Due to the continuous improvement of market demand, the capacity of the diesel engine production line has been continuously filled and filled, from an annual output of 24,000 units, to 38,000 units, to 70,000 units, although large-scale technical transformations have taken place. However, most of the newly added equipments are drill-and-boring machine tools. Due to the limitation of the production line and space, the milling equipment of the production line cannot be added. The efficiency and capability of the milling equipment can not meet the market demand and become a key bottleneck process. It is imperative to transform existing milling equipment, apply new processes and new technologies, and improve the milling efficiency of the production line.
1. Proposal for application of dense tooth face milling cutter
A detailed analysis of the process system of the milling process found that the main reason for limiting the improvement of milling efficiency is that the hardness and wear resistance of the cemented carbide insert are insufficient, and only a low cutting feed rate can be used. To this end, under the existing equipment basic conditions, the ways to improve milling efficiency may be:
(1) Using high-strength, wear-resistant blades
High-strength, wear-resistant inserts such as cubic boron nitride can significantly increase the milling feed rate of the workpiece. However, with the same number of inserts, powerful cutting power and machine strength must be required. If necessary, large flow is required. Supported by the cooling system, on the basis of the current domestic general-purpose milling equipment, the power and strength of the equipment are insufficient, the new flow cooling system is also difficult, and the development of high-strength and wear-resistant blade materials such as cubic boron nitride is developed in China. Still not mature, the cost of running foreign tools is too high. Therefore, there is still no realistic basis for using high-strength wear-resistant blades for the current conditions.
(2) Reduce the feed per tooth and increase the feed rate
During the milling process, the cutting force of each blade is proportional to the feed per tooth, reducing the feed per tooth, reducing the cutting force per tooth, and improving the workpiece milling at the same strength of the blade. The feed rate increases the milling efficiency. Therefore, reducing the feed per tooth is one of the ways to improve the milling efficiency. There are two ways to reduce the feed per tooth: increase the spindle speed and increase the number of teeth participating in the cutting.
1) Increase the spindle speed and reduce the feed per tooth. Although the spindle rotation speed is increased, the feed amount per tooth can be reduced, so that the feed speed of the workpiece can be increased correspondingly, and the milling efficiency can be improved. However, the spindle rotation speed is increased, the cutting linear speed is also increased, and the cutting heat generated by the blade is also improved. When the cutting heat exceeds the blade tolerance range, the blade will wear sharply. Under the condition of no effective blade cooling, it is difficult to realize according to the current domestic blade material.
2) Use a cleavage cutter to reduce the feed per tooth. With the cleavage cutter disc, the number of teeth participating in the cutting increases, the feed amount per tooth can be reduced accordingly. Under the same milling conditions, the feed speed of the workpiece can be increased accordingly, thereby achieving the purpose of improving the milling efficiency. Continuous optimization and improvement of the structure, the domestic hard alloy indexable dense tooth face milling cutter has matured, and the cost of the cutterhead is not much different.
In summary, through the evaluation and comparison of several schemes, the use of the dense-tooth face milling cutter is the simplest and most reliable and the year-on-year running cost is the best solution to improve the milling efficiency under the condition that the production line equipment is not changed significantly.
2, the practical application of the dense tooth face milling cutter in the production line
All the milling cutter discs of the Yancheng Hongqi single/double-sided combined milling machine for the cylinder block, cylinder head and clutch of all milling gray cast iron HT250 on the diesel production line are replaced with the fine-tooth face milling cutter, milling with a diameter of 500 The cutter head has been increased from the original 30 pieces to 60 pieces; the diameter 400 milling cutter disk has been increased from the original 24 pieces to 45 pieces; the diameter 315 milling cutter plate has been increased from the original 18 pieces to 36 pieces, basically increasing Doubled, the feed rate per tooth can be reduced by half, the feed rate can be doubled, the efficiency can be doubled, but the milling process is subject to complex machine tools, tooling, surface roughness requirements and many other factors. Influence, it is difficult to achieve the replacement process, the milling efficiency can be doubled, but from the actual application effect, at least the production efficiency can be increased by more than 30%, and the individual bottleneck process equipment is replaced by a powerful milling machine with high power and high rigidity. A goal of increasing production efficiency above 50% can be achieved.
The milling parameters used in the production of the fine-tooth face milling cutter are: cutting thickness 2 mm – 5 mm, single tooth feed 0.05. 0.15 mm / tooth, line speed 100-125 m / Min, special attention must be paid: for a specific blade material, if the line speed exceeds a critical value, the durability of the blade will be greatly reduced. Therefore, a balance point must be selected between the spindle speed and the linear speed and the production efficiency; After the face milling cutter, the feed rate is generally increased from 160-200 mm/min to 250.315 mm/min, and the milling efficiency is increased by more than 30%.
3. Case of application of dense tooth face milling cutter in production line
The number of teeth of the milling cutter is doubled to the original number of teeth. In theory, the milling efficiency can be doubled, but due to various factors, especially in the milling process of the fine-tooth face milling cutter, although the single-tooth feed The amount is reduced, but the number of teeth involved in milling is multiplied, and the cutting force and cutting heat of the entire cutter head are increased. Therefore, the following problems must be considered in practical applications:
(1) The motor power of the machine tool itself and the strength of the machine tool
Since the number of teeth participating in milling increases, the cutting force is also increased, and the required machine power and the rigidity of the machine tool are also enhanced. Therefore, when replacing the dense-tooth face milling cutter, it is necessary to evaluate the condition of the equipment used in the original production line, and determine the workpiece. At the feed rate, it is necessary to consider the appropriate dynamic load and the change of the cutting force after the new blade wears. Otherwise, the machine tool may have a high feed rate of the workpiece, causing vibration of the machine tool system and dragging of the table. The machine tool makes the knife and machine tool malfunction frequently and other unfavorable factors.
Case 1: In the front and back end steps of rough milling of the cylinder block of the production line, the milling thickness is 3 mlTI – 5 mm, the original old cutter head uses a feed speed of 160 mm / min, the machine milling state is good; replace the dense tooth face milling cutter After that, the cutting efficiency of 250 mm/min can be used to increase the milling efficiency by 55%. However, the result of the test is severe, the machine vibration is severe, the milling effect is not good, and the feed rate is reduced to 200 mm/min, and the milling effect is good. Milling efficiency is increased by 30%. In order to further improve production efficiency, a powerful milling machine was later replaced. The spindle power of the machine tool was increased from 7.5 kW to 15 kW. The rigidity of the machine tool was also strengthened, but the feed power of the table was not improved by 162. The feed rate of the machine tool was increased. With 250 mm/min, the machine has smooth milling, good milling and 55% increase in productivity. When the feed rate is increased to 315 mm/min, the milling efficiency can be increased by 95%. The machine tool spindle is well milled, but the table sometimes appears. Crawling phenomenon, the processing condition is not ideal, indicating that the spindle power of the machine tool and the rigidity of the machine tool are sufficient, but the feed power of the table is insufficient. Finally, the feed rate of the process is determined to be 250 mm/min, and the production efficiency is only increased by 55%.
(2) Effective area of workpiece milling
The larger the milling area of the workpiece, the larger the number of inserts involved in milling, and the greater the cutting force. For different effective milling areas, different workpiece feed speeds must be used to ensure high milling efficiency. Otherwise, the machine will also Vibration occurs, causing the knife to affect the quality of the processing.
Case 2: The left and right side processes of the cylinder block rough milling and the front and back end operations of the rough milling have the same milling width, but the effective milling area is different. The left and right sides form a discontinuous milling surface with a tower boss, etc., and many areas in the middle are not processed. The front and rear end faces are basically solid, which is a large-area solid milling. The effective milling area of the front and rear end faces is more than twice the effective area of the milling on the left and right sides; under the same conditions of the machine model, the cutter head structure and the milling depth, the rough The milling feed rate on the left and right sides of the milling can reach 315 mm/min, while the feed speed of the front and rear end faces can only reach 200 mm/min. Therefore, the effective milling surface affects the choice of milling parameters.
(3) Rigidity of fixtures
Due to the large number of teeth involved in milling, a large number of teeth frequently cut the surface of the workpiece, resulting in a high vibration frequency. If the rigidity of the fixture is not good, the natural frequency of the fixture is similar to the vibration frequency of the milling, which will result in “Resonance” phenomenon, therefore, in the application of the fine-tooth face milling cutter, it is necessary to pay attention to improve the overall rigidity of the fixture during tooling design.
Case 3: In the process of rough milling the bottom of the cylinder head, two identical equipments were used, but the fixtures were different. The tooling base of the first equipment was connected by four 25 mm thick cast iron bolts, and the fixture was hollow. The rigidity of the fixture is not very good. When the 400 mm close-tooth face milling cutter is used for milling, it produces very obvious vibration. In order to eliminate the vibration, we have tried the down-cut, up-cut, eccentric milling, and reduce the thickness of the milling, but the vibration Still can not be eliminated, and finally the method of removing a blade on the tooth surface milling cutter to remove the vibration eliminates the vibration, but the newly replaced dense tooth face milling cutter has no effect on improving the production efficiency; on the second device The tooling fixture used is a cast iron base that is integrally cast. The new replacement uses a 400 mm dense tooth face milling cutter. When the feed rate is increased by 30%, the milling is smooth and the production efficiency can be increased by 30%. Therefore, the density is adopted. When the face milling cutter is used, it is necessary to evaluate the rigidity of the fixture.
(4) Structural characteristics of the processed product
The structure of the cylinder block and cylinder head of the diesel engine is very complicated, and the overall rigidity of the product also significantly affects the milling effect. It is necessary to evaluate the structural characteristics of the product and select different milling cutter heads and milling parameters. Case 4: In the process of finishing the bottom surface of the cylinder block, the milling machine has been replaced with a fine-tooth face milling cutter with a light-cutting knife. Even at the same milling feed rate, the surface roughness of the new cutter is smaller than that of the old cutter. Poor, can not stabilize the requirements of the standard product drawings, the main reasons are two: First, the bottom side of the cylinder block is a gantry structure, with a floating length of 100 mm, the rigidity of the milled part is poor, when more dense teeth participate in cutting, A larger vibration frequency is generated, and when a rigid portion is cut, severe vibration is generated, resulting in a decrease in surface roughness after processing.
Second, the dense-toothed face milling cutter presses the indexable insert with a spring-tensioned structure. This structure is suitable for arranging denser blades, and the blade is easier, but the structure makes the indexable insert positive. The rake angle, the cutting force of the positive rake milling is larger, and the workpiece with poor rigidity is more likely to cause vibration, which affects the surface roughness after processing. The old cutter head adopts the wedge screw pressing structure, so that the cutter teeth are arranged sparsely, and it is not convenient to replace the indexable insert, but the structure can make
The blade forms a negative 3 degree rake angle for sharper milling, resulting in lower milling forces, lower milling vibrations and smoother milling. Therefore, the flank face milling cutter does not work under certain conditions.
With the continuous development of tool materials and tool structures, more advanced milling knives can be applied under the constraints of production line space and equipment, which can effectively improve the production efficiency. All the cylinders, cylinder heads and clutch shell production lines of the diesel engine described in this paper. After the coarse and semi-finish milling cutters are replaced by the dense-tooth face milling cutters, the production efficiency can generally be increased by more than 30%. The application of more advanced tools may require the support of higher equipment power or rigid strength, or large flow cooling technology, and needs to be evaluated in order to effectively utilize the performance of new technologies and processes.
Post time: Sep-07-2018