Honing solutions for engine blocks

The cylinder block is one of the important components of the engine, and cylinder hole machining is the most precise and difficult process in the cylinder block machining process. The cylinder bore is in contact with the piston in the engine and is subjected to various complex alternating loads. The piston is in a high-speed relative motion state in the cylinder bore for a long time. Therefore, there are very strict requirements for the shape, positional accuracy, and surface roughness of the cylinder bore machining process.

This article focuses on the common problems encountered during the honing process of cylinder holes in engine cylinder block production lines. Starting from the honing process of cylinder holes, a solution suitable for solving problems in large-scale flexible production lines is proposed, which solves the high failure rates of tool shaft failure and stroke shaft failure that often occur during cylinder hole honing. Through parameter optimization, tool material matching, and other methods, the problems of roughness and roundness exceeding the tolerance during the machining process are also solved, thereby improving the machining efficiency of the cylinder block line honing machine.

The honing machine usually consists of a servo system that drives the up and down movement and rotation of the honing shaft, a tool expansion mechanism that controls the expansion of the sand bar, and a detection device that controls the aperture size. The honing tool body (Figure 1) is matched with the sand bar base, and the expansion and retraction of the sand bar can be achieved through the expansion mechanism, thereby achieving honing of the cylinder hole. During honing, the expansion mechanism shrinks the top rod to the set position, and the sand bar shrinks to the set initial position through the retraction spring. At this time, the servo system controls the spindle to move above the machining hole, and the spindle begins to rotate at the set rotation speed, and moves downwards to the lower reversing point at the set reciprocating speed, and reciprocates between the upper and lower reversing points. At the same time, the expanding tool mechanism controls the expanding tool rod to push out the expanding core of the tool body, and the expanding core cone contacts the inclined surface of the sand bar base. When the expanding core moves forward, the sand bar begins to expand. When the sand bar expands at the set tool speed and comes into contact with the cylinder wall, cutting begins. At this time, the randomly distributed abrasive particles on the working surface of the sand bar form numerous blade tips. A part of the surface layer of the processed metal is cut off by the abrasive particles, while another part is pulled and squeezed by the abrasive particles, causing plastic deformation and bulging on both sides of the wear mark. Although there is lattice slip with the parent body, it is still on the parent body, but the bonding strength has been greatly reduced, making it easy to be cut off by other abrasive particles. At the same time, the detection device monitors the pressure changes of the gas detection through the gas detection hole on the guide bar of the blade body in real time, and monitors the cylinder hole size through the gas electric converter. When the monitoring value reaches the preset value, the tool expansion mechanism retracts the blade, the spindle rises to the initial position, and the honing cylinder hole is completed.

With the development of material technology, artificial diamond and cubic boron nitride abrasives have been widely used, pushing honing technology to a new stage. Nowadays, honing is not only used as a final machining process for high-precision requirements, but also as an intermediate process for cutting off larger margins. In short, honing has become an advanced machining method that can achieve low roughness values, high precision, and high cutting efficiency on the surface of the workpiece being machined.

The typical process of honing machine for machining cylinder holes is: pre inspection of cylinder hole diameter - rough honing - semi precision honing - precision honing - online measurement. Pre inspection mainly detects the diameter of incoming materials to prevent collision between honing tools and workpieces; Coarse honing mainly forms cylindrical holes with correct geometric shapes and basic surface roughness suitable for subsequent processing; Semi precision honing forms a uniform cross mesh pattern during the basic platform honing stage; And precision honing (platform honing) forms an ideal platform mesh cross-section; Finally, 100% online measurement is conducted to check whether the cylinder hole diameter machining meets the process requirements.

The platform honing process forms a very fine platform mesh structure in the cylinder bore, which reduces the consumption of lubricating oil and the supply of lubricating oil during emergency operation. In addition, the engine does not need to be run in. Platform honing generally includes three processes: rough honing, semi precision honing, and platform honing. In the first process, the workpiece is corrected by rough honing and stabilized by precision boring to achieve a certain shape and tolerance, in addition to forming a preliminary mesh structure. In the second process, the macroscopic geometric shape of the cylinder wall will be improved, such as the roundness, cylindricity, aperture, and roughness of the cylinder bore, and the basic mesh structure on the surface will also be processed. The mesh structure processed in this process will appear in the form of peaks and valleys. In the third process, the highest peak of each segment of the basic network structure is ground flat in a short period of time through platform honing, forming a small platform, which is the so-called platform support surface. The surface roughness value of this plane is very small, and it has a high and good support rate.

In machining applications, the surface of the honing cylinder hole needs to have specific functional characteristics, such as support performance, sealing performance, and lubricating oil retention performance. Based on these functional requirements, the surface of the parts must be designed and processed into specific shapes to meet the expected applications. In practical processing applications, a set of functional parameters should be set according to the special performance requirements of the surface. The functional characteristic parameters required for on-site production control are shown in Figure 2. The origin of these parameters is actually the peaks and valleys of a surface contour curve, as shown in Figure 3.

Based on the machining characteristics, control methods, and operation of honing machines, we need to maximize their effectiveness according to their features. We will also take timely measures to address common malfunctions and quality issues of the honing machine during the production process.