The electroplated diamond wire is mainly used for the opening and slicing of photovoltaic grade silicon wafers. It belongs to diamond sawing products and is also an electroplated diamond tool. Similar sawing tools as the diamond wire are diamond wire saws and diamond wire saws. For example, the diamond wire saw is also coated with diamond abrasive grains on the surface of the steel wire. It is generally used for manual reciprocating drawing of the inner hole surface of jade, agate and crystal crafts. It can also be used for reciprocating motion on a table saw machine for curves, It can be cut straight, and it can be wound around two winches like a diamond wire saw, and it can be used for cutting work after being tensioned.
From the above description, do you feel that they are very similar? Therefore, Müller and Sanchao, like many companies that make diamond saw blades, are members of the Superhard Materials Branch of the China Machine Tool Industry Association.
Due to the outbreak of the polysilicon wire cutting market, the diamond wire is extremely hot this year. It is expected that this situation will continue for some time, so many steel wire, silicon carbide, diamond, and photovoltaic companies have entered this field, and they want to share a piece of it. In order to let everyone better understand the diamond wire, this paper analyzes the structural characteristics and performance of the diamond wire from the perspective of electroplated diamond tools.
1. Characteristics of electroplated diamond tools
Since the diamond wire belongs to the electroplated diamond tool, we will first understand the structure and characteristics of the electroplated diamond tool. Figure 1 shows the structure of an electroplated diamond tool. It can be seen that its structure consists of three parts: a substrate, a plating layer (mostly electroplated nickel), and an abrasive. Among them, the abrasive is dispersed in the metal plating layer to form a working layer together to perform grinding; the substrate has a certain geometric shape, dimensional precision and surface roughness, and functions as a supporting plating layer.
The electroplated diamond tool has the following features:
- Structural features
The electroplated diamond tool has only two parts, the steel substrate and the electroplating working layer. The deposited metal thickness of the electroplated layer is generally 1/2~2/3 of the diamond particle size, which is very thin compared with the sintered diamond tool (except the brazing tool).
Due to the particularity of the electrodeposition process, various complex profiles or particularly small, particularly thin diamond tools can be produced by electroplating methods, and the manufactured tools are particularly accurate.
2) Plating characteristics
The electroplated metal of the electroplated diamond tool is formed by electrocrystallization. Under the condition of electroplating pretreatment and proper process control, the plating layer is very dense and has almost no pores. Therefore, the electroplated diamond tool is the most compact one of all the abrasive tools (the brazed diamond tool is also extremely dense), and the coating has the most complete contact with the diamond particles and the holding force is particularly large. It is precisely because the coating is dense and the diamond is firmly bonded, it can be used at a high concentration (the concentration of the embedded diamond in the embedded coating can be as high as 200%) without causing premature detachment of the abrasive grains, which is other methods (except for brazing). The diamond tools manufactured are incomparable.
Since electroplated diamond tools mostly use nickel or nickel-cobalt alloy as a bonding agent and dense structure, the hardness of the coating is very high, even reaching HRC40, which is significantly higher than other types of diamond tools. Therefore, the electroplated diamond tool is from a single layer perspective. Particularly wear resistant (second only to brazed diamond tools).
The diamond embedded in the coating can be randomly distributed by sand embedding method and obtain high concentration, or can be arranged in an orderly manner and artificially control the concentration of diamond. For the latter, the effect of diamond can be better utilized and chip removal can be improved, and grinding can be improved. effect.
3) Use characteristics
Due to the high abrasive concentration of the electroplated diamond tool, the processing efficiency is significantly higher than other tools at the same grinding speed; due to the large number of particles, the single abrasive load is small and the wear is small, so for the same thickness of the working layer The electroplating tool has a particularly high wear resistance; because of the wear resistance, the shape retainability of the electroplating tool is good, and the processing precision is naturally high; the single layer electroplating tool has a high cutting edge height, so the cutting is sharp, the chip removal is easy, and the friction is small. Less fever.
In summary, the single-layer electroplated diamond tool is characterized by high processing efficiency, high grinding ratio, good shape and precision retention, and high processing precision. But because it is a single layer, the total life is relatively low. There are also multi-layer electroplated diamond tools, but due to the compactness of the electroplating structure, high hardness and high toughness, the self-sharpness of the first layer of diamond after use is poor, and it needs to be improved by increasing the grinding force and increasing the flow rate of the coolant.
The manufacturing process of the electroplated diamond tool is a low-temperature electrodeposition process, which does not adversely affect the diamond, so there is no degradation in the quality of the diamond during use, which is very advantageous for the grinding process.
2, the characteristics of electroplating diamond wire
Comparing the characteristics of electroplated diamond tools, we one by one:
- Structural features
Figure 2 is the structure of an electroplated diamond wire. Consistent with the electroplated diamond tool: the steel wire is the base body and functions to support the plating layer; the diamond is dispersed in the electroplated layer and forms a working layer together with the electroplated layer to perform the grinding action. The thickness of the deposited metal of the plating layer is generally 1/2~2/3 of the diamond grain size, that is, the height of the diamond blade is generally 1/3~1/2 of the diamond grain size.
The steel wire serves to support the coating, so the steel wire must satisfy: a. have sufficient mechanical properties; b. have good affinity with the coating.
Sufficient mechanical properties, that is to say, the tensile strength, yield strength, rigidity (ring diameter) and torsional strength of the steel wire meet the predetermined requirements. The steel wire itself has poor performance. Even if the working layer is good, once the wire breakage is not acceptable, it will seriously affect the performance.
The affinity of the coating, that is to say the interface between the coating and the steel wire is stronger. In order to strengthen the bonding force between the steel base and the diamond sintered joint, the diamond saw blade will increase the transition layer if necessary, and sometimes the steel base is rounded or sandblasted. For the diamond wire, the busbar surface activation treatment is to increase the affinity between the wire and the coating and improve the bonding with the coating. How to evaluate the bonding strength of the coating is also a consideration for the company. The change in the tensile and torsional strength test results between the bare wire and the wire saw finished product, usually the intensity value becomes larger. The magnitude of the change reflects the bonding strength of the diamond wire coating to a certain extent. The greater the increase, the higher the bonding strength of the coating. At present, the winding method is mostly used to check the bonding strength by microscopic observation of the microscope. This method is inconvenient to quantify the calibration, and the test method of the intensity variation may be used as a reference method for detecting the bonding strength of the coating.
2) Plating characteristics
The performance advantages of the electroplating tool, such as high wear resistance, good shape retention, and high cutting precision, benefit from the compactness of the coating and the holding property of the abrasive. For the diamond wire products, we do not want diamonds to fall off during the cutting operation, so the coating is required to be dense and the diamond is firmly held.
The coating is dense, and the corresponding surface of the coating should be small and not too rough, which can be reflected by the “number of height distribution of the blade”. Figure 3 is the distribution of the height of the blade height of the two diamond wire products. The height of the blade edge in Figure 3-a is 1-2μm, the number of 2-3μm (green bar graph) is significantly more than that of Figure 3-b, which reflects Figure 3 -a’s diamond wire coating has a small number of small particles on the surface, and the plating density is poor.
The coating is firmly held by the diamond, and the wettability of the coating and the diamond is required. Therefore, the diamond diamond powder is mostly used for the diamond wire, and the wettability with the nickel plating layer is increased. The plating thickness, plating surface roughness and other indicators are related to the wire saw production process (especially the sanding process), the matching of the micro-powder plating activity and the sanding process, which is an important factor in determining the quality of the plating sand.
The diamond concentration of the coating, which is often referred to as the diamond edge rate, directly affects the cutting efficiency and is also a key indicator affecting the quality of the diamond wire. In general, the plating method has a strong grip on diamonds. Even if the diamond wire reaches the end of its life, it should not have threshing. This is also a prerequisite for the high yield of the electroplated diamond wire. For example, the “high-efficiency line” launched by Mei Chang has an edge-cutting rate of nearly 600 grains/mm, which is based on the premise that the coating is firmly held and the abrasive grains are evenly dispersed.
Diamond concentration, or edge rate, the current diamond fiber products vary greatly, from less than 100 grains / mm, to more than 500 grains / mm, due to the lack of testing equipment (more use of electron mirror points) and experience The ratio of the rate to the cutting parameters) is not very important for this indicator, and it is difficult to produce a series of products with different blade rates under the current situation that the technology of the diamond line production is immature and unstable, but we must understand This is an inevitable trend! Everyone still has to temper their internal strength and do more research!
The height of the blade of the electroplated diamond tool is generally 1/3 to 1/2 of the diamond particle size, and the height of the blade is large, which is one of the reasons for the sharpness and high efficiency of the electroplated product. The current Jinang line products, some companies’ processes are not too mature, the blade height is often not enough, that is, there are too many buried, or there are some virtual high abrasive grains or agglomerated nickel tumors on the surface of the coating, which needs to be edged. If the process is mature and reliable, the height of the blade can be guaranteed, of course, it can not be edged.
3) Use characteristics
As a diamond sawing tool, the diamond wire has the same characteristics of sawing tools, and because its base is steel wire, it has certain deflection and unique characteristics.
The parameters that characterize the cutting effect are: cutting efficiency, wire saw durability, slit size, and cutting defects. Cutting efficiency refers to the time of single cutting; wire saw durability refers to the length of the line used for single cutting; cutting defects are mainly wired bow ratio, TTV, line marks, knife lines and so on.
From the above analysis of the characteristics of the diamond wire coating, it can be seen that the main factors affecting the diamond cutting effect are: coating density, coating strength, blade height, edge yield, diamond dispersion uniformity (stack diameter), envelope diameter . For the users of the diamond line, it is necessary to be able to scientifically and reasonably match the cutting process parameters according to the characteristics of the diamond wire, so that the diamond wire can be used as much as possible to truly “use” and “use”.
For example, the diamond wire with high edge yield, good plating strength and small stacking diameter (ie, uniform diamond dispersion) can high wire speed and large feed rate; diamond wire with low edge rate and good plating strength can also be used faster. The speed of the line, but the amount of feed should be appropriate. In addition, combined with the power, overall rigidity, accuracy, etc. of the cutting machine, even if it is a “high-efficiency line”, if the power of the cutting machine is low, it will be “small horse-drawn cart” and cannot be used as “all things”.
Above, we simply analyzed some characteristics of the electroplated diamond wire from the perspective of the electroplated diamond tool, which helps everyone understand the diamond wire product and helps optimize the use of the diamond wire. Since it is too shallow to learn, it is inevitably wrong. I welcome everyone to give more comments and exchanges.