Powder Metallurgy

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  • Topic: Sintering, Powder metallurgy, Metalworking
  • Pages : 15 (4112 words )
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  • Published : March 25, 2013
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Powder metallurgy is the process of blending fine powdered materials, pressing them into a desired shape or form (compacting), and then heating the compressed material in a controlled atmosphere to bond the material (sintering). The powder metallurgy process generally consists of four basic steps: (1) powder manufacture, (2) powder blending,(3) compacting, (4) sintering. Compacting is generally performed at room temperature, and the elevated-temperature process of sintering is usually conducted at atmospheric pressure. Optional secondary processing often follows to obtain special properties or enhanced precision.[1] Two main techniques used to form and consolidate the powder are sintering and metal injection molding. Recent developments have made it possible to use rapid manufacturing techniques which use the metal powder for the products. Because with this technique the powder is melted and not sintered, better mechanical strength can be accomplished. History and capabilities

The history of powder metallurgy (PM) and the art of metals and ceramics sintering are intimately related to each other. Sintering involves the production of a hard solid metal or ceramic piece from a starting powder."While a crude form of iron powder metallurgy existed in Egypt as early as 3000 B.C, and the ancient Incas made jewelry and other artifacts from precious metal powders, mass manufacturing of P/M products did not begin until the mid-or late- 19th century".[2] In these early manufacturing operations, iron was extracted by hand from metal sponge following reduction and was then reintroduced as a powder for final melting or sintering. A much wider range of products can be obtained from powder processes than from direct alloying of fused materials. In melting operations the "phase rule" applies to all pure and combined elements and strictly dictates the distribution of liquid and solid phases which can exist for specific compositions. In addition, whole body melting of starting materials is required for alloying, thus imposing unwelcome chemical, thermal, and containment constraints on manufacturing. Unfortunately, the handling of aluminium/iron powders poses major problems.[3] Other substances that are especially reactive with atmospheric oxygen, such as tin, are sinterable in special atmospheres or with temporary coatings.[4] In powder metallurgy or ceramics it is possible to fabricate components which otherwise would decompose or disintegrate. All considerations of solid-liquid phase changes can be ignored, so powder processes are more flexible than casting, extrusion, or forging techniques. Controllable characteristics of products prepared using various powder technologies include mechanical, magnetic,[5] and other unconventional properties of such materials as porous solids, aggregates, and intermetallic compounds. Competitive characteristics of manufacturing processing (e.g., tool wear, complexity, or vendor options) also may be closely regulated. Powder Metallurgy products are today used in a wide range of industries, from automotive and aerospace applications to power tools and household appliances. Each year the international PM awards highlight the developing capabilities of the technology.[6]

Isostatic powder compacting
Isostatic powder compacting is a mass-conserving shaping process. Fine metal particles are placed into a flexible mould and then high gas or fluid pressure is applied to the mould. The resulting article is then sintered in a furnace. This increases the strength of the part by bonding the metal particles. This manufacturing process produces very little scrap metal and can be used to make many different shapes. The tolerances that this process can achieve are very precise, ranging from +/- 0.008 inches (0.2 mm) for axial dimensions and +/- 0.020 inches (0.5 mm) for radial dimensions. This is the most efficient type of powder compacting.(The following subcategories are also from this reference.)[7] This operation...
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