Introduction To EMG

Engineered Micro-Geometry™, also known by Conicity Technologies as Variable Edge Preparation, is the ability to apply and precisely distribute the edge prep on the cutting edge of a tool as a function of the thickness of the uncut chip. In basic terms, this means the tool is edge prepped, not in a conventional and uniform manner, but rather in a one that is unique to how the tool is going to be applied to the work piece material in the given operation. The following drawings have been highly annotated to better depict what occurs at the cutting edge and workpiece material interface. These illustrations show how the geometric shape and size of the edge preparation must be controlled in relationship to the feed rate and subsequent thickness of the uncut chip to realize optimum shearing of the workpiece material. This type of controlled edge geometry is the key to optimizing the performance of any tool resulting in maximum tool life, superior surface finish and flatness, and minimization if not elimination of burr formation. These drawings compare both uniform and variable edge preparation at a 1,000:1 drawing scale, clearly illustrating the benefits of Engineered Micro-Geometry (EMG™) and the dynamics occurring in the highly critical microscopic interfacial region that exists between the tool and workpiece during metalcutting.

Figure 1. Illustration of Conventional Uniform Edge Prep in Relationship to the Uncut Chip Thickness

Figure 1 illustrates the typical interfacial region for a tool with a uniform edge prep where the cutting edge is in contact with the workpiece material. In the illustration there are 3 regions or sections noted along the cutting edge. These sections are labeled Section A, B and C. Each section represents a critical region in the dynamic cutting edge – workpiece interaction zone. As stated earlier, a key parameter to control is the ratio of the feed rate-to-edge prep size where the edge prep size should never exceed the feed rate with the optimum being some percentage less than the feed rate. In general it not advisable to use an edge prep that is greater than 50% of the feed rate. Control of the feed rate and this ratio is important because the feed rate is a key variable in determining the thickness of the uncut chip. In most instances the term feed rate and uncut chip thickness are interchangeable. Understanding the synergistic effects that feed rate, uncut chip thickness, and edge prep size have on one another is key to understanding the dynamics occurring in the cutting edge-workpiece interfacial region.

In Section A the feed rate-to-edge prep size ratio is approximately 3:1 and the thickness of the uncut chip is greater than the edge prep size in this region. As one progresses along the cutting edge to Section B they should note the change that takes place between the edge prep size and the thickness of the uncut chip. The ratio of the uncut chip-to-edge prep size is now approximately 2:1 and the normal shearing action is being altered as the edge prep size approaches the thickness of the uncut chip as one moves further along the nose radius of the tool. In Section C the edge prep size has exceeded the thickness of the uncut chip, trapping and compressing material between the tool and the workpiece. The compressive forces and rubbing of the uncut chip will result in increased heating on both the tool and workpiece surfaces simultaneously causing the tool to cut improperly.

Figure 2 below is a cross-sectional representation of the interaction that takes place at each of these locations along the cutting edge for a tool with a uniform edge prep where:

Section "A" is a slice through the cutting edge that is perpendicular to the tool primary cutting edge and parallel with the tool feed direction. This shows the relationship between the size of the edge prep and the thickness of the uncut chip along the primary edge of the tool. The edge prep size is significantly smaller than the uncut chip thickness.

Section "B" is a slice taken through the cutting edge at approximately the middle of the tool nose radius, (@~45-degrees). This section shows the reduction in chip thickness size when compared to the size of the uniform edge prep. The size of the edge prep is starting to approximate the thickness of the uncut chip in this region.

Section "C" shows the significant size difference that exists between the edge prep on the cutting edge and the thickness of the uncut chip at the tangency point. This spot represents the last point of contact between the tool and workpiece. (This spot on the tool is perpendicular to the in-feed direction). The edge prep size has exceeded the thickness of the uncut chip.

Figure 2. Cross-sectional Views Comparing Uncut Chip Thickness and Edge Prep Size for a Uniform Edge Prepped Cutting Edge.

Figure 3. Illustration of Engineered Micro-Geometry (EMG)
in Relationship to Uncut Chip Thickness

Figure 3 illustrates the typical interfacial region for a tool with a Conicity EMG edge prep where the cutting edge is in contact with the workpiece material. In this illustration the same 3 critical regions or sections are noted along the cutting edge as in Figure 1. This time they are labeled as Sections D, E and F.

In Section D, E and F the size of the edge prep and the thickness of the uncut chip remain in unison, with no change in the ratio of the uncut chip thickness-to-edge prep size occurring anywhere along the dynamic interfacial region. As illustrated in Figure 4 below, the ratio of the uncut chip thickness-to-edge prep size is approximately 3:1 at any point along the active cutting zone. Thus the normal shearing action that occurs along the primary cutting edge is maintained as the cut transitions around the nose radius of the tool.

Figure 4 is a cross-sectional representation of the interaction that takes place at locations D, E and F along the cutting edge for a tool with a Conicity EMG edge prep where:

Section "D" is a slice through the cutting edge that is perpendicular to the tool edge and parallel with the tool feed direction. This shows the relationship of the size of the edge prep to the thickness of the uncut chip. This configuration is basically the same as shown in Section "A", in the uniform edge prep illustration.

Section "E" is a slice taken through the cutting edge at approximately the middle of the tool nose radius. This section shows the edge prep is reducing in size as the uncut chip thickness decreases, maintaining the same ratio as in Section D.

Section "F" shows the relationship between the edge prep and the thickness of the uncut chip on the workpiece when examined at a spot on the tool that is perpendicular to the in-feed direction. (This section represents the last point of contact between the tool and workpiece). The edge prep is still decreasing in size as the uncut chip thickness continues to decrease, maintaining the ratio seen in Sections D and E.

Figure 4. Cross-sectional Views Comparing Uncut Chip Thickness and Edge Prep Size for a Conicity EMG Edge Prepped Cutting Edge.

In summary, with Engineered Micro-Geometry, the edge prep size is distributed along the cutting edge maintaining a specific ratio of uncut chip thickness-to-edge prep size. For example, on an indexible insert or cartridge type tool the edge prep is blended around the nose radius of the tool with the change in the size of the edge prep mirroring the rate of change in the thickness of the uncut chip. More simply stated, as the uncut chip thickness decreases the edge prep size is decreased. A tool that has the EMG edge prep cuts “cleaner” and “freer”. The tool will cut more efficiently because the varying edge prep size is not allowing cut material to be trapped between the tool and workpiece. The controlled distribution of the edge prep size around the nose radius of the tool minimizes unwanted tool rubbing. Tool pressure and cutting forces will decrease, subsequently so will tool and workpiece temperatures. These are some of the benefits of EMG, ones that are applicable to nearly every cutting tool operation and application. This same technology can be applied to drills, endmills, reamers and any other form of cutting tool.