February 2020 Volume 2

FORGING RESEARCH

Introduction Forgings are typically produced using hardened H13 steel dies, and the forging process utilizes a lubricant sprayed onto the die faces prior to the production of each forged component (1) . The purpose of the lubricant is to decrease friction between the workpiece and the die, and minimize buildup of forged material onto the faces of the die. However, in several publications (2,3) , the forging industry has indicated that it would be beneficial to reduce or eliminate the use of conventional lubricants during the forging process. Recent research performed at the Colorado School of Mines (Mines) has demonstrated that PVD coatings applied to H13 steel dies used in aluminum die casting have been able to significantly reduce the amount of conventional organic lubricants used during die casting (4) . The goal of this project, therefore, was to extend the die casting research to determine if similar types of PVD coatings can be used to reduce the amount of conventional lubricants used during forging. The approach utilized in this study has involved

developing a laboratory testing methodology to measure the relative friction coefficients of PVD surface coatings relevant to the forging of aluminum alloys. The first stage of this project involved performing a literature review (5) to summarize previous research on the use of PVD thin film coatings on forging dies, as well as the use of thin-film coatings for lubrication applications at elevated temperatures, such as would be experienced by the tool during the forging of aluminum or steel. That literature review is too detailed to reproduce here, but based on findings of the review, the coatings listed in Table 1 were identified as suitable for this testing program. Several of these coatings listed in Table 1 have been tested in this study to determine if they can be applied to H13 steel forging dies and reduce the coefficient of friction between the workpiece and the die, and thereby reduce the amount of conventional lubrication that needs to be applied to the forging die.

Table 1: Summary of coatings identified in the literature review (5) . Table 1: Summary of coatings identified in the literature review (5) .

Type of Coating Single-layer hard coatings

Specifics

Suppliers

Temperature

Tribologix, Dayton, Ionbond

TiCN

<400°C

Super MoS 2

Tribologix

375°C

Ti-MoS 2

Teer in UK, Ionbond

<350°C

AlCrN-MoS 2 TiCN-TiMoS 2

Tribologix

Multi-layer hard coatings

Teer

CrN-DLC CrN-SiC

Phygen Phygen

<300°C <850 o C <350°C

i-Kote

Tribologix

Hard coating plus noble metal

Voevodin, Scharf & Samir at UNT

Noble Metals

<500°C

Highly lubricious oxide

--

None identified

High temperatures

Plasma Sprayed

PS400

NASA

Laser Textured Tribologix/Mines *The i-Kote coating was tested using two methods of surface preparation, H-etch, which has a higher level of etching of the substrate prior to coating, and L-etch (low-etch) Laser texture a TiCN coating

*The i-Kote coating was tested using two methods of surface preparation, H-etch, which has a higher level of etching of the substrate prior to coating, and L-etch (low-etch)

FIA MAGAZINE | FEBRUARY 2020 54