TOOL TALK: Carbide Insert Evolution (Pt. I)

Industries use of cemented carbide for cutting metals began in the 1930s.

Cemented carbide is a hard material that is used extensively in cutting tools that are intended for machining. Within an industrial context, references to carbide or tungsten carbide usually refer to this cemented composite.

Carbide cutters deliver many advantages. They provide a better surface finish on the machined part, and allow faster machining when compared to the use of high-speed steel (HSS) cutters. Carbide tools are able to withstand higher temperatures at the cutter-workpiece interface than standard high-speed steel tools, which is the principal reason for their faster machining capability. Carbide usually provides superior performance for the cutting of tough materials such as high alloyed steel or stainless steel, as well as in situations where other cutting tools would wear away faster.

Industries use of cemented carbide for cutting metals began in the 1930s. While some tools that feature relatively small sizes are wholly produced from carbide; others use carbide in the cutting area only. Originally the cutting area consisted of a carbide tip that was brazed or soldered to a tool body. However, in the 1940s cutting tool manufacturers began to produce cutting tools with the advantage of replaceable carbide segments that were mechanically mounted on to the tools body.

This clever innovation and the use of mechanical clamping, which provides much greater strength compared with the previously brazed connections, are now recognized as memorable milestones in the metalworking industry.

This major development led to impressive improvements in productivity within the area of machining operations. It was immediately possible to increase the load on the tool and to intensify operational metal removal rates. In addition to this cost effective method ensuring the simple and economical replacement of the cutting element when worn or in case of breakage, it allowed the manufacturing of cutting segment and the tool bodies to be divided. Depending on the shape of the inserts used, they could be quickly indexed ensuring the rapid change of a worn cutting corner by several methods, such as rotating the insert on its axis or by flipping it upside down. Initially the new cutting segments were known by several names, such as throwaway tips, interchangeable inserts, replaceable inserts, however, today the more widespread, generic term indexable inserts is used.

The technology used in the manufacturing of the indexable inserts is based on powder metallurgy, comprising of several manufacturing processes as follows:

• preparing carbide powder (mixing)

• pressing the powder (compacting)

• sintering compact

fig. 2

fig. 2

• post-sintering processing

• coating

In the past, inserts were produced by the use of manual machines. Hence, the application of various complex powder metallurgical processes was very difficult or even impossible to perform. The introduction of more progressive industrial equipment, featuring advanced automation and computer control, made the

technological processes more stable, controllable and reliable. Consequently, the mechanical properties of manufactured inserts became more uniform, predictable and repeatable; these factors allowed dramatic improvements in terms of the accuracy of sintered inserts by reducing production tolerances.

Today, a typical insert production press is a highly engineered device that is computer controlled. A moveable punch can be made from several “sub punches”, each operated separately. Some press designs encompass multi-axial pressing options. The remarkable progress in press technology enables the production of complex shaped inserts that are characterized by variable corner heights (Fig. 1). This capability enables the realization of optimal cutting geometry, which guarantees not only smooth and stable machining but also the increased accuracy of a machined surface (Fig. 2).

Additionally, the advantages provided by the use of modern CAD/CAM systems make it possible to improve the design and the shaping parts of pressing die sets. Also, the ability to simulate the pressing processes related to new sintered products, when they are at the beginning of their design stages, allows further design amendments and enhancements to be made.

Andrei Petrilin is technical manager of indexable milling, and Marcel Elkouby is material science engineer manager, material & coating development, both with ISCAR.

Andrei Petrilin, Iscar

Andrei Petrilin, Iscar

About the Authors

Andrei Petrilin

Technical Advisor

2100 Bristol Circle

Oakville, L6H 5R3 Canada

905-829-9000

Andrei Petrilin is the technical manager for ISCAR Tools.