the formation of a material stagnation area, namely a dead area, in the negative rake angle cutting process, the tool tip is protected, meanwhile, part of material is extruded into the machined surface of a workpiece, the surface hardness of the part is improved, and the stress distribution condition is improved. However, the focus of the current industry is still the positive rake cutting process, while the research on the negative rake cutting process and its critical material retention phenomenon is very limited, and meanwhile, the prediction of the cutting force and temperature field of the negative rake cutting process is still a difficult point in the art.
Currently, there are researchers who have made relevant studies on the material retention phenomenon before the blade edge by the material slip line method, for example, waldorf d.j. et al ("a slip-line field for using a blunt trailing edge for short temporal cutting, JManuf Sci Eng-Trans ASME,120(1998)693 and 699.) have established a new slip line field model for the plowing effect and shearing effect under the action of the blunt edge of the blade in the grinding process, which reveals the material retention and separation phenomenon at the blunt edge, but is only applicable to the positive rake angle or zero rake angle cutting process. For the negative rake angle cutting process, Fang ("Tool-chip in machining with large negative rake angle Tool, Wear,258(2005)890-897.) provides a slip line field model for dead zone shape prediction, and accordingly provides an iterative solution method for the slip line field geometry, however, in the model, the dead zone bottom edge is simplified to be parallel to the machined surface of the part, the main deformation zone is also replaced by a single plane, and the predicted dead zone geometry in the research is not verified by effective means. Thus, there remains a need for a more comprehensive and reliable model for negative rake cutting mechanisms.
Disclosure of Invention
The invention aims to provide a method and a system for predicting the distribution of a cutting force and a temperature field of a negative rake angle, which are used for efficiently and accurately predicting the cutting force result and the distribution of the temperature field of the negative rake angle.
In order to achieve the purpose, the invention provides the following scheme:
a method of predicting negative rake cutting force and temperature field distribution, comprising:
respectively acquiring an experimental cutting force, an experimental depth resistance, a cutting thickness value, a cutting speed, a cutter thermal conductivity, a workpiece thermal conductivity, a cutter thermal diffusivity and a workpiece thermal diffusivity under two groups of orthogonal experiments with variable cutting thickness and variable rake angles;
determining an experimental cutting force ratio according to the experimental cutting force and the experimental depth resistance;
determining an experimental cutting thickness ratio according to the cutting thickness value;
acquiring an initial dead zone angle, an initial friction factor angle and an initial shearing angle;
correcting a slip line field model based on a rigid-plastic deformation theory;
predicting a chip force ratio and a cut thickness ratio according to the corrected slip line field model based on the initial dead zone angle, the initial friction factor angle and the initial shear angle;
calculating an error value from the predicted chip force ratio, the experimental chip force ratio, the predicted cutting thickness ratio, and the experimental cutting thickness ratio;
obtaining a dead zone angle, a friction factor angle and a shearing angle when the error value is minimum;
calculating a geometric result of a slip line field, a cutting force and a cut-depth resistance according to the dead zone angle, the friction factor angle and the shearing angle;
And calculating a temperature field according to the geometric result of the slip line field, the cutting speed, the thermal conductivity of the cutter, the thermal conductivity of the workpiece, the thermal diffusivity of the cutter and the thermal diffusivity of the workpiece.
Optionally, the predicting a chip force ratio and a cutting thickness ratio according to the corrected slip line field model based on the initial dead zone angle, the initial friction factor angle and the initial shear angle specifically includes:
calculating a bow angle according to the initial dead zone angle and the initial friction factor angle;
calculating a slip line angle according to the bow angle and the initial shearing angle;
calculating an initial slip line field geometric result according to the initial dead zone angle, the initial friction factor angle, the initial shearing angle and the slip line angle;
and calculating the chip force ratio and the cutting thickness ratio according to the initial slip line field geometric result.
Optionally, the calculating a temperature field according to the geometric result of the slip line field, the cutting speed, the thermal conductivity of the tool, the thermal conductivity of the workpiece, the thermal diffusivity of the tool, and the thermal diffusivity of the workpiece specifically includes:
calculating the shear stress according to the geometric result of the slip line field;
Calculating local flow shear stress and material flow velocity of a main shear zone, a knife-chip contact zone, and a dead zone workpiece interface from the shear stress, the cutting speed, the dead zone angle, the friction factor angle, and the shear angle;
calculating the heat source intensity of the main shearing area according to the local flow shearing stress of the main shearing area and the material flow speed of the main shearing area;
calculating the heat source intensity of the cutter-chip contact area according to the local flow shearing stress of the cutter-chip contact area and the material flow speed of the cutter-chip contact area;
calculating the heat source intensity of the dead zone workpiece interface according to the local flow shear stress of the dead zone workpiece interface and the material flow speed of the dead zone workpiece interface;
and calculating a temperature field according to the heat source intensity of the main shearing area, the heat source intensity of the cutter-chip contact area, the heat source intensity of the dead zone workpiece interface, the heat conductivity of the cutter, the heat conductivity of the workpiece, the heat diffusion coefficient of the cutter and the heat diffusion coefficient of the workpiece.
Optionally, the obtaining an initial dead zone angle, an initial friction factor angle, and an initial shear angle specifically includes:
determining an allowable interval through a stress criterion;
An initial dead zone angle, an initial friction factor angle, and an initial shear angle are obtained within the allowed space.
The invention also provides a system for predicting the distribution of the cutting force and the temperature field of the negative rake angle, which comprises the following components:
the experimental data acquisition module is used for respectively acquiring experimental cutting force, experimental depth resistance, a cutting thickness value, cutting speed, cutter thermal conductivity, workpiece thermal conductivity, cutter thermal diffusivity and workpiece thermal diffusivity under two groups of orthogonal experiments with variable cutting thickness and variable rake angles;
an experimental chip force ratio determining module for determining an experimental chip force ratio according to the experimental cutting force and the experimental depth resistance;
the experimental cutting thickness ratio determining module is used for determining an experimental cutting thickness ratio according to the cutting thickness value;
the initial data acquisition module is used for acquiring an initial dead zone angle, an initial friction factor angle and an initial shearing angle;
the correction module is used for correcting the slip line field model based on the rigid-plastic deformation theory;
a prediction module for predicting a chip force ratio and a cut thickness ratio from the corrected slip line field model based on the initial dead zone angle, the initial friction factor angle, and the initial shear angle;
an error value calculation module for calculating an error value based on the predicted chip force ratio, the experimental chip force ratio, the predicted cutting thickness ratio, and the experimental cutting thickness ratio;
The data acquisition module is used for acquiring a dead zone angle, a friction factor angle and a shearing angle when the error value is minimum;
the first calculation module is used for calculating a geometric result of a slip line field, a cutting force and a cut-in resistance according to the dead zone angle, the friction factor angle and the shearing angle;
and the second calculation module is used for calculating a temperature field according to the geometric result of the slip line field, the cutting speed, the thermal conductivity of the cutter, the thermal conductivity of the workpiece, the thermal diffusion coefficient of the cutter and the thermal diffusion coefficient of the workpiece.
Optionally, the prediction module specifically includes:
the ship fore angle calculation unit is used for calculating a ship fore angle according to the initial dead zone angle and the initial friction factor angle;
the slip line angle calculation unit is used for calculating a slip line angle according to the bow angle and the initial shearing angle;
the initial slip line field geometric result calculation unit is used for calculating an initial slip line field geometric result according to the initial dead zone angle, the initial friction factor angle, the initial shearing angle and the slip line angle;
and the chip force ratio and cutting thickness ratio calculating unit is used for calculating the chip force ratio and the cutting thickness ratio according to the initial slip line field geometric result.
Optionally, the second calculating module specifically includes:
the shear stress calculation unit is used for calculating shear stress according to the geometric result of the slip line field;
a first calculation unit for calculating local flow shear stress and material flow velocity of a main shear zone, a blade-chip contact zone, and a dead zone workpiece interface, based on the shear stress, the cutting speed, the dead zone angle, the friction factor angle, and the shear angle;
the heat source intensity calculating unit of the main shearing area is used for calculating the heat source intensity of the main shearing area according to the local flow shearing stress of the main shearing area and the material flow speed of the main shearing area;
a heat source intensity calculating unit of the cutter-chip contact area, which is used for calculating the heat source intensity of the cutter-chip contact area according to the local flow shearing stress of the cutter-chip contact area and the material flow speed of the cutter-chip contact area;
the heat source intensity calculating unit of the dead zone workpiece interface is used for calculating the heat source intensity of the dead zone workpiece interface according to the local flow shear stress of the dead zone workpiece interface and the material flow speed of the dead zone workpiece interface;
and the temperature field calculation unit is used for calculating a temperature field according to the heat source intensity of the main shearing area, the heat source intensity of the cutter-chip contact area, the heat source intensity of the dead zone workpiece interface, the heat conductivity of the cutter, the heat conductivity of the workpiece, the heat diffusion coefficient of the cutter and the heat diffusion coefficient of the workpiece.
Optionally, the initial data obtaining module specifically includes:
the allowable interval determining unit is used for determining an allowable interval through a stress criterion;
an acquisition unit for acquiring an initial dead zone angle, an initial friction factor angle, and an initial shear angle within the allowable space.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects: predicting a chip force ratio and a cutting thickness ratio according to a corrected slip line field model based on the initial dead zone angle, the initial friction factor angle and the initial shear angle; calculating an error value from the predicted chip force ratio, the experimental chip force ratio, the predicted cutting thickness ratio, and the experimental cutting thickness ratio; obtaining a dead zone angle, a friction factor angle and a shearing angle when the error value is minimum; and calculating a geometric result of a slip line field, a cutting force and a cut-depth resistance according to the dead zone angle, the friction factor angle and the shearing angle. Based on the plastic slip characteristics of the material, the invention constructs a corrected slip line field model considering the dead zone form, the thickness of the pre-shearing zone and the main deformation zone, introduces a dimensionless cutting force ratio and a chip thickness ratio, and establishes a slip line field geometric iteration solving method, thereby obtaining a cutting geometry which is more accurate and reliable. The method solves the intensities of the heat source of the main deformation area, the heat source of the second deformation area and the heat source of the dead area respectively, and then substitutes the intensities into the established mirror image heat source model to realize the prediction of the temperature field of the cutter, the workpiece and the cutting chips.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a flow chart of a method for predicting the distribution of negative rake cutting force and temperature field in accordance with an embodiment of the present invention;
FIG. 2 is a schematic diagram of the operation of the method for predicting the distribution of the cutting force and temperature field with negative rake angle according to the embodiment of the present invention;
FIG. 3 is a schematic diagram of a proposed corrected slip line field model;
FIG. 4 is a velocity vector diagram corresponding to a slip line field;
FIG. 5 is a schematic diagram of a four heat source distribution;
FIGS. 6a, 6b and 6c are schematic diagrams of mirror image heat source models of a workpiece, a chip and a tool, respectively
FIG. 7 is a simulated velocity cloud and dead zone feature extraction;
FIG. 8 is a comparison of simulated dead zone configurations at different rake angles;
FIGS. 9a and 9b are the results of shear angle, slip line angle prediction and fitting, respectively, with rake angle;
FIG. 10 shows the fitting results of dead zone right and bottom edge lengths as a function of UCT;
FIG. 11 illustrates predicted material flow shear stress as a function of different UCTs;
FIGS. 12a, 12b are comparison of predicted (left) and simulated (right) results of tool and workpiece-chip temperature fields, respectively;
FIG. 13 is a comparison of tool rake surface temperature distribution prediction and simulation result extraction;
FIG. 14 is a three-dimensional image of the cutting edge of a cemented carbide tool used in a 304 stainless steel orthogonal cutting experiment;
FIG. 15 is a comparison of predicted and measured cutting force results under varying UCT conditions;
FIG. 16 is a block diagram of a system for predicting the distribution of negative rake cutting force and temperature field in accordance with an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a method and a system for predicting the distribution of a cutting force and a temperature field of a negative rake angle, which are used for efficiently and accurately predicting the cutting force result and the distribution of the temperature field of the negative rake angle.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
As shown in fig. 1, a method for predicting the distribution of negative rake cutting force and temperature field comprises:
step 101: and respectively acquiring an experimental cutting force, an experimental depth resistance, a chip thickness value, a cutting speed, a cutter thermal conductivity, a workpiece thermal conductivity, a cutter thermal diffusivity and a workpiece thermal diffusivity under two groups of orthogonal experiments of variable cutting thickness and variable rake angle.
Step 102: and determining an experimental cutting force ratio according to the experimental cutting force and the experimental depth resistance.
Step 103: and determining an experimental cutting thickness ratio according to the cutting thickness value.
Step 104: an initial dead band angle, an initial friction factor angle, and an initial shear angle are obtained. Determining an allowable interval through a stress criterion; an initial dead zone angle, an initial friction factor angle, and an initial shear angle are obtained within the allowed space.
Step 105: and correcting the slip line field model based on the rigid-plastic deformation theory.
Step 106: predicting a chip force ratio and a cut thickness ratio from the corrected slip line field model based on the initial dead zone angle, the initial friction factor angle, and the initial shear angle. The method specifically comprises the following steps:
s1061: and calculating the ship fore angle according to the initial dead zone angle and the initial friction factor angle.
S1062: and calculating a slip line angle according to the prow angle and the initial shearing angle.
S1063: and calculating an initial slip line field geometric result according to the initial dead zone angle, the initial friction factor angle, the initial shearing angle and the slip line angle.
S1064: and calculating the chip force ratio and the cutting thickness ratio according to the initial slip line field geometric result.
Step 107: an error value is calculated based on the predicted chip force ratio, the experimental chip force ratio, the predicted cut thickness ratio, and the experimental cut thickness ratio.
Step 108: and acquiring the dead zone angle, the friction factor angle and the shearing angle when the error value is minimum.
Step 109: and calculating a geometric result of a slip line field, a cutting force and a cut-depth resistance according to the dead zone angle, the friction factor angle and the shearing angle.
Step 1010: and calculating a temperature field according to the geometric result of the slip line field, the cutting speed, the thermal conductivity of the cutter, the thermal conductivity of the workpiece, the thermal diffusivity of the cutter and the thermal diffusivity of the workpiece. The method specifically comprises the following steps:
s10101: and calculating the shear stress according to the geometric result of the slip line field.
S10102: calculating local flow shear stress and material flow velocity of the main shear zone, the knife-chip contact zone, and the dead zone workpiece interface based on the shear stress, the cutting speed, the dead zone angle, the friction factor angle, and the shear angle.
S10103: and calculating the heat source intensity of the main shearing area according to the local flow shearing stress of the main shearing area and the material flow speed of the main shearing area.
S10104: and calculating the heat source intensity of the cutter-chip contact area according to the local flow shear stress of the cutter-chip contact area and the material flow speed of the cutter-chip contact area.
S10105: and calculating the heat source intensity of the dead zone workpiece interface according to the local flow shear stress of the dead zone workpiece interface and the material flow speed of the dead zone workpiece interface.
S10106: and calculating a temperature field according to the heat source intensity of the main shearing area, the heat source intensity of the cutter-chip contact area, the heat source intensity of the dead zone workpiece interface, the heat conductivity of the cutter, the heat conductivity of the workpiece, the heat diffusion coefficient of the cutter and the heat diffusion coefficient of the workpiece.
The working principle of the method for predicting the distribution of the cutting force and the temperature field with the negative rake angle provided by the invention is described in detail as follows:
as shown in fig. 2, the present invention describes an analytical prediction method using experimental measurement results and thermal parameters of tool-workpiece material, etc. as input quantities and cutting force-heat as output.
(1) Respectively obtaining cutting forces F measured under two groups of gamma orthorhombic experiments with variable cutting thickness t and variable front angle c m、Ft mAnd the chip thickness value tch mAnd cutting speed VcTool and workpiece thermal conductivity lambdat、λwAnd coefficient of thermal diffusion at、awAs an input quantity.
(2) Based on a rigid-plastic deformation theory, a workpiece material is regarded as perfect plasticity, namely, deformation meets a plane strain condition, a corrected slip line model is proposed by considering a pre-shearing zone and a material retention zone, namely, the formation of a dead zone and the thickness of a main shearing zone on the basis of a former slip line method, and the geometric solving process of a specific slip line field is as follows:
FIG. 3 is a corrected slip line field model proposed for the negative rake cutting condition, where the pre-shear zone height is known to be consistent with the dead zone ground lifting height from the material flow continuity, i.e., the pre-shear zone height is known to be consistent with the dead zone ground lifting height, i.e., the slip line field model is a corrected slip line field model
Where ρ is the bow angle, the dead zone angle, and ξ1Is the dead zone-workpiece interface friction factor angle; the slip line angle θ may be represented by the bow angle ρ and the shear angle φ
In the method, the dead zone angle, the friction factor angle and the shearing angle in the two formulas are three initial iteration variables, wherein the initial iteration variables are the dead zone angle and the friction factor angle xi1And the shearing angle phi should be taken within an allowable interval, and the allowable interval is determined by the following stress criterion:
in the above formula, eta is the angle between the outer surface of the chip and the slip line GI, and varies from pi/4 to 3 pi/4, P GAs the hydrostatic pressure at the vertex G, the following equation is used
PG＝k(1+2θ+2ζ)
In addition to this condition, other slip line field geometries should all take positive values. The angles and lengths of other slip line fields can be derived from the three
Wherein zeta is sector angle, gamma is tool front angle, absolute value is taken from formula, psi is dead zone left vertex angle, and xi3Is the angle of the friction factor of the knife-chip contact surfacecFor the length of the knife-chip contact, /)sAnd rsLength and width of the main cutting zone, respectively, /)mAnd lnThe dead band base and right side lengths, i.e., the dead band-workpiece interface and the dead band-tool interface lengths.
(3) Then, according to the plastic slip line theory, the cutting force Fc pAnd resistance to cutting depth Ft pExpressed in terms of shearing action and ploughing action
Wherein FEFAnd NEFIs the dead zone-the tangential and normal components on the work contact surface, i.e. the active surface of the plow, and FGFAnd NGFThe main shearing zone, i.e. the tangential and normal components of the shearing action surface, these four force components can be respectively used for the previously derived slip line field geometry (dead zone angle, friction factor angle xi derived in step (2))1Slip line angle theta, sector angle zeta, shear angle phi, and dead band base length lmAnd length of right side ln) Is shown below
In the above expression, w is the cutting width,. tausIs an unknown quantity of material flow shear stress, so a dimensionless cutting force ratio F is introduced c/FtWhile the ratio t of the thickness of the chip to the thickness of the undeformed chipchThe/t (t is the undeformed chip thickness, UCT) can also be expressed as the slip line field geometry
Finally, introducing variance delta D to measure the deviation between the predicted value and the measured value
Where Δ D will give an initial threshold depending on different conditions to obtain the best iteration result, determine the dead zone angle, the friction factor angle ξ, which minimizes the error1And shear angle phi.
(4) The iteration result (dead zone angle, friction factor angle xi) is then1And the shearing angle phi) is replaced into the slip line field geometric solving formula, the slip line field geometric results under different UCT and front angle working conditions are solved, and the dead zone form and the linear change relation of the shearing angle and the slip line angle along with the UCT and the front angle are calibrated according to the results
Wherein k is1，k2，k3，k4，b1And b2Is a constant to be calibrated; at the same time, the material flow shear stress τsThe cutting force or the cut-depth resistance can also be used for carrying out the inverse calculation:
the flow shear stress values obtained by the above two formulas are slightly different, the results are averaged, meanwhile, the flow shear stress results under different working conditions have (smaller) difference, and the average value of all groups is taken as the final result. Thus, other UCT and hook under slip line field geometries as well as cutting and depth cut resistance can be predicted.
(5) And (4) obtaining the local flow shear stress and the material flow velocity of the heat generating region, namely the main shear region, the cutter-chip contact region and the dead region workpiece interface by utilizing the slip line field geometry determined in the steps (3) and (4) and combining the corresponding velocity vector diagram, and calculating the corresponding heat source intensity. Fig. 4 and 5 are velocity vector diagrams and heat source distribution diagrams corresponding to the slip line field, respectively. The specific calculation is as follows:
in the above formula Vch，τcAnd q isseRespectively representing the material flow velocity, shear stress and heat source intensity at the knife-chip interface, Vs，τsAnd q isprRespectively representing the material flow velocity, shear stress and heat source intensity at the main shear plane, Vm，τmAnd q isdRespectively representing material flow velocity, shear stress and heat source intensity at the dead zone-workpiece interface.
(6) Fig. 6a, 6b and 6c show the created mirror image heat source models of the workpiece, chip and tool, respectively, determining the heat source position by creating a three-dimensional coordinate system and then substituting the previously determined heat source intensity to obtain the temperature fields of the workpiece, chip and tool:
in the three formulae, R1～R8And R1′～R8' distance from arbitrary point M (x, y, z) to integration point of primary heat source and mirror heat source, K0Representing Bessel functions of the second kind, SmThe induction heat source intensity ratio of the dead zone heat source on the dead zone-cutter contact surface is 0.2, wherein y t G，yt FAnd yt EThe result of the coordinate system transformation for three-dimensional coordinate system midpoints G, F and E:
wherein, xG, xF, yG, yF, and yE correspond to the X-Y coordinates of points G, F and E, respectively, in the three-dimensional coordinate system.
And for the knife-chip interface heat source, i.e. including a second heat source qseAnd dead zone induction heat source (1-S)m)qdAll are regarded as fixed rectangular heat sources, and a dynamic heat distribution equation B is introducedchipAnd BtoolTemperature matching at the interface of the two is realized:
wherein lcDenotes the length of the blade-chip contact, the initial heat distribution coefficient BcAnd BtAnd adjusting parameters C and delta B and indexes m and k according to specific working conditions.
Fig. 7 shows a negative rake cutting speed cloud chart result (left chart) obtained by using commercial finite element simulation software AdvantEdge, the workpiece material used for simulation is 304 stainless steel, the tool is made of hard alloy, the design rake angle is-20 degrees, the UCT is 0.1mm, the simulation dead zone form (right chart) can be seen to meet the model expectation, and the simulation slip line field geometric result can be extracted from fig. 7.
FIG. 8 is a comparison of six sets of variable rake angle simulation slip line field results, including slip line angle, shear angle and dead zone geometry data extracted in Table 1, and variable UCT simulation dead zone geometry results extracted in Table 2.
TABLE 1 comparison of slip line field geometry prediction and simulation results
TABLE 2 prediction of dead zone geometry under variable UCT
FIGS. 9a and 9b are linear representations fitted to the shear angle and the slip line angle, respectively, as a function of the rake angle; FIG. 10 is a linear fit between the dead zone bottom and right side lengths and the varying UCT; fig. 11 shows the shear angle and predicted flow shear stress variation for different UCTs, and it can be seen that the material flow shear stress fluctuates above and below the mean 605MPa, while the shear angle also shows a plateau, with slight increases affected by progressively higher cutting temperatures.
Fig. 12a and 12b respectively show the comparison of the model predicted tool, workpiece-chip temperature field and simulation results, it can be seen that the highest cutting temperature is located on the rake face and a certain distance from the tool nose, and the predicted chip temperature lines in fig. 12b are dense, because the model assumes that the predicted cutting temperature field reaches the transient steady state, and does not consider the complex time domain variation, the temperature distribution is greatly different from the simulated chip temperature distribution;
fig. 13 shows a comparison of the predicted and simulated results of the temperature distribution of the tool rake face of fig. 12a, which shows that the deviation of the two results is small, but the temperature distribution trend at the dead zone-tool interface is greatly different, probably because the invention shares a dynamic heat distribution equation with the dead zone induction heat source and the second heat source, and the actual dead zone-tool interface heat source intensity distribution needs to be further studied.
The modeling process of the present invention is fully and clearly illustrated below in conjunction with a specific example of machining 304 stainless steel with a cemented carbide turning tool.
In this embodiment, a 10mm side length triangular cemented carbide insert (holder model TCMT110204) was used, and the tool cutting edge obtained by using an Alicona optical surface measuring instrument (model: Infinite Focus G5 Plu) is shown in fig. 14, where the chamfering edge length of the tool is 400um and the chamfering angle is 13.2 degrees, and since the chamfering is long enough, the chamfered surface becomes the actual rake surface in the actual cutting experiment (UCT varies from 0.02mm to 0.14 um). The workpiece was made of 304 stainless steel, the lathe was of the type CAK5085nzj, the load cell was of the type Kistler9257B, the sampling frequency was 40kHz, and the specific cutting force values were obtained by calculating the average value over some interval in the middle of the sampled values.
By the relationship between the slip line field geometry, the ucted UCT and the rake angle in fig. 9 and 10, the slip line field geometry corresponding to the working condition and the cutter combination used in the experiment can be obtained, and the predicted value of the cutting force can be obtained by combining the determined material flow shear stress, and then compared with the experimental measurement result, as shown in fig. 15. The predicted cutting force result is well matched with the measurement result, but the predicted value and the measured value of the depth cutting resistance have great errors when the UCT is low, mainly because the model considers that the cutter is absolutely sharp, the actual cutter point has a certain fillet, the size effect is obvious under the working condition of the low UCT, and the depth cutting resistance can be increased sharply.
Compared with other methods, the method has the advantages that the material retention phenomenon is revealed, meanwhile, the cutting force and temperature field prediction of the process is achieved, and the method is verified to have higher accuracy and reliability.
As shown in fig. 16, the present invention also provides a negative rake cutting force and temperature field distribution prediction system, comprising:
the experimental data acquisition module 1601 is used for respectively acquiring experimental cutting force, experimental depth resistance, a chip thickness value, a cutting speed, cutter thermal conductivity, workpiece thermal conductivity, cutter thermal diffusivity and workpiece thermal diffusivity under two groups of orthogonal experiments with variable cutting thickness and variable rake angles.
An experimental chip force ratio determining module 1602 for determining an experimental chip force ratio based on the experimental cutting force and the experimental depth resistance.
An experimental cut thickness ratio determining module 1603 for determining an experimental cut thickness ratio according to the cut thickness value.
An initial data acquisition module 1604 to acquire an initial dead zone angle, an initial friction factor angle, and an initial shear angle.
The initial data obtaining module 1604 specifically includes:
the allowable interval determining unit is used for determining an allowable interval through a stress criterion;
An acquisition unit for acquiring an initial dead zone angle, an initial friction factor angle, and an initial shear angle within the allowable space.
And the correcting module 1605 is used for correcting the slip line field model based on the rigid-plastic deformation theory.
A prediction module 1606 for predicting a chip force ratio and a cut thickness ratio from the corrected slip line field model based on the initial dead zone angle, the initial friction factor angle, and the initial shear angle.
The prediction module 1606 specifically includes:
the ship fore angle calculation unit is used for calculating a ship fore angle according to the initial dead zone angle and the initial friction factor angle;
the slip line angle calculation unit is used for calculating a slip line angle according to the bow angle and the initial shearing angle;
the initial slip line field geometric result calculation unit is used for calculating an initial slip line field geometric result according to the initial dead zone angle, the initial friction factor angle, the initial shearing angle and the slip line angle;
and the chip force ratio and cutting thickness ratio calculating unit is used for calculating the chip force ratio and the cutting thickness ratio according to the initial slip line field geometric result.
An error value calculation module 1607 for calculating an error value based on the predicted chip force ratio, the experimental chip force ratio, the predicted cutting thickness ratio, and the experimental cutting thickness ratio.
A data acquisition module 1608 configured to acquire the dead zone angle, the friction factor angle, and the shear angle when the error value is minimized.
A first calculating module 1609, configured to calculate a slip line field geometry result, a cutting force and a cut-depth resistance according to the dead zone angle, the friction factor angle and the shear angle.
A second calculating module 1610 configured to calculate a temperature field according to the geometric result of the slip line field, the cutting speed, the tool thermal conductivity, the workpiece thermal conductivity, the tool thermal diffusivity, and the workpiece thermal diffusivity.
The second calculating module 1610 specifically includes:
the shear stress calculation unit is used for calculating shear stress according to the geometric result of the slip line field;
a first calculation unit for calculating local flow shear stress and material flow velocity of a main shear zone, a blade-chip contact zone, and a dead zone workpiece interface, based on the shear stress, the cutting speed, the dead zone angle, the friction factor angle, and the shear angle;
the heat source intensity calculating unit of the main shearing area is used for calculating the heat source intensity of the main shearing area according to the local flow shearing stress of the main shearing area and the material flow speed of the main shearing area;
A heat source intensity calculating unit of the cutter-chip contact area, which is used for calculating the heat source intensity of the cutter-chip contact area according to the local flow shearing stress of the cutter-chip contact area and the material flow speed of the cutter-chip contact area;
the heat source intensity calculating unit of the dead zone workpiece interface is used for calculating the heat source intensity of the dead zone workpiece interface according to the local flow shear stress of the dead zone workpiece interface and the material flow speed of the dead zone workpiece interface;
and the temperature field calculation unit is used for calculating a temperature field according to the heat source intensity of the main shearing area, the heat source intensity of the cutter-chip contact area, the heat source intensity of the dead zone workpiece interface, the heat conductivity of the cutter, the heat conductivity of the workpiece, the heat diffusion coefficient of the cutter and the heat diffusion coefficient of the workpiece.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (8)
1. A method for predicting negative rake cutting force and temperature field distribution, comprising:
respectively acquiring an experimental cutting force, an experimental depth resistance, a cutting thickness value, a cutting speed, a cutter thermal conductivity, a workpiece thermal conductivity, a cutter thermal diffusivity and a workpiece thermal diffusivity under two groups of orthogonal experiments with variable cutting thickness and variable rake angles;
determining an experimental cutting force ratio according to the experimental cutting force and the experimental depth resistance;
determining an experimental cutting thickness ratio according to the cutting thickness value;
acquiring an initial dead zone angle, an initial friction factor angle and an initial shearing angle;
correcting a slip line field model based on a rigid-plastic deformation theory;
predicting a chip force ratio and a cut thickness ratio according to the corrected slip line field model based on the initial dead zone angle, the initial friction factor angle and the initial shear angle;
Calculating an error value from the predicted chip force ratio, the experimental chip force ratio, the predicted cutting thickness ratio, and the experimental cutting thickness ratio;
obtaining a dead zone angle, a friction factor angle and a shearing angle when the error value is minimum;
calculating a geometric result of a slip line field, a cutting force and a cut-depth resistance according to the dead zone angle, the friction factor angle and the shearing angle;
and calculating a temperature field according to the geometric result of the slip line field, the cutting speed, the thermal conductivity of the cutter, the thermal conductivity of the workpiece, the thermal diffusivity of the cutter and the thermal diffusivity of the workpiece.
2. The negative rake cutting force and temperature field distribution prediction method of claim 1, wherein the predicting a chip force ratio and a cut thickness ratio from a corrected slip line field model based on the initial dead zone angle, the initial friction factor angle, and the initial shear angle specifically comprises:
calculating a bow angle according to the initial dead zone angle and the initial friction factor angle;
calculating a slip line angle according to the bow angle and the initial shearing angle;
calculating an initial slip line field geometric result according to the initial dead zone angle, the initial friction factor angle, the initial shearing angle and the slip line angle;
And calculating the chip force ratio and the cutting thickness ratio according to the initial slip line field geometric result.
3. The method of predicting negative rake cutting force and temperature field distribution of claim 1, wherein said calculating a temperature field from said slip line field geometry, said cutting speed, said tool thermal conductivity, said workpiece thermal conductivity, said tool thermal diffusivity, and said workpiece thermal diffusivity, comprises:
calculating the shear stress according to the geometric result of the slip line field;
calculating local flow shear stress and material flow velocity of a main shear zone, a knife-chip contact zone, and a dead zone workpiece interface from the shear stress, the cutting speed, the dead zone angle, the friction factor angle, and the shear angle;
calculating the heat source intensity of the main shearing area according to the local flow shearing stress of the main shearing area and the material flow speed of the main shearing area;
calculating the heat source intensity of the cutter-chip contact area according to the local flow shearing stress of the cutter-chip contact area and the material flow speed of the cutter-chip contact area;
calculating the heat source intensity of the dead zone workpiece interface according to the local flow shear stress of the dead zone workpiece interface and the material flow speed of the dead zone workpiece interface;
And calculating a temperature field according to the heat source intensity of the main shearing area, the heat source intensity of the cutter-chip contact area, the heat source intensity of the dead zone workpiece interface, the heat conductivity of the cutter, the heat conductivity of the workpiece, the heat diffusion coefficient of the cutter and the heat diffusion coefficient of the workpiece.
4. The method of predicting the distribution of negative rake cutting force and temperature field of claim 1, wherein said obtaining an initial dead band angle, an initial friction factor angle, and an initial shear angle comprises:
determining an allowable interval through a stress criterion;
an initial dead zone angle, an initial friction factor angle, and an initial shear angle are obtained within the allowed space.
5. A negative rake cutting force and temperature field distribution prediction system, comprising:
the experimental data acquisition module is used for respectively acquiring experimental cutting force, experimental depth resistance, a cutting thickness value, cutting speed, cutter thermal conductivity, workpiece thermal conductivity, cutter thermal diffusivity and workpiece thermal diffusivity under two groups of orthogonal experiments with variable cutting thickness and variable rake angles;
an experimental chip force ratio determining module for determining an experimental chip force ratio according to the experimental cutting force and the experimental depth resistance;
The experimental cutting thickness ratio determining module is used for determining an experimental cutting thickness ratio according to the cutting thickness value;
the initial data acquisition module is used for acquiring an initial dead zone angle, an initial friction factor angle and an initial shearing angle;
the correction module is used for correcting the slip line field model based on the rigid-plastic deformation theory;
a prediction module for predicting a chip force ratio and a cut thickness ratio from the corrected slip line field model based on the initial dead zone angle, the initial friction factor angle, and the initial shear angle;
an error value calculation module for calculating an error value based on the predicted chip force ratio, the experimental chip force ratio, the predicted cutting thickness ratio, and the experimental cutting thickness ratio;
the data acquisition module is used for acquiring a dead zone angle, a friction factor angle and a shearing angle when the error value is minimum;
the first calculation module is used for calculating a geometric result of a slip line field, a cutting force and a cut-in resistance according to the dead zone angle, the friction factor angle and the shearing angle;
and the second calculation module is used for calculating a temperature field according to the geometric result of the slip line field, the cutting speed, the thermal conductivity of the cutter, the thermal conductivity of the workpiece, the thermal diffusion coefficient of the cutter and the thermal diffusion coefficient of the workpiece.
6. The negative rake cutting force and temperature field distribution prediction system of claim 5, wherein the prediction module specifically comprises:
the ship fore angle calculation unit is used for calculating a ship fore angle according to the initial dead zone angle and the initial friction factor angle;
the slip line angle calculation unit is used for calculating a slip line angle according to the bow angle and the initial shearing angle;
the initial slip line field geometric result calculation unit is used for calculating an initial slip line field geometric result according to the initial dead zone angle, the initial friction factor angle, the initial shearing angle and the slip line angle;
and the chip force ratio and cutting thickness ratio calculating unit is used for calculating the chip force ratio and the cutting thickness ratio according to the initial slip line field geometric result.
7. The negative rake cutting force and temperature field distribution prediction system of claim 5, wherein the second calculation module specifically comprises:
the shear stress calculation unit is used for calculating shear stress according to the geometric result of the slip line field;
a first calculation unit for calculating local flow shear stress and material flow velocity of a main shear zone, a blade-chip contact zone, and a dead zone workpiece interface, based on the shear stress, the cutting speed, the dead zone angle, the friction factor angle, and the shear angle;
The heat source intensity calculating unit of the main shearing area is used for calculating the heat source intensity of the main shearing area according to the local flow shearing stress of the main shearing area and the material flow speed of the main shearing area;
a heat source intensity calculating unit of the cutter-chip contact area, which is used for calculating the heat source intensity of the cutter-chip contact area according to the local flow shearing stress of the cutter-chip contact area and the material flow speed of the cutter-chip contact area;
the heat source intensity calculating unit of the dead zone workpiece interface is used for calculating the heat source intensity of the dead zone workpiece interface according to the local flow shear stress of the dead zone workpiece interface and the material flow speed of the dead zone workpiece interface;
and the temperature field calculation unit is used for calculating a temperature field according to the heat source intensity of the main shearing area, the heat source intensity of the cutter-chip contact area, the heat source intensity of the dead zone workpiece interface, the heat conductivity of the cutter, the heat conductivity of the workpiece, the heat diffusion coefficient of the cutter and the heat diffusion coefficient of the workpiece.
8. The negative rake cutting force and temperature field distribution prediction system of claim 5, wherein the initial data acquisition module specifically comprises:
the allowable interval determining unit is used for determining an allowable interval through a stress criterion;
An acquisition unit for acquiring an initial dead zone angle, an initial friction factor angle, and an initial shear angle within the allowable space.
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