Workpiece surface roughness calculation method during turning based on tool wear
Technical Field
The invention relates to a method for calculating the surface roughness of a workpiece, in particular to a method for calculating the surface roughness of the workpiece during turning based on tool abrasion.
Background
The turning process is to use a turning tool to cut excess metal from a rotating workpiece to form a machined surface. The surface roughness of the workpiece is an important parameter for representing the processing quality of the workpiece, and has a remarkable influence on the service performance of the workpiece. Generally, the rougher the surface of the workpiece, the more stress concentrations tend to occur, thereby affecting the fit accuracy and increasing wear caused by the mutual movement of the workpieces.
Many scholars have studied how to predict the surface roughness of a workpiece based on the cutting amount of the tool and the geometrical parameters of the tool. Zhang oas et al established a surface roughness multiple regression prediction model based on cutting speed, feed amount and cutting depth in a paper "application of response surface method in surface roughness prediction model and parameter optimization" published in academic journal Shanghai university of transportation journal (No. 4: P447-451 in 2016), aiming at the turning of titanium alloy TC11 which is a difficult-to-machine material. In a paper "surface roughness prediction for precision turning of lenses", published in academic journal, "journal of mechanical engineering (2013, 15 th: P192-198), Wang Xingsheng et al established a workpiece surface roughness prediction model based on the radius of a cutter arc, the feed per circle, the back bite, the spindle rotation speed and the discrete angle for precision turning of mirror surfaces. However, the above models do not take into account the influence of the wear condition of the tool on the surface roughness of the workpiece. The abrasion of the cutter is inevitable in the turning process, the abrasion of the cutter generally comprises three stages of initial abrasion, normal abrasion and rapid abrasion, and the cutter is generally operated in the initial abrasion and normal abrasion stages. The effect of tool wear conditions on workpiece surface roughness is very significant.
In conclusion, how to simply and accurately calculate the surface roughness of a workpiece during turning according to turning parameters and the abrasion condition of a cutter has important guiding significance for researching how to optimize process parameters to reduce the surface roughness of the workpiece and improve the surface quality, and becomes a technical problem which needs to be solved by technicians in the field.
Disclosure of Invention
The invention aims to provide a simple and accurate method for calculating the surface roughness of a workpiece during turning based on tool wear. The technical scheme is as follows: the method comprises the following steps: 1) establishing a workpiece surface roughness calculation model during turning, 2) measuring and calculating each undetermined coefficient in the workpiece surface roughness calculation model by means of a roughness meter and a metallographic microscope, and 3) calculating the workpiece surface roughness during turning according to turning parameters and the wear amount of a rear tool face of a turning tool under the condition that a tool material, a workpiece material and a processing mode are the same.
The method is characterized in that:
in the step 1), based on a metal cutting theory, according to the relation between the turning parameters and the surface roughness of the workpiece and considering the influence of the abrasion condition of the cutter on the surface roughness of the workpiece, establishing a calculation model of the surface roughness of the workpiece during turning:
Ra=k×ap a×fb×Vc×VBd(1)
wherein R isaIs the workpiece surface roughness; VB is the wear amount of the rear cutter face of the turning tool and is used as a characteristic value of the wear condition of the cutter; a ispThe amount of the back eating is the amount of the back eating; f is the feed amount; v is the cutting speed; k. a, b, c and d are undetermined coefficients.
In the step 2), each undetermined coefficient in a workpiece surface roughness calculation model during turning is measured and calculated by means of a coarseness meter and a metallographic microscope, and after a tool material, a workpiece material and a processing mode are determined, a turning experiment is carried out to cover the initial wear stage and the normal wear stage of a turning tool:
for each turning process, respectively measuring the wear loss of the rear tool face of the turning tool before and after the processing, and taking an average value as the wear loss VB of the rear tool face of the turning tool in the turning process;
after turning is finished each time, selecting two sections on the machined surface of the workpiece, measuring the surface roughness of the workpiece at intervals of 60 degrees on each section, and averaging 12 measured values to be used as the surface roughness R of the workpiece in the turninga。
Selecting more than 20 groups of turning parameters to carry out turning experiments, and enabling the wear VB and the back bite a of the rear tool face of the turning toolpFeed f, cutting speed V and workpiece surface roughness RaSubstituting the formula (1) to obtain an overdetermined equation set, and calculating coefficients k, a, b, c and d to be determined based on a least square method.
In step 3), in the knifeUnder the condition that the material, the workpiece material and the processing mode are the same, for a group of new process parameters, according to the turning parameters and the wear amount of the rear cutter face of the turning tool, the surface roughness calculation model of the workpiece during turning obtained in the step 1) and the step 2) is used for calculating the surface roughness R of the workpiecea。
Compared with the prior art, the invention has the advantages that: the influence of turning parameters and the abrasion condition of the cutter is comprehensively considered to calculate the surface roughness of the workpiece during turning, and the calculation method is simple and high in precision; process parameter selection is facilitated to improve surface quality and reduce scrap rate.
Drawings
Fig. 1 is a flowchart of the present invention for calculating the surface roughness of a workpiece during turning based on tool wear.
FIG. 2 is a flow chart of calculation of undetermined coefficients in a tool wear-based turning workpiece surface roughness calculation model.
Detailed Description
The invention is described in further detail below with reference to fig. 1 and 2.
In the step 1), based on a metal cutting theory, according to the relation between the turning parameters and the surface roughness of the workpiece and considering the influence of the abrasion condition of the cutter on the surface roughness of the workpiece, establishing a calculation model of the surface roughness of the workpiece during turning:
Ra=k×ap a×fb×Vc×VBd(1)
wherein R isaIs the workpiece surface roughness; VB is the wear amount of the rear cutter face of the turning tool and is used as a characteristic value of the wear condition of the cutter; a ispThe amount of the back eating is the amount of the back eating; f is the feed amount; v is the cutting speed; k. a, b, c and d are undetermined coefficients.
In the step 2), each undetermined coefficient in a workpiece surface roughness calculation model during turning is measured and calculated by means of a coarseness meter and a metallographic microscope, and after a tool material, a workpiece material and a processing mode are determined, a turning experiment is carried out to cover the initial wear stage and the normal wear stage of a turning tool:
for each turning process, respectively measuring the wear loss of the rear tool face of the turning tool before and after the processing, and taking an average value as the wear loss VB of the rear tool face of the turning tool in the turning process;
after turning is finished each time, selecting two sections on the machined surface of the workpiece, measuring the surface roughness of the workpiece at intervals of 60 degrees on each section, and averaging 12 measured values to be used as the surface roughness R of the workpiece in the turninga。
Selecting more than 20 groups of turning parameters to carry out turning experiments, and enabling the wear VB and the back bite a of the rear tool face of the turning toolpFeed f, cutting speed V and workpiece surface roughness RaSubstituting the formula (1) to obtain an overdetermined equation set, and calculating coefficients k, a, b, c and d to be determined based on a least square method.
In the step 3), under the condition that the cutter material, the workpiece material and the processing mode are the same, for a group of new process parameters, the surface roughness R of the workpiece is calculated by applying the workpiece surface roughness calculation model obtained in the step 1) and the step 2) during turning according to the turning parameters and the wear amount of the rear cutter face of the turning toola。
The invention is realized in a CKJ6163 numerical control lathe. The turning workpiece is a 304 stainless steel bar, and 25 times of excircle turning orthogonal experiments are carried out by adopting a CNMG120408 hard alloy blade, an Axio-lab-A metallographic microscope and an RTP-120 multifunctional roughness meter. The turning parameters, tool wear and workpiece surface roughness in the experiment are shown in table 1.
TABLE 1 turning test and actually measured tool wear and workpiece surface roughness
Substituting 25 groups of data in the table 1 into the formula (1) to obtain an overdetermined equation set, and solving a coefficient to be determined based on a least square method, wherein the coefficient to be determined is as follows: k =20.29835, a = -0.03476, b =1.66432, c =0.03534, d = 0.02909. The calculation model of the surface roughness of the workpiece during turning is
Ra=20.29835×ap -0.03476×f1.66432×V0.03534×VB0.02909(2)
The mean square error of the calculated model of the workpiece surface roughness is 0.0102. Under the condition that the cutter material, the workpiece material and the processing mode are the same, a new set of process parameters is used for verifying the effectiveness of the workpiece surface roughness calculation method during turning, and the effectiveness is shown in table 2. The wear amount of the rear tool face of the used turning tool is 0.1097mm, the surface roughness of the workpiece during turning is 3.2634um calculated by the formula (2), the actually measured surface roughness of the workpiece is 3.3075um, and the calculation precision is 98.6%.
TABLE 2 verification test of the established method for calculating the surface roughness of a workpiece during turning
The method comprehensively considers the influence of the turning parameters and the abrasion condition of the cutter to calculate the surface roughness of the workpiece during turning, and has simple calculation method and high precision. The invention is beneficial to selecting technological parameters during turning, improving the surface quality and reducing the rejection rate.