Introduction
The Specificity of Wood Machining Tools and the Choice of Nitriding Technology
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application of very high rate of feed,
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extremely sharp cutting edges of the tools,
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intensive abrasive wear and high working temperature,
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low thermal conductivity and high anisotropy of mechanical properties of the machined material.
The Aim and the Scope of the Research
Experimental
The ASPN Device and Nitrided Tools
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system of gaseous atmosphere supply and evacuation containing gas inlet located axially under the upper cover of the chamber, gas deflector of a diameter of 660 mm and gas outlet located axially in the center of the worktable,
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system of discharge electrodes containing mesh active screen (cathode) 620 mm in diameter and 490 mm high and the anode of a diameter of 720 mm,
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worktable of a diameter of 600 mm,
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substrate holder.
Development and Optimization of the ASPN Process Parameters
Parameter value level | Parameter | |||
---|---|---|---|---|
Nitriding phase duration, h | Atmosphere composition, % | BIAS voltage, V | Substrate temperature, °C | |
Level 1 | 4 | 25% N2/50% H2/25% Ar | −100 | 500 |
Level 2 | 5 | 50% N2/50% H2/0% Ar | −150 | 525 |
Level 3 | 6 | 75% N2/25% H2/0% Ar | −200 | 550 |
Phase of the process | Parameter | Value |
---|---|---|
Heating | Atmosphere pressure | 2 hPa |
Atmosphere composition | 80% Ar/20% H2
| |
Atmosphere total flow | 1000 mL/min | |
Nitriding | Atmosphere pressure | 2 hPa |
Atmosphere total flow | 1600 mL/min | |
Cooling | Atmosphere pressure | 2 hPa |
Atmosphere composition | 100% Ar | |
Atmosphere total flow | 800 mL/min |
Process number | Parameter values | |||
---|---|---|---|---|
Nitriding phase duration, h | Atmosphere composition, % | BIAS voltage, V | Substrate temperature, °C | |
Process 1 | 4 | 25% N2/50% H2/25% Ar | −100 | 500 |
Process 2 | 4 | 50% N2/50% H2/0% Ar | −150 | 525 |
Process 3 | 4 | 75% N2/25% H2/0% Ar | −200 | 550 |
Process 4 | 5 | 25% N2/50% H2/25% Ar | −150 | 550 |
Process 5 | 5 | 50% N2/50% H2/0% Ar | −200 | 500 |
Process 6 | 5 | 75% N2/25% H2/0% Ar | −100 | 525 |
Process 7 | 6 | 25% N2/50% H2/25% Ar | −200 | 525 |
Process 8 | 6 | 50% N2/50% H2/0% Ar | −100 | 550 |
Process 9 | 6 | 75% N2/25% H2/0% Ar | −150 | 500 |
Parameter value level | Parameter | ||
---|---|---|---|
Nitriding phase duration, h | Atmosphere composition, % | Atmosphere pressure, hPa | |
Level 1 | 4 | 20% N2/30% H2/50% Ar | 2 |
Level 2 | 5.5 | 25% N2/25% H2/50% Ar | 3.5 |
Process number | Parameter values | ||
---|---|---|---|
Nitriding phase duration, h | Atmosphere composition, % | Atmosphere pressure, hPa | |
Process 1 | 4 | 20% N2/30% H2/50% Ar | 2 |
Process 2 | 4 | 25% N2/25% H2/50% Ar | 3.5 |
Process 3 | 5.5 | 20% N2/30% H2/50% Ar | 3.5 |
Process 4 | 5.5 | 25% N2/25% H2/50% Ar | 2 |
Investigation of the Nitrided Layers Properties
Results and Discussion
Results of the First Series of Experiments Executed According to Taguchi’s Orthogonal Table L9 (34)
Results of the Second Series of Experiments Executed According to Taguchi’s Orthogonal Table L4 (23)
Process number | Layer thickness, μm | Surface hardness HV10 | Maximum hardness HV0.05max | Fracture toughness (K
Ic), MN/m3/2
|
---|---|---|---|---|
Process 1 | 31.0 | 888 | 1185 | 18.33 |
Process 2 | 11.0 | 832 | 941 | 38.78 |
Process 3 | 16.4 | 849 | 992 | 38.72 |
Process 4 | 48.3 | 996 | 1318 | 16.50 |
Final Adjustment of the ASPN Process Parameters for Planing Knives Made from High Speed Steel
Process number | Parameter values | ||
---|---|---|---|
Nitriding phase duration, h | Atmosphere composition, % | Atmosphere pressure, hPa | |
Process V1 | 6 | 25% N2/25% H2/50% Ar | 2.5 |
Process V2 | 6.5 | 25% N2/25% H2/50% Ar | 2.3 |
Process V3 | 7 | 25% N2/25% H2/50% Ar | 2.3 |
Process V4 | 6 | 20% N2/30% H2/50% Ar | 2.5 |
Process V5 | 6.5 | 20% N2/30% H2/50% Ar | 2.5 |
Process V6 | 7 | 20% N2/30% H2/50% Ar | 2.5 |
Verification of the Created Nitrided Layers in the Sharpening Operation
Process number | Fracture toughness coefficient K
Ic, MN/m3/2
| Maximum spalling depth, μm | Type of spalling |
---|---|---|---|
Process V1 | 21.35 | 17.7 | Continuous |
Process V2 | 18.76 | 25.1 | Continuous |
Process V3 | 17.82 | 18.0 | Continuous |
Process V4 | 28.78 | 15.0 | Local |
Process V5 | 21.05 | 17.0 | Continuous |
Process V6 | 20.32 | 16.1 | Continuous |
Conclusions
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the total thickness of the nitrided layer is determined mainly by the substrate temperature and the pressure of the gaseous atmosphere, process duration and atmosphere composition have moderate effect, while the effect of the substrate BIAS is insignificant;
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the thickness of the compound layer is determined first of all by the composition of the gaseous atmosphere;
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the fracture toughness of the nitrided layer, which is critical for the performance of the planing knives, is almost completely determined by one process parameter—atmosphere pressure;
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in the ASPN processes optimized for planing knives, higher pressure and low nitrogen content should be applied in order to achieve high fracture toughness of the tools, whereas the thickness and surface hardness of the nitrided layer should be improved by increasing process duration.