Lapping process

The next layers consist of an electrodeposit of 20-40-pm thick copper studs, a deposit of 10-15-pm thick alumina overcoat, and lap open copper studs. The thick alumina layer is required to protect the magnetic and coil structures during machining and lapping processes and to prevent corrosion. 

The lapping process is a very complex three-body abrasion. During friction and wear processes, many AE signals could be generated because of the interactions, impact, dislocation, deformation, and removal of materials. In the area of tribology, AE was used to characterize wear mechanisms, discern plastic deformation and fracture, and to monitor active friction and wear processes. AE signals were related to friction coefficient, abrasive grit size, and wear rate. 

Ruiling, Zeng, Acoustic emission investigation of ceramic lapping process, MS Thesis, Kansas State University, Manhattan, Kansas, 1998. 

Setup for the acquisition of the acoustic emission signal in the lapping process. 

Taking into account the ideas mentioned above, one can say that the EPT is a relevant AE parameter for monitoring the lapping process. It is sensitive to the changes of load and plate rotation and can also monitor the roughness... 

For the AE system, a high-speed signal acquisition should be used to monitor the lapping process in real time. Many experiments on work parameters and the quality of lapped workpieces should be carried out to confirm the conclusions drawn so far. Based on the experimental results, a practical database can be established and used in real production. Some new programs should be developed to efficiently analyze AE signals and correlate them to surface integrity. 

As the contracting company (Warren Diamond Co.) is a member company, we can identify it as the primary beneficiary. The project s main goal is to optimize the lapping process, by finding a correlation between the process parameters (of which very important is the type of the slurry) and the final parameters of the ceramic parts (dimensional accuracy and surface roughness). Therefore, a part of the optimization process is concerned with a comparative study of the behavior of polycrystalline versus monocrystalline diamond slurry. The aspects that will be taken into account are the MRR and the grain size distribution. 

The final results are important for those who want to apply the lapping process to ceramic parts efficiently. Recommendations concerning the process parameters (rotation of the lapping plate, load per grain, and time) and the slurry (t) e and size of grains, optimum size distribution, and flow rate) that has to be used will be available to the member companies. 

As shown in Figure 10.2, the surface roughness decreases more rapidly with time at the beginning of machining. After approximately 15 min the surface roughness does not decrease significantly or even increases. After 15 minutes it is not recommended to continue the lapping process. 

Abrasive size is one of the most important factors in the lapping process influencing the MRR and surface roughness. 

During the lapping process, it is possible to have two types of stock removal mechanism. One of them we named as double fractme mechanism. The fracture is a macrofracture and is the effect of a grain that works like an indenter (Figure 11.1). 

Mono vs. polycrystalline diamond lapping of ceramics ID PMMC 1703. Acoustic emission monitoring of lapping process ID PMMC 1704. 

Chapter 8 also comes from the Precision Micro-Machining Center and presents a modem technique for monitoring the ceramic lapping process acoustic emission (AE). AE is well known as a tool to monitor the ceramic grinding process however, there are only a few studies regarding AE in the lapping process. 

Y.-E.P. Chang, Monitoring and Characterization of Grinding and Lapping Processes (Ph.D. Dissertation), University of California, Berkeley, 1995. 

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