Cemented carbide cutting tools have been in use since the late 1920s and are now ubiquitous in the machining world. Around 1950, carbide insert adopting tools became common in metalworking and are still considered a basic necessity like a turning tool holder.
The interchangeable cutters are usually constructed from a steel body that has machined components allowing for accurate positioning of the inserts. Steel tool bodies also provide a method for attaching the inserts along with a method for attaching the assembled body and inserts to the turning tool holder and machine tool.
Before the spread of tungsten carbide inserts, it was always necessary to remove solid cutting tools from machines in order to sharpen them. Tool sharpening was so much work that large manufacturers often had grinding departments to sharpen the tools. Therefore, the most important benefit offered by exchangeable tools is the ability to renew the cut edge without removing the cutting tool from production. Cutting edge renewal is usually done by releasing the insert and rotating it, or indexing it to a new cutting edge, or replacing a completely worn insert with a new one.
Solid drills, taps, and other types of cutting tools are still used depending on the application, but the interchangeable tip turning tool is the dominant tool in modern turning operations. Interchangeable tools successfully replaced the HSS tools, carbide tools, and custom-shaped tools that were common before the advent of CNC machines. The indexed turning tool in combination with the multi-axis movement of the CNC machine simplifies the creation of complex shapes, virtually eliminating the need for dedicated turning tools.
In addition, the use of indexable drill bits on a lathe offers distinct advantages over conventional HSS or carbide solid twist drills. The programmer often does hole with a replaceable drill bit, then go down from the center and cut the hole to a larger diameter, which can eliminate the need for a boring bar. CNC lathe turrets often suffer from misalignment due to wear, and machine misalignment can damage standard drills. Interchangeable drills, on the other hand, are more tolerant than standard drills when used on machines with questionable alignment.
The grooving inserts that made grooving tools multi-functional, as well as indexable drill bits, represent a significant advance in turning tools. The old grooving technology allowed cutting in one direction only; Grooved and turned inserts allow the user to make both radial and axial cuts.
There are many common features among interchangeable turning tools. Turning inserts are produced in common shapes such as rhombus, square and round. The shapes and sizes of these inserts are made in accordance with the standards set by the authorities such as ANSI and ISO. Their commonality gives the programmer and mechanic an almost unlimited choice of tile types and the most modern geometries. All major manufacturers of cutting tools produce turning inserts to these standards, so finding the best-performing insert is relatively easy.
Unlike turning tools, interchangeable milling tool bodies typically require insert shapes and geometries that are not common among manufacturers, forcing users to purchase inserts made specifically for the brand of milling cutter they are using. However, tool manufacturers have developed and offered families of milling tools that utilize their proprietary shapes in a variety of cutter bodies. Having a family of cutter bodies that accept the same insert reduces tool inventory while providing some flexibility for programmers and operators.
Most major toolmakers make custom indexable tools. Unlike the forms tools for turning, milling forming tools are still a viable way to complete complex geometry, especially when the shop is trying to reduce cycle times and cutting tool inventories. Parts with features such as many degrees, radii, and chamfers require multiple tools to create them. The advantages of custom, interchangeable shape combination tools are reduced cycle times, reduced tool inventory, and improved part quality.
Unfortunately, custom indexers are expensive and often require modified inserts, which also makes the inserts expensive. For these reasons, custom indexed tools are typically reserved for high production environments or for the production of very expensive parts.
A significant innovation in exchange milling was the development of plunge milling for the roughing of large cavities, such as those machined in molds. The tools used to roughen deep pockets or arms can be quite long. In traditional roughing operations, radial loading of long cutting tools the side-to-side cutting movement creates vibration. Plunge roughing is performed by axial tool feed that directs the cutting forces to the spindle taper where the machine tool is most rigid. Plunge roughing provides much higher metal removal rates when long tools are needed.
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