Machining Process and Solutions Introduction
Machining stainless steel generates high cutting forces, built-up edge, high heat, and work-hardened surfaces, making it prone to groove wear. Furthermore, chip control is difficult during stainless steel machining. While relatively easy to control in ferritic/martensitic materials, it is more complex in austenitic and duplex stainless steel machining.
Therefore, customers have a strong demand for stable tool life and good chip control. The AH6200 & T6200 series materials and their chip breakers are specifically developed for stainless steel turning, offering excellent cutting performance.
02. Workpiece Machining Challenges
① This workpiece is produced on an automated line, requiring stable tool life;
② Improving tool life reduces tool change frequency, thereby increasing production efficiency;
③ Good chip control.
03. Takola's Machining Method
Takola uses PVD stainless steel material-AH6225-combined with SM chip breakers, achieving excellent chip control and a tool life twice that of competitors.
04. Machining Case and Conclusion
Part Name: Connector;
Part Material: SUS304/X5CrNi18-9;
Machine Tool: CNC Lathe;
Cooling Method: Internal machine cooling;
Machining Type: External Diameter Turning;
Tool: ACLNR2525M12-A/CNMG120404-SM AH6225;
Cutting Parameters: vc=90m/min, ap=1mm, f=0.2mm/r.
05. Tool Advantages and Effects
① T6215: A CVD-coated material suitable for high-speed cutting, exhibiting excellent wear resistance in continuous cutting.
② T6225: A versatile CVD material covering everything from continuous cutting to lightly interrupted cutting. Provides excellent wear resistance in the medium-speed cutting range.
③ AH6225: A versatile PVD material that performs excellently in various stainless steel applications.
④ AH6235: Provides high reliability in intermittent cutting or deep-cut conditions.
Coated Tapered End Mills
01. Introduction to Stainless Steel Machining Performance and Applications
Stainless steel, due to its excellent corrosion resistance and good mechanical properties, has become an indispensable key material in modern industry. Based on its microstructure and performance characteristics, stainless steel can be mainly divided into the following five categories:
(1) Austenitic Stainless Steel: Non-magnetic, with excellent corrosion resistance, and possessing both high toughness and plasticity, it is the most common and widely used type of stainless steel. Typical applications include chemical equipment, food and pharmaceutical industries, medical devices, kitchen equipment, and household appliances.
(2) Ferritic Stainless Steel: Magnetic, with moderate corrosion resistance, high strength, and good thermal conductivity. Mainly used in automotive exhaust systems, appliance housings, building decoration, and kitchen utensils.
(3) Martensitic Stainless Steel: Magnetic, its strength and hardness can be significantly improved through heat treatment processes such as quenching and tempering. It has good wear resistance, but relatively weak corrosion resistance. Commonly used in the manufacture of cutting tools such as scalpels, shafts, bearings, valve parts, steam turbine blades, and tableware.
(4) Duplex stainless steel: Its microstructure consists of approximately 50% austenite and 50% ferrite, combining the advantages of both. For example, its strength is about twice that of austenitic stainless steel, and it has excellent resistance to chloride stress corrosion while maintaining good toughness and weldability. It is mainly used in marine engineering, seawater treatment equipment, highly corrosive environments in the oil and gas industry, and the pulp and paper industry.
(5) Precipitation hardening stainless steel: While maintaining good corrosion resistance and toughness, it can achieve very high strength through precipitation hardening treatment. Suitable for high-strength components in aerospace, nuclear industry parts, high-performance gears, shafts, springs, and other precision parts requiring high strength and certain corrosion resistance.
02. Characteristics and Challenges of Machining
① Significant work hardening: Due to the good plasticity of stainless steel, severe plastic deformation easily occurs during cutting, leading to a significant increase in the hardness of the machined surface, which in turn exacerbates tool wear and affects the surface quality of the workpiece. ② High cutting force: Stainless steel possesses both high strength and good toughness, resulting in significant plastic deformation during cutting. This leads to cutting forces approximately 50% higher than ordinary carbon steel, placing higher demands on the load-bearing capacity of machine tools and cutting tools.
③ High cutting temperature and difficult heat dissipation: The material's poor thermal conductivity makes it difficult to quickly dissipate the heat generated during cutting. A large amount of heat accumulates in the tool-chip contact area, causing the tool temperature to rise and significantly shortening its service life.
④ Difficulty in chip breaking and removal: The good plasticity and toughness make chips difficult to break naturally, easily forming continuous ribbon-like chips. These chips can not only entangle the tool or workpiece, causing scratches on the machined surface, but also affect operational safety and increase abnormal tool wear.
⑤ Easy tool adhesion and wear: Under high temperature and pressure, chip material easily adheres to the tool rake face, forming a continuously growing and detaching "built-up edge," which not only affects the stability of the cutting process but also worsens the surface roughness of the machined workpiece.
03. Improvement Measures Taken by Xiwei
① Optimize Tool Materials: Select appropriate tool materials based on machining requirements, such as coated cemented carbide (PVD coating), cermet, etc.; for applications with extremely high requirements for surface quality and efficiency, CBN tools can be used.
② Optimize Tool Geometry: Use sharper cutting edges and appropriately increase the rake and clearance angles to effectively reduce cutting forces, lessen tool wear, and improve cutting smoothness.
③ Improve Chip Control: By adopting a positive rake angle combined with a specially optimized chip breaker, the cutting process is made smoother while enhancing tool tip strength, achieving effective control over chip flow direction and shape.
④ Enhance Heat Dissipation: Appropriately increase the tool tip radius to improve heat dissipation conditions in the cutting area, thereby reducing tool operating temperature and extending its durability.
⑤ Optimize Cutting Parameters: Systematically optimize cutting speed, feed rate, and depth of cut to effectively suppress built-up edge formation while ensuring machining efficiency and workpiece quality, ensuring tool life and cutting stability.
04. Machining Case
Part Name: Steam Turbine Impeller;
Part Material: Precipitation Hardening Stainless Steel (17-4PH);
Machine Tool: 5-Axis Machining Center/HSK63;
Cooling Method: Water-soluble oil (internal cooling);
Machining Type: Finishing of Steam Turbine Impeller (Impeller Profile);
Tool Name: Coated Taper End Mill;
Tool Specifications: R3x8°x105xd25x165-4Z;
Cutting Parameters: vc=120m/min, fz=0.03mm/Z, ap=0.2mm.
05. Tool Features
① The tool adopts a large helix angle (40°) and unequal tooth pitch design, making the cutting process smoother, greatly reducing cutting force and cutting vibration, and effectively suppressing work hardening. The tool life is increased by more than 50% compared to ordinary coated carbide.
② Sharp Cutting Edge: Utilizing a large rake angle and clearance angle design, it produces a sharp cutting edge for easy material entry and better surface finish. Cutting force is reduced by 30%, increasing machining efficiency by 20%.
③ Chip Retention Space: The spiral grooves provide ample chip retention space, ensuring smooth chip removal and preventing tool breakage and workpiece surface scratches caused by chip clogging. This increases the yield rate from 90% to 98%.
④ Employing a wear-resistant nano-coating, suitable for high-speed cutting, further extending tool life.
06. Tool Features and Actual Machining Results
Statistical data shows that using the above alloy tapered end mills reduced the overall machining cost of turbine impellers by 30%.
