In metal processing, selecting the appropriate tool according to the characteristics of the workpiece being processed can give full play to the performance of the machine tool, increase production efficiency, and reduce production costs. Considering factors such as unit price, efficiency, life, and shortened auxiliary time, it can be seen that the use of high-speed, high-efficiency, and long-life tools will reduce the overall production cost of a single product.
The use of high-speed, high-efficiency machining centers has enabled metal processing to take a high-speed, high-efficiency path, but whether or not it can be effective depends on the choice of tools because cutting tools are the most basic, effective, and active tool for achieving high-speed, high-efficiency cutting. the elements of. We contacted the world-famous tool manufacturers, and studied all kinds of relevant data such as average tool costs and production costs in developed countries. We found that cutting tooling costs by 30% can reduce the production cost of one-piece parts by 1%, and increase the tool life by 50%. Reducing the production cost by 1%; increasing the processing efficiency by 20% can reduce the production cost by 15%. This fully illustrates the use of modern cutting technology, select high-speed, high-efficiency tools, give full play to the performance and efficiency of machine tools, and achieve high-speed, high-efficiency cutting, is the correct way for the production center to increase production efficiency and reduce production costs.
Advanced tool features
The high-speed, high-efficiency tools used in the machining center should have the following properties: in addition to the good hardness and wear resistance, high strength and toughness that general tools should have, they should also have:
1. Higher reliability - stable cutting, consistent quality, fewer tool changes and long life.
2. Higher installation accuracy and repeatability, good interchangeability and quick changeability.
3. Serialization, standardization, and generalization, as much as possible using machine clamps and transmission tools and multi-functional composite tools.
4. Good chip breaking, chipping and chip removal performance, to ensure that the cuttings do not wind on the tool and the workpiece, does not damage the processed surface, and does not interfere with the pouring of the cutting fluid.
There are many types of tools available for high-speed, high-efficiency machining centers. The following types of tools are commonly used tools:
1. Ceramic cutters are characterized by high hardness, good wear resistance, excellent heat resistance and chemical stability. They are not easily bonded to metal during processing and are widely used in CNC machining. Among them, alumina-based ceramic tools are suitable for carbon steel. , Alloy steel and cast iron material processing; silicon nitride-based ceramic tool is more suitable for alloy cast iron, chilled cast iron and other hard materials, cutting speed up to 500 ~ 1000m/min.
2. The polycrystalline diamond (PCD) cutter processing aluminum and aluminum alloy material has a very long life and good precision, cutting speed up to 1000 ~ 4000m/min, the United States Boeing high-speed milling aluminum alloy cutting speed has reached 5000 ~ 7500m / Min. Compared with PCD, CVD diamond tools have higher hardness, better wear resistance, smaller friction coefficient, stronger chemical stability and thermal stability, and a 2 to 3 times longer life than PCD. The disadvantage is that toughness is not as good as that of PCD. CVD diamond tools are considered to be a new generation of tool materials with a promising application in the processing of automotive engine products, especially aluminum and aluminum alloy materials.
3. CBN (Cubic Boron Nitride), Polycrystalline Cubic Boron Nitride (PCBN) tool material, with higher thermal stability and excellent chemical stability than PCD, VCD, in the environment of 1 200 ~ 1 300 °C It does not react with iron-based materials. Its hardness and wear resistance are close to that of diamond. It is very suitable for machining cast iron and hardened steel. The higher the hardness of the processed material, the more superiority of cubic boron nitride tools can be realized. In the processing accuracy, cutting efficiency, tool life and other aspects have unparalleled advantages, cubic boron nitride, polycrystalline cubic boron nitride tool materials are increasingly valued by countries around the world.
4. Coated tools can be divided into CVD and PVD coated tools according to different coating methods. According to the nature of the coating materials, they are divided into "hard" coated tools and "soft" coated tools, which can be divided according to different matrix materials. For carbide-coated tools, high-speed steel coated tools, and ceramic and superhard material coated tools, nano-coated tools have recently been developed. Coated tools can be flexibly selected for matrix and coating materials to give the tool the desired performance, improve processing efficiency, improve machining accuracy, extend tool life, and reduce processing costs.
Tool application case
In recent years, the Great Wall Company's sedan engine factory has established 3 flexible machine production lines using high-speed, high-efficiency machining centers of world-famous machine tool manufacturers. Together with the world-famous knives manufacturer Kennamet, the United States, they have carefully selected cutting tools in conjunction with the processed products. Realize high-speed and high-efficiency cutting.
1. KSCM-AluMill face milling cutter
Figure 1: KSCM-AluMill face milling cutter
In the cylinder and cylinder head production line, we used the KNEM KSCM-AluMill face milling cutter for face milling of aluminum alloy cylinder blocks and cylinder heads. The tool consists of a steel cutter head and an aluminum body, which reduces the weight while ensuring sufficient rigidity, and the bimetal structure also reduces machining vibrations. The tool has high metal removal rate, low processing burr and high processing efficiency, and is very suitable for high speed cutting. KSCM-AluMill face milling cutters have 5 types of tool holders. Different tool holders are used for rough and finish milling. They can achieve different surface roughnesses. They can also install rough and fine milling tool holders at the same time. Rough finishing Completed at one time, shorten the processing time and improve work efficiency.
In the actual processing, we chose two KD1415 and KD1420 PCD cutting tool holders that are suitable for machining low-silicon aluminum alloys and have high wear resistance and long life. KD1415 blade has high hardness and is suitable for machining uniform surface with uniform hardness. Therefore, it is used for the finishing of cylinder block, cylinder head up and down, and front and back surfaces; KD1420 tool holder has better blade toughness and is suitable for the balance Uniform, non-uniform hardness surface, used for roughing. After finishing, the flatness error of the large plane such as cylinder block, cylinder head, front and back, etc. is not more than 0.02mm, the minimum is 0.0034mm, the average flatness error is not more than 0.01mm, and the surface roughness is less than Ra0.8. The processing beat meets the requirements. When the KSCM-AluMill face milling cutter replaces the tool holder, it only performs axial adjustment and does not require radial adjustment. It has the characteristics of convenient adjustment, short adjustment time and high adjustment accuracy. When the Great Wall Company actually uses it, it achieves axial adjustment deviation. More than 0.003mm, the cutting load is evenly distributed to each tooth, which effectively prolongs the tool life. After several months of trial machining, the KSCM-AluMill face milling cutter has a good machining effect.
Only take the top of the cylinder block and the bottom surface as an example. The top surface is Φ100, Z12 (9 fine milling tool holders, 3 light fixture holders), and the amount of light is 0.008+0.002mm. The PCD insert is integrally welded. Processing parameters : V = 2500m/min, fz = 0.12mm/z, Vf = 11.5m/min; actual test pieces after finishing milling, surface roughness Ra0.8, flatness error < 0.004, beat meets requirements. Bottom fine milling cutter disk Φ200, Z24 (18 fine milling tool holders, 6 light fixture clamps), processing parameters: V=2500m/min, fz=0.12mm/z, Vf=14.3m/min; actual test after processing Parts, surface roughness Ra0.8, flatness <0.004mm, beat meets requirements.
2. Compound processing tool
Composite machining is a very effective means to improve the processing efficiency. Several processing contents are completed with one knife in one processing, which reduces the number of tool changes, saves auxiliary time, and improves production efficiency. A step drill is the simplest and most common type of compound machining tool. A drill with a chamfered edge is the simplest step drill. In the machining of cylinder block and cylinder head hole system, this simple step drill has been selected for hole drilling requiring chamfering and has achieved good results. For example, when the Kennedy straight groove 180° vertex TX step drill drills, the radial force during drilling is almost zero, and four linear lands are symmetrically distributed along the circumference, which leads to a good guide, and it also has the function of repairing light, making the straightness of the drilled hole. And the degree of position has been greatly improved. In the machining of cylinder block and cylinder head hole, the other composite drill used is a TF drill with three cutting edges around the circumference. The drill core is thicker and stronger than the two-edged drill bit, which makes up for the poor toughness of hard alloy. The special shape of the tip of the tip can be automatically centered without machining the center hole; the cutting edge increases the feeding amount per revolution (up to 20m/min when cutting aluminum), high strength, and can perform high-speed cutting (cutting aluminum Up to 1000m/min), which greatly shortens the processing time and improves the processing efficiency. It is especially suitable for deep-hole machining. The dimensional accuracy can reach up to H9, the position accuracy can reach up to ±11μm, and the roughness Rz20~25.
In the Great Wall crankshaft production line, the Kennametal SE cemented carbide stepped drill was selected, which has higher drilling roundness than ordinary high-speed steel drills. The drilled roundness of high-speed steel drills can reach up to 20 μm, while the SE drill bit Drilling roundness is only 1/5 of the former. According to this hole shape accuracy, we can completely consider to avoid the hole expanding process, and in some cases, can even replace the less demanding reaming hole (for example, screw thread thread hole). This drill is characterized by a shorter cutting edge, which can reduce the axial force by nearly 50%; the rake angle near the core is positive, so the cutting edge is sharper; the groove shape is parabolic and the core thickness is larger. The drill bit has higher strength and rigidity; there are two injection cooling holes, and the cooling conditions are good; the arc-shaped cutting edge and flutes are arranged in a reasonable manner, which facilitates the chip breaking into small pieces and can be smoothly discharged. The drill bit is used for drilling the front and rear ends of the crankshaft, and has good results
Figure 2: TF bit
Figure 3: SE drill
Figure 4: TX drill
3. Precision hole cutter
The rapid development of modern industry puts forward higher requirements on the dimensional precision, geometric shape and surface roughness of the hole, especially in the automotive industry, that is, requiring high precision and large quantities, and thus it is urgently needed for high-efficiency precision hole machining tools. Diamond reamers are a kind of precision tool developed to meet this need. The Kennametal-blade integrally welded PCD reamer was used in the cylinder head production line conduit and the bottom hole of the seat ring; the cylinder head cover positioning holes were machined using the Kennametal Bencere split-type PCD reamer. High-speed and high-efficiency cutting is realized, and the performance of the high-speed machining center is fully utilized, which greatly improves the processing efficiency. The actual spot sampling of some products? 8, 10 and 13 sets of three holes, the size of the variation within the range of 0.014, the maximum error in the size of the accuracy of less than 60% of the tolerance, the average error is less than 0.005mm, the surface roughness of the hole <Ra0. 8.
The cylinder crankshaft hole finishing and the machining of the camshaft hole in the cylinder head use the Kenner Bencere QUATTRO-CUT tool. The four-flute indexable insert is mounted in a high-precision sawtooth pocket with dimensional accuracy controlled in the μ class. Compared with traditional split-type tools, QUATTRO-CUT tools only need to adjust the radial height of the blade without adjusting the blade back cone, which shortens the adjustment time. According to the sampling test, the crankshaft hole is refined. Dimensional accuracy machining error <0.018mm, coaxial error <0.016mm, minimum error only 0.0021mm, roughness <Ra1.6; precision camshaft hole, coaxial error <0.007, minimum error 0.0014mm, roundness Error <0.002mm, position error <0.063, minimum error 0.0148mm, dimensional accuracy <0.018mm, minimum deviation 0.0044mm. The processing of both sets of holes can meet the requirements of the tempo, and the test has so far produced a total of several hundred pieces with good results.
4. Cylinder hole and crankshaft machining tool
Great Wall Corporation cylinder block production line, cylinder bore cast cast iron cylinder liner, cylinder bore rough machining is a large margin of cast iron processing, requires a knife with high strength and toughness, after careful use of the Kenner Fix-Perfect tool . The Fix-Perfect tool system is a product series with different combinations of positive and negative angles. Its characteristics are: the negative radial rake angle of the insert and the positive axial rake angle, and the positive axial rake angle reduces the axial cutting force, and The negative radial rake angle creates a good shear effect and facilitates chip breaking. The positive axial rake angle makes the cutting force toward the main shaft, which makes the milling cutter work more stable; moreover, the negative radial rake angle can make the “impact point†cut into the workpiece first away from the tool tip, and it can protect the tool tip. The blade is mounted, and the lower part of the blade has strong solid support, increasing the blade strength. Fix-Perfect tool processing accuracy, surface roughness are good, the only downside is that life is too low.
Figure 5: Fix-Perfect tool
In the crankshaft production line, the KM tool system is used for the machining of the main journal and front and rear end journals. The KM tool system was jointly developed by Kennametal of the United States and WIDIA of Germany. The basic shape of the KM tool system is similar to that of HSK. It is also a 1:10 short-spiral fit and double-sided positioning. The main difference lies in the difference in clamping mechanism. The KM handle is locked by a steel ball bevel. When clamping, the steel ball is pushed out along the inclined surface of the groove of the tie rod and clamped on the inclined surface of the locking hole on the handle and the knife The shank is tightened toward the spindle hole, and the shank is elastically deformed so that the end face of the shank is brought into close contact with the spindle end face. The KM tool system has the advantages of high rigidity, high precision, quick installation and easy maintenance. The test confirmed that the dynamic stiffness of the KM tool holder is higher than that of the HSK system.
Fig. 6: QUATTRO-CUT tool
Figure 7: KM Tool System
Figure 8: KM Tool System Operation Status
Conclusion
The high-speed and high-efficiency cutting of the production line consisting of a high-speed machining center is a systematic project. It is affected by various factors such as machine tools, cutting tools, materials to be processed, cooling lubrication and cutting parameters, etc. Only a large number of tests are conducted and data are collected fully, carefully and carefully. Analysis, continuous exploration of the law, the best combination of various factors in order to obtain the desired processing results.