The dynamics of chip formation and evacuation make grooving in turning operations unique in almost every way. Innovative insert designs and coatings can improve your grooving operation, but to be completely successful, there are some other things you should know.
It is important to understand the three main groove types: OD grooves, ID grooves and face grooves. Each has specific requirements in terms of applying the cutting tool to the work piece. OD grooving is generally the easiest, as gravity and coolant help with chip removal. Also, because the groove is visible to the operator, quality control checks are direct and relatively easy. However, potential obstructions in the workpiece design or workholding must be avoided. OD groove tools generally run best when the cutting tip is held slightly below center line.
ID grooving is similar to OD grooving, except that applying coolant and evacuating chips are more challenging. Here, best performance is achieved when the tool is run slightly above center line.
For successful face grooving, tools must be able to move in an axial direction and a clearance radius on the tool must match the radius being cut. Face grooving tools run best when held slightly above center line.
Machine design and condition are also fundamental considerations in any successful grooving operation. Some key machine characteristics required for success are: sufficient horsepower to run the tool at the correct speed range without stalling or shuddering; sufficient rigidity to perform demanding cuts without chatter; ample coolant pressure and flow to remove chips; and high accuracy. Additionally, proper machine alignment is critical to keeping grooves properly shaped and sized.
Familiarity with material properties such as tensile strength, work hardening characteristics and ductility are critical to understanding how the workpiece will respond to the cutting tool. Different materials require different combinations of speeds, feeds and cutting tool properties. Materials may also require special geometry for chip control or coatings to extend tool life.
Proper selection and application of the cutting tool will determine cost effectiveness. Grooving tools can generate workpiece geometry in two way: creating the entire groove form in a single plunge or using a series of plunges to rough the groove form to final size. After choosing a tool geometry, consider applying coatings that can improve chip evacuation.
Thinbit offers specialized tools for applications that call for cutting the entire groove form in a single plunge. The company’s Design-‘a-‘Groove series features multiple cutting edges that enable users to combine arcs, angles, chamfers, clearances and other geometries to match their specific requirements. Because the tools use inserts, which are available in 0.001-inch increments in widths ranging from 0.004 to .250 inch, individual sections of the form can be changed when worn. These custom geometries can simplify programming and allow users to run complicated parts on relatively simple machines. Specialized tools can also help hold form tolerances and decrease cycle times.
The company’s Groove ‘N Turn series is designed for using a series of plunges to rough out the groove form. After roughing, users can finish the groove and add features such as radii and chamfers. Groove ‘N Turn inserts range in width from 0.004 to 0.150 inch in 0.001-inch increments.
Form tools should be considered for high volume for high-volume workpieces. By generating all or most of the geometry in a single plunge, form tools can free up tool positions and reduce cycle times. Form tools are available in blocks created by an EDM or as a grouping of inserts. A disadvantage of non-insert form tools is that if one tooth breaks or wears more quickly than the others, the entire tool must be replaced. Thinbit offers an insert style of form tool that allows the user to change individual components of the form. An important consideration is controlling the chips the tool will generate and the horsepower required to cut the form.
Multi-function tools like Thinbit’s Groove ‘n Turn allow users to generate tool paths in both the axial and radial directions. This allows the tool to not only produce a groove, but also turn a diameter, interpolate a radius and produce an angle. The Groove ‘n Turn is also capable of multi-directional turning. That is, once the insert is engaged in the cut, it can travel axially from one end of the part to the other while maintaining constant contact with the work piece. Overall, this will result in more time spent producing chips instead of changing tools or cutting air. It also can help reduce overall part processing by enabling a machining center with a limited number of open toolchanger positions to perform more operations.
Proper planning the best order of operations requires consideration of elements like material strength both before the groove is produced and after, as the part may not be strong enough for proper feature generation after initial grooves are machined. This can prompt operators to run following tools to run at less-than-optimal feeds and speeds to decrease chatter. But running slower can result in increased cycle time, reduced tool life and erratic cutting performance.
Another consideration in choosing the best order of operations is whether a following operation will push a burr into an existing groove. Sometimes it’s best to leave this feature for last. Conversely, if the groove is wide relative to the diameter, it might be necessary to produce the groove first. Burrs that are generated inside a groove from operations following are difficult to remove and add extra work to the part. As a general rule of thumb, consider working from the point furthest from the collet first and producing grooves and other features after completing OD and ID turning is complete.
Feeds and speeds play a critical role in groove creation. Incorrect feeds and speeds can result in chatter, reduced tool life and poor cycle times. Factors affecting feeds and speeds include the workpiece material, cutting tool geometry, coolant type and concentration, insert coatings and machine capabilities. Secondary operations are often needed to correct issues resulting from incorrect feeds and speeds. While many sources may cite “the best” feed and speed information for a variety of tools, the most current and relevant information is generally obtained from the tooling manufacturer, like Thinbit. Many manufacturers employ a staff of technical support personnel that are intimately familiar with the tool’s capabilities and limitations. While any recommendation will require fine tuning to get the most out of an operation, the manufacturer is the best bet to get it right the first time.
Coatings provide significant improvements in carbide insert life. Cycle times and surface finishes are also improved because the coating provides a layer of lubricity between the cutting tool and the chip. Some common coatings in use today are TiAlN, TiN and TiCN. New coating combinations and variations are developed and introduced to the market regularly. For best performance, coatings must be matched to the material being machined.
Proper application of cutting fluid means getting ample supply of it to the cutting tip of the grooving insert and workpiece. Cutting fluid plays a dual role—keeping things cool during cutting and helping evacuate chips from the cut. Increased pressure at the cutting tip is effective at removing chips from blind ID grooves. For difficult grooving applications involving ductile, stringy materials, having high-pressure coolant is a definite advantage.
Coolant concentrations of water-soluble-oil based coolants can also be an input to successful grooving of difficult materials. While typical coolant concentrations range from 3-5 percent, concentrations up to 30 percent can be tested to increase coolant lubricity and provide a layer of protection at the cutting tool tip.
About the author: Ken King is COO of Thinbit.
blog comments powered by Disqus