High-chromium white cast iron is a material known for its excellent corrosion and wear resistance, along with high hardness and strength. Its tensile strength ranges from 650 to 850 MPa, while the as-cast hardness is between HRC 48 and 55, and after quenching, it reaches HRC 55 to 62. However, due to its high hardness and brittleness, the cutting process is unstable, making it difficult to machine effectively. If these challenges are not addressed properly, the application of this material can be severely limited.
Testing has shown that using carbide tools for machining high-chromium white cast iron leads to rapid tool wear, chipping, and poor surface finish, making them suitable only for rough machining. For finishing operations, ceramic tools can achieve lower surface roughness. However, ceramic tools have relatively low impact resistance, which makes them more prone to failure when machining brittle materials like high-chromium cast iron. Additionally, ceramic tools are expensive, so their use should be minimized where possible.
To avoid tool damage, selecting the right cutting parameters is crucial. This paper focuses on optimizing the cutting parameters for the outer surface of high-chromium white cast iron valve plates using composite ceramic tools, considering both tool performance and economic efficiency.
The influence of cutting temperature on the dynamic performance of composite ceramic tools is significant. As temperature increases, the mechanical properties of the ceramic material degrade, including reductions in tensile strength, yield strength, elasticity, and hardness. These effects can be modeled using empirical equations. Additionally, thermal stress generated during cutting can affect the tool's structural integrity.
Dynamic stress and strength calculations were performed using a three-dimensional finite element model. The maximum dynamic stress under combined cutting force and temperature conditions was determined. A dynamic strength condition was established to ensure the tool’s performance remains within safe limits.
An optimization model was developed to minimize the total cost of machining, taking into account material costs, machine time, tooling, and tool change expenses. Constraints such as cutting speed, feed rate, surface roughness, machine power, and tool life were also considered. Due to the complexity of the dynamic strength constraint, an iterative approach was used: first, optimal cutting parameters were calculated without considering the constraint, then the maximum dynamic stress was verified using finite element analysis. If the tool strength was sufficient, the parameters were accepted; otherwise, they were adjusted until the condition was met.
The calculation results showed that the optimal cutting speed was 109.8 m/min, with a feed rate of 0.1 mm/r. Testing confirmed that the tool did not chip, and the durability reached 65 points with a surface roughness of Ra = 1.6. In contrast, previous settings (V = 142 m/min, f = 0.2 mm/r) led to chipping issues.
In conclusion, the finite element method is a reliable way to analyze the temperature field and cutting forces acting on the tool. By optimizing the cutting parameters while considering tool strength and economic efficiency, it is possible to achieve low-cost machining of high-chromium white cast iron without causing tool damage.
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