Drill bit for machining the most hardened steel ho

2022-09-23
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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 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 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: "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. Due to the complex shape of spatial surface, it is difficult to deal with various sections, sizes, three-dimensional angles and so on, and the calculation and expression of tool structure design are very complex. In recent years, due to the increasing demand for CAE polyurethane and the continuous development of CAD technology, we can effectively find out the distribution of stress, strain and temperature field during cutting, so as to reasonably design the structure, but 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 linkage processing, 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 material, the mold steel is generally initially cut and processed on the guide pillar hole, injection hole, cooling water hole and cavity, and then heat treated. The heat treatment process often deforms the machined surface and parts, and the deformed parts need to be refined by grinding and other high-cost and low-efficiency methods to meet the requirements of the drawing. 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 as 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 production efficiency

disadvantages of traditional fried dough twist drill

drilling generally adopts fried dough twist drill. In order to drill holes on hardened steel, we must first improve the structure and shape of traditional fried dough twist drill. 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 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 cannot be made too deep or too wide, so there must be a certain width of horizontal edge at the front of the drill bit, and the front angle of the old fried dough twist drill horizontal edge is about -50 °. The horizontal edge can not be cut normally, but can scratch 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 forms the rake surface 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 is about 30 °, which is very sharp, but the blade strength is very low and easy to be damaged; 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 corner, the cutting speed at each point is also different, and the conditions and states of chip generation and removal are different

(3) after the drill bit is drilled, 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 depends 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 bit improvement and innovation

as shown in Figure 1, the structural improvement and innovation of MHS series bit developed by Mitsubishi include:

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

(2) improve the main cutting edge and spiral groove surface, and 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 there; The main blade is designed as a convex edge near the outer circle, so that the positive rake angle is reduced, so as to improve the cutting edge strength there. After the main cutting edge becomes a concave convex edge, the front cutting surface (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 general 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 belt support becomes a stable 4-sided support. The advantages of setting the guiding structure are:

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

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

· intermittent cutting can be carried out

· deep holes can be drilled. The structure with guide block has many advantages, which have long been adopted by major tool companies, such as MAPAL precision boring cutter with guide block, precision reamer, 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 when bearing axial force is 37% higher than that of previous products

mhs series drill bit processing examples have brought confidence to extruder enterprises

mhs series drill bits are the same as the materials used in Mitsubishi wstar series. The matrix is ultrafine cemented carbide TF15, and the surface coating is (al, Ti) n deposited with advanced miracle technology. The material brand is vp15tf, as shown in Figure 2. It is most suitable for drilling materials with hardness of HRC35 ~ 55

Figure 2 organizational structure of vp15tf

1 example of high-quality processing

(1) the main reason for poor drilling size and low accuracy is that the drill bit jitter causes the expansion of the hole, and the expansion exceeds the maximum allowable value of the hole, which is the unqualified product. 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 guidance, 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; 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, surface roughness is one of the processing quality evaluation standards. Due to the structural improvement, the vibration is suppressed, and the guiding structure still has a certain squeezing 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 then initial reaming and fine reaming

· cutting conditions. Workpiece material: SKD11; Hardness: hrc48 ~ 50; 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 example 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 (mold steel for plastic molding); Hardness: hrc40; 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. 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. Although the standard general configuration of bit dulling is not as good as the high-end configuration, it is generally measured by the VB value of the flank, which is usually set to 0.2 ~ 0.3mm. After the wear reaches this height, it should not be used anymore 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) chromium alloy stainless steel stavx (hrc33) example

as shown in Figure 6, under the cutting conditions of this example, after machining 180 holes, VB value only reaches 0.05mm, which is only 1/4 of the specified value, so multiple holes can be machined and reground. Figure 6 (c) shows the wear condition of the main rear, front knife surface 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; Bit: mhs0600l150b( φ 6mm); Processing hole depth: 115mm (through hole); Cooling method: water soluble cutting fluid; Cutting fluid supply pressure: 2MPa (internal cooling) if they are directly produced with formula from abroad

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

· guide hole cutting conditions. 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 conditions of this example, after machining 120 holes, VB value only reaches 0.1mm, which is 1/2 of the specified value, and processing can continue

· cutting conditions. Workpiece material: dac55 (die casting die steel); Hardness: hrc45; 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. Bit: mhs0600l030b( φ 6mm); Processing hole depth: 6mm; Cutting speed: 30m/min; Feed rate per revolution: 0.1mm/r

(3) example of alloy tool steel dh313 (HRC50)

as shown in Figure 8, the hardness of the workpiece material in this case is high, reaching HRC50, so the wear of the drill bit is faster than that in the previous two cases. After machining 100 holes

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