CNC Machine Tool - Characteristics, Types, Material, Affecting factors


CNC Machine Tool –

Tool is used to cut the material for making job. A large variety of tool is used in CNC/VMC machine. A good tool for CNC machine helps to improve the productivity of machine.

In this article, we will discuss following points on CNC cutting tool –

· CNC machine tool characteristics

· Factors affecting the tooling for CNC machine

· Types of CNC tool

· Material of CNC tool

1. CNC machine’s tool characteristics –

 A good CNC machine tool should have following characteristics –

· Rigidity of tool should be high that withstend higher cutting forces.

· Melting point should be high

· Tensile strength should be high

· Fusibility of CNC tool should be high

· Fatigueness of a good CNC tool should be low

· A good CNC tool should be with high accuracy

· Wearness should be low of a good CNC tool’

· Oxidation should be low

· Hardness and toughness should be high


2. Factors affecting two tooling for CNC machine-


 There are give some important factor which affected the life of CNC machine’s tool-

· Materials of job

· CNC machine type

· Required operations

· Cutting path
   
 . Production schedule

· Complexity of operations

· Skills of operator


cnc vmc machine tool


3. Types of Cutting tools for CNC machine – 



The cutting tool of CNC machine can be classified in many ways. But there are three way in which basis we can classified CNC machine tool –

(A) On the basis of CNC tool construction-

· Solid CNc tool

· Brazed CNC tool

· Inserted bit CNC tool

(b) On the basis of CNC tool materials-

· High speed steel (HSS)

· High carbon steel (HCS)

· Cemented carbides

· Coated Carbides

· Ceramics

· Silicon

· Diamond

· Born Ni tride

(c) On the basis of setting up of CNC tool –

· Pre-set CNC tools

· Qualified CNC tool

A. On the basis of CNC tool construction –


· Solid CNC tools- Generally there tools are made of high speed steels (HSS) and high carbon steel (HCS)


Characterstic – 

(a) High tensile strength

(b) High cmpressive strength

(c) Low war resistance

(d) High finishing

These Cnc tools have to grind regularly due to this they in crease the production time.

(ii) Brazed Cnc tools-: These tools are made trough forged process. It has forged shank of high tasile strength.

(iii) Inserted bit cnc tools-: These typs tools cnc machine. Tool change (grinding) time is high for solid cnc tool and brazed cnc tool as compared to inserted cnc tools .So these are used widely. Harden and special grade carbides must be used to achieve faster rate of metal removal. The index able inserts of tungsten carbide are further coated with a wear resistance layer of titanium carbide or titanium nitrite for desired results.

(B) On the basis of cnc tool materials-:

HSS tool material have quantities of tungsten(14%-18%),Molybdenum,chromium (3.5%-4.5%), Vanadium (0.5%-1.5%), and carbon (0.7%-0.9%). The mixture of tungsten molybdenum and chromium distributed through out the metal matrix provide very good hot hardness and abrasion resistance. The major alloying elements generally used in HSS tool is tungsten and molybdenum. Tungsten is costly, but molybdenum is cheap but has higher toughness. For same Hardness there care need to be exercised in hardening as decreasing taken place in molybdenum steels. It have narrow temperature range for heat treatment.

Characterstics of HSS-:

(a) High hardness

(b) Good wear resistance

(c) High toughness

(d) Reasonable cost.

(e) Suitable for high cutting speed

(ii) High carbon steel (HCS) -:

 HCS is the medium cutting tool and suitable for low cutting speed. They have good cold toughness but have low, at high temperature. Hardness of these tools depends on the presence of carbon quantity

(iii) Cemented carbide-:


 Cemented carbide are produced by cold compaction of the tungsten carbide powder in abider such as cobalt followed by liquid phase sintering. They are widely used in industries on cnc machines. It mostly contain tungsten (81%) Cobalt (13%) and carbon (5%).

Characterstices -:


(a.) Has high hardness, so caused on high speed

(b.) Cobalt content increase, toughness and impact strength of cemented carbide tool but decrease hardness and thermal conductivity.

(c.) Five grain carbides are harder compared to coarse grain carbides.

(d.) Multi grain carbide grades increase chemical stability, hardness and hot hardness.

(e.) These cnc tool has high brittleness.



(iv) Coated carbide-: 

Coated cnc cutting tool has two or three times like more as compared to uncoated tools. So use of these types tool is increasing day by day in industries. These coating such as aluminium oxide, titanium nitrite titanium carbide etc. are deposited generally on the carbide tool bits by using chemical vapour deposition process.

Characteristics -:


(a.) Life cycle is high

(b.) can used on high cutting speed easily

(c.) Have broad use for different machining process.



(v) Ceramics-:

 The materials like boron carbide, silicon carbide, aluminium carbide, titanium carbides are known as ceramics. These are prepared by sintering the elements at high temperature. Ceramics tools should be used with very high cutting speeds on steels. They are neither suitable for low cutting speed nor for intermittent cutting. Cutting fluid if applied should be in flooding with copious quantity of fluid to thoroughly wet the entire machine zone, as ceramics have very poor thermal shock resistance.

Characterstics-:

(a.) High compressive strength.

(b.) High resistance to oxidation.

(c.) Desired hardness at low and high temperature.

(d.) Poor thermal conductivity

(e.) Non-magnetic and non-conducting to electricity

(f.) These can not be wetted by molten meta

(g.) Longer tool life

(h.) Long built-up edge.

(i.) Lower coefficient of friction

(j.) Good machining & flexibility


(vi) Silicon-: 

This is tougher cutting tool material which is used to get high surface finishing. This is tougher than alumina involve interrupted cuts.

(vii) Diamond-:

 Being expensive material, its application is restricted to specific cases only in metal machining small diamond bits are used for precise jobs such as finishing operation on hard steels. 

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(C) On the basis of setting up of cnc tool-:


(i) Preset cnc tool-: This type tools is positioned in tool holdres in such a way planned in advance to ensure a continuous production cycle. These are loaded before start the programme or production in cnc machine at a particular position.

(ii) Qualified tools-: These types tool is fitted into a required edges is accurately positioned within close limits relative to a specified datum on the tool holder or slide is known as qualified tool.

Read Also - NC Machine - https://www.cncrules.com/2018/12/numerical-control-nc-machine.html