Modeling Notch Wear of Ceramic Tool in High Speed Machining of Nickel-based Superalloy

On the basis of theoretical analyses and calculations of high speed continuous impact force and tool notch surface temperature acted upon by burr and serrated chip edge, a notch wear model of low stress value and temperature impact fatigue was established. Saw-tooth-shaped burr and fin-shaped chip edge continuously impacts the rake face and flank face at high speed and high fre-quency, which results in a V-shaped notch wear. An experiment was done to validate that the saw-tooth-shaped burr does affect the notch wear. This model can be utilized to solve reasonably many problems that cannot be explained by any other theoretical assumptions.

An Experiment to Explain Depth of Cut Notch Wear of Ceramic Tools in Ni- based Super-alloy Machining

Inconel 718, a high temperature alloy, is extensive ly used in aircraft, gas engines and nuclear-power plants. It is generally known that the life of ceramic cutting tools in machining Inconel 718 is often restric ted by depth-of-cut (DOC) notch wear. In view of the number of various factors involved and the variety of tool materi als and cutting conditions available, the analysis of the DOC notch wear is very difficult. According to previous work concerning the DOC notch wear of ceramics tools, some Al 2O 3 - and Si 3N 4 -based ceramics tools have show n that the degree of tool notching depends on the thermal shock resistance of a tool material and thermal gradients (interrupted cutting, use of flood coolants) . Other observations suggest that there are chemical interactions between the to ol material and the work-piece. At the same time, an analytical technique based on thermodynamic properties for estimating cutting tool wear was proposed. Howe ver, so far, there is no concrete and convincing explanation for the DOC notch w ear. In all previous studies on the DOC notch wear, it is often assumed that notch we ar happened in the contacting region of the cutting tool and the work-piece, wh ile the exact position of notch wear is always neglected. In his article, He Ning measured the distance l n between tool nose and the center of DOC notch wear, and calculated the theoretical working length l d ― the ideal distance between the DOC notch center and the intersection of th e theoretical depth of cut line and the cutting edge. He found that l n is always greater than l d. It means that the position of the DOC notch is not at the depth of cut line, but out of the theoretical cutting area. He supposed that the saw-tooth shaped burrs and fin-shaped chip edges cause the DOC no tch wear, because only the saw-tooth shaped burrs and fin-shaped chip edges ha ve effect on the tools at the region of notch wear. Although He described the reason of notch wear and did some theoretical analysis of it, he has not done some experiments to verify it. In this paper, an experim ent was done to verify He’s assumption about DOC notch wear. In the present exp eriment, which has been done with the ceramic inserts (LT55), Working conditions at the region of DOC notch wear were analyzed. By using a KISTLER 9265B dyn amometer, the dynamic cutting force signals in three directions were pick up. By comparison between the theoretical frequency, with which the saw-shaped burr a nd fin-shaped chip edge impact on the region of notch wear, and the experimenta l results, it can be seen that the high frequency components of dynamic cutting forces mainly result from the impact effects of the saw-shaped burr and fin-sh aped chip edge. In high speed machining of nickel based alloys, DOC notch wear of ceramic tools is mainly because the impact effect of the burr and fin-shaped chip edge causes tools to be of fatigue damage, and the adherence between tool material and work piece material changes the direction of pressure stress and makes the micro-cra ck to appear and extend quickly.

NOTCH WEAR OF MACHINING NICKEL BASED ALLOYS WITH CERAMIC TOOLS

The performances of mixed ceramic and sialon ceramic tools in machining nickel based alloy are tested.The negative cutting edge inclination and small tool lead angle are recommended for reducing ceramic tool failure. So called“notching at depth of cut”is not actually at the depth of cutting line, but out of cutting area。 The real reason of notching is caused by shocking of “sawtooth”on sawtooth- shaped burr and fin- shaped edges of chip

Wear Mechanisms of Ceramic Inserts in Machining Nickel-Based Superalloy

The performances of ceramic inserts in cutting nickel-based alloy were investigated. A new cutting test-bed was devised and used to deburr. The burr height on the working surface with notch wear in deburring cutting was compared with that in normal cutting. The impact force, impact pressure, and impact frequency of the saw-tooth-shaped chip edge on rake face and cutting edge at different speeds were calculated, and the influence of chip edge on notch wear formation was analyzed. A new tool design for reducing notch wear was presented, which is flexible and can deburr effectively.

陶瓷刀具高速切削镍基高温合金沟槽磨损试验研究

通过陶瓷刀具高速切削镍基高温合金试验,计算了不同速度下切屑毛边对刀具前刀面和切削刃的冲击频率,分析了切屑毛边对沟槽磨损形成的影响;设计了去毛刺试验台,对比分析了去毛刺切削和常规切削时待加工表面切削毛刺尺寸和刀具沟槽磨损的大小。通过扫描电镜和能谱分析,对刀具沟槽磨损部位进行了观测与分析。试验结果表明,侧向切削毛刺和锯齿状切屑毛边是造成沟槽磨损的根本原因,黏结是加速沟槽磨损的重要因素。

镍基合金高速切削中锯齿状切屑毛边和刀具磨损研究

基于等腰三角形悬臂梁切屑毛边假设,建立了切屑毛边对刀具前刀面和切削刃的冲击强度、冲击频率模型。通过该模型,计算了不同切削速度下切屑毛边的冲击强度和冲击频率;通过扫描电镜和能谱分析,对切屑底部元素和刀具表面进行了分析。结果表明,锯齿状切屑毛边是造成沟槽磨损的重要原因。

齿轮传动箱断裂失效分析及预防

齿轮传动箱在使用中产生疲劳断裂 ,通过电镜观察 ,金相检验 ,力学性能测试及力学计算等方法进行分析 ,找出了引起疲劳破坏的原因 ,并提出了改进措施。

双相耐磨钢与高锰钢疲劳性能研究

为了确保Mn-Si-Cr-B系贝氏体/马氏体(B/M)双相高强低合金铸钢代替高锰钢,用于制备履带板,对其弯曲疲劳行为与高锰钢进行了对比研究。结果表明,虽然高锰钢的韧性远高于B/M双相钢,但是B/M双相钢的疲劳极限强度高于高锰钢,其缺口敏感性低于高锰钢,加入铬钼合金化的高锰钢,其疲劳性能并没有提高。用双相耐磨铸钢代替高锰钢铸造履带板,其疲劳寿命是有保证的。

新型超高强度钛合金大进给铣削刀具磨损机理研究

为了深入理解大进给铣削M28超高强度钛合金的刀具磨损机理,使用M35与P45硬质合金刀片进行了大进给铣削试验。试验观测了两种硬质合金刀片的磨损演变和磨损对切削力的影响,借助对磨损区域的扫描电镜观察和黏附物成分的能谱检测,分析了刀具磨损的机理。硬质合金刀片在大进给铣削M28时迅速磨损,刀片局部受到毛边与硬化层冲击发生沟槽磨损。随着刀具与黏附物间相对运动,硬质相颗粒不断被黏附物拔出,同时硬质合金基体受到剪切作用引发裂纹,最终产生片层状剥落。剥落程度的大小与硬质合金的粒度有关,由于大粒度硬质合金的耐磨性更强,P45硬质合金刀片的剥落程度相对M35更小。

金刚石压齿锯片在先进陶瓷加工中的应用评价

针对先进陶瓷材料的切割加工中存在着切割效率低、工具磨损快等问题,本文通过用金刚石压齿锯片加工氧化铝陶瓷的实验,研究锯片的磨损失效机制,探讨高效低成本的先进陶瓷切割技术。实验中用金刚石压齿锯片在不同加工条件下对氧化铝陶瓷材料和玉石进行切割加工,测量切割法向力和切向力,并跟踪锯片刃口形貌的变化及其磨损过程。实验结果表明,由于材料性质的差异,氧化铝陶瓷的切割力和力比均要明显大于玉石。锯片的磨损是由于该类型锯片的刃口上金刚石磨料浓度太低,而且结合剂的把持力不足导致金刚石大量脱落而失效的,并造成金属基体与工件间的摩擦加剧,切割比能也相应增加。

硬质合金材料及其涂层对不锈钢加工中刀具边界磨损的影响

硬质合金刀具在不锈钢加工中，其刀具耐用度主要是取决于后刀面边界磨损而不是主切削刃后刀面的平均磨损量。为了提高刀具耐用度，就必须减小后刀面边界磨损。本文对奥氏体不锈钢（ＳＵＳ３０４） 在车削及铣削加工中，采用Ｍ２０ 、Ｋ２０ 和Ｚ２０ 材料以及ＴｉＮ、Ｔｉ（Ｃ，Ｎ） 和（Ｔｉ，Ａｌ）Ｎ

精密切削纯铁材料硬质合金刀具刃口磨损特征演化

为研究纯铁材料精密切削时刀具刃口磨损特征演化规律,以涂层硬质合金刀具为研究对象进行纯铁材料精密切削试验。结果表明:涂层硬质合金刀具精密切削纯铁材料的磨损特征有后刀面均匀磨损带、主沟槽磨损、副沟槽磨损、刀尖磨损;主、副沟槽磨损长度都随着切削时间增加而增大且大于后刀面磨损量,沟槽磨损深度与沟槽磨损长度大致呈线性正相关;刀尖退化与后刀面磨损变化规律相互对应,切削初期磨损率大,随后磨损缓慢。