Additive manufacturing is a process also called 3D printing or direct digital manufacturing. Additive manufacturing technology started as a prototyping technique but is now quickly evolving towards an established advanced manufacturing process especially for the aerospace and biomedical industries. This technology allows producing a tri-dimensional metallic part directly from a computer assisted design (CAD). AM uses a source of energy to melt metal powder layer by layer in order to build a part accordingly to the CAD file. The source of energy is usually an electron or a laser beam. Additive manufacturing is useful to rapidly figure out the nature of the object in 3D and to test the design. This technology can be divided in 3 categories: prototyping, rapid tooling and rapid manufacturing which all uses the same process.
Additive manufacturing is particularly useful for expensive materials and complex parts. AM allows complete freedom of design. As an example, AM can often allow the design and manufacturing of a complex single piece part whereby traditional machining techniques would require the manufacturing and assembly of multiple parts. Therefore AM contributes to reduce costs and waste associated to conventional machining. AM also allows more efficient designs resulting in the reduction of the overall weight of parts.
Given the above benefits and constant progress in the performance and productivity of the equipment, additive manufacturing is rapidly developing in Europe, North America and Asia.
Highly spherical powders are ideal for AM which requires excellent flowability and high density uniform packing. A high level of purity of the metallic powders is also critical to reach good mechanical properties and to allow the powder to be recycled many times.
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The main applications for AM titanium parts can be found in markets that demand complex, high-value products:
- Medical and dental devices
- Consumer goods
- Motor sports
- Fashion industry
Main advantages of using Additive Manufacturing:
- Produces bone like and porous surfaces impossible to obtain through traditional surface treatment processes
- Freedom of design
- Can be applied at every phase of the product life cycle: from pre-development to the supply of spare parts
- Great manufacturing process for complex objects
- Rapid : 3 to 72 hours to build a prototype
- Reduces costs compared to machining while providing similar mechanical properties
- Can reduce weight
- Enables the use of material that is hard to to machine such as titanium aluminide
This technology dates from 1973, is very popular and is still growing at a rapid pace It is mainly used for the production of small parts of less than 150g.
Here are the 5 basic steps of the MIM process:
- Tooling: producing a mold
- Mixing: producing the feedstock (pea size particles) by combining metal powders with a multiple component thermoplastic binder system.
- Molding parts: At this stage, parts are fragile containing 40% of binder by volume.
- Stripping: Finishing step to remove the majority of the binder from the part in a controlled solvent system.
- Sintering: Final step. Removing residual binder by heating parts causing the parts to shrink uniformly to virtually full density.
MIM parts provide mechanical performances near or equal to machined parts. The MIM process can be used to produce parts with complex shapes that could not be machined. It is also ideal for the manufacturing of parts containing multiple and cross-drilled holes since it provides great strength, hardness and elongation performances.
Main advantages of MIM process:
- Decreased production time
- Decreased need for secondary treatment
- Reduction of overall costs by creating highly integrated castings and assemblies
Spherical metal powders benefit the MIM process due to their high packing density. Indeed, high sphericity translates into high powder loading capacity of the feedstock, lower binder costs and less shrinkage during the final phase of sintering. Superior flowability characteristics of spherical powders also favor a better dispersion of the powder with plastic resins. MIM generally uses finer particle size distributions in order to reduce porosities in the final parts. However, too fine powders of reactive metals such as titanium result in poor chemical composition, especially for the oxygen and hydrogen content. For titanium, MIM usually uses particle size distributions of 0-25 and 0-45 microns. Furthermore, manufacturers demand powders with low oxygen and carbon content since the control of carbon and oxygen concentration is critical to the MIM process.
Source: CPC plastics Highmag
The hot isostatic pressing process is used to produce full density parts with great mechanical properties even with the finest materials. This process combines high temperature (up to 2200ºC) and isostatic inert gas pressure (from to 100 to 3100 bar) in a high pressure containment vessel. Heat and pressure, applied simultaneously, eliminate internal voids and residual porosity therefore improving fatigue resistance of fabricated parts and resulting in a very fine grained structure.
Main areas of application:
- Medical and biomedical
- Precision casting
- Welding, joining and bonding
Commonly HIP processed parts:
- High quality titanium parts
- Super alloys castings
- Jet engine components
- Composite materials tools
- Generator shafts
- Bone replacement prosthesis
- Medical implants
- Great flexibility in the design, chemical composition, particle size distributions used and form
- Increases material properties such as resistance to stress, cracking and corrosion and removes air bubbles
- Allows manufacturing with irregular shapes and complex geometries
- Creates uniformity of properties in all directions (isotropic)
- Reduction of costly operations like machining and welding
- Improves process safety by the elimination of critical welds
- Possibility of graded structures (solid/powder) with perfect bonds between the layers
Industrially developed around 1980, powdered metal coating techniques are generally classified under 2 types:
- Cold spray coating
- Thermal spray coating
This process uses a gas to propel particles that strike the substrate, then flatten upon impact and bond to the substrate and to each other.
Cold spray coatings:
This is a solid-state coating process. A high-speed gas jet is used to accelerate cold powder particles towards a surface where metal particles are deformed and consolidate on the surface upon impact.
The process takes place at a temperature much lower than the melting point of the spraying material. Cold spray coating is especially useful for applications where parts are sensitive to the temperature of the process. A low oxygen content powder is very important for this process.
Applications are mainly for the aerospace, energy and military sectors and more specifically in:
- ccorrosion mitigation of sensitive materials
- surface restoration and sealing
- manufacture of sputtering targets
- fabrication of busbars on heated glass
- electrical and thermal conductive coatings
- biomedical and biocompatible materials on orthopaedic implants, prosthesis and dental implants
- Safety due to low temperature process
- Gradient deposits
- Suitable for many substrate materials
- High density, low porosity coatings
- Minimal substrate distortion even at very low thickness
- Minimal surface preparation needed
- Safer for the environment
- Metastable alloys can be deposited
Thermal spray coatings:
With this process, coated materials are melted or heated, then sprayed onto a surface. This is mainly used for so-called thick coatings (over 50 micrometers). Thermal spray coatings are mainly classified in 4 categories according to the source of energy used:
- Flame spraying
- Wire-arc spraying
- Plasma spraying
- High-velocity oxy-fuel coating spraying (HVOF)
- Gas turbine technology
- Electronics industry
- Aircraft industry
- Carbon fibres composites
- Versatility, almost any metal, ceramic or plastic can be thermal sprayed
- Cost effective mean to repair worn components and incorrectly machined parts
- Rapidity, around 3 to 60 lb/hr depending on the material and spray system
- Good for parts that require porosity
- Technology offers good wear and heat resistance
- Clearance and dimension control
- Corrosion and oxidation resistance
- Good electrical properties (resistance and conductivity)
Spherical powders with good flowability are interesting for this process because they can be fed more easily at a constant rate. Thermal spray usually requires powders with fine particle size distribution because short residence time in the hot zone can only melt efficiently particles below 45 microns.