Follow-up technologies in generative processes

Classification of the following techniques

Almost all rapid prototyping processes are based on the basic idea of building up a workpiece in layers from increments of material. A major disadvantage of the rapid prototyping process is based on this basic idea: the process-related structure of the model body in layers does not result in an optically smooth surface, but rather a surface characterized by stair or step effects. The surface quality of a rapid prototyping model body is therefore severely limited. The optically and haptically poor surface quality reduces the appearance of the product and thus has a negative impact on the expressiveness of the model. In order to fully exploit or even improve the informative value of a rapid prototyping model body, an optimization of the surface quality is essential.

Follow-up techniques expand the rapid prototyping process chain to include requirements for:

higher quantities,
better material properties,
optical and haptic quality and
Functionalization of the component

to guarantee.

The necessity of the follow-up technologies consists primarily in being able to verify certain end product properties already in the prototype stage or in the first place to enable the use of a prototype through its functionalization.

The following techniques are divided into four areas:

Casting and molding

In the sub-areas of casting and molding, it is not the model body itself that becomes the subject of further processing, but a casting mold that is molded or cast by it. With the subsequent molding technique, the model can be used several times. When casting, however, the model body is incinerated and is therefore only used once. With the help of the molds, real components can then be manufactured from different materials.

Coating

In the subsequent coating and post-processing techniques, the rapid prototyping model body itself remains the subject of further processing. The subsequent coating technology includes surface sealing and painting .

Surface seals are mainly used on porous surfaces of models. They form a barrier for the penetration of liquid or gaseous substances into the model. This prevents models from absorbing these substances and thereby influencing their properties. This z. B. the swelling of the models through water absorption or the dissolution of binders through external influences prevented. The substance for the surface sealing penetrates into porous models when it is applied, which in most cases increases the strength of the model. In some generative manufacturing processes, this is used specifically to increase the strength of the models or to compensate for the anisotropy of models. Surface sealing does not offer any possible uses in the context of this work. The specimens made of polyamide are not porous surfaces, but a semi-crystalline thermoplastic that is in the entropy-elastic range at room temperature .

The coating achieves specific optical properties. For this purpose, varnishes in different colors or clear varnishes are applied. Painting partially fulfills the same tasks as sealing. Furthermore, painting increases like surface sealing z. B. with paper models the model strength is considerable. The model surface often has to be prepared in other processing steps so that the paint does not peel off again. When painting, it must be noted that some model building materials used in additive manufacturing processes are attacked by the solvents contained in the paint and dissolve.

Stereolithography workpiece uncoated
Stereolithography workpiece with chrome layer
Stereolithography workpiece with silver layer
Stereo lithography workpiece with gold layer

post processing

The subsequent technique of post-processing can be subdivided into adding and removing processes. Coating is one of the applying processes. Post-machining can be done mechanically or chemically .

Coating with metals as an application process is carried out primarily to change or improve the appearance of a model or to give it functional properties such as conductivity . In addition, coatings - like surface sealing - act as barrier layers and thus offer protection against external influences. There are different coating methods that can be divided into chemical, electrochemical and physical coating. The model surface must be prepared accordingly, depending on the rapid prototyping process chain used and the application process, so that the metal layer can be deposited and does not come off again later. This requires electrostatic ionic bonds or bonds with a covalent character. The polar or functional groups required for this can be produced on the plastic substrate, for example, by plasma etching. The additional post-processing offers itself as a follow-up technique in which the model body itself is changed, for experiments in the context of this work. In addition to well-founded specialist knowledge, the electroplating department also offers the test facilities necessary for experimental tests.

The abrasive finishing processes include blasting, grinding, drilling, turning and polishing. These subsequent techniques are preferably used when geometries that cannot be produced, or can only be produced with difficulty, using generative production processes. In addition, they allow the geometry of the model body to be changed later - for example by adding holes. The abrasive post-processing methods offer the possibility of changing the surface in a targeted manner as well as over a large area. The application of the individual processes is linked to the material of the model body and its complexity, geometry. The subsequent technique of ablative post-processing is well suited for processing laser-sintered components made of polyamide.

Chemical post-processing can only be carried out by means of etching. It is strongly dependent on the material of the model body and its chemical properties such as the resistance to media. The pickling of plastics is mostly used before the metallic coating. For example, when pickling ABS plastic, the butadiene component of the base material is dissolved out in a chromium-sulfuric acid solution .

literature

B. Bertsche, H.-J. Bullinger (Hrsg.): Collaborative Research Center 374 Development and Testing of Innovative Products - Rapid Prototyping . University of Stuttgart 2000.
A. Gebhardt: Rapid prototyping, tools for rapid product development . Hanser Verlag, Munich 2000.
Rapid prototyping seminar . Technical Academy Wuppertal, Wuppertal 1995.
H. Müller: Rapid prototyping process - properties, application and processing . 2002.
R. addiction Trunk et al .: plastic metallization . 3. Edition. Eugen G. Leuze Verlag, Bad Saulgau 2007.
D. Mann: Plasma modification of plastic surfaces to increase the adhesion of metal layers . Springer Verlag (IPA-IAO Research and Practice, 189), Stuttgart, Univ., Fac. Mechanical Engineering, Diss., Berlin 1994.

Web links

Individual evidence

^ A. Gebhardt: Rapid prototyping, tools for rapid product development . Hanser Verlag, Munich 2000.
↑ Geuer, 1995
^ ^A ^b H. Müller: Rapid prototyping process - properties, application and processing . 2002.
↑ ^a ^b R. Suchtentrunk et al .: Plastic metallization . 3. Edition. Eugen G. Leuze Verlag, Bad Saulgau 2007.
↑ D. Mann: Plasma modification of plastic surfaces to increase the adhesion of metal layers . Springer Verlag (IPA-IAO Research and Practice, 189), Stuttgart, Univ., Fac. Mechanical Engineering, Diss., Berlin 1994.

[geb-1] A. Gebhardt: Rapid prototyping, tools for rapid product development . Hanser Verlag, Munich 2000.

[2] Geuer, 1995

[mül-3] A ^b H. Müller: Rapid prototyping process - properties, application and processing . 2002.

[sucht-4] R. Suchtentrunk et al .: Plastic metallization . 3. Edition. Eugen G. Leuze Verlag, Bad Saulgau 2007.

[mann-5] D. Mann: Plasma modification of plastic surfaces to increase the adhesion of metal layers . Springer Verlag (IPA-IAO Research and Practice, 189), Stuttgart, Univ., Fac. Mechanical Engineering, Diss., Berlin 1994.