Circular milling is a milling process in which a cylindrical surface is produced by the circumferential feed motion of a milling cutter. In recent years, due to advances in machining centers and tool manufacturing technologies, this milling process has been promoted and widely used.
At present, using this principle of circumferential milling, it has been widely used in milling, milling (outside) grooves, milling threads, chamfering, milling annular end faces, and milling and sinking holes and many other different processing tasks (Fig. 1).
Because this circumferential milling process has the advantages of high processing efficiency, a wide range of process use, and the ability to be combined with other processing technologies, this circumferential milling process is gaining more and more applications in industrial production, especially in the automotive industry.
Fig. 1: The circumferential milling process is used for many different machining tasks to realize the circumferential feed motion of the milling cutter. This is a prerequisite for circumferential milling. On the CNC machining center, it is possible to use circular interpolation of the X and Y axes. To realize the circumferential feed motion of the milling cutter, the spiral feed motion of the milling cutter can also be achieved through helical interpolation of the X-axis, Y-axis, and Z-axis, and various circumferential milling processes can be realized through the CNC program. At present, high-dynamic machining centers driven by linear motors and equipped with precise numerical control systems can not only reduce the basic time for circumferential milling, but also improve the machining accuracy of circumferential milling, which can be used instead of boring and milling and drilling through circumferential milling. The thread replaces the traditional tapping.
Milling holes using the circumferential milling process can basically be used in two ways and two tools. One is the use of a circumferential milling tool with a cylindrical cutting edge on a cylindrical cutter body or a circumferential milling cutter with a plurality of indexable cutting blades arranged on a cylindrical cutter body. Such cutters are generally used for machining shallow holes and milling. In the case of a hole, the spindle cutter performs a circular feed motion around the Z axis. The other is the use of multi-function end mills equipped with round inserts or diamond or rectangular inserts. These tools can be used to machine deep holes up to five times the tool diameter. When milling holes, the end mills perform spiral feed motion. The X-axis, Y-axis, and Z-axis of the machining center are linked (that is, the three-axis helical interpolation motion).
When using the first method to mill a hole, the cylindricity of the machined hole depends mainly on the geometric accuracy of the milling cutter. Regarding the shape accuracy of the machined hole, no matter which type of tool is used to perform the milling, the accuracy of interpolation of the numerical control system is mainly determined. The surface roughness of the machined hole is related to the accuracy of the tool and the selected cutting parameters.
Figure 2 is a schematic diagram of a milling hole using a multi-purpose end mill. When milling the hole, the rotating end mill performs a spiral feed motion about the Z axis and mills holes of the required size in one working stroke. For example, a hole with a diameter of 285mm can be machined with a 160mm diameter end mill, which can be completed in one working stroke without tool change. This saves five boring operations compared to conventional boring processes, which greatly simplifies the machining process and saves 73% of the machining time.
Using the circumferential milling process, both roughing and finishing can be performed. For the non-through holes, flat-bottomed holes, stepped holes or tapered holes can also be milled, and circumferential milling of the circumferential surface can also be performed on the bottom surface of the hole bottom.
Milling holes are always realized with multi-edged milling cutters. Compared with the boring process with single-edged boring tools, the milling holes can be used with a large number of back-side cutters, so the milling holes have a high processing efficiency. And even when the intersecting holes are intermittently milled, there is no chatter in the milling cutter.
At present, in a high-speed machining center driven by a linear motor, when a peripheral milling process is used to process a bearing housing hole of a car engine gearbox at a feed rate of 40 m/min, the out-of-roundness of the hole can reach 6 μm. Due to this good machining accuracy, this completely eliminates the need for subsequent finishing operations.
The use of the principle of circumferential milling can be used for milling screw holes and drilling and milling threads. The use of drilling and milling threads can not only simplify the production process, but also greatly shorten the processing time.
When the threaded hole is machined using the principle of circumferential milling, either the thread can be milled on the pre-machined thread bottom hole, or the threaded hole can be drilled on a solid material without the thread bottom hole pre-machined.
Milling screw holes can often be compounded with processes associated with drilling, chamfering, and boring hole boss faces, that is, machining some of the functional surfaces associated with threaded holes on a tool, using a drill Milling the thread compound tool for comprehensive machining not only reduces the number of tools but also greatly reduces the machining time. At present, this kind of drilling and milling thread technology has been widely applied to the machining of screw holes for engine parts such as engine transmissions, clutch housings, and cylinder heads. For example, the use of drilling and threading tools to machine M6 taps with a depth of 14.1 mm With a spindle speed of 20000r/min and a feed rate of 700mm/min, the machining time for one screw hole is only 1.2 seconds. In a high-speed machining center of a cylinder head flexible production line, using such a drilling and milling thread compound tool, it is less than 3 minutes to process 120 M6 screw holes on a plurality of cylinder heads.
Jel Precision Tooling uses a Drilling and Threading Compound Tool to machine the screw holes of the gearbox fastening holes. The gearbox body is an aluminum alloy casting. The blade of the composite tool adopts welding polycrystalline diamond, and the spindle speed is 20000r/min. During machining, the Drilling and Milling Thread Compound Tool is performed in order: Drill 22.5mm Thread Bottom Hole-Circumferential Milling M24X1.5 Screw Hole--Remove the burr from the screwed-in place--The reverse boring diameter is 24.5mm and the opening angle is 90 The chamfer of ° - a screw boss with a 36 mm outside diameter —— - inverted 1X45° inside and outside chamfers on the threaded bosses and screw holes. Since the processing of all functional surfaces is accomplished by one tool on a machine tool, this not only saves a lot of related tools and tool change processes, but also improves the machining accuracy and shortens the machining time (only 4 during the entire machining process). Second), thus greatly improving the production efficiency.
Fig. 2: Milling hole with end mill The use of a Drilling and Milling thread compound tool can process screw holes with the same screw pitch but different diameters. It can also be used to mill left-handed or right-handed threads and through-holes or through-holes. Since short chips are generated when milling threads, there is no chip jamming problem. Also because the drilling and milling thread is completed in one working stroke, it ensures the precise concentricity of the bottom hole of the thread and the thread and guarantees the accurate thread depth.
It can be seen from drilling and milling the thread compound tool from the above that the principle of circumferential milling can also be used to compound multiple machining processes such as milling holes, milling slots, and milling end faces with other machining processes to form a variety of different compound tools. For example, boring and counter chamfering, boring and milling ring grooves, boring and milling planes, boring and milling threads are integrated into one tool for machining.
In the past, when working with chamfers and holes on the back of a workpiece to perform chamfering, boring and grooving, as well as boring and threading, it was common to use two or more tools for two processes. Completed, if several functional surfaces require higher position accuracy or on the automatic line of the combined machine tool in order to save the number of processing work, it is necessary to use a controlled tool with a complex structure for processing.
For example, for the hinge holes at the two ends of the chain link where the chamfering needs to be chamfered, a compound cutter capable of circumferential milling can be used for machining. The composite cutter performs rough boring successively - fine boring - boring flat plane - in the hole Chamfers at top and bottom ports (through circumferential milling). Here, it should be pointed out that for the chamfering of the back of the hole, if the conventional machining method is often difficult to compound with the boring processing technology, and circumferential milling is used to chamfer the hole at the upper and lower ports, the compound tool only To perform this chamfering process, it is necessary to move a certain distance in the radial direction and perform circumferential milling by interpolating the X-axis and Y-axis of the machine tool.
Another example is the machining of a matching hole with a ring groove on the brake bracket. The ring groove in the hole can also be processed by means of circumferential milling. For this purpose, the boring and milling slots can be combined. Use a knife for machining. This kind of compound tool performs rough-boring, semi-finishing and fine-boring at the time of machining. The circumferential milling ring groove (circular interpolation through the X-axis and Y-axis). Here too, the processing is performed by means of circumferential milling of grooving which is difficult to carry out process compounding to one tool.
From some of the machining examples listed above, it can be seen that machining tasks such as boring, tapping, threading, cutting slots, grooving, countersinking, and chamfering can be completed by traditional machining methods. By means of the circumferential milling method, and thus optimizing the machining process, modern CNC control technology and multi-axis high-dynamic machine tools (machining centers) provide conditions for the realization of these process substitutions and optimizations. In the past, it was completely dependent on the actuation of complex mechanisms ( Some machining tasks that can be achieved with special tools such as eccentric drives, tie rod drives, and centrifugal force actuation, etc., now allow the tool to be machined circumferentially through the interpolation function of the control system, which not only simplifies the tool structure but also optimizes the machining process. .
The application of the circumferential milling process and its compound tool not only can shorten the basic time and auxiliary time, but also can optimize the machining and improve the machining accuracy of the workpiece.
In order to better use the circumferential milling process, attention should be paid to the selection of the machine tool and the design and manufacture of the tool when planning the production process flow of the workpiece. For high-precision machining tasks, high-dynamic machining centers or high-dynamic milling centers should be used. Because this kind of machine tool uses the direct drive and the fast CNC control system, has the very high dynamic response performance. The traditional machining center uses indirect transmission (such as screw and other mechanisms), it will produce transmission gap and error, in the interpolation movement due to mechanical transmission system delay will cause tracking error. The high-speed machine tool adopts a fast CNC control system to ensure extremely fast response speed and can make full use of the dynamic characteristics of the feed axis to make it move accurately, thereby greatly improving multi-axis interpolation accuracy and machining accuracy. Increasing tool manufacturing accuracy is another necessary condition for improving the accuracy of circumferential milling. For example, in order to improve the accuracy of diamond peripheral milling tools, some tool manufacturers use a CNC 5-axis WEDM machine tool to ensure the tool shape accuracy (up to ±3μm). In addition, in order to improve the cutting conditions of the circumferential milling cutters, the tool manufacturer has designed the indexable inserts to adopt a tangential arrangement on the cylinder of the milling cutter to form a positive rake angle, thereby reducing the radial cutting force. It helps to improve the shape accuracy of the machined hole.
It can be seen that with the advancement of machine tool dynamics and interpolation accuracy (nano interpolation), the further improvement of tool technology and its manufacturing precision, and the strengthening of cooperation between users and tool manufacturers, in the future, the circumferential milling process will Better promotion and application.
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