Table Of ContentMicroforming Technology
Microforming
Technology
Theory, Simulation, and Practice
Zhengyi Jiang, Jingwei Zhao, and Haibo Xie
University of Wollongong,NSW,Australia
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Foreword
Product miniaturization is a trend for facilitating product usage, enabling
product functions to be implemented in microscale geometries, and aimed at
reducing product weight, volume, cost, and pollution. Increased demands for
miniaturized products have led to rapid technological development of micro-
forming, one of the most popular micromanufacturing processes for
manufacturing very small metallic parts in the submillimeter range. As a
promising micromanufacturing technology, microforming possesses lots of
advantages including high productivity, ease in manufacturing complex
geometries, applicable toawiderangeofmaterials,excellentproductproper-
ties, short cycle, and low cost. From the viewpoint of production engineer-
ing, microforming is considered as an effective process to economically and
preciselymanufacturemicroproductsthatareessential whenbulkproduction
is required.
However, due to the unique characteristic of size effects existed in the
forming ofmetals inmicroscale, research on microforming becomes compre-
hensive because forming technology established in the macro world cannot
be simply miniaturized according to the theory of similarity. Size effects
have significant impact on the forming results, and the quality of formed
parts should be carefully taken into account in the forming of metals in
microscale. As a result, development of technology that is very applicable to
microforming process would be essential and significant for the forming of
high-quality micro products with excellent dimensional tolerance, required
mechanical properties and improved surface quality.
It is my great pleasure to witness this major work of Microforming
Technology: Theory, Simulation and Practice by Prof. Zhengyi Jiang,
Dr. Jingwei Zhao and Dr. Haibo Xie. The global microforming domain faces
major challenges which may be summarized by the common problem of size
effectsinmicroscale, increasingcomplexityofmicro productsand processes,
as well as increasing requirement towards quality. This book is a timely cap-
ture of the state-of-the-art development of microforming technology, cover-
ing theory, simulation and practice of the latest research findings and
achievements in micro cross wedge rolling, micro flexible rolling, micro
ultrathin strip rolling, micro deep drawing, micro hydromechanical deep
drawing, micro bending and micro compression, and has addressed as many
issues as possible involved in microforming to help getting a thorough grasp
xiii
xiv Foreword
of microforming technology by following a step-by-step process. I have
beyond doubt that this contribution will be invaluable to researchers as well
as graduate students inthe field ofmicroforming worldwide.
I sincerely congratulate the authors on having produced this splendid new
scholarly book, and I am very confident it will become a worthy and widely
recognized work. I look forward to this book’s success in proving that
“microforming” represents promising manufacturing technology which has a
bright future and will take a long time for research with the tremendously
increasingdemandfor micro products.
My best wishes to the authors.
Peter Robinson
University ofWollongong, NSW, Australia
October2016
Preface
The booming development of the micro products market has promoted the
rapid development of microtechnology production techniques. The micro-
forming of metals is a cost effective approach to the batch production of
complex, high performancemicro components for adiverse range ofapplica-
tions including medical devices, precision equipment, communication
devices, micro-electromechanical systems and micro fluidics systems.
Microforming differs from the conventional forming technology in terms
of material, processes, tools, and machines and equipment, due to the minia-
turization nature of the whole microforming system. Forming technology
established in the macro world cannot be simply scaled down to the micro
world to make high-quality miniaturized products. This is because it is
impossible to scale down all parameters in the microforming process accord-
ing to the theory of similarity, due to the existence of size effects in micro-
forming processes. A number of unexpected problems in key aspects of
mechanical behavior, tribology, and scatter of material behavior are encoun-
tered. As a result, low quality micro products, with high reject rates may be
manufactured if there is no appropriate strategy available for the design and
controlofmicroformingprocesses. Atpresent,there isstill lackof acompre-
hensive knowledge based on microforming technology. Challenges remain in
the high efficiency manufacturing of high-quality micro products due to the
common problem of microscale size effects, complexity of processes for
making micro products and the ever increasing requirement to improve prod-
uct quality and performance. A book that systematically addresses the com-
plex range of issues involved in microforming is thus very much in demand
to provide readers with a technical documentation that can be used in the
research, development and application of microformingtechnology.
Microforming Technology: Theory, Simulation and Practice is designed
to provide engineers, scientists, academics and graduate students with the
necessary comprehensive knowledge and information on microforming fun-
damentals, microforming theory, simulation models, numerical modeling of
microforming process, equipment and tools design, practical microforming
procedure, and microforming-related supporting system. Emphasis has been
placed on the simulation and practice of seven different types of microform-
ing methods, including micro cross wedge rolling (MCWR), micro flexible
rolling, micro ultrathin strip rolling, micro deep drawing (MDD), micro
xv
xvi Preface
hydromechanicaldeep drawing (MHDD),micro bending andmicro compres-
sion to help readers obtain a thorough grasp of the lasted research develop-
ments in microforming by following a coherent step-to-step process. This
requires an interdisciplinary approach drawing on relevant knowledge from
materials science, mechanical engineering, materials processing engineering,
and materials manufacturing engineering in order to clearly understand the
technical issues involved in this book. We have included as many references
as possible at the end of each chapter to provide readers a way to access rel-
evant information in relation tothe contentspresented.
The book consistsof four parts withatotal of20 chapters.
In Part I Introductory Overview. Chapter 1, Fundamentals of
Microforming states that the fundamentals of microforming including micro-
forming concept and microforming system followed by an introduction on
some typical microforming methods. Chapter 2, Size Effects in
Microforming describes the definition and categories of size effects, and dis-
cusses the problems caused by size effects in microforming. Strategies for
control ofsize effects inmicroforming are alsopresented.
In Part II Theory of Microforming. Chapter 3, Scaling Laws presents the
scaling laws that are applicable to microforming process, including scaling
in geometry, dynamics, mechanics, hydrodynamics, heat transfer, electro-
magnetic force, electrostatic force and electricity. In Chapter 4, Strain
Gradient Plasticity Theory, higher-order strain gradient plasticity theories,
including couple stress theory, phenomenological strain gradient plasticity
theory, and mechanism-based strain gradient plasticity theory that are widely
studied are introduced. A conventional theory of mechanism-based strain
gradient plasticity which does not involve the higher-order stress is also out-
lined. In Chapter 5, Crystal Plasticity Theory, two crystal plasticity (CP) the-
ories including rate dependent and rate independent theories which have
extensiveapplications inmicroformingarepresented.Amethod forsimplify-
ing the rate dependent CP theory is introduced in order to reduce calculation
process. The use of CP theory in combination with finite element method
(FEM) in commercial software ABAQUS is also introduced to illustrate the
application ofCPFEM insimulation.
In Part III Simulation of Microforming Process. In Chapter 6, Simulation
Models in Microforming, simulation models, including surface layer model,
mesoscopic model and Voronoi model, that are popular in the investigation
of microforming process are introduced, and the implementation methods of
Voronoi model in FE software ABAQUS/CAE is also described. Chapter 7,
Simulation of Micro Cross Wedge Rolling introduces the simulation process
of MCWR, using a developed novel material model based on Hall(cid:1)Petch
relationship, surface layer and composited model with grained heterogeneity
in 3D Voronoi tessellation. In Chapter 8, Simulation of Micro Flexible
Rolling, a FE model is established to numerically study the springback in
thickness direction during micro flexible rolling process, where 3D Voronoi
Preface xvii
tessellation has been applied to describe the grain boundary and generation
process of grains in the workpiece. The influences of processing parameters
on surface asperity flattening of workpieces are also numerically studied and
analyzed. Chapter 9, Simulation ofMicro UltrathinStrip Rollingpresents the
simulation of micro ultrathin strip rolling. The rolling deformation character-
istics of foil have been theoretically analyzed and a 2D elastic(cid:1)plastic FE
model is established to investigate the roll bite behavior in cold foil rolling
process where the contact pressure distribution and roll contour in the roll
bite are also discussed. Numerical investigation on the micro asymmetrical
rolling process for ultrathin strip is conducted, and the surface roughness
evolution and the effect of speed ratio in rolling are identified. In
Chapter 10, Simulation of Micro Deep Drawing, a Voronoi blank model is
developed for simulating the MDD process. Real microstructures and
Voronoi structures are applied in microstructural models through image-
based modeling method. Chapter 11, Simulation of Micro Hydromechanical
Deep Drawing presents the simulation of MHDD where the closed and open
lubricant pockets theory has been developed, and different coefficients of
friction are applied in different lubricant pockets. A critical hydraulic pres-
sure value that influences the wrinkling and earing occurrence and tendency
is identified. In Chapter 12, Simulation of Micro Bending, the scatter of
grain mechanical properties is calculated based on the results from micro
tensile tests and the mechanical properties of these grains are assigned to
each Voronoi tessellation to achieve the grain heterogeneity in ABAQUS/
CAE. A new FE model is built with Voronoi tessellation and grain heteroge-
neity to simulate the micro V-bending process. Chapter 13, Simulation of
Micro Compression develops a material constitutive model based on
Hall(cid:1)Petch relationship, composite model, surface layer model and grain
heterogeneity. FE simulation associated with Voronoi tessellation is carried
out to simulate the micro compression process with a consideration of
temperature.
In Part IV Practice of Microforming. Chapter 14, Practice of Micro Cross
Wedge Rolling introduces the design of MCWR machine and the forming
process. The surface wear of forming tool and the surface toughness evolu-
tion are investigated. The influences of springback and friction behavior on
the quality of rolled products are discussed, and the size effects on flow
stress areinvestigated inordertoimprovethemechanical propertiesofmicro
parts. Chapter 15, Practice of Micro Flexible Rolling deals with the flexible
rollingofaluminum alloythinstripintodifferentthicknessratiosandvarious
transition zone lengths, using an innovative micro-rolling mill. The micro-
structure and mechanical properties of the flexibly-rolled strip are systemati-
cally investigated and interpreted. Chapter 16, Practice of Micro Ultrathin
Strip Rolling presents the development of a micro ultrathin strip rolling
apparatus for manufacturing ultrathin foils with high accuracy. The rolling
limit is analyzed, and the lubrication behavior of foil rolling is analyzed
xviii Preface
based on the feature size effects of rolled material and lubricating status. In
Chapter 17, Practice of Micro Deep Drawing, MDD practice is described,
and the influences of grain size, foil thickness, punch size, and initial gap on
the punch force and displacement, friction and product’s quality are dis-
cussed. Chapter 18, Practice of Micro Hydromechanical Deep Drawing
developsaMHDDapparatusformanufacturing amicro-complex-shape com-
ponent. The developed MHDD system can prevent wrinkling by applying an
appropriate constant gap and the generated counter pressure. An appropriate
counter pressure applied in MHDD can reduce the frictional drawing force
and improve the forming limit and dimensions. Chapter 19, Practice of
Micro Bending introduces the practice of micro bending and investigates the
grain size effects on texture evolution ofannealed and micro V-bended phos-
phor bronze foil with various thickness/average grain size ratios. In
Chapter 20, Practice of Micro Compression, the practice of micro
compression ofpure copperat both room andelevatedtemperatures usingthe
desk-top servo-press machine is introduced. Micro compression tests with
assistance of laser heating are conducted to investigate the influences of
temperature in micro compression. The effects of feature size on the material
response inmicro compression are also discussed.
This book is designed to provide a comprehensive overview of the theo-
retical, numerical and practical issues involved in developing microforming
technology for those who are developing and producing metallic micro pro-
ducts and their forming technologies worldwide. We would like to thank all
the people including academic staff, higher degree research students and
technicians who have made contributions to thisbook.
ZhengyiJiang, Jingwei Zhao, andHaiboXie
University ofWollongong, NSW, Australia
October2016
Chapter 1
Fundamentals of Microforming
1.1 MICROFORMING CONCEPT
Product miniaturization is a global trend for facilitating product usage,
enabling product functions to be implemented in microscale geometries, and
aimed at reducing product weight, volume, cost, and pollution. Driven by
ongoing miniaturization in diverse areas including medical devices, precision
equipment, communication devices, micro-electromechanical systems
(MEMS), and micro fluidics systems (MFS), the demands for micro pro-
ducts, as shown in Fig. 1.1, have been tremendously increased. Such a trend
requires development of efficient theories and technologies for manufactur-
ing high-quality micro products with excellent dimensional tolerances,
required mechanical properties and improved surface quality.
For manufacturing micro products, the conventional metal forming
technology has been scaled down to microscale due to its process simplicity,
high production capability, minimized or zero material waste, and near-
net-shape production. Microforming, in the context of metal forming, is
defined as the forming of parts or geometrical features with at least two
dimensions in the submillimeter range by using mechanically based proces-
sing technologies. Products of this size are commonly used in electronics
production and other fields including the medical sector, MEMS, and MFS.
As a promising micromanufacturing technology, microforming has a lot of
advantages including high productivity, ease in manufacturing complex
geometries, applicable to a wide range of materials and excellent product
properties, as comparedto other processing methods such as turning, milling,
andlithographictechnologies.Fromtheviewpointofproductionengineering,
microforming is considered as an effective process to economically and
preciselymanufacturemicroproductsthatareessential whenbulkproduction
is required. With the booming development of micro products market, more
and more energy and resource will flow to the field of microforming, and
the manufacturingofmicro products willabsorb more attention.
Microforming can be regarded as a forming technology processed in the
so-called microfactory. A microfactory is a downsized manufacturing
system which represents an approach to manufacture miniaturized products
with less space and operational costs, and as well as reduced consumption
MicroformingTechnology.DOI:http://dx.doi.org/10.1016/B978-0-12-811212-0.00001-7
Copyright©2017ElsevierInc.Allrightsreserved. 3
