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Experimental study on efficient milling of casing parts

Release time:Apr 29, 2019 Visits:

Key words: machine parts; high-altitude milling; experimental study

The high-pressure turbine of the part of the Rollo company BR710 engine studied in this paper has a long problem in production management due to the long processing time of the milling process, low equipment power and long-term occupation of the five-axis machining center. While recognizing the problem, he conducted special research and conducted experimental research on two of the long processing times. The main content of the experiment is how to select the appropriate machining tool and determine the parameters suitable for processing the part. Parameters, reducing processing time and reducing processing costs. The specific details of the experiment of the 60 process and the 80 process are specifically described below.


I. Experimental study on the inner lace of No.60 process milling

The machining allowance of this process is 10mm. The original processing method is used to select Φ20R3 end mill for layered processing. Each layer is 3mm, and the unilateral side is 0.25mm. The processing time is long and the props are wasted. In order to ensure the quality of the parts. Under the premise, improve the processing efficiency, roughing to Φ100 corn milling cutter, non-standard knife body, blade: SPMT100408-RIC328, processing parameters are V = 30m / min, F = 40m / min. Firstly, the rough milling and two knives were used to complete the machining. During the machining process, the cutting was very smooth, and the blade wear was small after machining. Based on this, the test completed the rough machining of the part, and changed the machining mode into the tangential arc. The earth improves the processing efficiency, and the tool wear is serious after processing, and the next part can be processed after being replaced.


Second, No.80 process rough milling large end external profile test study

This process is the main rough milling process of the parts. It has many margins and is easy to be deformed. It adopts special tools for outsourcing, with internal support, and requires a force-limiting wrench for pressing. The pressing force of the pressing plate is 80NM, and the internal support is 30NM.


The following is a description of the specific speed-up content and improvement content according to the work steps:

(1) Application of ceramic tools in rough milling

The maximum amount of parts in this process is 7mm. The rough machining experiment has adopted ceramic blades, and the rough machining has a left side of 0.5mm. The ceramic blade is characterized by high strength, high hardness, high red hardness, high wear resistance, excellent chemical stability and low friction coefficient, and its cutting processing efficiency is 6 to 10 times that of ordinary cemented carbide tools. In the case of high-speed milling with modern ceramic inserts, it is essential to select the cutting speed, feed rate, depth of cut, width and tool type for the purpose of improving tool life and productivity. Therefore, in the application, you must pay attention to the following aspects:


1 machine tool requirements

Machine tool-parts-tools, the weak rigidity of the process system is the main reason for the reduction or collapse of the ceramic tool life. The rigidity of the machine tool cannot be considered simply. The rigidity of the parts, fixtures and tools must be considered at the same time. The DMU210P five-coordinate machining center used in the machining of this part has good rigidity, sufficient power and high number of revolutions. The external auxiliary fixture is used to add internal auxiliary support to the machining area, which reduces the stress generated during the machining process and causes the parts to be Deformation.


2 reasonable NC program

When using ceramic tools for high-speed milling, the milling method is usually used. When the internal profile is machined, when the tool is cut to the corner, the cycloidal cutting method is adopted to avoid sudden increase of the cutting force. High-speed cutting mainly adopts circuit cutting, which reduces the cutting in and cutting times of the tool through the uninterrupted cutting process and tool path, and obtains a stable, high-efficiency and high-precision cutting process.


3 selection of reasonable geometric parameters of ceramic tools

When selecting the reasonable processing parameters of the ceramic tool, it must be considered that the ceramic tool is a hard and brittle tool. How to ensure the stability of its use and the absence of chipping is an important basis for selecting the reasonable processing parameters of the ceramic tool; The continuity, economy and smoothness of the intermediate ring material milling are to be considered.


(2) Switch to face milling cutter finishing belt

The original finished intermediate ring belt was milled up and down using a Ф20R3 hard milling cutter. The surface of the milled island was milled up and down using a 16 full-end milling cutter. The disadvantage of this machining is that the high hardness of the part is high, and the machining cost is high. time. Later, the 50R6 face milling cutter was used to finish the middle ring belt and the Ф40R5 face milling cutter to mill the island surface. However, after machining with these two types of milling cutters, it was found that the surface of the machined parts was not the same height, and the height difference was 0.2 mm. Since the middle part of the tool was not machined, the surface height after machining was different. In view of this situation, using eccentric milling, taking the Ф50R6 face milling cutter as an example, the highest point of the cutting edge is at Ф35, and the cutting can not be performed in the middle of the tool. After the eccentricity is 12.5mm, the surface of the machined parts is 0.03mm. Left and right, meet the requirements of the design drawings.


(3) Use of U drill

Since the U-drill has not been used before, the hole is usually machined according to the traditional machining method. Dot-drill-ream-boring-reaming, for some large diameter holes and tolerances and position degrees It is not a very strict hole, and it takes a lot of time to process. The outer part of this part is recommended to use U-drill to machine the hole on the island.

First, let's briefly introduce the processing characteristics of U-drill:


1 processing efficiency is generally 2 to 3 times that of ordinary drills.

The 2U drill can be machined directly on the workpiece without the need to drill the pilot hole in the center.

3 The front end of the cutter body is equipped with a replaceable blade, which reduces the cost of use.

The difference between a 4U drill and a conventional drill bit is that the U-drill uses a blade - a peripheral blade and a center blade. After the tool is worn, the blade can be directly replaced without re-grinding. The use of the indexable blade saves material compared to the overall hard drill, and the blade is consistent. It's easier to control part size.


The 5U drill has good rigidity and can adopt a high feed rate, and the machining diameter of the U drill is much larger than that of the ordinary drill bit, and the maximum can reach Ф50mm~Ф60mm. Of course, the U drill cannot be made too small due to the characteristics of the insert blade. U diamonds below 10mm are rare.


6U drills need to replace the same type of different types of blades when encountering various materials. Other drill bits should be selected according to different materials.


7 Compared with hard drills, the accuracy of the hole drilled by U drill is still higher, and the finish is better, especially when the cooling and lubrication are not smooth, and the U drill can correct the position accuracy of the hole, and the ordinary drill bit will not work.


The dimensions of the holes on the island to be processed in this process are Ф20, Ф22, Ф29, Ф32, respectively. The original Ф16 drill bit is used to drill the bottom hole, and then the Ф16 milling cutter is used for layer milling, and the holes are sequentially machined to the size. The point is not good, one is a waste of time, respectively, the hole is milled from Ф16 to Ф19, Ф21, Ф28, Ф31, which needs to remove a lot of margin; the second is to waste the tool, using a solid carbide milling cutter to layer the hole, Moreover, the margin is large, the tool wears quickly, and the cost increases. Third, there is a quality hazard in the machining. When milling the hole, the operator needs to calculate the tool compensation value and input it into the machine tool, so that the artificial operation is easy to generate errors. The advantages of CNC machine tools are not fully utilized, and it is easy to cause the parts to be out of size.


Conclusion


In this paper, through the research on the two milling operations of the parts, the processing efficiency is improved, the precious production time is saved for the factory, and the processing cost is also reduced, which lays a foundation for the mass production in the future.

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