CNC Grinding: Outdated or Overlooked?

Our founder Abe Savitzky’s expertise in surface and form grinding led to our company’s early success in tool and die making. Back in the early 1950s, form grinding was the new technology that enabled much more precise and durable stamping dies to be designed and built. But it was a demanding process that required both skill and finesse, and as time went by, it became more difficult to find people who could master it.

Today, Wire EDM has all but replaced form grinding due to its automation and reliable consistency. So, is there still a need for form grinding? Most definitely. The key is in understanding how both processes work.

Grinding occurs in three phases. The first phase, the cutting mode, happens when there is sufficient interference and pressure between the abrasive grit and the metal workpiece to form a chip, as in milling. This is how the bulk of metal is removed.

The second phase, ploughing, occurs when the pressure is not sufficient to generate a chip, and the abrasive grit deforms, or ploughs, the metal to the sides, much like a farmer plowing fields. This removes a small amount of material and is used in semi-finishing operations.

The last mode is rubbing, and occurs when the pressure between the abrasive grit and the workpiece is too low to even plough the metal aside. It’s used as a final finishing pass when excellent surface finishes are desired.

When done correctly, grinding does not put excessive heat into the metal, so its metallurgical properties are maintained. Most experts agree that a properly ground stamping punch will have greater service life than one that has been Wire EDM’ed. It is also easier to hold extremely tight tolerances using grinding as compared to almost every other process.

Wire EDM is a highly automated process in which a thin wire is used to cut shaped openings in a metal workpiece via CNC control. It is a thermally based metal removal process in which large numbers of electrical sparks melt minuscule amounts of metal from the surface, which then form tiny round globules that are carried away by a water dielectric fluid.

As a result of this localized melting, a heat-affected zone is created that can significantly, and often adversely, affect the metallurgical properties of the workpiece. By taking sequentially lighter cuts using less power, this damage can be minimized. Wire EDM is a less costly process due to its high degree of automation and reliability.

So, exactly where does grinding fit within today’s precision parts manufacturing? Lots of places! When the tightest tolerances and highest performance and service life are required, grinding is still the preferred process. Today, most cutting tools are still form ground for tool life and cutting performance properties. Grinding is also capable of great economy when many parts can be stacked and ground together.

In addition, there are now two-, three- and more axis CNC-controlled surface grinders that go a long way toward automating the process and making it more reliable. And in many cases, it is less costly than Wire EDM. But grinding is definitely not for everyone because it requires more skill and finesse to learn and master, even using today’s automated equipment.

RS Precision has found that despite all the recent advances in CNC Milling and Wire EDM, there are still many strategic advantages to form and surface grinding. That’s because it is capable of producing highest-quality and best-performing features and surfaces, and of holding the tightest tolerances. It can also be highly economical when used with the right part and fixturing configurations.

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