Precision Boring Technology

Precision boring is a hole machining process that pursues ultimate precision. Its main feature is the use of specialized precision boring tools to achieve high-precision machining through precisely controlled cutting parameters. In practical operations, the selection of precision boring tools is crucial and typically needs to be determined based on the properties of the material being machined and the precision requirements, including the material and geometric parameters of the tool. The precision boring process requires strict control of cutting parameters. The cutting speed is generally chosen between 60-120 m/min, the feed rate is usually controlled at 0.1-0.2 mm/r, and the single-cutting depth generally does not exceed 0.5 mm. The selection of these parameters directly affects the machining accuracy and surface quality. At the same time, to ensure machining accuracy, special attention must be paid to the use of coolant, typically using a cutting fluid that provides sufficient cooling and lubrication to ensure temperature stability during the machining process. In specific applications, precision boring is most commonly used in the manufacturing of high-precision parts such as precision bearing housings, cylinder liners, and hydraulic valve bodies. These parts usually require the roundness error of the holes to be controlled within 0.005 mm, and the surface roughness to reach Ra 0.8 μm or better. To achieve such machining precision, it is necessary not only to select high-precision tools and appropriate cutting parameters but also to consider factors such as the accuracy of the machine tool and the rigidity of the fixtures.

Rough Boring Technology

Rough boring is a machining method that primarily aims to remove material efficiently. During the rough boring process, the operator mainly focuses on the efficiency of material removal, with relatively lower precision requirements. This machining method is usually used as a preliminary process before finish machining, reserving appropriate machining allowances for subsequent finish machining. When selecting cutting parameters, the rough boring process seeks to achieve a larger cutting volume. The cutting speed can generally reach 100-150 m/min, the feed rate can be selected between 0.3-0.8 mm/r, and the single-cutting depth can reach 2-5 mm. Such parameter settings can greatly improve machining efficiency, but they also require the machine tool to have sufficient power and rigidity. In actual operation, special attention must also be paid to chip evacuation, usually requiring the use of high-pressure cooling fluids and special chip evacuation groove designs. Rough CNC boring is mainly applied to the machining of large parts, such as marine engine blocks, large machine tool beds, etc. These parts typically involve a large amount of material removal and have high requirements for machining efficiency. During the machining process, it is necessary to focus on changes in cutting forces and workpiece deformation. If necessary, process measures such as intermediate tempering should be taken to release stresses and ensure machining quality.

Step Boring Process

Step boring is a highly efficient complex hole machining method characterized by its ability to complete the machining of multiple different diameters in one pass. With the use of specially designed step boring tools, the number of tool changes can be significantly reduced, thereby improving machining efficiency. In terms of tool design, special attention must be paid to the relative positions between the cutting edges and the matching of cutting parameters. The selection of machining parameters is particularly important in step boring. Since all the steps are cut simultaneously, the distribution of cutting forces is complex, necessitating a reasonable choice of cutting speed and feed rate. Generally, the cutting speed is chosen between 80-120 m/min, and the feed rate is controlled at 0.2-0.4 mm/r. Additionally, it is necessary to consider the distribution of cutting allowances between the steps to ensure a stable cutting process. Step boring is widely used in the machining of parts with multi-step stepped holes, such as valve bodies and bearing caps. This machining method not only ensures high machining efficiency but also maintains the coaxiality between the steps. In practical applications, special attention must also be paid to the manufacturing and maintenance of the tools, as step boring tools are costly to produce and their service life directly affects the machining cost.

Back Boring Technology

Back CNC boring is an important method for solving hole machining problems under special working conditions. It is mainly used for machining internal holes or back holes that are difficult to access with conventional tools. Back boring tools typically employ special mechanical structures or hydraulic mechanisms to achieve cutting movements in confined spaces. During the back boring process, the operation is challenging and requires precise control of the tool’s feed and expansion. The selection of cutting parameters is relatively conservative, with cutting speeds generally ranging from 40-80 m/min and feed rates between 0.1-0.3 mm/r. At the same time, due to the specialties of the machining position, higher demands are placed on chip evacuation and cooling lubrication. Back boring technology plays a crucial role in the machining of complex parts such as engine crankcases and valve bodies. Although this machining method is relatively less efficient, it is irreplaceable under certain special conditions. In practical applications, special attention must be paid to the selection and maintenance of tools, and it is necessary to develop specialized process procedures and operating protocols.

Five Chamfer Boring Processes

Chamfer boring is an indispensable process in modern machinery manufacturing. It not only improves the appearance quality of parts but more importantly, enhances the assembly performance and service life of the parts. The design of chamfer boring tools needs to consider both radial and axial cutting capabilities, usually achieved with a special blade structure for a stable cutting process. During the chamfer boring process, the selection of cutting parameters should comprehensively consider the size of the chamfer and the surface quality requirements. Generally, the cutting speed is chosen between 60-100 m/min, and the feed rate is between 0.2-0.4 mm/r. It is particularly important to note that the accuracy of the chamfer angle directly affects the assembly quality of the parts, so tool positioning accuracy must be strictly controlled during machining. Chamfer boring technology is widely used in the machining of parts that require a large number of chamfers, such as automobile engine blocks and valve bodies. Through reasonable process design, the chamfering process can be organically combined with other CNC boring operations to improve machining efficiency. In practical applications, attention should also be paid to the detection methods of chamfer dimensions and the establishment of a comprehensive quality control system.

Резюме

With the development of modern manufacturing, CNC boring technology continues to innovate. The five main types of boring methods each have their own characteristics and play important roles in different application scenarios. Mastering the technical features and application essentials of these machining methods is of great significance for improving machining quality and efficiency. In actual production, it is necessary to select the appropriate machining method and develop a scientific process plan based on specific machining needs to achieve the desired machining results.

Введение

Water jet machining, also known as water jet cutting, is a versatile and innovative manufacturing process that uses a high-pressure stream of water to cut through various materials. This technology has gained significant popularity in industries ranging from aerospace to automotive, and from food processing to art and design. Water jet machining is renowned for its precision, flexibility, and environmental friendliness. Unlike traditional cutting methods that rely on heat or mechanical force, water jet cutting uses the kinetic energy of water to achieve clean, precise cuts without altering the material’s intrinsic properties. This article explores the principles, applications, advantages, and limitations of water jet machining, as well as its future potential in modern manufacturing.

The Principles of Water Jet Machining

Water jet machining operates on a simple yet powerful principle: a high-pressure stream of water is directed at a material to erode and cut through it. The process can be divided into two main types:

1. Pure Water Jet Cutting: This method uses only water, pressurized to levels as high as 60,000–90,000 psi (pounds per square inch). The water is forced through a small nozzle, typically made of sapphire or diamond, to create a fine, high-velocity stream. Pure water jet cutting is ideal for softer materials like rubber, foam, paper, and food products.
2. Abrasive Water Jet Cutting: For harder materials such as metals, ceramics, and composites, an abrasive substance (usually garnet) is added to the water stream. The abrasive particles accelerate the cutting process by enhancing the erosive power of the water jet. This method can cut through materials several inches thick with remarkable precision.

The key components of a water jet machining system include:

• High-Pressure Pump: Generates the ultra-high-pressure water stream.
• Nozzle: Focuses the water into a fine, high-velocity jet.
• Abrasive Delivery System: Introduces abrasive particles into the water stream (for abrasive cutting).
• CNC Controller: Guides the nozzle along the desired cutting path with high accuracy.
• Catcher Tank: Collects the spent water and abrasive particles after cutting.

Applications of Water Jet Machining

Water jet machining is used across a wide range of industries due to its versatility and precision. Some of the most notable applications include:

1. Metal Fabrication

Water jet cutting is widely used in the metalworking industry to cut materials such as steel, aluminum, titanium, and copper. Its ability to cut without generating heat makes it ideal for materials that are sensitive to thermal distortion. This is particularly important in aerospace and automotive industries, where precision and material integrity are critical.

2. Stone and Tile Cutting

In the construction and interior design industries, water jet cutting is used to shape natural stone, ceramic tiles, and glass. The process allows for intricate designs and precise cuts, making it a favorite for creating decorative elements and custom fixtures.

3. Food Processing

Water jet cutting is a hygienic and efficient method for cutting food products. It is used to slice bread, cut meat, and portion fish without compromising food safety or quality. The absence of heat ensures that the food’s texture and flavor remain intact.

4. Composites and Plastics

Water jet machining is ideal for cutting composite materials, which are often challenging to process using traditional methods. It is used in the production of carbon fiber components, fiberglass, and other advanced materials.

5. Art and Design

Artists and designers use water jet cutting to create intricate patterns and shapes in materials like wood, acrylic, and metal. The technology enables the production of highly detailed and customized pieces.

6. Medical Device Manufacturing

In the medical industry, water jet cutting is used to fabricate precision components for devices such as implants, surgical instruments, and diagnostic equipment. The process ensures clean edges and minimal material waste.

Advantages of Water Jet Machining

Water jet machining offers numerous advantages over traditional cutting methods, making it a preferred choice for many applications:

1. No Heat-Affected Zone (HAZ): Unlike laser or plasma cutting, water jet cutting does not generate heat, eliminating the risk of thermal distortion, warping, or changes in material properties.
2. Versatility: Water jet cutting can handle a wide range of materials, from soft and delicate substances to hard and durable ones. This makes it a one-stop solution for many industries.
3. Precision: The process allows for extremely tight tolerances, with cutting accuracy as high as ±0.001 inches. This level of precision is essential for industries like aerospace and medical device manufacturing.
4. Environmental Friendliness: Water jet cutting is a clean process that produces no harmful fumes, dust, or waste. The water used can often be recycled, and the abrasive materials are non-toxic.
5. Minimal Material Waste: The narrow kerf (cut width) of the water jet reduces material waste, making it a cost-effective option for expensive materials.
6. No Tool Wear: Since water jet cutting does not involve physical contact between a tool and the workpiece, there is no tool wear, reducing maintenance costs.
7. Ability to Cut Complex Shapes: The CNC-controlled nozzle can follow intricate paths, enabling the cutting of complex geometries and fine details.

Limitations of Water Jet Machining

Despite its many advantages, water jet machining does have some limitations:

1. Cutting Speed: While water jet cutting is precise, it can be slower than other methods like laser or plasma cutting, especially for thick materials.
2. Material Thickness: Although water jet cutting can handle thick materials, the process becomes less efficient as thickness increases. For extremely thick materials, alternative methods may be more suitable.
3. Operating Costs: The high-pressure pumps and abrasive materials can be expensive to maintain and replace, leading to higher operating costs compared to some traditional methods.
4. Surface Finish: While water jet cutting produces clean edges, the surface finish may require additional post-processing for certain applications.
5. Noise and Vibration: The process can generate significant noise and vibration, which may require mitigation measures in some environments.

Innovations and Future Trends

Water jet machining continues to evolve, driven by advancements in technology and the growing demand for precision manufacturing. Some of the key trends and innovations in the field include:

1. Hybrid Cutting Systems: Combining water jet cutting with other technologies, such as laser or plasma cutting, to leverage the strengths of each method.
2. Automation and Robotics: Integrating water jet cutting systems with robotic arms and advanced CNC controls to enhance precision and efficiency.
3. 3D Water Jet Cutting: Developing systems capable of cutting complex three-dimensional shapes, opening up new possibilities for manufacturing and design.
4. Eco-Friendly Abrasives: Research into alternative abrasive materials that are more sustainable and environmentally friendly.
5. Improved Pump Technology: Advances in high-pressure pump design to increase efficiency and reduce energy consumption.
6. AI and Machine Learning: Using artificial intelligence to optimize cutting parameters and improve process control.

Вывод

Water jet machining is a transformative technology that has revolutionized the way materials are cut and shaped. Its ability to deliver precision, versatility, and environmental benefits makes it an indispensable tool in modern manufacturing. While it has some limitations, ongoing advancements in technology are addressing these challenges and expanding the potential applications of water jet cutting. As industries continue to demand higher levels of precision and efficiency, water jet machining is poised to play an increasingly important role in shaping the future of manufacturing. Whether it’s cutting intricate designs in metal, slicing food products, or fabricating medical devices, water jet machining proves that sometimes, the simplest element—water—can be the most powerful tool.

Functions of Cutting Fluid

Imagine the harsh working conditions when a twist drill rotates at astonishing speeds, penetrating deep into the workpiece for deep hole drilling. High temperatures, high pressures, and rapid rotation are extreme conditions that put immense stress on both the cutting tool and the workpiece. This is where cutting fluid steps in as a silent hero, playing a crucial role in cooling, lubricating, and cleaning during the drilling process.

Cooling Function

One of the primary functions of cutting fluid is cooling. During twist drill deep hole drilling, the friction between the tool and the workpiece generates a significant amount of heat. Without timely cooling, the tool is prone to damage due to overheating. Cutting fluid acts like a refreshing spring, carrying away the heat, protecting the tool, and ensuring the smooth progress of the drilling process.

Lubrication Function

In addition to cooling, cutting fluid also serves as a lubricant. During drilling, the contact area between the tool and the workpiece is very small, yet the pressure exerted is very high. Without sufficient lubrication, the tool can easily scratch the surface of the workpiece, affecting the quality of the hole. Cutting fluid acts like a lubricating film, reducing friction between the tool and the workpiece, decreasing wear, and improving the finish of the drilled hole.

Cleaning Function

Certainly, the cleaning function of cutting fluid should not be overlooked. During the drilling process, a significant amount of chips and metal powder is produced. If these chips are not removed in a timely manner, they can easily accumulate inside the drilled hole, leading to blockages and even damaging the tool. Cutting fluid acts like a diligent cleaner, continuously flushing the inside of the hole, carrying away the chips and metal powder, ensuring the hole remains unobstructed.

Distribution of Cutting Fluid

However, the distribution of cutting fluid in twist drill deep hole drilling is not uniform. Due to the limitations of the depth and diameter of the hole, it is difficult for the cutting fluid to reach the bottom of the hole directly. In some areas of the hole, the cutting fluid may form dead zones where the flow rate is very slow or almost non-existent. This results in the tool not receiving adequate cooling and lubrication in these areas, increasing the risk of tool wear and hole blockages.

How Cutting Fluid Affects Chip Removal

Chip removal is equally crucial in twist drill deep hole drilling. Chips are metal fragments produced during the drilling process, and if not removed promptly, they can easily accumulate inside the hole, forming blockages. Once a blockage occurs, it not only affects the quality of the hole but also puts tremendous pressure on the tool, which can lead to tool breakage. Therefore, timely chip removal is key to ensuring the smooth progress of the drilling process.

In twist drill deep hole drilling, the chip conveyance mechanism is relatively complex. Due to the limitations of the hole’s depth and diameter, chips cannot be easily expelled through the hole. They need to navigate through the tiny gap between the tool and the workpiece and then be carried out of the hole with the flow of cutting fluid. However, this process is fraught with challenges. The shape, size, and density of the chips all affect their conveyance efficiency. If the chips are too large or dense, they can easily form blockages inside the hole, leading to drilling failures.

Using 3D Simulation to Optimize Cutting Fluid Distribution for Improved Chip Removal

To optimize the distribution of cutting fluid and the removal of chips, scientists have conducted extensive research. They have utilized advanced 3D multiphysics simulation methods to conduct detailed simulations and analyses of the twist drill deep hole drilling process. These simulations not only reveal the flow characteristics of the cutting fluid inside the hole but also demonstrate the chip conveyance mechanism within the hole. Through these simulations, scientists have gained a deeper understanding of the reasons behind uneven cutting fluid distribution and inefficient chip removal, providing strong support for optimizing the drilling process.

In simulation studies, the coupled particle simulation (SPH-DEM) method has played a significant role. This method accurately simulates the movement and interaction of cutting fluid and chips inside the drilled hole. Through the SPH-DEM method, scientists can observe the flow trajectory of the cutting fluid within the hole, as well as the conveyance process of chips in the cutting fluid. These observations not only validate the accuracy of the simulation method but also provide an important basis for optimizing the distribution of cutting fluid and chip removal strategies.

In addition to coupled particle simulation, CFD (Computational Fluid Dynamics) simulation has also played a crucial role in the analysis of cutting fluid flow. CFD simulation can model the flow state of cutting fluid inside the drilled hole, including parameters such as flow velocity, pressure, and temperature. Through the analysis of these parameters, scientists can understand the distribution of cutting fluid within the hole, as well as the impact of different cutting fluid parameters on hole quality. These analytical results are of significant guiding significance for optimizing cutting fluid formulations and process parameters.

In the experimental validation phase, scientists designed a series of experiments to verify the accuracy of the simulation results. They selected different cutting parameters, types of cutting fluids, and concentrations for the experiments, and recorded data such as the quality of the drilled holes, the flow rate of the cutting fluid, and the chip removal situation. By comparing the experimental data with the simulation results, the scientists found a good consistency between the two. This not only verified the reliability of the simulation method but also provided strong support for optimizing cutting fluid distribution and chip removal strategies.

During the experimental process, the scientists also discovered some interesting phenomena. For example, under certain cutting parameters, although the flow rate of the cutting fluid was high, the quality of the drilled holes was not ideal. After analysis, they found that this was due to the formation of dead zones of the cutting fluid inside the hole, which resulted in insufficient cooling and lubrication for the tool in certain areas. To address this issue, they adjusted the injection angle and flow rate of the cutting fluid, successfully improving the distribution of the cutting fluid and enhancing the quality of the drilled holes.

In addition, scientists have also found that the chip removal is closely related to parameters such as the flow rate and viscosity of the cutting fluid. When the flow rate of the cutting fluid is too high, chips are easily carried away by the fluid; however, when the viscosity of the cutting fluid is too high, chips tend to form blockages inside the hole. Therefore, when optimizing the cutting fluid formulation, it is necessary to consider the flow rate, viscosity, and other parameters of the cutting fluid to ensure the smooth removal of chips.

Резюме

Through extensive experimentation and simulation studies, scientists have successfully optimized the cutting fluid distribution and chip removal strategies in twist drill deep hole drilling. They have found that by adjusting parameters such as the injection angle, flow rate, and viscosity of the cutting fluid, the distribution of the cutting fluid inside the hole can be significantly improved; at the same time, by optimizing the structure of the cutting tool and cutting parameters, the efficiency of chip removal can also be enhanced. These research findings not only improve the quality and efficiency of twist drill deep hole drilling but also provide valuable references for precision manufacturing in other fields.

The distribution of cutting fluid and chip removal in twist drill deep hole drilling is a complex and important process. Through scientific experimentation and simulation studies, we can gain a deeper understanding of the physical mechanisms and influencing factors in this process; by optimizing cutting fluid formulations and process parameters, we can significantly improve the quality and efficiency of drilling. In the future, with the continuous advancement of technology and the development of the manufacturing industry, it is believed that twist drill deep hole drilling technology will have an even broader development prospects and a wider range of applications.

Experimental Method

TiN, TiAlN, TiN-MoS?, and CrTiAlN composite coatings were deposited on YT14 cemented carbide cutters using a closed-field unbalanced magnetron sputtering ion plating equipment from Teer Company. The nano hardness and elastic modulus of the coatings were measured using a Nano Test 600 nano hardness tester. To reduce experimental errors, the hardness and elastic modulus values were the average of five measurements. The hardness of the coatings was also verified using a Vickers microhardness tester, and the morphology and phase structure of the cutter coatings were observed and analyzed using a Quanta 200 scanning electron microscope (SEM) and an Advance 8 X-ray diffractometer (XRD). The cutting tests of the coated cutters were conducted on a CNC machining center, with PCNiMoVA steel as the cutting material. The flank wear was observed and measured using a 30x tool microscope. The cutting time when the wear strip width on the flank face exceeded 0.6mm was used as the basis for evaluating the tool’s life, and the cutting life of the tools was compared.

Experimental Results and Analysis

Coating Hardness and Elastic Modulus Testing

Figure 1 shows the loading and unloading curves obtained during the nano hardness measurement process of the CrTiAlN composite coating. The loading and unloading curves not only provide the hardness of the CrTiAlN film but also its elasticity. Define R = (ha – h) / h as the elastic recovery coefficient, where ha is the indentation depth at maximum load, and h is the residual depth of the indentation after unloading. According to the definition of R, the greater the value of R, the greater the elasticity of the film. Therefore, based on the nano indentation curve in Figure 1, the hardness of the CrTiAlN film is 33 GPa, and the elastic modulus is 675 GPa. Figure 2 is a comparative analysis chart of the nano hardness of TiN, TiAlN, TiN-MoS?, and CrTiAlN coatings. It can be seen from the figure that the nano hardness measurement values of the four coatings are 18 GPa, 30 GPa, 15 GPa, and 33 GPa, respectively. The nano hardness ranking is as follows: CrTiAlN > TiAlN > TiN > TiN-MoS?.

Figure 3 shows the measured elastic modulus values of each coating. It can be seen from the figure that the elastic modulus of the four coatings are 214 GPa, 346 GPa, 164 GPa, and 675 GPa, respectively. The ranking of the elastic modulus is as follows: CrTiAlN > TiAlN > TiN > TiN-MoS?. This indicates that the elastic modulus of the coatings is directly proportional to their hardness. However, the CrTiAlN coating shows the greatest relative increase in elastic modulus, with a value significantly higher than other coatings, reaching 675 GPa, which suggests that the deposited CrTiAlN coating has both high hardness and high elasticity.

Meanwhile, the Vickers microhardness tester was used to perform microhardness verification tests on each cutter coating, with a indentation load of 15g and a duration of 10 seconds. The measurement results are shown in Figure 4. By comparing the coating nano hardness in Figure 2 with the coating microhardness values in Figure 4, it can be found that the microhardness variation trend of each coating is the same as the nano hardness variation trend, with the CrTiAlN coating having the relatively highest Vickers microhardness at HV1560.

Analysis of Coating Surface Morphology

The surface morphologies of the TiN, TiAlN, TiN-MoS?, and CrTiAlN coated cutters are shown in Figure 5. It can be observed from the figure that there is a significant difference in the surface morphology of the four coatings, indicating that the addition of composite elements has caused a great change in the crystalline state of the TiN compounds. Among them, the TiN coating surface phase tissue is uniform, with relatively fine particles, while the TiAlN coating surface morphology is relatively rough, with coarser particle tissue. The TiN-MoS? coating surface is distributed with a large amount of flaky mixed structure, mainly due to the uniform distribution of MoS? phase in the TiN coating, tending towards a composite structure in the mixed state, which serves a self-lubricating function. The CrTiAlN coating surface grains are relatively fine, the coating is dense and uniform, and the surface is distributed with a large number of hard points.

Drilling Test

The four types of coated cemented carbide cutters were used to machine PCNiMoVA steel, and the wear condition of the cutters was inspected to compare the durability of different coated cutters.

The cutting test conditions for the coated cutters were as follows: the cutting method was external cylindrical cutting, the cutting speed was 160 m/min, the feed rate was 0.15 mm/r, the cutting depth was 0.5 mm, and dry cutting was performed. The cutting time when the wear strip width on the flank face exceeded 0.6 mm was used as the basis for evaluating the tool’s life, and the cutting life of the tools was compared.

A comparison of the cutting life of the coated cutters is shown in Figure 6.

From the figure, it can be seen that under dry cutting conditions, the cutting life of the uncoated cutters was the shortest, and the service life of the coated cutters was significantly better than that of the uncoated cutters. Among them, the CrTiAlN coated cutter had the longest cutting life. The ranking of the cutting life of the four coated cutters was as follows: CrTiAlN > TiN-MoS? > TiAlN > TiN. This indicates that Cr and Al elements form hard phases in the TiN coating, and the addition of Al elements is beneficial for the formation of Al oxides, which avoids further oxidation during the cutting process, improves the oxidation resistance of the cutters, and is conducive to increasing the cutting life of the tools. Meanwhile, the MoS? lubricating phase helps to reduce the friction coefficient of the cutters, improve the anti-wear capability of the tools, and also extends the service life of the cutters.

In summary, due to the comprehensive utilization of the advantages of various coating components in the multi-component composite coatings, they achieve better comprehensive performance, ensuring excellent wear resistance and toughness, reducing the formation of built-up edge, and possessing mechanical shock and thermal shock resistance, which can greatly improve the tool life.

XRD Test Analysis

XRD analysis method was used to characterize the phase structure of the CrTiAlN tool coating with the best cutting performance, and the results are shown in Figure 7. The XRD spectrum analysis indicates that the crystal phases of the coating are mainly composed of Cr, CN, CEN, and TiN at room temperature, and the amorphous phase in the coating was not detected. At the same time, high magnification scanning analysis of the tool coating revealed a large number of hard phase particles distributed on the coating surface. Combined with X-ray diffraction analysis, it is known that these hard phases are mainly CN, CrN, TiN, and AlN phases. These hard phases are beneficial for improving the cutting life of the coated cutters.

Вывод

The author has prepared TiN, TiAlN, TiN-MoS?, and CrTiAlN composite coatings using a closed-field unbalanced magnetron sputter ion plating PVD coating process. Comparative tests on the mechanical properties and cutting performance of the coatings show that:

The nanoindentation analysis obtained the nano hardness ranking of the four types of cutter coatings as follows: CrTiAlN > TiAlN > TiN > TiN-MoS?. The elastic modulus of the coatings is directly proportional to their hardness.

Under dry cutting conditions, when drilling PCNiMoVA steel, the cutting life of the coated cutters is ranked as: CrTiAlN > TiN-MoS? > TiAlN > TiN. This indicates that the cutting performance of the multi-component composite coatings is significantly better than that of the simple TiN coating, suggesting a direction for the future development of coated cutters.

This paper aims to perform high-speed machining of TC4 titanium alloy using a vibration-damping end mill (end mill with unequal tooth pitch angles). The MATLAB software is used to perform a Fast Fourier Transform (FFT) on the milling force, with a focus on analyzing the impact of chatter on the machining of titanium alloys. The objective is to optimize the cutting speed while ensuring the quality of the machined surface and low cutting force, thereby improving cutting efficiency.

Dynamic Milling Force Model

To study the cutting stability, a reasonable dynamic model needs to be established. Compared to the workpiece with higher stiffness, the end mill can be considered as an elastic body. Since the end mill has a very high stiffness in the axial (z-direction) direction, the milling machining system can be simplified into a “spring-damping” system with two mutually perpendicular degrees of freedom in the x-direction (feed) and y-direction, as shown in Figure 1. Φj(t) represents the rotation angle of the end mill; hi(t) represents the dynamic chip thickness; fz is the feed per tooth.

Establishing the equations of motion for 2 degrees of freedom?movement:

In the formula: m, s, c, k represent the mass, displacement, damping coefficient, and elastic coefficient of the cutting system, respectively; Fx(t) and Fy(t) are the dynamic milling forces in the x and y directions, respectively. The milling forces studied in this paper are all Fy, and the motion equation is simplified to a single degree of freedom motion equation:

The milling force Fy(t) is related to the dynamic chip thickness hi(t) during the milling process and is a function of the end mill’s rotation angle φj(t), making it a periodic function. The variation frequency of the cutting force is the tool tooth passing frequency (TPF). Due to manufacturing and clamping errors causing the tool system to be asymmetric, its variation frequency is the spindle rotation frequency (SF).

The spindle rotation frequency (SF) is defined as:

In the formula: ω is the angular velocity of the spindle rotation, in radians per minute; v is the linear velocity of the spindle, in meters per minute; D is the diameter of the end mill, in millimeters; the unit of spindle rotation frequency is Hz.

The tool tooth passing frequency (TPF) is defined as:

In the formula: N represents the number of teeth on the end mill.

Milling Experiment

Experimental Setup, Workpiece Material, and Режущий инструмент

The milling experiment setup is shown in Figure 2. The machine used is a DAEWOO ACE-V500 machining center with a rated power of 15 kW and a maximum torque of 286.2 N?m. The milling force is measured by a Kistler 9257B three-coordinate force measuring instrument with a sampling frequency of 7,000 Hz. The cutting tool used is a 4-fluted variable pitch solid carbide end mill, and the distribution of the tooth pitch angles at the bottom is shown in Figure 3. The diameter of the end mill is 20 mm, and the overhang length is 74.3 mm. The workpiece material is TC4 titanium alloy.

Section 2.2: Experimental Design

The experiment was conducted using dry cutting and conventional milling. The cutting speed v, spindle rotation frequency (SF), and tool tooth passing frequency (TPF) are listed in Table 1. The feed per tooth fz, axial cutting depth ap, and radial cutting depth ae were kept constant at 0.08 mm/tooth, 20 mm, and 0.5 mm, respectively. The range of cutting speed varied from 80 to 360 m/min. Figure 4 shows the milling sequence, where the sequence numbers correspond to those in Table 1.

Experimental Results

Time-Domain Analysis of Cutting Forces

Figure 5 shows the relationship between the maximum amplitude of Fy and the cutting speed (v). From the figure, it can be observed that when the cutting speed is in the range of 80~160 m/min, the maximum milling force remains essentially unchanged. When the cutting speed reaches 200 m/min, the milling force suddenly increases, and when the cutting speed reaches 240 m/min, the milling force reaches its first peak. Subsequently, as the cutting speed increases,The cutting force significantly decreases until the cutting speed increases to 320 m/min, at which point the milling force reaches its minimum. When the cutting speed is 360 m/min, the milling force reaches its maximum value.

Analysis of Milling Force Spectrum

The frequency domain provides more information about the cutting process than the time domain. As the direct responder of the tool and workpiece, the milling force can describe the vibration condition of the cutting system. From the collected y-direction milling force Fy signal, a 4-second segment of data in the middle was selected and processed using MATLAB software for Fast Fourier Transform (FFT) to analyze the milling force spectrum and determine the machining condition.

Since the variation frequency of the milling force is TPF, the peaks of the milling force generally appear at TPF and its integer multiples (n·TPF) in the frequency domain. However, due to tool manufacturing and mounting errors, the variation frequency of the milling force is often SF, meaning the spectrum peaks of the milling force appear at SF and its integer multiples (n·SF).

Figures 6(a) to (h) show the milling force spectrum analysis at different cutting speeds. From the figures, it can be seen that when the cutting speed is 80 and 120 m/min, the peaks of the milling force spectrum appear at the spindle rotation frequency (SF) and the tool tooth passing frequency (TPF). When the cutting speed is 160, 280, and 320 m/min, the peaks of the milling force appear not only at SF and TPF but also at high frequencies. The peak at the spindle rotation frequency (SF) is larger at higher cutting speeds than at lower cutting speeds, which is due to the mass imbalance caused by tool eccentricity. As the cutting speed increases, the centrifugal force increases, leading to an increase in the y-direction milling force peak. When the cutting speed is 240 and 360 m/min, the larger peaks at high frequencies do not appear at SF and its integer multiple frequencies, indicating that chatter occurs in the cutting system at these times, with chatter frequencies of 734 Hz (v=240 m/min), 730 Hz, 1,111 Hz, 1,268 Hz, 1,363 Hz, and 1,459 Hz (v=360 m/min). Combined with Figure 5, it can be determined that when chatter occurs, the radial milling force increases significantly.

Machined Surface Quality

The Wyko NT9300 white light interferometer was used to measure the machined surface topography. This instrument uses the principle of optical interference and can achieve nanometer precision in topography measurement.

Figure 7 shows the machined surface topography measured by the white light interferometer. From the figure, it can be seen that when v=160 m/min, the surface topography is the best. When v=240 and 360 m/min, there is a large area of material removal on the machined surface. This is partly due to chatter, which increases friction, extrusion, and tearing between the tool and the workpiece, causing the tool to produce unstable vibrations on the workpiece surface, leading to overcutting in some areas. On the other hand, these violent movements cause the cutting temperature to rise, resulting in adhesion between the flank of the tool and the workpiece. As the tool moves, most of the adhered workpiece material is carried away by the tool.

By comparing Figure 5 with Figure 8, it is found that the roughness curve follows a similar trend to the cutting force curve. When chatter occurs (at cutting speeds of 240 and 360 m/min), both the cutting force and roughness reach their maximum values, proving that chatter not only increases the cutting force but also increases the surface roughness.

From Figure 8, it can also be seen that for stable cutting (cutting speeds of 80 to 160 m/min), the higher the cutting speed, the lower the surface roughness. Although stable cutting occurs at cutting speeds of 200 and 280 m/min, Figures 6(d) and (f) show that the high-frequency peaks of the milling force are significant, which affects the surface quality. When the cutting speed is 320 m/min, the cutting force is small, and the spectrum peaks are also small, but the surface roughness is poor. This is due to the tool eccentricity (larger peak at SF) having a significant impact on surface roughness at high cutting speeds.

Вывод

Under dry cutting conditions, when high-speed milling TC4 titanium alloy, chatter occurs at cutting speeds of 240 m/min and 360 m/min, with chatter frequencies around 730, 1,111, 1,363, and 1,459 Hz.

For stable cutting, the cutting speed has little effect on the magnitude of the milling force. However, when chatter occurs, the cutting force significantly increases, and the surface quality of the machining deteriorates.

At a cutting speed of 160 m/min, the surface roughness is low, and the cutting force is small, so 160 m/min can be recommended as the optimal cutting speed.

How to Solve Burr Issues

Chemical Deburring

Chemical deburring utilizes chemical energy for processing. Chemical ions adhere to the surface of the parts, forming a film with high electrical resistance and low conductivity, which protects the workpiece from corrosion. Since metalworking burrs are higher than the surface, they can be removed through chemical action. This method of deburring is widely used in fields such as pneumatic, hydraulic, and construction machinery.

High-Temperature Deburring

First, place the parts that need deburring into a tightly sealed chamber, then introduce the chamber into a hydrogen-oxygen mixed gas environment with a certain pressure. Ignite the mixed gas to cause an explosion, releasing heat to burn off the burrs without damaging the parts.

Roll Grinding Deburring

Place the parts and abrasive materials into a closed drum. As the drum rotates, a dynamic torque sensor, along with the parts and abrasive, generates a grinding action to remove metalworking burrs. Abrasives can be made of quartz sand, wood chips, alumina, ceramics, and metal rings, among others.

Manual Deburring

This method is more traditional and also the most time-consuming and labor-intensive. It mainly involves manually grinding with tools such as steel files, sandpaper, and grinding heads. The most commonly used tool in production now is the trimming knife.

Process Deburring – Edge Rounding

Edge rounding can refer to any action that removes the sharpness from the edges of metal components. However, it is typically associated with creating a radius on the edges of parts.

Edge rounding is not simply about removing sharpness or deburring, but about breaking the edges of metal components to improve their surface coating coverage and protect them from corrosion.

Removing metalworking burrs in Milling Parts

In milling parts, deburring is more complex and costly, as multiple metalworking burrs are formed at different positions with varying sizes during milling. It is particularly important to select the correct process parameters to minimize metalworking burr size.

Main Factors Affecting Burr Formation in End Milling

① Milling parameters, milling temperature, and cutting environment, among others, have a certain impact on burr formation. Some key factors, such as feed rate and milling depth, are reflected through the plane cutting angle theory and the Edge Engagement Sequence (EOS) theory.

② The better the plasticity of the workpiece material, the more likely it is to form Type I burrs. In the processing of brittle materials with end milling, if the feed rate or the plane cutting angle is large, it is conducive to the formation of Type III burrs (deficits).

③ When the angle between the end face of the workpiece and the machined plane is greater than a right angle, the increased support stiffness of the end face can suppress machining burr formation.

④ The use of cutting fluid is beneficial for extending tool life, reducing tool wear, lubricating the milling process, and thereby reducing the size of burrs.

⑤ Tool wear has a significant impact on machining burr formation. When the tool wears to a certain extent and the tip radius increases, not only does the burr size in the tool retracting direction increase, but type burrs may also form in the tool cutting-in direction.

⑥ Other factors, such as tool material, also have a certain impact on burr formation. Under the same cutting conditions, diamond tools are more effective in suppressing metalworking burr formation than other types of tools.

How to Effectively Handle Burrs Generated During Tool Retraction

To suppress burrs generated during tool retraction, eliminating the space where burrs are produced is an effective method. For example, measures such as chamfering can be taken to reduce the space before retracting the tool.

Using appropriate cutting conditions to suppress machining burrs should aim to minimize the amount of cutting residue, and it is necessary to select the most suitable tool and cutting conditions. Use tools with a large rake angle and sharp cutting edges. Increase cutting speed to improve cutting characteristics. Especially during finish cutting, it is essential to use the minimum cutting depth and feed rate.

The size of the space between the tool and the workpiece determines the size of the burrs. Let’s take a look at the relationship diagram below.

Резюме

In fact, during the machining process, burrs are inevitable, so it is best to address the metalworking burr issue through process improvements, avoiding excessive manual intervention. Using chamfering end mills can reduce the space where burrs are produced, effectively remove burrs, and is also a very suitable method for clearing burrs.

Mechanism of Tool Breakage

Abrasive Wear by HardParticles

This is mainly caused by mechanical wear from impurities in the workpiece material, hard particles such as carbides, nitrides, and oxides contained in the material matrix, and fragments of built-up edge. These hard particles scratch grooves on the tool surface. Abrasive wear by hard particles occurs in tools at all cutting speeds, but it is the main cause of wear in low-speed steel tools. At low cutting temperatures, other forms of wear are not significant. It is generally believed that the amount of wear caused by abrasive wear by hard particles is proportional to the relative sliding distance or cutting distance between the tool and the workpiece.

Adhesive Wear

Adhesion refers to the bonding phenomenon that occurs when the tool and workpiece material come into contact at atomic distances. It is a so-called cold welding phenomenon that occurs due to plastic deformation on the actual contact surface of the friction surfaces under sufficient pressure and temperature. It is the result of the adhesive force between the fresh surface atoms formed by the plastic deformation of the two friction surfaces. The adhesive points on the two friction surfaces are sheared or stretched and carried away by the opposite surface due to relative motion, which causes adhesive wear.

Adhesive wear can occur on the contact surfaces between two materials, whether on the soft material side or the hard material side. Generally, the breakdown of adhesive points occurs more frequently on the side with lower hardness, i.e., the workpiece material. However, the tool material often has defects such as uneven structure, internal stresses, microcracks, pores, and local soft spots, so the carbide tool surface also frequently breaks and is carried away by the workpiece material, forming adhesive wear. High-speed steel, ceramic, cubic boron nitride, and diamond tools can all experience wear due to adhesion. The size of the carbide grains in cemented carbide has a significant impact on the speed of adhesive wear. The temperature at which the tool material and workpiece material adhere to each other greatly affects the severity of adhesive wear. Other factors such as the hardness ratio of the carbide tool to the workpiece material, the shape and structure of the tool surface, as well as cutting conditions and the stiffness of the process system, all affect adhesive wear.

Diffusion Wear

Due to the high temperatures during cutting, and the fact that the carbide tool surface is constantly in contact with the freshly cut surface, which has high chemical reactivity, the chemical elements of the two friction surfaces may diffuse into each other. This results in a change in the chemical composition of both, weakening the properties of the tool material and exacerbating the wear process. Diffusion wear increases with the rise in cutting temperature. For a given tool material, as the temperature increases, the rate of diffusion initially increases slowly and then accelerates. Different elements have different diffusion rates, so the severity of diffusion wear is greatly related to the chemical composition of the carbide tool material. Additionally, the rate of diffusion is also related to the flow velocity of the chip layer on the tool surface, which corresponds to the velocity of the chip flowing over the rake face. Slower flow velocity results in slower diffusion.

Figure 1 shows the diffusion wear of WC-Co cemented carbide, indicating that tungsten carbide (WC) and cobalt (Co) have dissolved into the surface layer of the steel, and this surface layer has also melted at the interface. In the figure, the upper layer is steel, the lower layer is cemented carbide, and the middle white layer is the melted layer, which is in a locally melted area, with WC grains surrounded within it. Because the temperature is higher at the crescent-shaped depression on the rake face, the diffusion rate is high and wear occurs quickly. At the same time, since adhesion occurs when the temperature rises to a certain degree, diffusion wear and adhesive wear often occur simultaneously, easily forming a crescent-shaped depression.

Chemical Wear

Chemical wear occurs at certain temperatures where the tool material reacts chemically with surrounding media (such as oxygen in the air, extreme pressure additives like sulfur and chlorine in cutting fluids, etc.), forming a layer of compounds with lower hardness on the tool surface, which is then carried away by the chips, accelerating tool wear; or because the tool material is corroded by a certain medium, causing tool wear.

The main types of normal tool wear include hard particle wear, adhesive wear, diffusion wear, and chemical wear, and there are interactions among them. For different tool materials, under different cutting conditions, and when machining different workpiece materials, the primary cause of wear may be one or two of these types.

Methods to Improve Tool Performance

Because it is difficult to balance the wear resistance and toughness of cemented carbide tool materials, users can only select suitable tool materials from various grades of cemented carbide based on specific machining objects and conditions, which brings inconvenience to the selection and management of cemented carbide tools. To further improve the comprehensive cutting performance of cemented carbide tool materials, current research focuses include the following aspects:

Grain Refinement

By refining the grain size of the hard phase, increasing the intergranular surface area of the hard phase, and enhancing the intergranular bonding strength, the strength and wear resistance of cemented carbide tool materials can be improved. When the WC grain size is reduced to sub-micron levels, the hardness, toughness, strength, and wear resistance of the material can all be enhanced, and the temperature required for full densification can also be reduced. The grain size of conventional cemented carbide is 3~5μm, fine-grained cemented carbide has a grain size of 1~1.5μm (micron level), and ultra-fine-grained cemented carbide can have a grain size below 0.5μm (sub-micron, nano-level). Common grain refinement processes include physical vapor deposition, chemical vapor deposition, plasma deposition, and mechanical alloying. Since these grain refinement processes are not yet mature, nano-grains easily grow into coarse grains during the sintering of cemented carbide, and the general growth of grains will lead to a decrease in material strength. Individual coarse WC grains are often a significant factor causing material fracture. On the other hand, fine-grained cemented carbide is relatively expensive, which also restricts its promotion and application.

Surface, Overall Heat Treatment, and Cycle Heat Treatment for Carbide tools

Surface treatments such as nitriding and boriding on the surfaces of cemented carbide with good toughness can effectively improve their surface wear resistance. For cemented carbide with good wear resistance but poor toughness, overall heat treatment can change the bonding composition and structure in the material, reduce the adjacency of the WC hard phase, thereby improving the strength and toughness of the cemented carbide. Using cycle heat treatment processes to alleviate or eliminate stress at the grain boundaries can comprehensively improve the overall performance of cemented carbide materials.

Addition of Rare Metals

Adding rare metal карбидs such as TaC and NbC to cemented carbide materials can form complex solid solution structures with the original hard phases WC and TiC, further strengthening the hard phase structure. At the same time, it can inhibit the growth of hard phase grains and enhance the uniformity of the structure, which is greatly beneficial to improving the comprehensive performance of cemented carbide. In the standard P, K, M grades of cemented carbide, there are grades that have added Ta(Nb)C (especially more in the M grade).

2 The forming process and main characteristics of boundary notch in cemented carbide cutting tools

The boundary notch of cemented carbide cutting tools is a wear area,which is?relatively large,resulting from friction between main cutting edge and the surface of?the workpiece as the following Fig.1.Fig.1(a)shows a traditional wearing type of the?flank.The rake face A,and flank face Aa?are also shown.Fig.1 (b)shows the main?dimension of boundary notch of the lathe tool,in which VN represented the height of?boundary notch and C refers to the width.It is apparent that the greater the?dimensions of VN and C are,the greater it destroys the performance of tools and influences the machining quality.

By experiment,the forming process of the boundary?notch can be divided into the?following three steps:firstly,several micro cracks are produced at main cutting edge.Secondly,the mesh fractures are found in the boundary areas and they will spread.

Finally,the piece material will be denuded and the boundary notch is formed.In the?subsequent cutting process,the dimension of the boundary becomes bigger and?bigger.

Fig.2 shows the forming process of boundary notch of the cemented carbide?cutting?tools.

Main factors to influence boundary notch are mechanical performance of the?piece material,the cutter material,and geometry parameter of the cutter.The?following experiments were carried out in order to expound the forming mechanism?and evolution rules of the boundary notch.

3 Experiment conditions and testing measures for assessing boundary notch in cemented carbide cutting tools

The lathe C6130 and reversible cutting tool are used in the experiment.Five?cutter materials are employed.Main mechanical parameters of cutter material are?shown in Table 1.

The machining piece is the friction-welded line of the single hydraulic pillar.The?width of the welded line is 15mm and the machining allowance is 5.5mm.Besides,the above pillar is welded with 270SiMn and 45#steel.The relatively mechanical?performances of the welded line are shown in Table 2.

Based on manufacturing experience and relative information in China and other?countries about similar machining process,the chosen machining and tool geometry?parameters are shown in Table 3.

The boundary notch dimensions of the cemented carbide cutting tools (boundary?notch height VN and width C are directly attained by tool microscope.In order to?ensure reliability of the results,repeated experiments are carried out.The recurrent?performance is good.

Influences of Cutting angles

Influences of Cutting Edge Angle

The results of the variety boundary notch are shown as in Fig.4 when the cutting?edge angle is changed.From Fig.4 we can find that,with the lessening of the cutting?edge angle Kr,the dimensions of the boundary notch decrease.The reason is that?with the lessening of the cutting edge angle Kr,the length of the cutting edge that?acts on cutting becomes larger and the average loads on the cutting edge be?come?lighter.

Influences of Cutter Corner Radius r

The results of the variety boundary notch with the cutter corner changing are?shown as Fig.5.The boundary notch dimension decreases with the cutter corner radius?are becoming lesser.The reason is that with the increasing of the cutter corner radius,the impact-resistance performance.

Therefore,under the same cutting conditions,boundary notch dimensions (VN,C)decrease?when the cutter corner radius becomes lesser.

Influences of Negative Chamfer bal in cutting tool

The experiment results of the variety boundary notch are shown as in Fig.6 when?the width of the negative chamfer is changed.The dimension of the boundary notch?will decrease when the width of the negative chamfer ba decreases.Therefore,in?order to resist or decrease the cutter boundary notch,the lesser negative chamfer bal should be chosen.

Deburring Machining Process

The burrs have some influences on cutter boundary notch in metal machining?process.A deburring cutter is chosen to decrease the adverse influence on cutter.A?different result between deburring machining process and common machining process?is shown as in Fig.7.It can be seen that about 75%of the boundary notch is?decreased.So,burr is a main factor to produce and increase the boundary notch of the?cutter.

Вывод

From above experimental research and theoretical analysis,the following?conclusions are attained:

1)Boundary notch of the cutting tool can be expressed by boundary notch height?VN and boundary notch width C.The forming processes of boundary notch can be?divided into three steps:micro-tipping appears firstly;Then,mesh fractures expand;Finally,boundary notch results.

(2)Main factors that influence boundary notch of cemented carbide cutter are?piece material,cutter material and cutter geometry parameters.

(3)Deburring machining process and adjusting cutting tool geometry parameters(to reduce edge angle K,and width of negative chamfer ba,to increase cutter corner?radius re)can be chosen to decrease effectively boundary notch,which ensures the?quality of workpiece and cutting?performances of cutting tool.

Three-Axis Machining Center

The three-axis machining center is the most widely used, including the X, Y, and Z axes, also known as three-axis simultaneous machining centers. The three-axis machining center can perform simple plane machining, but it can only machine one side at a time. It can effectively machine materials such as metal, aluminum, wood, etc.

Functions and Advantages of Three-Axis Machining Centers

The most effective machining surface of a vertical machining center (three-axis) is the top surface of the workpiece. A horizontal machining center, with the aid of a rotating table, can only complete the machining of the four sides of the workpiece. Currently, high-end machining centers are developing towards five-axis control, allowing the completion of five-sided machining in one setup. With the configuration of a high-end five-axis simultaneous CNC system, high-precision machining of complex spatial surfaces can also be achieved.

Four-Axis Machining Center

The four-axis machining center adds an additional rotation axis to the three-axis, usually the A-axis. The rotation of the A-axis allows the workpiece to rotate around the vertical axis on the horizontal plane, enabling multi-face machining. The four-axis machining center is suitable for situations where machining is required on different faces of the workpiece, such as inclined surfaces, oblique holes, etc.

Features of Four-Axis Simultaneous Machining

(1) Machining that cannot be achieved by three-axis simultaneous machining machines or requires overly complex fixturing.

(2) Improvement of the precision, quality, and efficiency of free-form surfaces.

(3) The difference between four-axis and three-axis is the addition of one rotation axis. The establishment of the four-axis coordinates and their code representation:

Determination of the Z-axis: The direction of the machine spindle axis or the vertical direction of the workpiece fixture is the Z-axis.

Determination of the X-axis: The horizontal plane parallel to the workpiece mounting surface or the direction perpendicular to the workpiece’s rotation axis within the horizontal plane is the X-axis, with the direction away from the spindle axis being the positive direction.

Five-Axis Machining Center

The five-axis machining center adds another rotation axis to the four-axis, usually the C-axis. The rotation of the C-axis allows the workpiece to rotate around an axis perpendicular to the table, enabling more complex multi-angle and surface machining. The five-axis machining center is suitable for complex shapes, multi-angle machining, including spatial surface machining, special-shaped machining, hollowing-out machining, drilling, oblique holes, oblique cutting, etc. It is a means to solve the machining of impellers, blades, ship propellers, heavy-duty generator rotors, steam turbine rotors, large diesel engine crankshafts, etc.

What are the 5 axis? in a five-axis machining center?

X-axis: The X-axis is the horizontal axis of the machining center, controlling the movement of the tool in the horizontal direction. The movement of the X-axis affects the lateral position of the workpiece, determining its position and shape on the horizontal plane.

Y-axis: The Y-axis is the longitudinal axis of the machining center, controlling the movement of the tool in the longitudinal direction. The movement of the Y-axis affects the longitudinal position of the workpiece, determining its position and shape on the longitudinal plane.

Z-axis: The Z-axis is the vertical axis of the machining center, controlling the movement of the tool in the vertical direction. The movement of the Z-axis affects the height position of the workpiece, determining its position and shape on the vertical plane.

A-axis: The A-axis is the rotation axis of the four-axis and five-axis machining centers, controlling the rotation of the workpiece on the horizontal plane. The rotation of the A-axis allows the workpiece to rotate around the vertical axis on the horizontal plane, enabling multi-face machining.

C-axis: The C-axis is the rotation axis of the five-axis machining center, controlling the rotation of the workpiece around an axis perpendicular to the table. The rotation of the C-axis allows the workpiece to rotate around the rotation axis on the vertical plane, enabling more complex multi-angle and surface machining.

Types of Five-Axis Machining Centers

Vertical Five-Axis Machining Center

This type of machining center has two methods for the rotation axis: one is the worktable rotation axis.

The worktable, which is set on the bed, can rotate around the X-axis, defined as the A-axis. The general working range of the A-axis is +30 degrees to -120 degrees. There is also a rotating table in the middle of the worktable, which rotates around the Z-axis at the position shown in the illustration, defined as the C-axis. The C-axis can rotate 360 degrees. With the combination of the A-axis and C-axis, the workpiece fixed on the worktable can be machined on all five sides except the bottom surface by the vertical spindle. The minimum indexing value for the A-axis and C-axis is usually 0.001 degrees, which allows the workpiece to be subdivided into any angle for machining inclined surfaces and oblique holes.

If the A-axis and C-axis are linked with the XYZ three linear axes, complex spatial surfaces can be machined. Of course, this requires the support of high-end CNC systems, servo systems, and software. The advantage of this setup is that the structure of the spindle is relatively simple, the spindle rigidity is very good, and the manufacturing cost is relatively low.

Spindle Rotation Vertical Five-Axis Machining Center

The vertical machining center’s spindle has gravity acting downward, and the radial force on the bearings during high-speed idle operation is equal, resulting in good rotation characteristics. Therefore, the speed can be increased, with a general high speed reaching over 12,000 rpm, and the practical maximum speed has reached 40,000 rpm. The spindle system is equipped with a circulating cooling device, where the circulating cooling oil carries away the heat generated by high-speed rotation, is cooled to an appropriate temperature through a chiller, and then flows back into the spindle system.

The X, Y, Z three linear axes can also use linear encoders for feedback, with bidirectional positioning accuracy within the micron level. Since the rapid feed reaches 40-60 m/min or more, the ball screws for the X, Y, Z axes mostly adopt central cooling. Similar to the spindle system, the heat is carried away by the circulating oil that flows through the center of the ball screws after being chilled.

Резюме

In the field of CNC machine tools, three-axis machining centers have relatively simple processing capabilities, four-axis machining centers can achieve multi-face machining, and five-axis machining centers have a higher level of multi-angle and surface machining capabilities. The main difference between three-axis, four-axis, and five-axis machining centers lies in the number of axes and processing capabilities. The choice of a suitable machining center should be determined based on specific processing requirements and complexity.

Original Quality Issues of the Cutting Tools

Due to the weak quality awareness of some cutting tool manufacturers, the tools produced have some quality issues, such as:

(1) The most obvious quality issue is the unexpected fracture of the инструмент body due to poor quality of the tool body material and non-standard heat treatment.

(2) Issues such as chip adhesion, thermal cracking of the cutting edge, and severe tool breakage due to improper selection of the insert grade. Each insert grade is suitable for specific machining materials and cutting conditions, and generally, they can be selected based on the performance and application of the carbide grade. However, in practice, the selection often does not follow the regulations, allowing for a great deal of flexibility.

(3) Structural problems. Improper cutting angles, poor chip evacuation, too many teeth, poor strength, and unbalanced cutting forces are all hidden dangers that can lead to abnormal damage of the cutting tools. These factors are closely related to the manufacturing experience and technical level of the tool manufacturers.

Issues Related to Tool Usage

When indexable carbide cutting tools are used for certain finishing operations (such as precision boring or precision milling), the experience and technical level of the user are not highly demanding. However, when used for rough machining, higher requirements are needed. Tool-using manufacturers may cause abnormal damage to the tools, increase tool costs, and affect machining efficiency due to a lack of corresponding experience and technology. For example:

Tool breakage due to machine stalling

If the tool diameter is too large, the number of teeth is too dense, or the feed rate is too high, it can cause the machine’s power to be insufficient, leading to machine stalling and tool breakage, which is one form of abnormal tool damage. Therefore, considering the machine’s power capacity is a primary condition for cutting operations.

Cutting Fluid Issues

Cutting fluid plays a role in cooling, lubricating, cleaning, chip evacuation, and improving the quality of the machined surface during the machining process. However, cutting operations have different requirements for the properties, flow rate, and pressure of the cutting fluid. Whether to use cutting fluid depends on the machining conditions; it is not correct to assume that cutting fluid always has a beneficial effect. For example, if cutting fluid is added in the middle of cutting with an indexable carbide end mill, it will certainly damage the insert.

Poor rigidity of the process system

Due to the vibration of the process system, the loosening between the connecting components can occur, and if not inspected and discovered in a timely manner, it can lead to tool breakage. If the user is unaware that the insert is damaged and continues to use it, it will inevitably result in damage to the tool body.

Using a milling cutter with unequal pitch is one method to reduce vibration and improve cutting stability.

Improper selection of cutting parameters

Indexable carbide cutting tools require different cutting speeds and feed rates under different cutting conditions. Generally, tool manufacturers will provide recommended values that have been proven reasonable and reliable through cutting experiments. Blind use will inevitably lead to abnormal damage to the tools. For example, when a milling cutter engages with the workpiece, the cutting parameters should be appropriately reduced to prevent sudden impacts that could cause the milling cutter’s edge to break.

Issues caused by fastening screws

Because screws are small and relatively inexpensive to replace, their importance in the machining process is often not given sufficient attention by users. Some users, when installing inserts, use sleeves or other means to increase the torque, resulting in excessive pre-stress on the screws, making it impossible to loosen and replace the insert again, leading to the scrapping of the tool body. Sometimes, users mix up screw models, resulting in inappropriate clamping force. Others fail to conduct periodic inspections or replace damaged screws in a timely manner, creating potential safety hazards.

Exceeding the Scope of Use

Different types of indexable carbide cutting инструментs have their respective scope of use. Users must follow the guidelines to avoid abnormal damage. For example, indexable carbide spot drills are generally suitable for machining holes with a depth less than three times the diameter. If the depth is too great, it can damage the tool due to poor chip evacuation. Moreover, the surface to be machined must be flat, without grooves or protrusions; otherwise, vibration will occur at the moment of drilling, leading to edge breakage or even damage to the tool body. If there is a pre-drilled hole in the part, its diameter should not exceed 1/4 of the drill bit’s diameter; otherwise, the feed rate should be reduced, and so on.

Issues with the Workpiece Material

In addition to considering the above factors, sometimes there is still a high rate of tool breakage. At this point, one should consider whether the condition of the blank is poor, or if there is a severe sand inclusion situation, and methods to improve the condition of the blank should be considered.

Some Suggestions in Conclusion

(1) For users, it is advisable to purchase indexable carbide cutting tools produced by regular manufacturers, as these manufacturers provide technical documentation, usage instructions, and comprehensive after-sales service, generally ensuring that there are no original quality issues with the products.

(2) The using manufacturers should organize professionals to provide technical training on the use of indexable carbide cutting tools for operators, and constantly inspect and remedy any unfavorable factors that may arise during the entire machining process to avoid unnecessary losses and improve production efficiency.

The successful use of indexable carbide cutting tools not only depends on the quality of the tools themselves but is also related to every aspect of the entire machining system; for example, the performance of the machine tool, the reliability of workpiece clamping, the rigidity of the tool holder system, the rationality of blade selection, and the correct selection of cutting parameters all affect the machining results. Only by using the cutting tools correctly and reasonably can one avoid abnormal damage, improve machining efficiency, and achieve the maximum economic benefits.