Category: Auto insertion

Continuity Tube Life Expectancy

Applies to tubes used in Generation 8 clinch units.

The expected life span of a Continuity Tube is dependent upon a number of factors including:

• Lead Composition

A Continuity Tube that is subjected to steel leaded components will cause more stress between the cutter, the cutter Bushing, and the continuity Tube. Expect to experience a higher wear rate on a continuity tube that is subjected to stiffer lead material than a continuity tube that is subjected to softer leaded material.

• Lead Diameter

A larger lead diameter will cause more stress between the cutter, the cutter bushing, and the continuity tube. Larger leads being cut will accelerate the wear of a Continuity Tube.

• Tooling Maintenance

Worn Tooling (cutters and cutter bushings) will cause the scrap lead to ‘tear’ instead of cut with a sharp clean cut. This ‘tear’ in the lead will accelerate continuity tube on both the metal tube and the plastic surrounding the metal tube. The tooling should be changed at recommended intervals, sooner if tearing of leads is noticed.

• Working Environment (dust, humidity, temperature, etc.)

The continuity tube should be kept as clean as possible. Dust buildup caused as a result of the cut/form process and clinching process will grind into the metal tube and the plastic surrounding the metal tube possibly causing accelerated wear of the continuity tube.

There are too many variables associated with the performance of a continuity tube to allow Universal to list it as ‘consumable tooling’ and publish an estimated life span. The greatest life span will be generated by keeping the continuity tube as clean as possible, keeping the lead length within the middle of acceptable lead length range, and changing the cutters and cutter bushings on a regular basis.

Continuity Tubes and False Insertion Errors

Proper continuity lead sense is dependent upon the relationship between:

• the continuity tube
• the cutter
• the angle of the lead being cut
• the lead length as the leads are cut.

It is important the lead is bent and touches the continuity tube before the cut takes place, making the position where the lead enters the cut and clinch assembly very important.

As the cutter moves across to the cut position, the lead begins to bend in the direction of the continuity tube.  However, once the lead is pinched between the cutter and the cutter bushing, the scrap portion of the lead will no longer be pushed toward the continuity tube.  At this point the scrap portion of the lead will actually be forced in the opposite direction of the continuity tube as the cutter shears through the lead.

The following scenario describes what happens if the lead length is set too short.  In other words, the lead entrance to the cutter bushing set so the lead is very close the cutter bushing shear point.

By setting the lead length too short, (the lead too close to the cut point of the cutter bushing), the scrap portion of the lead will not be bent far enough to reach the continuity tube as the cutter bends the lead, resulting in a false insertion error.  In other words, if the lead reaches the cut point before it has been bent far enough to touch the continuity tube, a false continuity error may occur.

On the other hand, having the lead length too long may cause accelerated wear and damage to the continuity tubes.  Forcing the lead into the continuity tube with too much force will cause denting of the continuity tube and wear of the plastic insulation, resulting in premature failure and false continuity errors over time. 

Cutter Stroke Speed and false Continuity Errors

The length of time necessary to drive the Cutter from the home position, to the extended ‘cut’ position, can affect continuity sensing.  If the cutter speed is set too slow, the cutter air pressure is insufficient, or a mechanical assembly used in the operation of the cutter stroke binds, the cutter will not reach the component lead in the ‘window’ of time necessary for continuity to be sensed.  This will result in a false continuity error.  Examples of cutter stroke speed problems:

• Pneumatic flow control for the cutters not properly set
• Poor air flow from the valve to the cutter
• Binding in the mechanical linkage from the cutter piston to the cutter
• Lack of sufficient lubrication in the mechanical linkage from the cutter piston to the cutter
• Incorrectly set cutter backstroke (the starting position for the cutter)
• A torn O-ring on the cutter piston which causes a bind in the cylinder
• Lack of sufficient lubrication on the O-ring for the cutter piston

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