Development and application of the most popular he

Development and application of heavy-duty indexable NC tools

the popularization and application of indexable tools is one of the important development directions of metal cutting. Compared with welded cemented carbide tools, indexable tools have the advantages of high cutting efficiency, long tool life, good processing quality and significant comprehensive economic benefits. Therefore, they are increasingly widely used in machinery manufacturing and other industries in China. With the increasing application of domestic advanced CNC machine tools, the matching CNC indexable tools are also increasingly showing their importance. The use of indexable cutters on heavy-duty CNC machine tools is particularly of great technical and economic value. Although the heavy CNC indexable tools provided by foreign tool manufacturers have a high technical level, they are expensive. Buying a large number of imported tools will increase the production cost and increase the economic burden of enterprises. Therefore, it is of great significance to develop domestic heavy-duty indexable CNC tools that are inexpensive and suitable for national conditions. After more than 20 years of exploration and development, Harbin Turbine Works Co., Ltd. has independently developed a variety of heavy-duty indexable CNC tools, and has achieved preliminary results in production practice. Now, several kinds of cutting tools with relatively mature applications are introduced as follows, hoping to be beneficial to domestic peers

1 heavy indexable CNC lathe tool

the heavy indexable CNC lathe tool developed by our company mainly has two structural types: the integral polished rod eccentric clamping type and the modular lever clamping type. The structural diagrams are shown in Figure 1a and 1b respectively

(a) polished rod eccentric clamping type

(b) lever module clamping type

Figure 1 structural diagram of heavy indexable NC turning tool

1.1 polished rod eccentric clamping type indexable turning tool

1) reasonable selection of eccentricity when the polished rod eccentric clamping type indexable turning tool works, it is clamped by mechanical force and locked by cutting force, so when selecting the eccentricity, It is necessary to accurately calculate and select the type and introduction line of the brake pad shear test within the range of self-locking angle

2) guarantee of manufacturing accuracy of key parts when manufacturing turning tools, it is necessary to strictly control the position and size of the center of the eccentric shaft rotary hole and the locking two sides of the cutter groove, as well as the perpendicularity of the bottom surface of the cutter groove and the two sides (see Figure 2)

3) correct clamping of the blade when clamping the blade by rotating the eccentric shaft, the rotation direction should be consistent with the cutting force direction of the tool, so as to clamp the blade by using the cutting force to avoid loosening of the eccentric shaft due to vibration during cutting (see Figure 3)

Figure 2 key parts of the tool that need to ensure manufacturing accuracy

Figure 3 when clamping the blade, the rotation direction of the eccentric shaft is consistent with the direction of cutting force

practice has proved that the polished rod eccentric sensor developed according to the above requirements is an important part of the accuracy and force measurement stability of the experimental machine. The heavy indexable turning tool can be stably applied to horizontal or vertical heavy CNC lathes to complete the machining of ordinary carbon steel Intermittent or continuous machining of large shafts and cylinder parts made of alloy steel

processing example: processed part: Turbine Spindle (material: 34CrMo); Blade model: 4k251oh10 (42510h); The main geometric angle of the tool: the main deflection angle kr=75 °, the installation front angle of the tool slot g0=-8 °, the rear angle a0=8 °, and the blade inclination ls=- 8 °; Cutting amount: vc=60 ~ 80m/min, f=0.6 ~ 1.2mm/r, ap=12 ~ 18mm. After production verification, it can fully meet the requirements of spindle processing

1.2 modular lever clamped indexable turning tool

because the use of modular structure can make the tool multi-purpose, and can quickly replace the tool head, it is of great economic value. The heavy indexable turning tool developed by foreign tool manufacturers has widely adopted modular structure. The cutter head of the modular turning tool can be designed into different structures, types and geometric angles according to the processing needs, and can be clamped with three sides, four sides, rhombic, circular and various non-standard indexable blades to meet the processing of the outer circle, end face, profiling, grooving, thread, forming surface and other processes. The connection between the modular turning tool head and the tool bar can usually adopt two types: mechanical clamping and hydraulic tensioning. It is better to adopt lever clamping structure for modular cutter head for machining excircle and end face. Because the lever clamping structure can design (select) the force point at the best position, so that the two sides of the blade are in close contact with the two sides of the cutter slot, and at the same time, it can also form a downward clamping force to make the blade reliably fasten and position (see Figure 4), so it is more suitable for large (feed) cutting

Figure 4 Schematic diagram of lever clamping structure

2 heavy indexable CNC milling cutter

2.1 heavy indexable face milling cutter the heavy indexable face milling cutter developed by our company mainly has two structural types: unequal tooth back pressing type and unequal tooth modular type, and its structures are shown in figures 5A and 5b respectively

(a) unequal tooth back pressing type

(b) unequal tooth modular type

Figure 5 indexable face milling cutter structure

1) unequal tooth back pressing face milling cutter

the teeth of the standard type indexable face milling cutter are usually equal tooth distribution, and its disadvantage is that the cutter is prone to produce periodic vibration during cutting (sometimes it may also cause resonance), which intensifies blade wear or causes edge collapse, limits the improvement of cutting efficiency, and affects the machining quality of the workpiece. The unequal tooth back pressing face milling cutter has simple structure (except for the set screw, the cutter has only four parts: cutter body, locating ring, pressing block and blade), which is convenient to manufacture and reliable to use. Through orthogonal experimental design, when the radial forward angle gf=9 °, the axial forward angle gp=7 °, and the rear angle a0=7 °, the cutting efficiency of the milling cutter for machining martensitic stainless steel is twice that of the original standard face milling cutter, and the tool life is increased by 50%

processing example: processed parts: turbine blades (Materials: 1Cr13, 2Cr13); Blade material: YS25, M2, ym30; Recommended cutting parameters: rough milling: vc=120 ~ 160m/min, vf=300mm/min, ap=3 ~ 4mm; Finish milling: vc=200 ~ 250m/min, vf=150mm/min, ap=0.5mm

2) unequal tooth modular face milling cutter

the main advantage of this milling cutter is to save the cutter body and expand the application range of face milling cutter. By changing different types of modular cutter heads, the machining of plane, rectangular surface and circular arc forming surface can be completed. The milling cutter is mainly used for rough milling of alloy steel castings

2.2 heavy indexable slot milling cutter

indexable slot milling cutter is commonly used for slot milling and peripheral surface interpolation on CNC gantry milling machine and boring milling machine. See Figure 6 for the structure of the cutter. The cutter teeth of the tool are of equal tooth distribution type, and the indexable vertical blade with counterbore (blade model cne454) is selected, which is directly fastened in the tool block groove with conical head screws to meet the requirements of strong cutting. In order to ensure the assembly accuracy, the cutter block and cutter body are designed into concave and convex ring positioning keys respectively to ensure the minimum end face error. The diameter range of the developed milling cutter is 450 ~ 800mm; When machining alloy steel castings, the commonly used cutting parameters are: vc=120 ~ 160m/min, vf=200 ~ 250mm/min, ap=5 ~ 8mm

Figure 6 large diameter indexable slot milling cutter

2.3 indexable ultra precision milling cutter

this milling cutter is commonly used for the finishing of the joint plane of the cylinder block, which can realize milling instead of grinding (instead of scraping and grinding), and the roughness of the machined surface of the parts can stably reach Ra1.6 ~ 0.8 M. See Figure 7 (model yce434 -01) for the structural diagram of the tool. The cutting edges of the four cutter teeth on the end face of the tool are circular arc. In order to ensure the cutting accuracy, the blade often uses two teeth (if multi tooth cutting is adopted, the blade end jump needs to be controlled at ≤ 0.005mm), and the blade material is preferably cermet (such as yn10). When machining alloy steel, the recommended cutting parameters are: vc=180 ~ 220m/min, vf=400 ~ 600mm/min, ap=0.5mm

Fig. 7 indexable ultra precision milling cutter

3 large diameter indexable composite drill

when machining the large screw holes connected and tightened on the two planes of the cylinder block, the traditional process is to drill the bottom hole with a high-speed steel drill first, and then use an expanding drill (or boring cutter) to expand the bottom hole step by step to the required size. The disadvantages of this process are low cutting efficiency and short tool life. The new large-diameter indexable compound drill (see Figure 8) developed can change the drilling and expanding process into one-time completion. The compound drill is composed of a centering drill, a cutting head, a safety ring and a cutter bar (including a cooling ring). Centering drill (made of high-speed steel) can ensure the stability of drilling when drilling at high speed; The cutting head is composed of asymmetric multi edge indexable blades, and the indexable blade with convex triangle and dot chip breaking groove can ensure good strength and chip breaking performance. In order to ensure the stability of high-speed drilling, cemented carbide guide blocks are also spot welded on the cutting head (which is particularly important for machining through holes); The function of the safety ring is to protect the tool bar from damage during overload cutting. The diameter range of the large diameter indexable compound drill is 68 ~ 350mm, and the maximum machining depth is 6 times of the drill diameter

figure 8 large diameter indexable low-temperature groove adopts single-chip microcomputer technology to control composite drill

large diameter indexable composite drill is suitable for processing through holes of connecting screw holes of cast iron, carbon steel and alloy steel (forged and cast) cylinder block (if guiding measures are adopted, it can also be used for through hole processing). In order to ensure smooth chip removal and prolong the service life of the tool, the tool bar is equipped with a cooling ring. Under the action of pressure, the cutting fluid enters the inner hole of the tool bar through the cooling ring, and the chips are punched out of the hole while cooling the blade. The common cutting parameters of alloy steel materials processed by large-diameter indexable composite drill are: vc=60 ~ 80m/min, f=0.1 ~ 0.14mm/r. (end)