Heat management is important in any machining process – whether working with ceramics, carbides, steels, or any other type of material. With ceramic tooling in particular, a machine operator must take the higher melting point of ceramics into consideration. Ceramic tools need a certain amount of heat to operate but having too much or too little heat can lead to adverse consequences for both the part and tooling.
Improper heat management during machining has the potential to cause catastrophic failures. It’s necessary for machine operators to have the right knowledge to mitigate this when working with ceramic cutting tools. Heat management can make or break a machining application — so it’s critical to know how to control heat in these operations.
Heat Management with Ceramic Tools
Ceramic tools require a certain amount of heat in the “shear zone” – where the cutting tool meets the material being machined. The proper amount of heat in the shear zone softens the material, thus lowering the cutting forces so that the chip can be removed. Ceramic grades and materials have different melting points, so it’s important for a machinist to know what they’re working with in order to generate the right amount of heat.
“There is a balance of heat to go into the chip and the tool,” explains Denny Carpenter, senior sales engineer at Greenleaf Corporation. “Improper heat management often results in insert failure. Chipping, abrasion, flaking, fracturing, melt-down, catastrophic failure — all can happen quickly if the heat isn’t in the proper operating range for the material and insert.”
Each ceramic grade operates in different temperature zones, creating a wide range of operating temperatures for a machinist to work within. Some ceramic grades are very tough and require lower operating temperatures to create the shear zone. Those are often used in milling or interrupted turning operations where the heat is intermittent. Other grades have higher operating ranges required for the shear zone and are predominantly used for continuous smooth cuts or finishing passes.
Regardless of material or insert grade, an operator must manage the heat throughout the machining process by applying the proper speed and feed for the cutting tool based on the material and hardness. This will ensure that they create the right amount of heat to soften the material in the shear zone.
“The ideal speed and feed rate depends on the cutting tool and material. Some materials create heat much faster, making it more difficult to control and get into the chip,” says Carpenter. “Machine operators have to take the material, its properties, and the type of cutting tool into account.”
Why Heat Management is Important
If heat isn’t properly managed in a machining operation it can result in several issues for the tooling and part. Without the right amount of heat, the insert can lose its structural integrity.
If a machine operator doesn’t create enough heat in the operation it puts undo force on the top face of the insert, often causing top flaking. The insert can also fracture and chip if there isn’t enough heat for the material being machined, potentially leading to a catastrophic failure during the machining operation.
Too much heat can cause edge deformation, flank wear on an insert, or the edge of an insert to melt. With excessive heat, a tool or insert may fail and lose its ability to cut the material.
“Machinists have to plan how they’re going to deal with the heat that will be generated during an operation. If they open themselves up to premature tool failure, they’re likely going to end up scrapping the part,” Carpenter explains.
Heat management isn’t just about avoiding disaster, though. If a machine operator properly manages the heat, they can extend tool life and achieve better results in machining operations.
In addition to being important for the tool and insert, machinists also have to know how heat will affect the material being machined. This is dependent on several factors, such as type of machine, the amount of torque and rigidity, and how the part is positioned and held within the machine.
“Everything has to be accounted for, and machinists must figure out how to create the necessary amount of heat without creating too much,” Carpenter says. “It’s a balancing act: the process has to create the right amount of heat in the shear zone and then effectively carry away the majority of that heat with the chips.”
Effective Heat Management
Proper heat management has a lot of benefits in machining, so it’s critical for machinists to know how to control heat in different machining operations. To do this correctly when using ceramic tooling machine operators need to know the amount of heat needed for the material being cut, the grade of ceramic to use for the material and application, the geometry of the tool and insert needed, and the machine’s capabilities. All of this contributes to effective heat management in a machining operation.
Carpenter says the generalized rules for heat management when machining with ceramics are to have 80% of the heat generated in the shear zone carried away by the chip. That leaves only 10% of the heat going into the insert and/or cutting tool, and the remaining 10% into the machined part.
Machinists have to be careful with how much heat is going into the insert or part, because there can be negative effects if the heat isn’t controlled properly. So much so that a part’s structure can be affected when there’s improper heat management due to incorrect speed or feed rates. There will always be some heat going into a finished part, but a machine operator must effectively control the heat.
When turning with ceramics, coolant can often be used to alleviate heat in the finished part, and often helps with chip control as well. Pressure and placement of the coolant lines have an effect on the performance. Often, higher SFM is used to keep enough heat in the shear zone. However, coolant when milling with ceramics is very seldom recommended, due to thermal shock.
“There are methods to ensure a machinist is operating in the best temperature zone for their application,” Carpenter says. “They have to have the right depth of cut, edge prep on the insert itself, and feed rate to get it up into its operating range and then to stay there. All of this comes into play to help manage that heat and the proper range needed for the part and the insert grade being used.”
Several factors make up the controls a machinist has: lead angle of the insert, geometry of the insert, and an understanding of the operation being performed. Chip thinning can be used to advantage or can be a detriment if you don’t account for it. This is a major consideration for getting the proper level of heat into the chip.
Machining Confidently with Ceramics
Every tooling type has its own considerations and best practices when it comes to heat management. Ceramic tools are no different; machine operators just have to keep the higher melting point and other ceramic-specific properties in mind. It’s crucial to know how to work with this type of tool as more machine shops adopt ceramic tooling due to the product’s versatility and fast cutting speeds.
Due to its higher melting point, working with ceramic tooling is very different compared to carbide or steel. That material property allows machinists to run ceramic tools at higher speeds, effectively reducing machine runtime. However, it also opens up machinists to potential mistakes, such as not using enough heat in the operation.
To successfully work with ceramics and avoid mistakes, Carpenter recommends a machine operator start with the basics when machining with ceramic tools. Determine the material composition and actual hardness and make sure it has the properties necessary to create the required level of heat. Proper ceramic machining techniques are a must, as programming, approach, and methods of cut greatly affect the end result. Ramping, varying DOC, proper IPR, and a number of other techniques allow proper heat control in the operation and ensure success.
Carpenter also suggests reaching out to Greenleaf, given the company’s long history and extensive knowledge in machining with ceramic tools. “We’re trained with ceramic tooling and are very good at determining the proper speeds, feeds, and geometries that should be used in different materials and machining operations,” he says.
Greenleaf has a number of different products that can help avoid catastrophic failure from improper heat management, allowing machinists to stop the operation and identify the issue before ever scrapping a part. These include their whisker-reinforced ceramic inserts WG300, WG600, and WG700, as well as XSYTIN ceramics, to name a few. Explore their website to discover more of what Greenleaf has to offer. And to get an up-close look at tooling and other manufacturing products, learn more about attending the Manufacturing Technology Series of events.
Biography
Denny Carpenter, Greenleaf Corporation
Senior Sales and Service Engineer
Project Lead
Denny Carpenter has been with Greenleaf Corporation for 22 years, and currently works as a Senior Sales and Service Engineer and Project Lead. In addition to his tenure at Greenleaf, Carpenter has a total of 46 years of manufacturing experience. This experience includes positions as a tool maker and machinist, programmer, and a manufacturing engineer.
In his current position, Carpenter specializes is several different elements of tooling, including design, applications, appropriate tool and grade selection, and programming guidelines. He enjoys teaching and training people in methods and processes of manufacturing, with an emphasis on productivity and quality improvements.