Chip Control - Precision Machined Products Association

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 — 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

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.

Test text — 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 — 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.

Note the touch of heat discoloration shown on the chip as well. — 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.

Helping the Precision Machined Industry Adapt & Thrive

Adjusting to Unleaded-In Brass

What Does Ductility Mean?