Advances in edge preparation offer production advantages.

New advances in edge preparation technology have significantly increased the performance and life of cutting tools, enabling vast improvements in productivity for manufacturers of automotive, aerospace, medical, and other products.

Proper edge geometry affects tool performance in two specific ways. First, it heavily influences tool reliability. Properly honed tools can improve the repeatability of machining operations, assisting the drive toward lights-out manufacturing. Second, correct edge preparations improve tool life by reducing the common causes of failure, such as chipping, heat-induced failure, and built-up edge.

Tool end users can realize dramatic cost reductions and productivity improvements by applying state-of-the-art edge preparation to cutting tools, whether the tools are a manufacturer's generic line or an enduser's specific tooling. The return on investment for proper edge preparation services is quite high for both new and reground cutting tools.

Matters of geometry

Until recently, the methods of tool edge preparation have not advanced as rapidly as technologies related to the other components of cutting tools, such as material substrate, geometry, and coating. Edge honing was initially instituted to remove the rough edges produced in the powder metallurgy process of part manufacturing.

Although times have changed and cutting tool manufacturing technology has improved greatly, the need for the controlled removal and smoothing of the edges of the cutting tool after sintering and after precision grinding remains. During the past two decades of modern carbide tool development, more emphasis has been put on honing to enhance to 1 life and tool performance.

However, for many cutting tool manufacturers, creating edge geometries remains more art than science. More often than not, the honing process is still guided by the best educated guess, limited by machine variability and operator expertise. The conventional honing processes are highly prone to overworking the corners of the tool and can be difficult to control tool-to-tool because incoming part condition can vary. Consequently, edge-prep tolerances are generally wide and quality deviations are common. Even with today's ultra precise cutting tools, users still experience problems related to incorrect edge geometry.

Precise edges

Cresco, PA-based Conicity Technologies has developed Engineered MicroGeometry (EMG)--a technology that uses dense silicon-carbide filament brushes applied with computer numerical control (CNC). This process can consistently and precisely shape edges to tolerances of 0.0003". By way of comparison, that's one-tenth the thickness of human hair, an order of magnitude more precise than most conventional honing methods.

The EMG process is more consistent than the conventional methods, applying the same edge preparation to tool after tool. Moreover, the optimal microgeometry can be applied for each cutting application. In some situations, this means a uniform hone along the entire cutting edge. In other applications, it is better to vary the edge preparation. For example, the adjacent cutting edge can be prepped differently than the primary cutting edge to minimize unwanted tool rubbing. Such controlled distribution of the edge prep makes the tool cut more efficiently. This type of edge prep will generate less heat because less material is being trapped between the tool and the workpiece. Most often, this will result in a smoother finish.

The clearest and most direct benefit of proper edge preparation is increased tool life. EMG edge preparation services typically cost 10 to 20 percent of the cost of a replacement tool, and yet the process can extend the tool's life by 300 to 800 percent or more.

Proven savings

One of the Big Three auto manufacturers, for example, extended tool life when machining aluminum cylinder heads of V-8 engines from 60,000-80,000 heads to 275,000 heads by utilizing EMG for the 30 normally up-sharp PCD inserts on a 10" diameter cutter. A variable edge prep was applied to the PCD inserts. The EMG process also reduced burr formation and improved the work piece finish.

The economic benefit of increased tool life can be especially dramatic in aerospace and medical applications involving drilling and machining tough materials such as Inconel and titanium. For instance, EMG edge preparation improved tool life from 69 holes to more than 200 holes for a 0.250" carbide drill in 718 Inconel, the material chosen for aircraft landing gear forgings. In this case, the penetration of the drill was increased by 200 percent. In a separate application, 0.750" IC 80[degrees] CVD coated carbide insert was able to double its life, from 22 linear inches to 44 linear inches cut, through titanium and during a turning missile body application.

Total tool life is also a product of the number of regrinds that can be performed. In another automotive application, the number of holes drilled by a coolant-through carbide drill for connecting rods was increased from 1,500 to 3,200 holes after EMG edge preparation. Because the edge prep decreased the severity of tool wear, the number of times each drill could be reground was increased from a maximum of six to a minimum of 10. Therefore, the total productivity of each $150 drill was increased from 9,000 holes to 32,000 holes.

More significantly, in this case, the drills with EMG edge preparation performed well for an entire shift. Previously, drills needed to be replaced every 3.5 hours, and there was a problem with unpredictable breakage occurring seven to nine times per week. Now, drills are reground after each eight-hour shift, and breakage has been reduced to near zero. There is no longer the need to take the machine down and stop the production process for planned or unplanned tool changeover.

Maximizing tool life and eliminating breakage are critical in contemporary manufacturing, which increasingly requires tools that can perform reliably in untended settings. Proper edge preparation also results in a more consistent finished cut, an important advantage for unattended machining.

Advantages aplenty 

In an aerospace application drilling 718 Inconel, the EMG edge prep extended the life of a tool drilling helicopter rotors from 30 to 60 holes with no feed/speed change, just the addition of the edge prep. The edge preparation strengthened the cutting edge and minimized heat buildup in the tool. With a stronger cutting edge, the end user was able to double both feed and speed, increasing penetration rate by a factor of four while increasing the hole count to 120. The holes were also more precise, with reduced standard deviation of hole size by two-thirds. The increased feed rate, as well as the reduction of tool changeover time, has resulted in significant productivity increases.

An additional benefit of EMG edge preparation is the reduction of the scrap generated in the tool set up process. For example, artificial hip joints require holes to be thread milled. Typically, to get the tool to make a suitable thread that could be gaged, four to five parts were threaded, gaged, and scrapped during the tool "break-in" process. These scrapped parts are expensive. EMG edge preparation extended the thread mill life from 75 to 250 holes, reducing the frequency of the changeover process. Moreover, the edge prep improved the consistency of the thread making the first piece on the new tool acceptable, thereby, greatly reducing the amount of scrap pieces being produced while getting the tool to react properly. In total, the EMG process reduced scrap by more than 75 percent.

Proper edge preparation dramatically improves the reliability, performance, and life of new and reground cutting tools made of cemented carbide, cermet, ceramic, PCBN, and PCD. For a fraction of the cost of the original tool, Engineered Micro-Geometry ensures that edge preparation is optimized to take advantage of the three other elements of tool quality: the tool substrate, tool geometry, and tool coating. Conicity Technologies, www.rsleads.com/511tp-157

By Bill Shaffer

Executive Vice President, Conicity Technologies