Focusing on solving the problem of high-precision machining of the hole bottom end face of a sealed valve hole in an aviation valve body, we carried out independent research and adopted a motorized grinding end face device with adjustable/stabilized pressure, precision guide pair, spherical fit, and transmission and positioning error compensation. (ZL201820823098.4) The new process technology has successfully solved the process technical problems such as flatness, surface roughness, and verticality based on the axis of the guide hole that require high precision for the bottom end face of deep holes, and expanded the high-precision bottom end face of deep holes. The processing technology has the advantages of strong fixture practicability and high processing efficiency.
1 Preface
A certain servo valve product is designed with a special structure. A valve part is installed in a φ15H7 94mm deep hole in the valve body part. The valve outer diameter and the valve hole inner diameter are connected by a sliding valve coupling seal (see Figure 1). When the valve parts are forced to move in different positions, the oil circuit switching is realized [1]. When normally closed, the bottom plane of the valve hole is also the sealing surface. Its flatness, surface roughness, and perpendicularity to the hole axis are as high as IT7 and above. Its bottom surface structure and characteristic values are shown in Figure 2. shown.
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a) The position of the valve connecting holes B and C when opening
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b) Position of the valve connecting holes A and B when normally closed
Figure 1 Schematic diagram of slide valve coupling seal
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Figure 2 Schematic diagram of the bottom end face of the valve hole and the structure of the valve hole
If this technical achievement is successfully implemented, a deep hole bottom end surface grinding device with precision guidance, low pressure force, and stable controllability must be developed based on the plane grinding principle to achieve precision machining of the hole bottom end surface. Due to the technical blockade imposed by foreign aviation technology on our country, it is difficult to obtain relevant grinding technology. In the existing technology, for grinding the bottom plane of the hole, magnetic abrasive grinding technology is generally used [2], which has advantages in finishing processing of complex curved surfaces. , the surface roughness value decreases and the efficiency is higher, but the ability to change or improve the geometric accuracy such as the flatness of the ground plane is poor, so the versatility is poor. In the prior art, there is also a method of grinding the bottom end plane of the hole by using a grinding rod with an end plane. For example, the CN201361804Y patent document discloses a deep hole bottom grinding tool for a CNC boring and milling machine. However, this grinding component has not yet been used. It can take into account the perpendicularity requirements of the end surface to be ground and the axis of the reference hole. In the actual operation process, when grinding the bottom end plane of holes with different hole depths, it is necessary to pull out the cotter pin and then separate the grinding rod from the transmission rod. Only then can the grinding rod be replaced with the corresponding length. At the same time, processing deep hole and slotted structures is cumbersome, has low efficiency in the actual manufacturing process, and is inconvenient to install [3].
The grinding component (patent number ZL201820823098.4) independently developed by this technological achievement can not only take into account quality requirements such as flatness, surface roughness and perpendicularity relative to the reference hole axis of the bottom end surface of the hole, but also can be used for surface grinding of different hole depths. , it can be stopped directly and the corresponding grinding rod can be removed and replaced. The operation is more convenient and can further improve the grinding efficiency.
All existing key technologies have been solved, and various technical indicators have not only met the design quality requirements, but also reached the domestic advanced level. This technological achievement has been successfully promoted and applied in the production of valve body parts for servo valve products supporting a variety of national key aircraft models, generating considerable economic benefits and contributing to the development of my country's aviation industry.
2 Research ideas
2.1 Analysis of process difficulties
For deep hole processing, flat bottom processing is a traditional processing difficulty. Especially for the valve hole in this project, the ratio of hole depth to hole diameter exceeds 6:1, which belongs to deep hole processing. Due to poor tool rigidity and severe tool vibration and deflection, it is difficult for traditional turning and boring process methods to simultaneously ensure the surface roughness, flatness and perpendicularity to the reference hole at the bottom of high-precision deep holes. The existing grinding and polishing technology cannot take into account the three key indicators of this project, so it is necessary to carry out technical research on hole bottom end surface grinding.
In addition, the key characteristics of this project, the flatness of the bottom end face of the hole 0.01mm and the perpendicularity of the bottom end face of the hole and the axis of the valve matching hole 0.03mm, can be directly detected using three-dimensional coordinates, but the surface roughness value of the bottom end face of the hole Ra=0.1μm, due to The hole is deep and the surface roughness meter cannot perform direct detection, so a reliable indirect measurement method needs to be sought.
2.2 General idea
1) The φ15H7 hole is matched with the micro-clearance of the valve, making full use of precision coupling sub-processing technology to develop a precision guide post and guide bushing tooling to meet high-precision verticality and other requirements. Then, we draw on existing technology and plane grinding principles and experience to develop an adjustable The pressure/stabilizing force is applied, and the mechanism design such as ball joint connection and infinite error is adopted [4] to achieve precision machining of the bottom end face of the hole.
2) Grinding is a finishing process, suitable for processing with small micro-machining allowances, and the self-damage of grinding tools is serious. In order to improve production efficiency, it is necessary to develop a new process for processing the bottom of the hole before grinding.
3) In view of the difficult problem of measuring the surface roughness value Ra=0.1μm on the bottom surface of the hole, the method of first-piece cutting inspection is adopted to solve the problem.
Therefore, the key to the success of this project lies in the developed grinding tooling process equipment, which must simultaneously meet the requirements for surface roughness, flatness and verticality, and meet the requirements for on-site production efficiency.
2.3 Technical solutions
(1) Development of grinding device table: Independently develop a new type of motorized hole bottom end surface grinding device. In order to achieve high-quality and efficient grinding processing of the hole bottom end surface and meet the final requirements of the product, the most important thing is the hole bottom end surface grinding. The grinding device must take into account the flatness and surface roughness of the bottom end face of the hole, as well as the verticality requirements relative to the axis of the reference hole, and use high-precision matching holes as guides. In order to ensure this quality requirement, the project team independently developed a grinding device (grinding component ZL201820823098 .4).
Grinding the plane at the bottom of the hole is not only to obtain a smaller surface roughness value, but more importantly, to obtain a higher plane accuracy [5]. The smaller the flatness error value, the better, and it is necessary to reduce the (traditional) grinding operation The reliance on highly skilled operators during the process reduces labor intensity and thereby improves grinding efficiency.
(2) Structure of the grinding device: The designed and manufactured grinding device is a motorized hole bottom end surface grinding device (see Figure 3), which provides reliable power with the help of stepless speed adjustment and limitable tool height (such as coordinate boring machines and other equipment). The grinding device consists of 4 parts: a voltage regulating/stabilizing mechanism, a ball head auxiliary transmission mechanism, a guide pair and a grinding rod. Voltage regulating/stabilizing mechanism, controllable spring compression to stabilize the force on the grinding surface. The ball head auxiliary transmission mechanism facilitates clutch operation. The function of the ball head is to correct and compensate for the verticality error between the end surface of the grinding rod and the spindle axis when it is installed, ensuring that the working end surface of the grinding rod and the end surface to be ground are in reliable fit. This is the key The outer circumferential surface of the pin is designed to be lower than the center of the ball head. The guide pair is suitable for guiding when grinding the bottom of deep holes to ensure the perpendicularity requirements between the end surface to be ground and the reference hole. When designing a shallow hole bottom end surface grinding device, there is no need to design a guide, and the ball head can be automatically aligned directly so that the working end surface of the grinding rod fits the end surface to be ground. The grinding rod itself requires high manufacturing precision. For example, the flatness of the grinding end face and the perpendicularity of the grinding end face relative to the rotation reference axis are required to reach the micron level. At the same time, the vein size of the grinding rod end face affects the grinding quality and efficiency. It's also huge. The design experience of "well" grooves (groove width 0.25mm, depth 0.5~1mm, spacing 1mm and uniformly distributed) obtained through experimental verification has the effect of improving quality and efficiency when grinding the bottom end face of φ15H7 hole with a depth of 94mm. Better (see Figure 4 and Figure 5).
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Figure 3 Structure of grinding device
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Figure 4 Veins on the end surface of the grinding rod
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Figure 5 Comparison results of grinding effects
The production requirements for this device are also very high. During process construction, coupling parts with a matching gap of 0.004 to 0.006 mm need to be honed/grinded to process the inner hole, and centerless grinding/cylindrical grinding to process the cylindrical precision clearance to meet the positioning and guiding functions. For assemblies with a matching gap requirement of 0.03mm, processing techniques such as reaming/turning are adopted to meet the assembly requirements (see Figure 6).
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Figure 6 Actual work clothes
The practical steps for tooling are as follows.
1) Determine the amount of spring compression based on the elastic force of the spring (see Figure 7), draw a marking line on the outer surface of the guide rod (a red marker will suffice), and pre-tighten the jackscrew to fix it.
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Figure 7 Spring compression amount
2) The machine tool chuck holds the voltage regulating/stabilizing mechanism, as shown in Figure 8.
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Figure 8 Tooling test
3) Place the part correctly or fix it with a fixture so that the surface to be ground is in a horizontal state.
4) Adjust the machine tool or parts so that the concave spherical surface of the guide rod fits the convex spherical surface of the grinding rod, and check whether the installation is in place by loosening the jack screw.
5) Apply a uniform thickness of abrasive paste on the grinding end surface of the grinding rod, place the grinding rod into the corresponding hole, and manually confirm that the installation is in place.
6) Insert the pin rod into the hole corresponding to the ball head of the grinding rod, so that the exposed lengths of both ends of the pin rod are approximately equal, and manually confirm that the connection is reliable.
7) Set the machine tool parameters, start the machine tool for grinding operation, and stop after grinding for a single duration.
Enter the next operation cycle until the quality of the ground end surface is qualified. It should be noted that when taking out the grinding rod after each grinding cycle, water sandpaper should be used to clean the surrounding burrs.
This device meets the production needs of continuous and stable grinding operations. It not only enables the quality of the grinding surface to meet the design quality requirements, but also improves the grinding efficiency by more than 5 times compared with traditional manual grinding. In particular, the skill level requirements of the operator are greatly reduced, and no need Designating fitter technicians and personnel with skill levels above to operate (it is sufficient to be able to operate the equipment) greatly reduces the labor intensity of the operators.
Figure 9 shows the grinding test, and the empirical parameters were obtained through multiple tests. Experience data for φ15mm grinding surface 1: spindle speed 60r/min, spring elasticity 4.6N·mm, coating W5 grinding paste film thickness about 0.2mm, grinding duration 15s/time. Experience data for φ15mm grinding surface 2: spindle speed 60r/min, spring elastic force 4.6N·mm, coating M5 grinding paste film thickness about 0.4mm, grinding duration 2.5s/time. It should be noted that no matter which method is used, there is a risk of grinding scratches if the timeout is too long. The grinding paste should be replaced in time and the cycle operation should be carried out until the parts are qualified.
