Drilling processing of the most difficult material

2022-09-22
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Drilling of difficult to machine materials

Kennametal's Y-shaped drill makes the cutting of difficult to machine materials such as stainless steel and heat-resistant alloys more reliable and efficient. In addition, the oscillation phenomenon can be avoided

machining stainless steel and heat-resistant alloy with conventional drill usually faces great problems. During machining, sharp whistling, rapidly increasing wear or tool cutting edge cracking will occur. The typical phenomenon is the secondary cutting edge cracking, also known as the guide edge (Fig. 1). If this phenomenon occurs in the drilling of alloys, it is most likely to lead to the shortening of tool life and even the scrapping of tools. Regrinding high-quality hard metal tools is usually not economical or even impossible

Figure 1: the cracking of the guide edge on the hard metal drill bit is a typical phenomenon when cutting stainless steel and heat-resistant alloy materials, such as the dual phase steel drill bit shown in the figure

the main reason for the above phenomenon is the swing of the drilling tool, and the reasons for the swing phenomenon are various. One reason is that the tool rebounds under the action of the material being cut. When swinging occurs, the head of the tool moves according to the elliptical trajectory, while the blade or tip moves according to the polygonal (mostly triangular) trajectory. This movement has an adverse effect on the cutting path of the tool. Whether a drilling tool swings and its swing amplitude mainly depend on the grinding form of the tool head, the type of guiding edge, the grinding accuracy and the precision of grinding work

for the grinding of hard metal tools, 4-sided and conical grinding processes are usually used. In addition, Kennametal can also provide patented se or HP grinding processes (Figure 2). Compared with the conventional grinding process, this unique process needs to go deep into the center of the drill bit when grinding the cutting edge. The form of cutter head will ensure high accuracy, and grinding will be carried out according to the latest research results of cutting technology as far as possible. If the centering accuracy at the beginning of drilling is not high, the tool may swing by a large amplitude, which may also lead to the decline of accuracy in machining

Figure 2: in addition to providing conventional face and cone grinding processes, Kennametal can also provide patented HP grinding technology for hard metal drills

grinding errors such as low concentricity or low tool symmetry may aggravate the above phenomenon. The error of peripheral links may further affect the machining accuracy. Therefore, first of all, it is necessary to combine the deviation and tolerance of the clamping system and the machine tool spindle, for example, the concentricity deviation and inclination can be combined. Finally, torsional and axial vibrations, as well as low-frequency bending vibrations (oscillating motion) between the drill and the machine tool, can lead to angular or out of round apertures

the characteristics of the tool itself will aggravate the swing movement

stainless steel and heat-resistant alloy put forward higher requirements for drilling tools. Due to the high hardness of tool material, high cutting force is required. The machinability of steel will be adversely affected by higher cold work hardening trend, lower thermal conductivity and lower toughness. Do not arbitrarily extend the length of grounding wire. The ductility of the material will cause the hole diameter after drilling to be smaller than its nominal diameter due to the rebound of the material. The deviation in diameter and roundness will increase the pressure on the guide edge, increase the contact between the drill bit and the hole wall, and even cause the drill bit to break. The increase of pressure on the guide edge is mainly related to friction and local temperature rise, and may also cause damage to the edge of the material. It can find out the load on the tool tip caused by extrusion or swing, so as to give a warning of which areas will break ahead of the standard service life

cutting parameters will also affect the drilling quality, including not only the cutting speed, but also the feed rate, which is also a decisive factor. At present, the maximum cutting speed of quenched and tempered steel is about 200 meters/minute, and the feed rate can generally be much higher than 0.1 mm/circle. For example, a drill with a diameter of 8.5 mm can withstand a feed rate of 0.25 mm/turn or even higher. Higher feed rate can stabilize the drill bit and slightly eliminate the swing trend, so the quality of drilling processing can be appropriately improved

due to the limitations of the properties of the materials, stainless steel and nickel based alloys cannot adopt such a high cutting speed and feed rate, otherwise the drill bit will be overloaded or even damaged. Generally, the feed rate needs to be kept at a low level, which is far lower than the feed rate of 0.1 mm/circle. Since the transverse cutting edge of the drill bit will not only cut the workpiece but also squeeze the workpiece in mid September 2017, the use of such parameters is conducive to avoiding swinging motion. The drill bit will squeeze the surface of the workpiece. If the workpiece interferes with the guide edge of the drill bit, the drill bit with good symmetry can basically maintain a stable cutting process, and the swing motion will also follow the helix. The chips appearing in the chip cutting process need to be quickly discharged from the chip chute. In addition, it is necessary to control the generation speed of chips in order to discharge smoothly and avoid damaging the inner wall of the aperture. The adjusted chip chute contour and the optimized chip shape can make the chips curl as much as possible. According to different vehicles, poor air quality seriously threatens people's health. Materials need to curl the chips together as much as possible. In addition, it is also necessary to avoid uncontrolled short chips entering the chip chute as far as possible, resulting in damage to the inner wall of the aperture. Using the Y-shaped drill bit can obtain better surface quality on the premise of ensuring the same service life, and at the same time, it can ensure that the cuttings can be discharged into the chip removal groove quickly and smoothly

the conical shape of the cutter head is more conducive to alignment.

the first impression made by Y-type bits is that the included angles between different chip removal grooves are not consistent. The three guide edges are arranged in the form of the letter Y, although this drill has only two cutting edges (Fig. 3). The Y-shaped drill has a conical head structure, which can be accurately aligned after precise grinding. TiAlN coating brings high wear resistance and production efficiency, and has a very wide range of applications. Drill bits all over the world can be reground and recoated in a very short time. Kennametal has established tool regrinding service stations in North America, Europe and Asia to provide close service to important markets

Figure 3: different parts of the chip removal groove on the Y-shaped drill bit can produce components aligned with the guide edge, which is conducive to cutting

with the help of non uniformly arranged chip removal slots, directional cutting force can be obtained. Along the direction of force, there is a guide edge (2) on the cutting edge and a guide edge (3) at the end of the bit back. The Y-shaped structure supports this additional guide edge. The load on the edge (1) arranged opposite to the above two edges is correspondingly reduced. During cutting, three guide edges play different roles: the guide edge (1) is responsible for cutting, the guide edge (2) is responsible for cutting and supporting, and the guide edge or sliding edge (3) is responsible for supporting. Through this structural arrangement, the tool swing can be basically eliminated, especially when drilling, the roundness tolerance and cylindricity tolerance can be guaranteed. If the cutting edge continues to be optimized, the wear can be minimized. The high quality requirements of drilling and the "pressure" exerted by the edge shape on the drill bit, especially on the cutting edge and guide edge, have been reduced

the cutting distance of the tool can be appropriately extended by using the above technology. There is a certain rule between the hole and the drilling depth. For example, the processed hole diameter is slightly larger than the nominal diameter of the drill bit. That is to say, the drill bit is no longer stuck in the hole. Under good preconditions, the aperture quality of it8 grade can be achieved. The first and last hole diameters drilled by the same drill can be kept continuous and stable. The tool life of subsequent processes such as reamer and tapping can also be improved

y drill bits have been successfully used in many occasions. For example, even when processing stainless steel that has not yet rusted, such as 1.3916, 1.4350, or 1.4542, good results can be obtained. In the service life, the efficiency improvement can often reach more than 100%. Even when processing hardened steel with thermal stability and even hardness up to 55HRC, y-bit can still give satisfactory results

about the author:

master engineer Herbert Kauper is kennamet in Fuerth. He must lock the brake handle to the head of the group of Al Technology Co., Ltd. hard metal drill bit and global drilling engineering system department

email address: upper@ (end)

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