Here, lubricant floods tooling to reduce friction and enable safe prodcution of quality stamped parts. The shield in this press window helps contain lubricant, which can be reclaimed for re-use or safe disposal.
Photo courtesy of Stripmatic Products Inc., Cleveland, OH.
Forming fluids are critically important to the production of quality stamped parts and the service life of tooling and dies. This article describes the benefits imparted by stamping lubricants. It also describes delivery systems for forming fluids including manual application of lubricant and lubricant flooding as well as dripping, rolling and spraying.
Metal stamping is a capital-intensive process. Costs for production machinery, materials, material-handling equipment, utilities and other overhead, and human expertise are quite high. But given all this high-dollar investment, parts cannot be stamped successfully without the contribution of forming fluids.
Why is metal-stamping lubrication important?
During the metal-stamping process, hundreds or even thousands of tons of pressure are exerted on the sheetmetal to form a part. The forces acting on the material and the tooling and dies during the downward pressure of the ram and at the moment of snapthrough cause incredible stress throughout the metal-stamping system. With such forces come the bending, scraping and stretching of material around the tooling. This violent process produces friction as metal meets metal. It is this friction that leads to galling, chipping and other problems, ultimately leading to tool failure and production of costly scrap instead of money-making quality parts. Something is needed to prevent that metal-to-metal contact yet allow forces to transfer from the tooling to the part material. That something is the stamping lubricant. The function of a stamping lubricant is to minimize the contact between the tooling and the part material during forming. A proper barrier—in this case a proper forming fluid—leads to less press-tonnage requirements, increased tooling life and higher-quality stamped parts.
What factors determine stamping-lubricant performance?
The reasons why lubricants are important seem simple enough, but difficulties arise given the complexity of tool and part-material surfaces. Surface complexities extend far beyond the characteristics of the full tool-steel piece or the internal chemistry of the sheetmetal. Materials may have undergone surface treatments—they may be nitrided, carburized or decarburized—or may have some other form of coating. All of these conditions affect forming-fluid performance. In addition, a stamping lubricant is in contact with oxide layers on the surface of materials. Oxide layers may be contaminated with dirt, acids, oils, rust inhibitors, etc. Here again, stamping-lubricant performance is affected. Beyond chemistry and chemical interaction, surface quality of materials also affects lubricant performance. Sheetmetal surfaces, owing to prior processing undertaken to produce thin sheet in coil form, may hold residual stresses, and such processing may even alter the surface structure. Physical imperfections such as scratches and roughness also test the functionality of forming fluids. All or any of these conditions can result in tool damage, excessive die wear and production of substandard metal stampings.
Lubricant and metal-stamping researchers, having studied these seemingly endless material variables and complex interactions between materials, have developed a variety of stamping-lubricant families and formulations.
How are forming fluids applied?
We know that lubrication is key to successful sheetmetal stamping. Given that, stampers must determine the best method of applying lubricant so that it can perform at its best. Optimal application depends of the type of lubricant used, the type of tooling used, the amount of forming required to produce a part, the number of parts to be produced in a job run and the type of material being formed. Lubricant application also depends on the setup of a metal-stamping operation. Sometimes, limited room within and surrounding the press limits the type of applications available to the stamper.
Methods of application include:
- Manual application—Forming fluid may be brushed on or applied by hand with rollers. Though the simplest method, manual application is inherently imprecise. Proper coverage of the sheetmetal and tool surfaces is not guaranteed, nor is the proper amount. This method can also be costly, as it requires manpower, and personnel must wear proper attire when working so closely with stamping lubricants. In addition, the process demands that personnel be located in close proximity to machinery, necessitating proper safeguarding.
The following automated application methods often employ lubricant-storage tanks located near the stamping press or in a remote location. Forming fluid is pumped to the press and often is reclaimed.
- Flooding—With this method, the tooling and sheetmetal are awash with stamping lubricant. In such cases the stamping press may have an enclosure to prevent lubricant from escaping and to provide the means to recapture it. Though effective, the use of such large amounts of forming fluid often require parts cleaning following the metal-stamping operation.
- Dripping—Lubricant is dripped onto the sheetmetal prior to stamping or during the metal-stamping process. This method uses less forming fluid than flooding.
- Rolling—Automated rollers apply lubricant to the topside or underside (or both) of the sheetmetal prior to its entry into the work area of the stamping press. This method saves on lubricant usage and cleanup as compared to flooding and manual application.
- Spraying—Spray nozzles are positioned to apply precise amounts of lubricant to precise areas of the sheetmetal or tooling. Computer control of the process enables fine-tuning of the amount of stamping lubricant applied.
- How does your metal-stamping operation typically apply forming fluid?
- What efforts does your stamping company take to control release of stamping lubricant into the pressroom environment?