Excerpt from the article in the June 2005 issue of The Fabricator by Steven Rainwater
The activities, costs, and results of die lubrication do not neatly occupy related columns on a spreadsheet. When maintenance employees are deciding the best way to replenish fluid reservoirs, they usually do not review the previous quarter's shipping costs. When die designers select a tool steel, they usually do not focus on whether the fluid actuation is integrated with the press controls. When engineers determine a fluid viscosity, they seldom consider how many bundles of rags the press operators use each quarter. These seemingly unrelated categories and many others are related by die lubrication decisions.
Perhaps no other process in a stamping, forming, or fabricating facility reaches as broadly into the operation as die lubrication does. Yet, because it must be adapted to each manufactured part, lubrication sometimes is the last thing planned, and frequently it is approached haphazardly.
It's Worth the Effort
The truth is that a close look at the real impact of die lubrication should lead to measurable improvements. Carefully planned and executed die lubrication strategies can push significant efficiencies through an entire manufacturing operation.
The principal reason for applying fluids and lubricants in forming processes is to reduce friction and remove or dissipate heat. The heat and friction are generated at the point where the tool and the workpiece meet—that is, where the shaping, forming, bending, drawing, cutting, or punching takes place. The goal with die lubrication is to make sure an appropriate film of lubricant is at the interface between the tool and the workpiece to minimize or eliminate damage to the die and markings on the part.
The goal with fluid application is to find the best possible method to deliver the desired amount of lubricant to the area in the die where it is required and where it will do the most good. When determining the method, you should consider more than just the fluid delivery system.
You can select from dozens of ways to lubricate the interface between the die and the part. They range from those developed through thoughtful innovation to convenient workarounds using available resources. Most common die lubrication methods fall into one of two categories: direct die lubrication and direct stock lubrication.
Direct Die Lubrication
The most obvious way to lubricate the die is to apply fluid directly onto the surfaces that require protection. You can accomplish this by external spray, in-die spray, or drip/flood methods. The external spray method allows you to position nozzles in key locations around the die so they are pointed at the desired surfaces. In simpler applications, you can apply the lubricant by hand with a tank, a bottle, or even a brush. For in-die spray, you can integrate the nozzles with the die design, allowing fluid lines to be connected and lubricant delivered more precisely to critical spots.
Lubrication points that open up and spray or flood the die also can be designed into the tooling. This drip/flood method usually includes some type of pump to move the fluid from its container to the die. Each of these direct die lubrication methods enables the fluid to be applied at predetermined locations where friction exists or heat is generated.
The advantages of direct die lubrication include prolonged tool life, die protection, and precision routing of the fluid to its destination. It allows flexibility in positioning nozzles uniquely for different dies and plumbing permanent lines for use with multiple dies. The primary difficulty with direct die lubrication is that the fluid sometimes is applied where it is not needed. This increases consumption and requires appropriate and sometimes extensive attention to deal with the excess fluid.
Direct Stock Lubrication
Applying lubricant to the stock after the material handling process and before it enters the die also carries lubricant to the die. In some cases, lubricants are even applied when the coils or blanks are manufactured at the mill processing center.
The best way to lubricate stock is with a roller lubrication system. This method allows you to lubricate both sides of the stock uniformly. However, if the stock already has some contours or if the fluids are extremely thick, you might need to spray the lubricant onto the stock with directed spray nozzles.
You can apply the lubricant by hand-spraying it on with a spray bottle or by wiping it on with a sponge, flannel, or a brush. Or you can use the drip method, in which the lubricant falls from a container controlled by a petcock or other valve. The fluid falls either directly onto the stock or onto a piece of material that spreads it.
The benefits of stock lubrication are consistency, cleanness, control, and reduced fluid consumption. However, some complex dies require more fluid at certain key locations, which stock lubrication alone cannot provide. Additionally, it sometimes is difficult to achieve good results in stock lubrication when more viscous stamping fluids are used.
So, where is the impact of die lubrication most significant? It depends on how your company is organized. While the issues regarding die lubrication are nearly identical in all facilities, companies vary on how they organize the roles and responsibilities among the various departments. Following is a framework for evaluating the impact of die lubrication among four departments. This isn't a one-size-fits-all analysis. You'll have to tailor this so it fits your organization.