|
Prototyping evolves into mold-free production
New improved materials and advances in the productivity and accuracy of systems have brought new, highly interesting
applications within the reach of prototyping processes such as stereolithography or laser sintering. Customers are
increasingly benefiting from their specific advantages - immediate availability of parts, no need for production tooling and the ability
to achieve "impossible" shapes - for the direct production of real-use components.
"With modern prototyping technologies we are able to produce real-use parts directly from
CAD data without expenditure for tools. For many industrial applications this
opportunity is
extremely attractive", says Dr. Eng. Volker Grießbach, general manager of VG
Kunststofftechnik GmbH in Chemnitz (Germany). This company, which specializes in rapid
prototyping services, uses a broad variety of processes for the short-term production of
prototypes and prototype tools made of plastic or metal. Dr. Grießbach has experienced that
specifically with the generative processes of stereolithography (SL) and laser sintering
(LS),
the availability of improved materials has provided access to completely new
markets.
Instead of ordering only the prototypes, more and more customers want real-use parts. This tendency towards advanced
digital manufacturing (ADMsm) is particularly evident in the electronics industry. For such customers, VG Kunststofftechnik
routinely
produces connector housings, solenoid bodies or cases for small drives in batch sizes ranging from one to well above
10,000. In this context, the attainable productivity is related to the size of the part. In the building chamber of a Viper
SLA® system for example, about 1,000 housings for a miniature electronic connector can be built overnight, and a Vanguard
SLS® system may yield
500 and more coil bodies with square bores for connector pins per production cycle.
"With modern prototyping technologies we are able to produce real-use parts directly from CAD data without the expense of tooling."
Dr. Eng. Volker Grießbach
General manager of VG Kunststofftechnik
Improved materials
"Progress in material properties has been particularly noticed with the stereolithography
process", adds Jörg Grießbach, whose responsibilities with VG Kunststofftechnik include
data management and stereolithography production. Well into the second half of the
1990s, the photosensitive resins used for this process were so brittle and fragile that the parts produced
in this way could not be subjected to higher loads.
In the meantime the situation has changed dramatically: for example, the
accuGen™ 100
resin from 3D Systems exhibits mechanical characteristics comparable to those of ABS
plastic. The high accuracy attainable when using this material makes it possible to produce
very thin-walled parts, e.g. for micro-technology applications. Furthermore, it
exhibits a good temperature resistance up to 100 °C. On the laser sintering side, the
DuraForm® PA and GF materials
show properties largely corresponding to those of normal or glass fiber reinforced polyamide (PA). Here too, the high
degree of accuracy attainable makes it possible to create very thin-walled structures.
Demand for "impossible" geometries
"Current market trends are pushing the developers to create designs that force production
specialists to the feasibility limits of their processes", discloses Dr. Grießbach. This is the result of two principal trends: on the one hand, the need to make
efficient use of limited resources makes it essential to design extremely detailed and complex parts with ever thinner walls.
On the other hand, cost considerations enforce the reduction of the number of parts used,
leading to the creation of very complex structures integrating as many formerly separate
parts and functions as possible. In his discussions with customers, he is increasingly confronted
with the demand for parts that go well beyond the feasibility limits of established production
methods. Some modern mobile-phone casings are produced with walls that are so thin that
only a few years ago they would have been rejected as "impossible to produce", and some
"mega-parts" combine shapes and functions of seven to eight formerly distinct components.
This increased complexity implies higher expenditure for the creation of the required production
tools, for example additional slides and other movable mould parts to avoid undercuts,
with a consequent negative impact on costs and delays for the production of the tools.
The electronic industry discovers "mold-free" production
"The almost 'instant' availability of real-use parts without having to wait for weeks until the
production tool is ready is another strong argument for ADM", says J. Grießbach. This is especially attractive in the development phase of new products,
where short times to market are a decisive factor for success. Additionally, the generative laser-building process yields
degrees of freedom that are difficult, if not impossible, to achieve with conventional production technologies, such as the
creation of parts with undercuts, nearly closed inner voids or with curved inner flow channels, and the high accuracy of the
process makes it possible to produce parts with walls so thin or with small diameter bores so deep that it would not be possible
to extract them from a mould. Even integrated film joints or snap-on connections are state-of-the-art. He expects the
demand for ADM parts directly designed to take advantage of these features will jump considerably as soon as word of
these possibilities has gone round among designers.
Technology partnership along the value-generating chain
"This growing demand is a strong incentive to intensify R&D work to improve all aspects of
rapid prototyping technologies", says J. Grießbach. Along with materials and building
speed improvements, researchers should focus on reducing accuracy variances and increasing
material consistency. The main reason for this is that while for a pure prototype relatively high
dissimilarities to the final product are usually accepted, a real-use part will have to fulfill the
portfolio of characteristics defined for the part - with respect to dimensions as well as regarding
its material properties. This implies new technological and design challenges, since the
uniformity of part properties will have to be maintained regardless of the individual rapid prototyping system used for its creation or the batch of
raw material used for its production. Rapid prototyping materials currently displaying
"approximate" values for mechanical and physical properties on their label will have to be developed into engineering materials with narrow tolerances. Fortunately, his upstream partner, 3D
Systems, has identified these necessities and actively encourages the corresponding developments - together with producers
of SL and LS materials. On the other hand, the customers deciding to use such parts will also have to show much
creativity since, at least for the foreseeable future, ADM parts will not easily be able to
fulfill "properties according to standard xyz". The product designer will therefore be
challenged to a much higher degree than usual to critically review his usual
acceptance criteria and to cut them back to the minimum required. "On the other hand, he will be
rewarded by solutions clearly ahead of the current state of the art - and a time to market
well below usual standards", says Dr. Grießbach.
Company Profile
As early as the late 80s, Dr. Volker Grießbach recognized the importance of rapid
prototyping technologies. Soon after the reunification of Germany, he founded VG Kunststofftechnik GmbH as an engineering and prototyping services company.
Today, the company has some 20 employees and offers virtually the whole bandwidth of technologies and services for the
production of prototypes, from concurrent engineering and data conversion over prototype, tool and ADM part production
through to just-in-time delivery. The portfolio includes all the usual materials such as plastics, metals, ceramics and composites.
The equipment encompasses three modern stereolithography systems, a laser sintering plant and a ThermoJet®
3-D printer from 3D Systems, eight units for vacuum casting in silicone
moulds, an injection molding machine and a 5-axis
CNC machining center, and is complemented by tooling and investment-casting technologies. Furthermore, VG
Kunststofftechnik develops specialties of its own, such as a diffusion-
based process for the impregnation of prototypes with vivid colors.
|
