TECHNOLOGY OF STRENGTHENING TEETH OF MILLING CUTTER USING LIQUID NITRIDING

ABSTRACT

This article describes the technology of strengthening the teeth of milling cutters made of high-speed steel by liquid nitriding. Mainly, the influence of heat treatment and liquid nitriding processes on the hardness, strength, and formation of the carbon-nitride zone of the steel surface layer was studied. In the experiments, high-speed steels of grades R6M5 and R9F5 were taken as the basis. The results showed that as a result of 40 minutes of liquid nitriding at a temperature of 550-560 °C, a layer with high microhardness (1300-1500 HV) is formed on the steel surface. The article presents step-by-step steps for preparing cutting tools for nitriding, heat treatment, washing, cooling, and quality control. The proposed technology is important for increasing the frictional resistance of milling cutters, extending their service life, and ensuring machining accuracy.

АННОТАЦИЯ

В данной статье освещена технология упрочнения зубьев фрез из быстрорежущей стали жидким азотированием. В основном, изучено влияние процессов термической обработки и жидкого азотирования на твердость, прочность поверхностного слоя стали и формирование карбоно-нитридной зоны. В экспериментах за основу были взяты быстродействующие стали марок R6M5 и R9F5. Результаты показали, что в результате жидкого азотирования при температуре 550-560 °C в течение 40 минут на поверхности стали образуется слой с высокой микротвердостью (1300-1500 HV). В статье поэтапно представлены этапы подготовки режущих инструментов к азотированию, термической обработки, мойки, охлаждения и контроля качества. Предложенная технология имеет важное значение в повышении сопротивления фрезам трению, продлении срока их службы и обеспечении точности обработки.

Keywords:thermal treatment, liquid nitrogenation, high-speed steel, structure, austenite, hardness, impact toughness, tempering.

Ключевые слова: термическая обработка, жидкое азотирование, высокоскоростная сталь, структура, аустенит, твердость, ударная вязкость, закалка.

Introduction: In the world, the production of various types of cutting tools, increasing their operability, efficiency, and durability is one of the most important tasks, and in the implementation of these tasks, the technology of chemical-thermal treatment of cutting tools plays a large role. When operating cutting tools under high load and intensive wear conditions, their operability is determined by the physical-mechanical and technological properties of the tool's working surface. In this regard, the development and implementation of a technology for tempering a gear cutting cutter made of high-speed steel and nitrogen in a liquid state is of particular importance. [1]

Object of research. they are rapid-cutting steels of the R6M5 and R9F5 grades.

Research Methods. In the research work, analytical methods for measuring hardness (HBRVS-187.5), macro- and microstructure analysis (optical microscope MIM-7, Oxion Inverso) and electron microscopes, X-ray phase analysis (XRD-600 X), as well as standard methods permitted in CIS countries, were used to study the quantitative indicators of high-speed steel used for gear cutting.

Technology of strengthening gear cutters using the liquid nitriding method. The high cutting speed of the developed technological process can be used for fine-bladed tools operating in conditions of small transverse transmissions and retaining the cutting edge of the cutters and cutters with rigid tolerances (Fig. 1). It should also be noted that cutting tools before nitriding must meet the following requirements: [2]

Figure 1. Cervy and module frees

1) The hardness of the working part should not be less than 62-63 HRC, since the nitrided layer should be located on a solid base;

2) the surface layer of the device must be well loosened and not contain a large amount of residual austenite;

3) the surface layer should not contain calcine during grinding and the carbonized layer;

4) before grinding, the tool must be cleaned of oxide films with crushing chips;

5) after grinding and sharpening, the tools are cleaned of dirt and oils by washing in a soda solution in an instrumental machine;

6) To obtain dullness of the cutting edges of cutting tools when transporting tools from the initial operation to the final operation, it is necessary to use special containers (carts) for each type of tool. [3]

The cutters designed for hardening according to the proposed technology undergo the following technological cycles:

1. The cutters prepared for hardening are transported to the thermal shop;

2. Cutters manufactured for hardening in the thermal shop are placed in a basket;

3. The milling basket is loaded into a medium-temperature bath containing 100% NaCl and preheated to 800-820 °C;

4. The basket with cutters is kept in a bath by heating it at a temperature of 10°C per second for a given time;

5. The milling cutter basket is preheated and loaded into a high-temperature bath containing 100% BaCl2 for heating at 1200-1230 °C;

6. The basket with cutters is kept in a bath by heating at a temperature of 10 °C per second for a given time;

7. After holding, the basket with cutters is placed in a tank with oil for rapid cooling (hardening); [4]

8. A basket with hardened cutters is transported for loading into tool washing;

9. The basket with cutters has a temperature of 70-80 °C.

It is loaded into a washing machine with a 5% aqueous soda solution;

10. The basket with cutters, after washing, is transported for drainage;

11. The basket with the cutters is loaded into the unloading furnace at a temperature of 550-560 °C. 11. At the same time, the holding time is 1 hour;

12. The basket with the cutters is removed from the furnace for air cooling to room temperature after emptying. [5]

13. The basket with the cutters is transported to a hardness measuring device for controlling the intermediate hardness according to the Rockwell scale;

14. 5 milling cutters are selected and the hardness is checked. The hardness of the cutters according to the Rockwell scale should be 60-61 HRC;

15. Then the basket with the cutters is transported to be loaded into a liquid nitriding bath; [6]

16. The milling basket is loaded into a liquid bath with a temperature of 550-560 °C, containing 60% (NH₂) 2CO + 40% Na₂CO₃. Holding time is 40 minutes. In this case, the nitriding process is carried out in a liquid state;

17. After liquid nitriding, the basket with the cutters is removed from the bath and transported to the tool washing machine.

18. The basket with milling cutters is loaded into a washing machine with a 5% soda water solution at a temperature of 70-80 °C;

19. The basket with cutters after washing is transported for the final unloading operation;

20. A basket with cutters is loaded into an unloading furnace with a temperature of 300 °C for final unloading. At the same time, the holding time is 1 hour;

21. Baskets with cutters are removed from the furnace after emptying to cool in air to room temperature;

22. The basket with the cutters, after cooling, is transported to the control table for the control operation;

23. Sharpened cutters are removed from the basket. Each cutter undergoes 100% external inspection for cracks.

24. After checking the external appearance of the polished cutters, 5 cutters are selected to determine their hardness using the Rockwell method and the microhardness distribution in the PMT-3 device in the surface layer. The hardness of the hardened cutters should be 62-63 HRC, and the microhardness of the surface layer 1300-1500 HV. [7]

Note 1.

The heating time for hardening the cutters is the heating time of the cutter along the cross-sections and the holding time of the cutter at a given temperature. The heating time in the open state depends on the geometric shape of the cutter and its chemical composition and is determined according to literature data.

Note 2.

Every shift, the salt bath must be eliminated from oxidation by ferrosilicon. A single load of ferrosilicon into the bath is 250 grams.

Note 3.

The readings of devices showing the temperature of the thermal furnace and liquid nitriding must be monitored once a quarter. At the same time, instruments for measuring hardness and microhardness should be checked once a year.

Conclusion: technological modes of liquid nitriding with a bath temperature of 560 °C and a nitriding time of 40 minutes have been developed, allowing for obtaining high surface hardness of cutting tools made of high-speed steel with a hardness of 1300HV.

References:

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