Current situation and development of the hottest h

The current situation and development of high-speed machining technology

I. overview

the development trend of machining is high efficiency, high precision, high flexibility and greening. The development direction of machining is high-speed machining, which is becoming the mainstream of machining in developed countries. Over the past 50 years, the great progress of cutting technology shows this: today, the cutting speed is as high as 8000m/min, the material removal rate is 150 ~ 1500cm3/min, the hardness of superhard tool material is 3000 ~ 8000hv, the strength is 1000MPa, and the machining accuracy is from 10 m to 0.1 M. Dry (quasi) cutting is increasingly widely used. With the increase of cutting speed, the cutting force decreases by more than 25 ~ 30%; The cutting temperature increases slowly; The machined surface roughness is reduced by 1 ~ 2 grades; The production efficiency is improved and the production cost is reduced

Figure 1 high speed cutting speed range of different materials

high speed cutting technology is not only an advanced technology, its development, promotion and application will drive the progress and efficiency improvement of the whole manufacturing industry. In foreign countries, since Dr. Salomon of Germany put forward the concept of high-speed cutting in the 1930s, after half a century of exploration and research, with the progress of numerical control machine tools and tool technology, it began to be applied in the late 1980s and early 1990s and developed rapidly to be widely used in aerospace, automobile and mold manufacturing industries to process aluminum, magnesium alloys, steel, cast iron and its alloys, superalloys, carbon fiber reinforced plastics and other composite materials, Among them, the processing of cast iron and aluminum alloy is the most common

high speed cutting technology started relatively late in China. In the mid-1980s, it began to study ceramic tools for high-speed cutting hardened steel and its application in production. Then it attracted widespread attention to high-speed cutting. At present, high-speed steel and cemented carbide tools are mainly used. The cutting speed of cemented carbide tools is ≤ 100 ~ 200m/min, and the cutting speed of high-speed steel tools is within 40m/min. However, a large number of CNC machine tools and machining centers have been imported in the automobile, mold, aviation and engineering machinery manufacturing industries, and a number of CNC machine tools have been produced in China. With the in-depth study of high-speed cutting, some of these industries have gradually applied high-speed cutting technology and achieved good economic benefits

II. Theoretical basis of high speed machining

1 Chip formation characteristics

the chip morphology of different materials in different states is shown in Figure 2 and figure 3

(a) supply status, cutting speed 127.2m/min

continuous banded chips (E)

(b) hardness 325hb, cutting speed 125.5m/min

serrated chips

(c) hardness 325hb, cutting speed 250m/min

serrated chips

(d) hardness 325hb, Cutting speed 2600m/min

sawtooth chips about to be separated

Figure 2 chip morphology (longitudinal section micrograph) when cutting aisi4340 steel (40CrNiMoA) in different states at high speed

Figure 3 chip morphology when cutting carburized and hardened 20CrMnTi steel (HRC60 ~ 62) at 100 ~ 110m/min

workpiece materials and their properties and cutting conditions play a major role in chip morphology, among which workpiece materials and their properties are mostly used in machinery, vehicles ② Press the sample clamping key, and the upper collet of the instrument starts to run upward to move the clamping length. When the upper collet reaches the set clamping length, the electromechanical stops running, and the main components on it can have a decisive impact. General low hardness and high thermophysical properties K ρ C (thermal conductivity K, density ρ And specific heat capacity C), such as aluminum alloy, low carbon steel, unhardened steel and alloy steel, are easy to form continuous strip chips in a wide range of cutting speeds

high hardness and low thermophysical properties K ρ C workpiece materials, such as heat-treated steel and alloy steel, titanium alloy and super alloy, form serrated chips in a wide range of cutting speed. With the increase of cutting speed, the degree of serration increases until separate unit chips are formed

2) cutting mechanics

Figure 4 diagram of shear angle and force on rake face during right angle cutting

Figure 5 shear angle during high-speed cutting of 4340 steel (40CrNiMoA) φ Comparison between the calculated value and the measured value (Recht)

in the figure, FS is the shear force, and FM is the force required for the change of chip momentum during high-speed cutting; FF is the friction force acting on the flank

shear angle φ And friction coefficient μ (=tg β) The relationship between can be estimated by merchant formula

φ= P-b+g0422

experiments show that it is calculated in high-speed cutting φ The angle is in good agreement with the measured results

in the range of high-speed cutting, with the increase of cutting speed, the friction coefficient decreases, and the shear angle φ Increase, cutting force decreases

Figure 6 cutting force of Al2O3 based ceramic tool when end milling quenched and tempered 45 steel

Figure 7 generation and transmission of heat during cutting

3) cutting heat and cutting temperature

heat during cutting mainly comes from shear deformation work, tool chip and tool workpiece friction work. During dry cutting, the cutting heat is mainly transmitted by chips, workpieces and cutters, and the surrounding medium is less than 1%

Fig. 8 cutting heat flowing into each part during end milling of aluminum alloy

Fig. 9 cutting temperature of Al2O3 based ceramic tool when end milling hardened steel T10A (hrc58 ~ 65)

test results of the influence of cutting speed on cutting temperature. With the increase of cutting speed, the cutting temperature rises quickly at the beginning, but after reaching a certain speed, the increase of cutting temperature gradually slows down, or even rarely increases

4) surface roughness

with the increase of V, the machined surface roughness decreases. The ace-v500 machining center used in the experiment has a maximum speed of 10000r/min, and its first and second natural frequencies are 50Hz (3000r/min) and 113hz (6780r/min) respectively

Figure 10 effect of rotating speed on machining roughness when milling grooves with coated end mills

III High speed cutting tool materials

1) high speed cutting tool materials

diamond

Natural Diamond

polycrystalline diamond (PCD)

synthetic single crystal diamond

diamond coating

cubic boron nitride (PCBN)

ceramic tools: there are two types of alumina (Al2O3) based and silicon nitride (Si3N4) based

TiC (n) based cemented carbide (cermet)

coated tools.Excellent high speed steel, WC base TiC (n) - based cemented carbide and ceramics are the matrix. Composite coating

hard coating: ticn+al2o3+tin of CVD; TiCN+Al2O3； Ticn+al2o3+hfn, tin+al2o3, TiCN, TiB2, etc. Tialn/tin, TiAlN, etc. of PVD

soft coatings: high speed steel tools coated with chalcogenide (MoS2, WS2)

Ultra Fine Grain Cemented Carbide: WC based cemented carbide with fine grain (0..5 m), adding TAC NBC and other

powder metallurgy high speed steel (PM HSS) and high performance high speed steel Hss-e

Figure 11 schematic diagram of tool material application

2) rational application of high-speed cutting tool materials

during high-speed cutting, it is necessary to select cutting conditions such as reasonably matching tool materials and suitable processing methods for different workpiece materials in order to obtain the best cutting effect. There is no universal tool material

tool material properties

hardness: Diamond PCD> cubic boron nitride PCBN> Al2O3 based>si3n4 based>tic (n) based cemented carbide>wc based ultra-fine Grain Cemented Carbide> high speed steel HSS

bending strength: hss>wc base>tic (n) base>si3n4 base>al2o3 base>pcd>pcbn

fracture toughness: hss>wc base>tic (n) base>pcbn>pcd>si3n4 base>al2o3 base

heat resistance: pcd700 ℃ -800 ℃; PCBN1400℃-1500℃； Ceramic 1100 ℃ -1200 ℃; TiC (n) base 900 ℃ -1100 ℃; Ultra Fine Grain Cemented Carbide WC base 800 ℃ -900 ℃; HSS600℃-700℃。

rational application of high-speed cutting tool materials

machining aluminum alloy: diamond is most suitable for high-speed cutting. However, complex tools can be used for high-speed machining of structural aluminum and its alloys with monolithic Ultrafine Grain Cemented Carbide and its coated tools

machining steel and cast iron and their alloys: Al2O3 based ceramic tools are suitable for soft and hard high-speed cutting; PCBN is suitable for high-speed cutting of high hardness steel above HRC; Si3N4 and PCBN are more suitable for high-speed cutting of cast iron and its alloys, but not for cutting ferritic steel; WC based ultra-fine cemented carbide and its TiCN, TiAlN, tin coated tools and TiC (n) based cemented carbide tools, especially the overall complex tools, can process steel and cast iron

machining SUPERALLOYS: Toughened and reinforced alumina based and Si3N4 based ceramic tools (such as SiC whisker toughening) and Sialon ceramic tools are suitable for machining such alloys. PCBN tools can be machined at a cutting speed of m/min. Complex tools can be made of Ultra-fine Grain Cemented Carbide and coated tools

processing titanium alloy: generally, WC based ultra-fine Grain Cemented Carbide and diamond tools can be used. Better results can be obtained by using cutting fluid with good lubricating performance

IV. tool handle system for high-speed machining

jt or BT system: tool handle taper 7:24, single-sided contact

hsk system: tool handle taper 1:10, double-sided contact

jt tool handle (7:24) JT tool handle and spindle joint diagram

hsk tool handle (1:10) HSK tool handle and spindle joint diagram

tool handle and spindle contact

different tool handle systems, centrifugal force has a great influence during high-speed machining

7:24 spindle/tool handle connection

when the spindle speed reaches a certain limit value (n=15000r/min, f=15kn), the separation of the big end at the spindle/tool handle connection causes the tool handle to swing with the tool handle as the support under the action of cutting force, which greatly reduces the positioning accuracy and repeated positioning accuracy of the tool handle in the spindle taper hole, and cannot ensure the reliability of the connection

(a) the gap between the connecting surfaces (unit: m) (b) the contact stress between the connecting surfaces (unit: n/m2)

Figure 12 7:24 the connection between the tool handle and the spindle (rotating speed n=15000r/min, axial tension f=15kn)

while HSK is different

(a) clearance between connecting surfaces (unit: m) (b) contact stress between connecting surfaces (unit: n/m2)

Figure 13 hsk-a63 tool handle and spindle connection (n=10000r/min)

tool speed has an effect on radial clearance

(a) 7:24 (b) hsk-a63

Figure 14 effect of rotation speed on radial clearance (n=10000r/min)

the optimal speed range of 7:24 connection is 0~12000r/min, 12000~15000r/min can still be used, and more than 15000r/min, which cannot be used due to reduced accuracy. The optimal speed range of hsk-63a tool handle system is 0-30000r/min, beyond which the accuracy will be reduced

v. safety technology of high-speed machining

1) balance of high-speed rotating tools

the high-speed cutting rotating tool system must be balanced, but it should be balanced according to its use speed range, so as to achieve the best economic conditions. Generally, it must be balanced above 6000rpm to ensure safety. It is required that G ≤ 2.5, G is the balance quality (mm/s), that is, the parameter reflecting the relationship between tool balance and rotation speed

G=w × E=pnu=p · u · n30m30 · m

e - eccentric (G × Mm/kg)

m - cutter body mass (kg)

w - angular velocity (r/s)

m - unbalance (g)

n - rotating speed (r/min

r - unbalance radius (mm)

u - residual unbalance (G × Mm) residual unbalance u=m × R

dynamic balance line diagram

shanck dynamic balance instrument face milling cutter with blade thrown out at 5000 r/min

end milling cutter with handle with diameter of 12 mm bent and broken at 36000 R/min