 | New
Concepts in Milling Handbook A practical approach and illustrated guide to milling cutter selection and use <Table of Contents © 1973 Niagara Cutter Inc. |
| New
Concepts in Milling Handbook A practical approach and illustrated guide to milling cutter selection and use <Table of Contents © 1973 Niagara Cutter Inc. |
Selection of Speeds and Feeds and Cutting Tool Materials -
A definition of the formation of the chip, chemical composition of cutting tool materials and engineering charts for setting of speed and feed for a variety of materials
SELECTION OF HIGH SPEED STEEL CUTTING TOOL MATERIALS
Progress in cutting tool materials from the carbon steels through the high speed steels, super high speed steels, carbides and ceramics, is concerned with attaining increased wear resistance and increased red hardness. A corresponding reduction in strength or toughness is inevitable as wear resistance and red hardness properties increase.The tool engineer's job, therefore, is to select the cutting tool material with the properties that will provide efficient metal removal rates for their application. All the variables involved (part shape, machine condition, etc.) influence this decision and should be evaluated. High speed steel and carbide tool materials are discussed here because they are the most commonly used cutting tool materials.
CHART 5 SELECTION OF HIGH SPEED STEELS
Chemical Composition and Properties they Impart
The composition of high speed steel most commonly used in milling cutters is separated into four categories based on the wear resistance, red hardness, toughness and the variation of these properties. Determine the reaction the material you are machining has on the cutter. Choose the cutter material which will best resist this reaction.
HIGH SPEED STEEL SELECTION
The chemical composition of the commonly used high speed steels is listed in Chart 5. This chart also specifies the relative wear resistance, red hardness, toughness, and availability of 16 high speed steels. These steels are classified in four groups.Group I - General Purpose High Speed Steels.
The Group I general purpose high speed steels provide properties that permit efficient metal removal on 70 percent of the milling applications. The "M" steels contain molybdenum as their chief alloying element. The "T" steels contain tungsten. M-2 high speed molybdenum steel is used on most applications. Its chemical composition provides balanced wear, red hardness and strength qualities. It is readily available as a standard cutter and is stocked in blanks, forgings and bar stock for special milling cutters. It is economical, grindable and machinable. M-33, M-34, M-36 and T-5 have high cobalt content providing higher red hardness qualities at the cost of toughness of the tool. They are not as readily available and are selected for special milling applications where these properties are advantageous.Group II - Abrasion Resistant High Speed Steels.
The Group II high speed steels contain higher vanadium and carbon content. Higher vanadium carbide in M-3 provides superior wear resistance than is available in the Group I general purpose steels, with M-3 type II having the higher vanadium. M-7 also has higher than usual carbon and is often selected for milling cutters where greater wear resistance is needed.Group III - High Red Hardness High Speed Steels.
The Group III high red hardness high speed steels can be heat treated to 68 to 70 RC, but are generally heat treated to 66 to 68 RC. The high cobalt, high carbon combination provides higher red hardness than is available in the other groups. They also have very good wear qualities, but once again the improved red hardness and wear properties are at the expense of toughness. The M-40 series steels are selected for milling hardened steels up to 50 RC and as an alternate for T-15 on the hard-to-machine super alloys. Group IV - Super High Speed Steels.Group IV super high speed steels
The Group IV super high speed steels are hardened between 66 and 68 RC. They are, high tungsten, high carbon, high vanadium steels; T-15 also contains cobalt. M-4 is Slight ly tougher than T-15 but does not have the red hardness or wear resistance qualities of T-15. T-15 is used for milling hard metals and alloys, particularly stainless steels and superalloys. It is available as a standard in a limited number of milling cutters, but is readily available as a special on milling applications where high resistance to abrasion is needed. Each cutting tool material possesses ingredients that impart cutting qualities that lend themselves to certain conditions. Under normal operating conditions, it is usually best to utilize standard milling cutter materials. If they do not perform, the cutter material selection chart should be used to determine the properties needed (abrasion resistance, red hardness, strength) for the applications.
