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.

Podsumowanie

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 narz?dzie 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 narz?dzies 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.

The wear on the back face of the cutting tool has a more significant impact on machining accuracy and cutting force than the wear on the front face, and it is easier to control and measure. Therefore, the back face wear land width VB is usually used as the standard for tool bluntness. The wear process generally consists of three stages: the initial wear stage, the normal wear stage, and the severe wear stage. As shown in Figure 1, during the initial wear stage, due to the rough surface of the tool, the contact area between the cutting tool surface and the workpiece is small, resulting in higher compressive stress and faster wear, with a larger slope in the schematic curve. In the normal wear stage, after the initial wear, the tool surface has been smoothed, the contact area between the tool and the workpiece increases, and the pressure decreases, so the amount of wear increases slowly and relatively stably with the extension of cutting time. When the tool wears to a certain extent, the cutting force and cutting temperature increase rapidly, the wear accelerates drastically, and the cutting tool fails.

Tool Wear Mechanism

Tool wear is often the combined result of mechanical, thermal, and chemical actions. Generally, the following mechanisms are recognized for tool wear:

Abrasive Wear

This type of wear occurs due to the presence of hard particles between contact surfaces. The mechanism of abrasive wear mainly involves the continuous micro-cutting and scoring actions of the abrasive particles on the friction surface, resulting in the formation of grooves parallel to the direction of relative motion on the friction surface. The rate of abrasive wear is directly proportional to the normal load Fn and the wear coefficient K, and inversely proportional to the material hardness H. Generally, the higher the hardness of the cutting tool material, the better its resistance to abrasive wear.

Therefore, according to the theory of friction and wear, increasing the hardness and wear resistance of the cutting tool material, achieving an appropriate hardness/toughness ratio, and reducing the surface roughness of the cutting part of the cutting tool can all decrease the abrasive wear of the tool.

Adhesive Wear

This type of wear is caused by the attraction between molecules and atoms on the contact surfaces. Under sufficient pressure and temperature, plastic deformation occurs, leading to a phenomenon known as cold welding, which is the result of the adhesive forces between the fresh surface atoms formed by the plastic deformation of the friction surfaces. An ideal adhesive friction surface is not necessarily the harder the better; it should have a surface characteristic that combines soft and hard features, as shown in Figure 2, with a soft surface (I), a hard subsurface (II), and a gentle transition zone (III) below. In other words, from the perspective of adhesive wear, the tool surface should have good lubricity, the subsurface layer should have high hardness to provide support, and the gentle transition zone below prevents the occurrence of layer-by-layer spalling of the cutting tool material.

Therefore, according to the theory of friction and wear, appropriately improving the hardness/toughness ratio can reduce the cutting force and cutting temperature, which is beneficial for reducing adhesive wear of the tool.

Diffusion Wear

Diffusion wear generally occurs during high-temperature machining processes. When cutting metal, the chemical elements of both the chip, workpiece, and tool diffuse into each other in the solid state during contact, altering the original material composition and structure, which makes the tool material become brittle and accelerates cutting tool wear. This type of wear caused by the migration of elements in the solid state is called diffusion wear. It is a type of wear characterized by chemical properties.

Oxidation Wear on Cutting tool

During the cutting process, due to the increase in cutting speed or the poor thermal conductivity of the work material, the temperature between the tool and the chip reaches high levels (700~1000℃). The tool material or the chip reacts with oxygen to form corresponding oxide films. This is also a type of wear characterized by chemical properties. Generally, during cutting, the cutting tool is in close contact with the chip and workpiece, where oxygen content is low, while in areas away from the contact zone, oxygen content is higher, leading to severe oxidation wear. During high-speed cutting, where cutting temperatures are high, oxidation wear is more likely to occur. The degree of oxidation wear is determined by the cutting speed, the amount of oxygen, and the oxidation resistance of the tool material. Therefore, selecting cutting tool materials with better high-temperature stability and a smaller wear coefficient, or using physical methods to reduce cutting temperatures, such as coolant, can reduce the occurrence of oxidation wear.

Study on the Cutting Performance and Wear Mechanism of Coated Cemented Carbide Cutting Tools

Hard coatings have advantages such as high hardness, wear resistance, low friction coefficient, high resistance to high-temperature oxidation, and good chemical stability. They are widely used in tool machining. By applying surface coating technology to deposit a layer of high-performance coating on the tool substrate, the machining efficiency and cutting tool life can be improved. Under different machining conditions, coated tools exhibit different machining performances. In some cases, the cutting performance of coated cemented carbide tools may even be lower than that of uncoated cemented carbide tools. Therefore, by studying the cutting performance and wear mechanism of coated cemented carbide cutting tools, the modification mechanism of coated cemented carbide tools can be clarified, allowing for a reasonable selection of coating materials and structures, optimization of machining parameters and tool geometric parameters, and truly achieving the goals of high-quality, efficient, and low-cost machining.

Some scholars have studied the turning of 42CrMo4V steel with TiAlN coated cemented carbide inserts at different cutting speeds. The cutting speed significantly affects the failure mode of the tool. As the speed increases, the cutting force increases, and the stress on the coating increases, leading to earlier failure of the coating. Figure 3 shows the time at which failure occurs in the TiAlN coated cemented carbide insert at different cutting speeds. The coating failure process occurs because the stress on the coating exceeds the cohesive strength of the coating or the bonding force between the coating and the substrate, resulting in the formation of fragments. Subsequently, abrasive wear dominates the cutting tool failure process.

We have studied the wear mechanism of TiC coated cemented carbide cutting tools under different cutting speeds. The wear process of the coated inserts can be divided into three stages: the initial wear stage, the normal wear stage, and the final wear stage, as shown in Figure 5. As the cutting speed increases and the cutting time extends, the main wear mechanisms are diffusion wear, plastic deformation wear, and plastic fatigue spalling wear. In the initial stage of wear, severe friction occurs between the tool and the chips on the front and back surfaces of the cutting tool, respectively, resulting in plastic slip of the surface coating material in the opposite direction of cutting tool feed. This leads to plastic fracture of the coating material on the front and back surfaces, which is plastic fatigue spalling wear, and the coatings on the front and back surfaces are worn through at points R and F as shown in Figure 4. In the normal wear stage, although the coatings at points R and F are worn through, the surrounding coatings play a supporting role, thus delaying the expansion of the worn-through areas on the front and back surfaces of the tool.

?Names of the Various Parts of an End Mill

Names of the various parts of an end mill:

Structural Types of End Mills

Classified by the Number of Cutting Edges:

The cylindrical surface and end face of an m?yn końcowy usually have cutting edges distributed on them, which can engage in cutting simultaneously or individually. Based on the number of blades, end mills can be categorized into double-edge, triple-edge, quadruple-edge, and multi-edge types.

The fewer the number of blades, the larger the chip flute, but the worse the rigidity.

Comparison of the advantages and disadvantages of end mills with different numbers of blades:

According to the type of bottom end tooth shape

According to the shape of the cutting edge

General-purpose end mill

Widely used, applicable to slot machining, side machining, and step surface machining, etc. In addition, it can be used in all situations of rough machining, semi-finishing, and finishing.

Tapered end mill

Used for conical surface machining after general cutting, such as mold draft angle machining and concave portion machining, etc.

Gear-type end mill

The cutting edge is wavy, producing fine chips, with low cutting force, suitable for rough machining, not suitable for finish machining.

Forming end mill

A forming blade is a cutting edge that is shaped to match the contours of the workpiece being machined. Special shapes typically need to be custom-made based on the product’s shape and dimensions.

According to the blade arrangement of end mills

By tool material

End mills can be classified by material into: high-speed steel, solid carbide, carbide with coating, CNB, PCD, etc.

?

Key Points for Selecting End Mills

When using an end mill, multiple factors need to be considered to ensure machining efficiency, precision, and tool life. Here are some key considerations:

① Material of the workpiece: Different materials (such as steel, cast iron, aluminum alloy, plastic, composite materials, etc.) require tools with different characteristics. For example, when machining aluminum alloy, a specialized aluminum end mill can be chosen, which typically has good chip evacuation and heat resistance; when machining high-hardness materials, a carbide tool with a high-wear-resistant coating should be selected.

② Machining form and precision requirements: Choose the shape and number of cutting edges based on the shape of the machining surface (plane, slot, contour, etc.) and the required surface roughness. For instance, a ball nose end mill is suitable for complex surface machining, while a flat or rounded end mill is suitable for plane and edge machining. For high-precision machining, choose an end mill with higher arc precision.

③ Helix angle of the end mill: The helix angle affects cutting efficiency and tool life. When machining materials with poor thermal conductivity (such as stainless steel), a large helix angle can improve chip evacuation and heat dissipation, extending tool life. For thin-walled workpieces or machining with poor rigidity, a small helix angle can reduce cutting forces and avoid workpiece deformation.

④ Tool material and coating: Carbide is the most commonly used tool material. For different working conditions, selecting the appropriate carbide grade and coating (such as TiCN, TiAlN, etc.) can enhance tool performance. High-speed steel (HSS) is suitable for low-speed and low-hardness material machining, while carbide is more suitable for high-speed and high-hardness material machining.

⑤ Tool structure: Solid, brazed, and indexable tools each have their advantages. Solid tools have good rigidity and are suitable for precision machining; brazed and indexable tools are convenient for blade replacement and are suitable for mass production.

⑥ Number of flutes and shank structure: The number of flutes affects the tool rigidity and chip flute size. When the workpiece rigidity is low, it is advisable to choose a tool with fewer flutes to improve chip evacuation; the shank design (standard, long neck, tapered neck) needs to be selected based on the machining depth and workpiece shape. Tapered neck end mills provide better rigidity and machining accuracy.

⑦ Tool length: Under the condition of meeting the machining requirements, choose the shortest tool length as much as possible to increase stability, reduce vibration, and thereby improve the quality of machining.

⑧ Cost-effectiveness: Consider the tool cost and machining efficiency comprehensively and choose a cost-effective solution.

In summary, the selection of end mills is a process of comprehensive consideration, involving workpiece material, machining requirements, tool performance, cost-effectiveness, and other aspects. Correct selection can greatly improve machining efficiency, reduce costs, and ensure machining quality.

A notable property of wood is its anisotropy, which leads to distinctions between longitudinal, transverse, end-wise, and transitional cutting during the machining of solid wood. Wood-based panels and wood composite materials are made from wood monomers, such as veneers, shavings, or fibers, which are combined with adhesives under specific temperatures and pressures to form a composite material. The properties of these materials are determined by the wood monomers, their arrangement, and the characteristics of the adhesive. The machinability also varies due to the structure and the proportion and nature of the additives. For example, medium-density fiberboard (MDF) is nearly isotropic, with almost equal cutting resistance across the board; particleboard, due to uneven density distribution and differences between the surface and internal structure, has significant variations in cutting resistance; and blockboard, composed of glued solid wood strips, has differences in grain direction between the strips, thus exhibiting both similar and different properties compared to solid wood during machining.

Selection of Wood Milling Cutter Structure

Based on the nature and requirements of the cutting object, a comprehensive consideration from both technical and economic perspectives is necessary to select the appropriate milling cutter structure. Options include solid wood milling cutters (Figure 3), welded solid milling cutters (Figure 4), assembled milling cutters (Figure 5), and combined milling cutters.

Selection of Milling Cutter Cutting Parameters (Table 1)

The cutting parameters of a milling cutter include the cutting speed of the cutter, the feed rate of the workpiece, and the milling depth. The cutting speed of the milling cutter depends on the cutter’s rotational speed and diameter. The feed rate of the workpiece depends on the requirements for the surface quality of the machined surface. The surface roughness of the workpiece is largely determined by the feed per tooth during the cutting process. If the feed per tooth is too large, the machined surface will be too rough; if the feed per tooth is too small, the machined surface may exhibit burn marks.

Depending on the different milling objects and surface quality requirements, the recommended feed per tooth for wood products processing is generally as follows: for rough machining, Uz = 0.8~1.5mm; for finish machining, Uz = 0.4~0.8mm. If the feed per tooth is within 0.1~0.3mm, there is a risk of the machined surface being burned. For all wood products, the common feed per tooth is Uz = 0.3~1.5mm. For a smooth surface, the feed per tooth Uz = 0.3～0.8mm; for a medium surface, Uz = 0.8~2.5mm; for a rough surface or when surface quality is not a concern, the feed per tooth Uz = 2.5-5.0mm.

Stability of Milling Cutter Operation

The stability of the milling cutter during operation is the basis for ensuring machining accuracy and surface quality. This includes two aspects: first, the vibration of the milling cutter during cutting due to external force excitation; and second, the deformation of the milling cutter under the action of external forces. Vibration is related to the structure of the milling cutter, the method of installation, and unbalanced mass. When the frequency of the external excitation force is close to the natural frequency of the milling cutter,the wood milling cutter will resonate, and the amplitude will increase significantly. A considerable portion of the milling cutters used for wood cutting are installed in a cantilevered manner. In this case, the static force due to the cutter’s own weight and the dynamic force generated by high-speed rotation act in combination on the cutter shaft. Under the action of this force, the cutter shaft will deform, producing a certain degree of deflection.

Since tool vibration and cutter shaft deformation will ultimately severely affect the surface quality of the workpiece, it is necessary to limit the unbalanced mass of the milling cutter and to avoid the cutter’s rotational frequency from matching its natural frequency. Additionally, for cantilevered cutter shafts, it is essential to limit the mass of the wood milling cutter, which means restricting the length and diameter of the cutter.

Safety of Milling Cutter Processing

The safety of wood milling cutter processing includes restrictions on the rotational speed of the milling cutter, limitations on chip thickness (Figure 6，7), restrictions on the profile height of shaped wood milling cutters, and limitations on the thickness and projection length of the blades for assembled wood milling cutters.

The characteristic of wood milling processing is high speed, with the rotational speed of the milling cutter often exceeding 3000rpm. High-speed cutting brings a series of safety issues. When the spindle speed of the milling machine reaches 9000rpm, the use of assembled milling cutters should be prohibited except for shank cutters with a diameter less than 16mm; strict non-destructive testing of the welds on welded solid milling cutters should also be conducted. When the milling cutter leaves the factory, the manufacturer has marked the maximum allowable speed on the body of the cutter, and the user must strictly adhere to this regulation; under no circumstances should the maximum allowable speed be exceeded.

The limitation on chip thickness is a necessary measure to prevent severe overload of the milling cutter due to excessive feed. According to the regulations of the German Association of Woodworking Machinery and Tool Manufacturers, for manually fed machines, the thickness of the milling chips should not exceed 1.1mm, and there are certain requirements for the width of the chip flute for different cutting milling cutters. For semi-mechanically fed machines, the maximum thickness of the milling chips should not exceed 10mm. For fully automatic, mechanically fed machines, there are no restrictions on the thickness of the milling chips and the chip flute, but general safety regulations must be observed.

For shaped milling cutters, the profile height of the shaping contour is closely related to the clamping method of the cutter, the thickness of the workpiece being cut, and the diameter of the cutter. Once the thickness of the workpiece, the diameter of the cutter, and the diameter of the center hole are determined, the profile height of the cutter reflects the cutter’s own strength and rigidity, as well as its ability to withstand cutting resistance. Therefore, there must be limitations on the profile height to ensure safety when using the cutter. On multi-axis milling machines (four-sided planers) and double-end wood milling machines or mortising machines, the spindle shaft diameter must not be less than 30mm. Moreover, due to the space limitation for installing the cutter, the height of the shaped contour cannot be too high.

When designing the body of an assembled wood milling cutter, the issue of blade clamping must be considered. Whether it is a cylindrical or disc-shaped body, the blade clamping form must ensure that it can provide a sufficiently large clamping force to counteract the rotational centrifugal force. For the integral blades or inserted welded blades clamped radially by the pressure plate, there must be a minimum limit on the projection length of the blade, as well as the thickness and length of the blade. When the thickness and length of the blade are less than this minimum limit, it means that the use of the wood milling cutter should be strictly prohibited. Otherwise, there will be safety risks. Figure 8 shows the projection length and the thickness and length of the blade for assembled wood milling cutters.

Preface

With the rapid development of China’s automotive industry, the new energy vehicle industry has experienced exponential growth in recent years. Lightweight is a core topic in the new energy vehicle industry, and the core of lightweight is the transformation of traditional materials. Aluminum alloys, with their high strength and light weight, are indispensable materials for lightweight automotive manufacturing. The geometric shapes of auto parts are relatively complex, and the proportion of die-cast aluminum alloy parts in the whole vehicle is increasing, as is the demand for CNC machining of die-cast parts.

The CNC manufacturing of aluminum alloy auto parts mainly requires high efficiency, high stability of continuous production, and continuously reducing costs, which necessitates more detailed control and planning of the entire production process.

Formation of Chip Build-up during Aluminum Alloy Machining

The main characteristic of aluminum in the machining process is its low melting point, which is manifested as “stickiness” in the working conditions. Due to this characteristic and insufficient cooling in actual working conditions, the heat generated by friction during the microscopic machining process cannot be released in a timely or effective manner. As a result, the aluminum melts and adheres to the cutting edge and chip flute of the cutter. When it cools, it instantly solidifies and adheres to the cutter, forming a chip build-up, leading to the scrapping of the cutter. This issue is commonly referred to in the industry as “easy to stick to the cutter.”

Cutters are a consumable in the CNC machining process and account for a significant portion of cost expenditures. The cutting edge of aluminum alloy-specific cutting tools should be sharper, and the chip flutes need special polishing treatment and an aluminum alloy-specific coating to improve the chip evacuation efficiency. The high-efficiency production in the automotive industry necessitates that cutters must increase feed rates and linear speeds, which in turn increases the heat generated during cutting, increases the risk of aluminum melting and sticking to the cutter, and leads to increased costs due to the scrapping of cutters caused by chip build-up.

With the requirements of environmental protection, the CNC machining of aluminum alloys extensively uses MQL (Minimum Quantity Lubrication) as a substitute for cutting fluids. The low melting point characteristic of aluminum, combined with the reduced cooling effect of MQL, further promotes the formation of chip build-up. Tools scrapped due to sticking account for about 409% of the total conventional scrapping of tools. Since traditional methods for dealing with chip build-up generally involve knocking or smashing, very few treated tools can be reused. Therefore, a new solution is proposed.

Treatment Measures

The specific treatment measures of the new solution are as follows:

Remove the cutter with existing chip build-up.

Find solid NaOH and dilute it with water, then place it in a ceramic container.

Once diluted into a NaOH solution, immerse the cutter with adhered aluminum into the solution, ensuring the aluminum-adhered parts are fully submerged, and continue for 2 hours, or prolong the immersion time based on the actual situation. A comparison of the traditional treatment method and the new solution is shown in Table 1.

Chemical Mechanism of Treating Chip Build-up

Taking the commonly used AIS7Mg material for automotive parts as an example, the content of Al is about 93.59%, the content of Si is 6.59%, and the content of Mg is 0.259%. Both Al and Si can react with NaOH solution. Soaking in NaOH solution can remove the main Al components remaining on the cutter. The principle is that the metal reacts with NaOH to produce bubbles (5), which eventually causes the adhered aluminum to fall off. The chemical reaction equations are as follows:

The reaction equation between Si and NaOH is:

Si + 2NaOH + H?O = Na?SiO? + 2H?↑

The reaction equation between Al and NaOH is:

2Al + 2NaOH + 6H?O = 2NaAl(OH)? + 3H?↑

Final conclusion: The aluminum is removed, and the cutting tool can be reused.

Experimental Verification

The above theory was tested using taps. The reason for choosing taps is that in aluminum alloy machining, taps are among the higher-value cutters and are tasked with a longer service life mission. Moreover, their geometric shape is complex, and the grooves are narrow, making it basically impossible to clear the adhered aluminum using physical methods after the sticking phenomenon occurs. Testing this type of cutter is more meaningful and representative.

Due to the high heat generated during machining and possible insufficient cooling, the aluminum is instantly melted and sticks in the grooves, indicating that the tap can no longer be used, and the thread profile is damaged.

According to the above chemical theory, the tap with adhered aluminum (chip build-up) was completely soaked in NaOH solution. After complete immersion in NaOH, the tap was visually inspected, and the chip build-up in the grooves had completely fallen off, with residual aluminum debris in the experimental vessel. The treated tap was used again to machine workpieces, and the thread profile of the workpiece was found to meet the requirements, with the thread being qualified. The tap could be reused.

Wniosek

The automotive parts industry is characterized by mass production. The matching of new equipment and specially designed cutters requires a large amount of cutting verification during the initial setup. During the verification process, due to factors such as parameter matching, the breaking-in of new equipment, and the inexperience of the debugging personnel, the phenomenon of chip build-up on cutters is relatively common, leading to a straight-line rise in scrapping costs and production cycles. Additionally, issues such as changes in blank allowances and momentary cooling instability during the later stages of mass production, which lead to aluminum adhesion, have been effectively resolved after applying this method. This has greatly saved on cutter costs and processing time, increased the service life of the cutters, and significantly reduced the production costs for the enterprise.

The main body of the part is a weak stiffness structure, which is prone to instability during mechanical machining, especially when machining the outer wall of the ring and clamping the thin-walled ring.

Machining Analysis

The morphology of the typical weak thin-walled ring with a composite structure of bilateral axial supporting parts after machining with general mechanical machining techniques is shown in Figure 2. The following deficiencies are observed:

（1）Obvious tool marks in the middle of the bilateral axial supporting parts. The upper and lower parts of the bilateral axial supporting parts are formed during two separate machining steps: milling the shape of the thin-walled ring and milling the shape of the bilateral axial supporting parts. Due to the non-coincidence of the process benchmarks between the two steps, obvious tool marks appear in the middle of the bilateral axial supporting parts.

（2）Prominent vibration marks in the middle of the thin-walled ring shape. The wall thickness of the middle part of the ring body is 2mm, which results in significantly insufficient stiffness. During the machining of the thin-walled ring shape, the middle part is prone to instability, leading to the formation of obvious vibration marks. The superposition of these issues collectively results in the machining instability problem becoming a production bottleneck.

Process Optimization

To address the deficiencies of general mechanical machining techniques, a series of compound machining measures have been adopted, including the conversion control of process benchmarks to “bore-face-contour,” the gradual reduction of workpiece stiffness during machining, the reinforcement of stiffness combined with damping and vibration absorption, and the maximization of clamping area and stiffness. These measures aim to achieve stable machining of the weak thin-walled ring with the composite structure of bilateral axial supporting parts.

Precision Conversion of Process Benchmarks

(1) After rough machining the inner shape and end face, precision turn the inner circle and end face to form the process benchmark “bore-face.”

(2) The specific steps for milling the contour positioning benchmark are as follows.

1）Clamp the fixture in the vise (see Figure 3). The bottom surface of the fixture is aligned with the workpiece end face, and the cylindrical surface of the fixture is aligned with the axial direction of the workpiece inner circle. Use a dial indicator to align the fixture bottom surface with a flatness of ≤0.01mm and then secure it.

2) Clamp the workpiece on the fixture (see Figure 4). The workpiece end face and inner bore are tightly against the fixture’s positioning surface and are clamped with a pressure plate.

3)Symmetrically machine two identical precision milling positioning steps on the workpiece contour (see Figure 5). The step height is 20mm, which converts the process benchmark from “bore-face” to “contour.”

Steady-state Machining Control

(1) The specific steps for milling the thin-walled ring contour are as follows.

1）Clamp the workpiece with a vice on the precision milling positioning step (see Figure 6).

2) Embed polytetrafluoroethylene or nylon washers into the internal thread relief groove of the workpiece, and then use an external thread mandrel to screw into the internal thread of the workpiece to enhance the stiffness of the annular body cavity.

3) Machine the round corners of the bilateral supporting parts and the shape of the thin-walled ring (see Figure 7).

(2) The specific steps for milling the shape of the bilateral axial supporting parts are as follows.

Turn the workpiece around, and use an external thread mandrel (see Figure 8) to screw into the internal thread of the workpiece to enhance the stiffness of the annular body cavity.

Clamp the workpiece with a clamping block (see Figure 9), and secure it with a flat-nose pliers.

Perform finish machining on the shape of the bilateral axial supporting parts (see Figure 10).

(3) The specific steps for milling the outer step of the bilateral supporting parts?are as follows.

Clamp the fixture with a flat-nose pliers (see Figure 11).

Axially compress the thin-walled ring body of the workpiece with the fixture (see Figure 12).

Press the expanding ring into the inner circle of the workpiece’s thin-walled ring and align the inner circle of the expanding ring with the edge finder.

Machine the structures such as the outer side of the bilateral supporting parts, the step, chamfer, and thread to completion.

Machining Process

According to the optimized process plan, the specific machining process is as follows.

(1) Milling the profile positioning reference: The milling process for the profile positioning reference is shown in Figure 13.

(2) Milling the shape of the thin-walled ring: The shape of the thin-walled ring after milling is shown in Figure 14.

Currently, in mechanical manufacturing, due to the rapid updating and upgrading of products, there are higher requirements for the selection of parts. Particularly in the manufacturing of industries such as aerospace, large power stations, and ships, some difficult-to-machine materials like high-temperature alloys, titanium alloys, heat-resistant stainless steels, and composite materials have been widely used. Among them, the efficient processing of widely used and commonly employed high-temperature alloy materials has received more attention.

Using high-performance high-speed steel bimetal saw blades (with M42 as the edge material) to cut difficult-to-machine high-temperature alloys results in low cutting efficiency and a very short service life. Subsequently, saw blades made of cemented carbide with high hardness were chosen. Through testing and practical application, cemented carbide saw blades have achieved significant results in the blanking processing of high-temperature alloys, meeting the requirements of production schedules.

Design and Selection of Cemented Carbide Saw Blades

Cemented carbide saw blades have different materials and structures. In practical applications, we have found that not every type of cemented carbide saw blade can achieve good results in the blanking processing of high-temperature alloys. Only by making reasonable choices and using them properly can the desired results be obtained. Therefore, we have selected and compared four aspects: the structure of the saw blade, the form of the tooth shape, the material, and the reasonable selection of cutting parameters. The details are as follows:

Tool Structure

Cemented carbide saw blades typically adopt a tipped and welded structure. The tips of the teeth on cemented carbide saw blades have the advantages of high hardness, high wear resistance, and high fatigue resistance. However, their main drawbacks are brittleness, low strength, and poor resistance to impact.

After testing and comparative application (especially based on the final sawing blanking data comparison results), we believe that for the blanking of high-temperature alloys, the saw blade structure is best suited with coarse teeth and variable pitch cemented carbide saw blades. The reason we believe this is optimal is that during the sawing blanking of high-temperature alloys (particularly nickel-based high-temperature alloys), the chips have strong adhesion, making it difficult for the chips to be discharged smoothly. The intermittent formation and disappearance of built-up edge can easily cause the cutting edge to chip and the tool’s flank wear to intensify. Choosing coarse teeth not only increases the strength of the cutting edge but also enlarges the chip space, facilitating the use of a larger feed rate to improve cutting efficiency. The adoption of variable pitch can reduce cutting noise and vibration, making the cutting process more stable, which is beneficial for improving the durability of the tool. A schematic diagram of the variable pitch saw blade structure can be seen in Figure 1.

Selection of Tool Tooth Shape

Common tooth shapes for saw blades include standard teeth, hook-shaped teeth, and trapezoidal teeth, as shown in Figure 2.

1. Standard teeth have a cutting approach angle g=0°, with the tooth face perpendicular to the substrate, and the tooth slots are deep and narrow.
2. Hook-shaped teeth have a cutting approach angle g=5°～10°, with the tooth slots deep and wide.
3. Trapezoidal teeth have a cutting approach angle g=10°～15° and a back angle a=6°～8°, providing high tooth strength, suitable for heavy cutting.

For the processing of high-temperature alloy materials, in addition to selecting high-strength cemented carbide materials for the saw blades, the choice of tooth shape is also very important. Trapezoidal teeth have sufficient strength and are less prone to chipping during cutting. Due to the larger approach angle, the cutting resistance is also smaller than that of standard straight teeth. Practical verification has also proven that the choice of trapezoidal teeth results in better cutting performance compared to the other two tooth shapes.

Tool Material Grades

The grades of cemented carbide suitable for cutting high-temperature alloy materials mainly fall into two categories: Type M and Type K according to the ISO standard (now recommended as Type S). Based on the results of sawing comparison tests, the improvement in cutting efficiency between the two types of tool grades is not significant. However, in terms of sawing service life, the saw blades made of material equivalent to grade M15-M30 have a 15%～20% longer life span compared to those made of material equivalent to grade K05-K20 (when processing high-temperature alloys of the same specification and grade).

Selection of Cutting Parameters

The rational selection of cutting parameters is crucial for the blanking of high-temperature alloys. Proper cutting parameters ensure normal blanking of workpieces, significantly improve cutting efficiency and tool life, and also reduce the harsh noise generated by the adhesion and friction of chips between the tool and the workpiece during blanking. Based on our experimental application results for various nickel-based high-temperature alloy grades (considering efficiency and tool life comprehensively), the selected rational cutting parameters are as follows:

Cutting linear speed: 15～20 m/min

Feed rate (material removal rate): 6～8 cm2/min

The above cutting parameters have been determined through long-term experimental applications and are considered to be economically viable.

Actual Tool Benefits

Through the aforementioned four aspects of work, the use of cemented carbide saw blades for processing high-temperature alloys has achieved significant economic effects in the steam turbine factory:

After testing and comparing multiple data results, the current cemented carbide saw blades used for processing high-temperature alloys have improved the cutting efficiency by 5 to 8 times compared to the previously used bimetal saw blades. For example, when processing a GH4169 nickel-based high-temperature alloy blank with dimensions of 140×245, the original M42 bimetal saw blade took about 6 to 8 hours to blank one piece. However, with the selected cemented carbide saw blade for processing high-temperature alloys, the blanking time for one workpiece is only about 1 hour. Moreover, what is more prominent is the improvement in tool life.

When processing blanks of the above-mentioned grades and specifications, the original M42 bimetal saw blade could only blank one piece, whereas the current cemented carbide saw blade can generally blank 20 to 24 pieces (under reasonable cutting parameters and proper operation, one saw blade can even blank 40 to 50 pieces). Although the price of the current cemented carbide saw blade is about 5 times higher than that of the bimetal saw blade, in terms of cost-performance ratio and comprehensive economic benefits (especially as demonstrated by the comparison of the above typical example), using cemented carbide saw blades to process high-temperature alloys is very cost-effective. It achieves the goal of low cost, high tool life, and efficient processing.

Use of Cemented Carbide Saw Blades
Using cemented carbide saw blades for sawing and blanking high-temperature alloy materials is an efficient and ideal process method. However, improper use can lead to rapid wear of the saw blade’s teeth and even cause the saw belt to break, which not only fails to achieve the expected results but may also result in significant losses. Therefore, the correct use of cemented carbide saw blades is very important. There are strict requirements for using saw blades, which are mainly in the following three aspects:

Requirements for the Machine Tool
a. The sawing machine must have good rigidity and a certain level of accuracy to meet the requirements for stable processing with cemented carbide saw blades.
b. Select a sawing machine with a suitable power and specification based on the diameter (cutting area) of the workpiece.
c. The machine tool must be equipped with a good chip removal, cooling system, and saw blade guiding device.

Requirements for Operating the Use of Cemented Carbide Saw Blades
a. The workpiece must be clamped securely, and after clamping, check whether the clamping points (surfaces) are in the middle and upper part of the workpiece to ensure stability during processing.
b. Break-in of the saw blade: New saw blades must go through a break-in period before normal cutting to prevent premature damage to the teeth. After the break-in process, the teeth will wear normally; without it, the teeth will be destroyed prematurely. The feed rate during the break-in period should be 20%～30% of the normal feed rate.
c. Selection of tension force:Excessive tension can cause the saw belt to break; insufficient tension can damage the saw belt or cause cutting deviation. When using a cemented carbide band saw, the tension must be adjusted to 2200～2500 kg/m2.
d. Cooling and chip flushing during cutting: When using a cemented carbide band saw to blank high-temperature alloy materials, in order to reduce the cutting temperature, cutting resistance, and extend the life of the band saw, water-based extreme pressure cutting fluid must be continuously applied during sawing. Additionally, the chips produced during sawing should be cleaned synchronously with a steel brush.

Rational Selection of Cutting Parameters
For blanking high-temperature alloy blanks, the selection of cutting parameters directly ensures the normal progress of sawing. Reasonable cutting parameters also achieve higher cutting efficiency and tool life. Due to the poor machinability of high-temperature alloy materials, the cutting parameters should be much lower compared to other alloy steel materials. Practice has proven that the cutting parameters recommended in the above examples are more reasonable. If the feed rate (material removal rate) is too low, the wear on the flank of the tool will increase. Moreover, increasing the cutting speed and feed rate will also increase the cutting force and cause the chip slot to clog, leading to chipping and reduced tool life.

The Functions of the Different Parts of the Turning Tool

?Rake angle

The rake angle is the angle between the cutting face and the reference plane; it is an important indicator of how the cutting edge participates in the cutting process. The rake angle of the blade itself is usually a positive rake angle, and the shape of the cutting face can be a circular arc, chamfer, or flat surface. The size and sign (positive or negative) of the rake angle will affect the tool strength, cutting force, the tool’s finish machining capability, vibration tendencies, and chip formation. The rake angle has a significant impact on cutting force, chip evacuation, cutting heat, and tool life.

Impact of rake angle?size on cutting

1.A larger positive rake angleresults in a sharper cutting edge, but the strength of the cutting edge decreases.

2. A larger positive rake angle?reduces the cutting force; an excessively large negative rake angle?increases the cutting force.

?

Applications of different rake?angle sizes

K?t przy?o?enia

The relief angle has the function of avoiding the friction between the back tool face and the workpiece and making the tool tip cut into the workpiece freely.

Relief angle size and back tool face wear diagram

?Influence of relief angle size on turning tools

The relief angle is large, and the rear tool surface is worn less, but the strength of the tool tip is decreased, and the reverse is true when the relief angle is small.

Application of different size relief angle

Secondary rake angle

The secondary rake angle affects the mitigation of impact force, the size of the feed force component, the size of the back force component, and the chip thickness.

Impact of the size of the secondary rake angle on cutting

① When the feed rate is the same, a larger secondary rake angle increases the length of contact between the insert and the chip, resulting in a thinner chip thickness. This disperses the cutting force over a longer cutting edge, thereby improving the tool life.

② A larger secondary rake angle leads to an increase in the component force a’, which can cause bending when machining slender workpieces.

③ A larger secondary rake angle results in poorer chip handling performance.

④ A larger secondary rake angle leads to a thinner chip thickness and an increased chip width, making it difficult for the chip to break.

Secondary clearance angle

The angle designed to avoid interference between the machined surface and the tool (secondary cutting edge). It is usually between 5° and 15°.

Impact of the secondary clearance angle

① A smaller secondary clearance angle increases the strength of the cutting edge, but the tool tip is prone to heating.

② A smaller secondary clearance angle increases the back force, which can cause vibration during cutting.

③ For rough machining, a smaller secondary clearance angle is preferable; for finish machining, a larger secondary clearance angle is more suitable.

Inclination Angle

The inclination angle is the angle at which the cutting face is tilted. During heavy cutting, the tool tip at the starting point of the cut bears a significant impact force. To prevent the tool tip from being damaged by this force due to brittleness, an inclination angle for the cutting edge is necessary. In turning operations, it is generally set to 3°-5°;

① When the inclination angle is negative, the chips flow towards the workpiece.

When the inclination angle is positive, the chips are discharged in the opposite direction.

② When the inclination angle is negative, the cutting edge strength increases, but the cutting back force also increases, which can easily cause vibration.

Chamfering and blunting of the cutting edge

Chamfering and blunting of the cutting edge are treatments applied to the cutting edge to ensure its strength. Typically, this involves rounding or chamfering the cutting edge. The chamfer is a narrow band-like surface set along the cutting face or the back face. Usually, the grinding width is half the feed rate.

Influence of cutting edge grinding width on turning tools

① High cutting edge strength, reduced chance of chipping, and improved tool life.

② The wear on the flank face is likely to spread, resulting in a lower tool life. The width has no effect on the wear of the cutting face.

③ Increased cutting force, which can easily cause vibration.

Application of different tip widths

Tip radius

The tip radius is a key factor in turning operations. It has a significant impact on the strength of the tip and the roughness of the machined surface. The specific choice depends on the cutting depth and feed, and it will affect surface quality, chip breaking, and blade strength.

Influence of tip radius

Advantages of a larger tip radius:

① Improved surface roughness.

② Increased blade strength, less prone to chipping.

③ Reduced wear on the front and back of the tool.

Disadvantages of an excessively large tip radius:

① Increased cutting force, prone to vibration.

② Poor chip handling performance.

Application of different tool tip corner radius sizes

In addition, when selecting turning tools and parameters, it is necessary to consider factors such as the nature of the material being machined, the required precision, and the production volume.

Embracing the trend of three-dimensional parametric design technology, we have shifted to a new model of “parametric design (CAD) – grinding simulation (CAE) – cutting simulation analysis (CAE).” Designers no longer need to physically manufacture prototypes; instead, they can create the three-dimensional solid model of the tool by adjusting geometric parameters. Subsequently, cutting simulation technology is used to evaluate the performance of the design parameters, thereby optimizing the structural parameters of the tool. This transformation has significantly reduced research and development costs and cycles, injecting formidable competitiveness into tool manufacturing companies. Therefore, delving into the research of tool parametric design technology is of self-evident significance.

Techniques and Research Status Related to the Parametric Design of end milling?Cutters

The parametric design of integral end milling?cutters refers to the automatic and rapid generation of a three-dimensional solid model of the end milling?cutter by inputting structural dimension parameters such as the tool’s front angle, back angle, helix angle, diameter, and cutting edge length. To achieve the three-dimensional parametric design of end milling?cutters within a computer, it is necessary to first establish a mathematical description model of the cutter’s structural features. By employing theories and methods related to computational geometry, computer graphics, and Boolean operations, the modeling, display, and storage of the end milling?cutter in the computer are realized. Finally, the development of the parametric design software system is completed through the creation of a user interface and database. Therefore, the main research content of the parametric design of integral end milling?cutters includes the establishment of mathematical models and the software implementation.

The mathematical modeling of integral end milling?cutters involves using mathematical expressions of points, lines, or surfaces to describe the dimensional structure and topological relationships of each spatial structure of the end milling?cutter. The description method will directly determine the precision of the end milling?cutter model and the ease of software implementation. Currently, research on the mathematical modeling of end milling?cutters primarily includes structures such as bar stock, helical cutting edges, and chip flute cross-section lines.

Bar Stock Mathematical Model

As the manufacturing blank for integral end milling?cutters, the bar stock determines the basic structural parameters of the cutter, such as diameter and cutting edge length, as well as the selection of the tool holder. The mathematical model of the bar stock mainly includes two parts: the detailed modeling of the shank and the modeling of the cutter’s rotational contour. By dividing the end milling?cutter body into the shank, neck, and working parts (including the stem and head), and considering the features of the cutter’s shank (taper shank, straight shank, presence or absence of a positioning slot) and head features (rounded, ball-end, chamfered), a general mathematical model for the end milling?cutter bar stock is obtained based on the universal rotational body mathematical model, as shown in Figure 1.

Helical Cutting Edge Mathematical Model

The helical cutting edge curve of an integral end milling?cutter can alter the chip flow direction, increase the actual cutting rake angle, and extend the length of the cutting edge involved in cutting simultaneously, thereby improving the surface machining quality of the workpiece and the tool life. Therefore, the design of the cutting edge curve plays a crucial role in the design of end milling?cutters. The cutting edge curve of an integral end milling?cutter mainly consists of two parts: the peripheral cutting edge curve and the bottom cutting edge curve (for ball-end mills).

The helical cutting edges of end milling?cutters mainly come in three forms:

1.Constant pitch helical cutting edges, where the helix angle with the generatrix is a constant value, and the helix angle with the axis is also a constant value.

2.Based on the concept of helical motion, the method for establishing the geometric equations of constant pitch helices is discussed.

3.Using the velocity method and according to the theory of generalized helical motion of points and lines on any rotational surface, a generalized helix angle mathematical model is proposed, which relates the tangential velocity of a point undergoing helical motion to the angle between the generatrix of the rotating body, as well as the generalized helical line mathematical model. Furthermore, the mathematical models for constant pitch, constant helix angle, and general helical cutting edge curves on conical, spherical, and planar surfaces are derived, as shown in Figure 2.

From Figure 2, the general mathematical model for the helical cutting edge can be obtained:

where p(x) can be determined based on the shape of the milling cutter’s outer contour, and p(x) takes different values depending on the type of helix:

For equal-pitch cutting edges,?P is the pitch, and φ0 is the initial angle.

β is the angle between the helix and the generator of the cutter’s rotational body.

The bottom cutting edge curve of a ball-end end milling?cutter mainly includes three forms: straight cutting edge, equal helix angle edge, and orthogonal helical edge (equal pitch edge).

① A straight cutting edge refers to the cutting edge along the axial direction of the cutter’s ball-end portion being in a “straight line” shape. The straight cutting edge has a simple shape and is easy to sharpen, but during machining, it tends to have poor cutting stability due to sudden engagement and disengagement, and the cutting speed at the top of the edge is zero, which can lead to the formation of built-up edge at the top of the cutting edge. Therefore, in actual production, the bottom cutting edge of ball-end end milling?cutters often uses a helical cutting edge, as shown in Figure 3.

Based on the first fundamental form of the spherical surface, the equation for the equal helix angle helical cutting edge on the ball-end portion is obtained:

Where R? is the parameter and β is the helix angle. When the cutting edge curve is at the top of the ball-end mill, i.e., R = R?, the above equation does not hold, and a separate smooth curve that connects to the vertex needs to be designed.

An orthogonal helical cutting edge refers to the intersection line between the orthogonal helical surface formed by the straight generatrices always perpendicular to the axis of the mill and the spherical surface. Based on the equation of the spherical surface and the equation of the orthogonal helical surface, the equation for the orthogonal helical cutting edge is obtained:

Here, β represents the helix angle of the circumferential cutting edge, θ is the parameter, with 0 ≤ θ ≤ tanβ.

Mathematical Model of Radial Section Lines for end milling?Cutters

The actual chip flute of a end milling?cutter is produced by the grinding wheel moving in a helical path around the cutter’s axis, resulting in a space helical surface. The shape of the radial section line is influenced by the shape of the grinding wheel, its relative position and posture to the cutter, and the relative motion trajectory, making it difficult to precisely describe the section line shape with a mathematical model.

To simplify the calculation, during the parametric modeling of the cutter, the chip flute section line is divided into several parts: the cutting face, the flute bottom, the transition face, and the back face. The cutting face is simplified to a straight line segment, the flute bottom and the transition face are simplified to two arcs, and the back face is simplified to a straight line segment. Among these, the arc representing the flute bottom is tangent to the straight line segment of the cutting face, the core circle, and the transition face. The transition face is tangent to both the arc of the flute bottom and the straight line segment of the back face, as shown in Figure 4.

Research Status of Parametric Design Software for Integral end milling?Cutters

Parametric design software for integral end milling?cutters requires a user-friendly human-machine interface as well as the capability to display and store three-dimensional models of the cutters. Currently, there are mainly two development approaches: secondary development technology based on existing 3D CAD software and development technology based on the OpenGL graphics interface.

By utilizing the secondary development interfaces provided by software such as UG, SolidWorks, CATIA, Pro/Engineer, and AutoCAD, and calling library functions for modeling, transformation, and Boolean operations, the parametric design of end milling?cutters can significantly reduce the programming difficulty of the software system. To date, universities such as Shandong University, Southwest Jiaotong University, Northwestern Polytechnical University, Harbin University of Science and Technology, Xihua University, Northeastern University, and Xiamen University have conducted extensive research on the parametric design of end milling?cutters based on secondary development technology of 3D CAD software.

Parametric Design of Cutters Based on UG Secondary Development Technology

Shandong University has established a parametric design system for solid carbide end milling?cutters based on the grinding and manufacturing process of the cutters. They used UG/Open MenuScript to create system menus, UG/Open UIStyler to create a user interface in the UG style, and UG/Open GRIP along with UG/Open API for secondary development functions to create the three-dimensional solid model of the end milling?cutter. They compiled the program using VC++ and completed the development. Subsequently, they studied the modeling methods for detailed structures such as the tip radius and relief grooves and completed the development of two-dimensional engineering drawings. They also established three-dimensional models for milling cutters with unequal pitch. Northeastern University, based on the theory of helical lines and helical surfaces, completed the parametric design of end milling?cutters and forming cutters for machining chip flutes after classifying and analyzing the characteristics of CNC helical milling cutters. Northwestern Polytechnical University conducted parametric design for indexable cutters and flat-end end milling?cutters. Harbin University of Science and Technology established mathematical models for the helical lines and chip flute section lines of ball-end end milling?cutters and carried out parametric design for integral ball-end end milling?cutters. Xiamen University added a model for relief grooves, achieving the design of tapered ball-end milling cutters.

Parametric Design of Cutters Based on SolidWorks Secondary Development Technology

Xihua University and others, to meet the needs of Zigong Cemented Carbide Co., Ltd., have developed an object-oriented three-dimensional parametric cutter CAD system using SolidWorks as the development platform and VC++ as the development tool. By utilizing SolidWorks API for secondary development functions, combining dynamic link library technology, Oracle database technology, and ADO (ActiveX Data Objects) database connection technology, and based on the cross-sectional model of end milling?cutters, they have achieved parametric design for chip flutes, four-edge ball-end end milling?cutters, and indexable ball-end end milling?cutters.

Parametric Design of Cutters Based on CATIA Secondary Development Technology

Southwest Jiaotong University, with the assistance of CATIA/API functions and OLE Automation technology, has chosen Visual Basic (VB) as the development tool to develop a parametric design system for end milling?cutters. This system can realize parametric design for five major types of end milling?cutters, including ball-end end milling?cutters, conventional end milling?cutters, CNC end milling?cutters, high-speed end milling?cutters, and end mills. It can also achieve parametric modeling of solid blanks, cylindrical teeth, ball teeth, end teeth, transition teeth, and other detailed cutter structures.

Parametric Design of Cutters Based on AutoCAD Secondary Development Technology:

Northeastern University has chosen VB as the development tool for secondary development of AutoCAD, completing the development of standardized CAD/CAPP software. This software uses a method of disassembly and simplification, modularizing the structural features of end milling?cutters, and achieving computer-aided design for titanium alloy machining end milling?cutters through the invocation of various sub-modules.

Parametric Design of Cutters Based on Pro/E Secondary Development Technology

Lanzhou University of Technology has used the Pro/Toolkit tool for secondary development of Pro/E. Based on the mathematical models of the cutting edge curve, peripheral flute surface, peripheral relief surface, relief groove surface, and the main spiral?slot, relief surface, and spiral secondary groove surface of the ball-end end milling?cutter, they have achieved parametric design of the ball-end end milling?cutter by using surface merging, arraying, and solidification techniques. Tianjin University of Technology and Shanghai Jiao Tong University have established a parametric design system for two-tooth ball-end end milling?cutters, which includes design tools for the cutter body, chip flute, peripheral relief angle, end tooth rake angle, standard Gash, and end tooth relief angle.