Use, maintenance and management of extrusion dies

Use, maintenance and management of extrusion dies

In aluminum profile production factories, the extrusion dies cost accounts for about 35% of the profile extrusion production cost.

The quality of the extrusion dies and whether the extrusion dies can be used and maintained reasonably directly determines whether the extruder can produce aluminum profiles normally and qualified.

The working conditions of the extrusion dies in the extrusion production are very harsh.

It not only needs to withstand severe friction and wear under high temperature and high pressure, but also needs to withstand cyclical loads.

All of these require the extrusion dies to have high thermal stability, thermal fatigue resistance, thermal wear resistance and sufficient toughness.

In order to meet the above requirements, high-quality 4Cr5MoSiV1 (US temper H13) alloy steel is generally used in China at present,

Vacuum heat treatment and quenching are used to make molds to meet various requirements in the production of aluminum profiles.

However, in actual production, there are still some extrusion dies that fail to reach the predetermined output during extrusion.

In serious cases, they are even scrapped ahead of schedule when less than 20 pieces of billets are extruded or less than 2 times on the machine, resulting in the use of expensive mold steel.

The mold is far from realizing its due benefits.

This phenomenon is common in many domestic aluminum profile manufacturers.

Situation:

The cross-section of aluminum profiles is ever-changing,

Aluminum alloy profiles have important advantages such as being light weight and having good strength.

At present, many industries have adopted aluminum profiles to replace the original materials.

Due to the specificity of some aluminum profiles, the extrusion dies are difficult to design and manufacture due to the special profile section.

If the conventional extrusion method is still used, it is often difficult to achieve the rated output of the extrusion dies,

and a special process must be adopted to strictly control various production process parameters to carry out normal production.

Moreover, due to the special section of the extrusion die itself or the quality of the extrusion die itself, the extrusion die cannot be extruded to the rated output, which requires the sales staff to fully communicate with the technical department and the mold workshop when receiving the order.

At the same time, the extrusion die design and production department need to continuously optimize the extrusion die design technology, improve the precision of its production, and improve the quality of extrusion dies.

Investigate its cause, need to start from the following factors:

1. Choose the right extrusion press for production.

Before extrusion production, it is necessary to fully calculate the profile section, and determine the tonnage capacity of the extrusion press according to the complexity of the profile section, wall thickness and extrusion coefficient.

Generally speaking, λ>7-10.

When λ>8-45, the service life of the extrusion die is longer and the profile production process is smoother.

When λ>70-80, it is more difficult to extrude aluminum profile, and the life of the die is generally shorter.

The more complex the product structure is, the easier it is to cause insufficient local rigidity of the mold,

It is difficult for the metal flow in the mold cavity to become uniform, which is accompanied by local stress concentration.

During the production of extrusion, it is easy to block the die, or form twisted waves, and the extrusion die is easy to have elastic deformation.

And in severe cases, plastic deformation will occur, so that the extrusion die will be scrapped directly.

2. Reasonable selection of billet and heating temperature. The alloy composition of the billets should be strictly controlled.

At present, the extrusion factories require the billet grain size to reach the first-class standard in order to enhance plasticity and reduce anisotropy.

When there are air holes, loose tissue or central cracks in the billet, the sudden release of gas during the extrusion process is similar to “blasting”, which makes the local working belt of the mold suddenly unload and reload, forming a local huge impact load, which has a great impact on the mold.

The extrusion factories with conditions that can carry out homogenization treatment on the billets, and force cooling after holding at 550~570°C for 8 hours, the extrusion breakthrough pressure can be reduced by 7-10%, and the extrusion speed can be increased by about 15%.

3. Optimize the extrusion process.

In order to extend the service life of the extrusion die scientifically, the reasonable use of the extrusion die for production is an aspect that cannot be ignored.

Due to the extremely harsh working conditions of extrusion dies, reasonable measures must be taken in extrusion production to ensure the properties of the dies.

3.1 Take the appropriate extrusion speed

In the extrusion process, when the extrusion speed is too fast, it will cause the metal flow to be difficult to be uniform, the friction between the aluminum metal flow and the inner wall of the mold cavity will increase, the wear of the working belt of the mold will be accelerated, and the actual temperature of the mold will be higher.

If the residual heat generated by metal deformation cannot be taken away in time at this time, the mold may fail due to local overheating.

If the extrusion speed is appropriate, the occurrence of the above-mentioned adverse consequences can be avoided, and the extrusion speed should generally be controlled below 25mm/s.

3.2 Reasonable selection of extrusion temperature.

The extrusion temperature is determined by the mold heating temperature, the temperature of the billet container and the temperature of the aluminum billet.

If the temperature of the aluminum billet is too low, the extrusion force will increase or the phenomenon of cannot extrude under the maximum working pressure will easily occur.

The mold is prone to local micro-elastic deformation, or cracks will occur in the stress-concentrated parts, resulting in early scrapping of the mold.

If the temperature of the aluminum billet is too high, the metal structure will be softened, so that it will stick to the surface of the mold working belt or even block the mold (in severe cases, the mold will collapse under high pressure).

The reasonable heating temperature of the unhomogenized billet is 460-520°C.

The reasonable heating temperature of the homogenized ingot is 430-480°C.

3.3 In the early stage of the extrusion die application, reasonable surface nitriding treatment must be carried out on the die.

Surface nitriding treatment can greatly improve the surface hardness of the mold while maintaining sufficient toughness, so as to reduce the thermal wear of the mold during use.

It should be noted that the nitriding of the surface cannot be completed at one time.

During the service period of the mold, repeated nitriding treatment must be carried out 3-4 times.

Generally, the thickness of the nitriding layer is required to reach about 0.15mm.

A more suitable nitriding process is the first nitriding after the mold enters the factory for inspection.

At this time, since the structure of the nitrided layer is still unstable, it should be nitrided again after extruding 5-10 pieces of billets.

After the second nitriding, 40-80 pieces of billets can be extruded.

It is advisable not to exceed 100-120 pieces of billets after the third nitriding.

Before nitriding, the working belt must be polished, the cavity of the mold must be cleaned, and no alkali slag or foreign particles should remain.

Generally, the number of nitriding times of the mold does not exceed 4-5 times, because at this time, if the nitriding layer is not strained by the working belt, the structure of the nitriding layer has been relatively stable after repeated nitriding and extrusion production.

It should be noted that the nitriding can only be carried out after a suitable production process in the early stage of nitriding, and the number of nitridings should not be too frequent, otherwise, the working belt is easy to delaminate.

3.4 The working belt must be ground and polished before the extrusion die is put on the machine, and the working belt is generally required to be polished to a mirror surface.

Check the flatness and verticality of the mold working belt before assembly.

The quality of nitriding determines the smoothness of the work belt polishing to a certain extent.

The mold cavity must be cleaned with high-pressure air and a brush, and there must be no dust or foreign matter, otherwise, it is easy to damage the working belt driven by the metal flow, so that the extruded profile product has surface defects such as rough surface or scratches.

4. Use the correct alkaline cleaning method

After the extrusion die is unloaded, the temperature of the extrusion die is more than 500°C.

If it is immediately immersed in alkaline water, the temperature of the alkaline water is much lower than the temperature of the extrusion die. If the temperature of the extrusion die drops rapidly, the die is prone to cracking.

The correct method is to place the extrusion die in the air at 100-150°C after unloading and then immerse it in alkaline water.

For ordinary porthole dies, detailed operation is performed before unloading, which can greatly reduce the workload of mold immersion and shorten the mold immersion time.

The specific method is that after the extrusion is completed, the extrusion stem retreats before the extrusion cylinder, and the discard of extrusion remains in the extrusion cylinder, and then the extrusion cylinder retreats, and at the same time, some aluminum in the mold port hole can be pulled out along with the discard of aluminum, and then Then carry out alkaline immersion.

5. The use of the extrusion dies adopts the use intensity from low to high and then to low

When the extrusion die first enters the service period, the performance of the internal metal structure is still in the floating stage.

During this period, a low-intensity operation plan should be adopted to make the mold transition to a stable period.

In the mid-term of extrusion die use, since the performance of the mold is basically in a stable state, similar to a car that has just passed the break-in period, the use strength can be appropriately increased.

In the later stage, the metal structure of the mold has begun to deteriorate, and the fatigue strength, stability and toughness have begun to decline after long-term production and service.

At this time, the service strength of the extrusion die should be appropriately reduced until the mold is scrapped.

6 Strengthen the use and maintenance records of extrusion dies in the extrusion process, and improve the tracking record files and management of each set of dies

From the inspection of the extrusion die to the scrapping of the die after use, the intermediate time can be as short as a few months and as long as more than a year.

Basically, the user records of molds also record the various processes of profile production.

There are a large number of extrusion dies and many varieties.

Managing the use process of each set of dies will help the mold workshop administrators, die users and die design and manufacturing technicians to understand the real situation of each set of stock dies. Tooling track record includes:

(1) Manufacturing information of molds, including design drawings of each set of molds, production records, inspection records (precision value, hardness value), etc.

(2) The process information of each extrusion production of the mold, such as heating time, aluminum billet temperature, mold temperature, extrusion speed, extrusion force, breakthrough pressure, aluminum billet length, number of qualified products, profile linear density, Yield rate, etc.

(3) The first three mold repair plans for each set of molds, the nitriding treatment time, the time of entering and leaving the mold warehouse, the time and reason for scrapping or returning to the mold factory for maintenance, etc.

The collection of these records is very important for improving mold management, calculating mold costs, and optimizing molds Work such as designing and repairing molds, judging the quality of molds, improving the stability of extrusion production, rationally using molds, and determining the lower inventory of molds all have a direct impact.

The increasingly intensified competition in the aluminum profile market has forced aluminum profile manufacturers to invest a lot of energy in the procurement, use, maintenance and management of extrusion dies.

This requires companies to change their concepts while changing the previous extensive production management.

Only by doing a good job in statistical analysis and cost consumption management of molds can we adapt to the new market situation and seize opportunities in the market.