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Determination of springback gradient in the die on compacted polymer powders during high-velocity compaction
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.ORCID iD: 0000-0001-5760-3919
2006 (English)In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 25, no 1, 114-123 p.Article in journal (Refereed) Published
Abstract [en]

A uniaxial high-velocity compaction process for polymer powder using a cylindrical, hardened steel die and a new technique with relaxation assist was tested with various heights. The influences of the relaxation assist device on the process characteristics are discussed. Two bonded strain gauges and a high-speed video camera system were used to investigate the springback phenomenon during the compaction process. It was found that the relaxation assist improves the compaction of the polymer powder by locking the powder bed in the compacted form. It is shown that the high-velocity compaction process is an interruption process and that the delay times between the pressure waves can be reduced by increasing the height of the relaxation assist device. The delay times between the pressure waves are also strongly dependent on the strain rate. If the height of the relaxation assist device is increased, the first gross instantaneous springback, and the total elastic springback, are reduced. In addition, the density of the powder bed is increased. The relative times of the compacting stage, decompacting stage and the reorganisation of the particles can be also controlled by altering the height of the relaxation assist.

Place, publisher, year, edition, pages
2006. Vol. 25, no 1, 114-123 p.
Keyword [en]
high-velocity compaction; powder polymers; polyamide-11; relaxation assist; strain rates; relative green density; morphology; springback gradient
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-6227DOI: 10.1016/j.polymertesting.2005.09.002ISI: 000235262700017Scopus ID: 2-s2.0-31444445807OAI: oai:DiVA.org:kth-6227DiVA: diva2:10876
Note

QC 20100506

Available from: 2006-10-06 Created: 2006-10-06 Last updated: 2016-05-18Bibliographically approved
In thesis
1. Novel Technique to Improve High-Velocity Cold Compaction: Processing of Polymer Powders and Polymer-Based Nanocomposite High Performance Components
Open this publication in new window or tab >>Novel Technique to Improve High-Velocity Cold Compaction: Processing of Polymer Powders and Polymer-Based Nanocomposite High Performance Components
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Compaction of polymer powders and polymer-based nanocomposites by uniaxial high-velocity cold compaction (HVC), by high-energy ball milling (HEBM) and using a novel technique, relaxation assists, was investigated with a focus on the process parameters, the compactibility characteristics, surface morphology and friction. The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain the pull-out phenomenon, springback gradient, delay time, relative time of the pressure wave, and stick-slip phenomenon during the compaction process. Experimental results for different compaction profiles, different particle size distributions and different milling system for polymer-based nanocomposite are presented, showing the effect of varying the process parameters on the compacted material; the compactibility in the compacted bed, the uniformity of the compacted surface, the pull-out phenomenon, the springback gradient, the stick-slip phenomenon and the homogeneity of the dispersions of nanoparticles in the polymer powders in the solid state. It was found that the high-velocity compaction process is an interruption process and that the opposite velocity and pressure loss during the compaction process have a major influence on the quality of the compacted material. The relaxation assist device is a novel technique that has been successfully developed to improve the compaction process. The relaxation assists are parts of the piston and they are regarded as projectile supports. They are constructed of the same material as the piston, and the diameters are the same but the lengths are different. The relaxation assist device leads to an improvement in the compaction of powders, polymer powders and polymer-based nanocomposites by giving a more homogeneous opposite velocity and a better locking of the powder bed in the compacted form during the compaction process with less change in dimensions in the case of both homogeneous and heterogeneous materials. If the movement of the particles is restricted the powder bed attains a higher density and the total elastic springback is minimized. In addition, there is a more homogeneous dispersion of nanoparticles in the case of a heterogeneous material. A much better transfer of the pressure through the powder bed and a smaller loss of pressure lead to a more homogenous stick-slip of the particles and a higher sliding coefficient due to the overall friction during the compaction process.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2006:31
Keyword
polymer powders, nanocomposites, high-velocity compaction, high-energy ball milling
National Category
Production Engineering, Human Work Science and Ergonomics
Identifiers
urn:nbn:se:kth:diva-4133 (URN)91-7178-459-4 (ISBN)
Public defence
2006-11-03, E2, Lindstedsvägen 3, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20100630Available from: 2006-10-06 Created: 2006-10-06 Last updated: 2010-06-30Bibliographically approved
2. Improved high velocity cold copaction processing: polymer powder to high performance parts
Open this publication in new window or tab >>Improved high velocity cold copaction processing: polymer powder to high performance parts
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

A uniaxial High-Velocity Compaction (HVC) process for polymer powder using a cylindrical, hardened steel die and a new technique with relaxation assist was tested with a focus on the compactibility characteristics and surface morphology of the compacted materials using various heights of relaxation assist device with different compacting profiles.

Relaxation assist device was presented as a new technique to reduce springback, pull-out phenomenon and to improve the compaction process.

The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain pull-out phenomenon during the decompacting stage. In this study, polyamide-11 powders with different particle size distributions have been compacted with the application of different compaction profiles, e.g. different energies and velocities. It was found that the relative green density is influenced more by the pre-compacting (primary compaction step) than by the post-compacting (secondary compaction step).

Experimental results for different compaction profiles were presented showing the effect of varying the opposite velocity during the decompacting stage and how to improve the homogeneous densification between the upper and lower surface and the evenness of the upper surface of the compacted powder bed by using relaxation assists, and the influences of the relaxation assist device on the process characteristics. It was found that the relaxation assist improves the compaction of the polymer powder by locking the powder bed in the compacted form. In addition, the relative times of the compacting stage, decompacting stage and the reorganisation of the particles can be controlled by altering the height of the relaxation assist. It was found that the high-velocity compaction process is an interruption process and that the delay times between the pressure waves can be reduced by increasing the height of the relaxation assist device. Furthermore, the first gross instantaneous springback and the total elastic springback are reduced.

Two bonding strain gauges and a high-speed video camera system were used to investigate the springback phenomenon during the compaction process. Scanning electron microscopy (SEM) and image computer board Camera (IC-PCI Imaging Technology) were used to the study the morphological characteristics, the limit of plastic deformation and particle bonding by plastic flow at contact points, and pull-out phenomena.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 45 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2005:25
Keyword
high-velocity compaction, powder polymers, polyamide-11, relaxation assist, compactibility, relative green density, morphology, pull-out, springback
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-407 (URN)
Presentation
2005-09-21, Sal B1, Brinellvägen 23, Stockholm, 10:05 (English)
Opponent
Supervisors
Note
QC 20100506Available from: 2005-09-07 Created: 2005-09-07 Last updated: 2010-11-23Bibliographically approved

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