霸刀分享-CBN刀具在何时需要更换刀
CBN是在高温高压下合成的，其硬度仅次于金刚石，而且热稳定性远高于金刚石，化学稳定性好，和铁系金属元素在1200～1300℃时也不发生化学反应，因此CBN刀具主要应用于黑色金属材料，如铸铁/钢的高硬度难加工材料领域。
CBN刀具在加工过程中，根据加工工况可分为连续切削和断续切削，根据工况不同，其CBN刀具的换刀因素也不同，如连续切削中常见的换刀形式是磨损，而断续切削中常见的换刀形式有崩刃，裂纹等。下面小编就着重介绍一下CBN刀具断续切削时的换刀形式。
1.崩刃
这是CBN刀具断续切削钢和铸铁时常见的一种破损形式。它是在切削刃上产生的小缺口，刀刃上几个小缺口或被崩掉一小块。一般缺口尺寸与进给量相当或者稍大一些。如微崩刃的刀具在允许的磨损限度内还能继续切削，超差则需要更换。
2.剥落
端铣钢和铸铁时，在前刀面上常出现贝壳状的剥落。CBN刀具端铣淬硬钢(HRC58-65)时，前刀面上产生的较大面积的贝壳状剥落，出现此类磨损，可通过提高切削速度、降低进给量、使用有负倒棱，刃口经过钝化处理的刀片。
3.碎断
CBN刀具连续切削高硬度材料或者断续切削工件时常发生的破损形式，这是由于断续切削高硬度工件时冲击载荷过大、短时间切削后即发生的早期破损，虽然切削条件适当，但切削较长时间后，没有及时换刀，由于刀具材料疲劳就发生了这种大块的断裂。
4.裂纹
CBN刀具在较长时间的断续切削后，有因机械冲击而引起的平行于切削刃的机械疲劳裂纹，也有因热冲击而引起的垂直于或倾斜于切削刃的裂纹。当这些裂纹不断扩展合并后，就引起刀刃碎裂或断裂。
Ba Dao Sharing- When does the CBN tool need to be replaced
CBN is synthesized under high temperature and high pressure. Its hardness is second only to diamond, and its thermal stability is much higher than that of diamond. It also has good chemical stability and does not undergo chemical reactions with iron-based metal elements at 1200 to 1300℃. Therefore, CBN tools are mainly used in the field of high-hardness and difficult-to-machine ferrous metal materials, such as cast iron and steel.
During the processing of CBN tools, they can be classified into continuous cutting and intermittent cutting based on the processing conditions. Depending on the different working conditions, the tool changing factors of CBN tools also vary. For instance, the common tool changing form in continuous cutting is wear, while in intermittent cutting, the common tool changing forms include chipping and cracking. Below, the author will focus on introducing the tool changing forms when CBN tools are used for intermittent cutting.
1. Chipping of the blade
This is a common form of damage when CBN tools intermittently cut steel and cast iron. It is a small notch produced on the cutting edge, several small notches on the cutting edge or a small piece is chipped off. Generally, the notch size is comparable to or slightly larger than the feed rate. If the tool with micro-chipping can continue to cut within the allowable wear limit, it needs to be replaced if the wear exceeds the limit.
2. Peeling
When milling steel and cast iron, shell-like spalling often occurs on the rake face. When milling hardened steel (HRC58-65) with CBN tools at the end, a large area of shell-like spalling occurs on the rake face. Such wear can be achieved by increasing the cutting speed, reducing the feed rate, and using inserts with negative chamferes and blunting edges.
3. Breakage
The common form of damage that occurs when CBN tools continuously cut high-hardness materials or intermittently cut workpieces is due to excessive impact loads during intermittent cutting of high-hardness workpieces. Early damage occurs after a short period of cutting. Even if the cutting conditions are appropriate, if the tool is not changed in time after a long period of cutting, large block fractures occur due to the fatigue of the tool material.
4. Crack
After a long period of intermittent cutting, CBN tools may have mechanical fatigue cracks parallel to the cutting edge caused by mechanical shock, as well as cracks perpendicular to or inclined to the cutting edge caused by thermal shock. When these cracks continue to expand and merge, they cause the blade to shatter or break.