Nanjing Hezhan Precision Technology Co., Ltd., led by Xu Kun and Chen Guangming, presents ultra-high pressure water jet technology, a novel technology that aligns with the concept of green manufacturing. It integrates pumps, valves, seals, hydraulics, and automated control into a comprehensive new technology and process. Ultra-high pressure water jet cutting is a non-traditional cold cutting method with advantages unmatched by traditional cutting methods. This article discusses the basic working principle of CNC ultra-high pressure water jet cutting machines, the processing forms of water jet cutting, and the composition of water jet cutting machine tools. It also elaborates on the processing characteristics and application fields of CNC ultra-high pressure water jet cutting machines and provides an outlook on the development trend of ultra-high pressure water jet cutting technology. 1. Introduction In recent decades, with continuous scientific and technological discoveries, people have endowed droplets with impact energy far exceeding that of free fall, enabling the long-term phenomenon of water dripping through stone to be completed in an instant—this is water jet. To improve efficiency, water is pressurized and ejected through nozzles with smaller diameters, forming a high-speed, continuous or intermittent water jet—this is high-pressure water jet. Waterjet cutting, also known as water jet processing, uses the impact of high-pressure, high-speed water jets on a workpiece to remove material. Commonly called "water-jet machining," it utilizes ultra-high pressure (hundreds of MPa) water jets to cut, pierce, and remove surface material from various materials. Waterjet technology can achieve a variety of processing tasks, such as cutting, degumming, cleaning, drilling, trimming, grooving, and removing surface material. Industrial development and the emergence of new materials have placed new demands on processing methods. For example, the aerospace manufacturing industry uses special materials such as titanium alloys, carbon fiber composites, and reinforced plastic glass, which are difficult to cut or have quality issues with other methods. Unlike laser cutting, plasma cutting, and wire EDM, high-pressure waterjet cutting, due to its unique advantages, is an ideal or even the only processing method for these aerospace materials that are difficult to cut using other methods. High-pressure waterjet cutting is a non-traditional cold cutting method with advantages that traditional cutting methods cannot match. This article introduces the ultra-high pressure waterjet cutting technology used in industry, specifically explaining the processing characteristics and development direction of ultra-high pressure waterjet cutting machines. 2. Working Principle of Ultra-High Pressure Waterjet Cutting Machines The basic working principle of high-pressure waterjet processing technology is based on the principle of liquid pressurization. Through a specific energy conversion device (booster or high-pressure pump), the mechanical energy of the power source (electric motor) is converted into the pressure energy of water. The water, possessing enormous pressure energy, passes through a small nozzle, where the pressure energy is further converted into kinetic energy, forming a high-speed water jet that is sprayed onto the workpiece surface. When the water jet impacts the workpiece, the kinetic energy is again converted into pressure energy acting on the material. If the pressure energy exceeds the material's breaking strength, the material can be cut, achieving the processing purpose of material removal. Therefore, high-pressure waterjet is often referred to as high-speed waterjet. The working principle of an ultra-high pressure water jet cutting machine is as follows: ordinary water is filtered and then pressurized step by step through an ultra-high pressure booster to a pressure of about 200-400 MPa. Then, it is passed through a nozzle with a diameter of 0.1-0.3 mm (usually made of sapphire) to form a jet of water with a speed of up to 1000 m/s (about 3 times the speed of sound) and extremely high kinetic energy. This water jet is like a cutting tool, and under the control of a CNC system, it is used to cut the required material. [IMG=Figure 1 Schematic diagram of CNC ultra-high pressure waterjet cutting machine]/uploadpic/THESIS/2007/11/2007111410412756527O.jpg[/IMG] Figure 1 Schematic diagram of CNC ultra-high pressure waterjet cutting machine [IMG=Figure 2 Food processing with waterjet cutting machine]/uploadpic/THESIS/2007/11/2007111410413569947R.jpg[/IMG] Figure 2 Food processing with waterjet cutting machine [IMG=Figure 3 Cutting stainless steel plate with waterjet cutting machine]/uploadpic/THESIS/2007/11/2007111410415652693N.jpg[/IMG] Figure 3 Workpieces are cut and shaped by waterjet cutting machine cutting stainless steel plate. The schematic diagram of a CNC ultra-high pressure waterjet cutting machine is shown in Figure 1. As can be seen from Figure 1, the abrasive is first fed into the mixer via an abrasive supply device. Water from the water tank, after passing through an ultra-high pressure waterjet generator, becomes high-pressure water, which is then mixed with the abrasive in the mixer. Then, the waterjet cutting head is ejected from the nozzle at a high speed of hundreds of meters per second to cut the workpiece. Simultaneously, under the control of the CNC system, the waterjet cutting head moves in a plane according to the trajectory required by the user's machining program, ultimately cutting the workpiece as required by the user. Currently, waterjet cutting machines use an industrial computer as the hardware platform and a Windows 98 operating system as the software platform. This system features automatic programming, machining trajectory simulation, a user-friendly interface, and network communication capabilities. 3. Forms of Waterjet Cutting and Composition of Waterjet Cutting Machine Tools 3.1 Forms of Waterjet Cutting Waterjet cutting can be classified in terms of water quality (pure water cutting and abrasive cutting), pressure application method (hydraulic pressure and mechanical pressure), machine tool structure (gantry structure and cantilever structure), and drive method (stepper motor drive and AC servo motor drive). In terms of water quality, there are currently two types of ultra-high pressure water jet cutting used in industry. One is pure water cutting, which can easily cut soft materials of any shape with a kerf of about 0.1-1.1mm (as shown in Figure 2 for food processing). When the water pressure is above 100MPa, soft materials such as food, sponge, rubber, leather, fiber, plastic, paper, and textiles can be cut. The other is cutting with abrasive (commonly 60-100 mesh quartz sand and alumina, etc.), with a kerf of about 0.8-1.8mm (as shown in Figure 3 for steel plate cutting). The addition of abrasive gives the water jet the characteristics of a saw blade, increasing its cutting force. The power of the water jet is greatly enhanced. Abrasive water jet cutting can cut almost any hard material, such as metal, composite materials, stone, ceramics, and glass. Structurally, waterjet cutting machines can take many forms, such as gantry and cantilever structures with two to three CNC axes, which are often used for cutting sheet metal; and robot structures with five to six CNC axes, which are often used for cutting automotive interior parts and car linings. The simplest ultra-high pressure waterjet cutting machine has two CNC axes, with XY axis CNC movement controlled by CNC, and can achieve direct CAD/CAM conversion, truly achieving keyboard-free input and drawing-free processing. Any complex curve drawn in CAD can be directly cut into shape. 3.2 Composition of a Waterjet Cutting Machine Tool A CNC ultra-high pressure waterjet cutting machine tool consists of an ultra-high pressure waterjet generator system, a waterjet cutting head device, a CNC cutting platform, a CNC system, and its auxiliary devices. The high-pressure part is the heart of the waterjet cutting machine tool, and the CNC part is the brain of the waterjet cutting machine tool. [IMG=Figure 4 Structural Diagram of Gantry-Type CNC Ultra-High Pressure Waterjet Cutting Machine]/uploadpic/THESIS/2007/11/2007111410421559532A.jpg[/IMG] Figure 4 Structural Diagram of Gantry-Type CNC Ultra-High Pressure Waterjet Cutting Machine [IMG=Figure 5 CNC System for Dedicated Waterjet Cutting]/uploadpic/THESIS/2007/11/2007111410422926881L.jpg[/IMG] Figure 5 CNC System for Dedicated Waterjet Cutting As shown in Figure 4, this is a structural diagram of a gantry-type CNC ultra-high pressure waterjet cutting machine. The CNC cutting platform adopts a unique gantry double drive design, which has excellent versatility. The bed has good stability and will not vibrate or deform even at high speed. The machine tool adopts AC servo motor, high-precision ball screw and rolling guide to ensure high precision of parts processing. The high-performance water jet cutting special CNC system (as shown in Figure 5) is not only fully functional, realizes three-axis linkage control, has powerful network function, menu operation is simple and easy to learn, and ensures that the equipment has extremely high reliability. The machine and high pressure pump are controlled in the PC Windows environment. The perfect protection system can effectively prevent water and sand, making the machine durable. The centralized automatic lubrication system makes the equipment maintenance simple and convenient. 4 Processing characteristics of ultra-high pressure water jet cutting machine Compared with traditional cutting methods such as laser cutting, plasma cutting, and wire cutting, water jet cutting has the following processing characteristics: (1) Excellent cutting quality and high processing quality. Water jet cutting is an advanced "cold cutting" processing technology. Water jet cutting generates almost no heat and has no thermal effect on the workpiece material. Therefore, the workpiece will not have a heat-affected zone or thermal deformation, and will not cause changes or deterioration in the material's microstructure. This is especially advantageous for processing heat-sensitive materials such as titanium alloys. Water jet cutting does not produce cracks and can cut materials with very narrow gaps. The kerf is narrow (about 0.075 to 1.8 mm), which improves material utilization. Generally speaking, the kerf of pure water cutting is about 0.1 mm to 1.1 mm, and the kerf of abrasive cutting is about 0.8 mm to 1.8 mm. As the diameter of the abrasive nozzle's inner hole increases, the kerf becomes larger. Moreover, the kerf quality is good, with almost no burrs or flash. The cutting surface is vertical, and the kerf is smooth, flat, without cracks or slag. The cutting force is small. The transverse and longitudinal forces generated by the water jet on the workpiece are minimal. It does not generate direct surface pressure on the material, and there is almost no mechanical stress or strain. The workpiece deformation is small, and the processing accuracy is high. (2) High production efficiency. Waterjet cutting is fast, efficient, and low-cost. Because high-pressure water can generate extremely high energy after passing through a small-diameter nozzle, high-pressure water jet technology is very efficient and can concentrate a great deal of energy in a very small area. (3) Wide adaptability to workpiece materials. Because ultra-high pressure water jet cutting is almost "indestructible", there are almost no limitations on materials and cutting size, and it is known as a "universal cutting machine". It can be used for cutting various soft and hard materials, conductive and non-conductive materials, metallic and non-metallic materials, plastic and brittle materials, composite materials, etc. It can easily cut steel plates or hard marble, granite, etc., and is an ideal or only processing method for materials that are difficult to cut by other methods, such as titanium alloys and various composite materials. (4) Highly flexible. It can cut any contour, and the entry and exit points can be selected at any point on the workpiece surface. It can make all-round cuts, can start from any point, and has no limitation on the cutting direction. It can cut any complex shape and can complete various irregular processing, including various shapes, angles or slopes. The program is also easy to edit. (5) Good working environment and safe and reliable operation. Water jet cutting is safe. The distance between the water jet nozzle and the material being cut is 2-3mm, which is difficult for most people to reach. Because its working medium is water, there is no dust, no environmental pollution, no noise, and no harm during the cutting process. The cutting process is clean and dust-free, and has the functions of cooling, dust suppression, and lubrication. It can reduce a large amount of dust pollution to the environment and will not harm human health. It improves the working environment, the operating environment is clean and meets environmental protection requirements, and improves the safety of operators. No sparks or toxic gases are generated during cutting, which can effectively prevent fires. At the same time, due to the cooling effect of water, the workpiece temperature is low, which is very suitable for processing flammable and explosive materials such as wood and paper. This is very important for safety engineering, especially coal mine production. (6) Low processing cost. No secondary processing such as edge grinding is required, and no coolant is required, which can save time and reduce manufacturing costs. The processing "tool" is a high-speed and high-pressure water jet. The water jet does not wear and will not become dull during the processing. This reduces the time for tool preparation and sharpening. At the same time, the cutting quality is good and stable, the process consistency is good, and the efficiency is high. In addition, the waste produced by water jet cutting is usually quite valuable because it is in whole pieces rather than fragments and can be reused. (7) It has the characteristics of green manufacturing process. The source of cutting water and abrasive is sufficient. The working medium of high pressure water jet is water, which is not only abundant and easy to obtain but also cheap. People know that water resources are a renewable and pollution-free resource. Developing water energy has a positive effect on promoting national economic development, improving energy consumption structure, and reducing environmental pollution. [IMG=Fig. 6 Cutting sample of ultra-high pressure water jet cutting machine]/uploadpic/THESIS/2007/11/200711141042437312825.jpg[/IMG] Fig. 6 Cutting sample of ultra-high pressure water jet cutting machine (8) It is easy to realize automated control and simple to operate. The working mechanism of high pressure water jet has a small nozzle size and is easy to move, which makes it easy to realize numerical control control. It is easy to operate. All operations can be controlled by software, which is easy to understand and learn, and reduces the labor intensity of workers. In summary, high-pressure water jet technology aligns with the requirements of green manufacturing. The CNC water jet cutting machine, composed of a CNC water jet cutting platform and an ultra-high-pressure water jet generator, is a general-purpose cutting machine suitable for planar cutting of various materials, such as ceramics, stone, glass, chemical fibers, composite materials, and alloys, into arbitrary shapes. It is particularly suitable for architectural decoration stone mosaics, the clothing industry (cutting leather and fabrics), the automotive industry, and the food processing industry. Figure 6 shows a cutting sample from an ultra-high-pressure water jet cutting machine. Compared with traditional cutting processes, water jet cutting offers advantages such as narrower kerfs, smoother and flatter cuts, no thermal deformation, no edge burrs, faster cutting speeds, high efficiency, no pollution, safe and convenient operation, and low cost. 5. Application Areas of Ultra-High-Pressure Water Jet Cutting Technology The application of water jet processing technology to cutting represents a revolution in the cutting field. With the maturation of water jet technology and the overcoming of certain limitations, water jet cutting is a perfect complement to other cutting processes, with a very broad application prospect. Waterjet cutting can process a wide variety of materials, primarily non-metallic and metallic materials that are difficult or impossible to process using conventional cutting methods, especially some new and synthetic materials. Currently, ultra-high pressure waterjet cutting technology is widely used for planar cutting of various materials such as ceramics, stone, cement products, paper, food, plastics, fabrics, polyurethane, wood, leather, rubber, glass, synthetic fibers, metals, cemented carbide, mold steel, titanium alloys, tungsten-molybdenum-cobalt alloys, composite materials (such as fiber-reinforced metals and fiber-reinforced rubber with a metal matrix), stainless steel, aluminum alloys, high-silicon cast iron, and malleable cast iron, to achieve arbitrary shapes. Because ultra-high pressure waterjet cutting is virtually "indestructible," it is an ideal or even the only processing method for materials that are difficult to cut by other methods, such as titanium alloys and various composite materials. 6. Main application areas of ultra-high pressure waterjet cutting technology (1) Industrial manufacturing Ultra-high pressure waterjet cutting is applicable to almost all industrial fields, such as machine manufacturing, mold manufacturing, metal processing, aviation manufacturing, aircraft manufacturing, automobile manufacturing, stone processing and construction, ceramics, light industry, papermaking, rubber, textile and leather industry, electronics industry, food industry, etc. It is used to cut carbon fiber composite materials, various hard metals and non-metals, or materials with honeycomb structures. Taking the automobile manufacturing industry as an example, the processing of automobile interior decoration materials (such as car carpets, dashboards, headliners, etc.) accounts for 40% of waterjet processing. In addition, it is also used for cutting automobile rear racks, wheel covers and heat insulation materials. Due to the development of CNC technology, waterjet cutting can be easily automated by computer, so that it can cut workpieces with various curved shapes. At present, thousands of automatic waterjet cutting production lines have been installed at home and abroad. (2) Safety, disaster reduction, and environmental protection: High-pressure water jet technology is widely used in sectors that use a large amount of reinforced concrete structures, such as bridges and hydropower projects. It is especially effective in sectors with harsh natural conditions and dangerous work, such as coal, petroleum, chemical, military, and nuclear industries. It can operate efficiently, greatly reduce the labor intensity of workers, improve the working environment, and reduce and prevent dangerous accidents. In earthquake relief and post-disaster reconstruction, high-pressure water jet spraying for dust suppression and cutting concrete structures can play an important role. (3) Cutting or breaking buildings: High-pressure water jets can cut, drill holes, and break various buildings according to people's wishes. Therefore, it can be used to demolish old buildings, repair bridges, excavate trenches for laying cables or gas pipelines, break roads, etc. Although theoretically ultra-high pressure water cutting can cut any material, its application is still somewhat focused. Ultra-high pressure waterjet cutting has three main applications: First, it cuts non-combustible materials such as marble, ceramic tiles, glass, and cement products, which are materials that cannot be processed by thermal cutting. Second, it cuts combustible materials such as steel plates, plastics, fabrics, polyurethane, wood, leather, and rubber. While traditional thermal cutting can also process these materials, it easily produces combustion zones and burrs. Waterjet cutting, however, does not produce combustion zones or burrs, and the physical and mechanical properties of the cut materials remain unchanged, which is a major advantage of waterjet cutting. Third, it cuts flammable and explosive materials, such as ammunition and materials used in flammable and explosive environments, a process that cannot be replaced by other processing methods. Generally, if processing requirements can be met by methods such as laser, plasma, flame, wire cutting, sawing, and milling, waterjet cutting is not recommended. This is because waterjet cutting has higher operating costs; nozzles, guide sleeves, and high-pressure seals are all imported consumables and are expensive. However, waterjet cutting can be considered when you find that laser and plasma cutting can only cut very thin materials, produce excessive burrs, or create undesirable heat-affected zones. It can also be considered when flame cutting produces excessive burrs, poor surface finish, or a large heat-affected zone. Furthermore, it can be considered when wire cutting is too slow and cannot cut non-conductive materials. It can also be considered when milling generates excessive chips and waste. It can be considered when circular saws and band saws are too slow and cannot perform non-linear cutting. Waterjet cutting is essential when cutting flammable and explosive materials or in flammable and explosive environments. It is also crucial when you want to avoid producing toxic gases, require no secondary processing, avoid thermal effects, deformation, or micro-cracks, and yet achieve good edge quality and simultaneously cut small holes. In short, waterjet cutting is a versatile cutting method, but it is not optimal in certain situations, so specific analysis is necessary before making a choice. 7 Prospects for the Development of Ultra-High Pressure Waterjet Cutting Technology It is obvious that ultra-high pressure waterjet cutting has many advantages. Waterjet cutting technology can cut almost all kinds of materials, but it also puts forward higher requirements from a technical point of view. For example, CNC technology, waterjet pressure, cutting speed (movement speed of the cutting torch), nozzle shape and outlet diameter, wear resistance of nozzle materials, ultra-high pressure sealing problem, ultra-high pressure pressure vessel safety problem, ultra-high pressure reliability, booster design, mechanical structure design, abrasive selection, jetting technology, and ultra-high pressure waterjet cutting process technology are all the focus of attention in the industry. The development trend of ultra-high pressure waterjet cutting technology can be summarized as follows: (1) The main unit design is becoming more and more perfect. For example, the ultra-high pressure and high power of the main unit. At present, the waterjet pressure has exceeded 500MPa. Research and development of ultra-high pressure and high power of the main unit is very active. Designing a high-pressure system with higher working pressure and more stable pressure is one of the current research hotspots. For example, the high-pressure section of foreign machines is designed with two high-pressure generators, one of which is working and the other is on standby. The two high-pressure generators work alternately to ensure continuous operation of the machine tool. Its perfect automatic diagnosis and protection functions make it safer to operate and easier to maintain. The machine tool has high positioning accuracy, with a linear positioning accuracy of ±0.076mm and a repeatability of ±0.050mm. An automatic height adjustment system is designed to automatically adjust the distance between the cutting head and the workpiece during the cutting process to ensure excellent cutting quality and prevent the sand pipe from being broken. In addition, it can be developed into a form with multiple cutting heads, that is, one high-pressure system can drive 3 to 4 nozzles to cut at the same time. The sand-adding cutting head is equipped with an automatic sand feeding device. Height and collision sensors are used. An automated sand removal system is added, etc. (2) The cutting process parameters are continuously optimized to further improve efficiency, reduce abrasive consumption and reduce energy consumption. For example, the use of the optimal amount of abrasive can save costs. A workpiece material database is stored. Users can automatically change the processing parameters according to the type, thickness and processing requirements of the workpiece material. Operators can expand the database themselves. (3) The control system should pursue intelligent and numerical control. The functions of the dedicated waterjet cutting CNC system should be further improved, and intelligent control should be developed so that the process parameters can be adaptively adjusted during the processing. In particular, the development from a general two-axis control system to a five-axis control system for 3D contour cutting should be realized. A simple programming system with PC control and a graphical display interface should be adopted. The cutting path simulation demonstration can be used to check the cutting process, calculate the cutting path length and cutting time, and calculate the processing cost. (4) Further expand the application range of ultra-high pressure waterjet cutting. Five control axes can cut three-dimensional contours and can further expand the application range. It can be developed from two-dimensional cutting and deburring to hole processing and three-dimensional surface processing. Waterjet processing equipment combined with robots has emerged. The high-pressure water pipe is spirally wrapped around the robot arm. The robot arm and wrist can make the nozzle of the waterjet cutting head run quickly along a straight line or arc to achieve the purpose of 3D processing of workpieces. (5) In the future, research should be intensified in terms of manufacturing materials, processing technology, and assembly technology. Improving the reliability of equipment and the lifespan of vulnerable components, especially key components such as high-pressure pumps and nozzles, is crucial. Because water jets reach speeds of 2-3 times the speed of sound and pressures exceeding 500 MPa, many components like nozzles, sand pipes, and seals are prone to wear and have short lifespans, necessitating downtime for adjustment and replacement. Currently, high-pressure pumps and valve bodies can achieve a lifespan of 6000 hours, and nozzles 2000 hours, but most systems fall short of these targets. Therefore, improving material properties and implementing a series of wear-resistant measures to extend the lifespan of vulnerable components and reduce waterjet cutting costs is a key area for future research. Several high-end waterjet cutting systems have been imported from abroad for cutting titanium alloys, aluminum alloys, stainless steel, carbon fiber, aviation glass, and composite materials. However, due to problems such as slow processing speed, low efficiency, and unsatisfactory processing accuracy, they have not been widely adopted in my country. Researching the technology of high-pressure water jet cutting can improve processing speed and accuracy through process optimization, laying the foundation for its widespread application and enhancing my country's processing capabilities, particularly in the field of special material cutting. Ultra-high pressure water jet cutting technology is a green manufacturing technology aligned with current sustainable development trends. It is a novel cold-state high-energy beam cutting technology that has rapidly developed over the past 20 years, with widespread applications. The development of ultra-high pressure water jet technology reflects the growing acceptance and importance of the green manufacturing concept, which is considered a mainstream cutting technology for priority development in the 21st century. As a green cutting tool for the 21st century, ultra-high pressure water jet cutting machines have many advantages and promising application prospects, and are developing towards high efficiency, multi-functionality, intelligence, high precision, and environmental friendliness. As the "world's manufacturing center," China should quickly equip itself with advanced cutting tools to achieve higher productivity levels. (Proceedings of the 2nd and 3rd Servo and Motion Control Forums)