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Analysis of the demand for processing technology in the development of artificial joints
The history of artificial joint replacement technology spans almost a century, evolving from early explorations to its current relatively advanced stage. This progress has been driven by relentless efforts from both the medical field and engineering sectors, resulting in significant advancements in design concepts, medical materials, manufacturing techniques, and testing methodologies. These developments have greatly benefited countless patients.
With the support of clinical statistics and scientific analysis, particularly in manufacturing processes, modern technologies like reverse modeling, computer numerical control (CNC) machining, rapid prototyping, and high-energy beam processing (such as laser and electron beam applications) have enabled many design concepts to become feasible. Consequently, the field of artificial joint technology is undergoing a new wave of transformation and advancement. These changes have also led to heightened demands and expectations for manufacturing technologies.
(1) Despite the steady stream of innovative design ideas in recent years, the materials used remain relatively consistent and undergo gradual evolution. Artificial joints are medical implants placed within the human body, expected to last anywhere from 10 to 20 years or longer. Therefore, selecting materials for these joints is approached with extreme caution. After extensive use and industry approval, the most commonly utilized materials include titanium and its alloys, cobalt alloys, and ultra-high molecular weight polyethylene (bioceramics and animal-derived materials are less frequently used for machining, and this discussion does not cover them). A common characteristic of these materials is their challenging machinability. For instance, titanium and its alloys have poor mechanical cutting properties, primarily due to their low thermal conductivity. At higher cutting speeds, a significant amount of heat accumulates at the cutting edge, accelerating tool wear. Titanium is chemically reactive and poses a fire hazard at high temperatures. Additionally, its tendency to cause severe work hardening affects the surface finish and dimensional accuracy of the product. The continuous formation of long chips is another major challenge. Cobalt alloys, while praised for their hardness, also present difficulties due to their high heat resistance. Ultra-high molecular weight polyethylene, though less demanding in terms of hardness and strength compared to metallic materials, presents challenges due to its high viscosity, making chip breaking difficult, and the localized heating during cutting can lead to softening or melting, significantly impacting surface quality.
These challenges have presented numerous obstacles for manufacturers. Developing suitable tools has been a key objective for companies producing artificial joints. Ideally, tools designed specifically for these materials should exhibit excellent hardness, heat resistance, low wear, and effective guiding and chip-breaking capabilities. Managing the tangling of chips has been particularly problematic, often necessitating interruptions in processing to manually resolve issues. Collaboration among machine tool builders, software developers, and tool manufacturers could provide solutions, such as automated chip-handling devices, specific programs within the operating system, and tools with superior guiding or chip-breaking functions. Such innovations could significantly reduce the energy and time required by users for this task.
(2) Improving economic conditions and the growing precision demands of the medical profession have led to increasingly personalized expectations for patients. To cater to this trend, the design of artificial joint products has started to emphasize personalization and rapid manufacturing. However, due to constraints like manufacturing methods, processing cycles, costs, and security verification, achieving full-scale personalization remains challenging. As an alternative, multi-specification and multi-product offerings have entered the market, offering effective approaches to meet the anatomical needs of individual patients (see Figures 1 and 2).
A downside of multi-specification design is that when the overall production volume remains constant over a given period, the output for each product specification decreases, leading to more frequent changes in processes and increased time spent replacing and adjusting tools. For machines that require frequent product changes, the speed advantages provided by rapid features, such as fast movement and quick tool changes, are overshadowed by the substantial labor hours involved in tooling, tool changing, and program debugging.
Taking the typical CNC lathes and slitting lathes used by artificial joint manufacturers as examples, while there are usually positioning devices between the tool holders and tools, the accuracy is insufficient. When switching between different types and grades of tools during product changes, it is often impossible to quickly return to the previous processing state. Setting up an accurate positioning mechanism between the tool holder and the tool holder would allow fixing tool parameters in the machining program. Pre-calibrating the external tool ensures the installation accuracy between the tool and the tool holder. Once the tool holder is quickly loaded onto the holder, the original program can be directly called for trial cutting. After inspection and appropriate tool compensation, regular processing can commence. Achieving this concept would greatly enhance the efficiency of small-batch, multi-variety production modes.