With the constant development of science and technology, several new materials with high strength, high toughness, and high wear resistance are emerging to meet the special requirements of the performance of machine parts. However, cutting of these new materials also poses new problems for the study of metal cutting tools.
The great features in machining are: High strength, harsh work hardening, poor surface quality, large cutting deformation, high cutting force, high cutting temperature, fast tool wear and difficulty of chip breaking. For example, in a high manganese material, after plastic deformation, the austenite structure becomes a fine martensite structure, the work hardness increases from 180 to 220 HBS to 450 to 500 HBS, and work hardening is severe.
The depth of the chill layer can reach 0.3 mm or more. In addition, Kaohsiung steel has a thermal conductivity of 0.25 times that of No. 45 steel and a toughness of 8 times that of No. 45 steel. Not only does it increase cutting power, but it also makes it harder for chips to crack. With the use of indexable milling cutters from a production and processing perspective. Due to the improper selection of geometric parameters of the milling cutter and poor control of chip removal and chip breakage, knife crushing occurs frequently in strong cnc milling. Moreover, if the knife depth is large, axial positioning is unreliable, which affects the facilitation and application of throwaway milling cutters in difficult materials.
Analysis of Milling Contact State The choice of milling angle is directly related to the milling contact state. Good milling contact is one of the main issues in choosing a strong cutter angle. As shown in FIG. 1, when the milling cutter cuts into the work, the contact points between the rake face and the work to be cut can be regarded as four special points (U, V, S, T). Analysis shows that the starting point of contact should be chosen at a point away from the main cutting edge to prevent chips from chipping, which is best.
Selection of front cut angle gp and front feed angle gf According to the above analysis. Choosing the front angle of the milling cutter is important in order for the first contact point when the cutter is cut into the workpiece to be the U or V point. When the feed rake angle gf is smaller than the cutter cutting angle d1, the longer the cutter cutting time, the slower the striking process during cutter cutting. This reduces cutter damage caused by thermal cracking in cemented carbide milling cutters. Negative notch lap angle gp can improve the impact resistance of the cutter.
The negative feed rake angle gf not only increases cutting edge strength, but also facilitates chip curl, breakage and removal. Therefore, through analytical and experimental comparisons, a negative rake angle cutter angle, ie gp = -5 °, gf = -8 °, was selected.
Since both the cutting edge parameter selection depth of cut and the feed tip angle are negative, the cutting deformation during milling is large, the cutting force is large, and the milling temperature rises. Strong cutting requires large cuts and feeds, and wide and thick chip formation can reduce the temperature of the cutting area, but it is also important to choose a reasonable angle. Considering the rigidity of the system and improving the heat dissipation conditions according to the processing requirements of strong cutting. The main inclination angle kr = 75 ° is selected, and the secondary secondary blade structure (Fig. 2) is adopted to increase the strength of the tip. Length 2 mm), kr2’= 15 °. Further, an arc having a tip radius re = 1.5 ± 0.1 mm is ground at the tip of the tool. This type of tool tip not only improves tool strength, but also reduces friction on the sub-back blade facing the machined surface, reduces cutting force, lowers cutting temperature, and improves tool durability.
Blade Positioning Method: Positioning the blade on the knife pad not only meets the positioning accuracy and reliability requirements of the new blade, but also guarantees the positioning accuracy and reliability after the blade has been indexed. This is an important principle for choosing how to position the blades and the design requirements for the positioning components. This design uses a “three-point positioning” method. However, considering that strong milling has a larger cutting force than general milling, the positioning point on the knife pad loses its positioning ability due to strong extrusion deformation, which affects positioning accuracy and positioning reliability. Give Therefore, elongated surface positioning structures are adopted on both sides of the blade. In order to improve the reliability of positioning, the positioning surface of the knife pad has strict requirements for machining dimensional accuracy and position accuracy. The axial direction of the blade can be adjusted to control the end face of the cutting edge.
Clamp mechanism: The tightening mechanism is tightened by a front pressure wedge. The wedge angle of the wedge is selected to be 12 ° to meet the requirements for reliable tightening and convenient operation. When the tightening force point is on the upper part of the blade, a gap is created between the blade and the positioning surface of the blade, and the positioning reliability of the blade is lowered. In order to avoid this phenomenon, the blade is firmly coupled to the positioning surface of the blade, and the influence of the main cutting force (Fz) on the positioning accuracy of the blade can be overcome. The tightening force was selected to be 1/2 of the blade, then 1 mm upwards (Fj shown in FIG. 3), and this method proved to be effective.
Milling pocket processing
Milling pocket machining is one of the key processes in milling cutter manufacturing. Not only high processing accuracy of the sipe itself is required, but also high indexing accuracy between sipe is required. If the sipe grading accuracy is not high, the groove tolerance will be non-uniform. In order to control the amount of heat treatment deformation after quenching of the milling tool, first, after roughing the milling body, quenching and tempering treatment is performed to prepare a quenching structure. The second is to effectively avoid heat treatment deformation and cracking by using a tilt deformation quenching method. To improve the accuracy of sipe indexing, special grooves for grinding grooves are used to ensure the design requirements for sipe manufacturing accuracy and indexing accuracy.
Due to the cutting properties of difficult-to-cut materials, the choice of milling amount is generally next when milling high manganese steel, hardened steel, chilled cast iron, and other materials, especially for strong milling of steel parts. It is as follows. Milling speeds are slightly slower to lower the milling temperature, reduce tool wear, and improve tool durability. The laser cutting depth and feed rate are increased appropriately to ensure that the tool exceeds the depth of the work-hardened layer and reduces tool wear and chipping. However, it is also necessary to consider the problem that the milling force increases due to the increase in the milling depth and the feed rate, which causes vibration in the milling process and the tip is not easily broken.
- Experimental conditions
- Machine tool: X5020.
- Work: ZGMn13 180-200HB
- Milling cutter: d0 = 315 z = 16 YT798 Double secondary blade end milling cutter.
- Dosage: Vc = 25 m / min apfz = 0.2 mm / z.
Experimental Results 96 workpieces were continuously milled and two shifts were milled without abnormal wear such as chipping, knife cutting and hot cracking. Compared to other milling cutters, productivity is about 3 times higher and tool durability is 1.5 times higher.
Double blade powerful end mill cutters have reasonable parameters and construction, reliable clamp and positioning, large milling amount, excellent rigidity, high production efficiency and long tool life. Especially suitable for roughing and semi-finishing of difficult-to-cut materials such as high manganese steel, hardened steel, and high alloy steel. At the tool cutting exhibition sponsored by the National Knife Association, a powerful double-blade milling cutter was well received when machining high-manganese steel. Widely used by large companies such as Second Automobile and Dalian Diesel Engine Factory.