1 Introduction
Micro-machining is a kind of micro-manufacturing technology developed on the basis of traditional cutting to meet the processing requirements of micro-miniature structural parts. It has broad application prospects in many fields such as micro injection molds, optical components, integrated circuits, and computer peripherals. . The basic principle of micro-machining is to use a micro-cutting tool to remove excess material from a workpiece on a precision (or ultra-precision) cutting machine, making it a micro-precision part that meets the requirements in terms of shape, precision and surface quality.
The development of micro-cutting technology relies on the support of micro-cutting tool technology. Based on the characteristics of micro-cutting, this paper analyzes the basic requirements of micro-cutting for cutting tools, and focuses on the tool materials, tool design points and typical tool preparation techniques suitable for micro-cutting.
2 Basic characteristics of micro cutting tools
At present, there are many fine cutting methods that are mainly used for fine turning, fine vertical milling, fine flying cutting and fine drilling. The fine cutting tools used are micro turning tools, flat head and ball end mills, flying knives and drill bits.
Affected by the scale effect, the machining mechanism of tool grinding (breaking) damage, cutting force and cutting surface formation of micro-cutting is significantly different from conventional cutting, and the cutting resistance, friction and impact conditions of the tool are worse. . Tools suitable for micro-cutting should meet the following basic requirements:
(1) The overall scale is small, and the local feature scale is small.
For micro-miniature structures, such as frames, planes, curved surfaces, shafts, grooves, walls, holes, etc., which are widely used in micro-miniature systems, in order to adapt to the characteristics of micro-machining processing, high precision, and avoidance with the workpiece Interference, the overall dimensions of the cutting tool and the feature dimensions of the cutting portion must be reduced simultaneously.
(2) sharp cutting edge
Under micro-cutting conditions, in order to achieve a very small amount of material removal, the cutting depth and feed rate are usually on the order of micrometers, the cutting thickness is in the same order of magnitude as the tool edge radius, and the actual front angle of the tool will behave as a large negative. value. The influence of the cutting edge radius on the fine cutting performance cannot be ignored, and the cutting tool should have a sharp enough cutting edge. However, due to the limitations of tool material properties and manufacturing processes, the cutting edge radius cannot be reduced proportionally with the overall tool size reduction.
(3) good surface quality
The surface quality has a great influence on the performance of the micro-cutting tool. In order to achieve good micro-cutting accuracy and surface quality, micro-tools should have high surface integrity and small surface roughness and micro-forming defects. Poor surface quality not only increases the frictional resistance during micro-cutting, but also deteriorates the machined surface and weakens the tool strength.
(4) High strength and strong impact resistance
For rotary tools such as small diameter micro end mills and drill bits, fine cutting is performed at extremely high spindle speeds. The cutting portion of the micro-cutting tool should have sufficient strength and dynamic characteristics to withstand the high-frequency impact load during fine cutting.
(5) Good rigidity and strong resistance to deformation
In order to ensure the machining accuracy, the micro-tools should have high rigidity to reduce deformation and springback under the action of cutting force. In micro-milling, the axial and radial deformation caused by insufficient tool rigidity is the main reason that affects the machining accuracy. In the case of fine drilling, the fracture caused by the excessive deformation of the bit will cause the workpiece to be scrapped.
(6) Good wear resistance and uniform wear process
The cutting portion of the micro-cutting tool should have a sufficiently high hardness to ensure its wear resistance. Fine cutting with a blunt tool not only affects the machining accuracy, but also produces significant machining burrs, which makes it difficult to finish the surface.
(7) High dynamic balance accuracy
In micro-milling, the ratio of tool runout to feed is significantly greater than conventional cut. At very high spindle speeds, the cutting load between the cutting edges is extremely uneven, and the cutting force fluctuates severely, which will affect the stability of the cutting process and the reliability of the tool. In order to ensure the trajectory of the tool tip and the machining accuracy, the rotary cutters such as micro-milling cutters and drill bits should have extremely high dynamic balance accuracy. Before use, the dynamic balance test must be carried out along with the tool holder system.
(8) Tool clamping is accurate and reliable
The installation error of the micro-rotary tool is the main factor affecting the machining accuracy and reliability. The tool holding system should have high contact stiffness and repeatability and good high speed locking.
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