Abstract
The subject of the research is optimization of the parameters of the Active Screen Plasma Nitriding (ASPN) process of high speed steel planing knives used in woodworking. The Taguchi approach was applied for development of the plan of experiments and elaboration of obtained experimental results. The optimized ASPN parameters were: process duration, composition and pressure of the gaseous atmosphere, the substrate BIAS voltage and the substrate temperature. The results of the optimization procedure were verified by the tools’ behavior in the sharpening operation performed in normal industrial conditions. The ASPN technology proved to be extremely suitable for nitriding the woodworking planing tools, which because of their specific geometry, in particular extremely sharp wedge angles, could not be successfully nitrided using conventional direct current plasma nitriding method. The carried out research proved that the values of fracture toughness coefficient K Ic are in correlation with maximum spalling depths of the cutting edge measured after sharpening, and therefore may be used as a measure of the nitrided planing knives quality. Based on this criterion the optimum parameters of the ASPN process for nitriding high speed planing knives were determined.
Highlights
1.1 The Specificity of Wood Machining Tools and the Choice of Nitriding TechnologyThe specificity of machining conditions of wood and woodderivative materials consists of simultaneous occurrence of several factors that contribute to intensive wear of woodworking tools
Wide ranges of the values of the obtained layers properties, selected as the measures of the layers quality in the second series of experiments, i.e., the total layer thickness (11.0-48.3 lm), surface hardness (832-996 HV10) and the fracture toughness coefficient (15.50-38.78 MN/m3/2), indicate that the Active Screen Plasma Nitriding (ASPN) process is very sensitive to analyzed parameters, to the pressure of gaseous atmosphere
At higher pressure of the ASPN process the thickness and surface hardness of the nitrided layer drop significantly (Fig. 5a, b). It means that in the ASPN processes optimized for planing knives, higher pressure should be applied in order to achieve high fracture toughness of the tools
Summary
1.1 The Specificity of Wood Machining Tools and the Choice of Nitriding TechnologyThe specificity of machining conditions of wood and woodderivative materials consists of simultaneous occurrence of several factors that contribute to intensive wear of woodworking tools. Low alloy and high speed steels are common materials used for planing and shaping knives fabrication. Because of the advantageous features of these steel grades, i.e., relatively low price and easy manufacturing of special knifes, e.g., very long, with extremely low wedge angles or with special complex shapes, they cannot be replaced in many applications by any.
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