ASTM B331-20

Standard Test Method for Compressibility of Metal Powders in Uniaxial Compaction

SIGNIFICANCE AND USE
5.1 The compressibility value obtained by this test is a measure of a material characteristic of the powder.  
5.2 The test method is useful in research and development projects, as a quality control test in the evaluation and manufacturing control of metal powder production, and as an acceptance test for shipment of metal powder lots.  
5.3 In PM production operations, the test is helpful in determining pressing and tooling requirements for high density parts.  
5.4 Results may be affected by test conditions such as the type, amount, and method of lubrication, dwell time during compaction, and die material. The compressibility values may not necessarily agree with results obtained under production conditions.
SCOPE
1.1 This laboratory test method covers the determination of the compressibility of metal powders and metal powder mixtures as measured by the extent to which a test portion can be densified under controlled conditions in a specified die.  
1.2 Units—With the exception of the values for density and mass, for which the use of gram per cubic centermetre (g/cm3) and gram (g) units is the longstanding industry practice, the values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Sep-2020
• ICS: 77.160 - Powder metallurgy
• Technical Committee: B09 - Metal Powders and Metal Powder Products
• Drafting Committee: B09.02 - Base Metal Powders

Relations

• Refers: ASTM E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM B243-18 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Oct-2018
• Refers: ASTM E456-13A(2017)e3 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM E456-13A(2017)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM B243-16 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Jul-2016
• Refers: ASTM B962-15 - Standard Test Methods for Density of Compacted or Sintered Powder Metallurgy (PM) Products Using Archimedes’ Principle
• Effective Date: 01-Apr-2015
• Refers: ASTM B962-14 - Standard Test Methods for Density of Compacted or Sintered Powder Metallurgy (PM) Products Using Archimedes’ Principle
• Effective Date: 01-Sep-2014
• Refers: ASTM E456-13ae2 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Nov-2013
• Refers: ASTM E456-13ae1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Nov-2013
• Refers: ASTM E456-13a - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Nov-2013
• Refers: ASTM E456-13ae3 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Nov-2013
• Refers: ASTM B243-13 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Nov-2013
• Refers: ASTM E456-13 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Aug-2013
• Refers: ASTM B962-13 - Standard Test Methods for Density of Compacted or Sintered Powder Metallurgy (PM) Products Using Archimedes’ Principle
• Effective Date: 01-Apr-2013
• Refers: ASTM B243-12 - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Jul-2012

Overview

ASTM B331-20: Standard Test Method for Compressibility of Metal Powders in Uniaxial Compaction is an internationally recognized laboratory method developed by ASTM International. This standard specifies procedures for determining the compressibility of metal powders and metal powder mixtures by measuring their densification under controlled conditions in a specified die. Compressibility, as evaluated by this test, is a key material property for powder metallurgy (PM) applications, impacting production processes and the quality of final components.

The compressibility values derived from this standard are used to:

• Characterize metal powder materials
• Support research and development
• Guide quality control during powder manufacturing
• Serve as an acceptance test for shipped powder lots
• Inform pressing and tooling requirements in PM production

Key Topics

• Uniaxial Compaction: The method focuses on compressing a powdered metal sample in a single direction within a standardized die and evaluating the resulting green (unsintered) density.
• Controlled Test Conditions: The procedure ensures consistent results by controlling factors such as lubrication method, dwell time, compaction rate, and die material.
• Test Methods: Three main approaches are provided for assessing compressibility:
  • Green density at a specified compacting pressure
  • Graphing density across multiple compaction pressures
  • Measuring required pressure to reach a specified green density
• Sample Types: Both cylindrical and rectangular test specimens are permitted, with detailed dimensions and preparation requirements.
• Measurement Precision: The standard outlines requirements for apparatus (such as presses, balances, and micrometers) and specifies precision, repeatability, and reproducibility criteria.

Applications

ASTM B331-20 is widely applied across industries that utilize powder metallurgy and metal powders, including automotive, aerospace, electronics, and additive manufacturing. Specific applications include:

• Quality Control: Manufacturers adopt the test to ensure metal powders meet necessary compaction and density properties before shipment or use in production lines.
• Process Optimization: Powder metallurgy engineers use compressibility results to optimize compaction pressures, lubricants, and die materials for producing high-density, high-quality PM parts.
• R&D: Laboratories employ this test method for material development, comparing compressibility characteristics of new metal powder formulations or blends to enhance performance.
• Acceptance Testing: Buyers and suppliers rely on compressibility as a shipment acceptance criterion, providing a consistent and objective assessment of received powder lots.

Related Standards

ASTM B331-20 references several related standards essential for proper implementation and context within powder metallurgy quality assurance:

• ASTM B215 - Practices for Sampling Metal Powders
• ASTM B243 - Terminology of Powder Metallurgy
• ASTM B925 - Practices for Production and Preparation of PM Test Specimens
• ASTM B962 - Test Methods for Density of Compacted or Sintered PM Products Using Archimedes' Principle
• ASTM E456 - Terminology Relating to Quality and Statistics

Practical Value

By following ASTM B331-20, organizations can:

• Maintain consistent quality of metal powders in production and supply chains
• Reduce variability in PM part performance through standardized compressibility evaluation
• Make informed decisions in powder selection, tool design, and process control
• Benchmark different powders and processes with reliable density data

Keywords: ASTM B331-20, compressibility, metal powder, powder metallurgy, uniaxial compaction, green density, powder compaction, quality control, PM production, test method

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B331 − 20
Standard Test Method for
Compressibility of Metal Powders in Uniaxial Compaction
This standard is issued under the fixed designation B331; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* E456 Terminology Relating to Quality and Statistics
1.1 This laboratory test method covers the determination of
3. Terminology
the compressibility of metal powders and metal powder mix-
3.1 Definitions—For definitions of terms used in this test
tures as measured by the extent to which a test portion can be
method, refer toTerminology B243.Additional descriptive PM
densified under controlled conditions in a specified die.
information is available under General Information on PM on
1.2 Units—With the exception of the values for density and
the ASTM B09 web page.
mass, for which the use of gram per cubic centermetre (g/cm )
and gram (g) units is the longstanding industry practice, the
4. Summary of Test Method
values stated in inch-pound units are to be regarded as
4.1 Atest portion of metal powder is uniaxially compressed
standard. The values given in parentheses are mathematical
in a specific die under controlled conditions.
conversions to SI units that are provided for information only
4.2 The green density of the resulting compact is deter-
and are not considered standard.
mined.
1.3 This standard does not purport to address all of the
4.3 The compressibility of the powder is defined as the
safety concerns, if any, associated with its use. It is the
green density of the test compact at the compacting pressure
responsibility of the user of this standard to establish appro-
that was used.
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
5. Significance and Use
1.4 This international standard was developed in accor-
5.1 The compressibility value obtained by this test is a
dance with internationally recognized principles on standard-
measure of a material characteristic of the powder.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
5.2 The test method is useful in research and development
mendations issued by the World Trade Organization Technical
projects, as a quality control test in the evaluation and
Barriers to Trade (TBT) Committee.
manufacturing control of metal powder production, and as an
acceptance test for shipment of metal powder lots.
2. Referenced Documents
5.3 In PM production operations, the test is helpful in
2.1 ASTM Standards:
determining pressing and tooling requirements for high density
B215 Practices for Sampling Metal Powders
parts.
B243 Terminology of Powder Metallurgy
5.4 Results may be affected by test conditions such as the
B925 Practices for Production and Preparation of Powder
type, amount, and method of lubrication, dwell time during
Metallurgy (PM) Test Specimens
compaction, and die material. The compressibility values may
B962 Test Methods for Density of Compacted or Sintered
not necessarily agree with results obtained under production
Powder Metallurgy (PM) Products Using Archimedes’
conditions.
Principle
6. Apparatus
6.1 Compacting Tooling—A cemented carbide die or
This test method is under the jurisdiction of ASTM Committee B09 on Metal
alternatively, hardened tool steel die and two hardened steel
Powders and Metal Powder Products and is the direct responsibility of Subcom-
mittee B09.02 on Base Metal Powders.
punches capable of producing the compressibility test speci-
Current edition approved Oct. 1, 2020. Published October 2020. Originally
men.ThedesignsshowninPracticesB925fora cylindrical test
approved in 1958. Last previous edition approved in 2016 as B331 – 16.
specimen and a transverse rupture test specimen are examples
DOI:10.1520/B0331-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or of acceptable tooling.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
6.2 Powder Compacting Press—A compression testing ma-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. chine or powder compacting press, capable of applying an
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B331 − 20
adequate load with an accuracy of at least 61.0 % at a rate of 9.2.1 Either of two compressibility test specimens may be
approximately 30 tsi/min (400 MPa/min). selected to determine compressibility.
9.2.1.1 Cylindrical Compressibility Test Specimen—A short
6.3 Balance—Alaboratory balance readable to 0.001 g with
cylindrical compact 1.000 in. in diameter by 0.280 6 0.010 in.
a minimum capacity of 100 g.
thick (25.4 mm diameter by 7.11 6 0.25 mm thick), as shown
6.4 Micrometer—Standard outside micrometers or other
in Practice B925 as Cylindrical Powder Compressibility Test
suitable measuring instruments for determining the dimensions
Specimen.
of the green compressibility compacts to the nearest 0.0002 in.
9.2.1.2 Rectangular Compressibility Test Specimen—A
(0.005 mm).
short rectangular compact 1.250 in. long by 0.500 in. wide by
0.250 6 0.010 in. thick. (31.8 mm by 12.7 mm by 6.35 6
7. Gross Metal Powder Sample
0.25 mm), similar to that which is shown in Practices B925 as
7.1 The gross powder sample is a quantity of powder of
Transverse Rupture Strength Test Specimen—Thin.
sufficient mass to be split into the required number of powder
9.3 Powder Test Sample:
test portions. It shall be taken from the lot of powder that is to
9.3.1 The thickness of the compressibility test specimen is
be tested in accordance with Practices B215.
critical as the area of die wall contact has a strong effect on the
8. Preparation green density and the thicknesses specified have been deter-
mined to give equivalent results between the two powder
8.1 This test method contains procedures to be followed for
compressibility test specimens.
either lubricated or unlubricated metal powders. Lubrication is
9.3.2 The powder test portion shall be a powder charge of
generally necessary to assist in the compaction and ejection of
sufficient mass to produce either a cylindrical test specimen
the compressibility compact.
0.280 6 0.010 in. (7.11 6 0.25 mm) thick or a rectangular test
8.1.1 An alternative way of testing powder not containing a
specimen 0.250 6 0.010 in. (6.35 6 0.25 mm) thick.
lubricant is to use an otherwise unlubricated die after thor-
9.3.3 For a powder whose compressibility is not known, it
oughlymixingintothepowderasufficientamountofasuitable
may be necessary to adjust the mass of the powder charge
lubricant.
based upon the thickness obtained in an initial test.
8.2 Lubricated Powders:
9.4 Compacting:
8.2.1 Powder mixtures containing a lubricant shall be tested
9.4.1 Compact and identify three (3) duplicate compress-
in the as-received condition.
ibility test specimens of the shape that has been selected
8.3 Unlubri
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: B331 − 16 B331 − 20
Standard Test Method for
Compressibility of Metal Powders in Uniaxial Compaction
This standard is issued under the fixed designation B331; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This laboratory test method covers the determination of the compressibility of metal powders and metal powder mixtures as
measured by the extent to which a test portion can be densified under controlled conditions in a specified die.
1.2 Units—With the exception of the values for density and mass, for which the use of gram per cubic centermetre (g/cm ) and
gram (g) units is the longstanding industry practice, the values stated in inch-pound units are to be regarded as standard. The values
given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered
standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
B215 Practices for Sampling Metal Powders
B243 Terminology of Powder Metallurgy
B925 Practices for Production and Preparation of Powder Metallurgy (PM) Test Specimens
B962 Test Methods for Density of Compacted or Sintered Powder Metallurgy (PM) Products Using Archimedes’ Principle
E456 Terminology Relating to Quality and Statistics
3. Terminology
3.1 Definitions—For definitions of terms used in this test method, refer to Terminology B243. Additional descriptive PM
information is available inunder the Related Material sectionGeneral Information on PM of Vol 02.05 of theon the ASTM B09
web Annual Book of ASTM Standards.page.
4. Summary of Test Method
4.1 A test portion of metal powder is uniaxially compressed in a specific die under controlled conditions.
This test method is under the jurisdiction of ASTM Committee B09 on Metal Powders and Metal Powder Products and is the direct responsibility of Subcommittee B09.02
on Base Metal Powders.
Current edition approved April 1, 2016Oct. 1, 2020. Published April 2016October 2020. Originally approved in 1958. Last previous edition approved in 20102016 as
B331B331 – 16.– 10. DOI:10.1520/B0331-16. DOI:10.1520/B0331-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B331 − 20
4.2 The green density of the resulting compact is determined.
4.3 The compressibility of the powder is defined as the green density of the test compact at the compacting pressure that was used.
5. Significance and Use
5.1 The compressibility value obtained by this test is a measure of a material characteristic of the powder.
5.2 The test method is useful in research and development projects, as a quality control test in the evaluation and manufacturing
control of metal powder production, and as an acceptance test for shipment of metal powder lots.
5.3 In PM production operations, the test is helpful in determining pressing and tooling requirements for high density parts.
5.4 Results may be affected by test conditions such as the type, amount, and method of lubrication, dwell time during compaction,
and die material. The compressibility values may not necessarily agree with results obtained under production conditions.
6. Apparatus
6.1 Compacting Tooling—A cemented carbide die or alternatively, hardened tool steel die and two hardened steel punches capable
of producing the compressibility test specimen. The designs shown in PracticePractices B925 for a cylindrical test specimen and
a transverse rupture test specimen are examples of acceptable tooling.
6.2 Powder Compacting Press—A compression testing machine or powder compacting press, capable of applying an adequate
load with an accuracy of at least 61.0 % at a rate of approximately 30 tsi/min (400 MPa/min).
6.3 Balance—A laboratory balance readable to 0.001 g with a minimum capacity of 100 g to be used to determine the mass of
the compacted test specimen to the nearest 0.01 g.
6.4 Micrometer—Standard outside micrometers or other suitable measuring instruments for determining the dimensions of the
green compressibility compacts to the nearest 0.0002 in. (0.005 mm).
7. Gross Metal Powder Sample
7.1 The gross powder sample is a quantity of powder of sufficient mass to be split into the required number of powder test portions.
It shall be taken from the lot of powder that is to be tested in accordance with Practices B215.
8. Preparation
8.1 This test method contains procedures to be followed for either lubricated or unlubricated metal powders. Lubrication is
generally necessary to assist in the compaction and ejection of the compressibility compact.
8.1.1 An alternative way of testing powder not containing a lubricant is to use an otherwise unlubricated die after thoroughly
mixing into the powder a sufficient amount of a suitable lubricant.
8.2 Lubricated Powders:
8.2.1 Powder mixtures containing a lubricant shall be tested in the as-received condition.
8.3 Unlubricated Powders:
8.3.1 The needed lubrication may be supplied either by lubricating the walls of the die or by mixing a powdered lubricant into
the metal powder to be tested.
B331 − 20
8.3.1.1 Die-wall lubrication consists of coating the walls of the die with a thin film of lubricant prior to each compaction step
following the die-wall lubrication procedure in Practices B925.
8.3.1.2 Admixed lubrication consists of thoroughly mixing a small percentage of a powdered lubricant into the gross sample.
8.4 Compressibility test results may vary in accordance with the method of lubrication, type, and amount of lubricant.
8.5 Compressibility test results may vary depending on the rate at which the compacting pressure is applied.
8.6 The parties concerned shall agree on the method of lubrication and the details of the procedure.
9. Procedure
9.1 Testing Methods:
9.1.1 The test for compressibility of metal powder may be conducted in any of three ways:
9.1.1.1 Method 1—Compressibility defined as the green density obtained at a selected compacting pressure.
9.1.1.2 Method 2—Compressibility as a graph relating density as a function of at least four compacting pressures.
9.1.1.3 Method 3—Compressibility defined as the compacting pressure required to attain a target green density.
9.2 Test Specimens for Powder Compressibility:
9.2.1 Either of two compressibility test specimens may be selected to determine compressibility.
9.2.1.1 Cylindrical Compressibility Test Specimen—A short cylindrical compact 1.000 in. in diameter by 0.280 6 0.010 in. thick
(25.4 inmm diameter by 7.11 6 0.25 mm thick), as shown in Practice B925 as Cylindrical Powder Compressibility Test Specimen.
9.2.1.2 Rectangular Compressibility Test Specimen—A short rect
...