May 2022 Volume 4

MAINTENANCE

Forging FAQ and Troubleshooting, Part 2 By Frank Sobnosky Jr. and Ethan Black

In part one of this article series (February 2022 issue), we detailed two commonly asked lubricant related forging questions and their answers. We previously touched on clogged lubricant spray nozzles and foamy lubricant, two widespread and functionally critical issues found in forge shops. Each of these applications relates to the success or failure of the forging process. Today we will also detail two significant lubricant related forging questions. AML Industries gives practical, everyday solutions to common forging problems. So once again, let’s get to it! Why aren’t my forgings coming out properly formed after a long run of quality parts? There are many explanations for this, however, there is one reason that we see in the field regularly. This well-known problem is called part non-fill. It is important to understand that forging lubricants can contribute to several of the potential causes of non-fill. The first is the buildup of scale in the dies. This means that hot metal scale from the forging process settles in the die after the forging process is completed. This is remedied by properly descaling the dies after each forging by blowing air in the die to ensure that there is a clean die cavity for each forging. Similarly, applying too much lubricant to the die can lead to part non-fill, as sharp die angles can be filled with excess lubricant which prevents metal from flowing to that part of the die leading to misshapen parts. Let us take the example of a part with a complex geometry such as a crankshaft. Crankshafts have numerous sharp and deep angles in their die designs which are prime candidates to have lubricant and scale build up. This can lead to incorrect formation of parts as sharp die angles are not filled by flowing metal. Be sure to keep the forging die cavity clean, especially when complex geometries are involved. Even the best lubricant is ineffective when applied improperly or to a dirty die surface. Additionally, choosing an improper lubricant for the process can lead to part non-fill. Using the incorrect lubricant can lead to a lack of metal flow in the die which means that there is not enough lubricating medium available to assist the hot metal flowing to all parts of the die cavity. The proper lubricant applied precisely will lead to an effectively formed part without any excess lubricant buildup in the die. In applications like crankshaft forging, with their complex geometries and variety of forging depths, this is a key element to the success of the forging. Choosing the lubricant with the right properties such as lubricity, particle size, and binder package can make or break the best designed forging process. Part non-fill is a nuanced issue with several root causes, but these are the most common that we find in the field. Why are my dies wearing out so quickly? How is this related to my lubricant choice? The classic answer to this question is: it depends. Sometimes

abrasive die wear occurs, and every forge shop experiences different symptoms for this problem, including galling, scoring, pucking, pilling, lapping, etc. All of these symptoms contribute to the greater problem of excessive, abrasive die wear. Its root cause can include either the wrong lubricant being used, or the correct lubricant being applied improperly. Either of these scenarios will lead to improper wetting on the die surface and a lack of metal flow in these spots, impacting tool life and part finish. Forging processes with long dwell times such as those performed on hydraulic presses have enormous potential for oxidation of dry film lubricants and an oxidation resistant lubricant is needed. Furthermore, depending on the die temperatures in question, specific binder packages in the lubricant are optimized for proper wetting at that temperature. Improper application of the lubricant will leave certain areas of the die unprotected during forging, and this lack of parting between the tool and the workpiece can cause damage to both. An automated, atomized lubricant spray is always ideal, especially for low cycle time processes such as those done on mechanical presses. This produces a uniform coating on the die during each forging and reduces error, giving more consistent die protection. In each case, metal asperities align between the tooling and the workpiece and allow for this excessive, abrasive wear to occur. The goal of lubrication is to cover these rough areas on the metal surface and keep the tooling and workpiece protected. This is a matter of lubricant choice or application. In the case of forgings with long dwell times and high pressure, a lubricant that can manage the load and temperature ranges involved is important. Coating oxidation resistance, ideal particle size, and good wetting properties are all vital to the protection of the die and formation of the part. A lubricant tailored to this situation will withstand these conditions and protect the tooling from excessive wear. Once again, each of these problems have specialized solutions, and there are no one size fits all solutions to forging problems, especially those that involve lubrication. These answers are just a means of starting the problem-solving dialog.

Ethan Black Account Manager AML Industries Phone: 330-399-5000 Email: Eblack@amlube.com

Frank Sobnosky Jr. Chemical Engineer AML Industries, Inc Phone: 330-399-5000 Email: fsobnosky@amlube.com

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