Ultrasonic Machining Technology Makes Wonder in Medical-Grade Stainless Steel Machining 2023/07/21 About Stainless Steel and its Common Use General Material Properties of Stainless Steel (Figure 1. HIT ultrasonic-assisted micro-drilling on stainless steel workpiece) Stainless steel is a group of steel alloys that are known for their excellent corrosion resistance, durability, and high strength. Here are some of the key material properties of stainless steel: - Corrosion Resistance - Stainless steel is highly resistant to corrosion and oxidation. This is primarily due to the presence of chromium in the alloy, which forms a passive oxide layer on the surface of the material. This oxide layer acts as a barrier, protecting the underlying steel from corrosion caused by exposure to moisture, chemicals, and other corrosive substances. (Read more on Why is Stainless Steel Corrosion Resistant?) It gives stainless steel rather low maintenance requirements, since it reduces the need for frequent cleaning, painting, or coating to protect against corrosion even in demanding environments. - Heat Resistance - Stainless steel also has excellent heat resistance, making it suitable for applications under high temperatures. It can withstand elevated temperatures without significant loss of strength or deformation. (Read more on Stainless Steel - High Temperature Resistance) This characteristic is crucial in industries such as aerospace, automotive, and energy, where components may be exposed to extreme heat or thermal cycling. - High Strength and Ductility - Stainless steel exhibits high strength, making it suitable for various structural and load-bearing applications. The strength of stainless steel is influenced by factors such as alloy composition, heat treatment, and manufacturing processes. Stainless steel also possesses good ductility, which allows it to be easily formed and fabricated into different shapes. This characteristic is beneficial in various manufacturing processes, including bending, welding, machining, and forming. The ductility of stainless steel can be further improved by controlling the alloy composition and employing suitable heat treatments. - Hygienic Properties - Stainless steel is widely used in industries that require high standards of cleanliness and hygiene, such as food processing, medical (surgical), and pharmaceutical industries. It is non-porous, making it resistant to bacterial growth, easy to clean, and capable of withstanding repeated sterilization processes. Learn more detailed information on Stainless Steels - Specifications, Grades and Properties Different Grade Families of Stainless Steel Apart from the more general perspective on the material properties of stainless steel, the family of stainless steels is primarily classified into four main categories, including Ferritic, Austenitic, Martensitic, and Duplex, based upon their crystal microstructure. (Read more on Grading Systems for Stainless Steel) In general, austenitic and martensitic grades stainless steel, including SAE/AISI 304, 316, and 420, are often used in the making of medical and surgical equipment or spare parts. The following illustrates the comparison of these three commonly used stainless steel grades. (Figure 2. medical/surgical instruments made of stainless steel) - Austenitic - 304 Stainless Steel (SAE/AISI 304) - Composition 304 Stainless steel contains 18-20% chromium and 8-10.5% nickel, along with small amounts of carbon, manganese, and other elements. Corrosion Resistance It offers good corrosion resistance in a wide range of environments, including atmospheric conditions and mild chemical environments. Strength 304 Stainless steel has good tensile strength and yield strength, making it suitable for general-purpose applications. Industry Applications 304 Stainless steel is commonly used in various industries, including food processing, kitchen equipment, architectural applications, and chemical processing. (Learn more detailed information on Grade 304 Stainless Steel: Properties, Fabrication and Applications) - Austenitic - 316 Stainless Steel (SAE/AISI 316) - Composition 316 Stainless steel contains 16-18% chromium, 10-14% nickel, and 2-3% molybdenum, along with other elements. Corrosion Resistance It provides excellent corrosion resistance, particularly in harsh environments, such as marine or chloride-rich conditions. Strength 316 Stainless steel has higher tensile and yield strength compared to 304, making it suitable for applications requiring exposures under increased pressure. Industry Applications 316 Stainless steel is commonly used in marine equipment, chemical processing, pharmaceuticals, and medical implants where superior corrosion resistance is required. (Learn more detailed information on Grade 316 Stainless Steel: Properties, Fabrication and Applications) - Martensitic - 420 Stainless Steel (SAE/AISI 420) - Composition 420 Stainless steel contains around 12-14% chromium, with no or minimal nickel content. It also has a higher carbon content compared to 304 and 316. Corrosion Resistance It offers moderate corrosion resistance in mild environments but is less resistant to corrosive chemicals or chlorides compared to 304 and 316. Strength 420 Stainless steel has high hardness and good strength, making it suitable for applications requiring wear resistance, such as cutlery, surgical instruments, and moulds. The material can exhibit even higher hardness (up to HRC 50-55) after heat treatment, which allows it to be applied in environments under higher precision and stricter standards. Industry Applications 420 Stainless steel is commonly used in the production of blades, knives, scissors, surgical instruments, and moulds where hardness and wear resistance are crucial. (Learn more detailed information on Stainless Steel - Grade 420) In brief summary, 304 stainless steel (SAE/AISI 304) provides good general corrosion resistance and is suitable for a wide range of applications. 316 stainless steel (SAE/AISI 316) offers excellent corrosion resistance, particularly in aggressive environments, and has higher strength than 304. 420 stainless steel (SAE/AISI 420) has lower corrosion resistance but offers high hardness and wear resistance, making it ideal for applications requiring cutting or wear resistance properties. The choice between these grades depends on the specific requirements of the application, including corrosion resistance, strength, and wear resistance. Difficulties in Medical-Grade Stainless Steel Machining Machining stainless steel, including grades 304, 316, and 420, can present certain difficulties due to the material properties of these steel alloys. The following shows common challenges encountered in machining these stainless steel grades: Work Hardening Stainless steel grades, including 304, 316, and 420, have a tendency to work harden during machining. (Read more on Hardening Stainless Steels: A Brief Guide) As the material is deformed by the cutting tool, it becomes harder and more resistant to further cutting. This work hardening effect can lead to increased cutting forces, tool wear, and difficulties in achieving desired workpiece quality. In addition, stainless steel also tends to produce long, stringy chips, which may lead to chip accumulation and interfere with the cutting process and damage the workpiece or tool. The harder and more resistant to cutting the material gets, the more challenging it is for its chip evacuation. High Cutting Forces Stainless steel is known for its high strength and toughness, which results in high cutting forces during machining. These high cutting forces require robust cutting tools and machines capable of handling the stress. Managing these forces effectively is important to prevent tool breakage, chatter, and other machining issues. Heat Generation Stainless steel has low thermal conductivity (Read more on Thermal Activity in Stainless Steel Compared to Other Metals), which means that heat generated during machining tends to concentrate in the cutting zone. This can lead to elevated temperatures that may cause tool wear, tool deformation, and plastic deformation (Learn about Some Basics of Plastic Deformation Mechanism) in the material. (Figure 3. CNC machining on metal/steel alloy requires proper cooling methods) Tool Wear Stainless steel grades, especially 420, are relatively hard, which can cause serious tool wear during machining. The work hardening, high cutting forces, and heat generation contribute to tool wear and can reduce tool life. Therefore, selecting appropriate tool materials with high hardness and wear resistance, as well as optimizing cutting parameters, is crucial to mitigate tool wear issues. It's important to note that the specific difficulties in machining stainless steel can vary depending on factors such as the specific grade, workpiece geometry, cutting tool selection, and machining parameters. What Does HIT Ultrasonic Machining Bring to Medical-Grade Stainless Steel Machining? Ultrasonic High Frequency Oscillation HIT's ultrasonic-assisted machining technology provides the superimposition of the tool rotation with a high-frequency oscillation in longitudinal direction, generating over 20,000 times of micro-vibration per second. The mechanism helps reduce cutting forces and facilitates chip removal process. (Figure 4. HIT ultrasonic-assisted machining technology with high frequency oscillation in longitudinal direction facilitates chip removal process) The high-frequency oscillation in longitudinal direction allows for an intermittent contact between the tool and workpiece. This helps eliminate accumulative cutting heat around the tool tip, which results in great reduction in tool wear. Reduction in Cutting Force The reduction in cutting forces not only decreases frictions between the tool and workpiece, but also allows cutting speed and feed rates to be increased. This mechanism along with the high pressure (up to 70bar) coolant through spindle (CTS) feature also helps lower the heat generated during the machining process. It greatly improves the workpiece quality and stability in tool life and saves a huge amount of energy and processing time. (Figure 5. HIT ultrasonic-assisted machining technology helps reduction in cutting forces and brings more stability in tool life) Easier Chip Removal Process Facilitating chip removal or chip evacuation process also reduces frictions on both tool and workpiece caused by excessive amount of accumulative chips. Especially when the chips are long and stringy, it may lead to built-up edge (BUE) or chip re-cutting situations, which worsens workpiece quality and endangers tool life. The reduction in cutting forces with HIT's ultrasonic high-frequency micro-vibration allows the tool to cut off the material more easily with easier chip evacuation process. The elimination of entangled, accumulative chips also contributes to better workpiece quality and longer tool life. (Read more on Built-up Edge Formation in Stainless Steel Milling) Benefits in Machining of Stainless Steel In machining of medical-grade stainless steel, HIT ultrasonic-assisted machining technology helps reduce cutting forces, which allows the tool to cut off the material more easily with better chip removal. This mechanism contributes to better workpiece quality (elimination of burrs and better roundness in drilling holes) and tool life (better chip evacuation and prevention of entangled, accumulative chips around cutting tools). More information on HIT Ultrasonic Machining Technology 💡 Read more on the benefits of HIT ultrasonic-assisted machining on metal, alloy, hard steel materials: Facing the Challenges in Machining of Tungsten Carbide How to Drill Titanium: The Aerospace Fever in Titanium Drilling Two Successful HIT Cases of Stainless Steel Machining SAE 420 Stainless Steel: Micro-Milling & Micro-Drilling (Figure 6. HIT ultrasonic-assisted micro-milling and micro-drillilng 420 stainless steel workpiece) HIT helped one of its customers within the medical field with SAE/AISI 420 stainless steel micro-machining process in the making of minimally invasive surgical spare parts. The full length of the workpiece was only 4mm, with the slot width only 0.8mm. Doing fine milling and drilling of these micro-features with HIT BT30 ultrasonic machining module, the high frequency micro-vibration helped reduce cutting forces. This resulted in great reduction in feed/tool marks and burrs on the workpiece. (Figure 7. Comparison of workpiece quality between HIT ultrasonic-assisted machining and without ultrasonic on 420 stainless steel micro-milling and micro-drilling) HIT ultrasonic-assisted machining technology ultimately helped its customer enhance product yield rate from under 10% to 100%, not only saving up the time and preventing the risks of manual refining process, but also helping the customer win the case. This feature is applied in the Medical industry, especially being used for minimally invasive surgical spare parts, such as biopsy forceps, grasping forceps, etc. See detailed information of SAE 420 Stainless Steel: Micro-Milling & Micro-Drilling SAE 304 Stainless Steel: Micro-Drilling on curved surface (Figure 8. HIT ultrasonic-assisted micro-drillilng 304 stainless steel workpiece) HIT carried out micro-drilling on curved surface of SAE/AISI 304 stainless steel. By using HIT HSK-A63 ultrasonic machining module, the high frequency micro-vibration helped reduce cutting forces. This prevented the tool from deflection under the circumstance of not doing plunge milling (Learn more on what is Plunge Milling?) before the main drilling process. The reduction in cutting forces not only contributed to zero burrs around the drilling holes under microscope but also provided with better chip removal process. (Figure 9. Comparison of hole quality between HIT ultrasonic-assisted machining and without ultrasonic on 304 stainless steel micro-drilling on curved surface) HIT ultrasonic-assisted machining technology helped improve hole quality (with no burrs) and achieve 4 times longer tool life. (Figure 10. Comparison of tool wear between HIT ultrasonic-assisted machining and without ultrasonic on 304 stainless steel micro-drilling on curved surface) This feature can be applied in the Semiconductor industry and 3C Electronics industry, especially being used for vacuum plates, electronic spare parts, etc. See detailed information of SAE 304 Stainless Steel: Micro-Drilling on curved surface Medical-Grade Stainless Steel Machining FAQ Q1 How did HIT ultrasonic achieve great roundness in drilling holes without pilot drilling or plunge milling on stainless steel machining? A1 Poor hole roundness usually resulted from the high cutting forces tool received when it first contacted with the workpiece, which caused the tool to wonder and deflect. The high frequency micro-vibration (over 20,000 times per second) of HIT ultrasonic-assisted machining helps greatly reduce cutting forces. This mechanism prevented the tool from deflection due to the received high cutting forces when it first contacted with the workpiece. The high frequency micro-vibration also helped break chips more easily with better chip removal, which resulted in the elimination of burrs around the drillilng holes to achieve great hole quality on stainless steel. (Figure 11. HIT ultrasonic-assisted machining driver module) More information on HIT Ultrasonic Machining Module Q2 How to adjust machining parameters, such as feed rate, cutting speed, or ultrasonic power when I start machining stainless steel with HIT ultrasonic machining module? A2 Hantop Intelligence Tech. is a professional solution provider of advanced-material machining technology and smart automation modules. It aims to provide not only high-precision ultrasonic-assisted machining module products, but also professional knowledge on how to optimize the benefits customers can achieve with ultrasonic-assisted machining technology. This includes providing the optimized machining parameters (according to the target material and machining features) and services to ensure customers having the best experiences in using HIT ultrasonic machining module. Customers are not just buying a product from HIT, but obtaining ultrasonic machining knowledge and services from the most professional team. (Figure 12. HIT ultrasonic-assisted machining toolholders) Medical-Grade Stainless Steel Machining? Choose HIT Contact us if you are looking for a better way to improve machining efficiency, workpiece quality, and tool life, by following the trend of ESG. *References: AZO Material Eagle Stainless Tube & Fabrication, Inc. HardRok Engineering PTY LTD. KTH Royal Institute of Technology - School of Industrial Engineering and Management Masteel UK Ltd. SANDVIK Coromant Industrial Metallurgists, LLC. Thyssenkrupp Materials UK Ltd. Xometry ←Back