Choose the right graphite grade for the hottest ho

2022-08-14
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Horn mold: choose the right graphite grade

for mold manufacturers, horn mold may be a problem. This is because the structure is dense, and a very good surface finish is required, so that the plastic parts can be demoulded smoothly during injection molding. Usually, due to thousands of small holes, joint parts and small stiffeners, the mold cannot be polished. As a result, the required surface finish must be completed by electrical machining. If the typical 4u-6u Rmax surface processing is required, it can ensure that the plastic parts will not stick to the mold during demoulding. In order to finish such fine surface processing in EDM, graphite with uniform microstructure and small particle size must be used as electrode. Because the mold cavity is the mirror image of the electrode, and the final plastic part is the mirror image of the cavity, in order to obtain the best plastic part, it is very necessary to choose the best graphite

the horn mold has thousands of holes and small ribs, so the process requirements are very high. From electrode making to die EDM, high-strength and fine granular graphite is required. The particle size of graphite has made important breakthroughs in the high-performance and environmental protection of products, with an average of microns. There are many grades of graphite, so choosing the right graphite first needs to understand the physical properties of graphite and the impact of these physical properties on the EDM process and the fabrication of graphite electrodes

choose the correct graphite grade

small fine cavities that cannot be polished by hand need to rely on electrical processing to complete the required surface finish, so the selection of graphite grade must meet the above requirements. In general, superfine graphite is competent. It is necessary to understand the physical properties of graphite when selecting appropriate graphite

properties and characteristics of graphite

the classification of graphite is based on particle size. The average particle size of ultrafine graphite is less than 5 microns. In ultra-fine grade graphite, there are also great differences in physical properties and microstructure. Generally, only graphite with high strength, small particle size and uniform microstructure can achieve a mold with high dimensional accuracy and clear fine parts, and plastic parts with high surface quality can be injected

uniform microstructure

in the process of electrode manufacturing or electrical processing, in terms of the various properties of graphite, that is, the need for more 1-BODY machines, the most important is the uniform microstructure - the uniform distribution of pores and particles. The high-quality graphite has a uniform microstructure, and the structure of each graphite is consistent, and has remained the same over the years. Graphite with irregular internal evacuation and agglomeration has unexpected properties. Predictable results are necessary, especially for molds that require longer manufacturing time and cost, such as molds that require high dimensional and tolerance requirements or require electrical machining surface processing (rather than chemical or manual polishing)

hardness and strength

there are two important factors for electrode fabrication: Shore hardness range () and bending strength (>13000 psi)

materials in the above hardness range can make good and neat edges on the top of thousands of holes. For materials with shore hardness greater than 80, the feed and speed of machining should be lower. The hardness of small particle graphite material is too large, and it often cracks at the edge during machining, which is not conducive to the production of electrodes. It has large friction with the tool and is easy to wear the tool, which will affect the consistency of the hole diameter. The high wear rate and chipping angle of cutting tools will increase the processing cost. Too soft graphite will also cause problems. They will stick to the chip removal slot of the tool, slow down the machining speed, or cause dust to plug the hole, and then compress the hole wall to produce a scratch

if the bending strength of graphite material is greater than 13000psi, the material can avoid fracture when processed into ultra-fine and ultra deep rib electrode. Because these electrodes require meticulous technology to build an exchange and cooperation platform for sharing information, resources and achievements, it takes a long time to make the electrodes, and from the perspective of cost, the less the number of electrodes, the more cost-effective

ultra fine grade graphite electrode and plastic parts used in horn mold finished products

electrode

electrode loss in the electrical processing process can not be ignored, because high loss means that the electrode needs to be repaired frequently to complete fine parts. In addition, particles falling off the electrode into the final gap of the discharge will cause spots in the cavity and prolong the EDM time. Excessive electrode debris falling into the discharge gap will cause the machine tool to adaptively control the tool lifting and increase the gap between the electrode and the mold, or increase the tool lifting frequency to clean up large particles in the discharge gap. In this application, since the oil cannot be flushed, the debris should be minimized

during the discharge process, the molten metal is blasted out, which will lose the edge of the electrode. Graphite with low strength and loose microstructure cannot resist this impact, and large particles also continue to fall into the gap. Graphite with uniform microstructure and small particle size can reduce this loss. Therefore, electrode loss is also necessary to produce a cavity with accurate tolerance

electrode trace machining can help flush oil, clean up the discharge gap and improve the surface processing quality. The graphite material is required to have high strength when the rib electrode is processed in the trace, so that the rib material can be prevented from breaking during the electrode trace processing; This will also affect the quality of surface processing, especially inside the holes and ribs, and then affect the demoulding of plastic parts

using high-quality graphite materials for fine parts and surface processing of the cavity can make the plastic parts smoothly separate from the mold, thereby improving productivity and profits

enlarged view of high-quality graphite electrode

new grade graphite improves processing results

with the addition of ultra-fine graphite grade to new materials, EDM personnel found that the results were improved. What is worth mentioning here is a special graphite grade, edm-4, which has the following advantages:

◆ the average particle size is less than 4 microns, which can be engaged in fine surface processing with low loss

◆ the bending strength is increased to more than 15000 psi, which is conducive to the processing of ribs

◆ the ideal hardness range for electrode fabrication can be easily completed

these properties are very important for fine machining of electrodes. At the same time, in order to maintain a good metal cutting rate, it is also important to maintain these properties of the electrode

using graphite with these physical properties can reduce electrode loss (up to 10%) and improve surface finish (up to 5%). This grade of graphite with bending strength increased by 15% is also the best choice for making fine ribbed electrodes

results: for the application fields with high requirements, such as horn mold, it is very important to understand the influence of the physical properties of different grades on the processing cavity when selecting the graphite grade. Choosing the best graphite can produce high-quality cavities. The surface processing of the cavity is the mirror image of the electrode microstructure, so it is important to choose the best grade. When the cavity is completed and the first plastic part is produced, the sticking problem caused by the uneven cavity means that the cavity needs to be reworked or adjusted. Although the cost of selecting high-quality graphite is high, the value brought by the performance of high-grade graphite in the process of manufacturing and electrical processing is more valuable

do you know the graphite you use

the selection of graphite is very important for the completion of each work. It is necessary to understand the characteristics and physical properties of graphite of different brands and grades. According to different grades, it can be roughly divided into four kinds. Only in these four kinds can you achieve the desired effect. You need to be careful when choosing graphite. You need to know its origin and characteristics. Graphite of the same brand may also change over time, and may cause unpredictable consequences

using high-quality graphite can really reduce production costs. In fact, graphite electrode only accounts for a small part of the whole mold production cost. Because of its high wear resistance, the best graphite can be processed into a satisfactory cavity with fewer electrodes. Low loss also means that less graphite debris will be produced in the gap during continuous discharge. In addition, high-quality graphite is more active and effective in EDM than ordinary graphite with rough microstructure. At the same time, the accuracy of the cavity is also improved. In the continuous use of one graphite electrode to another, we can foresee the process of finishing. (end)

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