Periphery Ground vs Molded Indexable Milling Inserts - WIDIA

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.

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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.

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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 (.), 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.

I noticed that we only had one insert for our boring bar at work and went on MSC to order more. When I found the page with the different categories on inserts, I noticed that there were Boring Inserts and Milling Inserts. I know that they both come in all shape and sizes, but both do come in the triangular shape that I was needing. Now I ordered the right one, but I got to wondering, what is the difference in those two type of inserts? And are they interchangeable? Generally speaking, both yes and no ! Insert technology has come on in leaps and bounds in recent years. What has happened is that inserts have become more and more specialised. A different insert for each material type, different nose radius for different cuts and speeds. Almost to the point of a particular insert for every type of job.

So whilst from a hobbyist point of view they may be interchangeable, not from a commercial one ! I have my Valenite handy reference in front of me now . I've had this for 30 years minimum . At that time they had more than insert sizes and over insert selections . Multiply that by how many companies are now selling cutters ! Buy the size insert your tooling calls for and the grade suited for the material . Edit ........since . Tool seats and clamps very , chip breakers , clearance , tnr , different grades etc etc etc .