CN102615431A - Remanufacturing method for automatic laser cladding of gray cast iron cylinder cover - Google Patents

Abstract

The invention discloses an automatic laser cladding remanufacturing method for a gray cast iron cylinder head, which includes preparing gray cast iron laser cladding repair materials; performing non-destructive detection on the depth of "nose crack" cracks on the gray cast iron cylinder head; The "nose crack" part on the cover is pretreated before repair; the "nose crack" part on the gray cast iron cylinder head is profiling repaired by laser cladding; the stress is removed from the repaired part. The invention has precise forming dimensions, requires only minor post-processing, and has less thermal influence on the substrate; and the mechanical properties of the three-dimensional forming repair parts are excellent, which can well inhibit the whitening tendency of the bonding interface and effectively block the diffusion of carbon.

Description

An automatic laser cladding remanufacturing method for gray cast iron cylinder head

technical field

The invention relates to the field of equipment remanufacturing, in particular to an automatic laser cladding remanufacturing method for a gray cast iron cylinder head.

Background technique

Due to its cheap price, gray cast iron has the advantages of good casting performance, excellent vibration damping, good wear resistance, excellent machinability, high tensile strength, low notch sensitivity, good thermal conductivity, etc. , It is often used to make large castings in industrial production. Engine cylinder heads are one of the typical parts made from this material. Such large-scale components usually require complex heat treatment and manufacturing processes, as well as precise machining, etc., and special equipment is required for preparation, which is expensive and expensive.

However, in the process of use, due to the loose structure characteristics of gray cast iron itself and the splitting effect of flake graphite, the tensile strength, plasticity and toughness of gray cast iron are far lower than those of steel, and the mechanical properties are poor. Some impurity components also have a certain influence on the organization and structure of gray cast iron itself. These characteristics of gray cast iron lead to many defects in gray cast iron cylinder head, among which the most common type of defect is the generation of transverse cracks at the "nose bridge" between the valves. The cause of the transverse cracks is closely related to the structural characteristics of this part and the working environment . The cylinder head is subjected to high temperature during the working process of the engine, which requires timely cooling of the internal circulating water circuit, so the structural design of the cylinder head is relatively complicated, while the "nose bridge" part is a solid structure, and the cooling effect of the circulating water is weak. Under the action of high temperature and high pressure gas and the impact of large mechanical load, the fatigue fracture of this part will occur under the action of thermal stress.

If the cylinder head with fatigue fracture is directly scrapped and returned to the furnace as a waste product, the added value such as labor value and energy value during component manufacturing will be completely lost, and the obtained products can only be used as raw materials, causing great waste. In the industry, welding repair is often used for repairing. The common welding repair methods include manual arc welding and _CO2 gas shielded welding, but these methods have the following problems: the heat input is too large, which seriously affects the heat of the substrate, resulting in residual stress in the weld If it is too large, there will be white structure and hardened structure in the welded joint, and the weld will be easily cracked. Although the use of heterogeneous weld materials can reduce the whitening tendency of welded joints, there is still a lack of effective technical means for controlling the residual stress after multi-layer surfacing.

Contents of the invention

The purpose of the present invention is to overcome the defects that the weld seam formed by the existing welding repair method is easy to crack and the residual stress is large, thereby providing an automatic laser cladding remanufacturing method for the gray cast iron cylinder head, including:

Step 1), preparation of gray cast iron laser cladding repair materials; wherein,

The gray cast iron laser cladding repair material has the following physical and chemical properties: the strength is not lower than that of the matrix, the plasticity and toughness are high, and the crack resistance is outstanding; it can block the diffusion of carbon elements and significantly inhibit the interface whitening; it has good self-deoxidation, Slagging ability, excellent surface appearance quality, no pores inside; good wettability with gray cast iron substrate, excellent laser cladding formability;

Step 2), perform non-destructive testing on the depth of the "nose crack" crack on the gray cast iron cylinder head;

Step 3), pretreatment before repairing the "nose crack" part on the gray cast iron cylinder head, in the pretreatment, remove the crack at the "nose crack" part according to the crack depth detection result obtained in step 2), forming A groove, and then use the angle grinding wheel to grind the groove around until the fresh metal surface is exposed, and clean the groove and its surrounding surface with acetone solution;

Step 4), profiling and repairing the "nose crack" on the gray cast iron cylinder head by laser cladding; this step includes:

Step 4-1), performing single-track single-layer cladding on the groove on the gray cast iron cylinder head;

Step 4-2), forming a primer at the groove on the gray cast iron cylinder head;

Step 4-3), on the basis of the base layer generated in step 4-2), do multi-layer accumulation profiling repair;

Step 5), removing stress from the repaired part.

In the above technical solution, in the step 1), the gray cast iron laser cladding repair material is Ni-Cu alloy powder, the alloy powder includes C element with a mass fraction of 0.01% to 0.05%, mass fraction 2.0% to 4.0% Si element, 1.0% to 3.0% mass fraction of B element, 0.1% to 1.0% mass fraction of Fe element, 10% to 40% mass fraction of Cu element and mass fraction of Bal Ni element.

In the above technical solution, in the step 3), the groove is a "V"-shaped groove, and the bottom of the "V"-shaped groove is a rounded corner. For a groove with a depth of 10mm, the included angle of the groove is Not less than 80°.

In the above technical solution, in the step 4-1), the single-pass single-layer cladding at the groove on the gray cast iron cylinder head includes: performing single-pass single-layer cladding When using sideways synchronous powder feeding, high-purity nitrogen protection, laser power of 800 W, scanning speed of 150 mm/min, powder feeding voltage of 11 V, spot size of 3.5 mm, powder feeding carrier gas flow rate of 200 L/min h, the single layer thickness of the formed cladding layer is 0.5mm.

In the above technical solution, in the step 4-2), when forming the primer layer at the groove on the gray cast iron cylinder head, a single-pass laser cladding process is adopted, and during cladding, it is necessary to adjust The robot controls the angle between the axis of the laser beam and the groove surface within the range of 70-90°; the angle between the axis of the laser beam and the axis of the powder spray gun ranges from 10° to 45°, and the lapping rate of the primer cladding layer is 45° %.

In the above technical solution, in step 4-3), when performing multi-layer accumulation profiling repair, the accumulation coefficient is 0.5mm, and the cladding layer overlaps every 4 layers, the continuous cladding length is less than 50mm, and the laser shutter Stop once; at the same time, quickly hammer the cladding layer with a small hammer to eliminate internal stress; then continue to open the cladding until the bevel is almost full, and always maintain the backward powder feeding method during the cladding process.

The advantages of the present invention are:

The invention has precise forming dimensions, requires only minor post-processing, and has less thermal influence on the substrate; and the three-dimensional forming repair part has excellent mechanical properties, can well suppress the whitening tendency of the bonding interface, and effectively prevents carbon diffusion.

Instructions attached

Fig. 1 is the flowchart of the automatic laser cladding remanufacturing method of the gray cast iron cylinder head of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

In one embodiment of the present invention, a crack was initiated at the "nose bridge" between the inlet and intake valves of a cylinder head. The material thickness of the nose bridge was 14mm (the distance from the surface to the water jacket), and the depth of the crack was unknown. The material of the cylinder head was HT250. Hereinafter, taking this embodiment as an example and referring to FIG. 1 , the remanufacturing process of the cylinder head using the laser cladding remanufacturing method of the present invention will be described.

Step 1. Prepare special materials for gray cast iron laser cladding repair.

In order to meet the performance requirements of laser cladding accumulation forming of gray iron castings and avoid the common defects of gray cast iron cladding, the materials used for laser cladding repair of gray cast iron should have the following physical and chemical properties:

(1) The strength is not lower than that of the matrix, the plasticity and toughness are high, and the crack resistance is outstanding.

(2) It can block the diffusion of C element, and the effect of inhibiting the whitening of the interface is remarkable.

(3) It has good self-deoxidation and slagging ability, excellent surface quality and no pores inside.

(4) It has good wettability with gray cast iron substrate and excellent laser cladding formability.

According to the above physical and chemical properties, in this embodiment, the repairing material used is Ni-Cu alloy powder. The mass fraction of elements contained in the alloy powder is shown in Table 1, and the particle size of the powder is -140 to +325 mesh.

Table 1

Among them, Bal represents a margin.

In other embodiments, other materials can also be used as the repair material, as long as these materials can meet the aforementioned physical and chemical properties.

Step 2. Perform non-destructive testing on the depth of the "nose crack" crack.

In this step, in order to more clearly show the eddy current detection signals when the crack depths are different, the eddy current method is used to detect cracks with different depths respectively. As the crack depth increases, the amplitude of the eddy current signal increases gradually, but its phase change is not obvious. In order to realize the evaluation of the depth of the "nose crack" of the cylinder head, a mathematical model between the crack depth and the amplitude of the eddy current signal is established in this step.

y＝8.9334·e ^0.402·x (1)

Where: y represents the amplitude of the eddy current signal; x represents the crack depth.

Therefore, when the crack depth is within the range of eddy current detection, the actual measured eddy current signal amplitude is substituted into formula (1), and the cylinder head “nose crack” depth data can be obtained preliminarily, which provides a basis for the repair of the cylinder head.

Step 3. Perform pretreatment on the "nose crack" part of the cylinder head before repairing.

According to the depth and direction of the "nose crack" crack in the cylinder head detected in step 2, firstly, a deep "V"-shaped groove is made on the crack to remove the crack. The bottom of the "V"-shaped groove is rounded, in order to ensure that the laser can Reachability, for a groove with a depth of 10mm, the included angle of the groove shall not be less than 80°. Then use an angle grinding wheel to grind around the groove until the fresh metal surface is exposed, and clean the groove and its surrounding surface with acetone solution.

Step 4. Perform profiling repair on the "nose crack" part of the gray cast iron cylinder head by laser cladding. This step can include:

Step 4-1. Do single-pass single-layer cladding on the "nose crack" part of the gray cast iron cylinder head.

The YAG laser is controlled by a fiber-optic transmission robot, and the Ni-Cu alloy powder prepared in step 1 is synchronously fed into the Ni-Cu alloy powder by means of pneumatic powder feeding. A large number of orthogonal experiments are carried out on the HT250 substrate to evaluate the single The forming quality of the single-layer cladding layer. Evaluation indicators include: surface quality of the cladding layer (whether it is bright and continuous, whether there are cracks, inclusions, size and number of pores), microstructure, performance test (microhardness, residual stress), and determine the best laser melting on the HT250 substrate. overlay process parameters. It was found that the method of lateral synchronous powder feeding, high-purity nitrogen protection, laser power of 800W, scanning speed of 150mm/min, powder feeding voltage of 11V, spot size of 3.5mm, and powder feeding carrier gas flow rate of 200L/h, melt The single layer thickness of the cladding layer is 0.5mm, and the cladding layer has no pores and crack defects. At the same time, the surface of the cladding layer is continuous and bright, and the forming quality is excellent.

Step 4-2, forming the base layer.

Three-dimensional profiling repair usually requires multi-layer cladding, and the primer layer is the most important layer. As a layer directly combined with the substrate, the bonding strength of the primer layer and the substrate directly determines the bonding quality and crack resistance of the cladding layer; the present invention is aimed at laser cladding of gray cast iron, using Ni-Cu alloy powder to prepare the primer layer , the purpose is to make the matrix only have a small penetration depth, and use the molten Ni-Cu alloy to block the C element in the matrix at the interface, that is, the semi-melted area at the bottom of the cladding layer, reducing or even eliminating the whitening trend at the interface .

Using the above-mentioned single-pass laser cladding process, the primer layer is prepared in advance along the groove surface. During cladding, in order to ensure that the energy density in the spot area is in a standard Gaussian distribution, it is necessary to adjust the robot to control the angle between the axis of the laser beam and the groove surface. In the range of 70-90°; the angle between the axis of the laser beam and the axis of the powder spray gun is 10-45°, and the lapping rate of the primer cladding layer is 45%, and the cladding layer has a relatively high flatness at this time.

Step 4-3, multi-layer accumulation profiling repair

On the basis of the bottom layer in step 4-2, pile up layer by layer along the V-shaped surface, the stacking coefficient is 0.5mm, every time the cladding layer is overlapped 4 times, the continuous cladding length is less than 50mm, and the laser shutter stops once, that is, the short section Forming and intermittent cladding methods, while quickly hammering the cladding layer with a small hammer to eliminate internal stress. Then continue to open the cladding until it will fill the groove, and always maintain the backward powder feeding method (the angle between the axis of the powder spray gun and the axis of the cladding layer is less than 90°) during the cladding process. On the one hand, this method has higher On the other hand, it can effectively prevent the collapse of the corner size of the accumulated cladding layer. In order to leave a post-processing allowance, the cladding accumulation size must be larger than the original size of the "nose bridge" in all directions; in order to ensure a good interface between the cladding layer and the substrate, the cladding layer must span the distance between the cladding layer and the groove during surface cladding. The contact interface is 1~3mm deep into the surface of the cylinder head.

Step 5. Relieve the stress on the repaired part.

In order to further eliminate the internal residual stress of the deposited cladding layer, after the overall accumulation is completed, heat the repaired part and the surrounding area with a gasoline blowtorch to 200-400°C, keep it warm for about 1 hour, and cover the surface with asbestos, thereby inhibiting the delayed cracking tendency of the cladding layer .

The above is the implementation process of the laser cladding remanufacturing method of the present invention. For gray cast iron parts, the technical means of laser cladding adopted in the method of the present invention can produce a small penetration depth of the substrate, which has a very low dilution effect on the cladding layer, thereby reducing the diffusion of C elements , to prevent the formation of white mouth structure, and at the same time cooperate with the immiscibility of Ni, Cu alloys and C, block the C element at the bonding interface, and further inhibit the white mouth tendency. At the same time, the heat of laser cladding is concentrated and has little effect on the heat of the substrate. Under low power density, slow scanning forming, combined with external hammering and slow cooling measures, can effectively reduce the residual stress of the cladding layer and achieve thick forming. The purpose of cladding is to control cracking.

Claims (6)

1. An automatic laser cladding remanufacturing method of a gray cast iron cylinder cover comprises the following steps:

step 1), preparing a gray cast iron laser cladding repair material; wherein,

the gray cast iron laser cladding repair material has the following physical and chemical properties: the strength is not lower than that of the matrix, the plasticity and the toughness are high, and the anti-cracking performance is outstanding; can block the diffusion of carbon element and has obvious effect of inhibiting interface white mouth; the alloy has good self-deoxidation and slagging capabilities, excellent surface appearance quality and no air holes inside; the material has good wettability with a gray cast iron matrix, and the laser cladding formability is excellent;

step 2), carrying out nondestructive testing on the depth of the nose crack on the gray cast iron cylinder cover;

step 3), preprocessing a nose crack part on the gray cast iron cylinder cover before repairing, removing cracks on the nose crack part according to the crack depth detection result obtained in the step 2) in the preprocessing to form a groove, then polishing the periphery of the groove by using an angle grinding wheel until a fresh metal surface is exposed, and cleaning the groove and the peripheral surface thereof by using an acetone solution;

step 4), carrying out profiling repair on a nose crack part on the gray cast iron cylinder cover through laser cladding; the method comprises the following steps:

step 4-1), performing single-pass single-layer cladding on the slope on the gray cast iron cylinder cover;

step 4-2), forming a priming layer at the groove on the gray cast iron cylinder cover;

step 4-3), performing multilayer accumulation profiling repair on the basis of the base coat generated in the step 4-2);

and 5) removing stress on the repaired part.

2. The automatic laser cladding remanufacturing method of a gray cast iron cylinder head as claimed in claim 1, wherein in the step 1), the gray cast iron laser cladding repair material is Ni-Cu-based alloy powder including C element with a mass fraction of 0.01 to 0.05%, Si element with a mass fraction of 2.0 to 4.0%, B element with a mass fraction of 1.0 to 3.0%, Fe element with a mass fraction of 0.1 to 1.0%, Cu element with a mass fraction of 10 to 40%, and Ni element with a mass fraction of Bal.

3. The automatic laser cladding remanufacturing method of a gray cast iron cylinder cover according to claim 1, wherein in the step 3), the groove is a V-shaped groove, the bottom of the V-shaped groove is a round angle, and the included angle of the groove is not lower than 80 degrees for a groove with a depth of 10 mm.

4. The automatic laser cladding remanufacturing method of a gray cast iron cylinder head as claimed in claim 1, wherein in the step 4-1), said performing single layer cladding at the groove of the gray cast iron cylinder head comprises: when single-channel single-layer cladding is carried out, a lateral synchronous powder feeding mode is adopted, high-purity nitrogen protection is carried out, the laser power is 800W, the scanning speed is 150mm/min, the powder feeding voltage is 11V, the spot size is 3.5mm, the powder feeding carrier gas flow is 200L/h, and the single-layer thickness of the formed cladding layer is 0.5 mm.

5. The automatic laser cladding remanufacturing method of the gray cast iron cylinder cover according to claim 1, wherein in the step 4-2), when a priming layer is formed at the groove on the gray cast iron cylinder cover, a single-pass laser cladding process is adopted, and during cladding, a robot needs to be adjusted to control an included angle between the axis of a laser beam and the surface of the groove to be within a range of 70-90 degrees; the included angle between the laser beam axis and the powder spray gun axis ranges from 10 degrees to 45 degrees, and the lap joint rate of the priming cladding layer is 45 percent.

6. The automatic laser cladding remanufacturing method of a gray cast iron cylinder cover according to claim 1, wherein in the step 4-3), when multilayer stacking profiling repair is performed, the stacking coefficient is 0.5mm, the continuous cladding length is less than 50mm after every 4 overlapping passes of the cladding layer, and the laser shutter is stopped once; meanwhile, the cladding layer is rapidly hammered by a small hammer to eliminate internal stress; and then continuing to perform laser cladding until the groove part is fully piled up, and always keeping a backward powder feeding mode in the cladding process.

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