Original Date: 08/14/2000
Revision Date: 01/18/2007
Best Practice : Robotic Plasma Spraying and Ceramic Powder Manufacturing
Hydroxylapatite is a hexagonal, calcium-phosphate mineral used to promote bone growth onto orthopaedic implants. Looking for a way to reduce inventory, decrease costs, and control the powder’s material properties, Howmedica Osteonics decided to implement an in-house Ceramic Powder Manufacturing process to manufacture hydroxylapatite. A Robotic Plasma Spraying process is then used to coat the parts. This process involves loading the plasma gun with hydroxylapatite, and using a plasma flame to spray the partially melted powder onto the part.
Hydroxylapatite (HA) is a hexagonal, calcium-phosphate mineral used to promote bone growth onto orthopaedic implants. In the past, Howmedica Osteonics purchased HA from a vendor and used a multi-step robot/turntable machine process to apply the powder onto the parts. Looking for ways to reduce work in process (WIP) inventory, decrease HA costs, and control the powder’s material properties, the company decided to implement an in-house process to manufacture HA.
The Ceramic Powder Manufacturing of HA powder begins as a mixture of chemicals. The mixture is then analyzed by sintering a small amount from the batch. The material constituents are measured, and small amounts of the deficient ingredient(s) are added until the slurry has the correct HA chemistry. Ammonia is added to stabilize the mixture and impede further chemical reaction. The mixture is then spray dried to produce round particles of consistent size. After it is fed through an aerosol gun, the mixture travels in a hot cyclonic pattern to evaporate the water. Large and fine particles are also collected separately at the bottom of the system. The HA powder is then placed in saggers into large ovens, and sintered at approximately 2200°F for six hours to facilitate the growth of crystals. The powder densifies, removing small pores. The large and fine particles are then blended for homogeneity and sieved to ensure that 90% of the particles are less than 100 micrometers in size. Further testing is performed to ensure correct chemistry and purity, accurate density, and sufficient crystallinity. Prior to being coated, the orthopaedic implants are surface prepared, cleaned, loaded into a carousel application system, and preheated. Robotic Plasma Spraying is used to coat the parts. This process involves loading the plasma gun with HA powder, and using a plasma flame to spray the partially melted powder onto the part. The parts undergo a final cleaning and are inspected for mechanical integrity.
The in-house Ceramic Powder Manufacturing of HA provides Howmedica Osteonics with many cost savings and improved quality control. Among these benefits are:
Controlled size and roundness of the particulate allows for consistent application through the plasma gun. Manufacturing costs for HA powder has been reduced by 306%.
Carousel application system provides continuous gun operation, since parts are now preheated prior to spraying instead of being heated with the plasma flame.
Coating capacity is increased from 200 parts per day to 300 parts per day by using the carousel system.
Powder usage is reduced by 33% per implant.
Process time is reduced from seven minutes per part to three minutes per part.
Powder inventory costs are reduced from $117,000 to $7,200.
Current annual cost savings for powder manufacturing is $860,000.
Current annual cost savings of the coating system is $560,000.
Total resultant cost savings equals $1.4 million per year.
Product lead times and inventories have significantly been reduced.
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