Square Foot Manufacturing: Event-Driven Manufacturing by Means of Multifunctional Work Spaces

Abstract

This paper presents Square Foot Manufacturing (SFM) as new approach to realize changeability in the manufacturing process. SFM encompasses a down scaled manufacturing plant for machining small parts; it has reconfigurable structure and holds micro machining units (MMU) that are reduced in function and flexible in adjustment. Because they are sufficiently small it is easy to move these machine tools between individual operation steps and it is feasible to use more than one of them simultaneously machining one work piece.

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1 Copyright © 2008 by ASME
Proceedings of IMECE2008
2008 ASME International Mechanical Engineering Congress and Exposition
November 2-6, 2008, Boston, Massachusetts, USA
IMECE2008-66776
SQUARE FOOT MANUFACTURING - EVENT-DRIVEN MANUFACTURING BY
MEANS OF MULTIFUNCTIONAL WORK SPACES
Tobias Redlich
Institute of Production Engineering
Helmut-Schmidt-University / University of the
Federal Armed Forces Hamburg,
22043 Hamburg, Germany
tobias.redlich@hsu-hh.de
Jens P. Wulfsberg
Institute of Production Engineering
Helmut-Schmidt-University / University of the
Federal Armed Forces Hamburg,
22043 Hamburg, Germany
jens.wulfsberg@hsu-hh.de
Jörg Lehmann
Institute of Production Engineering
Helmut-Schmidt-University / University of the
Federal Armed Forces Hamburg,
22043 Hamburg, Germany
Franz-Ludwig Bruhns
Institute of Production Engineering
Helmut-Schmidt-University / University of the
Federal Armed Forces Hamburg,
22043 Hamburg, Germany
ABSTRACT
This paper presents SQUARE FOOT MANUFACTURING
(SFM) as new approach to realize changeability in the
manufacturing process. SFM encompasses a down scaled
manufacturing plant for machining small parts; it has
reconfigurable structure and holds micro machining units
(MMU) that are reduced in function and flexible in adjustment.
Because they are sufficiently small it is easy to move these
machine tools between individual operation steps and it is
feasible to use more than one of them simultaneously machining
one work piece.
INTRODUCTION
The actual development of discontinuous customer
demands in many fields of industry causes the need of
customized manufacturing approaches that essentially require
flexible manufacturing systems. But flexibility is a limited
concept to challenge this task. Consequently different scientific
discourses address the implementation of changeability within
the whole production process, because it is more comprehensive
than flexibility [1,2,3].
Furthermore there are several other requirements for
manufacturing systems to achieve a competitive position such
as cost effectiveness and the need of considering environmental
aspects. The following contribution presents an approach for the
practical implementation of a manufacturing system for small
parts developed by the Institute of Production Engineering
fulfilling these prescribed requirements.
CHANGEABILITY OF MANUFACTURING SYSTEMS
Generally the development of production technology aims
on improving the system characteristic "flexibility" to meet
customer demand despite its volatility [4]. Basically, the
increasing flexibility then comes along with a decline in
productivity.
Hence, one can find manufacturing systems with high
productivity and low flexibility such as transfer lines on the one
hand and for instance general purpose machines with low
productivity but high flexibility on the other hand (see Fig. 1).
Fig. 1: Classification of manufacturing systems
by flexibility and productivity (cf. [5])
IMECE2008-66776
Proceedings of IMECE2008
2008 ASME International Mechanical Engineering Congress and Exposition
October 31-November 6, 2008, Boston, Massachusetts, USA

2 Copyright © 2008 by ASME
However, even with greater flexibility (e.g. through put)
only a limited flexibility corridor "on the supply side" is
available. A break out of this corridor caused by the
discontinuity of demand, leads to opportunity costs for the
unsatisfied demand, or even bad investments in the worst case
(see Fig. 2, left). At this point there is a need for reconsideration
of the current demands on the general system characteristics of
manufacturing systems. While flexibility plays a vital but
secondary role, the umbrella term changeability offers a holistic
view on characteristics of manufacturing systems. Changeability
means pre-planned solution spaces, that offer the opportunity to
respond adequately to the changing needs (see Fig. 2, right).
Fig. 2: Difference between flexibility and changeability
From the angle of an object oriented notation changeability
could be considered a supertype class for characteristics of
manufacturing systems, which encompasses the subtypes
mutability, flexibility and reconfigurability (see Fig. 3).
Fig. 3: Object oriented view on changeability
and sub classes (cf. [6])
All attributes of the supertype changeability
(“standardization”, “mobility”, “reducibility and expandability”,
“modularity” and “capability of integration”) are passed to the
three subtypes. Furthermore the objects mutability and
reconfigurability cover additional characteristics that are not
covered by the class flexibility. “Generality in function and use”
and "networking ability" are assigned to the class mutability;
“structurability”, “combinability” and “reusability” belong to
the class reconfigurability. While the class flexibility is denoted
by the attributes “rapidity”, “individualization”, “reliability”
and “synchronous operation ability”.
For a broader view on the development of manufacturing
systems the authors consequently consider an increased
changeability more appropriate as a mere extension of
flexibility.
SQUARE FOOT MANUFACTURING
General concept
This paper presents SQUARE FOOT MANUFACTURING
(SFM) as new approach to realize changeability in the
manufacturing process [7,8]. SFM encompasses a down scaled
manufacturing plant for fabrication of small parts. It has a
reconfigurable structure and consists of micro machining units
that are reduced in function and flexible in adjustment. Because
they are sufficiently small it is easy to move these machine tools
between individual operation steps. Since they are miniaturized
and mobile it is feasible to use them in a multifunctional
(cascading) work space (see Fig. 4).
Fig. 4: SQUARE FOOT MANUFACTURING (cf. [7])
Self-adjusting clamping- and reference-preservation system
SFM encompasses a carrier system concept, allowing
repeatable clamping of work piece and MMU carriers [9].
Therefore the carrier’s position and orientation will be defined
through the plane base plate at the bottom side and three
positioning pins at two side walls (see Fig. 5). The cylindrical
positioning pins are arranged as an obtuse angled triangle at the
base plate. The carrier itself has the shape of a quadratic prism;
on its surface it holds the fixed MMU or a precision clamping
element for fixing the work piece. By rotating a work piece
carrier the work piece will be rotated too, while the reference of
the object will be preserved. Occurring deviations are
repeatable and result from the manufacturing tolerance of the
carrier and the position accuracy of the clamping element.

3 Copyright © 2008 by ASME
Fig. 5: Schematic view of the self-adjusting clamping- and
reference-preservation system
The clamping forces could be applied through ordinary
mechanical or magnetic clamping devices [10].
Because the reference between carrier and work piece or
carrier and MMU maintain during the whole manufacturing
process, it is easy to change work the piece’s and MMU’s
position and orientation. Even after change-over to another base
plate the position of work piece or MMU can be assumed as
known. The carrier’s reference data could be stored on RFID-
devices so the connected base plate systems could read out the
carrier specific data.
The characterized clamping and reference preservation
system also allows an automated equipment of the base plate
with work pieces and MMUs. Even industrial robots with low
positioning accuracy could carry out such handling tasks,
because the positioning pins could also act as electric contacts
(limit switches). While positioning a carrier on the base plate an
electric circuit will be closed if the carrier contacts to both the
base plate and a pin. The information that all three circuits are
closed means that the carrier is in the right position and needs
no further movement.
Machining operations are allowed as long as the carrier is
in the right position therefore all three circuits have to be
closed. Once the carrier moves, the circuit opens and the system
would stop operations to avoid damages because of an
unintentional movement of the carrier.
MULTIFUNCTIONAL WORK SPACES AND JOB WORK
SPACES
Concept of multifunctional work spaces
SQUARE FOOT MANUFACTURING offers a mounting plate
(base plate) with MMU and work piece carriers featured with a
self adjusting clamping system. As a result, all system elements
are easily reconfigurable. Given that, machine tools can be
replaced or removed easily and a multifunctional work space
can be realized through several machine tools processing on one
work piece simultaneously [11].
Concerning changeability this depicts the logical
advancement on the idea of multiple-technology work spaces
(see Fig. 6).
Fig. 6: Changeability of manufacturing systems
Regardless of how the multifunctional work space will be
realized, whether by several technologies in the work space of a
conventional machine tool or by mobile miniaturized machine
tools, there is a new aspect of production planning and control:
The overlap of work spaces of individual technologies.
There are several ways in which individual work spaces
could be combined. To describe the possible combination forms
the basics of the quantity theory may be used.
For instance a single coordinate may be element of several
work spaces (see Fig. 7a), within the meaning of quantity theory
this presents an intersection. If a work space is completely
surrounded by another (see Fig. 7b), the enclosed work space
represents a subset of the surrounding work space. In the
extreme case, if both work spaces contain only identical
elements, this means that the two quantities are equal. The other
extreme case would be the empty set; i.e. the work spaces do
not overlap and thus have no common elements (see Figure 7c).
Since the number of combined technologies within a
multifunctional work space may be considerably larger, the
overlapping of all existing individual work spaces could be
much more complex. So in addition to simple overlapping,
there is the possibility of cascading, a special form of
interlacing of several work spaces (see Fig. 7d)
Fig. 7: Characteristics of multifunctional work spaces

4 Copyright © 2008 by ASME
Impact on production planning and control
The impact on the planning of production processes by the
SFM-approach of multifunctional work spaces becomes
obvious considering that for manufacturing of a work piece not
only the adopted technology but also the individual machine
tools and their positions on the base plate have to be
predetermined. The number of alternative arrangements and the
resulting large number of possible process sequences is an
additional degree of freedom compared to the conventional
planning.
The base plate layout has to be configured work piece
specifically. For a flexible usage of the base, the positions of the
pins are not fixed, but pre-planned. This means the base plate
has to be prepared with boreholes in a grid pattern.
The SFM is a fully reconfigurable manufacturing facility.
In a repetitive production, the configuration for the required
machinery is easy to set up.
Job Work Spaces
Considering that multiple machines can operate
simultaneously in a multifunctional work space as given in
SQUARE FOOT MANUFACTURING, additional planning tasks
arise. As there are optimizing the manufacturing processes in
terms of the space interlocking and avoiding collisions.
But therefore the traditional consideration of work spaces
is no longer appropriate, as several MMUs process
simultaneously on one work piece and their work spaces thus
overlap. In fact it is more appropriate to consider the smaller
and more specific “Job Work Spaces” (JWS), which can be
defined for a particular machine tool operation step (see Fig. 8).
Fig. 8: Model work piece and Job Work Spaces (JWS)
The cascading of work spaces enables to temporal
aggregate various operation steps. Hence the manufacturing
process in the multifunctional work spaces can be depicted as a
sequence of manufacturing events in defined JWSs. For the
theoretical description of this problem it is suitable to use e.g.
the abstract machine theory. Using such a method, existing
problems of coordination such as scheduling and collision
avoidance can be resolved.
After preliminary research the additional degree of freedom
in the design of manufacturing processes through multi-
functional work spaces concluded time savings for the
manufacturing process (see Fig. 9).
Fig. 9: Impact on production planning and control
The great advantage here is, that with increasing
changeability of a manufacturing system, the impact of the
scheduling dilemma mitigates. With multifunctional work
spaces in general and with the concept of SFM in particular a
higher degree of the changeability of manufacturing is of
distance.
ECONOMICAL AND ENVIRONMENTAL ISSUES
While even for the manufacturing of micro parts ordinary
huge machine tools are used, manufacturing operations of
simple micro geometries for micro and macro parts often can be
carried out with one powered axis and do not need a complex
machine tool. Manufacturing accuracy can be improved and
process energies can be reduced by reducing and
predetermining machine tool characteristics such as work space,
spindle power or feed drives.
Considering that there is an increasing need for
miniaturized and micro parts there are obviously positive
environmental, economical and performance effects in using
miniaturized and functionally reduced machines and tools:
• Environmental effects
o Cutting energy, material, waste
o Easy contamination control
o Decrease of floor space requirements

5 Copyright © 2008 by ASME
• Economical effects
o short ramp up time
o Light investment
o Reduced energy costs
o Reduced running costs
o Flexible allocation (ubiquitous manufacturing)
• Performance effects
o Precision: static and dynamic stiffness, thermal
behavior, tolerances
o Speed / acceleration: reduced inertia
CONCLUSION
Finally the Square Foot Manufacturing characterizes a
concept that meets the demands on changeable manufacturing
systems:
The standardized self-adjusting and clamping-reference-
preservation system enables flexibility in positioning and
orientating of MMUs and work pieces. With such a system
manufacturing processes can be referred to as a scalable fixed-
site production, whereas the modularity of the components
promotes expandability and reducibility. But there’s not only
an internal option of expansion and reduction. Also the
integration of SFM-Systems into superior process chains is
practicable. To increasing the throughput level, it will be easy to
interlocking a number of "Square Foot Factories”.
Further, the proposed approach of multifunctional work
spaces leads to an additional degree of freedom in the
manufacturing planning, and the synchronous operation
ability and rapidity arise from the ability of processing more
than one technology simultaneously.
The use of micro machining units that are specialized to
accomplish standard operations with their reduced complexity
and functionality, contributes to generality of function and
use. In addition, SFM-mounting plates that can be configured
individually for different work pieces and machining tasks are
an indicator for the mutability. The work piece specific
structurability of the base plate and its reusability for several
operations also embodies system reconfigurability.
Eventually the small size of the overall system and its
components reasons high mobility.
Besides changeability demands the SQUARE FOOT
MANUFACTURING represents a highly effective concept
concerning economical and environmental aspects.
REFERENCES
[1] Reinhart, G. and Hirschberg, A., 2000, “Changeability in
Production Systems”, Proceedings of the 33rd CIRP
International Seminar on Manufacturing Systems, pp. 263-267.
[2] ElMaraghy, H.A., 2005, “Flexible and reconfigurable
manufacturing systems paradigms”, International Journal of
Flexible Manufacturing Systems, Vol.17 (4), pp. 261-276.
[3] Wiendahl, H.-P. et al., 2007, „Changeable Manufacturing –
Classification, Design and Operation“, Annals of the CIRP Vol.
56/2/2007, pp. 783-809.
[4] Eversheim, W., Schuh, G., Fricker, I., 2004, „Autonome
Produktionszellen, Ein Weg zur Emanzipation der Produktion“,
in Klocke, F. et al.: Autonome Produktion. Berlin: Springer, pp.
535-546.
[5] Freudenberg, R; Hermes, R.; Pfeifer, T.; Schmitt, R., 2006,
„Autonome Produktionszelle in Eversheim, W.; Pfeifer, T.;
Weck, M. (edit.), „100 Jahre Produktionstechnik“, Springer,
New York, pp. 671-684.
[6] Heger, C.L., 2007, „Bewertung der Wandlungsfähigkeit von
Fabrikobjekten“ Gottfried Wilhelm Leibnitz Universität
Hannover (Dissertation).
[7] Wulfsberg, J.P.; Redlich, T.; Lehmann, J.; Bruhns, F.-L.,
2008, „Square Foot Manufacturing - Ein wandlungsfähiges
Produktionssystem für die Fertigung von Mikroteilen“,
Werkstattstechnik online, Jg. 5/98 (2008), pp. 337-344.
[8] Lehmann, J.; Wulfsberg, J.P., 2005, „Angepasste
Fertigungsverfahren für skalierte Strukturen“, Proceedings 50.
Internationales Wissenschaftliches Kolloquium - Mechanical
Engineering from Macro to Nano, 2005, Ilmenau, pp. 321-322.
[9] Wulfsberg, J.P.; Lehmann, J.; Bruhns, F.–L., 2004,
„Selbstjustierendes koordinatentreues Spannsystem für die
Mikroproduktion“, Deutsches Patent– und Markenamt,
München, 2004, Aktenzeichen 10 2004 059 456.2.
[10] Wulfsberg, J.P.; Lehmann, J., 2003, „Spanntechnik für die
Mikrofertigung“, wt Werkstattstechnik, 3/93 (2003), pp. 146-
149.
[11] Wulfsberg, J.P.; Lehmann, J.; Bruhns, F.–L., 2005,
„Dynamisch-starre Kopplung von hybriden
Bearbeitungsräumen bei Desktop Manufacturing-Maschinen“
Deutsches Patent– und Markenamt, München, 2005,
Aktenzeichen 10 2005 024 693.1