Page 80 - Demo

78 ISCAR BRAZED TOOLSBrazed ToolsWe%u2019re all acquainted with carbide tipped drills for drilling holes in concrete, for household use. This drill gives a good example of a brazed tool. This tool has a steel body and a carbide cutting tip that is brazed onto the body.The %u201cgolden age%u201d of brazed tools in metalworking (Fig. 10.1) ended when cemented carbides (hard metals) were introduced featuring indexable carbide inserts.Fig. 10.1. Typical brazed tools. These tools prevailed in the carbide tool design for a long time.When compared to solid carbide tool designs, the brazed tool concept, much like tools with indexable carbide inserts, enables the effective utilization of cemented carbides - expensive cutting material. In addition, this concept ensures high accuracy because the tool cutting edge is formed by grinding. A worn tool can be reground. These are the main advantages of brazed tools. At the same time, there are disadvantages that eventually lead to limited use of the brazed tool concept.Brazed or Soldered?Principally, brazing and soldering relate to the same process: joining various materials together using a molten metal (filler) between these parts, while the filler has a lower melting point than the joined materials. The main difference between brazing and soldering is the process operating temperature, which is lesser for soldering, and the type of a metal filler. A brazed joint usually features higher strength when compared with a soldered connection. When related to cutting tools, using the term %u201cbrazed%u201d is more correct.The weakest point of the concept is the brazing process itself. This process requires heating the parts that are intended to be joined by use of the brazing process. The thermal-expansion coefficient of cemented carbides is substantially lower when compared to steel. This difference results in considerable tension stresses in the carbide tip%u2019s, and poses risk of breakage.Grinding plane surfaces with short carbide tips of a brazed tool creates no problems but generating a complex tip surface by grinding faces difficulties. This limits an effective chip former on the top section in comparison with indexable inserts.Manufacturing brazed tools is a complex and time-consuming process which demands special equipment. Despite the undoubted progress in brazing technology, a brazed connection requires thorough post-brazing inspection and strength tests.