Machining Economics 4 Factors

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The economics of precision machining can be understood with just 4 factors- Machining Cost, Material Cost, Tool Cost, and Cost of Non-productive Time (Set-up Costs).

Since material costs and nonproductive costs are constant, they are combined into the fixed cost line at the bottom.

The line labeled “machining cost” (which is made up of labor and overhead cost of time per piece) reduces with increasing speed by reducing operating (cycle) times.

The cost for tools, on the other hand, increases with increasing speed. This is because tool life decreases with increasing speed.

Since machining and tool costs vary with the speed of operation, a minimum total cost occurs at a definite set of conditions for material, tooling and operating speed.

Purchasing improved tools is one way to move the machining cost and total cost per piece curves to the right and down. As is adding coatings, improved metalworking fluids and their delivery, etc..

As long as the gain in speed and the resultant drop in cost to produce are larger than the cost of the improved tooling, or other process improvements, you can improve or further optimize the economics of your production.

Our industry has benefited greatly from the many improvements in tool materials, coatings, metalworking fluids and design improvements.

Are you taking full advantage?

Graph and discussion based on AISI Cold Finished Steel Bar Manual 1968

Speaking of Gutenberg

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One of the reasons I blog is for “Knowledge Retention.” I want to be sure that the stuff I know and take for granted makes the cut into the electronic realm.

In 5o years or so (the apparent limit of paper’s routine usefulness in my experience) the out of print books with the stuff that I practice will be pretty much lost.

old books — These won't be kept around as "useful."

We think we are living in an information age. Actually, the books that those of us over 50 learned from will be mostly lost, and we will be considered by history to have lived in the last “Dark Age.”

So my blogging is my “Project Gutenberg” for Metallurgy, Machining, Management and this Moment in time in our Market.

What knowledge do you (your people) have that will be lost when you (they) leave? What is your plan for assuring it is not lost?

Disney had a plan. Jobs had a plan.

What’s your plan?

Mine is speakingofprecision.

A Baker's Dozen Facts To Know About Inclusions In Steel

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Straight from the baker to you…

bakers-dozen — Making steel is just like this sort of ...

1) Inclusions are on the inside, not on the outside surface…
2) Inclusions are non metallic materials entrapped within a solid metal matrix.
3) Inclusions that are typically expected include Sulfides (Type A), Aluminates (Type B), Silicates (Type C) and Globular Oxides (Type D)
4) Other types of inclusions are called exogenous inclusions as they come from materials not expected to be entrained or entrapped within the steel- typically slag or refractory that might have broken off during steelmaking.
5) Inclusions are measured and rated in North America according to ASTM method E45
6) Bearing Quality Steels use a number of different practices in order to minimize the inclusion content (because inclusions would wear differently than the host metal, thus nucleating premature wear and failure.)
7) Steel Cleanliness, Steel Microcleanliness, and Inclusion content are all different ways of talking about the presence of these non metallic particles within the steel itself.
Three reasons inclusions are normally expected in plain carbon and alloy steel bar products in our shops:
‘8) Manganese sulfides are expected to be present as they aid machining.
9) Silicates are expected to be in non- free machining steels as silicon is added as a deoxidizer to assure the soundness (freedom from gas bubbles and voids) of the steel
10) Aluminates are also expected if the steel is ordered as Aluminum Fine Grain. the Aluminum scavenges Oxygen and nucleates the formation of fine grains of austenite.
11) The Manganese Sulfides promote free machining as they provide a place for the chip to break and help control welding of material (built up edge) on the tool edge. In leaded steels, the lead is closely associated with these manganese sulfide inclusions.
12) The Silicates and Aluminates in our common steel grades are of high hardness, abrasive, and are a primary reason for tool wear and edge chipping in ordinary steels.
13) A quick look at the certification tells us whether or not we will find these kinds of inclusions- just look at levels of Manganese, Sulfur, Silicon, and Aluminum.
For machining, in keeping with the baking theme, I like to think of Manganese Sulfide inclusions as “kinda like the raisins in raisin bread.”
Bakers dozen photo credit.