Plunge milling, also known as z-axis milling, is one of the most effective machining methods to achieve high metal removal rate cutting.
For surface machining, grooving machining and machining with large tool overhang length of difficult to machine materials, the machining efficiency of plunge milling method is much higher than that of conventional end milling method.
When a large amount of metal materials need to be cut off quickly, the machining time can be shortened by more than half by using the plunge milling method.
1. Characteristics and application of plunge milling
The working mode of plunge milling is similar to drilling.
The tool moves along the spindle direction, and the cutting edge at the bottom is used for drilling and milling combined cutting.
The schematic diagram of plunge milling method is shown in fig. 4-110.
Fig. 4-110 schematic diagram of plunge milling method
When the turbine blade is plungeed and milled, it can be milled from the top of the workpiece down to the root of the workpiece.
Through the simple translation of the X-Y plane, extremely complex surface geometries can be machined.
When plunge milling is implemented, the cutting edge of the milling cutter is formed by overlapping the profile of each blade.
The depth of plunge milling can reach 250mm without vibration or distortion.
The cutting direction of the cutter relative to the workpiece can be downward or upward, but generally downward cutting is more common.
When slotting and milling the inclined surface, the slotting and milling cutter makes compound movement along the Z-axis and X-axis directions.
In some processing occasions, spherical milling cutters, face milling cutters or other milling cutters can also be used for milling grooves, milling profiles, milling slopes, milling cavities and other processing.
The special plunge milling cutter is mainly used for rough machining or semi precision machining. It can cut into the concave part of the workpiece or cut along the edge of the workpiece.
It can also mill complex geometric shapes, including back chipping.
In order to control the cutting temperature, all plungeed milling cutters with shanks are internally cooled.
The cutter body and blade of the plunge milling cutter are designed to cut into the workpiece at the best angle. Generally, the cutting edge angle of the plunge milling cutter is 87 ° or 90 ° (see fig. 4-111), and the feed rate of each tooth is 0.08 ~ 0.25mm/z.
The number of plunges clamped on each plunge milling cutter depends on the diameter of the milling cutter.
For example, a milling cutter with a diameter of φ20mm can be installed with 2 blades, while a milling cutter with a diameter of φ125mm can be installed with 8 blades.
In order to determine whether the plunge milling method is suitable for the processing of a certain workpiece, the requirements of the processing task and the characteristics of the processing machine tool used should be considered.
If the machining task requires a high metal removal rate, the plungeion milling method can greatly shorten the machining time.
Fig. 4-111 plunge milling cutter
Another suitable occasion for using the plunge milling method is when the machining task requires a large axial length of the tool (such as milling large cavities or deep grooves).
Because the plunge milling method can effectively reduce the radial cutting force, it has higher machining stability than the side milling method.
In addition, when the parts to be cut on the workpiece are difficult to reach by the conventional milling method, the plunge milling method can also be considered.
Because the plunge milling cutter can cut the metal upward, it can mill complex geometric shapes.
For example, a 40 grade machine tool can be used to process deep grooves.
However, this kind of machine tool is not suitable for machining with a long edge spiral milling cutter.
This is because the radial cutting force generated by spiral milling is large, which is easy to make the spiral milling cutter vibrate.
Due to the low radial cutting force during plunge milling, it is very suitable for old machine tools with worn spindle bearings.
plunge milling method is mainly used for rough machining or semi precision machining.
A small amount of axial deviation caused by the wear of machine tool shafting will not have a great impact on the machining quality.
Compared with the conventional machining methods, the plunge milling method has high machining efficiency, short machining time, and can be applied to various machining environments.
It is not only suitable for the processing of single small batch disposable prototype parts, but also suitable for the manufacturing of large batch parts.
Therefore, it is a processing technology with great development prospects.
plunge milling is one of the most effective methods to achieve high removal rate in metal cutting with complex surfaces.
It is widely used in cutting parts with vertical sidewalls.
The machining efficiency of plunge milling method is much higher than that of conventional milling method, which can quickly cut a large number of metal materials.
In addition, plunge milling has the following advantages:
(1) Small lateral force reduces the deformation of parts.
(2) The radial cutting force acting on the milling machine during machining is low, so that the machine tool with low spindle stiffness can still be used without affecting the machining quality of the workpiece.
(3) The tool overhang length can be large, which is suitable for milling the surface of deep groove of the workpiece and prolonging the service life of the tool.
It is also suitable for grooving difficult to cut materials such as superalloys.
In addition, a special use of plunge milling is to process the blades of the turbine, which is usually carried out on a four – or five axis NC milling machine.
When the turbine blade is plungeed and milled, it can be cut from the blade top of the workpiece down to the blade root of the workpiece, and the extremely complex surface shape can be machined through the translation of the X-Y plane.
2. Application scope of plunge milling
Plunge milling method is very suitable for rough machining of die cavity, and is recommended for efficient machining of aviation parts.
One of the special uses is to plunge and mill turbine blades on three-axis or four-axis milling machines.
This kind of machining is usually used on special machine tools for plungeing and milling turbine blades.
It can be milled from the top of the workpiece down to the root of the workpiece.
Through the simple translation of the X-Y plane, extremely complex surface geometries can be machined.
During plunge milling, the cutting edge of the milling cutter is formed by lapping the profile of each blade.
The depth of plunge milling can reach the length diameter ratio of the plunge milling cutter is 5 without vibration or distortion.
The cutting direction of the cutter relative to the workpiece can be downward or upward, but generally downward cutting is more common, as shown in fig. 4-112.
Fig. 4-112 field processing diagram
1. Selection of plunge milling cutter
plunge milling method is a new method in NC machining, which is mainly used in NC machine tools.
Therefore, the selection of plunge milling cutter must be based on the principles and methods of NC tool selection.
At the same time, due to the particularity of plunge milling, it is necessary to select the tool type, structure and cutting parameters suitable for plunge milling.
CNC machine tools are characterized by high speed, high efficiency and high degree of automation.
Generally, they should include general tools, general connecting tool handles and a few special tool handles.
Common tools are classified as follows:
(1) According to the tool structure, it can be divided into:
2) Inlay form: it is connected by welding or machine clamp, which can be divided into two types: non transposable and transposable.
3) Special forms, such as compound cutting tools, vibration reducing cutting tools, etc.
(2) According to the materials used to manufacture cutting tools, they can be divided into high-speed steel cutting tools, cemented carbide cutting tools, etc.
2. Selection principle of plunge milling cutting parameters
The principles for reasonable selection of cutting parameters are:
During rough machining, productivity is generally improved, but economy and processing cost should also be considered;
In semi finishing and finishing, the cutting efficiency, economy and processing cost should be considered on the premise of ensuring the processing quality.
The specific value shall be determined according to the machine tool manual, cutting parameter manual and experience.
The following factors shall be considered:
(1) Back knife measure ap.
When the rigidity of machine tool, workpiece and tool allows, ap is equal to machining allowance, which is an effective measure to improve productivity.
In order to ensure the machining accuracy and surface roughness of parts, a certain margin shall be reserved for finishing machining.
The finishing allowance of CNC machine tools can be slightly less than that of ordinary machine tools.
(2) Cutting width ae.
Generally, ae is directly proportional to the tool diameter d and inversely proportional to the back cutting amount.
During the processing of economical NC machine tools, the general value range of ae is: ae= (0.6 ~ 0.9) d.
(3) Cutting speed vc.
Increasing cutting speed vc is also a measure to improve productivity, but vc is closely related to tool life.
With the increase of vc, the tool life decreases sharply, so the choice of vc mainly depends on the tool life.
In addition, the cutting speed also has a great relationship with the processing materials.
For example, when milling alloy steel 30CrNi2MoVA with an end milling cutter, vc can be about 8m/min;
When milling aluminum alloy with the same end milling cutter, vc can be more than 200m/min.
The spindle speed n is generally selected according to the cutting speed vc.
The control panel of the NC machine tool is generally equipped with a spindle speed adjustment (magnification) switch, which can adjust the spindle speed by an integral multiple during the machining process.
(4) Feed speed vf.
The feed speed vf shall be selected according to the machining accuracy and surface roughness requirements of the parts, as well as the tool and workpiece materials.
The increase of vf can also improve production efficiency.
When the roughness value of machined surface is required to be low, vf can be selected to be larger.
In the process of machining, vf can also be manually adjusted through the repair switch on the control panel of the machine tool, but the maximum feed speed is limited by the rigidity of the equipment and the performance of the feed system.
With the wide application of NC machine tools in production practice and the formation of quantitative production line, NC programming has become an indispensable step in NC machining.
In the process of NC programming, it is necessary to select cutting tools and determine cutting parameters in the state of human-computer interaction.
Therefore, programmers must be familiar with the selection method of cutting tools and the determination principle of cutting parameters, so as to ensure the machining quality and efficiency of parts, give full play to the advantages of CNC machine tools, and improve the economic benefits and production level of enterprises.
3. Structural features of plunge milling tool
The motion mode of plunge milling determines the tool structure.
Generally, the NC plunge milling cutter consists of four parts: blade, tool seat, tool handle and pull pin.
The blade must be installed on the matching tool seat.
Therefore, the tool angle of the plunge milling cutter is determined by both.
In practical application, the model and specification of the blade, tool seat, tool handle and pull pin must be unified.
plunge milling cutters generally perform axial feed and spiral interpolation.
The main cutting edge of the blade is generally long (at 10~15mm), and the auxiliary cutting edge depends on the brand of different manufacturers (at 5~15mm).
The cutting edge angle of the plunge milling cutter is 87 ° or 90 °.
The following is the plunge type and main technical parameters of a certain type of plunge milling cutter (see table 4-24).
Table 4-24 blade structure diagram and main parameters
|Blade brand||Blade diagram||Front corner of blade a/(°）||Back corner of blade (°）||Tool tip radius r/mm||Length of main cutting tool L/ mm||Length of auxiliary cutting edge w/mm||Blade thickness S/mm||Included angle between main cutting edge and auxiliary cutting edge N (°)|