In metal cutting, there will be different workpiece materials, different materials cutting formation and removal characteristics are not the same, how do we grasp the characteristics of different materials?ISO standard metal materials are divided into 6 different type groups, each type has unique characteristics in terms of machinability, this article will summarize them respectively.
Metal materials are divided into 6 categories:
(1) p-steel
(2) m-stainless steel
(3) k-cast iron
(4) n-nonferrous metals
(5) s-resistant alloy
(6) h-hardened steel
Cutting characteristics of different materials
01 - P steel
What is steel?
- steel is the largest group of materials in the field of metal cutting.
- steel may be non-quenched or tempered steel (hardness up to 400HB).
- steel is an alloy with the element iron (Fe) as the main component.It is made by a smelting process.
- unalloyed steels have a carbon content of less than 0.8% and have Fe but no other alloying elements.
- the carbon content of alloy steel is less than 1.7%, with the addition of alloying elements such as Ni, Cr, Mo, V, W, etc.
Within the range of metal cutting, group P is the largest group of materials because it covers several different industrial areas.
The material is usually long chip material, which can form continuous, relatively uniform chip.The specific form of chip usually depends on the carbon content.
-- low carbon content = tough, sticky material.
High carbon content = brittle material.
Processing characteristics:
- long chip material.
- chip control is relatively easy and smooth.
- low carbon steels are sticky and require sharp cutting edges.
- unit cutting force kc: 1500 -- 3100 N/mm2
- the cutting force and power required to process ISO P materials are within a finite range.
02 - M stainless steel
What is stainless steel?
- stainless steel is an alloy material with a minimum of 11-12% chromium.
- carbon content is usually very low (as low as 0.01%).
- alloys are mainly Ni (nickel), Mo (molybdenum) and Ti (titanium).
- a layer of dense Cr2O3 is formed on the steel surface to make it corrosion resistant.
In group M, the majority of applications are in the oil and gas, pipe fitting, flange, processing, and pharmaceutical industries.
The material forms irregular, thin sheet chips that have a higher cutting force than ordinary steel.There are many different types of stainless steel.Chip breaking properties (ranging from easy to almost impossible to break) vary depending on the properties of the alloy and the heat treatment.
Processing characteristics:
- long chip material.
-chip control is relatively smooth in ferrite, but more difficult in austenite and biphase.
- unit cutting force: 1800-2850 N/mm2
- high cutting force, chip formation, heat and work hardening are generated during machining.
03 - K cast iron
What is cast iron?
- there are three main types of cast iron: gray cast iron (GCI), ductile cast iron (NCI), and vermicular cast iron (CGI).
- cast iron is mainly composed of fe-c with relatively high silicon content (1-3%).
-carbon is more than 2%, which is the maximum solubility of C in the austenitic phase.
-cr (chromium), Mo (molybdenum) and V (vanadium) are added to form carbides that increase strength and hardness but reduce machinability.
K group is mainly used in automobile parts, machine manufacturing and ironmaking.
The chip formation of the material varies from an approximate powdery chip to a long chip.The power required to process the material group is usually small.
Note that there is a great deal of difference between gray cast iron (usually in powder form with chips) and ductile cast iron, which in many cases has broken chips similar to steel.
Processing characteristics:
- short chip material.
- good chip control at all operating conditions.
- unit cutting force: 790-1350 N/mm2
- abrasive wear will result from processing at a higher speed.
- medium cutting force.
04-N Non-ferrous metals
What is nonferrous metal material?
- this category contains non-ferrous metals with a hardness of less than 130 HB.
- nonferrous metal (Al) alloys containing approximately 22% silicon (Si) comprise the largest portion.
- copper, bronze, brass.
Aircraft manufacturing and aluminum alloy automobile wheel manufacturers dominate the N group.
Although the power required per mm3 (cubic inch) is low, it is still necessary to calculate the maximum power required to achieve a high metal removal rate.
Processing characteristics:
- long chip material.
- in the case of alloys, chip control is relatively easy.
- non-ferrous metals (Al) are viscous and require the use of a sharp cutting edge.
- unit cutting force: 350-700 N/mm2
- the cutting force and power required to process ISO N materials are within a finite range.
05-S Heat resistant alloy
What is a heat-resistant alloy?
- heat resistant alloys (HRSA) include many high alloy iron, nickel, cobalt or titanium-based materials.
Group: iron base, nickel base, cobalt base
Working conditions: annealing, solution heat treatment, aging treatment, rolling, forging, casting.
Features:
- higher alloy content (cobalt higher than nickel) ensures better heat resistance, higher tensile strength and higher corrosion resistance.
The s-group materials, which are difficult to process, are mainly used in the aerospace, gas turbine and generator industries.
The range is wide, but there are usually high cutting forces.
Processing characteristics:
- long chip material.
- chip control difficulty (serrated chip).
- a negative front Angle is required for ceramics and a positive front Angle is required for cemented carbide.
- unit cutting force:
For heat resistant alloys: 2400 -- 3100 N/mm2
For titanium alloys: 1300-1400n /mm2
- high cutting force and power required.
06 - H hardened steel
What is quenched steel?
- from the processing point of view, hardened steel is the smallest grouping.
- this group contains tempered steel with hardness >45 -- 65 HRC.
- in general, the hardness range for hard parts turned is between 55 and 68 HRC.
The hardened steel in group H is used in a variety of industries, such as the automotive industry and its subcontractors, as well as in the machine manufacturing and die business.
Usually a continuous, red-hot chip.This high temperature helps to reduce the value of kc1 and is important to help solve application problems.
Processing characteristics:
- long chip material.
- relatively good chip control.
Minus minus the front Angle.
- unit cutting force: 2550-4870 N/mm2
- high cutting force and power required.
