Choosing the right tool material is essential when machining tougher materials. There are generally three primary types of inserts available: carbide, ceramic, and CBN.

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Carbide Inserts

Carbide inserts can effectively cut materials with a Rockwell hardness C scale (HRC) rating of up to 55, although this requires a noticeable reduction in cutting speed. Tool life tends to be limited. Despite this, carbide inserts are the most affordable option among the three. These inserts are more durable and harder than regular carbide, featuring exceptionally precise and sharp cutting edges. They also show greater toughness than ultra-micro-grain carbide grades, along with remarkable wear and thermal cracking resistance.

Ceramic Inserts

Ceramic inserts perform superbly in the hardness range of 50 to 55 HRC, comparable to the cutting abilities of CBN. They enable higher spindle speeds but come at a significantly greater cost compared to carbide inserts. The high temperature hardness, heat resistance, and chemical stability of ceramic inserts are outstanding across all grades. Huana offers a diverse selection of ceramic cutting tool materials, which include compositions based on silicon nitride, alumina, and whisker geometries to suit customer requirements.

CBN Inserts

For materials exceeding 60 HRC, CBN inserts are the ideal choice as they can operate at the maximum spindle speed of the lathe. While they are the most expensive of the three options, they can be found in either single cutting edge or multi-tip configurations. Huana's versatile multipoint CBN inserts range from two to eight corners, significantly outperforming competitors in tool life, polish, precision, and accuracy. These inserts enable machining of ferrous materials up to 68 HRC, effectively handling both mild and heavy interruption cuts. Solid CBN inserts from Huana are used extensively across India for turning hard components like gears and cast-iron parts, such as brake drums.

Ceramic Inserts VS Carbide Inserts VS CBN Inserts For Different Materials

The Benefits and Drawbacks of Each

Considering all presented facts, lower-priced carbide inserts may end up being more costly when the time spent on indexing and replacing is factored in. Achieving true productivity requires a comprehensive understanding of the trade-offs between throughput, cycle time, and insert performance.

For instance, in a scenario involving a sintered titanium carbide gas turbine blade with coated carbide cutting inserts, effective performance could be achieved for merely five to ten minutes at 120 sfm. When producing high part volumes, acceptable insert life typically spans 15 to 30 minutes. However, when working with low part quantities, the short life and frequent tool changes become less critical. Yet, in full production contexts, extending insert life becomes crucial to minimize tool change time and manpower, optimizing machine efficiency and throughput. While carbide may suffice for turbine blade production in the short term, an increase in volumes could justify the use of tougher, albeit more expensive, CBN inserts.

If you are faced with the challenge of machining difficult materials, reaching out to your cutting tool supplier may provide insights gleaned from how others have tackled similar issues. Often, the journey begins with carbide inserts, gradually progressing towards harder and pricier cutters. It is worth noting that incorporating up-to-date insert geometries, robust toolholders, and optimized machining strategies can favorably utilize ceramic inserts, which can be more economical. The timing for transitioning beyond ceramic depends largely on the specific application, although many materials present comparable machining challenges.

1. Nickel-based superalloys

Parts for jet engines frequently use nickel-based materials, which may be substantial, measuring from 20 to 40 inches in diameter. Cycle durations tend to be long due to size and slow speeds (around 150 SFM), causing a single item to require machining over several days. Consequently, ceramic inserts are commonly preferred in this category as they can operate up to six times faster.

There are multiple sub-types of ceramic inserts, available in various colors and formulations, demonstrating diverse effectiveness in different applications. Ceramics excel when machining hardened steel, cast iron, and nickel-based alloys. Below are some recommendations for cutting specific materials.

2. Hardened Steels

Industries increasingly utilize harder steel alloys; steels hardened to 63 RC are now common in die and mold production. Previously, manufacturers machined components prior to heat treatment, but now precision machining of fully hardened tool steels is standard practice to prevent deformation. Milling completely hardened alloys can generate sufficient heat and pressure to cause plastic deformation in cutting inserts and rapid insert failure.

Generally, CBN inserts are widely used for turning hardened steel, capable of processing steel with hardness up to 70 HRC more efficiently than ceramic inserts. Nonetheless, CBN inserts come at a cost four times higher than ceramic alternatives. For steel hardness ranging between 45 and 55 HRC, ceramic inserts strike an excellent balance between cost and performance.

The high hardness of ceramic material leads to inherent brittleness, which can result in shattering if proper guidelines are not followed. However, through the learning of appropriate procedural techniques, machine shops can significantly enhance cycle time while maintaining a safe operation.

An example involved three re-boring passes to achieve necessary tolerance and finish on a particularly difficult component feature. Cermet cutting edges failed within just one pass due to material hardness and interrupted cutting. In comparison, advanced fine-grain carbide inserts managed six to nine cuts thanks to their robust physical vapor deposition (PVD) coating and precise cutting action. The tool manufacturer advised lowering cutting speeds from 300 sfm to 175 sfm, while sustaining depth of cut. At this reduced speed, it took around 20 minutes for carbide inserts to complete three passes in the bore, compared to nearly an hour with cermet cutters. The superior edge security provided by carbide inserts minimized the risk of disasters, such as broken edges damaging expensive workpieces.

The standard starting parameters for milling hardened steels using carbide inserts begin at about 100 sfm, with test cuts achievable at speeds between 150 and 180 sfm, generally feeding at approximately 0.003 to 0.004 inches per tooth. Insert geometries with neutral or slightly negative rake angles usually yield stronger edges than those with positive rake angles. When machining tough steels, round carbide inserts offer added durability without sharp edges.

Select carbide grades with enhanced toughness, as these offer superior edge security against the high radial cutting forces encountered with hardened steels and substantial entry/exit shocks. Specifically engineered high-temperature grades are capable of enduring heat generated by steels hardened to 60 RC. Shock-resistant carbide inserts featuring aluminum oxide coatings can also mitigate heat consequences while milling tough steels.

3. Superalloys

Heat Resistant Superalloys (HRSAs) designed for aerospace applications are finding broader uses in sectors such as automotive, medical, semiconductor, and power generation industries. Superalloys possess considerable toughness; certain titanium grades can be machined at a Brinell hardness of 330. Cutting zone temperatures exceeding 2,000°F can weaken molecular bonds, forming a flow zone for chips in conventional alloys. Conversely, HRSAs maintain their hardness throughout the machining cycle, thanks to their high heat resistance. The application of ceramic inserts for HRSA machining can dramatically reduce cutting time, leading to substantial cost and time savings; thus, this is a critical consideration for component manufacturing where machine delays can be exceptionally costly. Ceramic inserts facilitate enhanced metal removal rates, achieving speeds 20 to 30 times faster than typical carbide.

Machining superalloys can be challenging due to inherent difficulties. The choice of cutting inserts for HRSAs is predominantly dictated by the material and workpiece. Carbide inserts featuring positive rake geometry successfully cut thin-walled HRSA materials, while thicker components may benefit from ceramic inserts with negative cutting-edge geometry, yielding more effective ploughing action. Predominantly, toughened materials favor dry machining to maintain consistent edge temperatures, yet titanium may necessitate coolant even at reduced speeds.

Ceramic inserts operate best at high cutting speeds with reinforced geometries, generating considerable heat that helps plasticize the material, which the tool displaces during machining. Since using ceramics can adversely affect surface integrity, they are typically not suited for machining close to the finished component shape and are more appropriate for roughing operations.

For optimal performance, it is essential that ceramic milling tools effectively produce orange or white chips. Experimenting with and employing ceramic milling tools aimed at HRSA applications can be both exhilarating and productive. Machine stiffness, fixture stability, gauge length, and appropriate parameter selection play pivotal roles in utilizing the high wear resistance of ceramic substrates.

4. Metals Sintered

Advancements in powder metallurgy yield extra-hard sintered metals for diverse applications. One producer has developed a powdered nickel composite alloy featuring tungsten or titanium carbide, achieving hardness levels between 53 to 60 RC. The carbide particles embedded in the nickel-alloy matrix can attain hardness of 90 RC. When milling such materials, coated carbide inserts are susceptible to rapid flank wear, leading to flat cutting edges. Henceforth, microchatter arises from the presence of hard particles within the microstructure, amplifying insert wear. Under shear pressure, carbide inserts can also shatter when slicing through hard stock.

Conversely, effective machining of hard powders incorporating tungsten and titanium carbides is attainable with CBN inserts. Enhanced geometries help mitigate microchatter. In fact, one user reported that utilizing an improved CBN insert surpassed the performance of top carbide inserts by over 2,000 times while milling powdered composite alloy. Operating a five-insert face machine at 200 sfm and 0.007 inch feed per edge, test cuts of hard stock were completed at 75 percent faster rates than electrical discharge machining.

To maximize CBN efficiency, it is vital to maintain cutting parameters within a narrow range. When tackling sintered materials, achieving speeds up to 160 sfm and feed rates between 0.004 to 0.006 inch per tooth might seem sluggish, yet are quite productive. Test cuts of 30 to 60 seconds are ideal for determining precise machining settings. Initiating at moderate speeds and gradually increasing until significant edge wear occurs is advisable.

For optimal results, difficult materials should generally be machined dry to ensure consistent cutting-edge temperatures. Typically, a circular cutter with double-negative geometry yields the best outcomes, with depth of cut limited to 0.04 to 0.08 inch. Given the high shock loads during machining, machines and tooling must exhibit maximum stiffness, minimal overhang, and robust strength.

Conclusion

The longevity of inserts relative to removal rates is crucial for their effective application, particularly with carbide, ceramic, and CBN materials, the latter being most costly. Consequently, comparing tool wear becomes essential. Significant differences in size and surface polish emerge among the three materials in roughing, interrupted cuts, and finishing processes. Regardless of the type of insert employed, monitoring the tool remains vital. Continuously using worn inserts past their effective life can adversely affect the workpiece's outer material layer.

For inquiries regarding the insertion products that best suit your needs, contact HUANA.

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Composition:

Carbide Inserts are mainly made from tungsten carbide, a hard compound formed from tungsten and carbon atoms. Known for its remarkable hardness and wear resistance, tungsten carbide is an excellent choice for cutting tools. To enhance its characteristics, tungsten carbide is often combined with a binder material, usually cobalt. The cobalt binder improves toughness and strength, making carbide more resistant to chipping and fracturing during machining operations.

Ceramic Inserts, alternatively, comprise various ceramic materials. Common ceramic materials used include alumina (aluminum oxide) and silicon nitride. These ceramics offer excellent hardness and thermal stability. To improve their properties further, ceramic inserts are typically reinforced with materials such as silicon carbide or whiskers, enhancing toughness and fracture resistance.

Properties:

Carbide Inserts are celebrated for their hardness, wear resistance, and toughness. One of the hardest materials used in machining, tungsten carbide enables inserts to maintain a sharp cutting edge for extended periods. Their exceptional wear resistance ensures longer tool life, leading to fewer frequent tool changes. Additionally, carbide inserts exhibit toughness, allowing them to endure high cutting forces with reduced chipping or fracturing during machining operations.

Ceramic Inserts exhibit extraordinary hardness, high-temperature tolerance, and chemical stability. Harder than carbides, they handle higher cutting speeds and boast superior wear resistance. These inserts feature notable thermal stability, allowing them to function in high-temperature cutting situations without compromising their cutting edge. However, ceramics are generally more brittle than carbides, making them susceptible to chipping under specific conditions. Proper handling and precise machining parameters are crucial to avoid damage.

Applications:

Carbide Inserts are broadly utilized in numerous machining operations, including turning, milling, drilling, and threading. They excel at cutting hard materials like steels, stainless steels, cast iron, and many non-ferrous metals. Carbide is preferred for high-speed machining due to excellent heat resistance, allowing for maintenance of cutting edges at raised temperatures. They are also suitable for heavy-duty tasks involving significant cutting forces.

Ceramic Inserts excel in specialized machining processes requiring high-speed cutting, high-temperature resistance, or machining of hard-to-process materials. Industries such as aerospace, automotive, and die/mold manufacturing frequently employ them. Ceramic inserts perform efficiently with superalloys, hardened steels, and other heat-resistant materials that would wear down carbide inserts rapidly. However, due to brittleness, ceramic inserts may struggle with softer materials and necessitate adjustments to machining parameters to avoid damage.

Summary:

Carbide inserts offer a balance of hardness, toughness, and wear resistance, making them versatile for a wide array of machining applications. They are capable of cutting various materials while ensuring excellent tool life. In contrast, ceramic inserts provide extraordinary hardness, high-temperature resistance, and chemical stability, thriving particularly in high-speed and high-temperature scenarios with hard materials. However, their brittleness requires careful handling and consideration of specific machining parameters. Ultimately, the decision between carbide and ceramic inserts should depend on the distinct machining needs and materials being processed.

In addition to ceramic and carbide inserts, we also offer cermet and CBN options for your consideration. Contact us now for further information.

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