Choosing Between Periphery Ground and Molded Inserts in Indexable Milling Tools for CNC and 5-Axis Machining

Many metal cutting professionals may not realize that the way an indexable milling insert is manufactured has an impact on tool life and surface finish. Let’s start with the basics. There are two basic ways to ensure the size and edge prep of an indexable milling insert: A) either the insert is “pressed and sintered to size (PSTS),” meaning that the finish size and edge prep is engineered into the press molds and heating calculations, so that the insert meets the tolerance requirements, or B)  the insert is “periphery ground to size (PG),” meaning a secondary grinding process is used to bring the insert to the final size. Regular industry standard is following the “M” tolerance for PSTS inserts which allows for greater tolerance variation on the diameter. WIDIA global standard is set up to a tighter tolerance “P” for high precision PSTS inserts to achieve a better axial runout and positive impact in better tool life and surface floor finish.


Periphery Ground Inserts (PG)
For example: HNGJ0704ANFNLDJ, THM-U

  Press and Sintered to Size Inserts (PSTS)
For example: HNPJ0704ANSNGD, WS40PM

PG inserts are the first choice for finishing, high precision applications like die and mold. In addition, due to sharper edges, PG inserts are well-suited for machining of non-ferrous materials, like aluminum and brass.

Whereas, PSTS inserts are the first choice for semi-roughing and roughing applications. Inserts with tolerance class G, K, C, H are PG. Those with tolerance class P are PSTS.

The M class tolerance is much more wide open when it comes to the IC and the “M” dimension (distance from IC to the wiper flat). The P tolerance is a balanced, +/- 0,038 (.0015), for more consistent size.

To get the best surface possible, be sure to align the topography letters on the insert the same way each time. i.e. MM should start in the same position in each pocket and roll inward with each index.

Click here for more on WIDIA inserts.

To learn more about WIDIA, visit widia.com.

Author: WIDIA Machining Facets

For more than 90 years, WIDIA Products Group has defined excellence in innovation, technology, and customer service. Our philosophy is simple—be the best. We come from humble beginnings, but our diligence and fortitude keep us advancing in the market place. As an industry-leading manufacturer of cutting tools, WIDIA offers a complete portfolio of precision-engineered products. With thousands of Turning, Milling, Holemaking, Tapping, and Tooling Systems products; you will find everything you need from one single source. When you buy WIDIA products, you are buying the ultimate in performance and tool life. We live at the forefront of technology, always striving for the perfect blend of innovation and reliability. Match the most expansive portfolio of precision-engineered products with a global, specialized network of Authorized Distributor partners and you have power that only comes from WIDIA.

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