Technology has made hard milling more feasible

The conventional method of producing components from hardened tool and alloy steels has long been to rough in the soft state, heat-treat and then EDM or grind all critical features to size. But this decades-old paradigm began to change as cutting tools and tool coatings became more wear-resistant, toolholders became more accurate, machine tools became more rigid and CAM software became more capable. Pioneering machinists learned they could not only finish heat-treated mold and die components but rough them fully hard, significantly boosting productivity and reducing lead times

Navigating Uncharted Waters

Corey Greenwald is one such machinist. When the owner of the small shop he worked at in 1995 purchased a Yasda vertical machining center, he began experimenting with what seemed impossible at that time: milling CPM tool steel hardened to 64 HRC.

“People thought I was crazy,” Greenwald said. “But within six months, I was able to produce punch tooling for connecting rods that previously required four separate operations and 80 hours of manual work. I’d spend a couple hours getting everything ready, push the green button and come in the next morning to a set of four completed punches.”

Greenwald was so successful at this underutilized, often misunderstood machining practice that in 2004 he left to start his own company, Hard Milling Solutions Inc., Romeo, Michigan. He’s since made hard milling a science, carefully building a database of feeds and speeds, step-downs and step-overs, chip loads and other operating parameters that allows his shop to machine virtually any hardened material unattended, without tool breakage and without failure “a majority of the time,” he said.

Though there’s no such thing as a typical part at Hard Milling Solutions, this workpiece indicates the challenges faced by this Michigan job shop. Image courtesy of Hard Milling Solutions

There’s more to Greenwald’s success than the right parameters, however. He said he was among the first to adopt remote monitoring technology, mounting cameras on each machine and equipping employees with smartphones and laptops so they could keep an eye on production from outside the plant. The team also makes extensive use of broken-tool detection and in-process probing, allowing verification of critical process steps and corrective action to be taken when something goes awry.

As a result, Hard Milling Solutions has machined everything from forging dies for the automotive industry and knee and hip implants for medical applications to tab tooling for can manufacturers. All parts are made of superalloy or equally challenging grades of hardened steel, and all have tight tolerances.

“We have a 12-piece order on our floor right now for an aerospace customer,” Greenwald said. “The parts are made of 60-HRC A2 tool steel and have 0.0004″ tolerances all over the place. That’s a fairly typical requirement for us, but I have to say that every job is unique. Even today, we’re experiencing geometry and materials we’ve never seen before, so we are continuously being challenged. That’s what it takes to keep us engaged.”

Hard Choices

If a shop wants to follow in Hard Milling Solutions’ footsteps, it likely will need to climb “one heck of a learning curve” as Greenwald did, although much of the technology he uses is now commonplace. High-quality CNC machine tools comparable to the Makino V56 VMC that he started his company with, for example, are readily available.

This HPC milling chuck with an HSK spindle interface is one of the go-to toolholding solutions for hard milling. Image courtesy of Guhring

Ernie Dickieson, technical sales representative at CAD/CAM provider Open Mind Technologies USA Inc., Needham, Massachusetts, agrees that hard milling is among the most challenging of all machining operations. But he thinks that it is not nearly as difficult as it was even five years ago.

“CNC machines are more robust and rigid,” Dickieson said. “The cutting tools are much better. Perhaps most importantly, there’s far more information available now on how to cut hard materials. And from the programming perspective, I think we and others have done a great job at creating toolpaths that are smoother and more efficient, taking into account the harder materials. Overall, hard milling has become a very achievable task for most shops.”