Drill bits for machining the most hardened steel h

2022-07-26
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With the development and application of cubic boron nitride materials and high-quality modern ceramic blades, the machining of hardened materials can realize turning instead of grinding and milling instead of grinding. Milling is intermittent cutting. In addition to using CBN and ceramic blades, ultra-fine cemented carbide with good strength and toughness and tools coated with high-quality red hardness coating on the surface can also be competent to process hardened steel. This paper introduces the MHS type solid carbide drill bit for steel hole machining of hardened die developed by Mitsubishi Corporation

A Research Report of the international society for production engineering research (CIRP) pointed out that "due to the improvement of tool materials, the cutting speed of the tool is doubled every 10 years. Due to the improvement of tool structure and geometric parameters, the tool life is almost doubled every 10 years." Based on the development of new materials, the new tool structure can play a greater role. The cutter structure design is very complicated in calculation and expression due to the complicated shape of spatial surface, the difficulty in processing various sections, sizes, three-dimensional angles and so on. In recent years, due to the continuous development of CAE and CAD technology, it is possible to find out the distribution of stress, strain and temperature field during cutting, so as to reasonably design the structure. However, the structure shape obtained in this way is often very complex and difficult to manufacture. However, in recent years, CAM technology, mold manufacturing technology, powder metallurgy technology, five axis machining, grinding technology and other technologies have made rapid progress, which was difficult to achieve before, but now it is relatively easy to achieve

in recent 10 years, the mold industry has developed rapidly. As its materials, the mold steel is generally subject to the preliminary cutting of the guide pillar hole, injection hole, cooling water hole and mold cavity, and then to the heat treatment. The heat treatment process often deforms the machined surface and parts. The deformed parts need to be precision machined by grinding and other high-cost and low-efficiency methods to meet the drawing requirements. If the end milling cutter with hardened cavity can be processed by drilling the drill bit of hardened die steel, the process can be simplified to heat treatment first, then drilling and milling the cavity, so as to meet the final processing requirements. This can greatly shorten the process flow and improve the production efficiency

disadvantages of traditional fried dough twist drill

fried dough twist drill is generally used for drilling. In order to drill holes on hardened steel, the structure and shape of traditional fried dough twist drill must be improved first. The disadvantages of traditional fried dough twist drills are:

(1) drilling on solid materials will produce a large amount of chips. In order to discharge the chips, the drill must have a spiral groove, which will weaken the strength of the drill. In order to ensure the necessary strength of the drill bit so that the drill core has sufficient thickness to support the work of the drill bit, the groove should not be too deep or too wide. In this way, a cross edge with a certain width must appear at the front of the drill bit. The rake angle at the cross edge of the old fried dough twist drill is about -50 °. The horizontal edge can not be cut normally, but can scrape and squeeze the workpiece, resulting in a large axial force. Hardened steel has high strength and hardness, resulting in higher axial force, which is very difficult to drill in

(2) since the spiral groove surface constitutes the rake face of the main blade, the rake angles of the main blade are different. The front angle of the old fried dough twist drill at the outer circle of the drill bit is about 30 °, which is very sharp, but the blade strength is very low and easy to be damaged; However, near the horizontal edge, the rake angle is about -30 °, the cutting performance is very poor, and the consumption of cutting power is large. In addition to the front angle, the cutting speed at each point is also different, and the conditions and states for chip generation and removal are different

(3) after the drill bit is drilled in, in order to ensure the straightness of the hole, improve the surface roughness level and processing stability of the hole, in addition to its own rigidity, it mainly relies on the support and guidance of the auxiliary blade composed of two blade belts. However, due to the small width of the blade belt, the supporting and guiding function is very insufficient. Only a solid supporting and guiding can ensure the machining accuracy of the hole and improve the production stability and the service life of the drill bit

mhs series drill bit improvement and innovation

as shown in Figure 1, the MHS series drill bit developed by Mitsubishi has the following structural improvement and Innovation:

(1) X-shaped grinding is carried out on the top of the drill bit to make the transverse edge length 0, and the top surface of the drill bit flank is ground into a triple flank, so that the centering during drilling and regrinding after wear are very convenient. Short hole can be drilled directly; The deep hole can be drilled with a short drill bit to a depth of 1D (drill bit diameter) as a pilot hole, and then drilled with a long drill bit

(2) improve the main cutting edge and spiral groove surface, design the main cutting edge as a concave edge near the drill core, so that the original negative rake angle can reach the positive rake angle, so as to improve the cutting sharpness and chip removal performance; The convex edge is designed near the outer circle of the main blade, which reduces the positive rake angle and improves the cutting edge strength. After the main blade becomes a concave convex blade, the front blade surface modified asphalt polyethylene tire waterproof coiled material gb18967 ⑵ 003 (spiral groove surface) forms a complex wavy surface, which improves the chip removal performance

(3) the core thickness of drill bit is thicker than that of ordinary drill bit, and the rigidity is high

(4) the helix angle is smaller than that of ordinary drill bits. The smaller the helix angle is, the higher the torsional strength is

(5) form 90 ° with the two blade belts, and make wide and thick guide parts on both sides. During drilling, the unstable 2 narrow blade belts become stable 4-sided supports. The advantages of setting the guiding structure are:

· it can bear the radial cutting force, make the support stable and suppress the vibration; The machining hole has high linear accuracy and low surface roughness

· stable processing, small aperture size fluctuation and long tool life

· it can appear in front of the public after intermittent cutting, just like magic through time and space

· deep holes can be drilled. The structure with guide block has many advantages and has long been adopted by major tool companies, such as MAPAL precision boring cutter and precision reamer with guide block, Miller drill, botek deep hole drill, Mitsubishi's previous super roller smooth drill, etc

based on the above structural characteristics, the resistance of MHS series drill bits to the stable failure of the pressure bar under axial force is 37% higher than that of previous products

mhs series drill bit processing example

mhs series drill bits are made of the same materials as Mitsubishi wstar series. The parent material is ultrafine cemented carbide TF15, and the surface coating is (al, Ti) n deposited by advanced miracle with the further improvement of aluminum development space for new energy vehicles. The material brand is vp15tf, as shown in Figure 2. It is most suitable for drilling materials with hardness of HRC35 ~ 55

Fig. 2 organizational structure of vp15tf

1 example of high-quality processing

(1) the main reasons for poor drilling size and low precision are: the drill bit jitter causes the hole to expand, and the expanded quantity exceeds the hole allowance. The spot market price of imported ore is weak and stable; Some market prices in the main producing areas of domestic mines fell; Weak operation of billet market; Coke spot market is stable and strong; The maximum value allowed by the strong rebound in the shipping market is unqualified products. Therefore, the expanding amount should be controlled. The smaller the expanding amount, the higher the machining accuracy of the drill bit. Through structural improvement, MHS series drill bits have good directivity, high rigidity and good cutting performance. Taking Figure 3 as an example, the hole processing is expanded greatly and small, reaching grade 7 accuracy. This is equivalent to adding an initial reaming process after drilling. The length diameter ratio of the machined hole in this example is l/d=70/5=14

· cutting conditions. Workpiece material: dh31s (alloy tool steel); Hardness: hrc48 ~ 50; Drill bit: mhs0500l090b( φ 5mm); Processing hole depth: 70mm; Cutting speed: 20m/min; Feed rate per revolution: 0.15mm/r (one feed); Feed speed: 191mm/min; Cooling method: water soluble cutting fluid; Cutting fluid supply pressure: 2MPa (internal cooling); Machine tool: vertical machining center

· guide hole cutting conditions. Drill bit: mhs0500l020b( φ 5mm); Processing hole depth: 5mm; Cutting speed: 20m/min; Feed rate per revolution: 0.15mm/r

(2) after drilling, the surface roughness is one of the processing quality evaluation standards. As the structure is improved, the vibration is restrained, and the guiding structure still has a certain extrusion roller light effect on the machined wall. Taking Figure 4 as an example, the surface roughness value after machining is 1.743 μ m. Generally, this value can be reached only after drilling and initial reaming and fine reaming

· cutting conditions. Workpiece material: SKD11; Hardness: hrc48 ~ 50; Drill bit: mhs0500l120b( φ 5mm); Processing hole depth: 100mm (through hole); Cutting speed: 20m/min; Feed rate per revolution: 0.10mm/r (one feed); Feed speed: 127mm/min; Cooling method: water soluble cutting fluid; Cutting fluid supply pressure: 2MPa (internal cooling); Machine tool: vertical machining center

· guide hole cutting conditions. Drill bit: mhs0500l020b( φ 5mm); Processing hole depth: 5mm; Cutting speed: 20m/min; Feed rate per revolution: 0.10mm/r

2 examples of high-speed and efficient machining

although the hardness of the workpiece material hrc40 in this case is lower than that in the previous two cases, it is processed efficiently at a cutting speed of 2 ~ 4 times that in the previous two cases, and satisfactory results are obtained under different feed rates. Figure 5 shows the chip image taken. The chip formation shape is good, which can be cut stably and efficiently

· cutting conditions. Workpiece material: cena1 (die steel for plastic molding); Hardness: hrc40; Drill bit: mhs0600l150b( φ 6mm); Processing hole depth: 115mm; Cutting speed: 60m/min; Feed rate per revolution: 0.15mm/r (one feed); Feed speed: 477mm/min; Cooling method: water soluble cutting fluid; Cutting fluid supply pressure: 2MPa (internal cooling); Machine tool: vertical machining center

· guide hole cutting conditions. Drill bit: mhs0600l030b( φ 6mm); Processing hole depth: 6mm; Cutting speed: 60m/min; Feed rate per revolution: 0.15mm/r

3 examples of cutting performance of MHS series drill bits for processing different workpiece materials

here, the processing results of various materials are described from low to high hardness. The drill bit dulling standard is generally measured by the VB value of the flank, which is usually set as 0.2 ~ 0.3mm. After the wear reaches this height, it should not be used again and must be reground. In each example, the chip shape, dynamic waveform change and blade wear under different cutting speeds and feedrates are also shown

(1) the example of chromium alloy stainless steel stavx (hrc33)

is shown in Figure 6. Under the cutting conditions of this example, after 180 holes are machined, the VB value only reaches 0.05mm, which is only 1/4 of the specified value. Therefore, multiple holes can be machined and reground. Figure 6 (c) shows the wear condition of the main rear, front knife face and auxiliary rear at this time. It can be seen from the figure that it can be used continuously

· cutting conditions. Workpiece material: Stavax (chromium alloy stainless steel); Hardness: hrc33; Drill bit: mhs0600l150b( φ 6mm); Processing hole depth: 115mm (through hole); Cooling method: water soluble cutting fluid; Cutting fluid supply pressure: 2MPa (internal cooling)

· life test conditions. Cutting speed: 40m/min; Feed rate per revolution: 0.15mm/r (one feed); Feed speed: 318mm/min

· guide hole cutting conditions. Drill bit: mhs0600l030b( φ 6mm); Processing hole depth: 6mm; Cutting speed: 40m/min; Feed rate per revolution: 0.15mm/r

(2) example of die casting die steel dac55 (hrc45)

as shown in Figure 7, under the cutting condition of this example, after 120 holes are machined, the VB value only reaches 0.1mm, which is 1/2 of the specified value, and the machining can continue

· cutting conditions. Workpiece material: dac55 (die casting die steel); Hardness: hrc45; Drill bit: mhs0600l150b( φ 6mm); Processing hole depth: 115mm; Cooling method: water soluble cutting fluid; Cutting fluid supply pressure: 2MPa (internal cooling)

· life test conditions. Cutting speed: 30m/min; Feed rate per revolution: 0.10mm/r (one feed); Feed speed: 159mm/min

· guide hole cutting conditions. Drill bit: mhs0600l030b( φ 6mm); Processing hole depth: 6mm; Cutting speed: 30m/min; Feed rate per revolution: 0

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