In recent times, few machining operations have seen as much scope for cost-effective productivity enhancements as milling. By capitalising on the advanced insert coatings and free cutting, high feed tool geometries introduced over just the past two years, removal rates on face, profile and cavity milling can be increased significantly. 

In today’s ultra competitive global market, productivity has become an absolute priority for all manufacturing companies, but tooling specialist Iscar believes that significant productivity gains can be achieved relatively inexpensively through simple drop-in retooling on existing machines with existing personnel through minimal investment.

As an example, Iscar makes reference to the tool and die room in a large stamping house retooling two of its mainstay milling operations – cavity milling and face milling to square off die stock. Within days the removal rate rose 40 to 1 for the cavity work and 2.5 to 1 for the squaring-off. Savings totalled hundreds of thousands of dollars a year.

Look at the ripple effect and the story gets better. Finished die sets arrived in the pressroom sooner by days to weeks, so the pressroom could deliver finished stampings sooner. More importantly, the sales force leveraged the quick delivery capability to capture more bids.

Both throughput increases reflect the trend toward the performance strategy of feed faster and take more passes at lower depths of cut. For the cavity milling, the new segmented high feed high positive rake cutter fed at 350 IPM/0.030 inch depth of cut, up from 12 IPM/0.100 inch depth of cut – the best that was achievable with a solid carbide ball. For the squaring-off, the new free cutting five flute, high feed, high rake cutter feeds at 20 IPM – up from 6 IPM at the same depth used with a smaller zero rake two flute cutter.

The only thing holding these operations back previously was the tooling. The machines themselves had plenty of table speed, spindle speed and rigidity. Management correctly put the emphasis on raising the material removal rate (MRR) and not on tooling cost. After all, MRR affects more than 50% of machining cost and speed of delivery. By contrast, tooling cost rarely represents more than 3% of total cost and does nothing for speed. 

Fast changing landscape

Such gains in milling performance would have been unthinkable even two years ago. Iscar believes it’s the progress made since 2006 in insert coatings and geometries that have created today’s era of high performance milling.

Taking a closer look at some of Iscar’s own technological advances: the company claims its Sumotec insert coating treatments can improve insert performance by at least 15%. The treatment makes coatings smoother and more slippery, so tools last longer, run cooler and reduce cutting friction losses. This can make a big difference, especially on today’s popular light-duty CNC machines.

In addition, high positive rake inserts reduce cutting forces by cleaving off the stock rather than scraping it. The latest high positive inserts offer much stronger cutting edges, with even higher rakes and top face geometries that clear chips more efficiently and minimise re-cutting. Also, helical cutting edges ease the insert into the stock rather than slamming it in. They cut like scissors shearing paper, not an axe chopping wood.

High feed cutters with stronger bodies, recessed insert clamps for better chip flow internal coolant flow and larger gullets for better chip clearance can make a real difference – for example Helido H600 double sided inserts for fast feed face milling, available in carbide grades for stainless steel and high temperature alloys, alloy steels and cast iron. 

Tangentially speaking

Equally as influential are more versatile tangential mills, for faster roughing under adverse machining conditions in a wider range of applications. For decades, tangential mills have earned a reputation for surviving heavy slabbing operations, even on older worn machines with high horsepower and high chatter.

Today’s tangential mills come in smaller sizes to handle narrow grooving and in higher rakes, enabling them to handle some contour slabbing. No longer are tangential cutters limited to large area flat face milling. An example is the Iscar Sumomill which combines tangential orientation, the Sumo Tec coating treatment, helical inserts and high tooth density in a single tool. The Sumomill T290 can run at high table feeds, yet produce excellent surface finishes and no mismatch.

Another example is Chatterfree designs in solid carbide cutters. Asymmetric flute designs break up harmonics, eliminating the principal cause of failure in solid carbide cutters. Iscar’s latest Chatterfree endmills can cut slots in steel up to 2 x diameter and the company has also brought the concept to solid carbide tips in the Multi-Master and Feedmill line of replaceable tip mills enabling faster cutting and finer finish in rough or finish slotting, shoulder milling and cavity milling.

In addition, there are now better shredding inserts for heavy milling and profiling, especially on long chipping metals. Inserts combining Sumo Tec coatings, free cutting geometries and serrations eliminate the chip jamming and re-cutting often encountered when milling stainless steels, high temperature alloys and other nickel-based alloys. Latest examples from Iscar include the Finishred endmill, segmented or solid carbide; and Millshred segmented face mill. Both are designed for high feeds even on low power machines.

The underlying benefit of all these advancements is a much higher MRR in a wider variety of applications, especially – but not exclusively – on today’s fast feed, low power machines. And for the most part, these advances took place over the past two years so companies using older technology make the transition relatively simply. 

Top tips

In summary, Iscar offers some useful pointers in getting up to speed and becoming more productive:

• Focus on material removal rate (MRR) and machining cost per unit (CPU). Today more than ever, they are your key metrics in tooling for survival of your enterprise. If you focus on tool costs, typically less than 3% of CPU, you’re missing the point!

• If you haven’t retooled your milling plant-wide in the past two years, do it now. You’re already out of date. By the same token, each time you run a repeat job, consider retooling it as technology may have moved on since the last run.

• When setting feeds and speeds for a job, go for more parts in the bin over edge life. In the big picture, tooling cost is a drop in the ocean.

• Push the tooling to cut faster and use the manufacturer’s recommendations as a starting point only. On a new machine tool in particular, you can usually run much faster than base recommendations, and come out ahead economically.

• For heavy roughing work, take a fresh look at tangential milling. It has come a long way in the past two years.

• When ordering a new machine, seek tooling recommendations or at least a second opinion, from a full-line tooling producer because in general, specialist tooling providers will be more current about tooling than machine builders. With the right tooling, you can typically expect at least a 15% improvement in productivity.

• Be open-minded about proprietary tooling. Tooling providers invest their R&D resources on proprietary products lines, so they are bound to perform better. The performance differences between proprietary and generic tooling are substantial, and will definitely trump any risks from single source dependence.

• Buy that second cutter. You can swap out cutters and do the indexing offline. The gains in uptime will pay for the extra cutter after just a couple of shifts.

• Consider higher pitch cutters to feed faster, even on low-power machines. Don’t be bound by the old ‘three engaged teeth’ cliché. That guideline was aimed to reduce friction, before the era of slipperier coatings and freer cutting inserts.

• Ask for outside help. You’ll get better answers sooner. Tooling choices are too wide, and too fast changing to keep up with by yourself so invite qualified tooling vendors to assess your manufacturing needs and make suggestions. They will welcome the opportunity, and the advice is free.

Iscar
www.iscaruk.co.uk