整合均勻設計及克利金插值法於鎢鐵粉燒結放電加工之表面鍍層參數最佳化設計

Optimal Parameters for SurfaceModification by W-Powder SinterElectrical Discharge Machining withApplication of Uniform Design andKriging Interpolation Methods

本文首先選用U15*(157)均勻設計表，以鎢鐵壓粉體之壓力、鎢鐵粉之比例、放電持續之時間和放電電流大小作為控制因子，並以均勻實驗設計表規畫出4 因子15 水準的實驗組合，製作高溫燒結壓粉體電極並對模具鋼實行放電加工，並利用掃描式電子顯微鏡、洛氏硬度實驗機量測鍍層分佈率及洛氏硬度之數據。以克利金插值法，依實驗數據建立鍍層分佈率及洛氏硬度之克利金反應曲面模型。將克利金反應曲面視為目標函數，以非線性規劃法求解鍍層最大分佈率及洛氏硬度最大之最佳參數組合，經實驗驗證後得出以下的研究結果：1. 高溫燒結壓粉體電極對模具鋼放電經由均勻表實驗完成後，其最高的鎢粉層分布率為79.9%。將U15*(157)所得的數據應用克利金差值法建立出鎢粉層分布率反應曲面後再以非線性規劃法最大化鎢粉層分布率，得到的最佳之參數是壓粉體壓力785.8Kg、鎢鐵粉比例5.6g：1.4g、放電持續時間275s、放電電流5.61A。此最佳參數經實驗驗證，其鎢粉分布率為83.3%，提升3.34%。2. 高溫燒結壓粉體電極對模具鋼放電經由均勻表實驗完成後，其最高的洛氏硬度為HRC11。將U15*(157)所得的數據應用克利金差值法建立出洛氏硬度反應曲面再以非線性規劃法找最大化洛氏硬度，得到的最佳參數是壓粉體壓力1236.9Kg、鎢鐵粉比例5.63g：1.37g、放電持續時間371s、放電電流11.12A。此最佳參數經實驗驗證，其洛氏硬度值為HRC11.3，提升0.3。本研究顯示將均勻實驗設計、克利金插值法結合應用，於壓粉體燒結放電加工可得到最佳表面鍍層及最大硬度的品質特性，以所得之最佳化可提供業界參考並建立資料庫。

In this study, the U15*(157) uniform design table was selected to plan experiments with4 control factors and 15 levels. The four factors are the pressure of W-Fe electrode,percentage ratio of W-Fe powder, duration of discharge pulse, and discharge pulse current.The surface modification was conducted for SKD11 tool steel made from mixture powderof tungsten and iron in Wolfram Powder Sinter followed by Electrode DischargeMachining (EDM). The result data of experiments were measured by scanning electronmicroscopy (SEM) and Rockwell hardness testing.Based on the input and output data of experiments and Kriging interpolation method,the Kriging response surface models of tungsten powder percentage and the Rockwellhardness were created. By letting the Kriging models be the objective functions andapplying nonlinear programming method, the following results were obtained:1. In the 15 uniform experiments, the highest tungsten powder percentage is 79.9%.After applying Kriging interpolation and optimization, the optimal processparameters are as follows: powder pressure is 785.8kg, percentage ratio of W-Fepowder is 5.6g: 1.4g, discharging duration time is 275S, and discharging current is5.61A. The optimal result of tungsten powder percentage is 83.3%. The improvedrate of tungsten powder percentage was 3.34%.2. In the 15 uniform experiments, the highest Rockwell hardness is HRC11. Afterapplying Kriging interpolation and optimization, the optimal process parametersare as follows: powder pressure is 1236.9kg, percentage ratio of W-Fe powder is5.63g: 1.37g, discharging duration time is 371S, and discharging current is 11.12A.The optimal result of Rockwell hardness is HRC11.3. The improved rate ofRockwell hardness is 0.3.This study has demonstrated that the integration of Uniform design method andKriging interpolation method is able to achieve the optimization of surface modification ofSKD11 tool steel made from mixture powder of tungsten and iron in Wolfram PowderSinter with verification by experimental measurements. The industry can use the optimizedparameters for reference to create the database.