Landing Gear Component – this part receives coating in multiple outside and inside positions, additionally there is no other surface on the part that can be used to work from once the part is coated.
The part is a new design axle sleeve manufactured from Titanium with HVOF applied Tungsten Carbide in critical bearing positions (2 outside and 2 inside), which must be precision ground to final print specifications including a coating thickness requirement on bearing positions.
Landing gear axle sleeve
HVOF applied tungsten carbide
Takes place in four bearing positions, 2 ID and 2 OD
Parts with thin walls between outside and inside diameters present challenges in controlling coating thickness specifications due to out of round conditions before the part is coated and the finished grinding takes place. This is especially true when both inside and outside diameters are to receive coating and finished grinding.
Aircraft landing gear components are commonly engineered for both ID and OD coating and grinding due to the high stresses on the part during landing operations. The part is a new design axle sleeve manufactured from Titanium with HVOF applied tungsten carbide in critical bearing positions (2 outside and 2 inside). These positions must be precision ground to final print specifications. That includes a coating thickness requirement on bearing positions. Additionally there is no other surface on the part that can be used to work from once the part is coated.
The part print tolerances specified for the bearing positions, both pre-coat of the substrate and final tolerances after coat and grind, created variables that potentially compromised maintaining the critical coating thickness. The primary contributor to the variables is the out-of-roundness allowed in both pre and after coat/grind which were needed due to the thin wall (OD to ID) of the part. The out-of-roundness tolerance is necessary as machining of the substrate prior to coating resulted in diametrical out of roundness due to work holding. Additionally the part print specified a geometric control for both OD’s to each other and both ID’s to each other. An OD to ID control was not necessary for the part and component function. While the print tolerances allowed for out-of-roundness, the subsequent planned coating of all OD and ID positions would not allow any reference positioning of the substrate during grind to control the close coating thickness requirement creating a high risk of grinding through the coating in areas.
Because it is necessary to allow out-of-roundness of the machined substrate bearing positions before coating, IPG recommended the part design be controlled with a true position control of the OD’s to ID’s. With the acceptance of the control, IPG then recommend to the coating supplier to coat the outside positions alone and allow IPG to locate on the out-of-round non-coated ID with a specially designed work-holding fixture that would round the part into a true position allowing grinding to final OD tolerances and absolute control of the critical coating thickness. Using a CNC OD grinder, IPG is able to grind both OD positions in the same clamping achieving exact positioning of OD to OD. The part was then returned to the coating supplier for ID coating. IPG then used a specially designed work-holding fixture to locate on the finish ground OD’s and ground both ID’s in a CNC ID grinder resulting in ID’s with exact positioning of ID to ID and to both OD’s while controlling the coating thickness requirement.