Processing Technology of High Precision Slender Rod Control Valve

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The control valve is one of the important parts of the mechanical-electro-hydraulic control system, which is mainly used to realize the gear selection and shift of the control system, and is widely used in the shift control of transmissions such as mining machinery and oil and gas field production equipment. Its processing and manufacturing level is directly related to the reliability and smoothness of each shift of the transmission. 

The control valve is a slender rod part, its process manufacturing involves high-precision cylindrical machining with large aspect ratio, there are many oil grooves in the axial design, there are uneven eccentric oil holes in the radial design, and the oil grooves cross vertically with the oil holes, asymmetrically distributed, in the process of turning or grinding the outer circle, it often produces flexible deformation due to lack of rigidity, which affects the machining accuracy of the parts, and the qualified rate of product processing and production efficiency are very low.

Structural characteristics of control valve

The structure of the control valve is as shown in the following figure, and each section of the rod is designed with an arc-shaped oil groove. At the same time, the radial eccentric deep hole (the eccentric hole at φ D3 and the depth of the φ D4 hole near 280mm) is connected with the oil tank. The outer circle of the control valve and the inner hole of the valve body need to maintain a certain assembly gap (0.025~0.035mm) after assembly, and each gear shift of the hydraulic transmission is realized through the control system. During the machining process, the control valve is easy to produce deformation and vibration due to the influence of cutting force, cutting heat and clamping force.

The aspect ratio of the control valve is more than 40:1, which is a typical slender rod part with large aspect ratio, and there are uneven oil holes and grooves in radial and axial design. When finishing the outer circle, the machining rigidity of the part is poor, and it is easy to produce runout. The machining quality of the outer circle of the part is not easy to be guaranteed. The production type of this part is small batch production, and its outer circle dimension accuracy, geometric tolerance and surface quality are the key factors that affect the control valve to realize the gear shift ride comfort and reliability of the transmission.

Analysis of finish machining technology of control valve outer circle.

The precision machining of the outer circle of the control valve is a key procedure that affects the processing quality of the product. because of its large ratio of length to diameter, it is easy to produce flexible deformation, and affected by uneven distribution of oil holes and grooves, it is easy to produce pulsation in high-speed rotary machining, and the machining vibration is intensified. The deformation is large, and the product quality is not controlled. In order to solve the problem of finishing machining, pouring filling is often considered to enhance the machining rigidity of the parts.

Parts fillers are often used in the field of mechanical processing, such as paraffin wax, urea and low melting point alloy. In view of the structural characteristics of the control valve, in order to reduce the influence of uneven mass distribution of the parts, the filler of the control valve chooses low melting point alloy for pouring filling, which is similar to casting, so that the part forms a rigid body and rotates at a high speed. The radial round runout of the part is reduced, and the rigidity of the part is strengthened and is not easy to deform. The preparation method of low melting point alloy is very important, and the composition and proportion of the material have a great influence on the effectiveness of the pouring filling of the control valve.

After the control valve is filled with low melting point alloy, the machining rigidity is enhanced, but the length and diameter of the part is relatively large. if it is finished with the slender rod machining device, the machining rigidity of the part can be greatly improved. the adverse effects such as vibration and flexible deformation caused by cutting force are minimized to ensure the accuracy of outer circle dimension and the requirement of geometric tolerance. The specific process arrangements are as follows:

The main results are as follows: 

1) The low melting point alloy pouring is carried out on the control valve to be finished after finishing the oil hole and oil tank.

2) the slender rod machining device is used to lathe or grind the outer circle of the parts to ensure the dimensional accuracy, geometric tolerance accuracy and surface quality of the outer circle φ D1 and φ D2.

3) Dissolve the alloy, remove the alloy remaining on the oil hole and tank surface of the control valve, and clean the workpiece.

4) Clamp processing to remove the sharp edge burr produced by the finishing of the parts.

Preparation method of low melting point casting alloy

The pouring alloy of the slender rod control valve must meet the pouring filling requirements, and the alloy should have lower melting point, good rigidity, lower expansion coefficient, better bonding and detachability after pouring. The prepared alloy must meet the following requirements: 

(1 )It has a low melting point, but it is necessary to avoid melting of the filling alloy due to the cutting heat in the cutting process. In order to realize the state change of the filling alloy, it is easy to complete the alloy filling of the parts, and at the same time reduce the influence of thermal deformation on the parts, the melting point of the alloy is ideal at 110 ~ 150 . 

(2) Has sufficient stiffness to control the deformation of the part during machining < 10% of the part size tolerance. 

(3) The expansion coefficient of the alloy should be small to ensure that the shrinkage of the filling alloy in the part cavity is less than 10% of the part size tolerance at room temperature. 

(4) It has good binding ability and detachability. The combinability means that the filler has a good binding force with the parts during solidification, and the detachability means that the fillers after melting will not remain in the cavity of the parts, which will cause quality problems.

For the 45 steel material of the control valve, the low melting point alloy is mainly composed of bismuth, lead, tin and cadmium, which is non-toxic and harmless, meets the requirements of occupational environmental health, and the selected metal materials are commonly used and easy to purchase. 

Specific preparation method: taking bismuth metal as the main component, gradually adding lead, tin and cadmium metal elements, and constantly changing its content, strictly according to the proportion of bismuth 50%, lead 26.7%, tin 13.3% and cadmium 10%, after various metals are melted, stir evenly, and then cool and solidify, the low melting point alloy can be prepared. The melting point of the alloy is 138.5 and the coefficient of expansion during condensation is 0.05%.


Practice has proved that in the actual production process, reasonable processing methods and strategies are not only the guarantee of the processing quality of the high precision slender rod control valve, but also the key to improve the product qualified rate and production efficiency. 

When formulating the processing technology of parts, preparing low melting point alloys and designing tools for resistance to cutting force, we must carefully analyze and study the structural shape, machining accuracy and production type of the parts, and reasonably design and formulate feasible processing strategies. ensure product quality to meet the design requirements. The preparation method and processing application of low melting point alloy can be widely used in thin-walled parts such as slender rod shift valve or stainless steel which are difficult to process and require high precision.

Wayken Rapid Manufacturing Limited