Laser forming of titanium and other metals is useable within metallurgical constraints

Abstract

Laser Forming (LF) of many metals has been tested and modeled. Investigations with Ti have identified the amount of LF possible under many different conditions. Recent examinations of LF articles have shown the ability of the LF process to maintain appropriate metallurgy. In order to benefit from the strength of titanium, LF must be carried out in practice to avoid deleterious oxygen and nitrogen absorption as well as excessive thermal conditions that can change the state of the titanium surface. LF heats the sheet or plate of metal from one side with a moving deposition pattern that can be controlled to keep every point in the workpiece under a predetermined maximum temperature (Tm) or below too large a product of high temperatures and time. Otherwise a subnormal state will appear and affect strength and resistance to fatigue. Modeling carried out with finite element models indicate there is little LF in Ti unless there are momentary temperature excursions over 1000 K. 1000K is the normal long cycle process temperature limit accepted for Ti. It is adopted here as the lower temperature boundary for an integral of excess temperature (T – 1000 K) and time. That integral (∫Tedt) in practice is determined by temperature excursions in LF of Ti that last for seconds to minutes. Calculations for LF of Ti have been carried out for many varied conditions that span a range of Tm and a range of values of ∫Tedt and indicate substantial forming with one pass. Next tests were needed to find the values for Tm and for ∫Tedt that maintain the necessary Ti metallurgical state. In order to find the extent of the window of allowed process parameters for LF by means of a determination of Tm and ∫Tedt, Ti specimens were heated in a Gleeble testing machine. It provided quick Ohmic heating to specific Tm and quick cooling in the absence of oxygen and nitrogen to provide a range of values of ∫Tedt having good correspondence to the range of LF time profiles. Each individual Gleeble specimen had unique settings for the Tm and the heating rate; the set of tests covered a range of thermal conditions similar those evaluated by the modeling of LF. The Gleeble specimens were analyzed after they went through the heating tests for changed metallurgy to identify the limits for acceptable Tm and ∫Tedt. The modeling data base then provided the transient LF process parameters that could be acceptable with Ti as determined by the acceptable values for Tm and ∫Tedt that maintain the necessary Ti metallurgical state. Details of the metallurgical examinations on these Gleeble test specimens and on actual LF metal specimens (Ti, Inconel 625, Inconel 718, and steels) of interest in the LF program are presented. The useable parameter space for LF of Ti is presented along with resulting modeling predictions for the amount of forming that is possible while maintaining appropriate metallurgy.Laser Forming (LF) of many metals has been tested and modeled. Investigations with Ti have identified the amount of LF possible under many different conditions. Recent examinations of LF articles have shown the ability of the LF process to maintain appropriate metallurgy. In order to benefit from the strength of titanium, LF must be carried out in practice to avoid deleterious oxygen and nitrogen absorption as well as excessive thermal conditions that can change the state of the titanium surface. LF heats the sheet or plate of metal from one side with a moving deposition pattern that can be controlled to keep every point in the workpiece under a predetermined maximum temperature (Tm) or below too large a product of high temperatures and time. Otherwise a subnormal state will appear and affect strength and resistance to fatigue. Modeling carried out with finite element models indicate there is little LF in Ti unless there are momentary temperature excursions over 1000 K. 1000K is the normal long cycle proc...