As a process, the turning of hard parts has moved forward and it is now able to deal with routine and emerging needs.
Challenge: How to re-optimize hard part turning?
Solution: Correctly apply the latest blade numbers and slots based on the existing operating data.
Since its widespread adoption in the mid-1980s, hard-part turning (HPT) has made considerable progress as a processing technology. The development of machinery, parts and materials, quenching processes, cutting tools, and complete hard part turning settings has made hard part turning a highly efficient process and is mastered by any machining shop.
Hard part turning has many benefits, so it is necessary to analyze most of the applications that involve round hard parts. Although hard part turning should not be considered as an alternative to all grinding processes, in some applications, these two processes can complement each other.
Cubic boron nitride reduces cycle time and improves quality and productivity
The main advantages of hard part turning are:
• Easily adapt to complex part shapes • Quickly switch multiple parts • Can perform multiple operations in a single setup • High metal removal rate • Calculators can be used with trial turning Turning CNC lathes • Low investment in machine tool • Metal shavings available Good for the environment • No coolant is needed in most cases • Minimizes tool stocks and floor space • Surface finishes often have advantages.
Cubic Boron Nitride (CBN) is the most widely used hard part turning tool material because it meets the requirements imposed by most applications. It has a very high hardness (second only to diamonds) and can be combined with tougher blade brands. There are a number of newly developed CBN insert grades available today to meet a variety of evolving process requirements such as cutting speeds, feeds, continuous and interrupted cuts, surface finishes, and various operating conditions.
The combination of high cutting forces and high temperatures concentrated in the processing area produces high pressures. Therefore, in the hard part machining, the main manifestation of tool wear is the occurrence of crater wear on the cutting edge. Hard cubic boron nitride is the only tool material that meets these requirements and has a reasonable toughness. The latest developments in the CBN grade have provided a means to further limit wear, improve the safety of the cutting edge, expand the application range, and increase the cutting speed by up to 20%.
Productivity, quality consistency and process reliability are today's basic standards for hard part turning. Since hard part turning has developed into a widely used process and has the advantage of finishing parts after heat treatment, various requirements have been put forward in terms of processing efficiency.
As production efficiency is an increasingly important factor in the processing of hard parts today, tool development plays an important role. Development trends include increased cutting speed (some brands can reach 200 meters/minute or more), extended tool life, and improved predictability of tool life. The feed rate has also been improved, and the purpose of shortening the cutting time is achieved through the development of blade strength and groove type.
The blade brand is becoming increasingly ideal to meet the operating requirements of today's cutting field. Cubic boron nitride grades are usually preferred, followed by ceramic grades, which optimizes various application requirements:
• CB7015 is suitable for continuous cutting from occasionally stable to occasionally light interrupted cutting. It is mainly used for hardened steel.
• CB7025 is suitable for long continuous cutting to heavy interrupted cutting. It is often characterized by poor cutting conditions, such as burrs and non-beveling angles. It is mainly used for hardened steels.
• CB7050 is suitable for hard working conditions where the shape of the part is extremely different and there may be severe distortions or non-tilt interruptions. It is mainly used for hardened steel.
• GC6050 is a ceramic grade that complements CBN in some operations and is suitable for light continuous finishing in good conditions. It is mainly used for case hardened steels where surface quality is not critical.
For machining parallel or perpendicular to the centerline of the part, hard part turning of case-hardened parts shall use CB7015 series Xcel blades.
In terms of insert geometry, the cutting edges of the hard part machining inserts are relatively blunt due to the high cutting edge strength required. However, this does not mean that the groove type problem is not important. Although the chipbreaker is not part of the chamfer of the edge of the insert, the combination of honing, tip arc radius, wiper edge, and angle advancement is critical to performance and results.
Over the years, the wiper blade technology has revolutionized turning finishing. At the same time it also improves hard part turning. Nowadays, specially developed wiper blades can be used for hard part turning finishing and semi-finishing operations, and their feed rate capability is significantly higher than the conventional tip radius.
The Xcel insert geometry is a further optimization of the feed rate/surface finish of hard part turning. It carefully balanced the linear cutting edge and wiper technology with very low angles of entry. This small angle advances the angle of advancement of the rake main blade slightly above the depth of cut of the blade. It acts as a thinning chip, allowing a higher feedrate to be used. This will be beneficial to production efficiency and will help reduce blade wear at cutting depth boundaries. The Xcel concept reduces the cutting temperature and brings about a considerable increase in production efficiency.
Total
Today, hard part processing can be more widely optimized. As a process, it has now moved forward and is capable of handling various routine and new requirements. The realization of higher performance, more options, and the advent of a new generation of cutting tools have made this possible. Thanks to a series of new and improved cubic boron nitride grades, insert geometries and tool path strategies, hard part processing can reach newer and higher levels of competition.
What is a hard part turning?
Hard part turning (HPT) is a one-point turning of high hardness workpieces. Typically, the process has a hardness range of 58 to 68 HRc. Workpiece materials include hardened alloy steels, tool steels, case hardened steels, and heat treated powder metallurgy parts. It is mainly a finishing process, but it can also be a semi-finishing process that requires a high degree of precision in the dimensional profile and surface finish. In the past, these surfaces usually had to be ground.
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