Chapter 6 Powder Metallurgy (PM)

1. Chapter 6Powder Metallurgy (PM) 1302 310 Engineering Metallurgy Dr.Sukangkana Lee

2. Introduction • โลหะผงวิทยา เป็นกระบวนการขึ้นรูปชิ้นงานจากผงโลหะ โดยที่ผงโลหะจะถูกอัดในแบบเป็นรูปร่างตามแบบ และผงโลหะจะเชื่อมเข้าด้วยกันโดยการอบในบรรยากาศที่ควบคุม • จะทำให้ได้ชิ้นงานที่มีขนาดที่แน่นอน, ต้องการการตัดแต่งน้อย, มีผิวที่สวยงาม และสามารถผลิตในปริมาณที่มากได้

3. โลหะผงวิทยาถูกนำมาขึ้นรูปโลหะเพื่อผลิตชิ้นงานในอุตสาหกรรมต่าง ๆ ที่มีรูปร่างซับซ้อน หรือวัสดุที่ขึ้นรูปได้ยาก เช่น bearings, structural components and cutting tools กว่า 60 ปี • สามารถผลิตได้ทั้งวัสดุที่เป็นโลหะ และ วัสดุผสม • ชิ้นงานที่ผลิตได้จะมีความหนาแน่นสูง • สามารถผลิตชิ้นงานที่มีรูพรุนได้

4. คุณสมบัติทางกลของชิ้นงานที่ขึ้นรูปด้วยผงโลหะคุณสมบัติทางกลของชิ้นงานที่ขึ้นรูปด้วยผงโลหะ ที่มีความหนาแน่นต่างกัน เปรียบเทียบกับชิ้นงานที่ได้จากการรีดร้อน

5. Benefits • PM parts can be fabricated to final or near-net shape, thereby eliminating or reducing scrap metal, machining and assembly operation • Lower overall cost (less scrap lost) • High melting point metals and composite materials can be produced • PM is useful in making parts that have complex shapes or difficult to machine • Permits a wide variety of alloy systems • Produces good surface finishes

6. Benefits (Cont.) • Provides materials which may be heat-treated for increased strength or increased wear resistance • Provides controlled porosity for self-lubrication or filtration • Facilitates manufacture of complex or unique shapes which would be impractical or impossible with other metalworking processes • Is suited to moderate- to high-volume component production requirements • Offers long-term performance reliability in critical applications • Is cost-effective

7. Disadvantages • Porosity originates as the spaces between powder particles → low elongation • Expensive powder

8. Products and applications

11. Raw Materials Mixing Forming Sintering Optional Operations

12. Factors affected the QC of PM • Powder characteristic: Apparent density (AD), the irregularity and porous texture decreases AD • Powder preparation: most metal powder grains are coated by a thin oxide film but will be broken up during the pressing, stable oxide films e.g. SiO2 and Al2O3 cannot reduced during sintering leads to abrasive and tool wear • Type of compacting press, tool and die • Type of sintering furnace, atmosphere, time and temperature • Heat treatment

13. 5. Powder Manufacture • PM Standards: Fine powder particles < 20 µm • The finer the better preferably 2-10 µm Shape of Powders • Sponge-like for iron powder gives good green strength • Spheroidal particle gives high density and uniform distribution (see Fig. 2)

15. Powder production: There are four main processes • Solid-state reduction • Atomization • Electrolysis • Chemical

16. 1. Solid state reduction Solid state reduction is the most widely used for production of iron powder. Process: • Selected ore is crushed and mixed with carbon • Continuous furnace → Sponge iron • Further crushing • Separation of non-metallic material • Sieving→ Irregular fine sponge-like powder

17. Milling

18. 2. Atomization Atomization: air, nitrogen, argon (for oxidisable metal) and water are commonly used. The particle shape is controlled by rate of solidification of metal droplets. • Gas atomization gives spheroidal • Water atomized gives a more irregular shape. • Each powder produced by this method has the same chemical composition.

19. GAS ATOMIZATION Fine powder Collection chamber

21. 3. Electrolysis • By choosing suitable conditions, such as electrolyte composition and concentration, temperature, and current density, many metals can be deposited in a spongy or powdery state. • Further processing–washing, drying, reducing, annealing, and crushing–is often required, ultimately yielding high-purity and high-density powders.

22. Copper is the primary metal produced by electrolysis but iron, chromium, and magnesium powders are also produced this way. • Due to its associated high energy costs, electrolysis is generally limited to high-value powders such as high-conductivity copper powders.

23. Electrolytic

24. 4. Chemical process • Use for production of a high purity, < 5 m. • The powders produced can have a great variation in properties and yet have closely controlled particle size and shape. • Oxide-reduced powders are often characterized as “spongy,” due to pores present within individual particles.

25. Solution-precipitated powders can provide narrow particle size distributions and high purity. • Thermal decomposition is most often used to process carbonyls. These powders, once milled and annealed, exceed 99.5 percent purity.

26. Sponge iron-reduced ore

27. Isostatic compaction Vacuum melting and Cold forging Hot isostatic pressing Plus hot forging Direct hot isostatic pressing

28. Sinter-HIP • Sintered metals ~ 92% density is sufficient to ensure that open porosity at surface has been eliminated  HIPed to full density. • This process start from sintering then high pressure argon is introduced or vacuum sinter followed by HIPing in a separate apparatus for hard metal cutting tools.

30. Metal injection Moulding (MIM) Powder+ Binder Blending Granulation Injection Moulding Green body Debinding Brown body Sintering 99% Density Finished part