Punched slugs

Under slug generally refers to small pieces of waste that the stamping of sheet metal produced. The shape of these punching slugs depends on the cutting punch and die geometry. Punched slugs are recycled or used in later production processes.

Problems in the manufacturing process

Rising punched slugs

Rising punching slugs that do not end up in the waste container, but rather “lie sideways”, have always represented a frequently occurring disruption of the production process during punching. The higher the punching speed, the higher the probability of this phenomenon. Punching slugs are pulled up from the slug channel by the cutting punch during the punching process due to the process and / or material. Possible causes for this are:

• too large a cutting gap ,
• Sticking of the slug to the stamp by adhesion ,
• thick, resinous lubricant ,
• Burr formation on the slug due to tool wear ,
• Magnetic effect in the tool or material,
• unfavorable feeding to the waste container.

They often stay in the tool . The consequences are product damage, tool damage, process disruptions, additional set-up times and possibly time-consuming tool repairs. The following measures are known to avoid these undesirable effects:

• Grinding of the punch face in order to deform the punch
• Cutting stamp with spring-loaded impression pen
• Insertion of DAE ( dynamic stripping element ) into the die
• Holding claws in the die
• Apply compressed air to the cutting punch
• Embossing a small wart

Clogged waste openings

When the punching slugs accumulate in the openings through the tool (die, block) and are compressed, enormous lateral pressures are created. These can lead to the formation of cracks in the tool or even to the complete destruction of the die or tool. If the die side is destroyed by this process, subsequent defects often occur on the punch side. There is massive damage with high repair costs. Possible causes for the problem are:

• Operating errors during set-up (waste outlet openings not free, e.g. covered by documents)
• Worn cutting elements, as a result of which chips or a punch burr form and wedge the waste
• Unfavorable shape on the die (missing or insufficient taper)
• Insufficient use of lubricant , which leads to increased friction

prevention

High-performance tools or presses are more and more often equipped with sensors (force or ultrasonic sensors) and process monitoring systems or even with significantly more expensive camera systems in order to detect incorrect positions in the punched slug. These systems send a stop signal to the press control when a slug is detected. In this way, the punching slug can be removed by the press operator before he damages the tool or the product. The protection of tools and products is still not at the expense of productivity . The opposite is often the case. Production time is lost because the press stops if the punching slugs have gone wrong and the operator has to remove them first. However, the presses can run significantly faster with modern monitoring systems, since errors are reliably detected. The production costs are also reduced because possible damage to the tool is minimized by the monitoring.

The ejection of waste can also be monitored using optical or ultrasonic sensors . If the corresponding signal is missing for a specified number of strokes, the process is stopped.

In order to avoid costs for subsequent tool changes, a sensible waste attachment should be considered when developing new tools. In this way, the cause is combated at the earliest possible point in time. Under certain circumstances, expensive monitoring systems can be saved, which in turn also produce downtimes due to pseudo errors. The “zero-defect production” cannot be “checked”, so the punching process must be stable - right from the start.

If the appropriate tool design has been successful and additional safety systems have been integrated, the production speed can be adapted to the performance of the press or peripherals ( feed , straightener ).