Single Layer vs. The Matrix
But before we get into the differences, let’s see where there are some similarities. In contrast to both resin and sintered bonds, where the diamond grit is suspended within a matrix, electroplating and vacuum brazing are manufacturing techniques where the diamond is fully exposed. Without a matrix required to wear or erode, the diamond grit immediately attacks the working surface. This direct contact with the material makes electroplating and vacuuming brazing very aggressive.
Electroplating and vacuum brazing tools have a much higher concentration of diamond. The working surface or edge is fully concentrated with diamond grit. The diamond grit in resin and sintered bonds are like chocolate chips in a cookie. The diamond in electroplating and vacuum brazing is more like a chocolate bar, all chocolate. Silly analogy, but it get’s the point across, no? We’ll be quick to point out that both are good depending on the application.
Though electroplating and vacuum brazing have similar characteristics, their vastly different manufacturing processes result in some important microscopic differences.
The Process - Electroplating
Electroplating is process of plating one metal onto another by hydrolysis. A piece of metal, with a negative charge is placed in a metal salt solution that has a positive charge attracting one to the other. There's a great reference here from UC Davis. In the diamond electroplating process, the tool body (negatively charged) is placed in a tank where the diamond grit (positive charge) is “tacked” to the exposed surface. Nickel is then electroplated to strengthen the hold of the diamond grit to the body. The result is a single, very dense layer of diamond grit on the working surface or edge of the tool.
A wheel coming out of the tacking tank.
The Process - Vacuum Brazing
The process of vacuum brazing is vastly different from electroplating. Brazing is the process of joining two objects by melting a filler metal, into the joint. Wikipedia has a decent article here. In the diamond vacuum brazing process, nickel is melted around the diamond grit fusing the crystal to the tool body. In order for a proper fusion, there are two critical factors required. First, the surface must be free of any oxides. Second, very high but exacting temperatures need to be reached to properly melt the adjoining metal. Vacuum ovens are used to remove oxygen and provide the high temperatures required. The result is a very strong single layer of diamond grit.
A wheel being coated with diamond grit before being placed into the oven.
Though both electroplating and vacuum brazing produce a dense layer of diamond grit, the diamond grit used is not the same. In our very first article on synthetic diamonds, we touched briefly on the concept that synthetic diamonds are sorted into a variety of shapes that have variation in hardness from sharper more brittle to rounder more dense crystals.
Electroplating uses much sharper and pointed diamond crystals while vacuum brazing requires a more resilient diamond crystal to withstand the extreme heat and pressure conditions. This microscopic difference is fundamental in really understanding why these two processes are not interchangeable. Electroplated products are more aggressive but arguably more fragile, while vacuum brazed products are stronger but less sharp because of the duller, rounded crystals. These mechanics have a profound impact on selecting the correct tool for the material.
With a fully exposed diamond surface, electroplating and vacuum brazed products have a more expansive application than their resin and sintered counterparts. Another key factor to their broad capacity is that both electroplating and vacuum brazing allow for extremely complex shapes and forms not possible in resin and sintered products. Check out some really great images here in our custom tool section. This is a key common characteristic making the material and application list very long. From plastics, fiberglass, rubber and other composite materials to soft stone such as marble, limestone and even to certain metals and glass.
Electroplated tools, with their sharper diamond grit, will tend to tear through the surface and are often better suited for the composites and plastics category. Surfaces that are slippery (plastics) or sticky (rubbers) require more of a clawing action to remove material. Vacuum brazed tools will grind through materials and are better suited for softer stones such as marble and limestone as well as some metals where electroplated products would be tool fragile.
The same design, totally different applications.
One other important distinction between the two manufacturing techniques is tool dimension. This is an important annotation, because there are often restrictions that are notable. Electroplated tools can be much larger and are really only limited to the size of the tanks, while the internal dimensions of a vacuum oven will limit the tool dimension. The larger the blade, the more likely it will warp under heat and pressure. Also thin edges will ripple and deform in a vacuum oven. Small complex tools are more difficult in the electroplating process because they have a small surface area for the diamond to stick to. These tools are often more successful in the vacuum brazing process.
The Stripping Advantage
Possibly the greatest advantage of electroplated and vacuum brazed tools is that once these tools have been used, they can be stripped and re-plated or re-brazed. This greatly extends the life of complex and expensive specialized tools. Electroplating and vacuum brazing inherently have a malleability and scope beyond that of resin or sintered bonds, making them arguably kings of the diamond tooling industry.
We finish off our series on diamond bonds. Look forward to our new "The Basics" series where we review material characteristics such as natural stones, concrete and composites. Stay tuned!