In the machining operation of mechanical parts, hole processing accounts for a considerable proportion, similar to high speed milling, high speed, high precision drilling processing has been put on the agenda, high efficiency hole processing is an indispensable process to promote the rationalization of parts production. In recent years, the parts production mostly adopts the CNC machine tool as the center of the production form, for hole processing, but also mostly adopts the machining center, CNC electrical processing machine tools and other advanced equipment. No matter which field of hole processing, to achieve high precision and high speed is an important competitive means to obtain user orders.
Machining center (MC) conditions for high speed hole machining
The prerequisite of realizing high speed machining of hole is to use high speed machining center, and the high speed of machine tool must meet the following conditions.
Equipped with high speed rotary spindle
The bit has a center tooth like the end mill. Because there is a circular speed near the center tooth, the speed of the spindle must be high when the cutting speed is high. Especially in the use of small diameter drill, spindle speed is indispensable. In the future, with the progress of high speed hole machining, it is expected that the demand for spindles with a speed of 30,000 ~ 100000r/min will continue to increase. At the same time, due to the required high speed rotation time is very short and the requirement of Z (bit cutting direction) spindle extension length should be controlled in the minimum degree, therefore, the configuration of high speed spindle is an indispensable condition to achieve high speed and high precision hole processing.
The movable part has the function of agile movement
Spindle and table and other movable parts should be as much as possible to reduce the weight, in order to achieve rapid action, which is also a high-speed hole processing must have the condition. The processing time of a hole is only a few seconds, so it is necessary to shorten the tool movement time between holes, which is the key problem to achieve high efficiency cutting. The way to solve this problem is first of all, the action of movable parts must be flexible and fast. For example, even if high precision positioning accuracy is achieved, but such as the machine tool moving part of the action is not sensitive and fast enough, it is impossible to meet the current user proposed to achieve high-speed hole processing requirements. Usually with acceleration characteristics (G value) to judge the fast performance of the machine tool moving part, when G=0.8 ~ 1.5, it can be judged that the machine tool has a high speed performance of the machining center.
The proportion of the overall area of the worktable to the machine tool should be small
Serve AS THE USER OF PROCESSING CENTER, THE SPACE THAT THE PART PLACE OUTSIDE THEY HOPE WORKBENCH AND WORKBENCH OCCUPIES SHOULD AS FAR AS POSSIBLE A FEW LESS. Especially hole processing this kind of processing cost is higher and the added value is lower processing field, it is best to use the kind of compact structure of the processing center. Such as the RIken high speed CNC milling machine, its processing range of 300mm2, machine body accounted for the area of 950mm2, machine tool accounted for the area of about three times the size of the largest workpiece can be processed, the entire structure is quite compact. The spindle speed of the milling machine is 45000r/min, which can be used for high-speed cutting. The main axis is XY direction mobile structure (the work table can only move the Z axis), and its acceleration characteristic value G=1.5, indicating that the machine has the function of quick action.
The main shaft can supply coolant directly
In the process of drilling, processing L/D(the ratio of the diameter of the drill bit and the depth of the hole) in more than 5 holes must pay special attention to the problem of chip removal, it is best to choose the drill bit with the oil hole, in order to carry out stable processing. It is more convenient to replace the locking bolt of the clamping tool by supplying the coolant from the center of the spindle.
With hole machining CNC tool interpolation function
The characteristic of CNC cutting is that it can be used to control the trajectory of the tool reasonably. When CNC cutting the hole, spiral cutting, constant height walking tool, pair cutting and other tool interpolation methods can be used. The CNC control system with these functions can be applied in the hole processing.
Entered a new period of high-speed drilling
For a long time is the use of drill for high-precision hole, threaded hole and bolt hole processing, recently, this kind of processing has been rapidly developing to high-speed cutting direction.
High speed steel twist drill is still widely used in hole processing, but there is a gap in hole processing accuracy and efficiency among enterprises. The bulk of high-speed cutting bits are ceramic-coated hardmetals, such as those used by MAZAK and Morisei to process cast iron. Diamond-coated cemented carbide bit, DLC coated cemented carbide bit or bit with diamond sintered cutter teeth can be used in processing nonferrous materials such as aluminum alloy. In conclusion, many new high-speed cutting bits will continue to be developed in the future.
Among all kinds of coated bits, ceramic coated carbide bits pay special attention to wear resistance, heat resistance and lubricity, and their coating technology also adopts multilayer coating method, such as the use of TiAlN, TiN, TiCN and other composite nitrides to form a composite coating structure. The general trend of the cutting conditions of the bit is high speed, with the different materials being processed, the cutting speed can reach 200 ~ 300m/min respectively.
High speed bit cutting is a development trend of high speed and large feed, similar to the development trend of ball-end milling cutting conditions. The cutting practice shows that increasing the cutting speed is beneficial to rationalize the chip shape and improve the roughness of the machined surface. It is expected that it will continue to develop along the direction of high-speed cutting in the future. Increase the feed to chip cutting and chip removal and prolong tool life is very beneficial, therefore, the future will also continue to develop along the direction of large feed.
At present, high speed hole processing mostly adopts the spindle with liquid hole machining center, this equipment is conducive to improving the cutting speed of the drill bit. For example, when φ10mm coated carbide drill bit is used to process shallow holes in S45C material, the cutting speed can reach 250m/min, and the feed speed can reach 1600mm/min(equivalent to 0.2mm/r). Under this condition, it only takes about 1 second to process a hole. Hitachi Precision Machine Company and Brassa Industry Company adopt this condition for shallow hole processing. Under THESE CONDITIONS, IT TAKES ONLY 0.2 ~ 0.5 SECONDS FOR BRASSA COMPANY TO PROCESS SMALL DIAMETER HOLES IN ALUMINUM ALLOY ROD WITH a DIAMOND-coated carbide BIT. It is expected that the processing of small diameter holes will enter the high-speed processing period of one hole per second.
There are many factors affecting the bit life of high-speed cutting, such as edge wear due to high cutting heat, cutting vibration will lead to edge breaking, chip winding, and even cause bit fracture.
To reduce the impact of these faults on the bit life, the following technical measures can be taken:
Select tool materials with excellent wear resistance, suitable for high speed drilling, such as coated carbide, etc.
Select the cutting edge shape suitable for high speed cutting, such as determining the appropriate drill Angle and chamfering edge. Usually, the drill Angle can be selected from 130° to 140°, which can effectively reduce the cutting torque; In addition, cross grinding can be used to reduce the contact area between the cutting edge and the cut surface as much as possible. At the same time, should try to improve the shaft and cutting edge part of the pendulum accuracy and flange part of the height accuracy.
The clamping fixture with high clamping rigidity and high precision should be selected, and the weight of the clamping fixture should be reduced to facilitate quick action. For example, the hot - mounted structure of HSK shank is an ideal clamping system at present.
In high speed drilling, in order to improve the cooling and chip removal effect of the cutting edge, the liquid supply method can be used to supply the cooling liquid directly to the cutting edge to obtain a stable cutting effect. In addition to the cutting fluid, a small amount of vegetable oil and air can be added to the coolant to form a mixed mist coolant.
The development trend of indexable bit
A indexable bit is a tool with a replaceable blade that serves as a cutting edge and has a larger diameter than a conventional bit, although a small indexable bit of φ10mm has recently been developed. At present, the indexable bit has been serialized and can cover almost all kinds of products of the whole bit series. The bit blades are generally made of coated carbide materials, and only a few products are made of sintered high-speed steel, diamond sintered body, CBN sintered body and other materials. Indexable bits usually have only one blade, but may also have two blades, one for the center and one for the periphery. For large diameter holes, the drill can be fitted with more than two blades. A single blade bit is similar to an integral bit, with a triangular tip to reduce cutting resistance. In order to facilitate chip splitting, the blades are equipped with chip cutting slots. The clamping method of the blade varies from manufacturer to manufacturer. In most cases, one or more screws are used to tighten the blade. When there are more than 2 blades, the shape of the blade and the shape of the chip slot are different. The trend has been particularly pronounced recently.
At the beginning of the development of the indexable bit, it could only process holes with a depth of about three times the diameter of the bit, but now it has developed to be able to process deep holes of 5D to 8D(D is the diameter of the bit). The use of indexable bits is most effective when machining parts with uniform hole specifications. For example, the use of multi-blade drill bit, can simultaneously chamfering and countersink the hole inlet operations, which is very beneficial to improve the efficiency of hole processing.
CNC hole processing technology
CNC cutting is to make the cutting more reasonable processing method, CNC hole processing, can be used with multi-direction cutting function of end milling cutter, spiral cutting interpolation and contour cutting interpolation, etc., it requires the selection of as few tools as possible to a small number of holes for the most reasonable processing. Recently, the application of high speed milling for hole machining in production is an example of this kind of machining. High speed milling has the following characteristics:
The boring and chamfering can be carried out by using the ball end milling cutter and the drill bit with spiral interpolation.
Ball end mill with spiral interpolation method, taper hole continuous processing;
The end milling cutter for thread processing with screw interpolation method can be used for various thread hole processing;
End mill with contour cutting interpolation, can be semi finishing and finishing the hole.
In short, the tool interpolation function can be used to high efficiency precision machining of any size of high precision holes. Especially when using high speed milling, the load of each cutter tooth is relatively light, so the same coated carbide end milling cutter can be used for high speed and high precision hole processing of a variety of processed materials. In the future, this machining method is expected to be further used in dry cutting field.
High speed and high precision hole processing
In addition to using CNC cutting method for precision machining of the hole, but also using boring and hinging and other ways for high-precision machining of the hole. With the high speed of the machining center spindle, the boring tool can be used for high speed precision machining of the hole. It is reported that the cutting speed can be increased to more than 1500m/min when the aluminum alloy material is boring about φ40mm. This cutting speed can also be used when CBN sintered body is used as cutting edge to process steel, cast iron and high hardness steel. It is expected that the high speed boring machining will be popularized rapidly in the future.
In order to realize the high speed and high precision of boring machining, it is necessary to pay attention to the influence of tool tooth vibration on the surface roughness and tool life. In order to prevent the machining accuracy and tool life decline, the selected machining center must be equipped with a spindle with excellent dynamic balance performance, the selected boring tool must also have a high dynamic balance characteristics. In particular, the tooth part of the boring tool should be selected for high-speed cutting geometry, tool materials and clamping methods. The R of the end of the cutting edge should be larger to improve the machining efficiency; On the premise of obtaining the same roughness of the machined surface, the feed should be increased. But increase the feed should be enough, otherwise will increase the cutting resistance, is not conducive to improve the processing efficiency. The cutting edge belt should be set with a negative chamfer below 0.1mm, which can effectively maintain a stable tool life.
As for the tool material, it depends on the nature of the material being processed. Such as processing 40HRC below steel and other materials, can choose ceramic tool, this tool in V =300m/min above the high speed cutting conditions, can obtain good machining surface roughness and long tool life. Coated cemented carbide tools are suitable for high-speed cutting of steel under 60HRC. The tool life is very stable, but the cutting speed is slightly lower than that of cerm tools.
CBN sintered body tool is suitable for processing high hardness steel, cast iron and other materials, cutting speed up to 1000m/min above, and tool life is very stable. The edge belt part of the CBN cutter tooth should be properly chamfered, which is very beneficial for stable high-speed cutting and prolonging tool life. Diamond sinterED body tool can be used for ultra-high speed cutting of non-ferrous and non-ferrous materials such as aluminum alloy, which is stable in cutting and has a long life. It should be noted that when using diamond tool, the blade belt must be chamfered, which is an important condition to ensure the cutting stability.
In the aspect of articulated machining, high speed and high precision new cutting tools have not been seen yet, and the research and development work in this field seems to be in a stagnant state. High speed reamers are still used by some specific users for high speed and high precision hole machining. This reamer has a negative front Angle, high rigidity, good chip breaking effect, and allows stable precision hole machining under high speed cutting conditions. The reamer is characterized by the use of larger negative front Angle and odd number of cutter teeth, the high speed cutting speed is the past reamer can not achieve, therefore, can be said to be the design of the traditional concept of reamer bold breakthrough, is a high efficiency of the reamer tool.
High speed thread cutting tools
With the development of CNC cutting, some corresponding hybrid tool products have been developed, such as the new thread cutting tool that combines drilling and thread cutting, drilling and thread cutting can be completed in one stroke. This kind of compound tool makes the threaded hole machining more reasonable and the machining efficiency is greatly improved.
The new end mill used for thread cutting adopts spiral cutting and interpolation method. The end mill can process thread holes above M3, with good chip removal performance, and can obtain stable and high-precision machining effect. The general tap is also developing towards high speed cutting and processing of high hardness steel, and the application range of tapping tools is expanding.
The basic conditions of the tap to achieve high speed cutting are as follows:
Attention should be paid to the cutting function of the cutter teeth, for example, the selection of the cutter teeth design has a rear Angle tap, the cutting effect is more ideal;
The clamping of the tap should be selected with good rigidity of the fixture, such as the selection of spring fixture, hot fixture and so on.
Machining center and other machine tools should have high synchronization accuracy in the process of cutting rotation.
For high-speed tapping operations, stable high-precision and high-efficiency thread cutting can be achieved if the functions of tapping tools, tool tracks and cutting conditions, fixtures and machining centers used are satisfied.
Micro hole processing technology required in the future
With the development of IT-related industries, in recent years, the demand for components for devices used in the optical and electronic industries has increased rapidly, which has stimulated the rapid development of micro-shape and high-precision machining technologies. Among them, the development and application of micro - hole processing technology is particularly eye-catching. Micro hole processing has been used in the processing of printed circuit boards, including steel, a variety of processed materials, can be used to small diameter processing drill. For example, Dijet recently developed a twist drill that combines polycrystalline diamond and carbide as a single cutting edge. The drill provides high speed, high precision machining of aluminum, magnesium, graphite, and plastics, with significantly longer tool life. The helical Angle of the drill