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Walter USA has introduced indexable inserts with brazed polycrystalline diamond (PCD) cutting edges for the Xtra·tec XT M5130 shoulder milling cutter and most M4000 gravity turning inserts milling cutters, including the M4003 face milling cutter.

The PCD inserts are suitable for milling a variety of nonferrous workpiece materials, including aluminum, aluminum-silicon alloys, magnesium, magnesium-based alloys, plastics and fiber-reinforced plastics. Applications include automotive, aerospace and general mechanical engineering. Aviation in particular uses wrought alloys made of aluminum.

According to Walter, the new PCD inserts impart the finest surface finishes while shoulder, face and slot milling. The tools enable precise machining with reduced cutting forces and minimal vibration tendencies. In addition, the PCD inserts provide the shortest machining times due to their ability to mill at high cutting speeds. The inserts can be used dry, with emulsion of minimum quantity lubrication (MQL).

The surface milling cutters BCGT090304R-B85 WDN20 and BCGT120408R-B85 WDN20 positive rhombic inserts have one PCD cutting edge per insert and are for the Xtra·tec XT M5130 shoulder milling cutter.

The SDGW09T304-A88 WDN20 and SDGW120408-A88 WDN20 positive-square inserts are equipped with a single-edge PCD cutting edge. These system inserts with corner radius are for most M4000 milling cutters. The SDGW09T3AZR-A88 WDN20 positive-square insert uses a single full-edge PCD cutting edge, and in some applications two corners may be used. It is designed specifically for the M4003 face milling cutter from the M4000 series.

Machining of composites may look like machining metal, but that appearance is deceiving.fast feed milling inserts

Parts made of a composite material such as the carbon fiber reinforced plastic (CFRP) increasingly being used for aircraft components can be set up and run on the same machine tools as metal parts. The CFRP might even be machined with similar cutting tools as the metal parts, though this is less likely. As soon as the cutting edge hits the workpiece, however, machining composites is revealed to be fundamentally different. The very mechanism of material removal is different.

In metal cutting, that mechanism is plastic deformation. The material is softer than the tool, and the chip flows over the cutting edge.

But in machining of composites—the focus here will be CFRP—there is no chip to speak of. Instead, the material removal mechanism might be better described as shattering. Rather than shearing material Carbide Milling Inserts away, the impact of the cutting edge fractures the hard carbon fibers. In the process, the cutting edge undergoes considerable abrasion that can lead to rapid wear.

In any cutting tool application, tool geometry drives cutting performance and tool material drives life. This is true of composites machining as well. However, in composites, tool material also becomes a driver of performance. Composites can cause the tool to wear so rapidly that the geometry can change rapidly as well—unless the edge material can withstand the abrasion well enough to hold its geometry and stay sharp. A common phenomenon in machining composites is the drill that can machine two holes with good exit-side characteristics but shows delamination, splintering or other breakout defects as quickly as the third hole, simply because tool wear has produced a geometry that no longer cuts cleanly.

In a way, machining composites actually turns the machining process upside down, because the burden of the shop’s attention shifts to different parts of the process. An aircraft part machined out of metal might involve a high-power machine tool that relies on just commodity tooling and simple clamps to secure the work. By contrast, milling and drilling of composites can generally be done with a much lighter-duty machine. However, high-end cutting tools are likely to be required, as well as custom-built workholding that closely supports the part throughout the machining process to prevent its thin, rigid walls from vibrating and fraying.

Here is a summary of some of what a CFRP machining process is likely to require:

Carbide can work, though carbide tools machining composites often have to be changed frequently.

Diamond tooling is likely to last much longer. The choices in diamond tooling for CFRP include diamond grit plated onto a mandrel, diamond coating applied through chemical vapor deposition, or solid inserts made from polycrystalline diamond (PCD).

A more unusual choice developed specifically for composites machining is “veined” diamond tooling, in which a vein of diamond fills an engineered slot in a carbide shank.

The shattering of composites is like the deformation of metal in at least one way: Just as in metal cutting, the energy of the cut is still transformed into heat.

CFRP has a particularly hard time dissipating this heat. No chip is generated to carry the heat away, and the material has low thermal conductivity. The resulting heat buildup poses the danger of melting or otherwise damaging the matrix. Coolant might not help, because coolant might not be allowed in the machining of certain composite parts. Therefore, the tool and the tool path are all that remain to hold down the heat of machining.

Sharp angles are generally one of the keys to accomplishing this. Milling and drilling tools for composites feature high positive rake angles for a quick, sharp, clean cut that keeps heat to a minimum. Such tools also incorporate clearance angles that are sufficient to prevent the edge of the tool from rubbing as it passes.

Though the machining operations required for composite parts may be simple—often just drilling and trimming—the fixtures designed to support these parts can be small feats of engineering themselves.

In fact, the fixture for machining a composite part can represent a considerable engineering investment. Clean cutting, without fraying, delaminating or otherwise separating the layers, requires the part to be secured firmly against vibration. Vacuum fixtures form-fitted to the part are typical of composites machining. Shops that opt for mechanical clamping often employ pads to damp vibration.

The contoured shapes of composite aircraft parts generally demand a five-axis machine tool. Some shops machining metal parts may use the five-axis machine tools they already have in-house. However, the amount of power and torque required for hogging metal usually is not needed for composites, at least not for CFRP. In fact, CFRP and other composites are often machined efficiently on lighter-duty CNC routers that generally would never see a metal part.

To learn more about the considerations specifically related to milling composites, read Part 3: Milling Composites.

1.Processing characteristics of gray iron

Gray cast iron has the characteristics of brittleness and low tensile strength (cast iron structure can be regarded as iron-carbon alloy structure filled with graphite pores. The presence of flake graphite reduces the ductility and toughness of cast iron) and is a typical brittle material.

The graphite cavity structure of flake graphite in gray cast iron is easy to form cracks with sharp edges. During cutting, under the action of the cutting force of the tool, the crack develops along the direction of minimum resistance, resulting in chipping and fracture of the chip. Therefore, the gray cast iron forms breakable chipping chips during the cutting process. At the same time, the tool is in the intermittent cutting working state during the processing of the gray cast iron. When the graphite in the base body is cut, the tool is in the idle state, and the metal is cut. In the case of the base body, the cutting action of the tool occurs, and the tool continuously cuts into and cuts out, causing the high-frequency pulling and compressive stress cycles of the tool near the cutting edge. The alternating load causes the surface layer of the tool to fatigue and causes gravity turning inserts slight chipping at the cutting edge, reducing The cutting performance of the tool.

During the cutting process, the cut gray cast iron structure frequently breaks irregularly, causing an unstable change in the cutting force and a large impact on the cutting edge. When the gray cast iron is cut, typical chipping chips are generated. The deformation coefficient of the chip is small, and the contact length of the chip is extremely short, so that the cutting force and the cutting heat are concentrated in a small area of the cutting edge, and the tool has thermal shock wear.

The chipping debris and the falling carbide hard spots generated by the cutter when cutting gray cast iron often cause the surface of the workpiece and the back blade to grind, resulting in wear of the flank VB abrasive; the cutting temperature is bar peeling inserts obviously increased once the flank face is worn, The fine chipping and chipping easily enters the chipping interface. Under high temperature and high pressure, the iron element in the chip and the surface of the tool and the tool surface form an infinite replacement solid solution, resulting in diffusion wear, while the chip softens and adheres to the tool surface. The wear surface forms a uniform layer of adhesion resulting in bond wear. Once the edge of the cutting tool wears or chipping, the cutting force is sharply increased, the surface quality of the workpiece has been significantly reduced, and the edge is prone to breakage or collapse, which is easy to collapse;

2.The effect of main cutting angles

The 90 degrees of the main cutting angles will radially introduce the feed force into the thinner part of the workpiece material;

45 degrees of  main cutting angles will direct the force to the material supported by the wider base;

Gaps and burrs occur when the feed force exceeds the material strength. Brittle materials such as cast iron tend to have gaps, while more tough workpiece materials tend to have burrs. More tough workpiece materials often have burrs. It directs the feed force to the tougher part of the workpiece material. This reduces or eliminates the formation of workpiece nicks or burrs.

3.Effect of different cutting edge grooves

The use of a sharp grooved blade can effectively reduce the cutting force and reduce the occurrence of chipping. At this time, fz is limited by the average chip thickness of the blade. Try to choose a blade type with good strength but sharp edge (cutting light groove shape, large front angle, sharp but strong strength blade type (smaller blade width T), during roughing, if in working condition When it is not stable, when the large fz (more than 0.2) is used, the phenomenon of chipping will be aggravated, especially when the tool cuts in and cuts out the workpiece. After the blade wears more than 0.3, this phenomenon is also the same. Will increase.

4.The effect of different materials

Physical vapor deposition (PVD), coating applications are thinner and suitable for relatively sharp cutting edges. The coating increases lubricity and helps reduce the cutting forces generated between the tool and the workpiece, making the cutting relatively light. Especially for the edge collapse phenomenon during finishing, there will be a great improvement.

5.Other factors In the current machining market, for the processing of cast iron materials, from the actual processing results, the tool life of ductile iron materials (mainly burrs) (below QT450) is better than that of gray iron (mainly workpiece chipping). Workpiece chipping and burrs lead to a large factor in tool change. In addition to the 45 degrees lead angle we often use, the sharp-groove type of blade is used, which is relatively small for each tooth. It also strengthens the clamping rigidity of the workpiece itself (adding auxiliary support to weak parts), and can also change the position of the tool and so on.

Streamliner lathe toolholders feature coolant delivery through the shank and are said to be suited for low- or high-pressure delivery. To conserve coolant, the toolholders are equipped with interchangeable coolant-distribution plates for various volumes of air, mist or liquid. The coolant delivery is parallel to the top of the insert, which enables the coolant to have a positive effect at the shear zone. The close proximity of the coolant orifice to the insert’s cutting edge prevents the coolant stream from collecting air and VCMT Insert spreading apart. The resulting higher Tungsten Carbide Inserts density helps quench the chip faster to produce a tight curl and offer good chip control, the company says. In addition, the dense stream is said to reduce the amount of coolant evaporation compared to flood coolant delivery. The toolholder is available in 1" and 25-mm square shanks in right- and left-handed versions.

Avoid skimping on the diamonds in composite drilling applications, and you can avoid leaving your parts literally in the rough. That’s the idea behind the CX1, a drill from Seco Tools that employs a dome-shaped, solid polycrystalline Tungsten Steel Inserts diamond (PCD) tip to avoid the fraying and delamination problems common to PCD vein or dual-brazed tip designs. The tool also features a third drill flute that is said to improve stability compared to traditional twin-flute designs. Other benefits include high cutting speeds, long tool life, low friction, improved heat transfer, capability for multiple re-sharpenings and reliability.

The primary advantage of a solid PCD tip is edge sharpness, the company says. This is critical in composite applications because the thin fibers that constitute the material are difficult to cut. Failing to shear cleanly through these fibers can result in material fray and premature part replacement. Further, additional stress on the material created by insufficiently sharp cutting edges can reduce mechanical toughness through delamination. Such problems are more likely with coated PCD than a solid PCD tip because wrapping the coating around the cutting edges can create a dulling effect.

Compared to twin-flute, coated PCD drills, the CX1’s third flute reduces vibration and improves both stability and roundness in “plain” composite materials, the company says. Furthermore, the CX1’s dome-shaped tip features a double-angle geometry that is said to reduce uncut fibers and delamination in composite-only applications. Grinding this geometry would be impossible with tools that make use of brazing or similar PCD techniques, the company says. Plus, the dome cap also makes it possible for the drill point to be reconditioned.

The solid PCD dome tip also offers superior thermal conductivity, the company says. This results in enhanced product stability and higher cutting speeds. This thermal conductivity advantage is particularly important for composite materials that melt fast. Given that composite machining operations rarely employ coolant, it is important to transfer the heat away from the cutting area as quickly as possible.

Although solid PCD-tipped drills are more expensive than PCD-coated drills at the front end, the overall return on investment can be substantial when drilling a large number of holes. According to the company, the CX1 geometry can effectively drill two to three times more holes than a PCD-coated drill, essentially spreading VNMG Insert out the costs.

The company adds that investing in solid diamond-tipped drills also makes sense when hole quality is of the utmost importance. Delamination is becoming more of a safety concern for aerospace industry work because of the increasing use of composite materials, particularly in components that constitute the tail sections of airplanes.

The CX1 series includes a mix of dimensions for holes ranging from 0.125 to 0.375 inch in diameter. Chamfers can be incorporated into drill designs for further application flexibility. The company also offers special PCD geometries.

Although Horn initially built its reputation on grooving and part-off technology, pigeonholing the tooling manufacturer as a specialist in those areas alone would be a huge disservice to the company and any potential customers. Moreover, a broader product line isn’t the only factor in Horn’s becoming a bigger contender during the past few decades. The company itself has grown steadily as well, a trend that management expects to continue throughout 2013 and beyond. 

These were two major takeaways from “Technology Days,” a biennial event at the company’s headquarters in picturesque Tubingen, Germany. Along with more than 2,000 customers and dealers from around the world—a reportedly CCMT Insert larger crowd than in previous years—press members including me and Chris Koepfer, editor-and-chief of MMS sister publication Production Machining, enjoyed a busy three days of demonstrations, tours and technical presentations.

Although Horn’s grooving expertise was evident from the get-go, demos and placards also showcased products that ran the gamut from milling and turning to broaching, reaming and thread-whirling. Notably, not all of these offerings were selections from the company’s 20,000-strong line of standard tools. Many were custom-designed models—which represent more than 50 percent of the company’s total annual turnover. The merits of custom tooling was also the topic of a particularly interesting technical presentation, while others focused on high-feed-rate machining, cutting with ultra-hard diamond and CBN materials, and performing broaching on CNC machines. (Watch for in-depth coverage of these topics in upcoming issues of both MMS and PM.)

In the United States, standard and custom tools alike are manufactured at Horn USA’s facility in Franklin, Tennessee. The U.S. market’s strength and growth potential has spurred plans to more than double the size of that facility beginning this year.  The overall company is growing, too. With annual turnover expected to rise by € 5 million this year over the € 220 million reported in 2012, the company is constructing a new building at the Tubingen campus for additional capacity. That project is slated for completion in 2015.

These expansions follow close on the heels of the 2012 completion of another new facility in Tubingen: a 16,000-square-meter factory for Horn Hartstoffe, the company’s carbide manufacturing operation. Here, powdered carbide mixes are shaped into “green” inserts via three different processes: axial pressing, and, perhaps more notably, extrusion and injection molding. This aspect of Horn’s manufacturing process, as well as the custom machines it uses to grind inserts after sintering, CNC Carbide Inserts were among the most fascinating aspects of my trip. Click here for a brief virtual tour.  

While visiting CNC-using companies, I often witness practices that negatively impact productivity. I find it troubling that these practices are so common, despite the fact that Carbide Inserts they are simple to identify, diagnose and correct.

Making CNC operators share needed items. One company that I recently visited has a machining department that consists of six CNC machining centers spaced about 30 feet apart from each other. The machines use magnetic tables to clamp workpieces. It is imperative that these tables, and anything clamped on them, be perfectly flat and free of burrs. To this end, CNC operators use a relatively inexpensive circular sharpening stone to remove any burrs and ensure that the clamping surfaces (both on the workpieces and the magnetic tables) are flat. 

The sharpening stone is required every time a workpiece is loaded on a machine, yet the operators were sharing a single stone among all six machines. This meant that before an operator could load a workpiece, he had to find the stone and retrieve it. Each operator usually waited until he needed the stone to find it, and his machine sat idle until the stone was found.

This is but one example of how sharing items can reduce productivity. Others examples of items that workers routinely are required to share include vise handles and other hand tools,  perishable tooling (like inserts), gages, and workholding components. Obviously, productivity suffers if machines sit idle while workers locate needed items. The simple  and often inexpensive solution is to purchase multiples of these items and keep them at the machines/locations where they are needed.

Allowing CNC people to wait until they need an item before they retrieve it. Though there are exceptions, CNC people usually have some downtime during which they are not immediately required to do something. A setup person may have all the machines set up and running production. A CNC operator may be running a job that has a lengthy machining cycle; once the workpiece is loaded and the cycle is activated, there is a long period of time during which that operator is not required to do anything.

There are usually many things that could be done during this time to prepare for upcoming jobs, however, such as gathering tooling components, preparing gages, assembling cutting tools and even loading programs using a feature called “background edit.” Do not allow CNC people to wait until it is time to begin a particular operation before performing the related preparation tasks, especially if this means that machines will sit idle while this preparation is being completed. 

Making CNC people figure things out for themselves. Many CNC setup people and operators are left on their own to determine how to run their CNCs. While they may have come up with workable methods, and their ingenuity is sometimes admirable, they may not be using your machines as appropriately as is possible. This is especially true if several operators are involved in running a machine, each performing a given task in a different manner.

Use setup and production run documentation to outline general tasks that must be performed. Then, provide more specific documentation (and the related training) to ensure that every worker performs each task in the manner in which you want. This detailed documentation can be kept in a binder close by the machine at which related tasks must be performed. 

This means, of course, that you must first know the method(s) that best suit your needs. If you are in doubt, solicit help from machine builders, tooling manufacturers and other related companies. Or bring your CNC people together to discuss and decide which method works best for any given task.

Assuming that parameters set by the machine builder are appropriate for your needs. Parameters control countless CNC functions, and many of them affect the way CNC cycles are run in general. Machine builders tend to set certain parameters assuming worst-case scenarios, but your applications may not fall into this category.

Consider parameters that are related to canned cycles. The FANUC high-speed peck-drilling cycle G73 (used for breaking chips as a hole is machined), for example, uses a parameter to determine how far the drill will retract between pecks. Usually, a value of 0.1 mm or 0.005 inch, depending on your measurement system choice, is appropriate. Yet some machine builders set this parameter to an excessive Cemented Carbide Insert value, possibly as much as 2.0 mm or 0.1 inch. If the peck depth is set to 0.1 inch (Q word in the canned cycle) and the retract amount is set to 0.1 inch (in the parameter), it will take the machine almost twice as long to drill each hole as it should.

Other examples of parameters that machine builders sometimes set to worst-case values include the clearance amount for a G83 deep-hole peck-drilling cycle, and the retract amount for G71 and G72 rough-turning in multiple repetitive cycles on a turning center. Truly, any time you see a noticeable pause or excessive non-cutting time, take it as a signal that a parameter may be inappropriately set.

Walter USA has expanded its solid-carbide micro drill line with the addition of the DB131 Supreme micro pilot drill sizes and extended the DB133 Supreme micro drill offering to deep drills up to 30 × DC. According to Walter, these new drills are designed to help achieve maximum process Carbide Milling Inserts reliability with minimal dimensional variations and extended tool life in steel, cast iron, nonferrous, super alloys, hard materials and other materials (ISO P, K, N, S, H and O). Stainless steel (ISO M) is added to the list with internal coolant capability.

The use of Walter grades WJ30EL and WJ30ER is said to ensure that the drills provide superior wear resistance. In addition, the optimal cutting-edge preparation on the drill provide excellent surface finishes.

A new type of flute design reliably evacuates chips, even with the tinniest drills. This capability ensures that hole depths up to 30 × DC can be easily achieved with the DB133 Supreme micro drill with its 140° point angle. The DB131 Supreme micro pilot drill features a 150° point angle. Emulsion, oil or minimum-quantity lubrication (MQL) can all be used as a coolant with these drills.

The new DB133 drills Carbide Drilling Inserts without internal coolant are available in a diameter range from 0.020-0.116". (0.5-2.95 mm). The diameter range for the micro drills with internal coolant is 0.028-0.116". (0.7-2.95 mm). Length to diameter ratios (L/D) of 5, 8, 12, 16, 20, 25 and 30 × Dc are standard for micro drills with internal coolant and 5 and 8 × DC without internal coolant. This new drill design is effective for applications in the medical, watchmaking, general mechanical engineering, mold and die making, energy and automotive industries.

Hole drilling is the most common operation performed on a vertical machining center. When this operation involves drilling deep holes, it becomes one of the most challenging. However, there are very effective ways to meet this challenge.

The goal is to produce these holes accurately, repeatably and with superior surface finish—and to do so economically.

The most important ingredient in successful deep-hole drilling is understanding. You have to understand what happens inside the hole as it is being drilled and how this knowledge guides your choice of the most effective techniques.

The Dynamics Of Deep-Hole Drilling

Strategies for deep-hole drilling address three primary issues: evacuating chips without damaging the surface finish, delivering coolant to keep the drill and workpiece material cool, and minimizing cycle time. Other important factors include accuracy, repeatability and surface finish.

Typically, a deep hole is defined by the ratio of the diameter to depth. Usually a ratio of 5:1 or greater is considered deep-hole drilling. For example, a 5-inch deep by 1-inch diameter hole is considered deep, as is a 0.125-inch diameter hole that is 1 inch deep.

Chips must be small enough to move up the tool’s flutes and out of the way. Long, stringy chips can damage surface finish and cause premature tool wear or breakage. Coolant has to get to the tool tip to keep the tool and workpiece cool, as well as force chips out of the hole. A rigid machine tool with good damping characteristics and low spindle runout is required to hit targets for accuracy, repeatability and surface finish. Of course, the right drill geometry will make deep-hole drilling operations much more efficient.

Some materials form very small chips that flow out through the flutes easily. Other materials form chips that are long and stringy. One approach to controlling chip size and shape is the use of special machining cycles. Deep-hole cycles and peck drilling cycles are used to break chips so that they are small enough to flow up through the flutes on the tool without causing damage to the surface or promoting premature tool wear.

Generally, there are two types of deep-hole cycles. One uses equal pecking depths to reach the final depth. The other uses variable pecking depths, wherein each peck is followed by pecks of successively shorter increments.

Most machine tool controls offer deep-hole drilling cycles, which feed the drill into the material a specified distance, pull the tool all the way out of the hole and then feed it back into the hole. With this kind of deep-hole cycle, chips may fall into the hole when the drill pulls out and flood coolant washes in. This condition is especially likely to occur when cutting steel. When the tool feeds in again, it will hit any chips at the bottom of the hole. Chips encountered by the tool start spinning, forcing the pressure of the tool to cut or melt its way through the chip. On a manual mill, the operator would feel the chip spinning and would stop drilling to blow out the hole and clear stray chips. However, these drill cycles can be programmed to stop just above the last peck to avoid this situation.

An example of a variable peck cycle is one starting with a 1.00-inch peck. The next peck would only go 0.50 inch deeper, followed by one 0.25 inch deeper, with the last peck going only 0.05 inch deeper than the previous peck. As the drill goes deeper into the hole, the decreasing peck depths help eliminate chip impaction around the tool. The deeper in the hole that the drill gets, the more difficult it is for coolant to get to it, so pecks are used both to evacuate chips and get more coolant to the tool tip.

The ability to write special cycles with the machine tool control enables routines to be captured and, as with a fixed cycle, executed automatically whenever a new position is written into the program. (Such a subroutine feature is found on the Fadal control unit, for example.)

Peck drilling, although not solely a deep hole cycle, is used to break chips by withdrawing the tool only a small distance after each peck, eliminating the problem of chips falling back into the hole. The length of the peck determines the chip length, eliminating chips that wind around the tool and are commonly called angel hair. These chips cause coolant to dribble down the hole only to be thrown off and out by the drill, thus allowing heat to build up in the drill and cause excessive tool wear. Ultimately, this condition can lead to catastrophic tool failure. The disadvantage of deep-hole and peck cycles is that they take longer to finish each hole. It takes time for the tool to feed down, rapid out of the hole, rapid back and feed down again. Multiply the time for a peck cycle by the number of holes to be drilled, and the delay adds up. Even if total time per hole is increased by just seconds, hole drilling efficiency is diminished. On long production runs, these inefficiencies can be a serious issue.

Strategies for avoiding problems during deep-hole drilling operations include different types of coolant delivery. Three types of coolant systems are common to VMCs: flood coolant, low-pressure through-spindle coolant and high-pressure through-spindle coolant. With flood coolant, less and less coolant reaches the tool tip the deeper the drill penetrates the workpiece. Eventually, no coolant can get to the bottom, and machining occurs dry. As a result, chips become impacted in the flutes of the tool even though coolant is visibly flowing over the top of the hole. In fact, the hole ends up being dry cut, while the tool heats up and is subjected to premature wear or breakage.

Heat from the drill may also work harden or “heat treat” the workpiece in the vicinity of the hole. Friction from the drill heats the workpiece, and when coolant finally reaches the heated material, the coolant quenches it. On the subsequent peck, the drill encounters the hardened material, causing excessive tool wear or a broken tool and damaged part.

The essence of successful deep-hole drilling requires a method of getting coolant down to the tip of the drill where it can remove heat and evacuate chips. Coolant-through-spindle systems provide the best solution. Several builders of VMCs offer this feature as an option. For example, Fadal offers a 350-psi Coolant-Thru Spindle system that delivers coolant through the tool tip. Such features are fairly inexpensive methods for getting coolant to the bottom of the hole. Systems that deliver coolant at high pressure, such as the Chip Blaster, which boosts coolant pressure to 1,000 psi, provide even better chip evacuation.

With low-pressure coolant-through-spindle systems, the programmer can safely increase the depth of pecks and in some cases completely eliminate pecking cycles altogether, saving production time. With high-pressure coolant-through-spindle systems, not only is pecking eliminated or reduced, but higher feed rates and spindle speeds also can be used. As a bonus, this system extends the life of the tool. High-pressure coolant-through-spindle systems provide the best scenario for decreasing cycle time and increasing tool life.

The high pressure of the coolant breaks up chips and forces them up the flutes and out of the hole. Cycle times go down, because the pecking process is eliminated while spindle speeds and feed rates can be increased. With higher feed rates, chips tend to form better.

Delivering coolant through the spindle also improves the production of through-holes. When coolant cannot reach the tip of the tool adequately, and as the drill approaches the breakthrough point, material at the edge of the hole becomes thin and hot before being pushed away from the tool. With coolant delivered at the tool tip, heat is less likely to build up in the material as it thins, allowing it to be cut and not pushed away. A clean edge forms around the bottom of the hole. This condition makes the hole easier to deburr.

Drill geometry is a key factor in successful deep-hole drilling. Flute size and spacing affects chip evacuation, for example. Drills with open flutes enable chips to flow up and out of the hole more easily, especially with coolant-through-spindle systems. But without good coolant flow at the bottom of a hole, even open flute designs are subject to chip clogging and drill breakage.

Today’s technology enables toolmakers to design tools for drilling with features that better facilitate chip evacuation and minimize overheating. Made of higher-grade carbide steel for longer life, these tools feature new shapes, which assist deep-hole drilling operations. Because the tools are stiffer, they are less likely to wander in deep-hole drilling operations.

Some carbide tools are now available with coolant holes through their length for high speed machining. Although these tools get more coolant to the tip, they can be very expensive. Some of these new tools require high coolant pressure, high spindle speed and high horsepower to be effective. If the machine tool lacks these features, then investing in these tools is wasteful.

Standard tools for drilling feature a wide web at the tip. Some drill designs modify this web by splitting it and making it thinner. Further changes in the geometry of the tip may also occur. These special drill geometries, such as those produced on Winslow drill sharpening machines, improve deep-hole drilling. These drill points allow deeper holes to be made, plus they improve finish, straightness, accuracy, tool life and production rates.

Also, special coatings are sometimes utilized on the edge of the tool to minimize frictional heating. Coatings help form better chips and get them up and out of the hole more quickly. The increased cost of these coatings is justified by extended tool life.

Machine tool rigidity has a major impact on deep-hole drilling because the less stable the foundation of the machine, the more vibration the head and table will generate, causing the tool to break down. For deep-hole drilling, features to look for include castings with uniformly thick walls to avoid heat distortion, box ways with a large surface contact area, a very strong head and a column that does not flex. A low-vibration spindle is also required.

Lack of stiffness in the machine tool causes the column to bend when pressure is put on the head from deep-hole drilling operations. As a result, the drill may bend, decreasing accuracy and causing tool wear, eventually leading to a broken tool. With excessive pressure on the head, the drill enters at an angle and will miss the correct position.

Other features are also helpful. For example, a system for maintaining spindle speed as the load increases assures a constant chip load on the drill. If the spindle speed decreases during a cut due to tool load, the chip load will increase and risk breaking the tool. The spindle vector drive system on Fadal VMCs provides this function. Another Carbide Inserts feature found on these VMCs is dual spindle motor windings, providing low range speeds as high as 2,500 rpm and high range speeds of 2,500 to 10,000 rpm. This feature expands the capabilities of the vector drive spindle motor by doubling horsepower at high spindle speeds. Also useful in deep-hole drilling is Tool Load Compensation, enabling the programmer to designate a tool load that dynamically regulates the feed rate as cutting conditions vary.

Coolant through the spindle, drill tip geometry, carbide tooling, coatings and cycle selection are important factors when drilling deep holes. Each of these factors affects hole finish, integrity, production time, tool life and the burr at the bottom of the hole. The best scenario in deep-hole drilling is to use high-pressure coolant, a tool with open flutes, carbide tools CCMT Insert with a coating and a single peck to create the hole.

While most of us have to make do with the tools at hand, a wide choice of drills, features and machine tools is available. For any given job, there are multiple strategies, so knowing how different materials, drills, features and machine tools react in different situations will determine how well machining objectives can be achieved.

About the author: Daniel de Caussin has been with Fadal Machining Centers (Chatsworth, California) for 25 years, directing the applications, documentation, and training departments.

The SG Blaze Rapid Strip is a non-woven, depressed-center stripping and light-stock-removal disc from Norton, a brand of Saint-Gobain. The disc combines SG ceramic alumina grain and an open mesh structure to increase cutting speed and disc life. This open-structure design enables aggressive cutting on metal surfaces as well as the elimination of loading on sticky coatings, adhesives and soft metals. It also PVD Coated Insert will not snag or shed when used to deburr edges, the company says.

The discs can be used for removal of scale, corrosion or rust on cast iron, steels, aluminum, fiberglass and composites. WNMG Insert They also can be used for cleanup of flashings, epoxies and graffiti from metal, stone and concrete surfaces. Applying heavier pressure to the discs will strip and clean materials, while applying lighter pressure will provide a finish similar to a medium-grit fiber or flap disc, the company says.

The discs are available in sizes measuring 4.5", 5" and 7", and they feature a Type 27/fiberglass backing.