By Sarah Jordan

Cold spray additive manufacturing (CSAM) is a new process.  It is based on traditional cold spray technology.  The process works by accelerating powder particles to nearly the speed of sound.  This gives the particles the needed energy to bond to a material.

CSAM has been adopted for use in repair.  It is also used for component manufacturing.  It is a solid-state process.  This means that no melting occurs.  Typically, the temperature is below 400℉.  CSAM has been shown to work with most metals and alloys.  It also can work with metallic glasses, metal matrix composites (MMCs), and even polymers. The process has several benefits including:

• High deposition rate of up to 100 lbs. per hour. 
• There are larger build envelopes due to not needing an inert gas or vacuum.  This means larger parts can be made.
• Low energy use.
• Parts do not have heat affected zones.  They do not require a post process heat treatment.  This saves time, prevents distortion, and makes repairs easier.
• The process can join different metals to make new metal matrix composites.

With such beneficial capabilities, CSAM is utilized in many industries.  These include aerospace, defense, tooling applications, and more. 

A problem with CSAM has been that the material can fall short of the expected properties.  This is particularly true for harder metals which tend to have more porosity and less bonding. Attempts have been made to address this with post-processing.  Current techniques, however, can cause cracks, distortion, and thermal-induced metallurgy problems.  The application of heat is an issue for any CSAM that involves multiple metals.  When heat is applied the two metals can diffuse into one another, creating undesirable brittle intermetallics. 

Ultrasonic additive manufacturing (UAM) has recently been utilized as an alternative post-process technique.  Normally UAM is used to consolidate metal foils into a solid piece of metal.  The process uses high-powered ultrasonic vibrations (20,000 to 30,000 Hertz) in combination with downward pressure.  This creates a friction bond that joins the foils together. 

In the case of UAM as a post process, the metal foils were removed.  The UAM head was used on the CSAM surface to further consolidate the cold spray material.  The benefits of UAM as a post process are that it has similar characteristics to CSAM.  UAM is also fast, has large build envelopes, does not require an inert gas or vacuum, has low energy use, and is a solid-state process.

In the study, cold spray was used to produce MMCs made of two blends of metal powders.  The powders used were Cu-38Ni and CrC-30NiCr.  Then UAM was performed on cold spray deposits to further consolidate the material.  Testing included hardness, adhesive strength, tensile properties, porosity, and resulting microstructure.

The application of the UAM post-process showed great results:

• The ability to compress and level the surface coating and improve the surface finish.
• Hardness showed a slight increase of 2-5%.
• Adhesive strength increased 8-13%. 
• Yield strength increased 4-11%.   
• The grain size was also shown as being refined which can potentially improve the corrosion resistance. 

This is an initial study to use UAM as a post process.  The results appear very promising!

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6 responses to “What Could Make Cold Spray Additive Manufacturing (CSAM) Better? – UAM Post Processing”

1. Don Shrader says:

   November 17, 2021 at 9:43 am

   Mark,
   This sounds like a great extension of your UAM technology. Are you going to continue development in-house or go for some kind of SBIR program?

2. Julio villafuerte says:

   November 17, 2021 at 9:45 am

   Interesting perspective on a technique that has been used for sometime now. In fact additive manufacturing (AM) has used a number of thermal and solid state techniques for some years now, each one with its benefits and shortfalls. In the case of cold spray process for AM the benefit is faster build rates, no thermal effects, and ability to make large parts; shortfalls include lack of high spatial resolution and mechanical properties below equivalent material obtained by thermal processes

3. Kraig Miller says:

   November 18, 2021 at 5:23 am

   Hello,

   I have been thinking about a similar application to the Cold Spray + UAM process, where the powder material would be easier to source than getting the material in strips used for the typical Fabrisonic process.

   1) Do you machine the cold spray surface to improve the surface finish prior to UAM or can you leave the surface in the as cold sprayed condition?

   2) How thick of a cold spray thickness can you apply prior to utilizing UAM? I’m thinking it depends on the material type, but are you limiting the cold spray thickness to the thickness you would limit the strip thickness for the Frabrisonic process?

4. Vaclav Jetela says:

   November 18, 2021 at 6:31 am

   These first results are encouraging. I am looking forward to the results with other materials.

5. Mark Norfolk says:

   November 18, 2021 at 8:37 am

   Thanks Don, Our parent company EWI has several pieces of cold spray gear. We plan to continue down this path over the next year with IRD. However, if you see any good fits with SBIR topics, please let us know!

6. Mark Norfolk says:

   November 18, 2021 at 8:39 am

   Thanks Craig,
   1) We have experimented with both as sprayed and milled surfaces. We get better repeatability with milled surfaces.
   2) We don’t have a good feel for thickness yet. That is a great question we will be researching further.