Improvements

After machining the first Payload Bulkhead (SN 3), several suggestions for improvements were made to decrease weight and improve wire organization. This optimized version of the payload Bulkhead addresses these improvements by the following changes:

  1. Large pockets added to the face to reduce weight. The thickness in these reduced areas is now 0.050".
  2. Material in the center section was removed completely.
  3. Internal radii were increased increased from 0.0625" to 0.125". This increases strength and is more fitting for our tool availability.
  4. The rim thickness is decreased to 0.0625" in areas that do not have tapped holes.
  5. The large 0.875" dia hole was replaced by four holes that house connectors that will better organize the wires that pass through.
  6. The material was changed from 6061 to 7075-T651.

Creating Blank

The stock was waterjet out of a 12" x 12" x 1" plate of 7075 aluminum.

Payload Bulkhead Stock Rev3.DXF is attached. This is the file that was used to waterjet the octagon blanks.

The stock was cut with 16 sides instead of 8 sides to reduce the amount of turning that would need to be done after the milling operations.

 

After the blank profile was cut, two opposing faces were cleaned up on the mill. Holding the blank in the vice with these surfaces, the largest faces were faced and checked for parallelism.

 

 

 

Preparing CAM

The toolpath was created using HSMworks from the Solidworks CAD file.

The tools used in the CAM included:

  0.5" flat endmill

  0.25" ball endmill

  centerdrill

  1/8" flat endmill

 

The estimated machining time was 58:52

Milling

This part was machined on a CNC mill in The Deep

The stock was clamped in the vice and the origin was set to the center of the part using an edge finder. After the tool table was created and the Gcode file loaded, we tried to run the operation, but the Z axis was not moving. We noticed that the machine was set to 2 AXIS mode which caused this problem and switching to 3 AXIS mode solved it.

Turning

Chucked on the mandrel made for the last bulkhead and indicated in. Indicated in to 4 thou of runout.

Significant chatter found at 1200 RPM, reducing the speed to 700 RPM yielded much better results until the last spring pass.

Radial Indexing

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Manufacturing Defects

  • Broke an end mill on the rib pattern during a travel - oops
  • Broke an end mill during the pass-through milling, raised a burr, filed out
  • 10 thou thicker in the web than designed (.025 lbs heavier)

Suggested manufacturing improvements

  • Leave stock on bottom face and remove on lathe to reduce chatter from pocketing operations
  • Add chamfer mill path to break all corners
  • Reduce 1/8 in end-mill feed rate to 6 IPM
  • 1/4 in ball mill chatter, adjust feeds and speeds
  • Model to include made to fit geometry.

Design Improvements

Maybe the best bulkhead we've ever made...

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