Rotary dressing: new technology, new choices.
Because the grinding wheel is worn away as it is used, the wheel face must be periodically redressed and reformed to maintain dimensional tolerance and a free-cutting action. Proper dressing and forming maintain a precision form in the wheel face, and ensure that the entire output of a production run is within dimensional tolerances. Trends in dressing tools
Although the importance of dressing is well established throughout the metalworking industry, there is frequently little appreciation for the sophistication of dressing techniques, and the capabilities and limitations of the various diamond dressing methods.
Furthermore, the number of full-line suppliers who have the ability and expertise to produce the many types of shank tools and rotary dressers demanded by modern industry is small. Full-line suppliers are the only ones able to offer unbiased advice regarding selection of the optimal dressing method.
There are two basic types of diamond dressing methods. One is a diamond-tipped shank tool; the other is a rotary diamond dresser or dress roll. Shank tools dominated the market in the past, but increasing demands for product quality and process efficiency--in terms of production rates and costs--have contributed to a shift in user preference to rotary diamond dress rolls for large production applications.
Shank tools are relatively simple to design and apply. However, their inherent drawbacks--longer cycle time and shorter life--have resulted in an increasing use of rotary diamond dress rolls for forming and dressing grinding wheels.
Rotary dressers are far more complex than shank tools. They are generally motor driven. Although some dresser suppliers maintain a small inventory of rotary diamond dress rolls with simple forms, the vast majority of rotary dress rolls are custom engineered for specific applications defined by workpiece blue-prints. Most of the machines that use rotary dress rolls were designed for this type of dressing; the remainder were made for shank tools and were converted. Choosing the optimal dressing method
If a production run is short, then the investment in rotary dressers may not be cost effective. Rotary diamond dress roll costs range from about $500 to $8000, compared to $20 to $100 for shank tools.
If the production run is long, however, then the rotary dresser is far more cost effective. Rotary diamond dressers reduce downtime and produce highly consistent precision forms.
There are a number of ways to manufacture rotary diamond dress rolls, and no one method is the best for all dressing applications. In one method, commonly called hand setting, the diamonds are placed in a pattern over the face of the rotary dress roll. This pattern of the diamonds is generally a function of the design of the part produced and the dressing parameters of the operation (Figure 1).
A second method is frequently referred to as the random method. Diamonds and matrix are mixed together and pressed into a mold. Using this method, the diamonds are randomly distributed either in a single or deeper layer over the face of the rotary dress-roll (Figure 2).
There are many variations of the above two methods currently available.
Reverse plating is a relatively new, proprietary manufacturing technique that relies on computer-aided state-of-the-art manufacturing methods. The result is a rotary dress roll manufactured to exact tolerances (Figure 3). Reverse-plated rotary dress rolls: Pros and cons
One of the features of reverse plating is that little or no grinding is needed to achieve the final high-precision form of the dress roll. By eliminating extensive grinding as a way of achieving the final form, as much as 40 percent of the diamond's useful life, previously lost in grinding, is retained. Successful applications of reverse-plated rotary dress rolls can double the effective life of rotary dressers--particularly in very intricate designs (Figures 4 and 5).
Another reason for the extended life of reverse-plated rotary dress rolls is that they are not furnaced at high temperatures as are conventional rotary dressers. This eliminates the possibility of thermal deterioration of the diamonds that can occur if the temperature and atmosphere of the furnace are not carefully controlled (Figure 6).
Reverse-plated rotary dress rolls generally have a higher concentration of diamonds contacting the grinding wheel than those of conventionally manufactured rotary dress rolls. Because of this high concentration, reverse-plated rotary dressers have the potential of lasting longer (Figures 7, 8, and 9).
The extended life of reverse-plated rotary dress rolls can provide an economic advantage in long production runs of intricate workpieces due to higher production and reduced downtime. Longer rotary dress-roll life means more pieces produced per roll and lower dressing cost per piece ground.
Reverse-plated rotary dress rolls are not suitable for all applications, however. They may not be as cost effective for producing simple shapes as conventionally produced rotary dress rolls (Figures 10 and 11).
Because of the relatively high concentration of diamonds, the large, flat areas on fine, hard grinding wheels (finer than 80 grit, and harder than M grade) can become glazed during the dressing cycle. This can lead to loss of part geometry and burning of the workpiece. Glazing can be somewhat reduced by changing the dressing parameters. A complex set of options
No one diamond dressing method produces optimal results in all applications. All of the methods can be modified to meet the needs of a customer's particular application. Short production runs without very tight tolerances may find shank tools the most cost-effective alternative. Longer production runs with tighter tolerances call for rotary dressing.
Users who are manufacturing very intricate forms in high-volume production applications would do well to consider reverse-plated rotary dress rolls. This decision can result in substantial reductions in diamond dressing costs.
Often the choice of the best dressing method is not clear-cut. Applications engineering by full-line suppliers offers the user the widest range of choices to optimize dressing procedures. The exact product that produces optimal results for the customer is best determined by recommendations of the full-line supplier of diamond dressing products.
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|Publication:||Tooling & Production|
|Date:||May 1, 1984|
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