Die burst cause and prevention

2023-11-21 09:44:26

Mold burst cause analysis:

1. The mold material is not good and it is easy to break in subsequent processing.

2. Heat treatment: improper quenching and tempering process produces deformation.

3. Mold grinding flatness is not enough, resulting in deflection.

4. Design process: the mold strength is not enough, the knife edge spacing is too close, the mold structure is unreasonable, and the number of template blocks is not enough.

5. Improper line cutting: Pull the wire line cutting, the gap is wrong, did not make a clear Angle.

6. Selection of punching equipment: punching tonnage, punching force is not enough, and the mold is too deep.

7. Uneven stripping: no demagnetization treatment before production, no return tip; There are broken needles and broken springs in the production.

8. The material is not good: there is no leakage when assembling the mold, or rolling and blocking the shit, and the feet block the shit.

9. Production awareness: laminated stamping, positioning is not in place, no blow gun is used, and the template continues to produce when there are cracks.

How to prevent mold burst:

1 Stamping equipment

The accuracy and rigidity of stamping equipment (such as presses) are extremely important to the impact of die life. The stamping equipment has high precision and good rigidity, and the life of the die is greatly improved. In particular, the foot small gap or no gap die, carbide die and precision die must choose a press with high precision and good rigidity, otherwise, it will reduce the life of the die, and even damage the chess set.

2 Mold Design

(1) Accuracy of the guiding mechanism of the mold. In order to improve the life of the mold, it is necessary to correctly select the guiding form and determine the accuracy of the guiding mechanism according to the requirements of the nature of the process and the accuracy of the parts.

(2) Geometric parameters of the cutting edge of the die (convex and concave die). The shape, fit clearance and fillet radius of the convex and concave die not only have a great impact on the forming of the stamping part, but also have a great impact on the wear and life of the die. If the accuracy requirement is higher, a smaller gap value should be selected; On the contrary, the gap can be appropriately increased to improve the life of the mold.

3 Stamping process

(1) Raw materials for stamping parts.

① Use raw materials with good stamping process as far as possible to reduce stamping deformation force;

② Before stamping, the grade, thickness and surface quality of raw materials should be strictly checked, and the raw materials should be wiped clean, and the surface oxides and rust should be removed if necessary;

③ According to the type of stamping process and raw materials, softening treatment and surface treatment can be arranged if necessary, and the appropriate lubricant and lubrication process can be selected.

(2) Layout and edge.

Unreasonable reciprocating feeding and layout method and too small edge value often lead to sharp mold wear or convex and concave die gnawing. It is necessary to choose the layout method and edge value reasonably according to the processing batch, quality requirements and mold matching gap of the parts to improve the life of the mold.

4 Mold materials

① The use of the material should have high hardness (58~64HRC) and high strength, and has high wear resistance and enough toughness, heat treatment deformation is small, there is a certain heat hardness;

② Good process performance.

5. Hot processing technology

The hot working quality of the die has great influence on the performance and service life of the die.

(1) Forging process. This is an important link in the manufacturing process of mold work parts. The forging temperature range should be strictly controlled, the correct heating specification should be formulated, the correct forging force method should be adopted, and the slow cooling or timely annealing after forging should be adopted.

(2) Preparation of heat treatment. According to the different materials and requirements of the working parts of the mold, the preparatory heat treatment process such as annealing, normalizing or tempering should be used to improve the organization, eliminate the organization defects of the forged blank, and improve the processing technology.

(3) quenching and tempering. This is the key link in the mold heat treatment. Die quenching heating should pay special attention to prevent oxidation and decarbonization, should strictly control the heat treatment process specifications, in the case of conditions permit, vacuum heat treatment can be used. Tempering should be done in time after quenching, and different tempering processes should be used according to technical requirements.

(4) Stress relief annealing. For molds with high precision requirements, stress relief tempering treatment is also required after grinding or electric machining, which is conducive to stable mold accuracy and improve service life.

6 Machining surface quality

① The surface phenomenon of grinding burned parts must be prevented during the processing of die working parts, and the grinding process conditions and process methods (such as grinding wheel hardness, particle size, coolant, feed rate and other parameters) should be strictly controlled;

② Knife marks should be prevented on the surface of the working parts of the mold during processing. Sandwich, cracks, impact scars and other macro defects. The existence of these defects will cause stress concentration and become the source of fracture, resulting in early failure of the mold.

③ The use of grinding, grinding and polishing and other finishing and fine processing, to obtain a small surface roughness value, improve the service life of the mold.

7 Surface strengthening treatment

In order to improve the performance and service life of the die, the surface strengthening treatment of the die working parts is more and more widely used. Common surface strengthening methods are: liquid carbonitriding, ion nitriding, boronizing, vanadizing and electric spark strengthening, as well as chemical vapor deposition (CVD), physical vapor deposition (PVD) and salt bath to the workpiece surface immersion carbide plating method (TD).

8 Line cut metamorphic layer control

The cutting edge of the die is mostly wire cutting. Due to the thermal effect and electrolytic effect of wire cutting processing, the die processing surface produces a certain thickness of metamorphic layer, resulting in surface hardness reduction, micro-cracks, etc., resulting in early wear of the die of wire cutting processing, which directly affects the maintenance of the die punching gap and the edge is easy to break, shortening the service life of the die. Therefore, a reasonable electrical standard should be selected in the wire-cutting process to minimize the depth of the metamorphic layer.

9 Proper use and maintenance

In order to protect normal production, improve the quality of stamping parts, reduce costs and extend the life of the die, it is necessary to correctly use and reasonably maintain the die, strictly implement the "three inspection" system of the die (inspection before use, inspection during use and inspection after use), and do a good job of the die and maintenance overhaul.

Cracks need to be metallographic analysis of the mold






The solid solution of carbon and alloying elements dissolved in γ-Fe still maintains the face-centered cubic lattice of γ-Fe

The grain boundaries are straight and regular polygon. The residual austenite in the hardened steel is distributed in the space between the martensite needles.


a solid solution of carbon and alloying elements dissolved in A-Fe

The slow-cooling ferrite in hypoeutectoid steel is massive and the grain boundary is smooth. When the carbon content is close to the eutectoid composition, the ferrite precipitates along the grain boundary.


A compound of carbon and iron

In the liquid ferrocarbon alloy, the first single crystallized cementite (primary cementite) is massive, the Angle is not sharp, the eutectic cementite is skeleton-like, the carbide (secondary cementite) precipitated along the Acm line when the hypereutectoid steel is cooled down to Ar1, the eutectoid cementite is precipitated from the ferrite (tertiary cementite) when the ferrocarbon alloy is cooled down to AR1. Discontinuous sheet on secondary cementite or at grain boundaries.


Mechanical mixture of ferrite and cementite formed by eutectoid reactions in iron-carbon alloys

The interchip distance of pearlite depends on the degree of supercooling during the decomposition of austenite. The greater the degree of supercooling, the smaller the distance between the pearlite sheets formed at A1~650℃ the pearlite sheet layer is thicker, more than 400 times larger under the metallographic microscope can be distinguished parallel wide strip ferrite and thin strip cementite, called coarse pearlite, flake pearlite, referred to as pearlite formed at 650~600℃ pearlite magnification 500 times with metallographic microscope. Only a black line can be seen from the pearlite cementite, which can only be distinguished by 1000 times magnification, called the pearlite formed at 600~550 ° C with a metallography microscope magnified 500 times, can not distinguish the pearlite lamella, only see the black pellet structure, and can only be distinguished by an electron microscope magnified 10,000 times.

Upper bainite

A mixture of susaturated acicular ferrite and cementite, with the cementite between the ferritic needles

The phase transformation product of supercooled austenite at medium temperature (about 350~550℃) is a bunch of ferrite slats with roughly parallel orientation difference of 6~8od, and there are short carbide rods or small pieces arranged along the long axis of the slats. Typical upper bainite is feathery, grain boundary is symmetrical axis, due to different orientation, feathers can be symmetrical or asymmetric, ferrite feathers can be needle-like, point-like, block. If it is high carbon and high alloy steel, can not see the needle feathers; Medium carbon medium alloy steel, needle feathers more clear; Low carbon low alloy steel, very clear feather, thick needle. During the transition, the upper bainite is formed at the grain boundary first, and grows into the grain without penetrating the grain.

Lower bainite

Ibid., but the cementite is in the ferritic needle

Transformation products of supercooled austenite at 350℃~Ms. The typical morphology is a lenticular ferrite containing susaturated carbon, and there are small sheets of carbides arranged in one direction. In the crystal is acicular, needles do not cross, but can be conjunctured. Different from tempered martensite, martensite has layers, lower bainite is the same color, lower bainite carbide particle is thicker than tempered martensite, susceptible to erosion and black, tempered martensite color is lighter, not susceptible to erosion. The carbide dispersion of high carbon and high alloy steel is higher than that of low carbon and low alloy steel, and the needles are finer than that of low carbon and low alloy steel.

Granular bainite

The large block or strip ferrite contains a complex structure of many small islands

Supercooled austenite is the transition product at the upper part of the bainite transition temperature range. When formed, it is composed of massive ferrite formed by merging of strip ferrite and small island carbon-rich austenite. During the subsequent cooling process, carbon-rich austenite may be all retained as residual austenite. It may also be partially or completely decomposed into a mixture of ferrite and cementite (pearlite or bainite); It is most likely partially converted to martensite and partially retained to form a two-phase mixture called M-A structure.

Carbide free bainite

A single phase structure of ferrite, also known as ferrite bainite

The formation temperature is at the upper part of the bainite transition temperature range. Between the lath ferrites are carbon-rich austenites, and the carbon-rich austenites undergo similar transformations during the subsequent cooling process. Carbide-free bainite generally appears in low carbon steel, and is also easy to form in steel with high silicon and aluminum content.


Supersaturated solid solution of carbon in a-Fe

Formed in low and medium carbon steel and stainless steel and consisting of many parallel lath bundles, one austenite grain can be converted into several lath bundles (usually 3 to 5) of sheet martensite (aciculate martensite) : Common in high, medium carbon steel and high Ni Fe-Ni alloy, there is a suture in the needle martensite divided into two halves, due to different orientation can be needle-like or block, needle and needle 120o Angle arrangement, high carbon martensite needle grain boundary is clear, fine acicular martensite is cloth grain, known as cryptic martensite.


Eutectic mixture of austenite and cementite

Dendritic austenite is distributed on the matrix of cementite.

Tempered martensite

Martensitic decomposition results in very fine transitional carbides mixed with susaturated (low carbon content) A-phase structure

Martensitic decomposition results in very fine transitional carbides mixed with susaturated (low carbon content) A-phase structure

Tempered troostite

a mixture of carbides and a- phases

t is formed by the moderate tempering of martensite at 350~500 ° C. The microstructure is characterized by the distribution of very fine granular carbides in the ferrite matrix, the acicular shape has gradually disappeared, but it is still faintly visible, the carbides can not be distinguished under the optical microscope, only the dark structure can be observed, and the two phases can be clearly distinguished under the electron microscope, it can be seen that the carbide particles have grown significantly.

Tempered sorbite

The matrix is ferrite with uniform carbide particles distributed on the matrix.

It is formed by the tempering of martensite at a high temperature of 500~650℃. Its microstructure is characterized by a complex structure composed of isaemic ferrite and fine-grained carbide, the traces of martensitic plates have disappeared, and the shape of cementite has been clear, but it is difficult to distinguish under the light microscope, and the cementite particles can be seen under the electron microscope.

Granular pearlite

It is composed of ferrite and granular carbide

t is formed by spheroidizing annealing of hypereutectoid steel or tempering of martensite in the temperature range of 650℃~A1. It is characterized by the distribution of carbide particles on the ferrite.

Weil tissue

If the austenite grain is relatively coarse and the cooling rate is relatively suitable, the first eutectoid phase may be mixed with the needle (sheet) shape and the sheet pearlite, which is called the Weisberg structure.

In hypoeutectoid steel, the morphology of the Weischer-organized ferrites is lamellar, feathery or triangular, and the coarse ferrites are parallel or triangular. It appears in the austenite grain boundary, while growing intragranular in hypereutectoid steel, the shape of the wehstenitic structure cementite is needle-like or rod-like, and it appears in the interior of the austenite grain.