Cold Welding

Cold welding under vacuum and launch conditions

It is the aim of AAC to provide engin­eers with data on adhe­sion force: in worst case this force needs to be over­come by the open­ing mech­an­ism. This helps in design of mech­an­isms and reduces risk in fail­ure during final model test­ing. It offers on one hand determ­in­a­tion of cold weld­ing on bare metal contacts and on the other hand life-times of anti-adhe­sion coat­ings. AAC has created on basis of an ESA- agreed test proced­ure (STM-279) data on several typical combin­a­tions of space mater­i­als and coatings.

Testing is offered for custom­ers in 3 ways:

  • Consultancy and test­ing of candid­ate mater­i­als accord­ing to customer specificaitons
  • Launch-test” fret­ting in 3 steps (Air-LowVacuum-HighVacuum) to proof under launch conditions
  • Assessment of contact mater­ial combin­a­tion to cold weld­ing (determ­in­a­tion of adhe­sion forces or life time of coat­ings) in compar­ison to exist­ing data (STM-279).
    ([Link: http://coldweld....])
Cold welding due to fretting (“Fretting Test Facility”)

The fret­ting facil­ity enables the meas­ure­ment of the adhe­sion force between two mater­i­als in cyclic closed contacts which are subjec­ted to fret­ting. This means that pin and disc are oscil­lated in their contact plane with small amplitudes (50 µm). “Cyclic contact” means that the contact between the pin and the disc is closed and opened for several (thou­sand) cycles.

Cold_Welding_1After clos­ing the contact, fret­ting is applied for a select­able dura­tion. After stop­ping fret­ting, the contact is opened and at each open­ing the adhe­sion force, i.e. the force neces­sary to separ­ate both in vertical direc­tion, is meas­ured. High resol­u­tions down to 50 mN can be achieved. The test provides the tend­ency to cold weld­ing by a plot of the adhe­sion force as func­tion of cycles.

Cold welding due to impact (“Impact Test Facility”)

This facil­ity is similar to the fret­ting test device, however it enables to close the contact with an impact. It also enables ultra high vacuum down to 5.10-8mbar.