The characteristics and difficulties of medical device parts processing

2. Analysis of Difficulties in the Processing of Medical Device Products

1. Difficult to process titanium alloy materials

90% of medical device implant components are made of Ti6Al-4V titanium alloy. Due to its light weight, high strength and high biocompatibility, titanium alloy 6AL-4V has become the most commonly used material for medical implant devices. Titanium alloy 6AL-4V is usually used in the production of hip joints, bone screws, knee joints, bone plates, dental implants, and spinal connection components. Titanium alloy has the characteristics of work hardening. The cutting angle is large during the machining process, the chips produced are thin, and a relatively small contact area is formed on the tool. In addition, the high cutting force during the machining process, combined with the frictional force during chip flow, will comprehensively lead to excessively high local cutting heat of the tool. The poor thermal conductivity of titanium alloys prevents the cutting heat from being conducted quickly. As a result, a large amount of cutting heat is concentrated on the cutting edge and the tool surface. High cutting force and cutting heat will comprehensively cause crescent craters and cause rapid tool failure.
The relatively low modulus of elasticity makes titanium alloys more elastic than steel. Therefore, excessive cutting force should be avoided to ensure that the rebound of the workpiece is small. Thin-walled parts have a tendency to deform under tool pressure, causing chatter, friction and even tolerance problems. The key to solving the problem is to ensure the rigidity of the entire system. It is very necessary to use sharp cutting edges and correct geometry tools. In addition, titanium alloys have a tendency to chemically react and alloy with cutting tools at high temperatures, and their chips have a tendency to be welded to the surface of the tool.

2. Reliable and compact machine tool fixture

Medical equipment processing equipment needs to be able to process small and complex parts made of difficult-to-process materials (such as titanium alloy or stainless steel) with high accuracy requirements. For example, processing bone and joint replacement parts is quite complicated. Due to the poor cutting performance of the material being processed, the blank is usually a bar stock-which means that a large amount of metal needs to be removed. Therefore, part of the parts are cast into a shape close to the finished product, but this also adds to the trouble-the need to manufacture complex and expensive jigs. Another factor that increases processing complexity is the narrow tolerance range.
       Medical equipment parts and components have high requirements on material, processing accuracy, and surface finish, which requires high reliability of the processing system. As a result, extremely high requirements are placed on machine tools, fixtures, cutting tools, and CAM software. Workpieces are usually processed on advanced medical equipment processing equipment such as Swiss automatic lathes, multi-spindle machine tools and rotary tables. These machine tools are mostly characterized by very small size and very compact structure.
       The characteristics and requirements of medical device parts processing have undoubtedly promoted the development of processing technology and solutions to improve the competitiveness and production efficiency of small and medium-sized enterprises in processing medical devices.

3. Stable and efficient tools

Generally speaking, the medical device industry is different from other mechanical processing industries in three points:
First, the requirements for machine tools are relatively high. Advanced medical equipment processing equipment such as Swiss automatic lathes, multi-spindle machine tools and rotary tables are completely different from the usual machining centers and lathes. They are very small in size and very compact in structure. To comply with such requirements, the structure of the tool also needs a special design, the size of the tool is also required to be small, and the rigidity of the tool must be ensured at the same time. For example, the ISCAR SWISSCUT series is specifically aimed at cam-type machine tools, which reduces the problem of small processing areas and easy interference. The inserts can be easily replaced from both sides of the tool bar. The high-precision inserts and solid tool holder design ensure high Repeatability. MINCUT is the latest tool developed by Iscar, which can be used for both turning and milling. The small size tool has high rigidity and can be applied to multi-spindle machine tools or machining centers.
Second, it requires high processing efficiency. For medical equipment, the most important thing is the processing efficiency, that is, the processing cycle, which requires that the blade can be replaced in the shortest time. Iscar's MULTI-MASTER Transformers interchangeable cutter head series can be replaced with different milling cutter heads in just a few seconds. The concept of quick tool change has a good guarantee for the processing cycle. In addition, the tool life is required to be as stable and as long as possible. High-quality tools should be used as much as possible, with the overall coordination of coating, cutting edge, chip-breaking geometry, and tool structure. In this way, the 24-hour operation of the machine tool can be guaranteed, and it can compete with other competitors in the market with very high production efficiency, thereby gaining a competitive advantage.
Third, in terms of the workpiece itself, it is very different from other mechanical parts. Medical devices implanted in the human body first require a very good surface finish, a very high precision, and no deviation. This requires the cutting tool to meet high processing requirements from the design of the blade structure to the design of the blade coating. In addition, it also includes the repeated positioning accuracy of the blade, which can not ignore the high quality requirements while ensuring the efficiency improvement.

4. Complete solution

Iscar deeply analyzed the characteristics of implants in the medical device industry to improve the processability of these very critical components. Therefore, Iscar also designs and manufactures special tools, inserts and chip flutes to process titanium alloy Ti6Al4V and obtain the high-precision tolerance values required in this special field. In order to cooperate with such parts manufacturers to adopt their existing production equipment, Iscar also provides special tools to meet different applications.
The solid carbide end mills with sharp cutting edges developed by Iscar can be used to process concave parts without burrs. These end mills can achieve polishing milling with a maximum margin of 0.01mm in semi-finishing and finishing. We have also developed tools that are also used to process titanium alloys and stainless steel-PVD coating based on ultra-fine grain substrates to achieve high-speed machining with high cutting speed and high feed. The diameter of the milling cutter is small, and the deflection machining strategy can be used in programming. Its advantage is that the cutting speed on the outer diameter of the cutter can be obtained, the chip removal is smooth, the contact area of the cutting area is lower, and the cutting heat is lower.
Iscar's research and development department found that turning applications in the medical device industry, blade grades or chip flutes need to be improved. In order to meet the needs of users, ISCAR has developed high-quality ground blades, such as VCET, DCET, CCET, etc. The blade geometry is WF. Iscar's advanced production technology guarantees that such improved blades have polished chip flutes to achieve excellent surface quality for semi-finishing and finishing. In some special applications, ISCAR can provide VCGT inserts with MD chip flutes to obtain high surface quality. Iscar's JET-CUT series cutting knives, with blade widths of 3mm and 4mm, have high surface quality and long tool life. Originating from Iscar’s belief that there is no limit to upgrading, Iscar has developed HP high-pressure cooling system tools based on the TANG-GRIP series.
The use of proven technology and tools and verified cutting parameters can more timely face the processing of medical device parts and components launched on the market. Based on years of experience in the medical device industry, Iscar has also launched a tool kit for the medical device industry to cooperate with DMG machine tools to provide customers with turnkey projects.
Iscar saw the huge development prospects of medical machinery and invested a lot of manpower and material resources to develop special tools for medical equipment processing. Iscar established a dedicated medical device R&D department at its headquarters. There are 7 professional engineers engaged in program design. They have rich experience and have been engaged in the research of medical device processing tools for more than 12 years.
     At present, the proportion of knives used in the medical device industry in Iscar's knife products is about 6% to 7%, and it is expected that this proportion will rise to 10% to 12% in the next 2 to 3 years.