The Sandia National Laboratories in New Mexico, USA, conducted cutting experiments and research on miniature turning tools and milling cutters with dimensions of only 10 μm and 20 μm.
Although the term "micro-machining" can be used to refer to a variety of machining operations performed on a very small scale, researchers at Sandia National Laboratories avoid the micro-scale turning and milling of them. It is called "micromachining". They believe that the word "micro" in front of the word "processing" means that the workpiece can be processed to a size as small as 1 μm, which the laboratory can't do now. - At least not at the level of turning and milling, the micro-tools they have developed can produce workpieces up to 25 μm in size. In other words, although the level of processing that they have achieved cannot be called “micromachining,†it is closer to the goal of “micromachining†than almost any other metal cutting shop. Researchers at the San Diego National Laboratory refer to this level of processing as "meso-machining."
The micro-milling and micro-turning tools used in sub-micromachining are made by etching the cemented carbide and high-speed steel blanks with a focused ion beam. The micro end mills manufactured by this method can be as small as about 20 μm in diameter; the width of the mini turning tool can be as small as about 10 μm. This kind of micro-tool is an indispensable key process factor for sub-micromachining, because the applicable processing technology for using such micro-tools on machine tools is basically mature. At the Sandia National Laboratory, although it is still necessary to fully develop the micro-tools used in the sub-micro-cutting experiments, the machining machines used in the experiments have fully met the technical conditions for using micro-tools. Researchers can use micro-tools for sub-micromachining using precision machining tools from machine tool suppliers on the market.
One of the main reasons why the United States conducts submicron processing research is related to nuclear weapons. Some parts of the existing nuclear weapons in the United States need to be replaced frequently, and the structural appearance of these parts needs to be continuously improved. However, because each part of the nuclear weapon has an assembly relationship that is not allowed to change between the parts around it, the size and shape of each part must remain fixed. Therefore, in order to add new structural features to the part, the only way is to shrink more structures into the existing space, and sub-micromachining can be an effective means to achieve this goal.
Through a large number of experimental studies, Sandia National Laboratory has successfully milled grooves with a width of 20 to 30 μm on materials including aluminum, brass and 4340 steel, with a typical depth of cut of 1 μm. The laboratory's cutting experiments with a φ22μm carbide double-edged end mill showed that the micro end mill can be up to 50mm/min when machining aluminum parts under cutting conditions with a depth of 1μm and a rotational speed of 18000r/min. The feed rate is effectively cut, the tool milling time exceeds 6 hours, and no tool breakage occurs within the entire feed rate range.
The cutting reliability of the mini turning tool has also been confirmed. Typical cutting experiments have shown that a micro-tool with a width of 13 μm can cut a spiral groove with a depth of 4 μm on a 200 mm full length aluminum piece.
The geometry of a mini turning tool is similar to that of a conventional size turning tool, while the geometry of a micro milling cutter is different from that of a conventional size milling cutter. When the micro-milling cutter is formed by the focused ion beam, it is difficult to process the complex geometry of the typical standard end mill with chip flutes. Therefore, the micro-milling micro-milling cutter has a larger cross-sectional geometry. simple.
The cutting mechanism of micro-tools is basically the same as that of conventional-sized tools, and can be regarded as a "miniature version" of conventional tool cutting. Observations of the submicron milling process with an optical microscope show that the chips can be quickly discharged from the vicinity of the milling cutter. In addition, observations with an electron microscope have revealed that cutter marks have also appeared on the surface of the milled workpiece. The observations of submicron turning also clearly show that, like the common phenomenon of conventional size turning, after cutting with a submicro turning tool, it is often found that long chips are attached to the tool.
The above-mentioned submicron milling experiments were carried out at a Boston Digital machining center purchased in the last century. The machine has a displacement resolution of 1 μm, so the “touching off†tool setting method commonly used in manual milling machines can be used to position the micro-milling tool relative to the workpiece. The researchers used a manual method to continuously and slowly move the knife at a step of 1 μm each time until a small amount of chips appeared through the microscope, indicating that the milling cutter was just in contact with the workpiece.
Recently, the Sandia National Laboratory conducted an experimental study of submicron milling at a precision machining center at Willemin-Macodel. The submicron turning experiment was carried out on a diamond lathe at Moore Tool (although the micro turning tool material used was not diamond). The laboratory also conducted experimental research on submicrodischarge machining (EDM) on Agie's wire cutters and EDM machines. In addition, submicron laser processing is another important area of ​​laboratory micro-machining research.
At present, the micro-milling of the sub-micro-turning is more practical. For submicron milling, the factors that constrain its application are not difficult to replicate the complex geometry of conventional end mills, but another reason is that it is difficult to radialize the micromillings installed in the toolholders. The jitter is reduced to a tolerance of only 20 μm in diameter. Another problem is that there is currently little demand for submicron milling. The development requirements proposed by users of the San Diego National Laboratory have so far required milling cutters with a diameter of less than 130 μm. For some workpiece topography, such as the teeth of a miniature external gear, the laboratory tends to use wire cutting machines for electrical discharge machining (EDM). However, submicro-milling may be required if the teeth of the micro internal gears need to be machined.
Despite the above problems, experimental studies on various submicromachining methods, including submicron milling, are continuing. In order to avoid problems caused by milling cutter clamping and associated milling cutter slips, Sandia National Laboratory is experimenting with a dedicated spindle that can drive tool rotation without the need for a tool chuck. The developed spindle speed can be as high as 500000r/min.
Another common problem affecting submicron machining is the use of submicro tools that require a high level of expertise. Submicromachining is different from conventional machining. In conventional cutting, tools, workpieces, and machining programs can be replaced between different machines; submicron cutting requires the operator to understand the difference in the superposition of minor errors in different machining environments, and the specifics of the selection. How cutting parameters (such as cutting speed, feed rate, etc.) affect the machining accuracy of a particular machine. To become a skilled sub-micro-cutting operator, it may take many months to continuously learn and practice to master the technical knowledge and operating methods of sub-micro-cutting. This higher technical requirement greatly limits the popularization and application of submicron cutting technology. Even among the 50 or 60 skilled mechanical technicians at the San Diego National Laboratory, only a few people are proficient in this operating technique.
The development status of submicron processing technology can be summarized as follows:
1 Focused ion beam process (for manufacturing submicro tools): Machinable minimum topography size: 200 nm, tolerance 20 nm; material removal rate: 0.5 μm 3 / sec; processable material: any material.
2 sub-micro milling, sub-micro turning: can process the smallest shape size: 25μm (turning up to 10μm), tolerance 2μm; material removal rate: 10400μm3 / sec; processable materials: aluminum, brass, low carbon steel, PMMA plastic .
3 sub-micro-discharge machining (EDM): Machinable minimum topography size: 25μm, tolerance 3μm; material removal rate: 25 × 10 6th power μm3 / sec; workable materials: conductive materials.
Although the term "micro-machining" can be used to refer to a variety of machining operations performed on a very small scale, researchers at Sandia National Laboratories avoid the micro-scale turning and milling of them. It is called "micromachining". They believe that the word "micro" in front of the word "processing" means that the workpiece can be processed to a size as small as 1 μm, which the laboratory can't do now. - At least not at the level of turning and milling, the micro-tools they have developed can produce workpieces up to 25 μm in size. In other words, although the level of processing that they have achieved cannot be called “micromachining,†it is closer to the goal of “micromachining†than almost any other metal cutting shop. Researchers at the San Diego National Laboratory refer to this level of processing as "meso-machining."
The micro-milling and micro-turning tools used in sub-micromachining are made by etching the cemented carbide and high-speed steel blanks with a focused ion beam. The micro end mills manufactured by this method can be as small as about 20 μm in diameter; the width of the mini turning tool can be as small as about 10 μm. This kind of micro-tool is an indispensable key process factor for sub-micromachining, because the applicable processing technology for using such micro-tools on machine tools is basically mature. At the Sandia National Laboratory, although it is still necessary to fully develop the micro-tools used in the sub-micro-cutting experiments, the machining machines used in the experiments have fully met the technical conditions for using micro-tools. Researchers can use micro-tools for sub-micromachining using precision machining tools from machine tool suppliers on the market.
One of the main reasons why the United States conducts submicron processing research is related to nuclear weapons. Some parts of the existing nuclear weapons in the United States need to be replaced frequently, and the structural appearance of these parts needs to be continuously improved. However, because each part of the nuclear weapon has an assembly relationship that is not allowed to change between the parts around it, the size and shape of each part must remain fixed. Therefore, in order to add new structural features to the part, the only way is to shrink more structures into the existing space, and sub-micromachining can be an effective means to achieve this goal.
Through a large number of experimental studies, Sandia National Laboratory has successfully milled grooves with a width of 20 to 30 μm on materials including aluminum, brass and 4340 steel, with a typical depth of cut of 1 μm. The laboratory's cutting experiments with a φ22μm carbide double-edged end mill showed that the micro end mill can be up to 50mm/min when machining aluminum parts under cutting conditions with a depth of 1μm and a rotational speed of 18000r/min. The feed rate is effectively cut, the tool milling time exceeds 6 hours, and no tool breakage occurs within the entire feed rate range.
The cutting reliability of the mini turning tool has also been confirmed. Typical cutting experiments have shown that a micro-tool with a width of 13 μm can cut a spiral groove with a depth of 4 μm on a 200 mm full length aluminum piece.
The geometry of a mini turning tool is similar to that of a conventional size turning tool, while the geometry of a micro milling cutter is different from that of a conventional size milling cutter. When the micro-milling cutter is formed by the focused ion beam, it is difficult to process the complex geometry of the typical standard end mill with chip flutes. Therefore, the micro-milling micro-milling cutter has a larger cross-sectional geometry. simple.
The cutting mechanism of micro-tools is basically the same as that of conventional-sized tools, and can be regarded as a "miniature version" of conventional tool cutting. Observations of the submicron milling process with an optical microscope show that the chips can be quickly discharged from the vicinity of the milling cutter. In addition, observations with an electron microscope have revealed that cutter marks have also appeared on the surface of the milled workpiece. The observations of submicron turning also clearly show that, like the common phenomenon of conventional size turning, after cutting with a submicro turning tool, it is often found that long chips are attached to the tool.
The above-mentioned submicron milling experiments were carried out at a Boston Digital machining center purchased in the last century. The machine has a displacement resolution of 1 μm, so the “touching off†tool setting method commonly used in manual milling machines can be used to position the micro-milling tool relative to the workpiece. The researchers used a manual method to continuously and slowly move the knife at a step of 1 μm each time until a small amount of chips appeared through the microscope, indicating that the milling cutter was just in contact with the workpiece.
Recently, the Sandia National Laboratory conducted an experimental study of submicron milling at a precision machining center at Willemin-Macodel. The submicron turning experiment was carried out on a diamond lathe at Moore Tool (although the micro turning tool material used was not diamond). The laboratory also conducted experimental research on submicrodischarge machining (EDM) on Agie's wire cutters and EDM machines. In addition, submicron laser processing is another important area of ​​laboratory micro-machining research.
At present, the micro-milling of the sub-micro-turning is more practical. For submicron milling, the factors that constrain its application are not difficult to replicate the complex geometry of conventional end mills, but another reason is that it is difficult to radialize the micromillings installed in the toolholders. The jitter is reduced to a tolerance of only 20 μm in diameter. Another problem is that there is currently little demand for submicron milling. The development requirements proposed by users of the San Diego National Laboratory have so far required milling cutters with a diameter of less than 130 μm. For some workpiece topography, such as the teeth of a miniature external gear, the laboratory tends to use wire cutting machines for electrical discharge machining (EDM). However, submicro-milling may be required if the teeth of the micro internal gears need to be machined.
Despite the above problems, experimental studies on various submicromachining methods, including submicron milling, are continuing. In order to avoid problems caused by milling cutter clamping and associated milling cutter slips, Sandia National Laboratory is experimenting with a dedicated spindle that can drive tool rotation without the need for a tool chuck. The developed spindle speed can be as high as 500000r/min.
Another common problem affecting submicron machining is the use of submicro tools that require a high level of expertise. Submicromachining is different from conventional machining. In conventional cutting, tools, workpieces, and machining programs can be replaced between different machines; submicron cutting requires the operator to understand the difference in the superposition of minor errors in different machining environments, and the specifics of the selection. How cutting parameters (such as cutting speed, feed rate, etc.) affect the machining accuracy of a particular machine. To become a skilled sub-micro-cutting operator, it may take many months to continuously learn and practice to master the technical knowledge and operating methods of sub-micro-cutting. This higher technical requirement greatly limits the popularization and application of submicron cutting technology. Even among the 50 or 60 skilled mechanical technicians at the San Diego National Laboratory, only a few people are proficient in this operating technique.
The development status of submicron processing technology can be summarized as follows:
1 Focused ion beam process (for manufacturing submicro tools): Machinable minimum topography size: 200 nm, tolerance 20 nm; material removal rate: 0.5 μm 3 / sec; processable material: any material.
2 sub-micro milling, sub-micro turning: can process the smallest shape size: 25μm (turning up to 10μm), tolerance 2μm; material removal rate: 10400μm3 / sec; processable materials: aluminum, brass, low carbon steel, PMMA plastic .
3 sub-micro-discharge machining (EDM): Machinable minimum topography size: 25μm, tolerance 3μm; material removal rate: 25 × 10 6th power μm3 / sec; workable materials: conductive materials.
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