Page 31 - MetalForming July 2009

Other process improvements real- ized from in-die fastening include faster throughput, less material handling, reduced scrap, and minimized floor- space requirements. Also, in virtually all cases, the investment required for an in- die system will be less than that for comparable secondary fastening equip- ment with similar capabilities.
To optimize the productivity of an in-die fastening system, users should have a thorough understanding of potential problems and the vital role that troubleshooting can play in over- coming these problems and ensuring high equipment uptime. Troubleshoot- ing in-die systems generally requires a metal stamper to investigate among four major areas: the fasteners, the feed system, the in-die tools (or insertion heads) and the control system.
The Fasteners
While fastener parameters such as material hardness and plating cannot be ignored, the dimensional characteristics of the fasteners usually are the most important parameters affecting proper operation of an in-die fastening sys- tem. As with all manufactured parts, fas- tener tolerances are critical—the in-die system must be able to accommodate the largest possible dimensions without allowing fasteners in the smallest dimensions to jam.
This may seem straightforward, but operators must be prepared to consid- er stacked tolerances. Even if each indi- vidual feature on a fastener falls with- in tolerance, the stacking of the dimensions may produce a fastener outside the acceptable range. Metal- formers can lose an excessive amount of time modifying system components such as feed rails and die tooling to accept a particular fastener size, only to discover later that the next lot of fas- teners will not feed properly due to the modifications made.
Users can eliminate this possibility by assessing the tolerances for the various features of the fastener while also deter- mining the stacked tolerances of critical
dimensions. This approach will reliably define the parameter in terms of what will and will not feed in the system.
The Feed System
Prior to beginning production, met- alformers should consider running their feed system offline at production speed. This allows testing and troubleshooting prior to production. It also—should a problem occur during a production run—frees the press to run other jobs until the problem can be solved. (Note: This approach will work particularly well if the feed system is engineered for quick connection to the press and die. If it takes considerable time to set up and break down the system, running offline may not be practical.)
The most frequent problems involv- ing feed systems are jamming, slow feed rates, and upside-down or misoriented fasteners.
Jamming typically results from dimensional changes to the fastener, worn components such as feed rails and shuttles, or amplitude changes to the vibratory bowl or inline drives. Dis- cover fastener dimensional changes and worn components using measurements and visual inspection. Amplitude changes can be more difficult to discern. The three factors metalformers should consider: the amount of fasteners staged in the bowl, voltage changes in the elec- trical supply, and changes to the ampli- tude settings.
If too many or too few fasteners are staged in the bowl, the feed system may run too quickly or too slowly. The amount of fasteners is controlled by a hopper sensor, which sets the high/low limit for the amount in the bowl. A defective hopper sensor or a sensor set incorrectly will cause the bowl to run erratically.
Voltage changes can produce a sim- ilar effect. Typically, voltage can fluctu- ate due to changes in the load on the electrical line. If other equipment or machines are on the same circuit, the voltage may be affected as the equip- ment cycles on and off, affecting ampli-
tude. These settings are changed to compensate for one of the aforemen- tioned conditions. While changing the settings can temporarily solve the prob- lem, additional problems ultimately will occur. Feeder bowls are designed to run within a specified range and, when overfeeding, they will tend to jam.
Slow feed rates can be caused by similar problems, but there are addi- tional factors to consider. In pneumat- ically fed systems, blower time settings can affect feed rates. Here, the fasteners feed to the die individually as the press strokes. If blower times are excessive, less time may be available for fastener stag- ing and the shuttle must wait for the blower time to end before the next fas- tener can be fed from the bowl. Although these types of systems gener- ally are considered the most effective, care must be taken in setting blower times. When set properly, metalformers can achieve feed rates in excess of 60 strokes/min.
Broken bowl springs also may con- tribute to slow feed rates. These flat, hardened springs usually break at their attachment points and the cracks can be difficult to detect. Operators should inspect the springs carefully for fatigue cracks, and may need to remove the springs for a thorough inspection.
A properly designed and maintained system should not result in upside- down or misoriented fasteners. At min- imum, however, each feed track should contain a feature to prevent incorrect- ly oriented fasteners from passing to the die. The usual causes of misorient- ed fasteners are worn or missing tooling from the feed system, or dimensionally incorrect fasteners. If the tooling fea- tures are worn or have been removed, upside-down fasteners may, unfortu- nately, be fed, especially in the case of clinch nuts, where little difference exists between the fastener’s top and bottom.
In-DieTools
Problems with the in-die tool usually result in fastener-positioning problems, poor clinch performance or damaged
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