1. Powder Metallurgy
NANO54
Foothill College

2. Overview
History
Definitions
Benefits
Process
Applications

3. Introduction
Earliest use of iron powder dates back to 3000 BC. Egyptians used it for making tools
Modern era of P/M began when W lamp filaments were developed by Edison
Components can be made from pure metals, alloys, or mixture of metallic and non-metallic powders
Commonly used materials are iron, copper, aluminium, nickel, titanium, brass, bronze, steels and refractory metals
Used widely for manufacturing gears, cams, bushings, cutting tools, piston rings, connecting rods, impellers etc.

5. Powder Metallurgy . . . is a forming technique
Essentially, Powder Metallurgy (PM) is an art & science of producing metal or metallic powders, and using them to make finished or semi-finished products. Particulate technology is probably the oldest forming technique known to man
There are archeological evidences to prove that the ancient man knew something about it

6. Powder Metallurgy Producing metal or metallic powders
Using them to make finished or semi-finished products.
The Characterization of Engineering Powders
Production of Metallic Powders
Conventional Pressing and Sintering
Alternative Pressing and Sintering Techniques
Materials and Products for PM
Design Considerations in Powder Metallurgy

7. Powder Metallurgy (P/M)
Competitive with processes such as casting, forging, and machining.
Used when
melting point is too high (W, Mo).
reaction occurs at melting (Zr).
too hard to machine.
very large quantity.
Near 70% of the P/M part production is for automotive applications.
Good dimensional accuracy.
Controllable porosity.
Size range from tiny balls for ball-point pens to parts weighing 100 lb. Most are around 5 lb.

8. Process Capabilities A: highest, B: median, C: lowest Con’tional HIP
Injection Molding (IM)
Precision IM
Preform Forging
Metal
All
All (SA, SS)
All (Steel, SS)
Steel, SA
Surface detail B
B-C A
Mass, kg
0.01-5(30)
0.1-10
(e)
0.1-3
Min. section, mm
1.5 1
0.1 3
Min. core diam. mm
4-6
0.2 5
Tolerance +/-% 2
0.3
0.25
Throughput (pc/h)
5-20
Min. quantity
,000
1-100
10,000
100,000
Eq. Cost
A-B
A: highest, B: median, C: lowest
ME 355 Sp’06
W. Li

9. Design Aspects
(a) Length to thickness ratio limited to 2-4; (b) Steps limited to avoid density variation; (c) Radii provided to extend die life, sleeves greater than 1 mm, through hole greater than 5 mm; (d) Feather-edged punches with flat face; (e) Internal cavity requires a draft; (f) Sharp corner should be avoided; (g) Large wall thickness difference should be avoided; (h) Wall thickness should be larger than 1 mm.

10. Advantages / Disadvantages P/M
Virtually unlimited choice of alloys, composites, and associated properties.
Refractory materials are popular by this process.
Controlled porosity for self lubrication or filtration uses.
Can be very economical at large run sizes (100,000 parts).
Long term reliability through close control of dimensions and physical properties.
Very good material utilization.
Limited part size and complexity
High cost of powder material.
High cost of tooling.
Less strong parts than wrought ones.
Less well known process.

11. History of Powder Metallurgy
IRON Metallurgy >
How did Man make iron in 3000 BC?
Did he have furnaces to melt iron air blasts, and
The reduced material, which would then be spongy, [ DRI ], used to be hammered to a solid or to a near solid mass.
Example: The IRON PILLER at Delhi
Quite unlikely, then how ???

12. History of P/M Going further back in Time . . .
The art of pottery, (terracotta), was known to the pre-historic man (Upper Paleolithic period, around 30,000 years ago)!
Dough for making bread is also a powder material, bound together by water and the inherent starch in it. Baked bread, in all its variety, is perhaps one of the first few types of processed food man ate.
(Roti is a form of bread.)

13. Renaissance of P/M
The modern renaissance of powder metallurgy began in the early part of last century, when technologists tried to replace the carbon filament in the Edison lamp.
The commercially successful method was the one developed by William Coolidge. He described it in 1910, and got a patent for it in 1913.
This method is still being used for manufacturing filaments.

14. Renaissance of P/M
The Wars and the post-war era brought about huge leaps in science, technology and engineering.
New methods of melting and casting were perfected, thereby slowly changing the metallurgy of refractory materials.
P/M techniques have thereafter been used only when their special properties were needed.

15. P/M Applications Electrical Contact materials
Heavy-duty Friction materials
Self-Lubricating Porous bearings
P/M filters
Carbide, Alumina, Diamond cutting tools
Structural parts
P/M magnets
Cermets
and more, such as high tech applications

16. Hi-Tech Applications of P/M
Anti-friction products
Friction products
Filters
Electrical Contacts
Sliding Electrical Contacts
Very Hard Magnets
Very Soft Magnets
Refractory Material Products
Hard and Wear Resistant Tools
Ferrous & Non-ferrous Structural parts etc
THESE COMPONENTS ARE USED IN AIR & SPACE CRAFTS, HEAVY MACHINERY, COMPUTERS, AUTOMOBILES, etc…

17. Powder Metallurgy Merits
The main constituent need not be melted
The product is porous - [ note : the porosity can be controlled]
Constituents that do not mix can be used to make composites, each constituent retaining its individual property
Near Nett Shape is possible, thereby reducing the post-production costs, therefore:
 Precision parts can be produced
 The production can be fully automated, therefore,
 Mass production is possible
 Production rate is high
 Over-head costs are low
 Break even point is not too large
 Material loss is small
 Control can be exercised at every stage

18. Powder Metallurgy Disadvantages
Porous !! Not always desired.
Large components cannot be produced on a large scale [Why?]
Some shapes [such as?] are difficult to be produced by the conventional p/m route.
WHATEVER, THE MERITS ARE SO MANY THAT P/M,
AS A FORMING TECHNIQUE, IS GAINING POPULARITY

19. Powder Metallurgy An important point that comes out :
The entire material need not be melted to fuse it.
The working temperature is well below the melting point of the major constituent, making it a very suitable method to work with refractory materials, such as: W, Mo, Ta, Nb, oxides, carbides, etc.
It began with Platinum technology about 4 centuries ago … in those days, Platinum, [mp = 1774°C], was "refractory", and could not be melted.

20. Powder Metallurgy Process
Powder production
Blending or mixing
Powder compaction
Sintering
Finishing Operations

21. Powder Metallurgy Process

22. 1. Powder Production
Many methods: extraction from compounds, deposition, atomization, fiber production, mechanical powder production, etc.
Atomization is the dominant process
(a)
(b)
(c)
(a) Water or gas atomization; (b) Centrifugal atomization; (c) Rotating electrode

23. Powder Preparation
(a) Roll crusher, (b) Ball mill

24. Powder Preparation

25. 2. Blending or Mixing
Blending a coarser fraction with a finer fraction ensures that the interstices between large particles will be filled out.
Powders of different metals and other materials may be mixed in order to impart special physical and mechanical properties through metallic alloying.
Lubricants may be mixed to improve the powders’ flow characteristics.
Binders such as wax or thermoplastic polymers are added to improve green strength.
Sintering aids are added to accelerate densification on heating.

26. Blending
To make a homogeneous mass with uniform distribution of particle size and composition
Powders made by different processes have different sizes and shapes
Mixing powders of different metals/materials
Add lubricants (<5%), such as graphite and stearic acid, to improve the flow characteristics and compressibility of mixtures
Combining is generally carried out in
Air or inert gases to avoid oxidation
Liquids for better mixing, elimination of dusts and reduced explosion hazards
Hazards
Metal powders, because of high surface area to volume ratio are explosive, particularly Al, Mg, Ti, Zr, Th

27. Blending Some common equipment geometries used for blending powders
(a) Cylindrical, (b) rotating cube, (c) double cone, (d) twin shell

28. 3. Powder Consolidation
Cold compaction with 100 – 900 MPa to produce a “Green body”.
Die pressing
Cold isostatic pressing
Rolling
Gravity
Injection Molding small, complex parts.
Die pressing
ME 355 Sp’06
W. Li

29. Compaction
Press powder into the desired shape and size in dies using a hydraulic or mechanical press
Pressed powder is known as “green compact”
Stages of metal powder compaction:

30. Compaction Increased compaction pressure
Provides better packing of particles and leads to ↓ porosity
↑ localized deformation allowing new contacts to be formed between particles

31. Compaction
At higher pressures, the green density approaches density of the bulk metal
Pressed density greater than 90% of the bulk density is difficult to obtain
Compaction pressure used depends on desired density

32. Friction problem in cold compaction
The effectiveness of pressing with a single-acting punch is limited. Wall friction opposes compaction.
The pressure tapers off rapidly and density diminishes away from the punch.
Floating container and two counteracting punches help alleviate the problem.
W. Li

33. Smaller particles provide greater strength mainly due to reduction in porosity
Size distribution of particles is very important. For same size particles minimum porosity of 24% will always be there
Box filled with tennis balls will always have open space between balls
Introduction of finer particles will fill voids and result in↑ density

34. Density variation can be minimized by proper punch and die design
Because of friction between (i) the metal particles and (ii) between the punches and the die, the density within the compact may vary considerably
Density variation can be minimized by proper punch and die design
and (c) Single action press; (b) and (d) Double action press
(e) Pressure contours in compacted copper powder in single action press

35. Compaction Pressure of some Metal Powders
Metal Powder Pressure (MPa) Al Al2O Brass Carbon Fe W WC

36. Compaction of metal powder to form bushing
Typical tool and die set for compacting spur gear

37. A 825 ton mechanical press for compacting metal powder

38. Cold Isostatic Pressing
Metal powder placed in a flexible rubber mold
Assembly pressurized hydrostatically by water (400 – 1000 MPa)
Typical: Automotive cylinder liners →
FFT: Advantages?

39. 4. Sintering Parts are heated to 0.7~0.9 Tm.
Transforms compacted mechanical bonds to much stronger metallic bonds.
Shrinkage always occurs:

40. Sintering – Compact Stage
Green compact obtained after compaction is brittle and low in strength
Green compacts are heated in a controlled-atmosphere furnace to allow packed metal powders to bond together

41. Sintering – Three Stages
Carried out in three stages:
First stage: Temperature is slowly increased so that all volatile materials in the green compact that would interfere with good bonding is removed
Rapid heating in this stage may entrap gases and produce high internal pressure which may fracture the compact

42. Sintering: High temperature stage
Promotes solid-state bonding by diffusion.
Diffusion is time-temperature sensitive. Needs sufficient time

43. Sintering: High temperature stage
Promotes vapor-phase transport
Because material heated very close to MP, metal atoms will be released in the vapor phase from the particles
Vapor phase resolidifies at the interface

44. Sintering: High temperature stage

45. Sintering: High temperature stage
Third stage: Sintered product is cooled in a controlled atmosphere
Prevents oxidation and thermal shock
Gases commonly used for sintering:
H2, N2, inert gases or vacuum

46. Sintering Time, Temperature, and Indicated Properties

47. Liquid Phase Sintering
During sintering a liquid phase, from the lower MP component, may exist
Alloying may take place at the particle-particle interface
Molten component may surround the particle that has not melted
High compact density can be quickly attained
Important variables:
Nature of alloy, molten component/particle wetting, capillary action of the liquid

48. Hot Isostatic Pressing (HIP)
Steps in HIP

49. Combined Stages Simultaneous compaction + sintering
Container: High MP sheet metal
Container subjected to elevated temperature and a very high vacuum to remove air and moisture from the powder
Pressurizing medium: Inert gas
Operating conditions
100 MPa at 1100 C

50. Hot Isostatic Pressing
It may sound like some new, exotic dry cleaning process and though many have heard of "HIP", Hot Isostatic Pressing, few of us understand the many benefits of this materials process. Since it's largely misunderstood, many conservative engineers are reluctant to adopt HIPping as an element in their manufacturing designs, thus missing a valuable process tool.
HIP is a process that subjects a material simultaneously to both high temperature and high gas pressure, usually Argon, in vessels equipped with sophisticated control systems and telemetry.
Typically, the temperature is selected to permit limited plastic deformation of the material being processed in the solid state at an argon gas pressure of 15,000, 30,000, or at times, 45,000 psi (1,000 to 3,000 atmospheres) is isostatically exerted on the heated parts for a period of time. The chamber is then slowly cooled, depressurized and the parts removed.

51. Combined Stages Produces compacts with almost 100% density
Good metallurgical bonding between particles and good mechanical strength
Uses
Superalloy components for aerospace industries
Final densification step for WC cutting tools and P/M tool steels

52. Slip-Casting Slip is first poured into an absorbent mould
a layer of clay forms as the mould surface absorbs water
when the shell is of suitable thickness excess slip is poured away
the resultant casting

53. Slip: Suspension of colloidal (small particles that do not settle) in an immiscible liquid (generally water)
Slip is poured in a porous mold made of plaster of paris. Air entrapment can be a major problem
After mold has absorbed some water, it is inverted and the remaining suspension poured out.
The top of the part is then trimmed, the mold opened, and the part removed
Application: Large and complex parts such as plumbing ware, art objects and dinnerware

54. 5. Finishing
The porosity of a fully sintered part is still significant (4-15%).
Density is often kept intentionally low to preserve interconnected porosity for bearings, filters, acoustic barriers, and battery electrodes.
However, to improve properties, finishing processes are needed:
Cold restriking, resintering, and heat treatment.
Impregnation of heated oil.
Infiltration with metal (e.g., Cu for ferrous parts).
Machining to tighter tolerance.

55. Special Process: Hot compaction
Advantages can be gained by combining consolidation and sintering,
High pressure is applied at the sintering temperature to bring the particles together and thus accelerate sintering.
Methods include
Hot pressing
Spark sintering
Hot isostatic pressing (HIP)
Hot rolling and extrusion
Hot forging of powder preform
Spray deposition

56. Characterization of Powders
Size of powders 0.1 um – 1 mm
Sieve size quoted as mesh number
Particle D = 15/mesh number (mm)
325 mesh 45 um

57. Atomization
Produce a liquid-metal stream by injecting molten metal through a small orifice
Stream is broken by jets of inert gas, air, or water
The size of the particle formed depends on the temperature of the metal, metal flowrate through the orifice, nozzle size and jet characteristics

58. Electrode Centrifugation
Variation:
A consumable electrode is rotated rapidly in a helium-filled chamber. The centrifugal force breaks up the molten tip of the electrode into metal particles.

59. Finished Powders Fe powders made by atomization
Ni-based superalloy made by the rotating electrode process

60. P/M Process Approaches
Reduction
Reduce metal oxides with H2/CO
Powders are spongy and porous and they have uniformly sized spherical or angular shapes
Electrolytic deposition
Metal powder deposits at the cathode from aqueous solution
Powders are among the purest available
Carbonyls
React high purity Fe or Ni with CO to form gaseous carbonyls
Carbonyl decomposes to Fe and Ni
Small, dense, uniformly spherical powders of high purity

61. P/M Process Approaches
Comminution
Crushing
Milling in a ball mill
Powder produced
Brittle: Angular
Ductile: flaky and not particularly suitable for P/M operations
Mechanical Alloying
Powders of two or more metals are mixed in a ball mill
Under the impact of hard balls, powders fracture and join together by diffusion

62. P/M Summarizing: Powder Metallurgy is sought when -
It is impossible to form the metal or material by any other technique
When p/m gives unique properties which can be put to good use
When the p/m route is economical
There may be over-lapping of these three points.

63. Summary Powder metallurgy Metals and ceramics Particles and heat
Compaction and fusion
Interesting chemistry

64. References
Wikipedia Powder Metallurgy (
Wikipedia Sintering (
All about powder metallurgy
Powder Metallurgy -
John Wiley and Sons – Fundamentals of Modern Manufacturing Chapter 16 (book and handouts)

65. Powder Metallurgy Text
Appendix 1
Powder Metallurgy Text

66. Powder Metallurgy John Wiley and Sons
Powder Metallurgy (PM)
Metal processing technology in which parts are produced from metallic powders
• In the usual PM production sequence, the powders are compressed (pressed) into the desired shape and then heated (sintered) to bond the particles into a
hard, rigid mass
− Pressing is accomplished in a press-type machine using punch-and-die tooling designed specifically for the part to be manufactured
− Sintering is performed at a temperature below the melting point of the metal

67. Why Powder Metallurgy is Important
• PM parts can be mass produced to net shape or near net shape, eliminating or reducing the need for subsequent machining
• PM process wastes very little material - about 97% of the starting powders are converted to product
• PM parts can be made with a specified level of porosity, to produce porous metal parts
− Examples: filters, oil-impregnated bearings and gears

68. More Reasons Why PM is Important
• Certain metals that are difficult to fabricate by other methods can be shaped by powder metallurgy
− Example: Tungsten filaments for incandescent lamp bulbs are made by PM
• Certain alloy combinations and cermets made by PM cannot be produced in other ways
• PM compares favorably to most casting processes in dimensional control
• PM production methods can be automated for economical production

69. Limitations and Disadvantages
with PM Processing
• High tooling and equipment costs
• Metallic powders are expensive
• Problems in storing and handling metal powders
− Examples: degradation over time, fire hazards with certain metals
• Limitations on part geometry because metal powders do not readily flow laterally in the die during pressing
• Variations in density throughout part may be a problem, especially for complex geometries

70. PM Work Materials
• Largest tonnage of metals are alloys of iron, steel, and aluminum
• Other PM metals include copper, nickel, and refractory metals such as molybdenum and tungsten
• Metallic carbides such as tungsten carbide are often included within the scope of powder metallurgy

71. Engineering Powders
A powder can be defined as a finely divided particulate solid
• Engineering powders include metals and ceramics
• Geometric features of engineering powders:
− Particle size and distribution
− Particle shape and internal structure
− Surface area

72. Measuring Particle Size
• Most common method uses screens of different
mesh sizes
• Mesh count - refers to the number of openings per
linear inch of screen
− A mesh count of 200 means there are 200
openings per linear inch
− Since the mesh is square, the count is the same in
both directions, and the total number of openings
per square inch is 2002 = 40,000
− Higher mesh count means smaller particle size

73. Interparticle Friction and
Flow Characteristics
• Friction between particles affects ability of a powder to flow readily and pack tightly
• A common test of interparticle friction is the angle of repose, which is the angle formed by a pile of powders as they are poured from a narrow funnel

74. Observations
• Smaller particle sizes generally show greater friction and steeper angles
• Spherical shapes have the lowest interpartical friction
• As shape deviates from spherical, friction between particles tends to increase

75. Particle Density Measures
• True density - density of the true volume of the material
− The density of the material if the powders were melted into a solid mass
• Bulk density - density of the powders in the loose state after pouring
− Because of pores between particles, bulk density is less than true density

76. Packing Factor = Bulk Density
divided by True Density
• Typical values for loose powders range between 0.5 and 0.7
• If powders of various sizes are present, smaller powders will fit into the interstices of larger ones that would otherwise be taken up by air, thus higher packing factor
• Packing can be increased by vibrating the powders, causing them to settle more tightly
• Pressure applied during compaction greatly increases packing of powders through rearrangement and deformation of particles

77. Porosity
Ratio of the volume of the pores (empty spaces) in the powder to the bulk volume
• In principle, Porosity + Packing factor = 1.0
• The issue is complicated by the possible existence of closed pores in some of the particles
• If internal pore volumes are included in above porosity, then equation is exact

78. Chemistry and Surface Films
• Metallic powders are classified as either
− Elemental - consisting of a pure metal
− Pre-alloyed - each particle is an alloy
• Possible surface films include oxides, silica, adsorbed organic materials, and moisture
− As a general rule, these films must be removed prior to shape processing

79. Production of Metallic Powders
• In general, producers of metallic powders are not the same companies as those that make PM parts
• Virtually any metal can be made into powder form
• Three principal methods by which metallic powders are commercially produced
1. Atomization
2. Chemical
3. Electrolytic
• In addition, mechanical methods are occasionally used to reduce powder sizes

80. Conventional Press and Sinter
• After the metallic powders have been produced, the conventional PM sequence consists of three steps:
1. Blending and mixing of the powders
2. Compaction - pressing into desired part shape
3. Sintering - heating to a temperature below the
melting point to cause solid-state bonding of particles and strengthening of part
• In addition, secondary operations are sometimes performed to improve dimensional accuracy, increase density, and for other reasons

81. Blending and Mixing of Powders
• For successful results in compaction and sintering,
the starting powders must be homogenized
• Blending - powders of the same chemistry but
possibly different particle sizes are intermingled
− Different particle sizes are often blended to reduce
porosity
• Mixing - powders of different chemistries are
combined
− PM technology allows mixing various metals into
alloys that would be difficult or impossible to
produce by other means

82. Compaction
Application of high pressure to the powders to form them into the required shape
• The conventional compaction method is pressing, in which opposing punches squeeze the powders contained in a die
• The workpart after pressing is called a green compact, the word green meaning not yet fully processed
• The green strength of the part when pressed is adequate for handling but far less than after sintering

83. Sintering
Heat treatment to bond the metallic particles, thereby increasing strength and hardness
• Usually carried out at between 70% and 90% of the metal's melting point (absolute scale)
• Generally agreed among researchers that the primary driving force for sintering is reduction of surface energy
• Part shrinkage occurs during sintering due to pore size reduction

84. Densification and Sizing
Secondary operations are performed to increase density, improve accuracy, or accomplish additional shaping of the sintered part
• Repressing - pressing the sintered part in a closed die to increase density and improve properties
• Sizing - pressing a sintered part to improve dimensional accuracy
• Coining - pressworking operation on a sintered part to press details into its surface
• Machining - creates geometric features that cannot be achieved by pressing, such as threads, side holes, and other details

85. Impregnation and Infiltration
• Porosity is a unique and inherent characteristic of PM technology
• It can be exploited to create special products by filling the available pore space with oils, polymers, or metals
• Two categories:
1. Impregnation
2. Infiltration

86. Impregnation
The term used when oil or other fluid is permeated into the pores of a sintered PM part
• Common products are oil-impregnated bearings, gears, and similar components
• An alternative application is when parts are impregnated with polymer resins that seep into the pore spaces in liquid form and then solidify to create a pressure tight part

87. Infiltration
An operation in which the pores of the PM part are filled
with a molten metal
• The melting point of the filler metal must be below
that of the PM part
• Involves heating the filler metal in contact with the
sintered component so capillary action draws the filler
into the pores
• The resulting structure is relatively nonporous, and
the infiltrated part has a more uniform density, as well
as improved toughness and strength

88. Alternative Pressing and Sintering
Techniques
• The conventional press and sinter sequence is the
most widely used shaping technology in powder
metallurgy
• Additional methods for processing PM parts include:
− Isostatic pressing
− Hot pressing - combined pressing and sintering
©2002 John Wiley & Sons, Inc. M. P. Groover, “Fundamentals of Modern Manufacturing 2/e”
Materials and Products for PM
• Raw

89. Materials and Products for PM
• Raw materials for PM are more expensive than for other metalworking because of the additional energy
required to reduce the metal to powder form
• Accordingly, PM is competitive only in a certain range of applications
• What are the materials and products that seem most suited to powder metallurgy?

90. PM Materials – Elemental Powders
A pure metal in particulate form
• Used in applications where high purity is important
• Common elemental powders:
− Iron
− Aluminum
− Copper
• Elemental powders are also mixed with other metal powders to produce special alloys that are difficult to formulate by conventional methods
− Example: tool steels

91. PM Materials – Pre-Alloyed Powders
Each particle is an alloy comprised of the desired
chemical composition
• Used for alloys that cannot be formulated by mixing
elemental powders
• Common pre-alloyed powders:
− Stainless steels
− Certain copper alloys
− High speed steel

92. PM Products
• Gears, bearings, sprockets, fasteners, electrical contacts, cutting tools, and various machinery parts
• Advantage of PM: parts can be made to near net shape or net shape
− They require little or no additional shaping after PM processing
• When produced in large quantities, gears and bearings are ideal for PM because:
− The geometry is defined in two dimensions
− There is a need for porosity in the part to serve as a reservoir for lubricant

93. PM Parts Classification System
• The Metal Powder Industries Federation (MPIF) defines four classes of powder metallurgy part designs, by level of difficulty in conventional pressing
• Useful because it indicates some of the limitations on shape that can be achieved with conventional PM processing

94. Design Guidelines for PM Parts - I
• Economics usually require large quantities to justify cost of equipment and special tooling
− Minimum quantities of 10,000 units are suggested
• PM is unique in its capability to fabricate parts with a controlled level of porosity
− Porosities up to 50% are possible
• PM can be used to make parts out of unusual metals and alloys - materials that would be difficult if not impossible to produce by other means

95. Design Guidelines for PM Parts - II
• The part geometry must permit ejection from die after pressing
− This generally means that part must have vertical or near-vertical sides, although steps are allowed
− Design features such as undercuts and holes on the part sides must be avoided
− Vertical undercuts and holes are permissible because they do not interfere with ejection
− Vertical holes can be of cross-sectional shapes other than round without significant difficulty

96. Design Guidelines for PM Parts - III
• Screw threads cannot be fabricated by PM; if required, they must be machined into the part
• Chamfers and corner radii are possible by PM pressing, but problems arise in punch rigidity when angles are too acute
• Wall thickness should be a minimum of 1.5 mm (0.060 in) between holes or a hole and outside wall
• Minimum recommended hole diameter is 1.5 mm
(0.060 in)