How to Match Your Resin Bond Grinding Wheels to the Workpiece

Superabrasive grinding wheels have two equally important components. While the grit, (diamond or CBN) does the work, it couldn't function without a partner holding it in place. In the case of resin bond grinding wheels, that partner is phenolic resin.

The hardness of the phenolic, along with grit size and concentration, determines wheel life, material removal rate, and final surface finish. CDT controls these three parameters precisely, allowing users to match a wheel to the particular workpiece material and type of grinding operation. However, selecting the best wheel depends on understanding the relationship between hardness, grit size and concentration and the wheel wear mechanism.

 WHEEL WEAR MECHANISMS

 As grit cuts through the workpiece material the edges become dull. Allied to that, chips from the cutting process erode the resin, releasing old grit and exposing fresh edges. The rate at which fresh grit is exposed is critical. Dull edges tend to rub against the workpiece, cutting forces go up and more heat is generated, perhaps burning the workpiece. Conversely, if grit is released early the grinding wheel is wearing faster than necessary, resulting in more frequent replacement.

HARDNESS 

Hard workpiece materials, like ceramics and carbides, tend to dull cutting edges quickly, yet because the chips are small and brittle, resin wear is low. In this situation, to ensure a sufficient supply of fresh new cutting edges it's best to use a softer wheel.

Softer materials, like steels and high nickel alloys, (which should be ground with CBN rather than diamond,) produce longer, more ductile chips. These erode the resin faster which, in a soft wheel, results in excessive wear.

Manufacturers of resin bond grinding wheels adjust hardness by varying the mix of fillers in the phenolic resin. The resulting wheel hardness is expressed on a scale from A (softest) to Z (hardest) although superabrasive wheels are generally available just for the range from O through U. If a wheel outside of this range is thought necessary, consult with product specialists here at CDT.

CONCENTRATION

This refers to the proportion of superabrasive grit in the resin and is expressed on a scale of 25, 50, 75, and 100. The highest value indicates a weight to volume ratio of 72 carats per cubic inch, which works out to about 25% by volume.

A higher concentration means more cutting points, which results in faster material removal, but also increases wheel cost. Concentration also affects surface finish: a lower concentration would typically be used for finishing than for roughing.

GRIT SIZE

Larger abrasive particles remove more material on each pass, so coarser grits are used for rough machining and when grinding softer materials. Smaller particles lower cutting forces, so are used for harder materials as well as finishing operations.

MATCH THE WHEEL TO THE WORKPIECE

The choice of grinding wheel depends on the nature of the workpiece material and whether roughing or finishing. Harder materials generally should be ground with a softer wheel and small grit size. Softer materials are better ground with harder wheels and larger grit. Grit concentration should be chosen to suit the type of grinding operation – roughing or finishing.

If in any doubt as to the hardness of wheel to use, consult a grinding wheel specialist.

Common Fluting Mistakes — and How to Fix Them

Flute Polish or Flute Burnish?
There is an increasing need for high-quality carbide mills and drills with polished flute faces. Your customers are demanding a surface grinding tool that has a shiny flute, evacuates a metal chip better, and runs at faster speeds.

Sometimes your customer just wants your tool to look like the “other guy’s” tool. Unfortunately, a burnished flute face can be mistaken for true polish. Toolmakers have the challenge of making a cost-effective tool that has great performance and a great finish on the flute face.

Common Fluting Mistakes
Some toolmakers turn to hybrid wheels that grind the flute in no time, but these grinding wheels really don’t polish all that well.

To improve appearances and achieve a smooth finish, a lot of toolmakers use nonwoven products to polish after fluting. But do flute polishing cloths really polish, or do they just burnish the surface?

For a Quality Flute Polish
For a flute cleaning and polishing that really penetrates the surface, you have to remove some material to get through the grind lines leftover after flute grinding.

A resin bonded grinding wheel can give you a finish that is as good or better than nonwoven polishing products, but the resin bonded wheel also removes material from the flute face, taking out subsurface damage.

Resin bond is made by mixing abrasive grit with a phenolic resin. The resulting compound is molded to shape before being baked in an oven. This produces a grinding wheel that's tough, with the resilience to take impacts without shattering. By adding copper and other fillers to the resin base, grinding wheel manufacturers can tailor the properties of the finished grinding wheel to a wide variety of applications.

With resin bond, you can make a tool that not only looks just as good as the “other guy”, but also is actually better quality than the other guy. Resin-bonded superabrasive grinding wheels provide:

• Shock-resistance

• Excellent surface finish

• Low maintenance

The Extra Effort Sets You Apart
The right wheel can help you polish up your act. CDT’s resin bond flute polishing wheel performs as good as it looks — producing a quality tool that shows. We offer resin bond polishing wheels to work in oil or emulsion on all CNC cutter grinders. These grinding wheels can run at high speeds and are available in grits as fine as 1200 or more based on finish requirements.

Grinding wheel manufacturers have years of experience and there are few fluting applications we haven't encountered. Our engineers can help you get the right grinding and polishing solution for your particular application.

Why Use Plated Diamond or Cubic Boron Nitride Tools?

Layering metal parts via electrolysis with special substances that improve their strength or appearance and protect parts from oxidation and corrosion is called electroplating. Typically less than .05 millimeters thick, coatings applied during the plating process are either metallic, diamond, or cubic boron nitride. Decorative objects such as jewelry or tableware are usually plated with silver or gold while steel and iron items are plated with zinc, chromium, nickel or tin. However, grinding tools require cubic boron nitride or diamond coatings to optimize their functioning, provide better cutting action and deter rapid deterioration of tools. 

Advantages of Electroplated Diamond Tools

Tools sent through an electroplating process that coats them with a diamond layer cleaved by a tough nickel alloy retain their precise proportions and original structure throughout their working life. Unlike resin bond or metal bond diamond products involving diamond particles that have been cached in bond and joined together by embedded resin or metal binder, electroplating facilitates the protrusion of diamond fragments to extend beyond the bond matrix. This further provides electroplated diamond tools with the exceptional ability to cut freely and rapidly without generating excessive heat. Less heat generation means better grinding efficiency, reduced risk of cracks or burns on the workpiece's surface and a significant decrease in equipment energy consumption.

Electroplated diamond tools are well-suited to process:

• Abrasive or hard non-metallic entities such as asphalt, stone, ceramics, concrete, semiconductor materials and glass.

• Non-ferrous metals (copper, aluminum and their alloys) and pliable but tough materials (resin and rubber, for example).

Since diamonds react with iron, cobalt, nickel, chromium and vanadium under elevated temperatures produced during grinding actions, diamond tools should not be used to process common steels and tough alloy steels. For work involving these materials, electroplated cubic boron nitride tools are recommended.

Advantages of Electroplated Cubic Boron Nitride Tools

Considered the best technological advancement made for facilitating grinding of superalloy and hardened ferrous materials, cubic boron nitride is second to diamonds on the hardness scale and offers nearly five times the abrasion resistance afforded by traditional abrasives. Electroplated CBN tools also provide the following additional benefits not found in any other electroplated tools:

• Remarkable thermal conductivity and chemical resistance

• Enhanced surface integrity for grinding hardened cobalt-based superalloys as well as nickel and hardened alloy steels

• Eliminates the expense of post heat-treat grinding operations

• Produces polished surface finishes by providing taut dimensional management of tools to users

• Creates no bit-dulling grit

The ability to induce nanostructuring of carbon boron nitride has allowed engineers to further increase the hardness of CBN by incorporating the Hall-Petch Effect, which describes the "tendency for hardness to intensify as grain size is decreased". In addition, carbon boron nitride's chemical resistant and strong thermal stability properties make it well-suited to machine ferrous materials that cannot be machined by electroplated diamond tools.