Molds repair by brush plating

Molds play an extremely important role in the national economy. At present, my country's mold technology cannot fully meet the needs of modern industrial development, and its level is nearly 20 years behind that of developed countries. The main problem is that the manufacturing cycle is long, the life is short, and the precision is low. The production can only meet about half of the demand, so the current urgent problem is to improve the life of the mold. The easiest, most economical and most realistic way to improve the life of the mold is to use brush plating technology.

The brush plating technology has been researched, developed, applied and promoted in my country for more than 20 years. This new technology has solved many key problems such as maintenance in key national projects, creating direct economic benefits of more than 3 billion yuan. The brush plating technology has won the first prize of the National Science and Technology Progress Award, and it is a new technology promoted by the country for three consecutive five-year plans.

Application of brush plating

Brush plating technology is widely used in mold manufacturing and failure repair. For some large and difficult-to-move molds, because the brush plating equipment is relatively simple, the process is flexible, and it is easy to carry, you can go to the site for surface brush plating. Surface brush plating can also be used to repair local defects in the mold cavity or worn parts after use. Due to the short repair cycle and great economic benefits, the repair cost generally only accounts for 0.5% to 2% of the workpiece cost, and the wear resistance, hardness and surface roughness of the repaired surface can reach the original performance indicators, so the surface reinforcement purpose. Applying brush plating technology to molds can increase the life of hot forging molds for auto parts (such as crankshafts, connecting rods, gears, etc.) by 20-100%. The main reason is that the brush plating layer has good red hardness and wear resistance. and anti-oxidation ability; electric brush plating can also greatly improve the life of cold working molds, which is attributed to the high hardness and good anti-adhesion properties of the electric brush plating layer; the use of amorphous electric brush plating can make various cold and hot The service life of the mold is further increased by 50~200%.

The basic principle of brush plating

The brush plating technology requires special DC power supply equipment. The positive pole of the power supply is connected to the plating pen as the anode during brush plating; the negative pole of the power supply is connected to the workpiece as the cathode during brush plating. Plating pens usually use high-purity fine graphite blocks as anode materials, and the graphite blocks are wrapped with a layer of cotton and wear-resistant polyester-cotton sleeves. During brush plating, the pen immersed in the plating solution moves on the surface of the workpiece at a certain relative speed and maintains a proper pressure. At the part where the plating pen contacts the workpiece, the metal ions in the plating solution diffuse to the surface of the workpiece under the action of the electric field, and the electrons obtained on the surface are reduced to metal atoms, and the crystals are deposited to form a plating layer. Thickening, so as to achieve the purpose of plating and repair. Brush plating equipment mainly includes power supply, plating pen and anode and various auxiliary materials.

Brush plating power supply unit

The brush plating power supply is the main equipment in the brush plating process, which consists of the main circuit and the control circuit.

Surface preparation and temperature control for brush plating

Before brush plating, the mold parts need to be surface prepared, so that the workpiece to be plated shows a fresh and clean substrate, so that it can be firmly combined with the plating layer. Surface preparation includes surface processing before plating, surface degreasing and surface rust removal. During the whole process of brush plating the mold, both the mold and the plating solution should be operated at 40~50℃.

Brush Plating Solution

The key to the brush plating technology is the formula of the brush plating solution.

◆Surface pretreatment solution

The surface pretreatment solution mainly includes electro-cleaning solution for electrolytic degreasing and activation solution for electrolytic etching on the surface.

◆Mold commonly used brush plating solution

①Special nickel

Nickel sulfate 395~397g/L Sodium chloride 14~16g/L

Acetic acid 68~70g/L Hydrochloric acid 20~28g/L

②Ni-tungsten D alloy plating solution

Nickel sulfate 395g/L Sodium tungstate 23 g/L

Boric acid 31 g/L Citric acid 42 g/L

Cobalt sulfate 2 g/L Anhydrous sodium sulfate 6.5 g/L

Magnesium sulfate 2 g/L Manganese sulfate 2 g/L

Glacial acetic acid 20mL/L Formic acid 35mL/L

Sodium Fluoride 5 g/L Sodium Lauryl Sulfate 0.01~0.001g/L

In addition to nickel-tungsten alloys, nickel-cobalt alloys developed in recent years are especially suitable for brush plating on mold surfaces due to their hardness as high as 550HBW, good wear resistance and low coating stress.

Example 1: Brush plating repair treatment of motor shaft hole punch

The edge processing of the lower die of the die is over 0.1mm, the material is Cr12, and the size is repaired after quenching. First, the bottom layer is plated with special nickel, and then nickel-tungsten D is plated as the working layer. Its process operation is as follows:

(1) Degreasing with organic solvent acetone.

(2) Degrease with electric cleaning solution, connect the mold parts to the negative electrode, the working voltage is 12~15V, and the time is 15~30s.

(3) Rinse thoroughly with clean water.

(4) use

The chromium activation solution is activated, the mold parts are connected to the positive electrode, the working voltage is 12~15V, and the time is 10~30s; then the voltage is reduced to 10~12V, and the time is 10~20s, so that the surface of the workpiece is silver-gray.

(5) Plating the bottom layer with a special nickel plating solution, wipe for 3~5s without electricity, connect the mold parts to the negative electrode, the working voltage is 18~20V, flash plating for 3~5s, then the working voltage is reduced to 15V, and the relative movement speed of the cathode and anode is 10~15m /min, coating 2mm.

(6) Plating the working layer with nickel-tungsten D plating solution, the working voltage is 10~15V, and the relative movement speed of the cathode and anode is 6~20m/min. Plating thickness up to specified dimensions. Before working, the temperature of the plating solution should be heated to 30~50℃.

Example 2: Combined die size recovery and surface strengthening

The material is T10A steel. After many years of use, the single side wears 0.2mm. In order to restore the size and strengthen the surface, the bottom layer (special nickel) is first plated, and then the nickel-tungsten D alloy is plated as the wear-resistant surface. T10A belongs to medium carbon steel, and its operation process is as follows:

(1) Polish the surface with sandpaper and whetstone.

(2) Wipe with organic solvent.

(3) Degrease with electric cleaning solution, connect the working parts of the mold to the negative electrode, the working voltage is 10~14V, the relative movement speed of the cathode and anode is 4~8m/min, and the electric cleaning time is as short as possible to reduce the amount of hydrogen permeation of the working parts of the mold, and the working parts of the mold. The water droplets spread evenly on the surface without dry spots.

(4) Wash thoroughly with clean water.

(5) Activated with the activation solution prepared by hydrochloric acid and sodium chloride, the working parts of the mold are connected to the positive electrode, the working voltage is 10~14V, the relative movement speed of the cathode and anode is 6~8m/min, and the activation time should be based on the plating pen and the working parts of the mold are plated Depending on the size of the surface, the contact time of one part is 30~60s, and the surface of the working part of the mold can be uniformly black and gray.

(6) Wash thoroughly with clean water.

(7) Activated with the activation solution prepared by sulfuric acid and ammonium sulfate, the working part of the mold is connected to the positive electrode, the working voltage is 18~25V, and the contact time of one part is 30~60s, so that the surface of the working part of the mold is silver-gray.

(8) Wash thoroughly with clean water.

(9) is the same as (5) in Example 1.

(10) is the same as (6) in Example 1.

The new progress of brush plating technology research

◆Brush Plating Amorphous Coating

The general brush plating is crystalline. If a special plating solution is used, the metal ions deposited during brush plating are irregularly arranged in the plating, and an amorphous plating with an amorphous structure can be obtained. This coating has excellent physical, chemical and mechanical properties and is an economical way to increase mold life. Table 1 shows the application effect of amorphous brush plating on the mold.

Under normal temperature conditions, the brush plating method is applied, and the Co-Ni-P series alloy brush plating solution can be used to obtain an amorphous brush plating layer. Among them, the brush plating layer obtained by adding the plating solution containing niobium additive with low Co++ concentration has the best performance. The coating has high hardness and good wear resistance at room temperature and high temperature.

◆Brush plating composite coating

Composite brush plating is a kind of composite electroplating, and its essence is to obtain composite material (composite coating) on the surface of workpiece substrate by electrochemical deposition. At present, nickel-based baths are used for composite brush plating. For example, molybdenum disulfide is added to the nickel bath for self-lubricating coatings; Al2O3 is added for wear-resistant and anti-corrosion coatings, and diamond powder is added for high-anti-wear coatings. coating.

The hot forging die is applied with Ni-Co-ZrO2 composite brush plating. The coating has good wear resistance, anti-adhesion, high temperature oxidation resistance and high temperature fatigue resistance. It combines well with the matrix and can improve the life. The study confirmed that the strengthening mechanism of the composite coating is mainly fine-grain strengthening and second-phase particle strengthening, and the strengthening effect depends on the dispersion of the second-phase particles and the firmness of the matrix metal.