等負載銑削加工中製程參數設定策略及其對刀具壽命的影響

Abstract

隨著航太科技、電子產品、通訊設備、醫療器械與電動車產業的快速發展，近幾年來材料的銑削加工技術已被廣泛應用在這些領域的產品製程中，而自動化的加工機台必須有正確的加工條件，才能穩定的生產來創造效率，提升材料良率，降低刀具損壞或斷刀的影響，達成高經濟效率。銑削加工的參數儼然成為加工材料製程的主流研究之一。 銑削適應性控制加工是經由控制切削力，來達成恆定負載的加工。本研究就前饋控制及回饋控制建置系統進行探討，方便於日後在生產線上能實際應用。若要優化加工結果，就需了解銑削的加工機制進而透過最大進給率及最大磨耗量的估算，來設置加工參數及建立控制模型，進而得出一套銑削參數設定的策略來改善傳統銑削加工靠經驗建置加工參數的問題。本研究以刀具與工件的接觸應力模型計算刀具所能承受之最大切削力，並以主軸電流作為控制切削力的參數，建置回饋控制與前饋控制系統，在兩種不同的控制模式中調控進給率來進行適應性控制加工。並透過對刀具磨耗的監測，來研究銑削適應性控制加過程工中磨耗的機制，進一步驗證適應性控制加工參數設定的策略對改善傳統加工之刀具壽命的效果。 傳統的銑削加工方法常常是由老師傅的經驗來設定加工參數，為避免加工機器、工件及刀具的故障，會使用較為保守的固定進給率來加工。採用適應性控制在加工過程中適當調整進給率，是可以有效的提高加工效率的方法。已經有許多關於切削力適應性控制的控制器設計相關的研究，但這些研究都集中在如何調控切削力的方法上。很少討論以主軸電流作為控制切削力訊號，來建立在適應性控制中，切削力與刀具磨耗之間的關係，並作為適應性控制加工參數的設定方法。本研究提出了銑削加工的接觸應力模型假設，經由接觸應力模型來計算刀具所能承受之最大切削力，再推估出最大切削力對應的最大進給率，與相對應的最大主軸電流，由此開始進行適應性控制製程參數的設定策略，包括設定主軸參考電流及進給率上限和下限。設定主軸參考電流和進給速率上限，以維持切削力在刀具所能承受的安全值。而將進給率下限設定在刀具磨耗的安全範圍內，以避免刀具崩壞或嚴重磨耗。 在前饋與回饋控制的實驗結果皆驗證，當進給率下降至下限值時，本論文提出的參數設定方法可以使刀具磨耗維持在設定範圍內，控制良好且沒有刀具損壞。

In recent years, with the rapid progress of aerospace technology, electronic products, communication equipment, medical equipment and the electric vehicle industry, the milling processing technology of materials has been widely used in product processes in these fields. The automated machining machine must have correct processing parameters to stabilize production to create efficiency, improve the quality of materials, reduce the effects of tool damages, and achieve high economic efficiency. The parameters of this milling processing have become one of the mainstream research projects on material processing. The adaptive control of milling process is to achieve a constant load machining by controlling the cutting force. Constant load milling processing is mainly divided into feedforward control and feedback control, as well as complicated neural network control and fuzzy control. The latter two are less likely to be used at the actual application of the processing site. The feedforward control and feedback control models were studied in this dissertation. To optimize the processing results, we need to understand the processing mechanism of milling, and then set the processing parameters and establishing a model through the estimation of the maximum feedrate and maximum grinding range, thereby improving the problem of traditional milling processing parameters. In this study, the spindle current was used as the parameter for cutting force adaptive control, and feedback control and feedforward control were constructed for constant load machining. By monitoring tool wear, the mechanism of the wear process in constant load milling processing was studied. Further verified the effect of the constant load machining parameter setting strategy on improving the tool life of traditional machining. Traditional milling processing methods often set processing parameters based on the experience of master craftsmen. In order to prevent failures of processing machines, workpieces and tools, a more conservative constant feedrate is used for processing. However, the processing efficiency of this method is difficult to further improve. Using adaptive control to appropriately adjust the feedrate during processing is an effective method to improve processing efficiency. There have been many studies related to the design of controllers for adaptive control of cutting forces, but these studies have focused on how to regulate cutting forces. There is little discussion about using spindle current as a cutting force control signal to establish the relationship between cutting force and tool wear in adaptive control, and as a method for setting constant load machining parameters. This study proposed a contact stress model hypothesis for milling processing, and uses the contact stress model to calculate the maximum cutting force that the tool can withstand. Then estimate the maximum feedrate corresponding to the maximum cutting force and the corresponding maximum spindle current. From this point on, the setting strategy for the constant load process parameters was began, including setting the reference spindle current and the upper and lower limits of the feedrate. Set the spindle reference current and feedrate upper limit to maintain the cutting force at a safe value that the tool can withstand. And set the lower limit of the feedrate within the safe range of tool wear to avoid tool collapse or serious wear. The experimental results of feedforward and feedback control both verified that when the feedrate drops to the lower limit, the parameter setting method proposed in this paper can maintain the tool wear within the set range, with good control and no risk of tool damage. The set processing parameters were further used for end milling, slot milling and the mixed milling processes to verify the feasibility of simple microfluidic mold processing, and also obtain good control results. In this study, the strategy for setting constant load machining parameters proposed was superior to traditional fixed feedrate machining in terms of tool life and material removal rate. Traditional fixed feedrate milling processes estimate tool life through the cutting length. However, this study used the change in feedrate decrease to estimate the change in tool wear and predict the tool change timing. And experimental results had verified that this method had better tool life than traditional fixed feedrate milling. The experimental results of feedforward control effectively improved the poor surface finish caused by rapid up and down changes in feedrate in feedback control. The surface quality of the workpiece was better than that of traditional fixed feedrate milling. When the feedrate was reduced to reach the lower limit, the tool wear is also verified to be maintained within the set safety range, which could effectively prevent excessive wear of the tool and predict the tool replacement opportunity. The adaptive milling parameter setting strategy and stress model proposed in this study had better results in material removal rate, surface roughness and tool life than traditional fixed feedrate processing.