Development And Application Of Advanced Tool Materials, coated carbide, cermets, coronite, high performance ceramics ~ MECHTECH GURU

Development And Application Of Advanced Tool Materials, coated carbide, cermets, coronite, high performance ceramics

 Development And Application Of Advanced Tool  Materials: 
  •    Coated carbides 
The properties and performance of carbide tools could be substantially improved by
1.       Refining microstructure 
2.      Manufacturing by casting – expensive and uncommon 
3.      Surface coating – made remarkable contribution. 
 Thin but hard coating of single or multilayers of more stable and heat and wear resistive materials like TiC, TiCN, TiOCN, TiN, Al2O3 etc on the tough carbide inserts (substrate) by processes like chemical Vapour Deposition (CVD), Physical Vapour Deposition (PVD) etc at controlled pressure and temperature enhanced material removal rate (MRR) and overall machining economy remarkably enabling,
  • reduction of cutting forces and power consumption 
  •  increase in tool life (by 200 to 500%) for same VC or increase in VC (by 50 to 150%) for same tool life 
  •  improvement in product quality 
  •  effective and efficient machining of wide range of work materials 
  •  pollution control by less or no use of cutting fluid through 
Ø reduction of abrasion, adhesion and diffusion wear 
Ø  reduction of friction and BUE formation 
Ø  heat resistance and reduction of thermal cracking and plastic deformation.
The cutting velocity range in machining mild steel could be enhanced from 120 ~ 150 m/min to 300 ~ 350 m/min by properly coating the suitable carbide inserts. About 50% of the carbide tools being used at present are coated carbides which are obviously to some extent costlier than the uncoated tools. Different varieties of coated tools are available. The appropriate one is selected depending upon the type of the cutting tool, work material and the desired productivity and product quality. The properties and performances of coated inserts and tools are getting further improved by;

  • Refining the microstructure of the coating
  • Multilayering (already upto 13 layers within 12 ~ 16μm)                                      
  •  Direct coating by TiN instead of TiC, if feasible 
  •  Using better coating materials. 

  • Cermets 
These sintered hard inserts are made by combining ‘cer’ from ceramics like TiC, TiN orn ( or )TiCN and ‘met’ from metal (binder) like Ni, Ni-Co, Fe etc. Since around 1980, the modern cermets providing much better performance are being made by TiCN which is consistently more wear resistant, less porous and easier to make. The characteristic features of such cermets, in contrast to sintered tungsten carbides, are :

  •   The grains are made of TiCN (in place of WC) and Ni or Ni-Co and Fe as binder (in place of Co)
  • Harder, more chemically stable and hence more wear resistant 
  • More brittle and less thermal shock resistant
  •  Wt% of binder metal varies from 10 to 20% 
  • Cutting edge sharpness is retained unlike in coated carbide inserts
  •  Can machine steels at higher cutting velocity than that used for tungsten carbide, even coated carbides in case of light cuts. 
Application wise, the modern TiCN based cermets with bevelled or slightly rounded cutting edges are suitable for finishing and semi-finishing of steels at higher speeds, stainless steels but are not suitable for jerky interrupted machining and machining of aluminium and similar materials. Research and development are still going on for further improvement in the properties and performance of cermets. 
  •   Coronite 
It is already mentioned earlier that the properties and performance of HSS tools could have been sizeably improved by refinement of microstructure, powder metallurgical process of making and surface coating. Recently a unique tool material, namely Coronite has been developed for making the tools like small and medium size drills and milling cutters etc. which were earlier essentially made of HSS. Coronite is made basically by combining HSS for strength and toughness and tungsten carbides for heat and wear resistance. Microfine TiCN particles are uniformly dispersed into the matrix. Unlike a solid carbide, the coronite based tool is made of three layers; 
  •  the central HSS or spring steel core 
  •  a layer of coronite of thickness around 15% of the tool diameter 
  •  a thin (2 to 5 μm) PVD coating of TiCN.                                                                                                                                                                                                                                        Such tools are not only more productive but also provides better product quality. The coronite tools made by hot extrusion followed by PVD-coatring of TiN or TiCN outperformed HSS tools in respect of cutting forces, tool life and surface finish. 
  •   High Performance ceramics (HPC) 
Ceramic tools as such are much superior to sintered carbides in respect of hot hardness, chemical stability and resistance to heat and wear but lack in fracture toughness and strength.

     Through last few years remarkable improvements in strength and toughness and hence overall performance of ceramic tools could have been possible by several means which include;
  •   Sinterability, microstructure, strength and toughness of Al2O3 ceramics were improved to some extent by adding TiO2 and MgO 
  •  Transformation toughening by adding appropriate amount of partially or fully stabilised zirconia in Al2O3 powder 
  •  Isostatic and hot isostatic pressing (HIP) – these are very effective but expensive route
  • Introducing nitride ceramic (Si3N4) with proper sintering technique – this material is very tough but prone to built-up-edge formation in machining steels 
  •  Developing SIALON – deriving beneficial effects of Al2O3 and Si3N4 
  •  Adding carbide like TiC (5 ~ 15%) in Al2O3 powder – to impart toughness and thermal conductivity 
  •  Reinforcing oxide or nitride ceramics by SiC whiskers, which enhanced strength, toughness and life of the tool and thus productivity spectacularly. But manufacture and use of this unique tool need specially careful handling 
  •  Toughening Al2O3 ceramic by adding suitable metal like silver which also impart thermal conductivity and self lubricating property; this novel and inexpensive tool is still in experimental stage.                                                                                                                                The enhanced qualities of the unique high performance ceramic tools, specially the whisker and zirconia based types enabled them machine structural steels at speed even beyond 500 m/min and also intermittent cutting at reasonably high speeds, feeds and depth of cut. Such tools are also found to machine relatively harder and stronger steels quite effectively and economically. 

Next Post »