摘要
在加工过程中,相反的两相特性增加了SiCp/Al复合材料加工难度,难以获得良好的表面质量。为了提高其切削性能,本文开展20vol%SiCp/Al复合材料铣削加工试验研究,比较常温和低温条件下TiAlN涂层和TiAlSiN涂层两种铣刀的切削性能。结果表明,在低温条件下,两种刀具的切削力增加,铣削后表面铝基体的开裂及剥落等缺陷均显著改善,加工表面损伤减小且粗糙度降低,低温铣削能获得更好的表面质量。此外,在常温与低温条件下TiAlSiN涂层比TiAlN涂层铣刀的切削力小,低温条件下TiAlSiN涂层铣刀表面完整性和切屑形貌优于TiAlN涂层铣刀。
关键词
SiCp/Al具有优良的力学强度、韧性、耐磨性等,受到了航空航天、汽车制造业等高新技术领域的广泛关
SiCp/Al复合材料的加工一般采用干切削,切削热成为影响加工质量的关键因素。以液氮作为冷却介质的低温加工是一种清洁切削技术,在提高难加工材料的表面质量与加工效率等方面具备独特优
涂层刀具是将刀具基体与硬质薄膜表层接合,可有效减少刀具切削力、切削热、表面粗糙度及加工振
在立式精密加工中心(ACE-V45,DAEWOO)上进行铣削试验,使用的铣刀为TiAlN与TiAlSiN涂层球头铣刀,其牌号分别是AMB2060TTT5515和HSB2060S090170TT5505,除了涂层材料不同外,两把刀具的几何结构参数一致。铣削过程中产生的铣削力由安装在机床上的Kistler dynamometer 9256C2 测力仪测量。
本试验采用搅拌铸造工艺制备的20vol%SiCp/Al复合材料,SiC的平均粒径约为15 μm,铝合金基体材料为Al-Zn-Mg-Cu系列超高强度铝合金。工件尺寸8 mm×20 mm×10 mm,将工件从两端夹紧(
图1 液氮喷淋铣削装置
Fig. 1 Liquid nitrogen spray milling device
如
此外,TiAlSiN涂层的摩擦因数较
在SiCp/Al复合材料加工过程中,不仅有基体和增强颗粒的弹塑性变形,还有颗粒的断裂破坏及其对基体的挤压及耕犁。在扫描电镜下对SiCp/Al复合材料的典型表面形貌进行观察(
图2 扫描电子显微镜下铣削表面损伤
Fig. 2 Milling surface damage under SEM
常温条件下TiAlN涂层刀具与TiAlSiN涂层刀具引起的表面损伤程度相似,都能观察到深的裂纹、基体开裂及较大的基体剥落,表面质量相差不大。但低温下TiAlSiN涂层刀具引起的表面损伤明显减少,能观察到孔洞、裂纹及基体开裂明显改善,这对切削加工的表面质量的控制非常有利。
图3 铣削表面三维轮廓
Fig. 3 Three-dimensional profile of milling surface
经过对两种刀具加工表面轮廓的对比后,发现低温条件下表面损伤明显减少,获得的平均表面粗糙度明显优于常温条件下获得的平均表面粗糙度。低温条件下使用TiAlSiN涂层铣刀加工的表面粗糙度值最低,质量最优。加工表面的扫描电镜特征(
为了研究低温对切屑形貌的影响,使用扫描电子显微镜对常温及低温条件下的切屑进行了观察。如
图4 切屑形态及其内表面微观形貌
Fig.4 Macro morphology of chip and the micro morphology of its non-free surface
通过观察
(1)在低温条件下TiAlN和TiAlSiN两种涂层铣刀获得的铣削力要高于常温条件下的铣削力,分别提高了25.6%和23.7%。无论常温还是低温条件下,TiAlSiN涂层刀具的铣削力均小于TiAlN涂层刀具的铣削力。
(2) 与常温条件相比,低温条件铣削后表面铝基体的开裂及剥落等缺陷均显著改善,表面损伤较小。常温条件下,TiAlN涂层刀具与TiAlSiN涂层刀具引起的表面损伤程度相似,但在低温条件下TiAlSiN涂层刀具引起的表面损伤明显减小。低温条件下的铣削表面粗糙度降低,使粗糙度达到0.69和0.46 μm,特别是TiAlSiN涂层刀具加工表面粗糙度最小。液氮低温铣削有助于提高SiCp/Al复合材料加工表面质量,且低温条件下使用TiAlSiN涂层刀具可大幅改善加工表面质量。
(3) 低温条件下相对常温条件下较易断屑。此外,低温条件下的切屑内表面明显优于常温条件下的切屑内表面。TiAlSiN涂层刀具加工后的切屑内表面干净光洁。
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