Lessons Learned  Mass Droduction  One of the main lessons learned was that for mass production, it is worth some up-front time and expense  to develop tooling and fixtures in order to save time later on. In order to more efficiently fabricate the 140  actuators, several mass production techniques were incorporated. For example, the application of dry film  lubrication usually requires masking to prevent the dry lube from being applied to sensitive areas. This  masking has traditionally been applied one unit at a time using  tape or a painted on compound. For this program, however,  special masking tools and holding fixtures were designed and  built ahead of time to streamline this operation. Another  aspect of mass production that we learned was that is well  worthwhile to spend more at the machining stage to save time  during the assembly stage. For example, match drilling for  alignment pins is always problematic in titanium in a clean  room. For this program the alignment holes were put in ahead  of time while the parts were being machined. At assembly the  parts went together very easily with no match drilling required  as shown in Figure 15.  Recast from EDM  Electro Discharge Machining or EDM was used to machine  many of the critical areas on the actuator because it results in  very good dimensional accuracy and repeatability. However,  the EDM process produces a recast layer on the surface of  the part. For a flexure, this recast layer can reduce the fatigue  life of the part by up to 10 times. Multiple passes in the EDM  process at Ball have resulted in a thin recast layer of about  0.0033 mm (0.00013 in), which is easily removed with light  chemical etching. Figure 15. Production Tooling  For one particular flexure, however, standard etching did not remove the recast layer. Additional etching to  remove the recast layer made the flexure area too thin. A review of the drawing and discussions with the  vendor revealed a misunderstanding of the process. A specific EDM process sequence has since been  defined, which results in a thin recast layer and acceptable flexure dimensions after recast removal.  Inspection techniques have also been developed to simplify the verification of recast removal.  Thermal straming  Titanium a poor thermal conductor and the gearmotor generates heat during operation, which affects the  length of the actuator. In order to test the actuators in a timely manner, heat straps were attached to  several points on the actuator. Again with mass production as a goal, special clamps were made so that  the thermal straps could be easily attached and removed.  Pathfinder for the EDU  It is usually good practice to have an Engineering Development Unit (EDU) as a precursor to building a  flight unit. JWST took advantage of this "lesson learned" that has been cited by many authors. The EDU  for JWST consisted of 18 units to be used as follows: 7 actuators for the Primary Mirror Assembly, 6  actuators for the Secondary Mirror assembly, 2 actuators for a life test and 3 actuators for spares. With so  many units to build, it was decided to turn one of the spare actuators into a "pathfinder" unit, which is  essentially a first article development unit for the EDU. One actuator was taken from the initial build and  designated as the pathfinder. This unit was the first to be assembled and the first to be tested. Any new  testing or fixture was proven out on the pathfinder. To maintain schedule and to have processes verified in  advance, certain shortcuts were allowed on this unit. For example, although the components were cleaned  to a flight level, the pathfinder parts were not subject to an external particle count.  25 1