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Electron beam melting: Impact of part surface properties on metal fatigue and bone ingrowth
Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kvalitets- och maskinteknik. (Sports Tech Research Centre)ORCID-id: 0000-0002-7690-2110
2019 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Abstract

The aim of this thesis is to investigate aspects on how additive manufacturing (AM) contributes to functional bone implants with the use of the electron beam melting (EBM) technology. AM manufactures parts according to computer-aided design, and the EBM technology melts powder using an electron beam, which acts similar to a laser beam. The topics discussed in this thesis are related to surface roughness that originate from the melted metal powder, and the thesis tries to define some aspects that affect implant functionality. Process parameters steering the electron beam and biocompatibility arising from the surface texture were the initial parts of the PhD studies, and the other half focused on post-processing and fatigue, which are important for medical and industrial applications. There are six studies in this compilation thesis. They are abbreviated as P - process parameters, M - medical applications, and F - fatigue. Studies P, M2, F2, and F3 are journal articles, and M1 and F1 are conference proceedings.

Study P used design of experiments to investigate how process parameters affect the surface roughness of as-built EBM-manufactured parts and concluded that beam speed and energy (current) were the most important parameters that influence the surface roughness.

In studies M1 and M2, EBM-manufactured specimens of cobalt-chromium and titanium alloys were used to evaluate biocompatibility. The blood chamber method quantified the reactions of the human whole blood in contact with the metal surfaces, and the results showed how the as-built EBM surface roughness contributed to coagulation and bone healing.

Rotating beam fatigue equipment was used in studies F1–F3 and study F1 discussed the size effect on fatigue loaded as-built specimens and included specimens with different sizes and with or without hot isostatic pressing (HIP). Study F2 compared as-built and machined specimens and study F3 investigated how Hirtisation, which is a patented electrochemical surface treatment, and HIP affect the fatigue properties that originate from the electrochemical polishing surface topography. The studies showed that a decreased surface roughness increased the fatigue resistance while the stress concentrations (Kt) in the surface of EBM-manufactured specimens decreased.

The thesis concludes that EBM-manufactured as-built surfaces are suitable for direct contact with the bone, and that HIP does not improve the fatigue resistance of parts with as-built surfaces, where crack initiation starts at notches.

Abstract [sv]

Svensk sammanfattning

Denna avhandling behandlar frågeställningar inom tillverkning av benimplantat med additiv tillverkning (Additive Manufacturing, AM), med fokus på EBM-tekniken (Electron Beam Melting, smältning med elektronstråle). Additiv tillverkning bygger produkter utifrån datorkonstruerade modeller (Computer Aided Design, CAD), och EBM-tekniken gör detta genom att smälta ihop metallpulver med hjälp av en energirik elektronstråle likt en laserstråle. Avhandlingen fokuserar på ytstrukturen från det smälta metallpulvret och hur dess egenskaper påverkar funktionen av EBM-tillverkade produkter. Under första delen av doktorandarbetet var fokus på processparametrar som styr elektronstrålen och biokompatibilitet, och under den senare delen har arbetet riktats mot efterbearbetningsmetoder och utmattningsegenskaper, vilket är viktigt för medicinska implantat och industriell användning. Avhandlingen är skriven på engelska och studierna som sammanläggningen består av är döpta och numrerade med förkortningarna P-Processparametrar, M-Medicinska applikationer och F-Fatigue (Utmattning). Avhandlingen består av fyra tidskriftsartiklar kallade studie P, M2, F2 och F3 och två konferensbidrag studie M1 och F1.

Studie P undersökte med hjälp av försöksplanering (Design Of Experiment, DOE) hur processparametrarna påverkar ytgrovheten för EBM-tillverkade produkter och resulterade i att elektronstrålens förflyttningshastighet och energi har störst inverkan på ytgrovheten.

Studierna M1 och M2 använde kobolt-krom- respektive titanlegeringar, tillverkat med EBM-tekniken, och undersökte biokompatibiliteten med hjälp av blodkammarmodellen som kvantifierar blodets reaktioner vid kontakt med metallytan. Resultaten visade att den mycket grova ytan som EBM-tillverkade implantat har, stimulerar till koagulation och implantatinläkning.

Roterande utmattning användes för studierna F1-3, och studie F1 avhandlar hur EBM-tillverkade provstavar med olika storlekar och med eller utan tempererad tryckbehandling (Het Isostatisk Pressning, HIP) påverkar resultaten. Studie F2 jämförde hur den EBM-tillverkade ytan och en maskinbearbetad yta påverkar materialegenskaperna, och studie F3 undersökte hur Hirtisering, en patenterad elektrokempoleringsmetod, och kombinerat med HIP påverkar utmattningsegenskaperna. Studierna visar att minskad ytgrovhet med elektrokempolering ökar hållfastheten samtidigt som spänningskoncentrationerna (Kt) minskar i ytan för EBM-tillverkade ytor.

Avhandlingen visar att EBM-tillverkade ytor lämpar sig för benkontakt och att HIP inte förbättrar utmattningsegenskaperna om den råa ytan behålls.

sted, utgiver, år, opplag, sider
Sundsvall: Mid Sweden University , 2019. , s. 73
Serie
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 291
Emneord [en]
Additive Manufacturing (AM), Electron Beam Melting (EBM), As-built surfaces, Bone Ingrowth, Metall Fatigue, Machined Surfaces, Hirtisation, Hot Isostatic Pressing (HIP)
HSV kategori
Identifikatorer
URN: urn:nbn:se:miun:diva-35182ISBN: 978-91-88527-82-0 (tryckt)OAI: oai:DiVA.org:miun-35182DiVA, id: diva2:1270469
Disputas
2019-01-15, Q221, Akademigatan 1, Östersund, 09:15 (svensk)
Opponent
Veileder
Tilgjengelig fra: 2018-12-14 Laget: 2018-12-13 Sist oppdatert: 2018-12-14bibliografisk kontrollert
Delarbeid
1. Blood coagulation on electron beam melted implant surfaces, implications for bone growth
Åpne denne publikasjonen i ny fane eller vindu >>Blood coagulation on electron beam melted implant surfaces, implications for bone growth
2011 (engelsk)Inngår i: Proccedings of EBS 2011, Dublin, 2011Konferansepaper, Poster (with or without abstract) (Annet vitenskapelig)
Abstract [en]

INTRODUCTION

Implants for arthroplasty, plates and screws for orthopedics, maxillofacial and dentistry are more frequently being customised. Ti and CoCr alloys are common materials for bone implants. Surface roughness, porosity and choice of material may have an impact on the bone ingrowth. EBM (Electron Beam Melting) is a 3D-printing technique melting metallic powder layer by layer according to the corresponding CAD (Computer Aided Design) model of implants1.With EBM technology customised implants can be manufactured with a lower cost compared to conventional technologies2. Implants for bone replacement made from CT images with EBM technology will fit accurate and lead to simpler and better planed surgeries also3. The EBM technique, as such, is always resulting with rough surface on the implants (typically 20-45µm). That roughness can be controlled, in some extent, by changing the process parameters. Some authors claim that roughened surfaces are promoting bone ingrowth4.

This work was aiming on the question: are EBM made surfaces good for bone ingrowth and is it possible to change the bone ingrowth by varying the machine settings? In order to answer this question a number of coin like specimens of CoCr were manufactured with the different surface roughness. The blood chamber model has shown how the first steps of bone healing were proceeding on specimen surfaces, indicating how the coagulation and complement systems can behave in vivo5.

 

EXPERIMENTAL METHODS

The manufacture of the test specimens was carried out with Arcam A2 EBM® equipment.  Process parameters were changed in the software EBM controle6 and three groups of eight specimens with different parameter setting were made. The specimens were then tested with whole blood from two individuals in a modified version of the blood chamber model named above7. Surface roughness was characterised with a stylus profiler Dektak® 6M.

 

RESULTS AND DISCUSSION

Table 1 percents Ra (average roughness) and plt (platelets) activated for each group.

 

                                         Table 1

group         Ra mean      std                    plt mean   std

1              35.0µm        3.24µm           92.9%       5.25%

2              28.5µm        2.14µm           85.3%       7.61%

3              28.2µm        1.75µm           84.4%       10.3%

 

The results indicate that rougher surfaces are more thrombogenic which could imply that they are more suitable for bone ingrowth then smooth surfaces. Increase of total surface area (due to larger roughness) might be a reason for the improved trombogenic response.

 

 

Figure 1 shows how many platelets were stuck on the specimen surfaces. Horizontal lines represent mean values and standard deviation.

 

CONCLUSION

The surface properties of EBM produced implants are affected by the made parameters. The results in Figure 1 corresponds well with previous results that rougher surfaces promotes bone ingrowth4. The increased thrombogenicity and platelet binding with rougher surfaces indicates that EBM made surfaces can affect the final bone response and will possibly suit as implant material.

 

REFERENCES

1. Raennar, L.E., et al., Efficientcooling with tool inserts manufactured by electronbeam melting. Rapid Prototyping Journal. 13:128-35, 2007

2. Cronskaer, M. Applications of Electron Beam Melting to Titanium Hip Stem Implants

3. Mazzoli, A., et al., Direct fabrication through electron beam melting technology of custom cranial implants designed in a PHANToM-based haptic environment. Materials and Design. 30:318-3192, 2009

4. Frosch, K.H., et al., Metallic Biomaterials in Skeletal Rapair. Eur J Trauma. 32:149-59, 2006

5. Thor A., et al.. The role of whole blood in thrombin generation in contact with various titanium surfaces. Biomaterials. 28:966-97, 2007

6. Arcam AB (www.arcam.com)

7. Hong, J., et al., A new in vitro model to study interaction between whole blood and biomaterials. Studies of platelet and coagulation activation acid the effect of aspirin. Biomaterials. 20:603-611, 1999

sted, utgiver, år, opplag, sider
Dublin: , 2011
Emneord
Additive manufacturing, rapid prototyping, electron beam melting
HSV kategori
Identifikatorer
urn:nbn:se:miun:diva-17891 (URN)2-s2.0-84887000027 (Scopus ID)
Konferanse
24th European Conference on Biomaterials –September 4th–9th, Dublin 2011
Tilgjengelig fra: 2012-12-20 Laget: 2012-12-18 Sist oppdatert: 2018-12-14bibliografisk kontrollert
2. The Effect of EBM Process Parameters upon Surface Roughness
Åpne denne publikasjonen i ny fane eller vindu >>The Effect of EBM Process Parameters upon Surface Roughness
2016 (engelsk)Inngår i: Rapid prototyping journal, ISSN 1355-2546, E-ISSN 1758-7670, Vol. 22, nr 3, s. 495-503Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Purpose-The surface roughness of products manufactured using the additive manufacturing (AM) technology of electron beam melting (EBM) has a special characteristic. Different product applications can demand rougher or finer surface structure, so the purpose of this study is to investigate the process parameters of EBM to find out how they affect surface roughness. Design/methodology/approach-EBM uses metal powder to manufacture metal parts. A design of experiment plan was used to describe the effects of the process parameters on the average surface roughness of vertical surfaces. Findings-The most important electron beam setting for surface roughness, accorDing to this study, is a combination of speed and current in the contours. The second most important parameter is contour offset. The interaction between the number of contours and contour offset also appears to be important, as it shows a much higher probability of being active than any other interaction. The results show that the line offset is not important when using contours. Research limitations/implications-This study examined contour offset, number of contours, speed in combination with current and line offset, which are process parameters controlling the electron beam. Practical implications-The surface properties could have an impact on the product's performance. A reduction in surface processing will not only save time and money but also reduce the environmental impact. Originality/value-Surface properties are important for many products. New themes containing process parameters have to be developed when introducing new materials to EBM manufacturing. During this process, it is very important to understand how the electron beam affects the melt pool.

Emneord
Additive manufacturing, Electron beam melting, Process parameters, Surface roughness
HSV kategori
Identifikatorer
urn:nbn:se:miun:diva-25708 (URN)10.1108/RPJ-10-2013-0102 (DOI)000379421200006 ()2-s2.0-84971264825 (Scopus ID)
Tilgjengelig fra: 2015-08-24 Laget: 2015-08-24 Sist oppdatert: 2018-12-14bibliografisk kontrollert
3. Micro- to Macroroughness of Additively Manufactured Titanium Implants in Terms of Coagulation and Contact Activation
Åpne denne publikasjonen i ny fane eller vindu >>Micro- to Macroroughness of Additively Manufactured Titanium Implants in Terms of Coagulation and Contact Activation
Vise andre…
2017 (engelsk)Inngår i: International Journal of Oral & Maxillofacial Implants, ISSN 0882-2786, E-ISSN 1942-4434, Vol. 32, nr 3, s. 565-574Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Purpose: This study aimed to evaluate how as-built electron beam melting (EBM) surface properties affect the onset of blood coagulation. The properties of EBM-manufactured implant surfaces for placement have, until now, remained largely unexplored in literature. Implants with conventional designs and custom-made implants have been manufactured using EBM technology and later placed into the human body. Many of the conventional implants used today, such as dental implants, display modified surfaces to optimize bone ingrowth, whereas custom-made implants, by and large, have machined surfaces. However, titanium in itself demonstrates good material properties for the purpose of bone ingrowth. Materials and Methods: Specimens manufactured using EBM were selected according to their surface roughness and process parameters. EBM-produced specimens, conventional machined titanium surfaces, as well as PVC surfaces for control were evaluated using the slide chamber model. Results: A significant increase in activation was found, in all factors evaluated, between the machined samples and EBM-manufactured samples. The results show that EBM-manufactured implants with as-built surfaces augment the thrombogenic properties. Conclusion: EBM that uses Ti6Al4V powder appears to be a good manufacturing solution for load-bearing implants with bone anchorage. The as-built surfaces can be used "as is" for direct bone contact, although any surface treatment available for conventional implants can be performed on EBM-manufactured implants with a conventional design.

Emneord
bone ingrowth, coagulation, customization, electron beam melting, surface roughness
HSV kategori
Identifikatorer
urn:nbn:se:miun:diva-31544 (URN)10.11607/jomi.5357 (DOI)000404520600022 ()28494040 (PubMedID)2-s2.0-85019955342 (Scopus ID)
Forskningsfinansiär
Swedish Research Council, 2013-65X-05647-34-4EU, FP7, Seventh Framework Programme, 602699EU, FP7, Seventh Framework Programme, 262948
Tilgjengelig fra: 2017-09-05 Laget: 2017-09-05 Sist oppdatert: 2018-12-14bibliografisk kontrollert
4. Fatigue properties of Ti-6Al-4V manufactured using electron beam melting
Åpne denne publikasjonen i ny fane eller vindu >>Fatigue properties of Ti-6Al-4V manufactured using electron beam melting
2017 (engelsk)Inngår i: Proceedings Euro PM 2017: International Powder Metallurgy Congress and Exhibition 2017, Brussels: EPMA European Powder Metallurgy Association , 2017Konferansepaper, Oral presentation with published abstract (Fagfellevurdert)
Abstract [en]

The interest in powder bed fusion additive manufacturing methods, such as electron beam melting (EBM), is increasing constantly and main business areas driving the development are aerospace and implant manufacturers. EBM manufactured parts have a rather coarse surface roughness mainly originating from the layer thickness and the powder grains melted by the electron beam. Thus, there is an interest in understanding how the surface properties influences the fatigue performance of the material. In this study, EBM manufactured Ti-6Al-4V was investigated at high cycle fatigue using rotating beam and different types of specimens regarding geometry, as-built and hot isostatic pressing (HIP) post-processing were evaluated. The results confirm that as-built surfaces affect the fatigue limit and a small size specimen geometry for rotating beam fatigue testing is proposed as a part of material and process verification.

sted, utgiver, år, opplag, sider
Brussels: EPMA European Powder Metallurgy Association, 2017
HSV kategori
Identifikatorer
urn:nbn:se:miun:diva-32484 (URN)2-s2.0-85056550071 (Scopus ID)978-1-899072-49-1 (ISBN)
Konferanse
International Powder Metallurgy Congress and Exhibition, Euro PM 2017; Milano Congressi (MiCo)Milan; Italy; 1 October 2017 through 4 October 2017
Tilgjengelig fra: 2017-12-18 Laget: 2017-12-18 Sist oppdatert: 2018-12-14bibliografisk kontrollert
5. Influence of the surface topography of additive manufactured Ti6A14V on fatigue and calculations of the stress concentration factor
Åpne denne publikasjonen i ny fane eller vindu >>Influence of the surface topography of additive manufactured Ti6A14V on fatigue and calculations of the stress concentration factor
(engelsk)Inngår i: Artikkel i tidsskrift (Fagfellevurdert) Accepted
HSV kategori
Identifikatorer
urn:nbn:se:miun:diva-35213 (URN)
Tilgjengelig fra: 2018-12-14 Laget: 2018-12-14 Sist oppdatert: 2018-12-14bibliografisk kontrollert
6. Fatigue properties of electrochemical polished and hot isostatic pressed Ti6A14V manufactured by electron beam melting
Åpne denne publikasjonen i ny fane eller vindu >>Fatigue properties of electrochemical polished and hot isostatic pressed Ti6A14V manufactured by electron beam melting
(engelsk)Inngår i: Artikkel i tidsskrift (Fagfellevurdert) Submitted
HSV kategori
Identifikatorer
urn:nbn:se:miun:diva-35214 (URN)
Tilgjengelig fra: 2018-12-14 Laget: 2018-12-14 Sist oppdatert: 2018-12-14bibliografisk kontrollert

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