Tool coating principle and feasibility analysis

According to the principle of metal cutting, in normal cutting, the wear of the tool mainly includes the following types: flank wear; rake face wear, that is, crater wear;

Tool coating refers to the application of a thin layer of refractory metal or non-metallic compound with good wear resistance by vapor deposition on the surface of cemented carbide or high speed steel (HSS) substrate with good strength and toughness. A chemical barrier and thermal barrier reduce the diffusion and chemical reaction between the tool and the workpiece, thereby reducing crater wear. The coated tool has the characteristics of high surface hardness, good wear resistance, stable chemical properties, heat and oxidation resistance, low friction factor and low thermal conductivity. The picture shows the cutting conditions of coated and uncoated tools by Oerlikon Balzers.

Micro-schematic diagram of uncoated tool and coated tool cutting left: Uncoated tool, serious built-up edge due to large friction coefficient, etc. Right: Tool after coating, friction coefficient is small, no obvious built-up edge physics Vapor deposition (PVD) is a physical vapor phase reaction growth method. The deposition process is carried out under vacuum or low pressure gas discharge conditions, i.e., in a low temperature plasma. The material source of the coating is a solid material that, after "evaporation or sputtering", produces a new coating of solid material on the surface of the workpiece that is completely different from the properties of the substrate. The PVD coating materials are mainly TiN, TiCN, CrN, TiAlN, AlTiN, AlCrN, WC/C, DLC and diamond. For different application fields, different coating materials are required. The thickness of the coating is usually only a few microns and the hardness is 2 to 5 times that of steel. Oerlikon Balzers coatings invented the coating technology to replace titanium with chromium, and in 2004 launched a single-layer AlCrN coating under the trade name "Balinit Alcorna". The high red hardness of AlCrN coating keeps its performance stable under extremely high heat load. It is proved to be excellent in high speed cutting and dry (or quasi-dry) cutting conditions. The coating has high hardness and resistance. The abrasiveness makes the machinable material hardness reach HRC70.

The product material of the through-shaft is 49CrMo4. The heat treatment technical requirements are: induction hardening effect hardening layer depth 5-7mm, surface hardness 50-55HRC, heart is quenched and tempered structure, hardness requirement 35-40HRC. Theoretically, it is completely applicable to the through-axis of the coated tool after cutting heat.

A spline hob was used and the process was tested after coating with Oerlikon Balzers. The process method is as follows: hot pre-grinding outer circle C-knurling key D——after heat C straightening-heating knurling key B, the original knurling key process is transferred to heat and processed.

In the case where the original cutting parameters are constant (S=250r/min F=13m/min), the machining noise is significantly reduced. The quality of the processed products was tracked, and 10 pieces of spline spline bounce and M value fluctuations were randomly selected. It can be seen from the recorded data that the machining precision of the coated tool after hot rolling is consistent with the drawing requirements. Accuracy requirements can cancel the deviation. When the amount of variation of the M value is decreased, the amount of backlash variation after assembly with the flange is increased, thereby improving assembly precision.