MPM Stays Competitive with Interrupted Quench and Quenchant Selection

This case study was edited from material supplied by Heatbath/Park Metallurgical – Detroit, MI.

Taken from Heat Treating Progress – September/October 2005.

This case history examines how a Michigan company improved its heat treating operations – and its competitiveness – by changing its quenchant.

Michigan Production Machining Inc. is a supplier of precision finished and partial-finished components to automakers and Tier 1 and 2 automotive suppliers.  Its customer list includes General Motors, Daimler Chrysler, Magna DriveTrain, Metaldyne, and Visteon.  True to its name, production machining dominates MPM’s 240,000 ft.2 of shop floor.  MPM has two facilities: one in Macomb, MI; and another in Saginaw, MI, which supplies powertrain parts to Saginaw Metal Casting Operations.

MPM also does CNC turning, milling, and broaching.  Parts arrive as nodular (ductile) iron forgings or castings – ASTM A395, A476, A439, A536 and SAE J434.  Nodular iron, once known as spheroidal-graphite cast iron, contains nodules of graphite embedded in a ferrite or pearlite matrix.  The nodules arrest the development of cracks and enhance the metal’s ductility.

For several programs, notably gears and cams, induction hardening, and hardening and tempering, are important value-added services.  MPM operates four induction hardeners.  The company designs its own “figure 8” coils with the help of its equipment suppliers and develops its process recipes based on customer requirements.  One critical ongoing program is the post-machining scanned induction hardening of cam shafts at a power level of 200kW, 10 kHz.  Parts are quenched to above the martensitic threshold, then air-cooled for one hour.  Martensitic transformation begins in the cooling rack.  When parts reach ambient temperature, they’re tempered for one hour at 500°F.

“The process is unque,” says MPM general manager Tony Anderson, “because it is an interrupted quench of nodular iron.  What it produces is the best metallurgical structure possible for subsequent grinding operations and for the part’s final use in the engine.  It’s the best structure because the number one issue – the biggest challenge – is met:  these parts do not crack.  And, they meet specs: less than 10 percent retained austenite, and a minimum Rockwell of 52.”

Tacky, Tacky

Development of this process was not achieved in an afternoon.  “The R&D on this program took a year,” offers Anderson.  The reason was mostly related to the quench part of the cycle.  The product used at the time, specifically on powdered metal and other components, produced a cosmoline effect on the cams during test processing – similar to a rust- inhibiting coating.  “And it was tacky – like flypaper,” says Anderson, “so the equipment was a mess.”  A solvent and paint scraper were needed to remove the sticky residue from equipment.  “Workers fared even worse,” he said,  “because they stuck to the floor.

“Keep in mind that this was an established, brand-name product,” says Anderson, and this particular aqua-based polymer was used for induction projects elsewhere.  We might have tried to work with it, except that performance was poor:  cracking was common at the parameters we had established.”

It also created operational problems.  “It wouldn’t tolerate contamination, so bath life was shorter than we wanted.  And that sticky characteristic wasted a lot of chemical from dragout,” explains Anderson.  “Also, it blocked our inductors.”

Polymer Technology

Keeping its original process plan intact, MPM aggressively sought alternatives.  Among the numerous products tested at MPM was a relatively new polymer technology developed and manufactured by Heatbath/Park Metallurgical, Detroit, MI.  The product, called Polyquench 15XN, was introduced in 2000 and was engineered specifically for induction and direct hardening applications.  It had proved particularly advantageous for intricate components where drag-out is more of an issue.  The product was recommended for use on carbon steel, alloy steel, cast iron, malleable iron and ductile iron.

Polyquench 15XN is a nitrite-free, organic, nonflammable polymer.  In the bath, it forms a solid, lubricious film that deposits on the surface of the hot metal and controls the transfer of heat from metal to quenchant.

Notably, this film is not at all sticky.  This means drag-out and chemical costs are minimized, and that it can be easily washed from parts, equipment, and workers with plain water.

The polymer was engineered for extended use.  It stays in solution in all operating conditions, and resists chemical, thermal and mechanical breakdown, even when part metallurgy changes, or there is bath contamination from normal processing.  A bactericide protects the concentrate from degradation but does not have the downside of creating dermatitis issues.  And the product does not have an odor.

Polyquench 15XN is soluble in water at all concentrations.  At lower concentrations, the cooling response is fast – like water – but more uniform, so hardness is also uniform and repeatable.  The cooling response slows as concentration is increased.  Similarly, increasing temperature retards the cooling response.

The quenchant has a relatively wide temperature range, made possible by the polymer’s ability to remain soluble even at boiling.  It contains both a rust inhibitor and antifoaming agent.

Following a year of testing, Michigan Production Machining, in 2002, installed the Heatbath quenchant in all four of its hardening stations.  Operation is at 10 percent, the same concentration as its previous polymer quenchant.  Cost savings are substantial – in the range of 45 percent according to Anderson, based partly on drag- out reduction.  This is despite the fact that these cams have lots of lobes where quenchants can get entrapped.”  The other part of the cost saving, says Anderson, “is that we’re only dumping half as often.  We’re literally getting twice the bath life we had before.”  Given a competitive environment that gets more intense every year, he notes, those savings are significant.

Growing Value – Added Operations

“You don’t really sell ‘quality’ anymore.  That’s a given.  Without exceptional quality, you don’t even get to the table.  Once there, what you are selling is price – and customer service.”

“One of our priorities now,” adds Anderson, “is growing our value added operations.  We realize that our continuing success depends on our ability to offer greater value – whether we’re rough-machining or finish machining.  And at a price that reflects every efficiency and cost-savings possible.

“It’s rare when a simple change such as a quenchant can make this much difference,” says Anderson.

“It has certainly proved its worth for the two shifts of cams we run every day.”

There are new programs planned at MPM for axle shafts and gear clutches.

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