Except liquid-phase sintering, infiltration and direct sintering, there are some new technologies of tungsten copper come out recently, which make the structure and micro-structure of tungsten copper electrode more stable.

4. Fiber Reinforcement

Fiber reinforcement replaces directional refractory metal grain (tungsten powder) with directional fiber to mix with copper powder or cold pressing. After sintering, it has excellent transverse mechanical properties, thermal conductivity, electric conductivity and good erosion resistance.

5. Electric arc melting

It uses tungsten copper (by Powder Metallurgy, PM) as soluble electrode, and melting in consumable electro-arc furnace in vacuum or at inert atmosphere. After rapid solidification, aging and solution treatment, it can get tungsten copper composite material, which has fine grain, high density and good anti-ablation.

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Except liquid-phase sintering, infiltration and direct sintering, there are some new technologies of tungsten copper come out recently, which make the structure and micro-structure of tungsten copper electrode more stable.

3. FGM (Functional Gradient Material)

W-Cu composite material is kind of new material that tungsten copper composite layer is between Cu and W. It can apparently relax the heat stress by mismatch between tungsten and copper properties. There are two techniques for FGM, one is that discontinuous gradient layer, such as traditional powder piling, which has faults among each layer, the other is that continuous gradient layer, such as slip casting, settle casting, centrifugal casting, which takes advantage of natural transfer to forming continuous contents.

To some extent, FGM sintering is similar to traditional PM (Powder Metallurgy) process, which can be specifically divided into solid-phase sintering, liquid-phase sintering and dipping sintering. In addition, some processes adopt non-sintering method, such as plasma coating, laser-cladding, electrophoresis deposition and centrifugal casting.

More information about tungsten copper electrode technologies, click here:

http://news.chinatungsten.com/en/tungsten-information/80086-ti-10266 
http://news.chinatungsten.com/en/tungsten-information/80123-ti-10291

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Except liquid-phase sintering, infiltration and direct sintering, there are some new technologies of tungsten copper come out recently, which make the structure and micro-structure of tungsten copper more stable.

2. In-situ reactions

Tungsten copper electrode always adopts passive pressure infiltration casting, but it has an unavoidable disadvantage that tungsten skeleton will be oxidized, which decreases the associativity of matrix and the properties of product. In the process of in-situ reactions, enhanced phase is forming in metal liquid and do not expose in the air so that it is isolated from outside and the properties will be improved. The process is that mix tungsten and copper powder (WO3 and CuO), and sinter in the air after forming (CuWO₄), then reduce in H₂. Finally, put the blank into copper solution. The relative density of tungsten copper composite material can reach 99% in such this way.

More information about tungsten copper electrode technologies, click here:

http://news.chinatungsten.com/en/tungsten-information/80086-ti-10266

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In part 7 we know that the micro drilling by a tungsten carbide micro drill can also be applied to integrated circuits with finer quality compared to lithography and electroplating technology. Here we talk about the major disadvantage of the micro drills.

Micro drilling has one major disadvantage because of the tungsten carbide micro drill geometry. Because of the drill point, a flat-bottomed hole can not be produced. If one is attempting to produce cylindrical cavities in a micro mold, there must be a relatively thick plating base under the mold material, or the structural substrate of the mold could act as the plating base. To fully develop the diameter of the hole, projected onto a plane perpendicular to the drilling direction, requires the drill point to extend 30% of the drill diameter beyond the depth of the fully developed hole. For holes in the 100 micrometer region, requires a thick plating base to be deposited. One method for creating flat-bottomed blind holes is to use an end milling tool instead of a drill. The disadvantage to this procedure is that drills have a typical L/D ratio of 4 to 14 while end mills typicall have a ratio of only 1.5 to 3.

 (The end. This article is divided into several parts and this is part 8, for part 7 please refer to http://news.chinatungsten.com/en/tungsten-information/80115-ti-10285)

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In part 6 we know that the micro drilling speeds and feeds are varied according to materials, but not in high speed in order to avoid the tungsten carbide micro drill staying in the hole bottom. Here we talk about the applicability of micro drilling in integrated circuit industry as a complementary process to lithography and electroplating.

The applicability of micro drilling as a complementary process with features produced by lithography and electroplating has been investigated. A cross section of a copper micro gear made by lithography is shown. The average roughness of the hub wall is 0.4 micrometers. A micro drilled hole in the same material gave a roughness of 0.15 micrometers over a much longer bore length. Micro drilling can also be used to augment lithography for mesoscopic (millimeter and larger) sized components. Often parallelism of deep holes is of concern. To determine typical values for parallelism of micro drilled holes, glass fibers were inserted into a number of holes drilled with a very slow starting sequence. This is necessary to ensure the tungsten carbide micro drill does not walk on the surface of the part and that the hole axis aligns with the un-deflected axis of rotation of the drill. Holes with a length-to-diameter ratio of 8 were drilled at 4000 rpm. The three-dimensional misalignment of the inserted fibers was measured to be 0.08 degrees (1.5 milliradians), which included skewing of the fiber in the hole due to oversize of the hole which was estimated to be 0.5 micrometers.

(To be continued. This article is divided into several parts and this is part 7, for part 6 please refer to http://news.chinatungsten.com/en/tungsten-information/80077-ti-10281; for part 8 please refer to  http://news.chinatungsten.com/en/tungsten-information/80116-ti-10290)

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Except liquid-phase sintering, infiltration and direct sintering, there are some new technologies of tungsten copper come out recently, which make the structure and micro-structure of tungsten copper more stable.

1. Rapid directional solidification

Based on good thermal and electric conductivity, rapid solidification remarkably improves the strength and erosion resistance of tungsten copper electrode at high temperature. However, the cooling rate of rapid solidification is still lower so that solidification structure has sufficient time to grow up and coarsening, which may cause severe support segregation and decrease the properties of tungsten copper.

Given concern such situation, it need to improve the cooling rate by increasing the gradient temperature of the solid-liquid interface in the process of solidification. There are many kinds of rapid directional solidifications, such as SDS (Supercooling Directional Solidification), laser rapid directional solidification with ultra-high temperature gradient and electromagnetic shaping directional solidification.

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The general process of powder direct sintering is that: W powder, Cu powder mixed + forming additives → forming →degreasing → sintering → after-processing. Therefore, researchers start their study with ultra-fine powder manufacturing, molding process and sintering process.

2. Forming

At the present, the most popular forming process is compression molding, and the research of MIM (Metal Injection Molding) is boosting gradually. Relative researchers study the process of W-30Cu nano composite material. Using direct sintering, we can get relative density high than 96% of tungsten copper electrode.

3. Sintering

The granularity of nano tungsten copper W-Cu composite powder is small and it is active so that the grain will grow up easily during the sintering process. The traditional liquid=phase sintering will exacerbate grain rearrangement, gathering, combination and growth, which has an effect on the properties of sintering material directly.

It is similar to the method of suppression of WC grain, there are two methods for controlling the growth of grain, one is that adding inhibitors, the other is improving the sintering technology. The enhanced sintering technology includes that HIP (Hot Isostatic Pressing), microwave sintering, extra-high voltage sintering, electromagnetic field sintering, plasma spark sintering, impact sintering and so on.

More information about tungsten copper electrode powder direct sintering, click here:

http://news.chinatungsten.com/en/tungsten-information/79974-ti-10240 
http://news.chinatungsten.com/en/tungsten-information/80018-ti-10242

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In part 5 we know that the usage of fluid helps clear the chips and reduce drilling thrust force on the tungsten carbide drill and the chips affect in different ways for different hardness of materials. Here we explain the speeds and feeds of micro drilling process.

The recommended speeds and feeds for micro drilling are as varied as the materials which can be drilled. Micro drilling is not generally a high speed process since dwelling of the tungsten carbide micro drill at the bottom of the hole can cause hardening of the work piece leading to increased drilling forces. For most metals, typical spindle speeds are in the 2000 to 4000 rpm range and feeds are in the range of one micrometer per revolution, or so. Care must be taken when drilling plastics to avoid melting of the material which can lead to adhesion of the plastic to the tungsten carbide micro drill. This can cause drill breakage or poor sidewall smoothness.

(To be continued. This article is divided into several parts and this is part 6, for part 5 please refer to http://news.chinatungsten.com/en/tungsten-information/80076-ti-10280)

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In part 4 we know that the micro drilling process is a series of precisely linked connection and motion of the tungsten carbide micro drill, mandrel, pulley, drive belt, and external motor, etc. Here we talk about the usage of fluid and removal way of a drill from the hole in a peck cycle to reduce chips affection on hole quality.

Tungsten carbide micro drills must be used in a peck cycle wherein the drill is repeatedly withdrawn and reinserted into the hole being drilled. This is necessary to help clear chips from within the hole. A thin cutting fluid is also recommended to aid in chip clearing. The fluid should be moving, as in an air-oil mist rather than stagnant. Stagnant fluid will allow chips to reenter the hole along with the drill. The effect of not using a fluid is clearly shown. The hole has more, large chips, on the order of 5 micrometers in size, and the drilling thrust force under such a condition is typically higher than if the chips are cleared from the hole. With no fluid to help clear chips, two hole is packed with chip debris and the axial force on the drill is typically several times (2-3) higher than with fluid.

In very soft materials, complete removal of the tungsten carbide micro drill from the hole each peck cycle can cause a slight taper near the hole entrance. This can be avoided by incomplete removal of the drill. For softer materials, chip removal is not as severe a problem since the machining forces for such materials is normally lower than for hard materials but chips left in the hole can cause the drill to wander from an axial path and can result in a drilled hole with a center which does not lie along a line.

(To be continued. This article is divided into several parts and this is part 5, for part 4 please refer to http://news.chinatungsten.com/en/tungsten-information/80043-ti-10264; for part 6 please refer to http://news.chinatungsten.com/en/tungsten-information/80077-ti-10281)

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In part 3 we know that A tungsten carbide spade-type micro drill has a large thrust force compared to the diameter of the drill during micro drilling process and the drill point angles vary according to its work piece materials. Here we talk about the mechanism of micro drilling process.

A micro drilling spindle uses a vee-block bearing arrangement. The tungsten carbide micro drill is mounted in the mandrel and is fabricated integral with the mandrel. The mandrel rides against four convex diamond surfaces which are the only points of contact. So long as the tungsten carbide micro drill was ground with the mandrel supported in a similar manner, the drill will be concentric about an axis. That axis may not coincide with the mandrel axis but that is not significant as long as the offset is not sufficient to cause excessive vibration, and it normally is not. A small pulley is fastened to the drill mandrel and a drive belt passes around the pulley and drives the drill from an external motor. The belt tension is the only force holding the mandrel against the diamond pads and a slight upward component of the belt tension is used to retract the drill. The upper end of the mandrel rides against a ceramic material which provides the drill thrust force. This disk may also rest against a force sensor to measure drill thrust force which is often used to indicate the extent of drill wear.

(To be continued. This article is divided into several parts and this is part 4, for part 3 please refer to http://news.chinatungsten.com/en/tungsten-information/80042-ti-10262)

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