A New Approach to the Cause of High Pressure Die Steel Erosion, Pitting and Breakout - Cavitation (T10-051)
Jerald Skoff,  Badger Metal Tech, Inc.,  Menomonee Falls, WI.



There is an urgent need to create more awareness of a long overlooked mode of failure in high pressure die cast tooling – cavitation.  Because of a limited lack of in depth study and difficulty in simulating, in the lab, the effect of cavitation in the high pressure die casting (HPDC) industry, this paper will be more informative than technical in nature. The information provided will show that cavitation is a leading cause of high pressure die casting die breakout, pitting, erosion, and sometimes the accompanying premature cracking. There is a direct correlation between the cavitation that occurs in other fluid dynamics, which has been studied for well over 100 years, and molten metal flow in high pressure die casting. Fluid cavitation leads to catastrophic damage of turbo machinery, thrust propulsion, hydraulic pumps, propellers for ships, and dam spillways.  High pressure die casting dies can now be added to the list.  It will be shown that there are steps that can be taken to significantly buffer cavitation breakout, pitting, and erosion effect in high pressure die casting dies.

Follow with Open Panel - Gary Lockwitz (T10-052) Steve Midson (T10-053)
                                                Gary Lockwitz and Jerry Skoff (T10-054)

This paper will present the present state-of-the-art of an ongoing research program whose objective is to develop a 'smart' die coating based on a thin film piezoelectric sensor embedded into a tribological coating system. The design and deposition of both the thin film piezoelectric sensor and the overall coating system will be discussed in detail. The effect of deposition parameters using pulsed closed field unbalanced magnetron sputtering (P-CFUBMS) on the piezoelectric response of the thin film sensor will be given and the overall coating design concepts will be discussed together with future research and development directions for this 'smart' coating system.
 

A great deal of research has gone into die steel used for a die cast tool cavity: grain size of the steel for a cavity; effect of the specific heat treat process on the life of the cavity; effect of compressive stresses induced into the cavity by outside forces; and, surface coatings applied to the cavity. These are all important factors, but very little research has gone into the effect of the scratches from the polish of the cavity surface. Recently, a cavity for a cosmetic part was run and observed with 20X magnification regularly during its life. At this magnification heat checks could be seen as early as 1425 shots. These heat checks seemed to be directly related to the polishing scratches left in the die during the tool build. Based on these results, a trial was set up where a cavity was polished as normal (300 stone), except for the cavity fillet radii which was diamond polished. In this trial, the cavity was run as normal in production. It was compared at a pre-determined frequency to the baseline cavity for tool life with photographic documentation. This continued until tool life was exhausted. After the run, the tool was reviewed and it was observed that the fillet radii on the cavity (corner radii on the casting) did not heat check as rapidly as normal. On this first cavity tool life was increased greatly over previous cavities. This new process (diamond polishing the fillet radii) has been conducted on multiple cavities since, and all regulated tests display similar positive results. The supplier is confident enough with the results that they have increased the guaranteed tool life by 25%. This paper will present the results of these trials, and the tremendous increase in die life seen (>40% increase in average tool life) for this cosmetic part.

This paper explains the benefits of induced compressive stress and ferritic nitrocarburizing (FNC). The author will discuss the history, physics/chemistry, controls, benefits, limitations, and lastly the “how and why” to effectively combining each process. It is the authors goal to bring awareness, and understanding regarding the processes so that more die casters will integrate them singularity or combined into both their proactive and reactive die maintenance programs. There is a need for more studies considering the benefits shown in similar experiments. By doing so, both dollars and energy savings are possible.

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