刀具磨床結構與磨刀過程動態行為之研究

Structure Characteristics and Process Dynamic Behavior of a Cutting-Tool Grinding Machine

許晉銘(Jin-Ming Hsu)

指導教授 ： 林盛勇

國立虎尾科技大學/工程學院/機械與電腦輔助工程系碩士班/碩士(2014年)

https://doi.org/10.6827/NFU.2014.00247

摘要

由於現代切削技術的進步，再加上科技的日新月異，促使產品精密度的要求越來越高，高精度刀具的需求也相對提高。刀具之刀刃研磨是刀具製造上最重要的技術，也是決定刀具幾何形狀精度及切削性能之關鍵。切削刀具是加工業的重要利器，刀具品質的好壞，直接影響刀具的性能、刀具壽命、刃口磨損、切削效率、切削加工精度、切削表面品質等。為了得到較好的刀具研磨品質，若能掌握機台結構本身的剛性與動態特性，將有助於機台結構設計製造上的補強及避免結構共振的發生。
本研究主要以實務性的做法來探討刀具磨床結構特性與磨削過程的動態行為。首先，針對刀具磨床進行數值與實驗模態分析，探討刀具磨床結構的自然頻率、阻尼比與模態振型。透過實驗模態分析求得部件及整機系統的結構特性，並找出結構較脆弱處予以補強，亦可用來修正數值模擬的分析模型，作為後續結構改善設計之依據。接著，進行刀具研磨實驗並監測磨削過程的動態情形，改變主軸轉速、進給速度、磨削深度等來進行刀具研磨加工，量測研磨過程主磨區之振動與研磨後刀刃面的表面粗糙度，以利相互比對。由實驗模態分析結果得知，在可能發生共振的頻率範圍內計有五個模態容易引發結構共振。據此，針對前三個模態之自然頻率分別轉變為對應的主軸轉速，反覆進行各模態轉速之微調並監測其振動振幅之變化，直至機台結構產生共振為止。實驗結果證明，於各模態共振頻率，振幅明顯攀升約2-3倍，刀刃表面粗糙度也出現較差的情況，且微調後的各模態轉速頻率值亦相當接近實驗模態分析結果。此驗證了實驗模態分析的結果與實際刀具研磨的結果於共振頻率的監測上有很好的一致性。本文有效地預測刀具磨床的動態特性，可供加工業者研磨時避開共振轉速，使研磨時在穩態的磨削下進行加工，有助於提升磨削加工之效率。

關鍵字

模態振型 ； 共振頻率 ； 動態行為 ； 刀具研磨

並列摘要

Due to the advances in modern cutting technology coupled with the ever-changing of science and technology, precision product demand is prompting increasingly. As a result, the demand for high-precision cutting-tool is also enhanced. Cutting-edge grinding is the most important manufacturing technique for cutting-tool machining and it determines the accuracy of tool geometry and cutting performance. Cutting-tool is an important tool for machining manufacturer since its quality directly affects the cutting-tool performance, cutting-tool life, abrasive wear of the cutting edge, cutting efficiency, machining accuracy, machined surface quality, etc. If the structure stiffness and dynamic characteristic of the machine-tool can be handled properly, it will be helpful to reinforce the structure design and manufacturing, and to avoid the possible occurrence of resonance vibration on structure.
This study investigates the structural characteristics and dynamic behavior of a cutting-tool grinder in a practical approach. First of all, the numerical and experimental modal analyses are performed for a cutting-tool grinder, and the natural frequency, damping ratio and mode shape of the structure are obtained consequently. The structure characteristics of the major sub-systems and whole system of a machine-tool can be obtained from the experimental modal analyses. The structure weaker zones may be located and strengthened, and the analysis result can also be used to modify the numerical analysis model and taken as a basis for subsequent improvement design on structure. Then, the cutting-tool grinding experiments are conducted by changing the process parameters such as spindle speed, feed rate and grinding depth. The dynamic behavior was monitored during the grinding process at the same time. In addition, on-line measurement of grinding vibration around the primary grinding zone and off-line measurement of surface roughness on cutting-edge were conducted for cross comparisons among different grinding condition combinations. According to the results obtained from the modal analysis, within the possibly resonant vibration range there are five vibration modes which are easily to excite the structure and induce resonant vibration. Based on this basis, the first three natural frequencies corresponding to vibration modes were transferred to corresponding spindle speeds. During the search processes on resonant frequency, each modal spindle speed was changed gradually and the vibration amplitude is monitored repeatedly in the sucessive grinding experiments. This action is not ceased until the resonant vibration on the machine-tool is occurred excitedly. Experimental results show that the vibration amplitude is obviously raised about 2-3 times of the generally stable state in each modal spindle speed case. The surface roughness is also worse when the resonant vibration is occurred. Furthermore, each final modal spindle speed after gradual adjustment is very close to the natural frequency which was obtained from the experimental modal analysis in this study. This verification illustrates that it has a good consistency between the experimental modal analysis and this practical approach for resonant frequency search of a cutting-tool grinder. This study effectively predict the dynamic characteristics of a cutting-tool grinder and the results obtained can provide as a reference for cutting-tool grinding worker to avoid the possible occurrence of resonant vibration during grinding. It is very helpful for improving the cutting-tool grinding efficiency.

並列關鍵字

mode shape ； resonant vibration frequency ； dynamic behavior ； cutting-tool grinding

參考文獻

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