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Dynamics of the processing center of the process! What is the fundamental reason?

Source: Browse:197 The release date:2024.05.17 [ Large medium small ]


For the machining center, the tool is a consumable tool, and it will cause damage, wear, and crash during the processing process. These phenomena are inevitable, but there are also controllable reasons such as unscientific operations and irregular operations, and improper maintenance. Finding the root cause can better solve the problem.

 

01 The manifestation of the knife damage

 

(1) Cutting blade default

When the workpiece material organization, hardness, and unevenness of the balance, the large front angle causes the cutting blade strength to be low, the rigidity of the craft system produces vibration, or disconnected cutting, when the blade grinding quality is not good, the cutting blade is prone to contrasting. That is, a small collapse, gap, or peeling in the blade area. After this happens, the tool will lose part of the cutting ability, but it can continue to work. In continued cutting, the damage part of the blade area may expand rapidly, resulting in greater damage.

 

(2) The cutting blade or the tip of the knife is broken

This damage method is often produced in a worse cutting condition than the cutting blade micro -contrasting, or the further development of the micro -contrasting. The size and range of the broken crash are greater than the contrast of the contrast, making the tool completely lose the cutting ability and has to terminate the work. The tip of the knife is often called the tip.

 

(3) Break blade or tools

When the cutting conditions are extremely harsh, the amount of cutting is too large, there are impact loads, and the blade or tool material is slightly cracking. When the welding, the blade grind in the blade, there are residual stress, and if the operation is accidental Caused. After this damage form occurs, the tool cannot continue to be used, resulting in scrap.

 

(4) Step layer of the blade

For materials with large brittleness, such as hard alloy, ceramics, PCBN, etc. with high TIC content, due to defects or potential cracks in the surface tissue, or due to welding and blade grinding, there is residual stress on the surface layer. During the cutting process When it is not stable enough or the surface of the knife is tolerated, the surface layer is easily peeled when the intercourse is affected. The peeling may occur on the front knife surface, and the knife may occur on the rear knife surface. The possibility of peeling of the coating tool is more likely. The blade is slightly stripped and backward, and it can continue to work. If it is severely peeled, it will lose the cutting ability.

 

(5) Plastic variant of the cutting site

Due to the low strength of the steel and high -speed steel, plastic variables may occur in its cutting site due to low strength. When the hard alloys work directly in high temperature and three -way compression state, the surface layer is also generated, and even the plastic deformation surface of the cutting blade or the tip of the cutter causes collapse. The collapse usually occurs in the case of large cutting dosage and hard processing. The elastic modulus of the TIC -based hard alloy is less than the WC -based hard alloy. PCD and PCBN basically do not have plastic deformation.

 

(6) The heat cracks of the blade

 

When the tool load and thermal load that is affected by the transformation, the surface surface of the cutting part is inevitable to cause the thermal stress of the cross due to repeated thermal expansion and contraction, which will cause the blade to fatigue and crack. For example, when the hard alloy milling cutter is milling at high -speed milling, the blade tooth is constantly impacted and thermal stress, and combed cracks are produced on the front knife surface. Although some tools do not have obvious alternating loads and cross -transition stress, due to the inconsistent temperature of the surface and inner layers, the thermal stress will also be generated. In addition, the internal defects are inevitable. Therefore, the blade may also cause cracks. When the crack is formed, the knife can continue to work for a while. Sometimes the crack is quickly expanded and the blade is broken or the knife surface is severely peeled.

 

02 Causes of knife wear

 

(1) Fruits wear

In the processing material, there are often tiny particles with extremely high hardness, which can draw grooves on the surface of the tool. This is the abrasive wear. The abrasive wear exists in each surface, and the front knife surface is the most obvious. Moreover, abrasive wear can occur at various cutting speeds, but when the cutting temperature is low, the wear produced by other reasons is not obvious due to the low cutting temperature, so the abrasive wear is the main reason. In addition, the lower the hardness of the tool, the more severe the abrasive hemp loss.

 

(2) Cold welding wear

When cutting, there is a lot of pressure and strong friction between the workpiece, cutting, and the front and rear knives, so cold welding will occur. Due to the relative exercise between the friction, the cold welding will be ruptured by one party, causing cold welding wear. Cold welding wear is generally serious at medium cutting speed. According to experiments, crisp metals are stronger than the anti -cold welding capacity of plastic metals; multi -phase metals are smaller than unilateral metals; metal compounds are less oriented than single -cold welding; chemical element cycle table B national elements and iron cold welding tendencies. Cold welding is serious when high -speed steel and hard alloys are cut off at low speed.

 

(3) Disclosure and wear

During the contact of cutting and tooling at high temperature, the chemical elements of the two sides spread each other in the solid, changing the component structure of the tool, making the surface layer of the tool fragile and exacerbating the wear of the tool. The diffusion phenomenon always maintains the continuous diffusion of objects with high depth gradient to deep gradient low objects.

 

For example, at 800 ° C, the cobalt will spread quickly to dandruff and workpieces. WC is decomposed into tungsten and carbon spread to steel; PCD knife is higher than 800 ° C when cutting steel and iron materials are higher than 800 ° C. At the time, the carbon atom in PCD will be transferred to the surface of the workpiece to form a new alloy with a large diffusion intensity, and the surface of the knife is graphitized. The diffusion of cobalt and tungsten is serious, and the anti -diffusion capacity of titanium, , and is strong. Therefore, YT -class hard alloy has better abrasion resistance. When the ceramic and PCBN are cut, when the temperature is as high as 1000 ° C ~ 1300 ° C, the diffusion and wear are not significant. Because the workpiece and dandruff are the same as that of the tools, thermal power is generated in the contact area during the cutting area. This thermal power has the effect of promoting diffusion and accelerating the wear of the tool. This diffusion and wear under the action of thermal potential is called "thermoelectric wear".

 

(4) Oxidation wear

When the temperature rises, the wear of softer oxide on the surface of the tool is formed by the softer oxide and the friction of dandruff. Such as: oxidation reactions such as cobalt, carbides, titanium carbide, etc. in the oxygen and hard alloys in the time and space of 700 ° C ~ 800 ° C, and a softer oxide; at 1000 ° C, PCBN has a chemical reaction with water vapor.

 

03 The wear form of blade

(1) The front knife and surface loss

When cutting plastic materials at a large speed, the part of the cutting force is close to the cut force, and under the action of crumbs, it will wear a crescent concave, so it is also known as the time of the crescent depression. In the early stage of wear, the front angle of the tool increased, which improved the cutting conditions and facilitated the crumbs of the scroll. Case. When cutting crispy materials, or cutting plastic materials at a lower cutting speed and thin cutting thickness, crescent depression is generally not produced.

 

(2) Darration of knife tip

The tip of the knife is the wear of the rear knife surface of the knife tip and the wear on the neighboring editor's rear knife surface. Because the heat dissipation conditions here are poor and the stress concentration is concentrated, the wear speed is faster than the rear knife surface. Sometimes a series of small grooves that are equal to the amount of feed on the vice rear knife surface are called grooved wear. They are mainly caused by the hardening layer and cutting lines of the processed surface. When cutting and hardening, it is most likely to cause ditch wear. The cutting tip wear has the greatest impact on the roughness and processing accuracy of the workpiece.

 

(3) The rear knife surface wear

When a large cutting thickness and cutting plastic material, due to the existence of dandruff, the rear knife surface of the tool may not contact the workpiece. In addition, the rear knife surface usually contacts the workpiece, and a wear band is formed on the rear knife surface. Generally, in the middle of the working length of the cutting blade, the rear knife surface is evenly worn evenly. Therefore, the degree of wear of the rear knife surface can be measured with the correction bandwidth of the rear knife surface of the cut blade.

 

Because various types of tools will almost cause cutting surface wear after different cutting conditions, especially the cutting crispy material or smaller cutting thickness cutting plastic material. The measurement of width VB is relatively easy, so VB is usually used to indicate the degree of wear of the tool. The larger the VB, not only will the cutting force increase, cause cutting vibration, but also affect the wear of the tip of the knife, which will affect the processing accuracy and the quality of the processing surface.

 

04 How to prevent damage to knives

(1) For the characteristics of the processing materials and parts, the materials and brands of various types of tools are reasonably selected. Under the premise of having a certain hardness and abrasion resistance, it is necessary to ensure that the tool material must have the necessary toughness.

 

(2) Reasonably select the geometric parameters of the tool. By adjusting the angle of the front and rear angles, the main partial angle, the blade inclusion angle; Rubing a negative edge on the cutting blade is an effective measure to prevent the collapse.

 

(3) Ensure the quality of welding and blade grinding, and avoid various defects caused by welding and blade. The tools used in key processes should be grinded to improve the surface quality and check whether there are cracks.

 

(4) Reasonably select the amount of cutting to avoid excessive cutting force and high cutting temperature to prevent the knife from being damaged.

 

(5) As much as possible to ensure that the process system has a good rigidity and reduce vibration.

 

(6) Take the correct operation method to make the knife be unbearable or less to withstand the load of mutation.

 

05 Causes and countermeasures for the knife crash

 

(1) Improper selection of blade cards and specifications, such as the thickness of the blade is too thin or the thick and crispy cards are selected during rough processing.

 

Countermeasures: Increase the thickness of the blade or install the blade, and choose a brand with high bending strength and toughness.

 

(2) Improper selection of geometric parameters (such as too large front and rear corners, etc.).

 

Countermeasures: You can reset the knife from the following aspects.

1) Properly reduce the front and rear corners;

2) Use a larger negative blade inclination;

3) Reduce the main partial corner;

4) Use a larger negative downward edge or blade mouth arc;

5) Repair the transitional cutting blade to enhance the tip of the knife.

 

(3) The welding process of the blade is incorrect, resulting in excessive welding stress or welding cracks.

 

Countermeasure:

1) Avoid using three -sided closure knife groove structure;

2) Select the weld correctly;

3) Avoid the use of oxygen flame heating welding, and heat preservation after welding to eliminate internal stress;

4) Use the structure of mechanical clip as much as possible.

 

(4) Improper blade grinding method, resulting in grinding stress and grinding cracks; excessive vibration of the blade of the blade of PCBN milling blade, which makes the load of individual knife teeth overweight and can also cause knife.

 

Countermeasure:

1) Use intermittent grinding or diamond sand wheel grinding;

2) Select the softer sand wheels, and often repair the sand wheels to keep sharp;

3) Pay attention to the quality of the blade grinding and strictly control the amount of vibration of the milling cutter.

 

(5) The selection of cutting dosage is unreasonable. If the amount of dosage is too large, the machine tool is stuffed; when cutting is disconnected, the cutting speed is too high, the amount of feed is too large, and the cut depth of the cutting depth is too small; the cutting high manganese; When steel and other materials have a large tendency of hardening, the feed fees are too small.

 

Countermeasure: Re -select the cutting amount.

 

(6) The reasons for the structural reasons such as the underlying surface of the knife groove of the mechanical clamping knife or the blade of the blade are excessive.

 

Countermeasure:

1) Repair the bottom of the knife groove;

2) Reasonable arrangement of the position of the cutting fluid nozzle;

3) The hard -quenched knife pole adds a hard alloy pad under the blade.

 

(7) Excessive wear of tools.

 

Countermeasure: Change the knife or replace the cutting blade in time.

 

(8) Insufficient cutting liquid flow or incorrect injection method, causing a sudden heat and cracking of the blade.

 

Countermeasure:

1) Increase the flow of the cutting solution;

2) Reasonable arrangement of the position of the cutting fluid nozzle;

3) Use effective cooling methods such as spray cooling to improve the cooling effect;

4) Reduce the impact on the blade.

 

(9) The tool installation is incorrect, such as: cutting the car knife is too high or too low;

 

Countermeasure: Re -install the tool.

 

(10) The rigidity of the process system is too poor, resulting in too much cutting vibration.

 

Countermeasure:

1) Increase the auxiliary support of the workpiece to improve the rigidity of the workpiece;

2) Reduce the extension length of the tool;

3) Properly reduce the rear corner of the tool;

4) Adopt other vibration measures.

 

(11) Anyonese operation, such as: When the tool is cut into the middle of the workpiece, the action is too fierce; the knife has not been retreated, that is, parking.

 

Countermeasure: Pay attention to the operation method.

 

06 Causes, characteristics and control measures for the formation of dandruff tumors

 

(1) Reasons for formation

 

In the part of the cutting blade, in the contact area of the knife and the dandruff, due to the high pressure, the bottom metal of the chips is embedded in the micro -uneven peak valley on the front knife surface, forming a real metal in the same gap, which generates adhesion. This part of the knife and crumb contact area is called a bonding area. In the bonding area, a thin layer of metal material layer will be stranded on the front knife surface at the bottom layer of dandruff. This part of the metal material of dandruff has been severely deformed and strengthened at the appropriate cutting temperature. With the continuous flow of dandruff, under the action of subsequent cutting, the stagnant accumulation material has been relatively slippery from the upper layer of dandruff, becoming the foundation of dandruff tumors. Subsequently, the second layer of stagnation cutting materials will be formed on it, so that the stratigraphy accumulation is constantly forming a dandruff tumor.

 

(2) Features and the effects of cutting processing

 

1) The hardness is 1.5 ~ 2.0 times higher than the material material. It can be cut instead of the front knife surface. It has the effect of protecting the cutting blade and reducing the wear of the front knife surface. Cause the corner of the knife to wear;

2) The working corner of the knife after the formation of dandruff tumors has increased significantly, which plays a positive role in reducing dandruff deformation and reducing cutting force;

3) Since the chip tumor is protruding from the cutting blade, the actual cutting depth is increased, which affects the size and accuracy of the workpiece;

4) Dedicate tumors will cause the "plow ditch" phenomenon on the surface of the workpiece, affecting the roughness of the surface of the workpiece;

5) The fragments of the chip tumor will bond or embed the surface of the workpiece to cause hard points, affecting the quality of the processed surface of the workpiece.

 

From the above analysis, it can be seen that chip tumors are particularly unfavorable for cutting and processing.

 

(3) Control measures

 

Do not make the bottom layer of dandruff and reinforce or deformation of the front knife surface, the following measures can be avoided by the occurrence of dandruff tumors.

 

1) Reduce the roughness of the front knife surface;

2) Increase the front corner of the tool;

3) Reduce cutting thickness;

4) Using low -speed cutting or high -speed cutting to avoid the cutting speed of easy to form dandruff tumors;

5) Proper heat treatment of workpiece materials to improve its hardness and reduce plasticity;

6) Cutting fluid with good anti -adhesion (such as vulcan -containing chlorine -containing polar pressure cutting fluid).


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