This article mainly discusses the precautions for using Gun drilling machine tools to process stainless steel materials, as stainless steel is a difficult material to machine and has special requirements for cutting tools. Let’s take a look below

1. Briefly describe the types of stainless steel and the characteristics of machining with gun drilling machines

Stainless steel can be classified into three categories: ferritic stainless steel, austenitic stainless steel, and martensitic stainless steel. Stainless steel has high high-temperature strength and hardness, high plasticity and toughness, and a severe tendency to work hardening. Chips are not easy to cut, curl, and break, and the friction between knives and chips, as well as between knives and workpieces, is severe. The cutting specific energy consumption is high, and most of the energy is converted into heat energy, which increases the cutting temperature. This causes a surface hardening layer in the cutting area. In addition, the thermal conductivity of stainless steel is low, with less heat carried away by the chips and more heat transferred into the tool, resulting in an increase in tool temperature and wear.

The processing superiority of the above three types of stainless steel is ranked from easy to difficult as ferritic stainless steel>martensitic stainless steel>austenitic stainless steel.

Note: Usually, alloy steel with Cr content greater than 12% or Ni content greater than 8% is referred to as stainless steel. Cr12MoV is known as mold steel, but due to its Cr content reaching 12%, its processing performance is similar to that of stainless steel. When selecting parameters and tools, it is necessary to follow the requirements for processing stainless steel, otherwise it will cause tool wear too fast and lead to tool breakage.

2. Precautions for selecting cutting tools for Gun drilling machine:

2.1 The selection of hard alloys should be based on the principles of tool materials with high hardness, good adhesion resistance, and toughness. TaC or NbC fine-grained and ultrafine grained hard alloys should be selected.

Note: The grain size of hard alloys directly determines the wear resistance of cutting tools.

2.2 Selection of Gun drill tool coating.

In recent years, there has been an increasing selection of tool coatings, by coating the surface of the tool with high melting point, high hardness, good wear resistance, low friction coefficient, and anti bonding metal and non-metallic compounds with a thickness of one to several micrometers. Thus solving the contradiction of higher hardness and lower bending strength of tool materials.

The following coatings are recommended for stainless steel materials.

TiAlSi coating, Al2O3 coating, TiC coating, TiN coating, etc

2.3. Selection of metal cutting fluid during gun drilling process

For the processing of stainless steel materials, the cooling performance and extreme pressure lubrication performance of the cutting fluid are both important. During turning (including single edge tool boring) and end milling, for rough and semi precision machining, 5% -10% anti friction extreme pressure emulsified cutting fluid or microemulsified cutting fluid can be selected. Effective liquid supply methods can be used to increase flow and flow rate to ensure sufficient supply of cutting fluid; Increase the dilution concentration to 10% -20% during precision machining, or use anti friction extreme pressure cutting oil.

Note: Cutting fluids containing chlorine series extreme pressure additives are particularly effective for stainless steel processing.

2.4 Precautions for cutting amount using Gun drilling machine tools

In order to reduce the thermal hardening effect of the processing area and suppress the generation of chip deposits and scales, the cutting parameters when using hard alloy cutting tools for processing are lower than those for processing general carbon steel workpieces.

The cutting speed is generally VC=30-60m/min; Feed f=20-30mm/min.

The AP cutting depth should be as deep as possible to cut through the thermal hard layer generated during the machining process. Only in this way can the tool life and processing quality be guaranteed.