Hot-press sintering is currently the most prevalent and fundamental process for manufacturing diamond saw blades, particularly those designed for cutting stone and concrete. It may be understood as a single, precise process combining forging and casting.
1. Definition of Hot Press Sintering Process
Hot press sintering technology constitutes a powder metallurgy process wherein diamond and metal matrix composite powders are subjected simultaneously to elevated temperatures and unidirectional mechanical pressure within a single hot press under a protective atmosphere. This combined thermal and mechanical action induces rapid densification, yielding fully compacted, high-strength composite tool heads. In essence, it involves 'heating and pressing concurrently to achieve single-step forming'.
2. Detailed Steps of the Hot Press Sintering Process
1) Ingredients and Mixing
Matrix powder: Typically composed of multiple metal powders. Framework materials: Tungsten, tungsten carbide, cobalt, iron powder – provide hardness and wear resistance. Binder metals: Cobalt, nickel – exhibit good wetting and retention properties for diamond. Low-melting-point metals: Copper, tin, manganese, silver, etc. – form a liquid phase during sintering to promote densification.
Diamonds: Select appropriate grade, grain size, and concentration based on the cutting material.
Thoroughly blend the matrix powders with the selected diamond particles in a mixing machine.
2) Moulding
The mixed powder is loaded into high-strength graphite moulds. Graphite moulds exhibit excellent high-temperature resistance, self-lubricating properties, and electrical conductivity.
The shape of the mould cavity determines the final dimensions and form of the cutting tool.
3) Hot Press Sintering
Placement: Position the powder-filled mould between the upper and lower press heads of the hot press sintering machine.
Evacuation or Protective Gas Flushing: Evacuate the furnace chamber or introduce hydrogen or nitrogen gas to prevent oxidation of metals and diamond at elevated temperatures.
Heating: Heat the mould and powder to the sintering temperature (typically 700°C - 1000°C) via resistance heating from the graphite mould itself or induction heating. This temperature exceeds the melting point of low-melting-point metals within the matrix but remains well below diamond's stable temperature limit (strict control is essential, otherwise diamond graphitisation occurs).
Pressurisation: Simultaneously with heating or upon reaching a specified temperature, unidirectional axial pressure (typically 10–30 MPa) is applied to the mould via a hydraulic system.
Isothermal pressure holding: Maintain the process at a predetermined temperature and pressure for a specified duration, during which critical transformations occur. A liquid phase forms, with low-melting-point metals (such as copper or tin) liquefying to create a liquid metal film enveloping solid powder particles and diamond. Under pressure and liquid-phase lubrication, solid particles undergo rearrangement and densification as they slide and reposition, filling voids. Atomic Diffusion and Alloying: Different metallic elements dissolve and diffuse within the liquid phase, forming new alloyed phases. The diamond particles are entrapped, with the molten matrix material wetting and enveloping them. Upon cooling, this process mechanically embeds the diamonds while generating chemical bonding (e.g., cobalt exhibits strong affinity for carbon within diamond).
4) Cooling and Demoulding
Cease heating and cool under pressure or after depressurisation. Remove the densely sintered, formed cutting head from the mould.
5) Subsequent Processing
After grinding and cleaning, the cutting head is bonded to a steel substrate to form a complete diamond saw blade.
