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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?"

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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Grinding Advice You Probably Didn’t Know

Posted August 19, 2014 10:30 AM by Milo
Pathfinder Tags: finger cots gloves grinding tips

Our post on No Gloves When Working on Grinders has prompted a number of responses.

Here are some additional reasons why you should not even need gloves when working on grinders and grinding machines.

Issue: "There are sharp edges or burrs that will cut me if I hold the part. The grinding will be to remove the burrs."

Response: Use a file to knock down the burrs so that you can safely hold the part for grinding. Or use leather finger cots to grip the part for grinding.

We permitted these for use on belt grinders for holding small parts.

Issue: "The part gets too hot to hold."

Response: Then you are grinding wrong. Here is a list of some of the things that can go wrong by letting the heat of grinding get out of control:

  • Remove the temper from Steel. Especially on tools, loss of temper means loss of tool hardness and edge life. A drop from Rc63 to about Rc48 for a couple of tenths (0.0002-0.0005) can contribute to side wear and edge failure.
  • Crazing or checking on Carbide can be caused by burning during grinding.
  • Work Hardening. Overly shiny surfaces are usually the clue that work hardening has occurred.
  • Creation of untempered martensite.

Untempered martensite can be formed in high carbon and alloy steels by getting high surface temperature from grinding- red heat- then quenching in water.

  • Untempered martensite is very brittle and reduces toughness.
  • Keeping the work cool continuously while grinding is an important aspect of preventing damage to work, the wheel, and injury from occurring to the worker. Hogging off material and infrequently quenching is a great way to destroy a tool by grinding
  • Water needs to be plentiful to absorb the heat from grinding, and frequently used to reduce heat buildup in the work.
  • Take multiple small passes and cool in between in a large bath of water while grinding to minimize heat build up.

Of course, wearing the required PPE, making sure the grinding wheel is properly dressed, all guards are in place and properly adjusted are also key to safe grinding in our shops.

Bottom line: If the work is too hot for your fingers, it may be approaching the danger zone regarding loss of mechanical properties and function in end use.

11 comments; last comment on 09/28/2014
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Gloves and Grinders – UNSAFE OSHA

Posted August 15, 2014 10:00 AM by Milo
Pathfinder Tags: gloves grinders osha Tools

If there is a worse combination than grinders and gloves, I don't know what it is, except perhaps for gloves and a drill.

We posted a really cool video on our career blog about making a light saber sword here. But we were shocked to see the guys in the video wearing heavy leather gloves while working with grinders.

Never wear gloves with grinders. Or operate grinders with guards removed.

By "grinders," we mean abrasive belt grinders, bench grinders, pedestal grinders, surface grinders, and also abrasive cutoff machines.

No Gloves!

Sanders, polishers, and buffers that involve rotating wheels or transversing motion are also included in this classification for the purposes of hazard analysis.

Here are 6 reasons to not wear/not permit the wearing of gloves while working with Grinders or Grinding Machines

  • Amputations
  • General duty of employer to provide a workplace free of recognized hazards
  • Gloves can catch on rotating equipment and pull operators hands into the equipment
  • Rotation of grinding wheels is at high RPM's
  • Operator cannot get hand out of glove when it catches
  • Equipment horsepower and machine material properties exceed those of the operators flesh

We did a quick calculation and a 12″ grinding wheel and 3600 rpm and arrived at a speed on the periphery of 120 miles per hour.

No time to react.

More info on preventing amputations from OSHA


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

38 comments; last comment on 08/20/2014
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Carbon Steel Without Manganese?

Posted August 05, 2014 11:00 AM by Milo
Pathfinder Tags: manganese manufacturing roll steel

Manganese ties up Sulfur before it can chemically combine with Iron to form Iron Pyrite. Iron Pyrite occurs at grain boundaries and leads to hot shortness (brittle behavior) at rolling temperatures.

More than fools gold, Iron Pyrite can prevent steel from being hot worked by inducing "hot shortness."

We saw that several people found our blog with the search term "Carbon Steel Without Manganese."

So we'll take this opportunity to answer that.

We have already written about 5 Facts about Manganese in Steel which explains the contributions of Manganese to a steel's properties.

But lets answer the question - is there a Carbon Steel without Manganese?

The answer to that is No.

Here is the primary reason why. Iron Pyrite.

There are always small amounts of sulfur in steel, and Sulfur combines with the iron in the steel to form Iron Pyrite. Iron Pyrite is also known as iron sulfide, though a more descriptive name might be Iron persulfide.

Regardless, this material is formed as sulfur in the melt reacts with iron , and this material segregates at grain boundaries., causing intergranular brittleness. This causes it to break, rather than behave in a ductile fashion and reduce under the pressure of the rolls.

By adding Manganese to the melt, Manganese preferentially ties up the available sulfur, forming manganese sulfides. this prevents the formation of iron pyrites in the grain boundaries, preserving the ductility of the steel at rolling temperatures.

That is why every steel that we have encountered contains enough Manganese to react with the sulfur in the melt.

Steel without Manganese? Nope, I've never encountered it. And that is a good thing!

Photo credit


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

7 comments; last comment on 08/08/2014
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