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Basic knowledge of CNC blades

Part 1: Cemented Carbide

1 Concept; it is made of refractory metal compound (hard phase) and binder metal (binder phase) produced by powder metallurgy
Composite materials. Commonly used carbides include: WC TiC TaC (tantalum carbide) NbC (niobium carbide), etc.
Commonly used binder: The strength of Co Ni Fe cemented carbide mainly depends on the content of cobalt.
The two factors of cemented carbide, including strength and hardness, are mutually contradictory. As the strength increases, the hardness energy will decrease. The distinction of cemented carbide models is the distinction between the nodes of these two parameters.
2 Features of cemented carbide
1) High hardness and high wear resistance
2) High elastic modulus 3) High compressive strength
4) Good chemical stability (resistance to acid, alkali, high temperature oxidation)
5) Low impact toughness
6) Low expansion coefficient, thermal conductivity and electrical conductivity, but cemented carbide is brittle and cannot be cut; compared with tool steel, cemented carbide has the following advantages:
a Improve the service life of the tool;
b Improve cutting efficiency and labor efficiency;
c Improve the finish and accuracy of the workpiece;
d It can process difficult-to-process materials such as heat-resistant alloys, effect alloys, and extra-hard cast irons that are difficult to process with high-speed steel.
3 concept;
Continuous cutting: During the cutting process, the cutting edge is always in contact with the workpiece.

Intermittent cutting: During the cutting process, the cutting edge is intermittently in contact with the workpiece.

High-speed cutting: an advanced technology for cutting parts at a speed several times higher than conventional cutting.
4 Accuracy grade of CNC blade

Common tool materials include high-speed steel, cemented carbide, coated cemented carbide, ceramics, cubic boron nitride and diamond.
The main types of workpiece materials are:
steel
P, stainless steel
M, cast iron
K, non-ferrous metals
N, high-quality alloy
S, hardened
Precision grade of CNC blade:
E.g. model
CNMG120408
, The third letter
M
Indicates the manufacturing accuracy of the blade. The composition, structure and performance of cemented carbide
1
Cemented carbide mainly includes the following parts
Wc—wear-resistant phase
Co—ductile phase
Tic Tac Nbc—hard phase
Crc Vc (vanadium carbide)-suppression phase
Structure: Two-phase structure and three-phase structure, and the three structures determine the quality of cemented carbide.
Cemented carbide matrix (framework)
+
The structure and shape of the blade (flesh and blood)
+
Coating (skin)
2 Classification of cemented carbide
1) Tungsten-cobalt (WC+Co) cemented carbide (YG) is equivalent to type K
2) Tungsten-titanium-cobalt (WC+TiC+Co) cemented carbide (YT) type is equivalent to P type
3) Tungsten-tantalum-cobalt (WC+TaC+Co) cemented carbide (YA) is equivalent to G type
4) Tungsten-titanium-tantalum-cobalt (WC+TiC+TaC+Co) cemented carbide (YW) is equivalent to M type and P type

Steel processing class M

Stainless Steel Difficult to Process Material Type K

Cast iron and non-ferrous metals Class G

Mine geological tools

*
Performance:

Density, hardness, bending strength, coercivity, cobalt magnetism, etc.
.
3
Cemented carbide production process

Traditional process

Process flow of CNC blade

Ingredients → ball milling → spray drying → pressing → sintering → wool inspection → grinding → semi-inspection → passivation → cleaning → coating → final inspection

Mixture preparation: what are the ingredients?

It is prepared through those steps (mixing-wet grinding-drying-sieving)

The uniform distribution of the ingredients determines the pressing performance and the quality of the entire product

4
Alloy production

Medium for wet grinding?

alcohol

Ethane

acetone

4
Alloy production

Medium for wet grinding?

alcohol

Ethane

acetone

The concept of pressing: Fill the die hole with the mixture, and then press the press to squeeze the powdery mixture to have a
Shape and size products

Suppression is usually divided into three stages?

1) The density of the briquettes increases rapidly with the increase of pressure; the pores decrease sharply.

2)
The density of the compact increases slowly, because the pores are in
1
Eliminate a lot during the stage, and continue to pressurize just to make the particles elastically buckle
Deformed.

3)
The increase in pressure may reach the yield limit and strength limit of the powder material, and the powder particles will produce plastic under this pressure.
Sexual deformation or brittle fracture. Because of the brittle fracture of the particles, fragments are formed to fill the pores, and the density of the briquettes increases.

The concept of grinding:

The finishing method of removing a very thin surface layer from the workpiece with abrasive tools and abrasives (grinding
Cutting
:
The grinding tool rotates at a higher linear speed to process the surface of the workpiece. Grinding processing includes; end face grinding, peripheral grinding, special-shaped grinding, and machining center.
Grinding is just the name of the process, and the process flow is more than just grinding.
The definition of passivation (rounding): Some treatments are carried out on the cutting edge of the blade to increase the strength of the cutting edge and the use of the tool.
Use life.
The purpose and function of passivation processing;

1 Improve the strength of the cutting edge, increase the service life of the tool and the stability during the cutting process;
2 Eliminate microscopic gaps and cracks;

3 Make the cutting edge smooth and reduce burrs;

4 Improve coating application;

Coating concept: in cemented carbide or high-speed steel with better strength and toughness
(HSS)
On the surface of the substrate, the vapor deposition method is used
Method to coat a thin layer of refractory metal or non-metal compound with good wear resistance
Function: Coated tools have high surface hardness, good wear resistance, stable chemical properties, heat resistance and oxidation resistance, and coefficient of friction
The characteristics of small size and low thermal conductivity can increase tool life compared to uncoated tools during cutting
3~5
More than twice, increase the cutting speed
20%~70%
To improve machining accuracy
0.5~1
Level, reducing tool consumption costs
20%~50%
.

There are two coating methods commonly used in production at present:
Physical Vapor Deposition (PVD)
Method and chemical vapor deposition (CVD) method


Post time: Jul-28-2021