Changes are coming to the way orthopedic implants are produced.  According to James R. Schroeder, founder of Vantus Technology, traditional processes used wrought stock, and cast or forged parts, followed by machining and grinding to produce the overall configuration required. Portions of the implant that required polishing, such as bearings, were then further processed, according to Mr. Schroeder’s comments, originally recorded in BoneZone.

Though appropriate for mass production, those conventional processes are not always suitable for custom manufacturing. Moreover, these processes do not readily adapt to complex geometries and shapes that can provide superior properties and functions. Accordingly, new forms of direct digital manufacturing are now being used to produce superior orthopedic devices.

Advanced manufacturing technology can be separated into three primary categories; subtractive, additive and surface-treatment technology. Subtractive manufacturing technology (SMT) removes material from an existing base part. The base part can be produced from primitive shapes derived from wrought stock (square, rectangular or cylindrical), more refined shapes such as castings produced from molds, or forgings produced from dies. A fixture or vise is used to position and secure the base part for subsequent subtractive machining processes.

EBM produces a near-net-shape knee component. The component is semi-finished using subtractive machining operations and then polished. Courtesy, Vantus.

The subtractive process begins with a roughing operation that removes most of the unwanted material, leaving a smaller and more uniform amount of material to be removed later with finishing operations. Typically, multiple setups and subtractive machines are required to achieve the semifinished part configuration. Milling, drilling, surface grinding, cylindrical grinding, electrical-discharge and chemical-erosion machining are all examples of subtractive manufacturing operations to remove material from the base part.

Additive manufacturing technology (AMT) works in an opposite manner. An additive operation begins with a substrate plate placed to build the near-net-shape part. Next, metal powders are melted together under computer control to build the part point by point and then, layer by layer, based on a 3D CAD model. Several types of AMTs exist, using either lasers or electron beams to melt metal powders. Some apply a flat layer of metal powder whereas others deliver the powder via a jet nozzle. With either type, only those regions that are melted by the laser or electron beam become part of the finished device. Additive manufacturing systems that use a powder-bed configuration can produce many parts in a single build.  In contrast, additive manufacturing systems that deliver metal powder via a jet nozzle build one part at a time.

Either type of system, subtractive or additive, can produce a metal part in a fraction of the time needed to rough mill near-net-shape parts from wrought stock, machine a mold for casting parts, or produce a die for forgings. Once the near-net-shape part is complete, the substrate plate is removed and the part is ready for finishing.

SMT and AMT are sometimes described as rapid prototyping technologies. But prototyping technologies produce mostly plastic parts, primarily to validate conceptual designs during a product development process. The AMT discussed here produces fully functional,
near-net-shape, metal parts that, with further finishing, can be used directly in a clinical application. Subtractive processes are then used to finish both types of parts for the medical applications discussed here.

Vantus Technology Corp.
www.vantus.com

MPF