Stability and process control of single-diamond grinding based on clustering of processing morphology data
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摘要: 硬质模具钢磨削过程中，加工深度的变化会引起磨削力变化，导致其加工状态不稳定。采用大颗粒单点金刚石磨削硬质模具钢，基于其加工表面的形貌特征分析磨削过程的动态特性及稳定性，探究工艺参数对加工效率和表面质量的影响，以实现其高效率高质量的磨削加工。首先，对单点金刚石磨削系统进行动力学建模，采用加速度传感器测量磨削振动信号并进行工作模态分析，求解磨削系统的固有频率和阻尼比。然后，基于不同加工工况的表面波纹度和表面粗糙度数据，关联进给深度和砂轮转速与稳定工况时的数据聚类，且与磨削稳定时的叶瓣图区域匹配，拟合出磨削系统刚度和磨削力系数，构建稳定磨削过程中的进给深度和砂轮转速实时调控区域。最后，通过模具钢的磨削实验验证及分析其加工效率和质量。结果表明：磨削过程的模态分析与加工表面形貌特征的聚类匹配能够映射磨削稳定域的加工工艺参数；在磨削稳定域内，采用更大的材料去除率可将模具钢的平均表面波纹度从1.203 μm降低到0.635 μm，平均表面粗糙度从0.267 μm降低到0.143 μm；且在相同的材料去除量下，磨削稳定域加工的模具钢表面粗糙度平均下降74%。因此，在加工过程中依据加工表面特征化的磨削稳定域实时调整进给深度和砂轮转速，可同时提高工件的加工质量和效率。Abstract:
Objectives In the precision grinding process of hard mold steel workpieces, the subtle changes in machining depth can significantly cause dynamic changes in the magnitude and the direction of grinding forces, which directly lead to unstable machining conditions and affect machining accuracy and surface quality. To this end, the data clustering analysis is used to analyze the machining morphology data of the workpiece, and the stable single-point grinding of the workpiece is achieved through process control. Methods Using large particle diamond single-point grinding for hard mold steel, the dynamic characteristics and the stability of the grinding process are analyzed based on the morphology characteristics of the diamond processing surface. The influences of the process parameters on diamond processing efficiency and surface quality are explored to achieve high-efficiency and high-quality diamond grinding. Firstly, the dynamic modeling of the single point diamond grinding system is carried out, and the grinding vibration signal is measured by an accelerometer. The working mode analysis is performed to solve the natural frequency and the damping ratio of the machining system. Then, using a laser confocal microscope to obtain surface waviness and surface roughness data under different processing conditions, the feed depth and the wheel speed are correlated with the data clustering under stable conditions, and matched with the blade diagram area under stable grinding conditions to fit the stiffness and the grinding force coefficients of the processing system. A real-time control area for feed depth and the wheel speed during the stable grinding process is constructed. Finally, the machining efficiency and the quality of the mold steel are verified and analyzed through grinding experiments. Results The modal analysis of the grinding process and the clustering matching of the machined surface morphology features can map the machining process parameters in the stable domain of the grinding process. The working mode analysis method is applied to the stability analysis of single-point diamond grinding die steel, and the natural frequency and the damping ratio of the process system can be obtained under the working state. The natural frequency of the single-point diamond grinding die steel process system is fn = 363 Hz, and the damping ratio ξ = 0.027. The clustering analysis method is applied to the machining state classification, and the machining surface can be divided into stable machining and unstable machining according to the internal relationship between the surface waviness Wa and surface roughness Ra data. The surface morphologies of the two types of machining are obviously different. The surface of the stable processing state is smooth and flat, while the surface of the unstable processing state has a large area of plastic deformation and a large number of burrs. The surface machining quality of single-point diamond grinding die steel differs greatly under stable and unstable machining conditions. The average surface waviness Wa of single-point diamond grinding mold steel in the stable processing state is 0.635 μm, and the average surface roughness Ra is 0.143 μm. The average surface waviness Wa in the unstable state is 1.203 μm, and the average surface roughness Ra is 0.267 μm, which is about twice that of the stable state. The experimental points after clustering analysis are matched to the relevant areas on the grinding stability lobe diagram, and the experimental verification is carried out to obtain the system stiffness coefficient k = 7 × 106 N/m and the grinding force coefficient km' = 3 × 1015 N/m3 of the single-point diamond grinding die steel process system. Conclusions In the stable processing state, the single-point diamond grinding die steel can achieve a greater material removal rate while ensuring the surface quality as much as possible, thus improving the processing efficiency. In the case of the same amount of material removal, the surface roughness Ra of the stable region processing state is reduced by 74% on average compared with that of the unstable region processing state, which realizes the high-efficiency and the high-surface-quality machining of high-hardness metal materials. -
Key words:
- single-diamond /
- grinding stability /
- cluster analysis /
- surface quality /
- surface roughness
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图 6 单点金刚石加工表面的波纹度轮廓曲线
Figure 6. Waviness profile curve of single-diamond machining surface
图 7 单点金刚石加工表面的表面粗糙度曲线
Figure 7. Surface roughness curve of single-diamond grinding surface
图 8 表面波纹度与表面粗糙度的聚类分析
Figure 8. Cluster analysis of surface waviness and surface roughness
图 10 单点金刚石磨削的稳定性叶瓣图
Figure 10. Grinding stability lobe diagram of single-diamond grinding
图 11 验证实验中工件表面的SEM形貌
Figure 11. SEM morphology of workpiece surface in verification experiment
图 12 验证实验中工件表面的表面波纹度曲线
Figure 12. Surface waviness curves of workpiece surface in verification experiment
图 13 验证实验中工件表面的表面粗糙度曲线
Figure 13. Surface roughness curves of workpiece surface in verification experiment
图 14 材料去除量与表面质量关系图
Figure 14. Diagram of relationship between material removal amount and surface quality
表 1 D-star工件材料参数
Table 1. Parameter of D-star workpiece material
参数 数值 密度 ρ / (g·cm−3) 7.75 弹性模量 E / GPa 200 热导率 K / [W·(m·K)−1] 24.7 硬度 / HRC 52～55 
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表 2 磨削加工实验条件
Table 2. Experimental conditions for grinding processing
实验条件 规格或取值 金刚石粒度代号 16/18 砂轮直径 D / mm 150 砂轮转速 N / (r·min−1) 1 800, 2 100, 2 400, 2 700 进给速度 vf / (mm·min−1) 50 进给深度 h / μm 4, 6
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表 3 磨削稳定性叶瓣图参数
Table 3. Grinding stability lobe diagram parameters
参数 数值 固有频率 fn / Hz 363 阻尼比 ξ 0.027 刚度系数 k / (N·m−1) 7 × 106 磨削力系数 $ {k}'_{{\mathrm{m}}} $ / (N·m−3) 3 × 1015 磨粒宽度 b / m 2.8 × 10−5
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表 4 磨削加工实验条件
Table 4. Experimental conditions for grinding processing
参数 取值 砂轮转速 N / (r·min−1) 2 100, 2 700 进给深度 h / μm 5, 7
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表 5 磨削稳定性实验验证结果
Table 5. Experimental verification results of grinding stability
参数 加工状态 N = 2 100 r/min, h = 5 μm 稳定 N = 2 100 r/min, h = 7 μm 稳定 N = 2 700 r/min, h = 5 μm 不稳定 N = 2 700 r/min, h = 7 μm 不稳定
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