Lubricant application key to optimal metal stamping results
Every metal stamping process has, at its core, three key components that contribute to its overall success: the work material being stamped, the proper tooling, and the correct lubricant to help aid material flow inside the tool. A successful stamping operation requires that all three components are carefully selected to achieve their desired purpose. The part material is chosen for the desired strength of the finished part. The tooling is designed to produce the required part geometries. The lubricant is specified for its friction-reducing performance between the part material and the tooling. However, an important aspect of lubrication—the method of applying the lubricant in the actual production setting—is frequently overlooked during the process design stage, but it is as critical as the lubricant itself.
Lubricant and Its Application Go Hand-in-Hand
Selecting the proper lubricant for a stamping process is not a trivial process. A whole field of study, referred to as tribology, exists for understanding the interaction between two moving surfaces in contact with each other. Studying tribology helps increase the understanding of critical operation parameters within the metal stamping process, such as friction, wear, and lubricity. Tribologists and lubrication engineers often run several tests to determine how well a particular lubricant will work between two surfaces. During these tests, lubricant is applied between a material that is a proxy for the tooling and a second material that is a proxy for the part material. Lubrication evaluation tests include the cup draw test, twist-compression test, pin and V-block test, 4-ball wear test, and ball-on disk test. Each of these tests simulates the stamping process. The test lubricant can prove its effectiveness within the scope of the test. While each of these tests is slightly different, each is useful for verifying certain parameters of the process. At the most basic level, all of these tests will measure how much force is required to get the two surfaces to move relative to one another for a given contact pressure between two surfaces. The tests also can determine at what point things start to fail. A series of controlled testscan be run to evaluate the performance of lubricants. However, the actual delivery method of lubricant to the process is often an afterthought, and this afterthought can lead to incredible inefficiencies within the overall process. It’s just as important that the proper amount of lubrication be applied to the tooling or material in the right place at the right time. An ineffective application method can defeat the purpose of the lubricant’s properties that have been so carefully tested and specified. At least three negative symptoms within the stamping process are a red flag that the application process is not a good fit:
1. Mess. The first symptom is a wet, slippery, greasy mess as a result of lubricant overapplication. When a system is not specified to deliver the lubricant where needed, neatly and properly, the alternative is to apply a lot of lubricant everywhere. When lubricant is overapplied, the parts, scrap, and tooling coming out of the press leave trails of lubricant throughout the facility by part bins, dies, and forklifts. This causes unsafe, slippery conditions; requires excessive part cleaning; and creates an overall messy environment. Too often operators live by the motto that more is better; however, with lubrication this is not always the case.
2. Inadequate, Inconsistent Coverage. The second symptom of an inadequate lubricant application system is spotty, inconsistent coverage. Stamping processes are impeded by dripping nozzles, misaimed spray tips, and a lack of process monitoring to ensure proper lubricant delivery. Part quality and tool life can suffer. Part cracking and premature tooling wear lead to excess scrap and increased machine downtime.
3. Waste and Cost. The third symptom of an inadequate lubricant application system is wasted lubricant as evidenced by full press pits and empty lubricant dispensers. When lubricant ends up on the floor, it is no longer carrying out its intended purpose. Frequent pumping and disposal of fluids from press pits is a large, unnecessary charge. Washing parts that are covered with excess lubricant is an added expense as well.
Contact or noncontact application?
Two basic methods for applying lubricant to a part are contact and noncontact. Contact methods include applicators that roll coat, wipe, or submerge and squeegee the material. Contact applicators can provide the neatest application and provide consistent coatings over the entirety of the part material, top and bottom. Noncontact lubrication generally refers to a spray type of application. Spray applicators can use airless spray, air-assisted spray, or electrostatic spray nozzles. Each of these has its place, but the main benefit of noncontact lubrication is that nothing but the . . .