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Speaking of Precision

Speaking of Precision is a knowledge preservation and thought leadership blog covering the precision machining industry, its materials and services. With over 36 years of hands on experience in steelmaking, manufacturing, quality, and management, Miles Free (Milo) Director of Industry Research and Technology at PMPA helps answer "How?" "With what?" and occasionally "Really?"

My Steel Won't Harden!

Posted February 27, 2015 11:30 AM by Milo
Pathfinder Tags: harden metal quench steel

There are only a handful of things to check when your steel parts fail to respond to quench and temper heat treatment.

Here's my list in decreasing probability order:

Time, temperature, quench, suitable steel.

  1. Mixed steel / wrong steel being heat treated.
  2. Decarburization on the surface.
  3. Failure to heat it above the austenitizing temperature.
  4. Failure to hold it for sufficient soaking time. (This can be especially problematic with induction processes)
  5. Failure to quench fast enough.

So someone could say "Well you didn't mention that the steel had a microstructure that interfered with the process and is preventing us from getting the hardness required."

To them I would say "Please see items 3 and 4 above."

Photo credit Da Wei Induction Heating Machine Inc.

Editor's Note: CR4 would like to thank Milo for sharing this blog entry, which you can also read here.

2 comments; last comment on 02/27/2015
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Adjusting to Unleaded-In Brass

Posted February 10, 2015 12:30 PM by Milo
Pathfinder Tags: brass lead machining

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-tool for heavier feeds rather than higher speeds, your shop can also be successful at making parts from these newer, more challenging grades.

Same yellow color, just no Lead in the grain boundaries

It is widely established 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 (sfm)] 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 % 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 birds-nest prone. With these grades payespecioal 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 Metal working fluids- Chances are that they will have a fluid that will help manage thiose extra BTU's 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.

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 resultant 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.

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.

For more details on grades and recommendations, read our article Adjusting to Unleaded.

Editor's Note: CR4 would like to thank Milo for sharing this blog entry, which you can also read here.

6 comments; last comment on 02/10/2015
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Ancient Orichalucum Metal Ingots Recovered from Shipwreck Off Sicily

Posted January 16, 2015 10:00 AM by Milo
Pathfinder Tags: ingot metal shipwreck

According to Discovery News this week, "Gleaming 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 39 ingots found on the sandy sea floor represent a unique finding."

"Today most scholars agree 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."

Ancient Origins reports "The name orichalucum derives from the Greek word oreikhalkos, meaning literally "mountain copper" or "copper mountain". According to Plato's 5th century BC 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…

Editor's Note: CR4 would like to thank Milo for sharing this blog entry, which you can finish reading here.

9 comments; last comment on 01/21/2015
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What Does 'Ductility' Mean?

Posted December 02, 2014 10:21 AM by Milo
Pathfinder Tags: ductility machining metal

The ability of a material to deform plastically without fracturing, is called ductility. In the materials usually machined in our shops, ductility is measured by determining the percent of elongation and the percent reduction of area on a specimen during a tensile test.

Ductility is often indicated by chip control issues in certain steels, as the chip readily deforms but does not separate from the work piece. This can result in persistent burrs attached to the work .

Ductility arrives in our shops as indicated by burrs.

Ductility can also mean long stringy chips that can form a dreaded "birds nest" engulfing the tool and work piece.

Birds nest chips present a very real danger to operators. Ductility can hurt!

Long necklace chips are another sign of ductile materials in machining.

Long continuous chips resulting from ductile material can be controlled to keep them away from work piece and tool.

Short chips curled into "sixes and nines" showing a bit of heat discoloration are typical of less ductile materials and dutile materials machined at proper parameters using chip breakers and high pressure coolant delivery.

Chips that look like sixes or nines showing a bit of heat discoloration are desired for safe practice.

In our machining practice we would prefer materials that are "crisp" rather than ductile.

In order to successfully deal with ductile materials, strategies such as chip control features on inserts, wiper style inserts, through tool coolant, interrupted cuts, chip breakers, and high pressure coolant can be considered.

Dialing in the appropriate feeds, speeds and depth of cut are crucial too.

Birdsnest photo courtesy Garage Journal

All other photos by author.

Editor's Note: CR4 would like to thank Milo for sharing this blog entry, which you can finish reading here.

1 comments; last comment on 12/03/2014
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The Atlantic Apprenticeships: Why Germany Is So Much Better at Training Its Workers

Posted October 28, 2014 11:00 AM by Milo
Pathfinder Tags: apprentice employment training

The need for talent is a universal concern- in Germany and in North America. The German apprenticeship model is effective in Germany. But can it be successfully transplanted here?

The Atlantic recently posted an article discussing the German Apprenticeship model here

Machinists are in high demand.

They gave 3 key differences between German and US ideas of apprenticeships:

  1. The first thing you notice about German apprenticeships: The employer and the employee still respect practical work. German firms don't view dual training as something for struggling students or at-risk youth. "This has nothing to do with corporate social responsibility," an HR manager at Deutsche Bank told the group I was with, organized by an offshoot of the Goethe Institute. "I do this because I need talent."
  2. The second thing you notice: Both employers and employees want more from an apprenticeship than short-term training. Our group heard the same thing in plant after plant: We're teaching more than skills. "In the future, there will be robots to turn the screws," one educator told us. "We don't need workers for that. What we need are people who can solve problems"-skilled, thoughtful, self-reliant employees who understand the company's goals and methods and can improvise when things go wrong or when they see an opportunity to make something work better.
  3. A final virtue of the German system: its surprising flexibility. Skeptical Americans worry that the European model requires tracking, and it's true, German children choose at age 10 among an academic high school, a vocational track, or something in between. But it turns out there's a lot of opportunity for trainees to switch tracks later on. They can go back to school to specialize further or earn a master craftsman's certificate or train as a trainer in the company's apprenticeship program-and many do.

Beyond ROI

The question that most North American businessmen have when discussing this issue is ROI- Return On Investment.

In Germany, according to the article, the State pays the training expense for each apprentice-

In the U.S., Companies will have to foot the bill for almost all expenses themselves.

Trained and credentialed employees will have the freedom to leave the employer, arguably before that employer can get any return on their training investment. see our post "What if I train them and They Leave?"

We think that the cost problem and the ROI problem can be solved, with work, here in North America.

But the problem that we need to solve first is what The Atlantic piece calls "the biggest obstacle:"

American attitudes toward practical skills and what Germans still unabashedly call "blue-collar" work. In America… we're suspicious of anything that smacks of training.

I know as a parent, there is a lot of social pride at having ones children attend university.

But I am starting to see that the real pride is not about the university that one's child attends, it is rather the fact that they got a job capable of offering a return on the Investment of all those college expenses.

The real pride for parents these days is being able to say that their child in fact has a full time job. Is living independently. And is not overburdened with debt.

In North America, the way to accomplish this is by "earn as you learn" to pursue a degree after getting a well paying career started. Often the employer provides tuition assistance.

Getting started in a well paying career in advanced manufacturing can be as simple as a one semester training program at a local community college. Not years and years of loans and expenses and fees with no immediate ROI. Earn as you learn makes ROI simultaneous with your efforts, not some dreamed for, long in the distant future hoped for outcome.

Prospects for employment remain strong in the precision machining industry:

In September 2014, ~97 % of respondents (76/78 companies) expect Employment prospects to increase or remain the same over next three months. Prospects for employment remain strongly positive.

What is going to be the key for adopting apprenticeships here in North America?

I think that it will be the realization by all affected- businesses, potential employees, parents of students, educators, government officials- that there truly exists a critical need for talent.

In Germany, everyone knows this. Over here, well, for sure the employers do. everyone else- that is anyone's guess.

5 comments; last comment on 10/30/2014
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Pipe Steel: Internal Defect

Posted August 29, 2014 11:00 AM by Milo
Pathfinder Tags: defects pipe steel test

The majority of defects encountered in steel bars in our shops are found on the surface. Internal defects can also be encountered, and we posted about central burst (chevron) defects here. This post describes Pipe Steel.

Definition: A central cavity formed by contraction of the metal during solidification is called pipe.

When this cavity is found in wrought or cast products, this is also called pipe.

Pipe steel centerline defect in wrought steel bar. We had this specimen hard chrome plated and made it into a bookend.

In the days of ingot casting, the location of the shrinkage cavity was controlled by ingot mold design and the addition of hot tops to assure that after cropping the material containing the void off, there would remain sufficient sound material to roll into product.

Today with modern computer controlled billet and bloom casting processes, pipe steel and center porosity is very seldom encountered.

Recently a question was asked about centerline defects on cast billets in one of my LinkedIn Groups.

"hello can any one tell us why some times whe have holes along the center of the billets just casted thanks"

Despite a lack of specifics about grade, deoxidation, and many other factors, we can make some comments based on the fact that this is continuously cast billets according to question.

Here are my comments addressing the continuous billet casting process and how it can be implicated in the creation of centerline voids (pipe steel defects).

The three key parameters in the casting process that are most likely to result in centerline pipe are

  1. Casting speed
  2. Superheat
  3. Electromagnetic Stirring. EMS amperage and frequency (Together they drive intensity.)

1. Casting Speed- Incorrect casting speed can result in pipe/ centerline looseness/ porosity. This can be aggravated by issues with mold level control. Slow down your casting speed to get sufficient solidification.

2. Superheat is critical to maintaining the proper fluidity and solidification dynamics in the mold. Liquid metal shrinks in three steps; 1) volume decreases the liquid cools goes from the pouring temperature to the freezing temperature; 2) volume decreases as the metal solidifies. This is reinforced by the driving out of dissolved gases as the metal freezes; 3) the metal shrinks as it cools from solidification temperature to ambient temperature.

3. Electromagnetic Stirring (EMS)- If you macroetch transverse sections of the billets and still see columnar rather than equiaxed grain structure in the cast billet, it is a sign that the EMS is ineffective.

There are a host of other operating parameters as well as chemistry and processes that can contribute to porous centers or central cavity pipe steel defects. Here is a list of questions to help address these:

Do you have adequate cooling water through the molds? Are you running EMS? What is the metallurgical distance on this caster? What is the mold level control? Evidence of turbulence into the mold? Meters per minute for casting speed? Shrouding status on nozzles? What was superheat? What was water flow?

Do you have chemistry in control, steel deoxidized, so that the large void is a result of solidification shrinkage, not divorce of gas from the liquid steel? What is grade? What was deoxidizer?

Continuous casting of steel is a complex process with a large number of operating parameters and processes that need to be in close control. Understanding how these parameters can impact the final product is critical to eliminating defects that result from lack of control.

Editor's Note: CR4 would like to thank Milo for sharing this blog entry, which you can finish reading here.

1 comments; last comment on 08/31/2014
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