Hard Protective Layers on Forging Dies—Development and Applications

Abstract

The article presents a summary of many years of activities in the area of increasing the durability of forging dies. The results of comprehensive research work on the analysis of the destructive mechanisms of forging dies and the possibility of increasing their durability with the use of modern surface engineering methods are presented. Great possibilities in terms of shaping operational properties of forging dies by producing hybrid layers of the “Nitrided Layer + PVD Coating” (NL + PVD coating) type were confirmed. An analysis of changes in forging dies durability under various operating conditions was performed, i.e., forging—die—forging press—pressures. It has been shown that the variety of parameters of the forging process, including forgings’ geometry and weight, materials, precision, pressures applied, and, what is very important, quality of machines, makes it very difficult to compare the effectiveness of various PVD coating solutions in the process of increasing the durability of forging dies. Hybrid layers of the “NL + PVD coating” type create great possibilities in shaping the operational properties of tools and machine elements. However, in each application a precise diagnosis of the wear mechanism and the design of an individual PVD coating material solution is required.

Hot die forging with nitrided and thermally stabilized DLC coated tools

“…the coating is applied on nitrided surfaces. Nitriding counteracts early coating cracking, which is associated with softer surface layers below the coating (also known as "egg shall" effect) [5].…”

Studies on a Robotised Process for Forging Steel Synchronizer Rings in the Context of Forging Tool Life

“…Increasing the service life of forging tools, and thus reducing the number of sets of tools used for a given batch of products, is a solution to meet rising costs. Today's manufacturing techniques and methods offer a whole spectrum of possibilities for affecting the service life of forging tools [14][15][16][17][18][19], however, a common requirement as to the effectiveness of these procedures is the repeatability and stability of the forging process itself, which is in principle achievable only through the use of automation and robotisation.…”

Strategic Selection of Refractory High-Entropy Alloy Coatings for Hot-Forging Dies by Applying Decision Science

“…Given the external forces in the forging process that typically fall within the range of 500 to 1000 MPa, it is evident that the die material is likely to undergo deformation when exposed to temperatures exceeding ~427 • C (800 • F) [10,11]. These die materials are also susceptible to thermal and mechanical fatigue due to transformational stresses and the nature of the forging process, respectively [12]. During the hot-forging process, dies are preheated to mitigate the chilling effect on the workpiece, which reduces the need for repeated reheating of the workpiece and enhances the thermomechanical processing of the forged products, thus improving their quality at the expense of softening the die during its service [13,14].…”

“…Furthermore, the performance of these materials hinges on the localized temperature at the interface between the die and the forging stock. This issue is exacerbated in press operations with prolonged dwell times and higher contact pressures, potentially impacting die longevity [3,[10][11][12][13][14]. In scenarios involving the forging of steel, superalloys, and titanium alloy products that require hot forming temperatures of up to ~1205 • C (2200 • F), surface temperatures on the die exceeding ~650 • C (1200 • F) can be reached.…”