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Purpose

The leading edge (LE) protects the fin from the aerodynamic heating. It also moves the elastic center and the center of mass forward. It adds considerable stiffness to the fin. 

 Materials

For Machining:

Raw Materials:

  1. 1/4" Thick 316 Stainless Steel Plate
  2. Fin Preform (FC002). For testing fit. 

Tooling and Machines:

  1. 1/8" TiAlN Coated Carbide 4 Flute End Mill for Stainless Steel (McMaster  8883a11)
  2. Mill (At least 5000 rpm and set up for mist or flood coolant)

Fabrication

Machining

Machining stainless steel is difficult. Do not expect the process to go as smoothly as machining aluminum. If you have never worked with stainless steel before, ask for help, expect to break an endmill or two, and buy extra stock and tooling because you will probably need it.

For the slots, using a slot saw works fine with phenolic and aluminium. But for stainless steel, HSS tools performs very poorly and it's better to do the slots with an end-mill.

I. Making the Blanks

  1. Get sheet stock that has the thickness of the final leading edge.
  2. If you have not used the waterjet before, ask for help.
  3. From the CAD model, make a .dxf drawing of the part. Check dimensions.
  4. Using the related Waterjet software, copy-paste and orient the part such that you can get as many parts from the stock as possible. Make sure that all of the pieces fit in the frame of the stock.
  5. Check settings related to thickness, material etc., make sure they are correct.
  6. Follow the procedure for waterjetting. After getting the first piece, make sure dimensions are correct.

II. Machining the Slot

  1. Break all edges. 
  2. Secure the blank in the vise. 
  3. Set the speed to 5000 rpm, and the feed to 15 ipm. 
  4. Turn on the coolant.
  5. Plunging 1/16" at a time, cut the slot. Power feed is your friend.
  6. Once you have reached the desired depth, test the slot width with the Fin Preform. Run .005" finishing passes until it fits snugly. 

III. Machining the Taper

There are a couple ways to go about this. The first is to use a tapered end mill. This worked well on phenolic. However, now there is a concern that the tapered end mill will not have a uniform chip load and would be a poor choice on stainless steel. The alternative is to tilt the head of the mill or set up an angled work holding. 

IV. Finishing

  1. Attach sand paper to a flat plate, Sand outer faces through 1500 grit.
  2. Polish outer faces.
  3. Clean and degrease all surfaces with acetone in preparation for bonding with the fin preform.

V. Inspection

  1. Measure the full length of the leading edge. Confirm that it is within spec.
  2. Measure the width of the leading edge. Confirm that it is within spec.
  3. Measure the bluntness of the tip. If it is not within spec, sharpen the leading edge until it is within spec.

 

 

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