Slow Down to Speed Up: Understanding Optimized Roughing

by Jay Ball, Product Manager Solid Milling - North America, Seco Tools, LLC

Modern machine tools provide an ideal platform for achieving the benefits of optimized roughing, but many shops continue to miss out on its advantages. This strategy's up side includes longer tool life, better surface finishes, shorter cycle times and reduced machine wear, but it tends to intimidate many machinists because it takes them outside their comfort zones.

Knowledge is power, and it's tough to implement any productivity method unless you understand it. That's the big barrier for many shops with high-speed machine tools: the mistaken belief that if your equipment can go fast, it always should run at its highest possible speed. If that were true, we'd drive to the grocery store at 110 mph because that’s the top speed of most automobiles.

For machine tools, the flaw in the "always as fast as possible" philosophy is simple, once you think about it: Depending on the part design, the equipment actually can't sustain its highest speeds and feeds throughout a cut path. When spindle speeds are kept high, the cutting tool’s angle of engagement increases through complex features and in corners. But those high RPMs force feed rates and stepovers both to drop. This combination of high spindle speed and slow feeds produces the classic scenario in which a cutting tool/end mill rubs rather than cuts, producing heat and friction that induce premature tool wear – and that scenario impedes proper chip development as well.

Tell machinists to slow their machine RPMs so they can speed up their overall cycle times, and they most likely won't believe it. Yes, it sounds counterintuitive, but when RPMs match sustainable feeds and stepovers, shops achieve better results – including more than 50% longer tool life in many cases. Simply put, matching speeds with feeds maintains a constant chip load.

Along with the "need for speed" and its impact on machining results, some shops also fail to grasp the logic of the optimized roughing process. They understand that producing good parts typically means making good chips, but they're not clear on the connection between optimized roughing and its results.

What shops often do know, however, is that their part surface finishes are subpar and their tool wear is high. Typically, they're engaging the full diameter of a cutter, creating a large angle of engagement, but they're not using the full length of the flutes. Changing the cutter engagement solves both problems: surface finish and tool wear. In fact, the best way to see how optimized roughing works is to implement it and look at its results.

Just as it's important to remember the advantages of optimized roughing, it's critical to know when to apply the method in the first place. Not every part qualifies as a good candidate. Try engaging full flute lengths to machine a complex mold cavity, for example, and you quickly see that you'll never achieve a good chip load on this job with this approach. However, if you train yourself to think of optimized roughing when you see a part with straight prismatic walls, you'll be on the right path.

As you look at your workflow, ask yourself whether you're matching speeds and feeds at sustainable levels. Look at the data coming from your equipment and see if your machines can run at the speeds you program, or if your hardware is trying to protect itself with reduced feeds and stepovers. This method works with any suitable workpiece and any type of tool, from the tiniest of diameters on up, provided that the part’s geometries and features allow it.

Along with the information you're getting from your equipment, take a moment to talk through your needs with your machine tool supplier. Here at Seco Tools, we've developed reference tables that show you workable baseline values for speeds, feeds, angles of engagement and stepovers, values you can achieve with ease if you use the right approach to your machine tools. We're always happy to help our customers maximize their productivity. After all, what good is great hardware if it can’t be used effectively? Productivity and efficiency are the keys to profitability, and we want to see our customers succeed.

How Chipbreakers Save Your Parts

by Aaron-Michael Eller, Product Manager - ISO Turning & Advanced Materials, Seco Tools

Chipbreakers make critical contributions to machining operations with turning inserts in ways that shops often overlook. First and foremost, chipbreakers focus on the safety of everyone who works with or near machining equipment. Long, stringy "bird's-nest" chips carry edges as sharp as razor wire and can cause severe injuries to anyone who touches them, let alone gets caught up in them. With the right chipbreakers, these hazards never develop. Ideally, chips form tight conical curls about 1 inch long to create maximum compaction in the chip hopper as they fall away from the workpiece, into the evacuation system and away from the machine.

The right chipbreaker means fewer insert changes, less rework and fewer opportunities for chips to make damaging contact with a workpiece. Proper chip development and management eases the operator's task and leads to longer tool life, which in turn promotes efficiency, productivity and profitability. The right chipbreaker also enhances part quality and can deliver a substantial cost savings. Which of these two parameters matters more to an individual shop? That depends on workflow, job selection and part quantities.

In a facility that focuses on aerospace, medical or automotive parts, with high finish requirements on every component, part quality becomes the primary concern, even more than tool life, because of the high value of each individual workpiece. Conversely, in a shop that produces higher-quantity parts that demand less in terms of surface finishes and specification tolerances, longer tool life equals fewer tool changes and longer production runs for greater profits.

The reality of modern machining is that specific jobs require equally specific tools, chipbreakers included. Consider the fundamental differences between chipbreakers on roughing tools and finishing tools. On a roughing insert, the chipbreaker sets slightly back of the cutting edge to add strength and support heavier depths of cut or higher feed rates. At the shallower depths of cut used in finishing processes, the chipbreaker sets closer to the cutting edge to direct the chip off the workpiece and make it form from the chipbreaker instead of burnishing the cutting edge of the insert.

New developments in machine tools, materials and parts mean new challenges for chipbreakers. High-speed machining prompts an overall push to higher cutting parameters. Greater depths of cut and higher feed rates also mean greater tool pressure, which raises machine load. Optimized lead angles increase the engagement of the insert and raise metal removal rate at the same time that they add security to the cutting edge. All of these considerations increase the average thickness of the chip and make it easier for the chipbreaker to do its job.

Increased feed rates, along with heavier depths of cut, assist mechanical chip breaking. Engaging the entire edge of the insert helps reduce a common failure mode called depth of cut notching, in which repeated cutting action on one area of the insert creates a notch in the cutting edge and drastically shortens tool life.

Abrasive materials, including workpieces produced through additive manufacturing, also pose challenges for tools and chipbreakers. Turning hard materials with the right chipbreaker causes few problems because the material is easy to manage. By contrast, workpiece materials with transitions between hard and soft surfaces can create bird's-nest chips at the transition. All of these situations call for careful chipbreaker selection in consultation with the manufacturer of the tools.

To achieve ideal results from chipbreakers, try new technologies and don't hesitate to look beyond familiar chip breaking solutions. For example, on our Secomax CBN inserts, Seco Tools offers a flowing radii chipbreaker, which is laser machined to the cutting edge to allow for a continuous flow of material off the insert and onto the chipbreaker. If we had ground the chipbreaker instead of laser machining it, the process would require approaching the workpiece from multiple angles to achieve the right profile, which causes sharp edges and corners that don't allow for free chip flow. Before you begin your next cut, let us help you think through your tooling and your approach. Seco Tools Technical Sales Representatives can help customers solve their chip breaking challenges, often over the phone.