With the rapid development of nanomaterials, powder granularity becomes smaller and sintering temperature is decreasing, which is beneficial for products densification. Using ultra-fine or nano tungsten copper powder can directly sinter at the lower temperature so that it is the new research direction of tungsten copper processing. 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.

1. Powder preparation

There are many methods of ultra-fine tungsten copper powder, mechanical alloying and co-reduction is the most popular. Mechanical alloying (MA), the powder technology invented by American in 1970s, which milling with W and Cu powder in ball grinder. During the milling, it uses inert gas for protection in case of powder oxidation.

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For instance, the density of W60-Cu tungsten copper electrode increases 12.7-12.8g/cm³ to 13.2-13.3g/cm³ after hot isostatic pressing (HIP), the hardness increases 50-70HRB to 80HRB, the bending strength increases 550-750MPa to 1000MPa and the electric conductivity can reaches 60%IACS. Foreign scholars adopt cold-rolling to tungsten copper machining and study the effects of distortion on properties. The result shows that with the increasing distortion, hardness and strength will be remarkably improved and annealing in time will promote the mechanical properties.

In conclusion, tungsten copper electrode infiltration has many advantages, such as high density, good thermal and electric conductivity. However, there are some problems that difficult for complex-shape machining, copper solidifying phase uneven distribution and the higher cost of surplus copper removal.

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The most of study of infiltration focus on qualitative analysis in the parameters, such as temperature, holding time, atmosphere and so on. For tungsten copper, infiltration mechanism refers to copper solution moisturizes porous tungsten skeleton, which flows along the gap of the grain and fills in the pore of the matrix by capillary force. It is important that proper temperature will ensure the small viscosity and large surface tension.

Generally, infiltration often uses H₂ (reducibility) for reducing the oxide of tungsten skeleton, which improves the moisture of the skeleton and the density of tungsten copper electrode. On the contrary, if we use oxidizing gas or carburization atmosphere, the porosity and density or other properties will be remarkably decreased. The study of after-processing includes repressing, hot forging, heat pressing, high temperature insostatic pressing (HIP) and so on. HIP can effectively eliminate the porosity and defects of infiltration.

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Compared with extrusion molding, Injection molding has been widely used, it makes porous tungsten blank by injection molding. The researchers adopt injection molding to make tungsten skeleton and observe 10%, 15%, 20% tungsten blank. Tungsten skeleton pre-sintering at 900℃, infiltrating 90-120min at 1500℃ can get tungsten copper composite material with 99.2% density, 1500MPa breaking strength.

The sintering process of porous tungsten skeleton plays an important role in tungsten copper electrode infiltration, including sintering temperature, holding temperature, sintering atmosphere, gas aggregate and so on. Sintering temperature choose by tungsten powder granularity, distribution of granularity, suppression density and other factors.

The experiment result shows that 5-9μm (tungsten powder granularity), 1000℃ (pre-sintering temperature), 1350℃ (infiltration temperature) is the ideal condition for tungsten copper electrode. In another experiment, researchers study tungsten copper contact of high-voltage switch sintering in the N₂ atmosphere, which find that there is non-oxidation, non carbonization in joint surface and tungsten powder grains distribute uniformly with Cu covered.

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In part 5 we know that there are about 5 distinct solid tungsten carbide end mill types, among HSM type featuring short cutting edge, larger corner radii, and HPM featuring long cutting edge length, chip dividers, helix angles, etc., are just popular milling cutter types. Here we talk about replaceable solid carbide head end milling system.

 (The end-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/79930-ti-10235)

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In part 4 we know that solid tungsten carbide end mill selection depends most importantly on machining strategy concerning feeds, speeds, depths of cut, which includes two directions: performance driven selection or application driven selections. Here we talk about the basic solid tungsten carbide milling cutter types.

Milling Cutter Type Choices

With approximately five distinct solid tungsten carbide end mill types in existence today for common applications in metallic materials, one generic tool type stands out as being somewhat outdated. It’s a solid tungsten carbide cutter that dates back to the days when small end mills were made of high speed steel (HSS). Historically referred to as the first generation of solid carbide end mills, it has the typical geometrical features that were used in HSS tools at the end of the 1970’s except that its base material has been switched to solid carbide which was found to be suitable for the task at that time. These types of cutters today define the lower end of the market both in terms of cost and performance.

The second group of cutters which in contrast is highly contemporary is the high speed milling type (HSM) of cutters defined for high cutting speeds. These tools typically feature a rather short usable cutting edge length and their design is optimized for maximum stability. With the application of high cutting speeds, high temperatures are generated and this heat typically accumulates in the tool corner. This is the reason why HSM end mills most often have larger corner radii for extra protection against plastic deformation in this area.

The third group for high performance milling (HPM) that holds tools specifically designed for high depths of cut and larger arc of engagement. The depth of cut being the optimizing factor here, the tool design reflects this with long cutting edge length and chip dividers to make large chip volumes more manageable. Helix angles and chip cavity capacity are other visible elements of importance. Increased cutter core diameters are also found with these tools. Their aim is to increase tool stability and again reduce deflection.

 (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/79882-ti-10226; for part 6 please refer to http://news.chinatungsten.com/en/tungsten-information/79931-ti-10236)

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In part 3 we know that solid tungsten carbide end mills have relatively sharp edges and an edge preparation is necessary for the coatings to adhere firmly to the substrate and avoid edge breakage, thus increase the stability, functionality and life span of cutting tools .Here we talk about machining strategy.

 (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/79881-ti-10225)

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In part 2 we know that solid tungsten carbide end mills have different temperature handling characteristics versus insert milling cutters, and so for diameter below 10mm, carbide end mills are suggested, but for large diameter, insert milling cutters are suggested. Here we talk about coatings and edge preparations.

Coatings And Edge Preparations

Coatings are applied to solid tungsten carbide end mills to increase wear resistance and isolate the area where the heat is generated from the substrate of the tool, in which it could potentially accumulate and affect the tool life span negatively. Additionally, solid tungsten carbide end mills have relatively sharp cutting edges, it is thus very important to have correct coating adhesion between the substrate material and the coating layers. In particular, with smaller diameter solid cutters, cutting edge sharpness is a crucial element contributing to tool performance. An ideal cutting edge would consist of a sharp cutting edge with the highest possible hardness without the risk for breakage. This can be in part achieved with an appropriate edge preparation. Most often, the style, shape and sharpness of the (cutting) edge preparation sets different solid carbide milling cutters apart both in terms of generated work quality and tool life levels reached.

A relatively sharp cutting edge is achieved through grinding both the top rake face as well as the clearance face on the tool. The line where the two faces meet each other is referred to as the cutting edge. Cutting edges will need reinforcements or a so called edge treatment/honing in order for the coating to better adhere to it and prevent edge breakouts. In other words, some of the edge sharpness is traded for stability and coating functionality, which in turn leads to longer tool life. It can even be discussed that the edge preparation has the highest importance of all followed by both substrate type and coating technology.

 (To be continued. This article is divided into several parts and this is part 3, for part 2 please refer to http://news.chinatungsten.com/en/tungsten-information/79854-ti-10211; for part 4 please refer to http://news.chinatungsten.com/en/tungsten-information/79882-ti-10226)

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In last part  we know that a solid tungsten carbide end mill is in many ways different from an insert milling cutter, such as, they have different types of coatings and substrates, same tolerances but different material stiffness and thus precision levels, and arc of tool contact. Here we go on exploring the characters of solid tungsten carbide end mill system.

Solid tungsten carbide end mills and steel based insert milling cutters have completely different characteristics in temperature handling and this should be reflected in the cutting strategy selection. Considering these facts and putting things further in perspective one has to look at tool dimensions too.

In the smaller diameter range below 10 mm there are very few insert based alternatives to solid tungsten carbide cutters and the choice is clearly going toward solid end mills. The opposite applies for tools with large diameters where solid carbide tools are not a viable choice for economical reasons. This leaves us with the intermediate range of sizes between 10 to approximately 25 mm where many system overlaps exist. The complexity of the shape to be machined, its accessibility and tolerances to be held are the guiding stars for initial tool selection here.

 (To be continued. This article is divided into several parts and this is part 2, for part 1 please refer to http://news.chinatungsten.com/en/tungsten-information/79853-ti-10210)

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A basic question often asked when one has both an insert based cutter and a solid carbide cutter is which one is the best and in what areas do they excel? This is not so much a question of one being superior over the other but rather a question regarding the features of a specific type of cutter and how that particular tool should be applied to deliver good results.

An insert milling cutter is different from a solid tungsten carbide milling cutter in many ways. Different types of coatings and different types of substrates are used with solid carbide cutters as compared to insert based systems and that makes for a number of significant feature differences between these two main groups. If some of the features in one of these two groups becomes more important in a certain application, then that tool is perhaps more suitable for the application.

Tolerances on both tools can be equally narrow, statically, but since solid carbide as a material is much stiffer compared to a steel shank tool with a mounted insert, it is prone to less bending and thus has a higher level of precision under the influence of cutting forces during machining.

Another important fact to remember is the arc of tool contact. The arc of tool contact or in other words the length of the circumference of a particular tool that is in contact with a machined part is directly linked to the amount of heat that is generated and absorbed into the tool, component or chips.

 (To be continued. This article is divided into several parts and this is part 1, for part 2 please refer to ; for part 16 please refer to )

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