Cutting Tools: In the Groove
- October 29, 2011
Shop Metalworking Technology speaks with Kurt Ludeking, product manager at Walter USA, Waukesha, WI, about developments in grooving tools and cutting techniques.
Shop Metalworking Technology: Multi-function grooving/turning tools have been in existence for many years, but not everyone understands their function and their benefits. Can you briefly describe the key functions of multi-function grooving tools and how they could benefit a manufacturer?
Kurt Ludeking: Multi-function grooving tools, as their name suggests, make it possible to perform multiple operations using the same tool and insert. The tools are designed for rigidity in parting off operations, radial grooving, and also are capable of axial groove-turning. One benefit is that the tool and insert inventory is kept small for the manufacturer. Reduction of machining time is another big benefit, because you don't have to make as many tool changes while machining the workpiece.
On complex components that require many tools in the turret, a multi-function grooving tool can help make more space available, reducing the need for multiple set-ups. Performing axial turning or even facing with a grooving tool not only reduces the number of tools needed, but can also provide a better surface finish than a single point turning tool under the same conditions.
Probably the biggest advantage is the increase in tool life by using the groove-turning strategy for wide grooves since the tool wear is balanced on all areas of the insert, not just on the main cutting edge as it would be when making multiple plunges. Also, it is easier to maintain good chip control with this method, providing a very reliable process.
SMT: Grooving small parts can sometimes present challenges for a manufacturer, particularly for precision work in the medical field, for example. What are the top three problems and how can manufacturers overcome these problems with today's grooving tool technology?
KL: Tool pressure, selecting the correct tool and insert for the workpiece material, and chip control are usually the biggest challenges in working with small parts. These three factors overlap, so decisions in one area can affect performance in other areas.
Keeping the tool pressure low is critical to avoid part deflection and holding the required dimensions. This is generally addressed by using the sharpest tool possible without generating chatter or vibration. Although inserts with a ground cutting edge will have the sharpest edge, advances in pressing and honing technology have made it possible to keep much sharper edges without grinding than was possible only a few years ago.
Selecting the correct tool for the workpiece material involves the micro-geometry of the cutting edge, the carbide grade, and getting the correct macro-geometry of the insert. Let's start with the macro-geometry – because of the tight tolerances in small part machining, the depth of the groove must often be flat within +/- .001. Depending on the shape of the cutting edge, the insert may not give a "flat” bottom to the groove that meets the tolerance. Some grooving inserts and "universal use” inserts are designed with curved cutting edge that leaves a convex curvature on the bottom of the groove. Although the curvature is small, generally only 0.0005” or so, it does use up a large fraction of a tight tolerance. Look for an insert with a straight cutting edge to ensure that the groove bottom is as flat as possible.
Continuing with the micro-geometry of the cutting edge, what is needed is an edge that cleanly cuts the material, but also provides a stable process. This edge geometry must be very accurate since feed rates for small parts are often very low to keep tool pressure under control. A sharp edge helps with this, but sharp edges can also be prone to chipping, which makes the process less reliable.
The micro-geometry will also affect the beginning of chip formation, so that brings us to the chip control issue. The factors to consider here are what feed rate and depth of cut will be used. There must be a balance between what the part geometry can tolerate and processing time – to get chip control and reduce process time, you often need higher feed and depth of cut, but these conditions can work against holding tight tolerances for delicate workpieces because of increased deflection caused by tool pressure. In addition, sometimes the machine capabilities prevent using ideal parameters to get chip control – for example rpm limits keeping the surface speed low. Choosing an insert geometry that works in a wide range of conditions and materials makes chip control easier.
SMT: How does a manufacturer decide between going with grooving inserts or
solid carbide tools? Is it only a cost consideration or does a manufacturer have to consider other machining parameters depending on the type of grooving tool he chooses?
KL: For external tools, there are really no good reasons to use solid carbide tools – they are higher cost and don't provide any significant advantage. For internal tools it becomes a question of minimum bore size and rigidity required to perform the required operation. If possible, it is always more cost effective to use an indexable tool because of the cost of solid carbide tools. Where the minimum bore is too small for an indexable tool or the depth of the operation is more 4-5 times the bar diameter, then a carbide tool is the best solution.
SMT: What would you say are the key advances in grooving in the past five
years and what was the driver of these technological changes?
Advances in grooving technology have come from several fronts. One of the most significant is the development of PVD Aluminum Oxide coatings that provide the heat and crater resistance of Al2O3 with the sharp edge and toughness of PVD coated carbide. Walter is the only company in the industry with this technology. The products cover the range of applications from high hardness/wear resistance through high toughness for interrupted cuts and low cutting feeds.
Other important advances have come in chip form geometry development. Many new geometries handle a large range of work piece materials with good chip control, and universal geometries can be used effectively in different operations like parting, radial grooving and axial turn-grooving.
Finally, manufacturing process advances have made grooving inserts and tools more reliable, extending tool life and providing the manufacturer with very stable processes compared to what was possible just a few years ago. An important point here is that the features and technology of the insert geometry, the carbide grade, the toolholder design, and the manufacturing technology all work together to provide the best performance in any application.
SMT: Are there any issues with grooving processes that cutting tool suppliers
have not addressed yet and still find a challenge to overcome?
New material developments continually bring new challenges, as do new machine concepts that require different connections between the tool and the machine. Advances like cryogenic cooling such as the Walter Cryo-tec may eventually be available for parting/grooving operations, and will bring new opportunities to provide even better tools and processes for manufacturers. And as always, demands from manufacturers for faster, more versatile, and more reliable grooving processes will continue to drive developments in grooving technology.