Surface-infusion treatment extends life of tool & die casting components.

In 2001, the Hayes Lemmerz International Inc., Northville, Mich., facility in Bristol, Ind., was looking to raise the productivity of its process line. The firm discovered that the face mill machining operation responsible for cutting the datum surface on its aluminum drive train knuckle components was not running at the maximum recommended load. The speeds and feeds were set to provide a repeatable, quality cast component within the limitations of the fixtures. However, these settings were on the low end of the recommended performance for this type of operation.

The modifications needed to improve the performance would be costly due to the amount of fixtures contained in the machine line and would require weeks or months to implement due to production requirements. An alternative approach would be to raise the speed and feed proportionally, thereby maintaining the same force on the fixture.

A standard, off-the-shelf, face mill utilizing a polished sharp insert was installed and tested with a slight improvement over the existing face mill but the gain was not large enough to cost-effectively make the change. The firm experimented with various standard physical vapor deposition (PVD) coatings and polycrystalline diamond (PCD) but did not find what it was looking for until it tried tungsten carbide (TC) inserts that had been coated with a cubic zirconia surface-infusion treatment by C3 International LLC, Alpharetta, Ga.

Running at 4,100 sfm, the treatment extended the inserts' life by 43%. The treatment also enabled speeds to be increased to 6,800. Hayes Lemmerz also found that it could turn its faster CNCs at 8,500 sfm with no problems. Increased RPMs, combined with fewer change-outs for inserts, has increased throughput by up to 17% (16,000 pieces/yr.).

The treatment is a coating and an infusion process whereby the zirconia penetrates the substrate of the treated steel or carbide several hundred angstroms deep, serving as an anchor that secures the thin zirconia film to the surface of the treated material. The thinness of the material (typically two-tenths of one micron) means that there are no real changes in the treated component's dimensions.

The zirconia attaches directly to the material treated without the need for intermediate bond layers, eliminating the need for a contact-bonding agent. The stable and finely grained cubic zirconia (3nm) forms at low treatment temperatures (450C,842F) and continues to maintain the cubic zirconia structure at room temperature. This low-temperature allows for the treatment of components without deforming them or exposing them to high-temperature structural changes that can impair their underlying material strength.

The treatment is based on the ability to get the cubic zirconia to form at the surface accompanied by an infusion of zirconium into the treated metal carbide at low temperatures--less than 450C (842F). Once the zirconia treatment is performed, the zirconia stays in place even though the treated parts are used in hotter applications--as high as 1,500C (2,748F).

A formulation similar to the zirconia treatment used on cutting tools also has proven useful in aluminum diecasting. Treatments on steel can prevent "liquid metal attack" or aluminum soldering. Oak Ridge National Labs found that this treatment has given more than an 800% life extension to the H-13 steel sheaths used to protect thermocouples when dipped into molten aluminum. The treatment is now being used on aluminum diecast molds as well as core pins, ladles and other tooling that is susceptible to liquid metal attack.

Select No. 002 at www.moderncasting.com/info