CuCr alloy material machinery manufacturing process and application

CuCr alloy material machinery manufacturing process and application

2022-05-24 13:35:37 5

In the vacuum copper-chromium contact materials, CuCr25, CuCr50 (mainly used in China) is often used in vacuum circuit breakers, the CuCr material components due to the existence of a pseudo-alloy form, maintaining the excellent performance of Cu, Cr each. CuCr contact material is also more and more widely used, but its manufacturing process requirements are becoming more and more delicate and strict.


1. Problems with the original process

In the vacuum CuCr contact material, the molding method mainly includes: solid phase sintering method, arc melting method, vacuum solution casting method and vacuum melt infiltration method, etc. The copper-chromium contacts are mainly formed into rough billets according to the customer's demand by choosing the above suitable forming methods, and then finished products are obtained after machining, such as turning, milling, clamping and other processes.


As shown in Figure 1, the contact requires a clean surface, no oxidation, oil, handprints and rust spots and other knife marks, while the workpiece should ensure that the parts are free of deformation, falling blocks, air holes, sand eyes and inclusions, etc. However, in the actual manufacturing process of CuCr contacts, the surface of the workpiece often shows oil, falling blocks and yellow spots, and the tool wear is serious and the service life is short, resulting in a rough surface of the machined parts, which does not meet the technical requirements of the drawing .


At present, CuCr contacts are mainly divided into two categories according to their shapes: slotted contacts and non-slotted contacts.


As shown in Figure 2, CuCr25 uses solid phase sintering method to obtain rough billets, and after the contact is turned and processed, it needs to be completed by milling and slotting processes. In order to improve the efficiency, now often use the wet cutting method, the process is now: ingredients → press molding → vacuum sintering → re-pressing → fine turning (outside diameter, end face processing amount of 1mm, 0.5mm) → slotting → clamping (deburring, polishing, cleaning, drying) → testing → packaging (plastic bag vacuum packaging) → shipping.


 

As shown in Figure 3, CuCr45 is a non-slotted contact. Among them, the finishing turning process must be dry cutting (after improvement), and the blank material adopts the arc melting method (using imported equipment from Germany). The manufacturing process: forming (arc melting) → rough turning → sawing → heat treatment → rough turning (outer diameter and end face leave 1mm and 0.5mm respectively) → finishing → testing → packaging (plastic bag vacuum packing) → shipping.


The above two types of contacts site conditions are as follows.

The first type of slotted contacts using wet cutting method, high processing efficiency, tool selection is now selected for processing Al, Cu, Ti alloy type inserts (all improved); a blade (2 tips) can be processed 350 pieces, but the surface has a watermark, oil, surface unclean phenomenon is prominent, placed in the air easy to appear yellow spot phenomenon, such as the use of dry cutting, tool tip sticky copper phenomenon is serious, the workpiece surface rough, blade Short service life, and the subsequent milling process must also use cutting fluid processing, the same will have a watermark oil, surface unclean phenomenon.


The second type of non-slotted contacts, processing using dry cutting, tool life is short, an insert (2 tips) only 100 to 120 pieces of processing, and then continue processing, contact plate work surface roughness, tool tip sticky copper phenomenon is serious; and the use of cutting fluid processing, inspection contact plate work surface, surface roughness is better, but the surface can not meet the surface roughness standards, using the SITA cleanliness tester test, the surface roughness of the workpiece. Qualification standards require RFU value ≤ 12, the actual measurement of any sampling 5, the average value of 43.7, after the process of ultrasonic cleaning, the contact surface still can not reach the surface roughness test requirements.


2. Analysis of the problem

For CuCr contact material manufacturing process to appear above phenomenon, the first type of CuCr25 material analysis. cuCr material its group elements Cu, Cr mainly in the form of pseudo-alloy, such as Cu, Cr alloy phase, at 1 076 ℃, Cu in Cr solubility of 1.28%, while Cr in Cu solubility of 0.7%, at 600 ℃, then Cr is almost insoluble in Cu At 600°C, Cr is almost insoluble in Cu and Cu is insoluble in Cr, so that two combined pseudo-alloy mixtures are actually formed.


At the same time, the corresponding contacts were tested for hardness, CuCr25 hardness HB70-100 (CuCr30, CuCr40, CuCr50 hardness of HB75-100, 78-120, 80-120, respectively). According to the contact material soft with hard pseudo-alloy characteristics, the processing of the selected tool blade must have sharp but also need to ensure wear resistance of these two characteristics, that is, processing Cu to ensure that the blade sharp to avoid turning tool tip stick Cu, but Cr and will increase the tip wear.


The operator is required to wear rubber gloves when machining CuCr contacts, so as to avoid the appearance of handprints on the contact surface. The use of cutting fluid processing, improve the efficiency, but the workpiece contact surface oil is also generated, therefore, after the turning and milling process, by the clamping process to remove burrs, polishing contact surface, and then through ultrasonic cleaning, drying to obtain a clean surface.


For non-slotted contacts, using the wet cutting method, the contact surface is smooth and the roughness is up to standard, but the surface must be polished, ultrasonic cleaning, drying and other processes to achieve the contact surface roughness requirements, increasing the process and cost; while using the dry cutting method, as long as the tool blade selection and matching is reasonable, through reasonable processing parameters (F, S, ap) to adjust, the site directly processed to achieve the contact After processing, timely inspection and packaging operations are carried out, and the processes are closely connected to minimize the exposure of CuCr contacts to air storage time, so as to avoid oxidation of the workpiece resulting in yellow spots.


Also on the CuCr contact raw material chrome powder tracking, as shown in the attached table, found that both domestic or imported from Germany, there are still yellow spots appear, because there are a small amount of chrome powder impurities such as iron, iron rust and easy to oxidize metal and other impurities is the main cause of yellow spots; on the other hand, also related to the humid environment, wet weather to speed up the oxidation of iron metal and other impurities; there is another situation, in the dry cutting process, the Turning process leads to contact heat, this heat will lead to slow oxidation of the contact, which requires strict implementation of the manufacturing process requirements, such as in the car cutting processing parameters, reasonable match the amount of tool eating (ap), feed rate (F), spindle speed (S), to avoid processing to produce huge heat; in the manufacturing process, occasionally found that the surface of the contact disc has a black spot phenomenon, but at present there are many reasons for the black spot in Explanations, some believe that the Cr powder particle size and composition, the less Cr powder particle size and composition, the less chance of black spots, here, this paper does not analyze one by one, the specific causes of black spots need to be further explored!


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