Page 43 - MetalForming September 2011

Lean and SMED
Single-minute exchange of dies (SMED) is one of the many lean-man- ufacturing methods for reducing waste during stamping production. It pro- vides a quick and efficient way of changing over a manufacturing process from the current product to running the next product. This rapid change- over allows stampers to minimize pro- duction-lot sizes and reduce work-in- process (WIP) inventory.
The phrase “single minute” does not mean that all changeovers and startups should take only one min., but that they should take less than 10 min. In other words, a single-digit minute.
What simple procedures can a stam- per and its die setters take to accomplish SMED? For starters, maintain dies at a common shut height. This avoids the need to adjust shut height when changing dies. If it is not practical to use a common shut height for all dies, aim for a common shut height for those dies that get moved in and out of the press most often.
Dies also should be set up to run at a common feed or passline height. Generally, this should be as high as possible. Presses operated near their maximum shut-height adjustment maximize adjustment-screw engage- ment. A common passline height will avoid the need to make vertical adjust- ments to the feeders or loaders in coil- and blank-fed presses. Also, making the passline height as high as possible provides for steep scrap chutes to opti- mize scrap discharge.
Die Clamps,
Counterbalance Pressure, etc.
A die-clamp standard can save time by eliminating decisions at the press, such as which stud or finger clamp is needed, as well as clamp placement. Optimize the use of a die setter’s time by creating a die-change tool kit that contains everything needed. Another setup-time reducer is use of automat- ed clamping mechanisms that require very little adjustment, with as few tools
as possible. Magnetic die holders also are available for stamping presses, completely eliminating the need for clamps. These permanent-magnet die holders are failsafe—electric power is only used to turn them off.
An often-overlooked step during die setup is the adjustment of counterbal- ance pressure. When the counterbal- ance air-pressure setting is too high, excessive clutch wear can result. Mean- while, low pressure settings can lead to excessive brake wear and can cause the brake to dangerously overheat.
Safe press operations require that the counterbalance have enough capacity to hold the slide, the upper die and its attachments at any point in the stroke without the brake applied. In almost every plant, the die setter’s safe- ty and accident-prevention responsi- bilities include installation of protective devices, and checking and adjusting the devices to ensure that they work properly. The press counterbalance system is no exception. MF
Tooling Technology
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