伺服數控電動壓床壓型參數最佳化以改善碳化鎢超硬合金燒結後品質不良之研究

The Optimization Study of Pressing Parameters for Tungsten Carbide Hard Metals using Servo-motorized Electric press to Improve Product's Quality after Sintering

廖明輝(Ming-hui Liao)

指導教授 ： 傅尹坤

國立中央大學/工學院/機械工程研究所碩士在職專班/碩士(2015年)

摘要

WC-Co系鈷基碳化鎢超硬合金已被廣泛地使用在金屬切削及耐磨耗產品的應用；碳化鎢(WC)提供必需的硬度及耐磨耗性，而鈷(Co)則做為結合碳化鎢金屬並提供合金所需的韌性與延展性。碳化鎢超硬合金在應用時，具有良好的抗腐蝕性、硬度與耐磨耗性；但在粉末冶金產業，以傳統機械與油壓壓床生產碳化鎢超硬合金時，面臨的生產技術瓶頸主要有三:
一、壓型產品在燒結後破裂不良
二、壓型產品在燒結後尺寸精度不良
三、壓型產品在燒結後變形導致矩型度不良
本研究在探討個案公司在引進新型伺服數控電動壓床後，應用並發揮伺服數控電動壓床的模具動作曲線模擬與智慧程式產生器功能，同時結合有限元素分析法的模流分析及以田口方法與反應曲面法來進行穩健實驗設計，進行壓型參數最佳化實驗，成功克服上述三項粉末冶金產業碳化鎢超硬合金生產三大技術瓶頸。實驗結果顯示:

一、 改善產品在燒結後破裂不良之壓型參數最佳化

運用伺服數控電動壓床的模具動作曲線紀錄與模擬功能，並應用有限元素分析的模流分析結果，即產品會產生破裂的區域是在密度變化梯度較大區域而不是在密度最大區域。調整模具動作曲線加入欠充填動作及同步加壓動作及兩段保壓動作，以降低應力及密度變化。另外將送料鞋填粉，由原本單次填粉改為兩次填粉則可改善粉末填粉至中模模穴均勻性。在壓型初期粉料鬆動的時候，模具的作動與移動方式對產品成形後是否會破裂的影響不大，但當粉末密度於壓型過程逐漸加大後，在壓型過程最後階段同步控制上沖頂壓向下與中模浮動向上，精確控制模具彼此之間動作曲線的互動與調整，對產品燒結後是否破裂的影響最大也最為關鍵。

二、 改善產品在燒結後尺寸精度不良之壓型參數最佳化

運用田口方法與反應曲面法來進行壓型參數最佳化設定，改善刮刀產品在燒結後的產品精度，最佳壓型參數條件為壓高H=3.5 mm、壓重W=22.445 g，可得到符合公差長度 50.1–50.4 mm的 L平均燒結後長度50.18 mm 至50.32 mm。經由變異數分析，粉料變異的顯著值遠大於壓高與壓重變異之顯著值，故粉料變異對燒結後L長度之影響可被忽略。經由最佳化壓型參數設定，在燒結後產品L長度即可進入公差，減少需加工研磨長度進公差的二次加工成本及減少因長度小於50.1 mm造成的產品剔退成本。

三、 改善產品在燒結後變形矩型度不良之壓型參數最佳化

經由應用伺服數控電動壓床之模具動作曲線模擬功能及相關壓型參數設定之最佳化，改善鎚頭產品在燒結後的矩型度不良，最佳壓型參數條件為在正向送料鞋方向、產品斜面放在碳板接觸面及不要放氧化鋁紙、仿形充填dx3及dx4調整為70%以調整模穴前後之填粉量改善填粉不均問題、調整模具動作曲線設定，增加粉末在中模中間填粉量並增加上沖壓力。同時，經由本研究發現，產品矩型度及平整度主要受產品燒結方向影響，在產品與碳板接觸面放氧化鋁紙，雖可改善產品表面的凹凸不平，但卻會造成產品在燒結後容易變形而影響到產品的矩型度。

關鍵字

碳化鎢超硬合金 ； 伺服數控電動壓床 ； 模具動作曲線 ； 田口方法 ； 反應曲面法 ； 液相燒結

並列摘要

Due to the high hardness and wear resistance, WC–Co cemented carbides have been used extensively for metal cutting and wear application tool materials in the manufacturing industry; Tungsten carbide (WC) offer essential hardness and abrasion resistance, and cobalt (Co) as combining tungsten carbide and offering toughness that the cemented carbide needs . The ultra hard alloy of tungsten carbide has good hardness,corrosivity and abrasion resistance; But in the powder metallurgy industry, while producing cemented carbide with the traditional mechanical presses or hydraulic presses, the production technology bottlenecks faced are mainly three: First, the product’s cracking defect after sintering Second, the product’s size defect after sintering due to shrinkage Third, the product’s deformation after sintering cause squareness defect

This research is to study the case company after introducing new servo-motorized electric press , how to employ the servo numerical control function for upper punch, die and core rod movement curve simulation and intelligence program generator function , combine with finite element method modeling simulation ,Taguchi method and respond surface methodology for robust experimental design , after carry on the pressing parameter optimization experiment, succeed in overcoming above-mentioned powder metallurgy three technical bottlenecks for cemented carbide production. The following conclusions can be drawn based on the experimental results in this study.

First, improving the product’s cracking defect after sintering by pressing parameter optimization
Using servo-motorized electric press servo numerical control function for upper punch, die and core rod movement curve simulation ,apply the findings of FEM modeling for spray nozzle density distribution related to cracking, put into under filling movements and pressurize synchronously movements and two section holding pressure that can reduce stress and density change during blank compacting period . Besides, modify powder feeding shoes to fill out powder by twice can help to improve powder filling density uniform, in the early pressing stage which powder is still loose , the movement and interaction of the die and upper punch have little effect on product for whether have cracking defect after sintering, but when the powder density gradually increasing while pressing period, especially in the final stage , the synchronization control upper punch top pressing down and die of floating upward, precisely control and adjustment of interaction between the punch and die movement curve ,is the most critical point for spray nozzle product whether have cracking defect after sintering .

Second, improving the product’s size defect after sintering by pressing parameter optimization
Taguchi method and Response Surface Methodology(RSM) was employed to analyze and optimize pressing parameter for conveyor scraper and improve the L size precision of the scraper product after sintering, the best pressing parameter decided by dual response surface methodology are pressing height H =3.5 mm and pressing weight W =22.445 g, can get L length from 50.18 mm to 50.32 mm which meet with the length tolerance between 50.1-50.4 mm. Via Analysis of Variance (ANOVA) analyzing showing significance value of powder variation value is far greater than pressing high and pressing weight significance value , so the powder variation can be neglected to the influence of L length after sintering. Set up the tooling movement curve via the optimization pressing parameter, the conveyor scraper product’s L length can meet the size tolerance after sintering, so can reduce the re-grinding cost for L size larger than 50.4 mm and reduce the L size defect scrap lost amount for L size smaller than 50.1 mm.

Third, improving the product’s squareness defect after sintering by pressing parameter optimization
The action will be applied via using servo-motorized electric press numerical control function for punch and die movement curve simulation to improve the hammer product’s squareness defect after sintering, the best pressing parameters are as following: powder feeding shoe should be the forward direction, put the inclined plane of the hammer product on the contact surface of the graphite tray, do not put aluminum paper, adjust profile filling dx3 and dx4 parameter as 70% to adjust the amount of powder to fill before and after the die cavity and thus can improve the problem of uneven powder filling, adjust the die movement curve setting, increase powder filling in the middle of the die and increase the upper punch pressure. At the same time, through this study found that the hammer product’s squareness and flatness after sintering are mainly affected by product’s contact surface and direction related to graphite tray, put aluminum paper on product’s contact surface with graphite tray, although the uneven surface of the product can be improved, but it will cause the product after sintering easily deformed and affect squareness of the product.

並列關鍵字

Tungsten Carbide Hard Metals ； Servo-motorized Electric Press ； Tool Pressing Movement Curve ； Taguchi Method ； Response Surface Methodology ； Liquid -Phase Sintering

參考文獻

[36] 張伯瑜，「真空燒結及熱均壓處理對奈米碳化鎢超硬合金燒結性質與

[37] Akshay Kumar, K. Singh and O.P. Pandey, "Sintering behavior of

[20] Cong Mao & Yinghui Ren & Hangyu Gan & Mingjun Zhang & Jian Zhang

[29] Henderson RJ, Chandler HW, Akisanya AR, Chandler CM, Nixon

functionally gradient WC–Co composites”, Int. Journal of Refractory