Large bore probe
The IOMS probe for inspecting cylindrical honed surfaces was developed for inspecting the surface finish of engine blocks on an engine block production line. The probes can inspect the entire surface of every cylinder of every engine block at the speed of a production line, automatically determine whether a cylinder has an acceptable or defective surface finish, and provide a permanent record of the inspection. The probe can be used to inspect cylindrical surfaces of any component that requires a specific pattern of machining marks to achieve a proper surface finish.
Honing is the last machining operation performed on an engine block before it goes to assembly, where it becomes part of a complete engine. The honing process produces a specific cross hatch pattern on the cylinder wall that ensures the proper amount of oil is retained for lubrication of the cylinder-piston-ring interface. If the surface of the cylinder does not have the proper surface finish the engine can be noisy, burn oil and be less fuel efficient.
Modern mass production equipment is very good at manufacturing identical parts. This is also the case if parts are defective. To minimize scrap it is necessary to detect defective parts as soon as they are produced. It would be even better to detect parts that are drifting out of tolerance before they become defective. Up until the development of the IOMS probe there were no inspection systems both sufficiently sensitive and sufficiently fast to perform this task on a production line.
While manufacturing defective parts generates scrap and adds to the cost of production, production costs can increase dramatically if these defective parts are permitted to enter the assembly stream. If defects are not detected until an engine is assembled, defective engines will have to be disassembled to identify the cause of the defect, and the engine assembly line as well as the block line may have to be shut down until the source of the problem is identified. If the defective engines have started to be assembled into vehicles, both the vehicle and engine assembly lines may have to be shut down until the root cause of the problem is found. The worst case would be when assembled vehicles have been shipped to the customer and have to be returned for warranty repair.
The IOMS probe works by scanning the surface of a cylinder with a laser beam, collecting the return light and analyzing the data that is generated with computer software. The result of the analysis is presented as either a red or green light for each cylinder arranged in the same order as the cylinders in the block (see Figure1).
Figure 1. Display generated for inspection of a four cylinder engine
If a block is defective it can be shunted off the line for further inspection. The data for any block can be retrieved without affecting the operation of the line. To see the result of an inspection of any cylinder, the 3D button can be clicked for that cylinder to generate a graph of return laser signal as a function of location on the cylinder surface. This is shown for the case of an acceptable surface finish in Figure 2 and a defective surface finish in Figure 3. The horizontal axes are circumferential location in degrees and depth from the top of the cylinder in mm. In Figure 3 the red ridge along the length of the cylinder indicates a region of non clean up, in which residual boring marks were not removed by the honing process. Figure 3 shows that part of a cylinder can have an acceptable finish while a different part can have a defective finish. Therefore, an inspection technique that is capable of inspecting the entire surface of a cylinder is needed to ensure surface finish quality.
Figure 2. Acceptable finish Figure 3. Defective finish
In addition to identifying residual boring marks the probe can also identify honing defects. This is shown in Figures 4 and 5. In Figure 4 the graph indicates excessive dwell of the honing tool in the bottom half of the cylinder. Figure 5 shows the graph produced when the honing stones were not retracted when the honing tool was removed.
Figure 4. Graph indicates excessive dwell of honing tool in cylinder
Figure 5. Graph produced by non retraction of honing stones in cylinder
Other types of defects that affect engine performance can also be detected using this probe. These include chatter and inadequate or excessive metal removal with the honing tool. Block design defects, such as inadequate support for cylinder walls resulting in defective honing patterns on cylinder surfaces, have also been observed.
If a problem is detected by the probe, the location of the defect will be identified, but it may not always be obvious what the problem is to a human inspector. To address this problem we have developed a modified probe that can produce an image of the machining mark pattern. This probe is expected to be used off line to further inspect blocks that have been shunted off the production line as a result of the laser probe inspection. A graph of a machining mark pattern produced by this probe is shown in Figure 6. The horizontal axis is in degrees and the vertical axis is in mm. The cross hatch angle increases with depth in the cylinder because the honing tool spins at a constant rate, but the axial velocity of the tool varies with position as the tool moves in and out of the cylinder. The cross hatch angle can be obtained at any point in the cylinder using our software program by clicking on the location at which the cross hatch angle value is desired.
Figure 6. Image of the machining mark pattern produced in a combustion cylinder by a honing tool