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Problems on punching think strip with TIN coated material

Stripper unable to return, this seem to be simple issue, but we took months to found out the root cause and came out with the fool prove solutiion..

  ;

piercing This is a Progressive tool we designed. It is intended to run at a speed of 80 spm to progressively punch 60 holes of 0.5 mm diameter into a tin-coated area. The product is extremely sensitive to oil and dust. Therefore, no lubricant was utilised during the entire punching process.

The tool will be punching into a 0.1mm thick polymer which is coated with a 0.05 mm thick copper strip. The area to be cut was coated with Tin of 0.1-0.15 mm thick.

Issue encountered: Stripper jams after every 20-30,000 strokes.

Observation: Galling Effect occured on the tips of each punch.

galling

It was suspected that thoes punches surface were too rough, causing temperature to increase with each punch. Hence, the tin melted and was welded on the punch’s surface. Overall, this led to an increased in friction between the punches and stripper guide holes.

Countermeasure:

polish small punchWe polished all small punches to a surface finish of Ra 0.05. In addition, we coated them with TiCN to reduce friction.


Unfortunately, there was no significant improvement and the stripper still jammed after ~40,000 strokes of continuous punching.

We re-polished all punches and coated them with TiCN, reduced the stripper guiding land from 1.0 mm to 0.5mm to further reduce contact areas.
After this modification, no stoppages were observed after 5 days of continue production.

stripper unable to returnStripp guide reduced from 1.0mm to 0.5mm

 

 

 

Conclusion
When cutting soft materials with low melting points, Galling Effect occurs as soft material will build up on the punches surface. This increases the stripping force and might cause the punch to break off. Surface of cutting elements such as punches, have to be as smooth as possible to reduce friction between material to be cut and cutting elements. Polishing it to Ra 0.05 and coating with TiCN is advisible.

 

Reducing unnecessary guiding, thus reducing surface contact, to avoid excessive friction is the key.

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