In the U.S. mold manufacturing industry, maintaining a leading position in technology may be the difference between profitable and general companies. Although various strategies can be adopted to increase the profitability of enterprises, the easiest strategy to improve the efficiency of enterprises is to adopt advanced cutting tool technology. This article will introduce and analyze the latest developments in cutting tool technology, with a view to benefiting mold manufacturing companies in improving tool technology.
To improve tool technology, it is important to have reliable basic knowledge of tool technology. The core elements that determine the quality of cutting tools are the tool body, tool geometry and surface treatment technology. Among these elements, there are some features that are crucial to the cutting process of the mold.
Tool base
What do we need to know about the tool matrix? If it is not difficult to do so, you may wish to pick up the H13 or D2 hardened steel workpiece by picking up the hard alloy tool at hand. As most mold manufacturers know, not all tool steels have the same properties. In fact, if you have ever experienced the change from cutting P20 to cutting D2 hardened steel, you can correctly understand the content of this article. This is critical because it also applies to cemented carbide substrate materials. By definition, cemented carbide materials can actually be divided into four types (see the table below. Source: OSG Tap & Die).
Carbide classification table
Carbide Classification - Grain Size
Micron Grain Cemented Carbide -1.0～1.3μm
Submicron grained carbide-0.6-0.9μm
Ultra-fine microcrystalline carbide - 0.4 ~ 0.5μm
Nano Series Microcrystalline Carbide-0.1～0.3μm
The smaller the size of the cemented carbide grains, the higher the hardness of the cemented carbide substrate and the better the wear resistance. Subdivided further, the cemented carbide substrate includes two key characteristics: toughness and hardness.
(1) Toughness
The toughness of the matrix is ​​defined as the magnitude of the radial force (N/mm) applied to the matrix material before it fractures. The transverse rupture strength (TRS) is usually used as a measure of the toughness of the matrix.
(2) Hardness
Hardness can be determined simply by the size of the indentation left on a given test material when a precise load is applied to a hard probe. The harder the material, the stronger the resistance to deformation.
The cobalt content in the cemented carbide matrix directly affects the material's transverse rupture strength (TRS) and hardness. Cobalt is the main binder element in cemented carbide. Increasing the cobalt content can increase the toughness (TRS) of the matrix material, but at the same time it will reduce the wear resistance of the material due to the decrease in hardness. Conversely, if the cobalt content is reduced, the hardness and wear resistance of the material will increase, while the toughness will decrease.
High-level cutting tool manufacturers have studied and mastered the performance differences of various matrix materials, and can use different matrix materials for different processing applications (from easily warped aluminum processing to high-speed milling of hardened die steel). Design and manufacture of unique tools.
Tool geometry
The emergence of new high-speed machine tool processing technology has also put forward higher requirements on tool performance. These tools should maintain stable cutting performance under high spindle speeds and high feed rate machining conditions. In the field of high-speed/high-hardness milling, the market for ordinary carbide tools has become smaller and smaller. Although such tools are not completely out of the market, the advanced machine tools that are currently popular in the market are no longer used 20 years ago or even 10 years ago. The carbide cutters were designed years ago because the market has completely changed. In the field of hard milling, the design of tool geometry must meet both rigid and precision requirements.
For the overall circular cutter, the main indicator reflecting the rigidity of the cutter is the core diameter. The standard core diameter of the end mill is 50% of its diameter. Because hard milling requires higher tool rigidity, the core diameter used accounts for 60% to 70% of the diameter, thus sacrificing some of the chip pocket space, and the reward is to increase the mass of the cutter body and increase the rigidity. Milling of hardened material provides better support for the cutting edge. Since the depth of cut rarely exceeds 10% of the tool diameter, the reduction of chip pocket space does not become a problem.
In 3D milling, the "accuracy" of the tool usually refers to "radial accuracy." The radial accuracy of the ball end mill can reflect the degree of manual grinding after the mold cavity and the core have been processed. High-precision ball end mills need to detect radial accuracy every 10°, and the accuracy of ordinary end mills is often much looser. As a result, the tool's tolerances are transferred to the workpiece during machining. Additional manual grinding hours.
Tool surface treatment
The machining principle of high-speed cutting and hard milling leads to a steady rise in the cutting heat generated during machining. Therefore, the standard PVD coating (such as TiN or TiCN coating) no longer has the advantage, TiAlN coating is undoubtedly the best choice, the first reason is that TiAlN coating has a higher oxidation temperature, making it more suitable for cutting High temperature and stable processing occasions. As the temperature rises, the aluminum contained in the TiAlN coating rises to the surface of the tool to form an aluminum oxide film, which provides better lubricity and expands tool performance. The oxidation temperature of TiAlN is usually about 800°C. In hard milling, the tool life of a multilayer TiAlN coating can be increased by about 35% to 50% over a single TiAlN coating.
Technical innovations in tool bases, geometric parameters and coatings
Processing practices show that the application of cutting tools in the matrix material, geometric parameters and surface coating of innovative technologies, promote the rapid development of mold processing technology.
(1) New Tool Base Material (Hard Milling of Micro Workpieces)
Traditional process: Milling of hardened workpieces (such as D2 or CPM-9V with a hardness range of HRC 59 to 62) using a hard alloy ball end mill with a diameter of 3 mm or less is very labor-intensive. In many cases, the same tool is also used for finishing. Because the tool diameter is so small relative to the workpiece size that the milling time is usually more than 1 to 2 hours.
New process: Milled CBN ball end mills are a new generation of tools developed for hard milling. Compared with TiAlN coated carbide end mills, the tool hardness increases from Hv2800 to Hv4500, which means that CBN tool life can be 5 to 10 times that of cemented carbide tools. Today, advances in grinding technology have made it possible to mill the CBN tool's helical edge. In the past, the accurate sharpening of the CBN spiral edge was considered difficult to achieve because of the easy deformation of the grinding wheel during grinding. In the past, only the use of milling inserts and inserts to achieve the hardened steel finishing of hardness HRC70, can now be completed using CBN overall round tools, the result is to reduce the long-term tool costs, improve the surface finish and eliminate the cause Change the tool marks caused by the tool.
(2) New Tool Geometry Design Technique (Example 1: Low Spindle Speed, High Feed Rate Machining)
Traditional process: Due to the inability to achieve the spindle speed necessary for faster cutting speeds and larger feeds, mold shops lacking high-speed machine tools (15,000 to 40000 r/min spindle speed) have to be forced to sacrifice processing cycle time, resulting in production Inefficient, unable to compete with competitors using high-speed machine tools.
New process: A new generation of tools designed with patented technology enables low-speed/high-feed milling. This new tool geometry design uses a three-dimensional negative-cutting angle, with its negative rake angle varying from small to large along the length of the cutting edge.
This new tool geometry design eliminates the need to use variable helix angle end mills to eliminate resonances in machining. These new endmills use the same helix angle and index, but their cutting angles are gradually changing to reduce cutting forces (loads) and cutting heat. This three-dimensional composite cutting edge essentially uses the concept of radial chip thinning, and therefore produces smaller chips and can withstand greater chip loads. This new design, combined with the addition of chip flutes, allows the tool to use higher feed rates without having to increase the spindle speed as in the past. This tool is designed for processing machines with suitable control technology (predictive software) and spindle speeds in the range of 4000 to 12000 r/min.
Another important advantage of this cutting pattern is that even when the overhang of the tool is increased or the machining load can be kept constant with a large stock of blanks, this means that half rough and half finishing can be reduced. The required tools are equivalent to saving precious time and processing costs when processing large molds. Moldmakers will no longer be limited to lower metal removal rates when machining spindles with spindle speeds below 15,000 r/min.
(3) New technology for tool geometry design (Example 2: Mold waterline processing)
Traditional craftsmanship: The mould waterline is usually drilled or drilled with a carbide tip. Under the condition of using high-pressure coolant, the drill drills at a low feed rate of 1 to 2′′/min, and it is necessary to continuously drill drills to ensure the discharge of chips. Using this traditional process, drilling a 9 The "deep 7/16" waterline takes 90 seconds to complete.
New technology: Integral carbide internal twist drill designed specifically for machining the mold water line can process deep holes with a length-diameter ratio of up to 30 times without drilling jerk, and the feed rate can be as high as 18-30". /min, which can reduce the processing time from the original minutes to several seconds.In addition, the tool life is extended, the surface finish is improved, and the machining accuracy can be stably maintained within 0.001′′.
This new generation of internally cooled carbide twist drills uses a specially designed groove pattern and a thin drill tip to produce finely divided chips that can be discharged smoothly, keeping the drilling torque from the top of the hole to the bottom of the hole. Constant.
(3) New surface coating treatment technology (hardened die steel with processing hardness HRC50 or more)
Traditional technology: Hardened die steels with a hardness of HRC50 or more are usually machined with TiAlN coated carbide tools. To date, many die shops have been very satisfied with the hard milling cutter technology. The best cutters on the market today are generally capable of milling hardened materials with HRC60 hardness at surface cutting speeds up to 400sfm. However, in the mold processing industry, the limit to further increase the cutting speed always comes from the fact that the tool coating cannot withstand the failure due to the high temperature caused by the increased cutting speed. As mentioned earlier, the TiAlN coating has an oxidation temperature of approximately 800°C, beyond which the coating will break and the tool will naturally fail.
New Process: The new multi-layer TiAlN coating developed with nano-coating technology breaks through the performance limitations of traditional TiAlN coatings and its oxidation temperature has been raised to 1350°C. In addition, the surface hardness of this nanocoating was also increased from the conventional TiAlN coating Hv2800 to Hv3600.
The advantage of nano-coating technology is that it can make full use of higher spindle speeds when machining hardened steels because it allows higher cutting speeds. The nano coating's cutting speed (525sfm) is increased by 30% to 45% compared to the normal TiAlN coating's cutting speed (400sfm), which translates into faster cycle times without sacrificing tool life.
Conclusion
In the United States, the competition between mold makers is fierce. Although compared with three years ago, the operation status of the mold companies has obviously improved, but the facts show that in the United States mold manufacturing industry continues to change today, only those companies that always stand in the forefront of technology research and development will continue to thrive.
It is important to realize that it is time to re-examine tooling strategies that were once thought to have been optimized to ensure that it is always in a technologically advanced position. The advanced tooling technology mentioned in this article shows that the minimum investment in new tooling technologies can result in tremendous growth in productivity, tool life and, most importantly, production efficiency.
To improve tool technology, it is important to have reliable basic knowledge of tool technology. The core elements that determine the quality of cutting tools are the tool body, tool geometry and surface treatment technology. Among these elements, there are some features that are crucial to the cutting process of the mold.
Tool base
What do we need to know about the tool matrix? If it is not difficult to do so, you may wish to pick up the H13 or D2 hardened steel workpiece by picking up the hard alloy tool at hand. As most mold manufacturers know, not all tool steels have the same properties. In fact, if you have ever experienced the change from cutting P20 to cutting D2 hardened steel, you can correctly understand the content of this article. This is critical because it also applies to cemented carbide substrate materials. By definition, cemented carbide materials can actually be divided into four types (see the table below. Source: OSG Tap & Die).
Carbide classification table
Carbide Classification - Grain Size
Micron Grain Cemented Carbide -1.0～1.3μm
Submicron grained carbide-0.6-0.9μm
Ultra-fine microcrystalline carbide - 0.4 ~ 0.5μm
Nano Series Microcrystalline Carbide-0.1～0.3μm
The smaller the size of the cemented carbide grains, the higher the hardness of the cemented carbide substrate and the better the wear resistance. Subdivided further, the cemented carbide substrate includes two key characteristics: toughness and hardness.
(1) Toughness
The toughness of the matrix is ​​defined as the magnitude of the radial force (N/mm) applied to the matrix material before it fractures. The transverse rupture strength (TRS) is usually used as a measure of the toughness of the matrix.
(2) Hardness
Hardness can be determined simply by the size of the indentation left on a given test material when a precise load is applied to a hard probe. The harder the material, the stronger the resistance to deformation.
The cobalt content in the cemented carbide matrix directly affects the material's transverse rupture strength (TRS) and hardness. Cobalt is the main binder element in cemented carbide. Increasing the cobalt content can increase the toughness (TRS) of the matrix material, but at the same time it will reduce the wear resistance of the material due to the decrease in hardness. Conversely, if the cobalt content is reduced, the hardness and wear resistance of the material will increase, while the toughness will decrease.
High-level cutting tool manufacturers have studied and mastered the performance differences of various matrix materials, and can use different matrix materials for different processing applications (from easily warped aluminum processing to high-speed milling of hardened die steel). Design and manufacture of unique tools.
Tool geometry
The emergence of new high-speed machine tool processing technology has also put forward higher requirements on tool performance. These tools should maintain stable cutting performance under high spindle speeds and high feed rate machining conditions. In the field of high-speed/high-hardness milling, the market for ordinary carbide tools has become smaller and smaller. Although such tools are not completely out of the market, the advanced machine tools that are currently popular in the market are no longer used 20 years ago or even 10 years ago. The carbide cutters were designed years ago because the market has completely changed. In the field of hard milling, the design of tool geometry must meet both rigid and precision requirements.
For the overall circular cutter, the main indicator reflecting the rigidity of the cutter is the core diameter. The standard core diameter of the end mill is 50% of its diameter. Because hard milling requires higher tool rigidity, the core diameter used accounts for 60% to 70% of the diameter, thus sacrificing some of the chip pocket space, and the reward is to increase the mass of the cutter body and increase the rigidity. Milling of hardened material provides better support for the cutting edge. Since the depth of cut rarely exceeds 10% of the tool diameter, the reduction of chip pocket space does not become a problem.
In 3D milling, the "accuracy" of the tool usually refers to "radial accuracy." The radial accuracy of the ball end mill can reflect the degree of manual grinding after the mold cavity and the core have been processed. High-precision ball end mills need to detect radial accuracy every 10°, and the accuracy of ordinary end mills is often much looser. As a result, the tool's tolerances are transferred to the workpiece during machining. Additional manual grinding hours.
Tool surface treatment
The machining principle of high-speed cutting and hard milling leads to a steady rise in the cutting heat generated during machining. Therefore, the standard PVD coating (such as TiN or TiCN coating) no longer has the advantage, TiAlN coating is undoubtedly the best choice, the first reason is that TiAlN coating has a higher oxidation temperature, making it more suitable for cutting High temperature and stable processing occasions. As the temperature rises, the aluminum contained in the TiAlN coating rises to the surface of the tool to form an aluminum oxide film, which provides better lubricity and expands tool performance. The oxidation temperature of TiAlN is usually about 800°C. In hard milling, the tool life of a multilayer TiAlN coating can be increased by about 35% to 50% over a single TiAlN coating.
Technical innovations in tool bases, geometric parameters and coatings
Processing practices show that the application of cutting tools in the matrix material, geometric parameters and surface coating of innovative technologies, promote the rapid development of mold processing technology.
(1) New Tool Base Material (Hard Milling of Micro Workpieces)
Traditional process: Milling of hardened workpieces (such as D2 or CPM-9V with a hardness range of HRC 59 to 62) using a hard alloy ball end mill with a diameter of 3 mm or less is very labor-intensive. In many cases, the same tool is also used for finishing. Because the tool diameter is so small relative to the workpiece size that the milling time is usually more than 1 to 2 hours.
New process: Milled CBN ball end mills are a new generation of tools developed for hard milling. Compared with TiAlN coated carbide end mills, the tool hardness increases from Hv2800 to Hv4500, which means that CBN tool life can be 5 to 10 times that of cemented carbide tools. Today, advances in grinding technology have made it possible to mill the CBN tool's helical edge. In the past, the accurate sharpening of the CBN spiral edge was considered difficult to achieve because of the easy deformation of the grinding wheel during grinding. In the past, only the use of milling inserts and inserts to achieve the hardened steel finishing of hardness HRC70, can now be completed using CBN overall round tools, the result is to reduce the long-term tool costs, improve the surface finish and eliminate the cause Change the tool marks caused by the tool.
(2) New Tool Geometry Design Technique (Example 1: Low Spindle Speed, High Feed Rate Machining)
Traditional process: Due to the inability to achieve the spindle speed necessary for faster cutting speeds and larger feeds, mold shops lacking high-speed machine tools (15,000 to 40000 r/min spindle speed) have to be forced to sacrifice processing cycle time, resulting in production Inefficient, unable to compete with competitors using high-speed machine tools.
New process: A new generation of tools designed with patented technology enables low-speed/high-feed milling. This new tool geometry design uses a three-dimensional negative-cutting angle, with its negative rake angle varying from small to large along the length of the cutting edge.
This new tool geometry design eliminates the need to use variable helix angle end mills to eliminate resonances in machining. These new endmills use the same helix angle and index, but their cutting angles are gradually changing to reduce cutting forces (loads) and cutting heat. This three-dimensional composite cutting edge essentially uses the concept of radial chip thinning, and therefore produces smaller chips and can withstand greater chip loads. This new design, combined with the addition of chip flutes, allows the tool to use higher feed rates without having to increase the spindle speed as in the past. This tool is designed for processing machines with suitable control technology (predictive software) and spindle speeds in the range of 4000 to 12000 r/min.
Another important advantage of this cutting pattern is that even when the overhang of the tool is increased or the machining load can be kept constant with a large stock of blanks, this means that half rough and half finishing can be reduced. The required tools are equivalent to saving precious time and processing costs when processing large molds. Moldmakers will no longer be limited to lower metal removal rates when machining spindles with spindle speeds below 15,000 r/min.
(3) New technology for tool geometry design (Example 2: Mold waterline processing)
Traditional craftsmanship: The mould waterline is usually drilled or drilled with a carbide tip. Under the condition of using high-pressure coolant, the drill drills at a low feed rate of 1 to 2′′/min, and it is necessary to continuously drill drills to ensure the discharge of chips. Using this traditional process, drilling a 9 The "deep 7/16" waterline takes 90 seconds to complete.
New technology: Integral carbide internal twist drill designed specifically for machining the mold water line can process deep holes with a length-diameter ratio of up to 30 times without drilling jerk, and the feed rate can be as high as 18-30". /min, which can reduce the processing time from the original minutes to several seconds.In addition, the tool life is extended, the surface finish is improved, and the machining accuracy can be stably maintained within 0.001′′.
This new generation of internally cooled carbide twist drills uses a specially designed groove pattern and a thin drill tip to produce finely divided chips that can be discharged smoothly, keeping the drilling torque from the top of the hole to the bottom of the hole. Constant.
(3) New surface coating treatment technology (hardened die steel with processing hardness HRC50 or more)
Traditional technology: Hardened die steels with a hardness of HRC50 or more are usually machined with TiAlN coated carbide tools. To date, many die shops have been very satisfied with the hard milling cutter technology. The best cutters on the market today are generally capable of milling hardened materials with HRC60 hardness at surface cutting speeds up to 400sfm. However, in the mold processing industry, the limit to further increase the cutting speed always comes from the fact that the tool coating cannot withstand the failure due to the high temperature caused by the increased cutting speed. As mentioned earlier, the TiAlN coating has an oxidation temperature of approximately 800°C, beyond which the coating will break and the tool will naturally fail.
New Process: The new multi-layer TiAlN coating developed with nano-coating technology breaks through the performance limitations of traditional TiAlN coatings and its oxidation temperature has been raised to 1350°C. In addition, the surface hardness of this nanocoating was also increased from the conventional TiAlN coating Hv2800 to Hv3600.
The advantage of nano-coating technology is that it can make full use of higher spindle speeds when machining hardened steels because it allows higher cutting speeds. The nano coating's cutting speed (525sfm) is increased by 30% to 45% compared to the normal TiAlN coating's cutting speed (400sfm), which translates into faster cycle times without sacrificing tool life.
Conclusion
In the United States, the competition between mold makers is fierce. Although compared with three years ago, the operation status of the mold companies has obviously improved, but the facts show that in the United States mold manufacturing industry continues to change today, only those companies that always stand in the forefront of technology research and development will continue to thrive.
It is important to realize that it is time to re-examine tooling strategies that were once thought to have been optimized to ensure that it is always in a technologically advanced position. The advanced tooling technology mentioned in this article shows that the minimum investment in new tooling technologies can result in tremendous growth in productivity, tool life and, most importantly, production efficiency.