Grinding machine innovations boost productivity.
In a keynote address last year at a meeting of CIRP (International Institute for Production Systems Research), Dr Richard L Kegg, director, machine-tool research, Cincinnati Milacron Inc, observed that, in most manufacturing organizations, relatively few engineers are expected to solve critical production problems that arise daily. Therefore, it's to their advantage that manufacturing operations be predictable. The greater the frequency of surprises, the greater the demand on time and talents, which are scarce human resources these days.
Of all machining processes used to shape workpieces by incrementally removing metal, grinding is the preferred method when high-quality surface finishes and precise size-tolerances are required. Yet, grinding is the least understood of the common metal-removal processes, and its parameters are judged by manufacturing engineers to be the most difficult to predict.
Many engineers feel they lack basic knowledge of the relationship between changes in process variables and grinding results. A change in grinding speed, for example, may increase or decrease wheel wear; workpiece surface finish subsequently may improve or degenerate.
Moreover, once a grinding process is planned, it then becomes important to achieve, maintain, and--in later setups-- duplicate consistent results. Inconsistent results plague manufacturing engineers who must deal with grinding processes.
Several factors cause inconsistencies in grinding performance. For example, it yaries as wheel size changes from a new to a worn wheel. In other metalcutting operations, a dull tool can be resharpened, but in grinding the "tool' actually wears away, requiring dressing of the cutting surface. Hence the tool is being consumed.
Dressing also is a problem because dressing-diamond wear can cause varying performance. Changes in performance also can occur with identical wheels from the same manufacturer or between wheels of the same specification from different makers.
Because of these variations, engineers traditionally have relied on grinding experience rather than theory or data. Even literature on grinding sometimes contradicts practice. As a result, skills often are substituted for knowledge. Grinding is a process demanding the most operator skill to achieve satisfactory results. In production grinding, the time and difficulty in getting the process running aren't too critical; however, when grinding smaller batches, the time for setting up and producing the first acceptable part may be greater than the time for running out the entire batch. In these cases, because of the unpredictability of parameter changes, it takes more tries to reach an acceptable performance level, during which time a skilled operator is being used and capital investment isn't being utilized productively.
According to Dr Kegg, there are several issues that must be confronted. One is the need for improving finished part quality, especially in batch grinding operations. To bring this about, there is a need for automatically compensating for thermal deformation, as well as for automatic control of surface finish, workpiece size, and taper. There also is demand for in-process sensing of workpiece roundness, and improved ability to control surface integrity.
Another issue is the growing pressure to reduce in-process inventory. Smaller, more frequently produced lot runs help accomplish this. But, in grinding operations, costly setups and the unpredictability of controlling grinding parameters make this difficult. Thus, it is felt, industry needs to bring the advantages of numerical control to grinding.
Operations must be combined and grinding completed in one setup. Moreover, grinding machines need to be more versatile and programmable. There is a need for flexible loaders, dressers, gages, and sensors capable of operating over a range of conditions. Finally, the trend toward reducing the need for operator skills demands that control strategies be developed for using sensing signals to automatically control the process.
While shaping metal by abrading a workpiece surface can be classed as a single, generic metalworking process, grinding actually encompasses several distinct operations. Centerless, external, chucking, cylindrical, internal, surface, creep feed etc, are but a few of the terms used to describe the variety of grinding methods.
By the same token, there are hundreds of companies worldwide involved in producing grinding machines. Each claims features designed to simplify the process and overcome some of the problems inherent in grinding technology.
Advances are being made by many companies. While it's impossible to list them all here, we have reviewed some of the technical achievements made by a number of grinding-machine builders. Although not all of the innovations are exclusive to a given machine builder, a review of the concepts may help readers faced with the problem of improving grinding operations. Each of the accompanying boxes describes specific design innovations by some of Europe's leading machiner builders.
|Printer friendly Cite/link Email Feedback|
|Author:||Green, Richard G.|
|Publication:||Tooling & Production|
|Date:||Oct 1, 1984|
|Previous Article:||Automatic assembly; how to make a robot as good as a housewife working to pay off a mortgage and three sets of braces.|
|Next Article:||Broaching tries for a bigger bite.|