As Director of Technology and Industry Research for PMPA, Miles brings 38 years of hands-on experience in areas of manufacturing, quality and steelmaking. He helps answer "HOW?","WITH WHAT?" and "REALLY?"
Tool life can vary when machining carbon and alloy steels despite the use of our best technology and our efforts to control our processes. This post discusses factors in the steel that can lead to tool failure. Here are six factors that can affect tool life in your shop:
Variations between suppliers. Suppliers’ melt processes, scrap practices, melt recipes and reduction in cold drawing and straightening practice can significantly affect the way the chip breaks, the resulting built up edge on the tool and the resulting surface finish, even though the grade is the “same.”
Variations in chemistry. A potential subset of variations between suppliers, the fact is that a plain carbon grade with 0.005 weight percent sulfur will not machine at all like the material with 0.025 weight percent sulfur.
Variations in grain size. While this factor is typically more relevant in stainless steels, when machining forgings, blocky structures resulting from excessive forging temperatures can result in inconsistent machining performance.
Variations in microstructure. In this case, it is not so much about the grain size, as it is about the structure present. This is particularly problematic in the ~0.40 weight percent carbon alloy grades such as 4037.
Decarburization or scaling on the work surface. Decarb can result is a carbon poor gummy surface, only to then transition into a fully carbon-containing microstructure. Scale on the work surface can result in excessive tool wear, because of the very high hardnesses of the various iron oxides that may be present (Hematite, the red oxide of iron, Fe2O3, has a microhardness of approximately 1030 DPH.
Deoxidation /high inclusion count. Free machining grades such as 12XX and 11XX steels are typically sold to a “coarse grain practice” with no deliberate additions of grain refiners or deoxidizers. Sometimes, you may find deliberate additions of Silicon to 1144 in order to improve the internal soundness of the steel. The resulting silicates can abrade the edge of the tool when running at the surface feeds expected for a resulfurized steel. The addition of aluminum as a grain refiner can cause rapid edge wear as well. Rarely, very rarely, one might encounter exogenous inclusions entrapped in the steel from melt and casting. These can be real showstoppers.
The takeaway: Purchasing the same item from different suppliers hurls the range of global variation at your machining operations. Standardizing on a single supplier for an item will allow you to get to a steady state in your process.
Our cheat sheet for moving from leaded steel to unleaded steel provides a roadmap for adjusting to unleaded brass.
Unleaded brasses are not necessarily harder to run than leaded brass. They are just different. By recognizing and accommodating for their lack of lead, and the different thermal conductivity, differences in chip forming, and the need to up-tool for heavier feeds rather than higher speeds, your shop can also be successful at making parts from these newer, more challenging grades.
It is widely acknowledged that lead promotes machinability. To get the maximum production from automatic machines, additions of lead have been commonly used in metals, particularly steels and brasses. In brass, dispersed in the grain boundaries, lead acts as an internal lubricant: It reduces friction, and thus heat. By reducing the heat, lead allows the metals to which it has been added to be machined at much higher speeds than the comparable non-leaded grades. These higher speeds (rpm or surface feet per minute) result in shorter cycle times to produce each part. Short cycle times mean less expensive parts.
Leaded brass offered these historical advantages:
Excellent surface finish
Forgiving of machine mis-adjustments
No thermal issues
Fast cycle times
No chip control issues
When machining non-leaded materials, we have to somehow maintain surface finish, get to commercially feasible cycle times, and deal with less than ideal chip characteristics.
What are some strategies for machining the new unleaded brasses?
Increase the feed. Since we lost the lead and the ability to run at higher speeds, increasing the feed can help us get to equivalent cubic inches of removal rates.
Improve the machine rigidity. Heavier feeds mean that your machine needs to be adjusted and solid. It also means more horsepower required— again mandating a rock-solid setup.
Improve the tool. 4 percent lead is very forgiving of tool quality; the new nonleaded grades are the opposite—they present a number of challenges to your tools. Improved materials, geometry and coatings are key to machining unleaded brasses with minimum issues. Also, they will require fewer replacements, helping to get more net production at the end of the shift.
Improve the chip management. Some unleaded grades replace the lead with zinc, resulting in a grade with a type III chip—stringy and bird’s-nest prone. With these grades, pay special attention to drills selected, and try inserts with chip control features to help you manage that chip.
Deal with the increased heat. The lead helped to reduce friction and heat in the leaded grades. With the lead removed, you will have increased heat generated. Carbide is more forgiving of heat, as are tool coatings. Talk to your supplier of metalworking fluids. Chances are, they will have a fluid that will help manage those extra BTUs and maintain your tools’ edges.
Change your ideas about machining brass. Unleaded brass machines more like steel than brass as long as you think of it like leaded brass, you will fight it. Instead, think of it as just a yellow version of 1215 steel or stainless and your expectations will be much closer to reality.
Unleaded brasses are not necessarily harder to run than leaded brass. They are just different. By recognizing and accommodating for their lack of lead and the resultant different thermal conductivity, differences in chip forming, and the need to up the tool for heavier feeds rather than higher speeds, your shop can also be successful at making parts from these newer, more challenging grades.
The market for our precision machined parts continues to be evolve. Evolve your thinking and processing to adjust to the realities of unleaded materials to remain a viable and preferred supplier.
According to "Discovery News" this week, in an article titled "Atlantis' Legendary Metal Found in Shipwreck,"cast metal called orichalucum, which was said by Ancient Greeks to be found in Atlantis, has been recovered from a ship that sunk 2,600 years ago off the coast of Sicily. The article says, "The 39 ingots found on the sandy sea floor represent a unique finding."
In continues, “Today, most scholars agree that orichalucum is a brass-like alloy, which was made in antiquity by cementation. This process was achieved with the reaction of zinc ore, charcoal and copper metal in a crucible.
“Analyzed with X-ray fluorescence by Dario Panetta, of TQ – Tecnologies for Quality, the 39 ingots turned to be an alloy made with 75-80 percent copper, 15-20 percent zinc and small percentages of nickel, lead and iron.”
An Ancient Origins article reports, “The name orichalucum derives from the Greek word oreikhalkos, meaning literally ‘mountain copper’ or ‘copper mountain.’ According to Plato’s 5th century B.C. Critias dialogue, orichalucum was considered second only to gold in value and was found and mined in many parts of the legendary Atlantis in ancient times.”
Maybe the greenhouse gasses emitted by Atlantis’ cementation industries producing orichalucum caused the seas to rise, covering Atlantis.
Employers, the requirements below are now in effect. A new wallet card issued by OSHA will help your supervisors understand the changes to Injury and Illness Reporting Requirements that are now in effect, as of January 1.
What are the new requirements? Under the final rule, employers must report the following events:
Each fatality resulting from a work-related incident, within 8 hours of the death. This requirement applies to all fatalities occurring within 30 days of a work-related incident. See Sec. 1904.39(a)(1) and (b)(6).
Each in-patient hospitalization resulting from a work-related incident, within 24 hours of the hospitalization. This requirement applies to all in-patient hospitalizations occurring within 24 hours of a work-related incident. See Sec. 1904.39(a)(2) and (b)(6).
Each amputation resulting from a work-related incident, within 24 hours of the amputation. This requirement applies to all amputations occurring within 24 hours of a work-related incident. See Sec.1904.39(a)(2) and (b)(6).
Each loss of an eye resulting from a work-related incident, within 24 hours of the loss of an eye. This requirement applies to all losses of an eye occurring within 24 hours of a work-related incident. See Sec. 1904.39(a)(2) and (b)(6).
- Federal Register
Get the wallet card and review the upcoming changes with your team.
Yes, the tool is more expensive, but it might be worth it.
I remember the first time I sat down to work on quadratic equations and discovered there was more than one possible solution to the equation.
How many of us realize that every day in our businesses, we are solving equations that have more than one solution? How many of us realize that we have a choice between solutions, and that lowest price doesn’t necessarily mean lowest cost to us?
At Horn Technology Days, I attended a session on Customer Specific Tool Solutions presented by Todd Hayes. Todd started his presentation with a challenge to the assumption that ROI is only about dollars.
As Todd put it, “ROI is not just about dollars. Increase my tool life. Increase my machine operating time, increase my accuracy (especially on features tied to another), reduce my time in cut by simultaneous machining. Give me my weekend back. Let me run lights out.”
This rang true with me. When I produced steel for machine shops, the purchasing agent was always looking at lowest price per pound for the steel.
I told him that what he should be looking at is the lowest cost to produce the part. Steel price was just one part of that cost. The cost to machine it was another. Todd was talking about creating special tools to solve problems in production.
For short runs, the cost of a special tool is prohibitive. Even though not all of us are quoting short runs, how many of us are still using short run thinking? How many of us are solving for lowest tool price rather than optimum output? Ask yourself:
What if the custom tool (or special steel grade) saved me several changes per day on several machines?
How much more machine operating time will I gain?
How much utilities will I save by not needing all the CFM of compressed air that we all overuse when we change a tool?
How much will I save because I have eliminated variability and/or have better control over the chip so I do not have to inspect for chip weld and out of spec surface finishes?
I am not exhorting you to go out and buy specialty tools for every job, just like I was not asking my customers to buy the premium machining grades of steel for every job. But I am asking you to recognize and challenge your assumptions about how you decide to purchase, just as I had to recognize and challenge my assumptions that there was only a single “solution” to those equations I faced in class that day.
Lowest price on purchases or lowest cost of production? Two solutions—you get to choose one.