When working with tougher materials, selecting the appropriate tool material becomes even more crucial. Inserts can be made of carbide, ceramic, or CBN; these are normally the three primary options.
Carbide inserts
Carbide inserts are able to cut through materials with a Rockwell hardness C scale (HRC) rating of up to 55, although the cutting speed has to be significantly decreased. Tool life is quite limited as well. Carbide inserts, on the other hand, are the least expensive to acquire out of the three options. These types of inserts are more durable and harder than carbide, and they come with cutting edges that are extremely precise and sharp. They even have more toughness than ultra-micro-grain carbide grades, as well as cutting edges that are sharper, and they have outstanding resistance to wear and thermal cracking.
Ceramic inserts
Ceramic inserts perform exceptionally well in the region of 50 to 55 HRC, when the cutting data is equivalent to that of CBN. These inserts allow for greater spindle speeds to be obtained; nevertheless, the cost is significantly more than that of carbide inserts. Ceramic inlays lead to increased levels of productivity. The high temperature hardness, heat resistance, and chemical stability are all superior across the board for each and every grade. In order to fulfil the requirements of its customers, Huana provides a wide selection of ceramic cutting tool materials, including those based on silicon nitride, alumina, and whisker, as well as a number of different geometries.
CBN inserts
When the hardness of the material is greater than 60 HRC, CBN inserts are the ideal option since they can be operated at the greatest spindle speed the lathe is capable of. In addition to having the highest price tag, this option can either have a single cutting edge or come as a multi-tip insert. Huana’s line of multipoint CBN inserts, which includes anything from two corners to eight corners, outperforms those of any other customer in every measurable aspect of performance, including tool life, polish, precision, and accuracy. Machining ferrous materials with a hardness up to 68 HRC may be accomplished with the use of CBN Inserts, and both mild and heavy interruption cuts can be made with these tools. All throughout India, our Solid CBN inserts are being put to good use for turning hard parts with or without interruption, such as gears, as well as cast-iron components like brake drums.
Ceramic Inserts VS Carbide Inserts VS CBN Inserts For Different Materials
The Benefits and Drawbacks of Each
Take into consideration all that was submitted. When the amount of time spent indexing and replacing inserts is taken into account, lower-priced carbide inserts that are capable of doing the job in terms of tolerance and surface polish may end up being more expensive. A true grasp of the tradeoffs including throughput, cycle time, and insert performance is required in order to achieve real productivity.
Milling a sintered titanium carbide gas turbine blade with coated carbide cutting inserts was effective in one example that involved a specific application and limited production volume. Just five to ten minutes of good cutting performance may be expected from the carbide cutting edge while operating at 120 sfm. While working with challenging materials and producing a high volume of parts, the acceptable insert life is commonly set between 15 and 30 minutes; however, when producing a low rate of parts, the short insert life and frequent tool changes are not serious limitations. In full production, however, a longer insert life becomes vital in order to reduce the amount of time spent changing tools and the amount of manpower required, as well as to maximize machine utilization and throughput. Carbide is a good material for the turbine blade for the time being, but if manufacture of the item is increased to a greater volume, the application may justify using CBN inserts, which are tougher but more expensive.
In the event that you find yourself in a situation in which you need to machine a tough material, you should think about contacting your cutting tool supplier. The manner in which other businesses have tackled the issue might provide suppliers with ideas for potential solutions. When there is a need for experimentation, the rigorous process of trial and error often begins with carbide inserts and then progresses on to cutters that are harder and more expensive. In many cases, the use of up-to-date insert geometries, rigorous toolholders, and optimized machining procedures allows for the use of ceramic inserts that are significantly less expensive. When it is time to progress beyond ceramic will depend on the application, but broad groups of materials all present similar machining issues.
- Nickel-based superalloys
Jet engine parts frequently contain nickel-based materials. Some of these parts are substantial and have a diameter ranging from 20 to 40 inches. Long cycle durations are the result of the size and the sluggish speeds (around 150 SFM). A single item may be machined over the course of several days. Ceramic inserts are a common choice in this market as a result of their ability to run up to six times quicker.
Several sub-types of ceramic inserts exist. These sorts come in a variety of colours and compositions and show to be more beneficial in various applications. When cutting hardened steel, cast iron, and nickel-based alloys, ceramics work superbly. Here are some suggestions for cutting certain materials.
- Hardened Steels
Harder steel alloys are being used in more applications. Steels hardened to 63 RC are now widely used in the die and mould business, although tool steels were originally thought to be hard at 45 RC. To prevent heat-treating deformation, mould manufacturers who formerly merely machined components before heat-treating now precision-machine completely hardened tool steels. When milling completely hardened alloys, the heat and pressure can produce plastic deformation in cutting inserts and quick insert failure.
Another widely used technique for turning hardened steel is the use of CBN inserts. CBN can process steel up to 70 HRC quicker than ceramic inserts. However, they cost four times as much as ceramic inserts. For turning hardened steel between 45 and 55 HRC, ceramic inserts provide a good compromise between cost and performance.
However, the severe brittleness features of the ceramic material are caused by its increased hardness. Therefore, ceramic inserts may shatter if the right instructions are not followed. On the other hand, by learning the right procedures, machine shops may drastically cut cycle time while still maintaining a secure process.
Three re-boring passes are necessary to obtain the requisite tolerance and finish on one especially difficult feature deep inside the component. Cutting edges made of cermet wore out in fewer than one pass due to the hard material and interrupted cutting. Given that a damaged edge may completely destroy a component, this was very concerning. Advanced fine-grain carbide inserts, on the other hand, endured six to nine cuts thanks to their strong physical vapour deposition (PVD) covering and precise cutting action. The tool manufacturer advised decreasing cutting speed from 300 sfm to 175 sfm while maintaining the same depth of cut in order to take use of the carbide inserts. At this slower speed, three passes in the bore took around 20 minutes with carbide inserts versus almost an hour with cermet cutters. More importantly, the increased edge security provided by the carbide inserts reduced the possibility that a broken edge would scrape an expensive workpiece.
The standard starting point for machining parameters to mill hardened steels with carbide inserts is 100 sfm. Test cuts can accelerate to speeds between 150 and 180 sfm. 0.003 to 0.004 inches per tooth on average are fed. Stronger edges are often provided by insert geometries with neutral or slightly negative rake than by positive-rake inserts. When cutting strong steels, round carbide inserts provide additional benefits. The profile offers a more durable tool without exposed sharp edges.
Think about toughened grades while selecting a carbide grade. They offer edge security against hardened steels’ high radial cutting forces and severe entrance and exit shock. Instead, specifically designed high-temperature grades can survive the heat produced by steels that have been hardened to 60 RC. High temperatures produced by milling tough steels can also be mitigated by shock-resistant carbide inserts with an aluminum oxide coating.
- Superalloys
Heat resistant superalloys (HRSAs) created for the aerospace sector are finding a wider range of uses in automotive, medical, semiconductor, and power generation. Superalloys are tough; certain titanium grades can be machined at 330 Brinell hardness. Cutting zone temperatures above 2,000°F weaken molecular bonds and generate a flow zone for chips in typical alloys. HRSAs, on the other hand, retain their hardness throughout the machining cycle due to their high heat resistance. Using ceramic inserts for HRSA reduces cutting time, which can result in considerable cost and time savings, which is crucial because machine delays can be costly in the component segment. In HRSA, ceramic inserts enable better metal removal rates and can attain speeds up to 20 to 30 times faster than standard carbide.
Superalloys are cut slowly due to their difficulties in machining. The cutting inserts used to manufacture HRSAs are determined by the material and the workpiece. Carbide inserts with positive rake geometry will successfully cut thin-walled HRSA material. Thick-walled components, on the other hand, may necessitate ceramic inserts with negative cutting-edge geometry to provide a more productive ploughing motion. While most tough materials prefer dry machining to maintain consistent edge temperatures, titanium requires coolant even at extremely low speeds.
Ceramic inserts require very high cutting speeds with reinforced geometries, and in order to operate, it must create an enormous amount of heat to plasticize the material, which is then displace by the tool. Because ceramics can have a detrimental impact on surface integrity and topography, they should not be utilised for machining close to the completed component shape; rather, they should be used for roughing operations.
Ceramic milling equipment will not operate if your chips are not orange or white. Making the decision to experiment with and deploy ceramic milling tools for HRSA applications is both thrilling and efficient. Machine stiffness, fixturing stability, gauge length, and suitable parameter selection are critical because to the higher wear resistance of the ceramic substrate.
- Metals Sintered
Powder metallurgy advancements are generating extra-hard sintered metals for a variety of uses. To attain hardness ranging from 53 to 60 RC, one producer created a powdered nickel composite alloy including tungsten or titanium carbide. The nickel-alloy matrix’s carbide particles can reach 90 RC. Coated carbide inserts suffer from fast flank wear when milling such materials, and their primary cutting edges wear flat. Microchatter is caused by extra-hard particles inside the microstructure, which increases insert wear. Carbide inserts can also shatter when shear pressure is applied when cutting hard stock.
CBN inserts make it possible to cut hard powder metals incorporating tungsten and titanium carbides in a productive manner. Microchatter can be overcome using advanced geometries. One user milling the powdered composite alloy discovered that an improved CBN insert outlasted the best carbide inserts by more than 2,000 times. A five-insert face machine operating at 200 sfm and 0.007 inch feed per edge finished hard stock test cuts 75 percent quicker than electrical discharge machining.
To make the greatest use of CBN, cutting parameters must be kept within a narrow range. When cutting sintered materials, speeds of up to 160 sfm and feed rates of 0.004 to 0.006 inch per tooth look sluggish, yet they are quite productive. Test cuts lasting 30 to 60 seconds are ideal for determining precise machining settings. Begin at moderate speeds and gradually increase until the cutting edges exhibit significant wear.
Difficult materials should normally be machined dry in order to keep cutting edges at a constant temperature. A circular cutter with double-negative geometry is most effective in most circumstances, and the depth of cut is normally limited to 0.04 to 0.08 inch. To meet the high shock loads during machining, machines and equipment must have maximum stiffness, minimal overhang, and maximum strength.
Conclusion
The longevity of inserts in proportion to removal rates is a significant requirement for their economical application, particularly with materials such as carbide, ceramic, and CBN. The latter is significantly more costly. As a result, comparing tool wear becomes crucial. In roughing, interrupted, and finishing cuts, the three materials exhibit significant variances in size and surface polish. It is critical to monitor the tool regardless of the type of insert utilized. If worn inserts are kept in service past their useful life, they may have a detrimental impact on the workpiece’s outer layer of material.
Contact HUANA to buy the insert that best meets your requirements.
