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Journal of Materials Processing Technology 212 (2012) 2238– 2246

Contents lists available at SciVerse ScienceDirect

Journal of Materials Processing Technology

journa l h omepa g e: www.elsev ier .com/ locate / jmatprotec

evelopment of a micro-forming system for micro-punching process oficro-hole arrays in brass foil

ie Xua,c, Bin Guoa,b, Debin Shana,b,∗, Chunju Wanga,b, Juan Li c, Yanwu Liuc, Dongsheng Quc

Key Laboratory of Micro-Systems and Micro-Structures Manufacturing, Ministry of Education, Harbin Institute of Technology, Harbin 150080, ChinaSchool of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, ChinaSchool of Mechatronics and Engineering, Harbin Institute of Technology, Harbin 150001, China

r t i c l e i n f o

rticle history:eceived 10 December 2011eceived in revised form 16 June 2012ccepted 23 June 2012vailable online xxx

eywords:icro-forming systemicro-punching

a b s t r a c t

Micro-forming technology poses much higher demands on positioning accuracy, velocity and mass pro-duction, and the common forming machines cannot satisfy these requirements using traditional drivemethods. Micro-forming equipment using novel drive methods with high speed and high precision hasbecome an important research field for industrial application. In the paper, a novel drive mechanism wasdesigned with a symmetric distributed double linear motors and a micro-forming system was developedwith micro-punching tools and automatic feeding apparatus for metal foil. The servo control systemof this micro-forming system was designed using SIMOTION D445, and a parallel control model wasadopted with a single motor module to solve the synchronous control problems of double linear motors.

eedingicro-hole arrays

rass foil

Micro-punching process of brass foil was studied with the micro-forming system, and micro-holes of600 �m, 300 �m and 150 �m in diameter were manufactured with high dimensional accuracy. An arrayof 50 × 4 micro-holes, each 600 �m in diameter, was manufactured using an automatic feeding apparatusguided by a microscopic visualization system for assisted localization. The results indicate that the micro-forming system with high-accuracy and high-speed is suitable for the mass production of micro-scaleparts.

. Introduction

With the development of micro-electro-mechanical systemsMEMS), micro-forming, defined to be the production of parts andtructures with at least two dimensions in the sub-millimeter rangeGeiger et al., 2001), becomes an important technology. Reviews of

icro-forming by Engel and Eckstein (2002) and Vollertsen et al.2006) highlight the key technologies and indicate that micro-orming is a promising way to fabricate micro-parts because ofts significant advantages in mass production, providing controlleduality and low cost. Some miniaturization/micro parts have beenabricated with micro-forming, such as micro gears (Shan et al.,009), micro heads (Chan and Fu, 2012), micro cups (Hu et al.,

012) and micro holes (Rhim et al., 2005). However, micro-formingechnology is still at laboratory research status and few industrial

icro-forming process chains have been realized due to the size

∗ Corresponding author at: Key Laboratory of Micro-Systems and Micro-tructures Manufacturing, Ministry of Education, Harbin Institute of Technology,# Yikuang Street, Harbin, Heilongjiang Province, 150080, China.el.: +86 451 86402775; fax: +86 451 86418732.

E-mail addresses: xjhit@hit.edu.cn (J. Xu), bguo@hit.edu.cn (B. Guo),handb@hit.edu.cn (D. Shan).

924-0136/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.jmatprotec.2012.06.020

© 2012 Elsevier B.V. All rights reserved.

effects in micro-forming (Vollertsen et al., 2009), including microbulk forming (Wang et al., 2012) and micro sheet metal forming(Xu et al., 2012), when the component feature sizes are reducedto a few hundreds or tens of microns. Machines, forming-tools andhandling of micro-parts are critical elements which significantlydetermine industrial applications of micro-forming.

During the last 15 years, the development of miniature formingequipment has attracted considerable interest from both researchorganizations and industries (Qin et al., 2010). As referred in thekeynote paper on micro-forming (Geiger et al., 2001), there arethree strategies to design tools and machine systems for micro-forming. The first category machines like Omega F1 series fromYamada Dobby are conventional mechanical presses with highspeed which are equipped with high precision guides and specialfeatures to increase the precision (Yamada Dobby, 2009). How-ever, the stoke height is limited to 20 mm, the force cannot becontrolled freely during operation, and stroke control is also notpossible. A micro superplastic forward-extrusion apparatus devel-oped by Gunma University by scaling down from conventionallength scale belongs to the second category (Saotome and Iwazaki,

2001). Another prototype machines have been built using lineardriver for micro forming processes. For example, a micro-formingapparatus was developed by Wang et al. (2007) with a piezo-electric actuator which can be controlled by force or by position.

J. Xu et al. / Journal of Materials Processing Technology 212 (2012) 2238– 2246 2239

emes

HtaAw4lm(hp

n(2mpomdmderebfomhbmtof

mavibwha

Fig. 1. Drive mechanism sch

owever, the PZT output stroke of less than 1 mm will be restrictedo only special application field. The principle of using linear motorss a vertical press drive was patented by the firm Schuler (1999).

linear-motor-driven micro-forming press was firstly developedith a stroke rate of 1200 strokes/min and a maximum force of

0 kN, which can be connected to industrial production lines foronger micro-forming process chains (Schepp, 2001). A versatile

icro-forming press was developed by Niehoff and Vollertsen2008) using four linear motors with a two-axis design, which canelp to improve the forming quality of the micro-deep-drawingrocess.

In addition, some special equipment has been developed withew strategies and approaches for the micro tools fabricationBrinksmeier et al., 2008), feeding and machinery design (Qin,006). For example, Joo et al. (2005) designed a micro-punchingachine with tool alignment, which can meet the requirements of

rocess accuracy for 25-�m-sized holes. Chern et al. (2006) devel-ped a micro-punching machine with vibration electrical dischargeachining (EDM) and mass punching of micro-holes of 200 �m in

iameter was demonstrated. Broomfield et al. (2009) developed aicro-hole, multi-point punching system using a micro-punch and

ie fabricated by Micro-EDM, and micro-holes of 50 �m in diam-ter were manufactured with a smooth sheared surface and highepeatability. To satisfy the requirements of mass-production, Yangt al. (2009) proposed a new micro-forming and in-process assem-ly technology of a unit part with three components, which wasabricated in a precise progressive die. Razali et al. (2009) devel-ped a new, ultra-high precision feeder with a linear actuationethod for micro-sheet forming application. These new strategies

ave promoted the developments of micro-forming technology,ut the lacks of a micro-stamping press, feeding and processes inicro-forming are not of sufficient precision and reliability for high

hroughput micro-manufacturing applications. Therefore, devel-pment of new micro-forming system equipped with tooling andeeding sections becomes an important research issue.

In this paper, a micro-forming system driven by double linearotors is developed and equipped with a micro-punching tool and

precision automatic feeding apparatus guided by a microscopicisualization for assisted location. Micro-punching processes arenvestigated with the micro-forming system, and the optimum

lanking parameters are obtained. Based on the results, micro holesith minimum diameter of 150 �m and arrays of 50 × 4 micro-oles were successfully fabricated with high dimensional accuracynd good cross-section quality.

with double linear motors.

2. Development of a micro-forming system with high speedand high precision

2.1. Drive mechanism design for the micro-forming system

The micro-forming system is intended to solve the problemsof micro-punching processes for micro-holes of 1 mm to 50 �m indiameter. Therefore, a novel micro-forming system with high speedand high precision becomes an important issue. The electric lin-ear motor is a new drive mode without an additional transmissionmechanism, which has advantages of high speed, high acceleration,high precision and free force and motion control. Thus, the drivemode of linear motor becomes a perfect choice for micro-formingmachine, as an alternative to conventional rotary machineries.

To decrease the effect of the attraction force between the pri-mary and secondary sections in the linear motor, a symmetricdistribution type of drive mechanisms were designed with dou-ble linear motors as shown in Fig. 1. The two linear motors wereinstalled with opposite orientations. The secondary sections arechosen as mover connected with slider and the primary sections arechosen as stator connected with press frame. The attraction forcescancelled each other out because of the symmetrical distributionof the double linear motors. As a result, only 25% of the attractionforces can occur in the worst case, which also helps improve thelife-span of linear guides.

The secondary section is connected to both sides of the sliderthrough the middle via holes. Thus, a tensile stress will be gener-ated in the slider due to the attraction force between the primarysection and secondary section of the double linear motors. How-ever, the slide should not be subjected to tensile forces because thetensile strength of granite is very low. To improve the lifespan ofthe slider, steel bushings were used to connect the magnetic boardswith the slider, as shown in Fig. 1(b). This arrangement transfersthe tensile force generated by the attraction force from the granitestone slider to the steel bushing. Meanwhile, a compressive stresscan be generated by adjusting the pre-load tension force of thescrews, which can protect the granite by changing the stress stateof the slider.

The components of drive mechanism are composed of primarysections and secondary sections of double linear motors, guider

rail and carriage, brakes and hard stone slider as shown in Fig. 2. Toguarantee the high precision of micro-forming machine, four pre-cision linear guiders were used as the guidance mode. A naturalgranite stone was used for the press slider, which had a planarity

2240 J. Xu et al. / Journal of Materials Processing Technology 212 (2012) 2238– 2246

ogmatoabTp

alpUwmmoafm1t

Table 1Technical parameters of the linear motor.

Type Maximum Maximum Attraction Cooling

control software (Siemens Co., Germany). The SIMOTION D445 unit

Fig. 2. Components of the drive mechanism.

f 1 �m in length. The natural stone free of any residual stressesuarantees absolute stabilization in shape and maintains align-ent. Furthermore, the granite stone with the similar density to

luminum makes the slider light in weight, and also can reducehermal distortion because the thermal expansion coefficient isnly one-third that of aluminum. In addition, the granite material,s a magnetic vane, can reduce the mutual interference of the dou-le linear motors and improve the adverse influence of end effects.herefore, a special granite stone which can improve the dynamicroperties is suitable for the slider of a micro-forming system.

As mentioned above, the drive force is a decisive factor in guar-nteeing high speed and high acceleration. To choose a suitableinear motor, a dynamic analysis of the micro-forming system waserformed using the ADAMS software (Mechanical Dynamics Inc.,SA). Two types of trajectories, each with an S-type velocity curve,ere developed. In the first trajectory, the press operates with aaximum velocity of 1 m/s, and in the second trajectory, the pressoves with a maximum stroke rate of 1000 stroke/min and 2 mm

f stroke length. The drive force and acceleration were calculatednd are shown in Fig. 3. The results show that maximum driveorces of 6600 N and 6620 N must be supplied by the double linear

otors when the press is operating with the maximum velocity of m/s and the maximum stroke rate of 1200 stroke/min, respec-ively. Therefore, the maximum drive force of the double linear

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35-4

-2

0

2

4

6

8

-40

-20

0

20

40

60

80

Driving fo rce

Acc

eler

atio

n (

m/s

2)

Dri

vin

g f

orc

e (K

N)

Time (s)

Accele ration

(a) Maximum velocity

Fig. 3. Drive force of the motor w

force (N) velocity (m/s) force (kN) methods

1FN3450-2N 4400 4.5 12.2 Water

motors should be at least 8000 N to account for the influence offriction.

On the basis of the dynamic simulation results, the 1FN3450linear motor of the Siemens Company was chosen, and the technicalparameters are shown in Table 1. The calculations show that themaximum acceleration of the micro-forming system is more than6 g, which can satisfy the requirements of a micro-forming process.

2.2. Structure design and analysis of the micro-forming system

The entire structures of the micro-forming system, includingthe drive mechanism, the press frame and base, the upper plate,the connection plate and the buffer, were designed as shown inFig. 4. The primary section is connected to the press frame bythe connection board, and the secondary section is connecteddirectly to the slider. Braking and buffering of the press are impor-tant factors that must be considered to avoid damaging the linearmotors and the stone slider. The micro-forming press was fixed ona vibration-isolation platform that is anchored to the ground byshock absorbers to reduce vibration. The press frame was a weldedstructure with reinforcement plates included to improve the framestiffness. The worktable was fixed to the press frame not only forthe installation of micro-forming tools but also to provide stiffnessto the micro-forming system. The height of the worktable can beadjusted to three positions, approximately 100 mm apart, 200 mm,300 mm or 400 mm in height. The width of the installation spaceis 450 mm, which can accommodate various micro-forming pro-cesses.

2.3. Servo control system design for the micro-forming pressusing SIMOTION

The servo control system of the micro-forming system, whichwas designed with SIMOTION D445 (Siemens Co., Germany), isshown in Fig. 5 and consists of an SIMOTION D445 Control Unit,a single motor module, a power module, a rectifier module, a step-per motor control module, an I/O device and a PC running the Scout

is the core section and handles execution of all of the control com-mands of the servo control system. The motion controls for thelinear motor and the stepper motor driving the XY feeding plate

0.00 0.01 0.02 0.03 0.04 0.05 0.06-8

-6

-4

-2

0

2

4

6

8

-40

-30

-20

-10

0

10

20

30

40

Driving force

Acc

eler

atio

n (

m/s

2)

Dri

vin

g f

orc

e (K

N)

Time (s)

Acce lebra tion

(b) Maximum strok e rate

ith the typical trajectory.

J. Xu et al. / Journal of Materials Processing Technology 212 (2012) 2238– 2246 2241

f the

aI

mstdtttiardiwmm

Fig. 4. Construction o

re performed by the D445 with the single motor module and theM174 module, respectively.

To solve the synchronous control problems of double linearotors, a parallel control model was adopted and conducted by a

ingle motor module which can transfer the command informationo both linear motors at the same time. The relative positions of theouble linear motors are very important for synchronous opera-ion since the output properties of the linear motors depend on theransition angle of the three-phase alternating current. Accordingo the parameters of the linear motors, the difference in the revers-ng angle between the two linear motors must be less than 10◦ tovoid interaction of the outputs of the double linear motors. Theeversing angles of the two linear motors were measured at fiveifferent positions after installation, as shown in Fig. 6. The results

ndicate that the difference in the reversing angle is less than 3◦,

hich can satisfy the installation requirements of the double linearotors. The position and velocity signals of the linear motors wereeasured with a grating scale fixed on the slider. Data acquisition

Fig. 5. Servo control system of the micro-fo

micro-forming press.

and on-line monitoring were performed with the human–machineinterface WinCC using OPC technology.

The performances of micro-forming system were evaluated bymeasuring the velocity and accuracy. The maximum velocity ofthe micro-forming system was tested, and it was determined that1.1 m/s can be achieved at a maximum acceleration of 5 g anda stroke height of 200 mm. A minimum velocity of 5 �m/s canbe achieved with sub-micron positioning accuracy. The repetitivepositioning accuracy of the micro-forming system was evalu-ated with an optical position-measurement system, which useda laser interferometry system (SP500, SIOS) based on a He–Nelaser with a wavelength of 632.8 nm. Five different stroke val-ues (s = 1 mm, 2 mm, 4 mm, 10 mm, 20 mm) were chosen, anda velocity of 100 mm/s and an acceleration of 1 g were used.Each test was performed 30 times, and the real-time data col-

lection was conducted with the rapid data-acquisition system inthe servo control program. The positioning repeatability accuracywas calculated according to the ISO standard 230-2: 2006. The

rming system with SIMOTION D445.

2242 J. Xu et al. / Journal of Materials Processing Technology 212 (2012) 2238– 2246

0 1 2 3 4 5 6

-156

-155

-154

-153

-152

-151

-150

3o

Rev

ersi

ng a

ngle

a /

o

Number

the first linear moto r

the se cond line ar moto r

Fig. 6. Measurement results of the reversing angle.

Table 2Performance indices of the micro-forming system.

Performance index Value Performance index Value

Maximum force (N) 8800 Maximum stroke (mm) 220Maximum velocity (m/s) 1.1 Position resolution (�m) 0.12Minimum velocity (�m/s) 5 Repetitive accuracy (�m) 0.25

pwfslrr

essirwh

F

osition resolution of the micro-forming system was measuredith the same method. The performance indices of the micro-

orming system were obtained as shown in Table 2. The resultshow that the maximum force, maximum velocity, position reso-ution and repeatability are 8800 N, 1.1 m/s, 0.12 �m and 0.25 �m,espectively, which can satisfy the high speed and high precisionequirements for the micro-forming system.

The maximum stroke rate is a significant factor in the economicfficiency of the micro-forming system, which depends on thetroke height and acceleration. The maximum stroke rate was mea-ured at an acceleration of 1 g and a velocity of 100 mm/s, as shownn Fig. 7. The results show that more than 1000 strokes/min can beeached at a stroke of 1 mm. The maximum stroke rate decreasesith increasing stroke height until it reaches 200 spm at a strokeeight of 10 mm.

0 2 4 6 8 10 120

200

400

600

800

1000

1200

0

50

100

150

200

250

300

Str

ok

e ti

me

(ms)

Stroke frequency

Str

ok

e fr

equen

cy (

spm

)

Stroke high t (mm)

Str oke ti me

Accelerati on= 1g

Velocit y=100mm/s

ig. 7. Curves of stroke frequency vs. stroke height of the micro-forming system.

Fig. 8. Automatic feeding mechanism with microscopic visualization for assistedlocalization.

2.4. An automatic feeding apparatus with microscopicvisualization for assisted localization

Automatic feeding of metal foil with high speed and high accu-racy is a challenge in micro-punching processes for fabricatingmicro-hole arrays. A pneumatic feeder or a servo feeder with spe-cial attachments for guiding metal strips can feed metal foil with athickness of between 20 �m and 100 �m. A feed rate of 1000 spmand a feeding accuracy of 10–30 �m can be achieved, which cansatisfy the requirements of micro-forming (Razali et al., 2009).However, the positioning accuracy of the metal foil feeder cannotsatisfy the demands of micro-punching processes for micro-holearrays using only traditional mechanical positioning methods withpilot pins. In addition, the position of the first punched hole isdifficult to locate because of the zero error of the servo feeder sys-tem. To solve this problem and improve the positioning accuracyof the feeder, an automatic feeding apparatus with microscopicvisualization to assist in localization was designed for manufac-turing micro-hole arrays. The apparatus is composed of an XYmoving plate, a feeding arm and a high-resolution CCD, as shown inFig. 8. Stepper motors were chosen as the feeder driver with high-accuracy. The XY moving plate can be precisely controlled by thestepper motor control module in SIMOTION.

The feeding error can be measured and compensated for usingimage edge extraction and circle positioning of the positioningmarkers in the metal foil. The visualization system coordinates (x, y)are defined in the CCD visual plane, and the specimen coordinates(x′, y′) are defined in the plane of the metal foil. The positioningerror (�x, �y) of the feeder from system zero to the marked holecan be determined by{

�x = xexp − xint

�y = yexp − yint

where (xint, yint) are the center coordinates of the marked hole inthe vision system coordinates, and (xexp, yexp) are the center coordi-nates of the marked hole, which are measured by image processing.Thus, the positioning error (�x, �y) can be used to compensate forthe zero error of the servo feeding system.

The zero error of the XY feeding plate was measured usinga micrometer and the visualization system according to the ISOstandard 230-2: 2006. The results show that the zero error values

were ±23.0 �m and ±23.4 �m as shown in Table 3, indicating thatthe visualization system is suitable for measuring the positioningaccuracy. The positioning error was measured by the visualizationsystem, and the results show that the zero error caused by the

J. Xu et al. / Journal of Materials Processing Technology 212 (2012) 2238– 2246 2243

Table 3Measurement results of visualization location accuracy.

Accuracymeasurement

Zero error (�m) Positioningerror (�m)

Positioningrepeatability (�m)

Micrometer Visual

pfnam

3f

3

ibt0fgqipattcfbca

mbdwvpas

Fn

2.5% 5% 7. 5% 10 % 12.5 % 15%

0

40

80

120

160

200

Hei

gh

t of

the

cross

sec

tion

(μ

m)

Height of smooth zone

Height of fractu re zone

Micro-hole diameter: 60 0μm

Foil thic kness : 20 0μm

Blanking velocity: 10mm /s

inspection

Results ±23.0 ±23.4 ±1.9 2.2

hotoelectric switch of the XY moving platform can be decreasedrom 23 �m to 1.9 �m. The positioning repeatability of 2.2 �m isearly the same as the positioning accuracy of the XY feeding platend can therefore satisfy the feeding precision requirements foricro-punching.

. Micro-punching processes for micro-hole arrays in brassoil

.1. Experimental tools and parameters

The micro-punching tool was designed and fabricated as shownn Fig. 9, and featured an alignment error of less than ±1 �metween the guide bushing and the die hole along the punch cen-er axis (Xu et al., 2011). A WC-Co alloy with an ultra-fine grain of.6 �m was used as the micro-die material. The micro-punch wasabricated with a high dimensional accuracy of ±1 �m by micro-rinding as shown in Fig. 9(b). In order to improve the surfaceuality of micro-punch, surface finishing process was adopted by

on beam irradiation with Ar plasma (Xu et al., 2009) and the micro-unch with good surface quality was fabricated with the incidentngle of 45◦ for 120 min, as shown in Fig. 9(c). In order to providehe flexibility to conduct the different micro-blanking processes,he female die and micro-punch with different feature dimensionan be changeable in one micro-punching tool. To obtain the dif-erent relative blanking clearance c/t (ratio of the single clearanceetween micro punch and female die c to foil thickness t), the singlelearance c was decided by changing the diameter of micro punchnd keeping the diameter of female die as a constant.

Commercial brass foils of C2680 were selected as the testaterial. To determine the optimal process parameters of micro-

lanking, micro-punching processes of micro-hole of 600 �m iniameter on brass foil of 200 �m in thickness were investigatedith the different relative blanking clearance c/t and blanking

elocity as shown in Table 4. No lubricant was used in the micro-

unching experiments. To evaluate hole dimensional and shapeccuracies of micro holes, the micro-hole diameter, height of cross-ection and tapering were defined considering the distribution

ig. 9. Micro-punching tool: (a) photo of micro-punching die; (b) micro-punch withon-treated process; (c) micro-punch after surface finish by ion beam irradiation.

Relative blanking cl earan ce c/ t

Fig. 10. Effects of blanking clearance on the cross-section of a micro-hole.

of punched holes cross section such as rollover, burnish (smoothzone), fracture and burr (Joo et al., 2005). The profile dimen-sions and height of cross-section of micro-hole were measuredwith Scanning Electron Microscope (Hitachi, S-4300). The surfaceroughness of smooth section of the micro-hole cross-section anddimensional accuracy of micro-holes array were measured withthe confocal scanning laser microscope (Olympus, OLS3000). Themeasurement tests were carried out with five specimens for eachmicro-hole and the results were averaged.

In order to verify the high precision performance of micro-forming system, micro-punching processes for much smallermicro-holes of 300 �m and 150 �m in diameter were carried out onthe brass foil of 150 �m and 80 �m in thickness, respectively. Thedie dimensions and parameters of the micro-punching process areshown in Table 4. In the end, batch manufacture tests of micro-holearrays of 600 �m in diameter were conducted using an automaticfeeding apparatus.

3.2. Influences of blanking conditions on micro-punchingprocesses

The effects of blanking clearance on the height of the smoothzone and the fracture zone of micro-hole of 600 �m in diameterwere investigated using a blanking velocity of 10 mm/s, and theresults are shown in Fig. 10. The results show that the height of thesmooth zone increases and the height of the fracture zone decreaseswith decreasing relative blanking clearance. When the relativeblanking clearance is less than 7.5%, the height of the smooth zonecan reach 80% of the foil thickness, and the height of the fracturezone is very small. Fig. 11 shows the effect of blanking clearanceon the tapering angle of a micro-hole, and the results show thatthe tapering of the micro-hole increases linearly with increasingrelative blanking clearance. The results indicate that the blank-ing clearance is the main factor in determining the quality of themicro-hole. The surface quality of a micro-hole can be effectivelyimproved with a smaller blanking clearance. However, a blankingclearance that is too small can easily cause mold wear and dam-age, which decreases the die life. Therefore, the optimum relativeblanking clearance in micro-punching of brass foil is 5%.

The influences of blanking velocity on the distribution ofmicro-hole cross-sections were studied with the relative blankingclearance of 5%, and the results are shown in Fig. 12. The resultsshow that the height of the smooth section increases and the height

of the fracture section decreases with increasing blanking velocity.However, the distributions of the smooth section and fracture sec-tion are uneven because of the non-uniform deformation at highblanking velocity.

2244 J. Xu et al. / Journal of Materials Processing Technology 212 (2012) 2238– 2246

Table 4Die dimensions and parameters of the micro-punching process.

Diameter of micro-hole/d (�m) Foil thickness/t (�m) Diameter of micro-punch (�m) Relative blanking clearance c/t Blanking velocity (mm/s)

600 200 600 ± 1.0 2.5–15% 2.5–50300 150 300 ± 1.0 – –150 80 150 ± 1.0 – –

2.5% 5% 7.5% 10% 12.5% 15%0

2

4

6

8

10

Micr o-hole dia meter: 600μm

Punchin g velocity: 10mm /s

Tap

erin

g a

ngle

α (

o)

Relative blanking clearance c/t

Fig. 11. Effects of blanking clearance on the tapering angle of a micro-hole.

0 10 20 30 40 500

40

80

120

160

200

Micro-hole dia mete r: 60 0μm

Relati ve blan kin g clearance: 5%

Foil thic knes s: 20 0μm

Hei

gh

t of

cross

sec

tio

n (

μm

)

Hei ght of smooth zone

Hei ght of fractu re zon e

mTmwii

Blanking ve loci ty (mm /s)

Fig. 12. Effects of blanking velocity on the cross-section of a micro-hole.

In order to eliminate the effect of curvature of side surface,icro-region of 10 �m × 10 �m was selected as measure area.

he surface roughness is estimated by the average value of ten

easurement points and the variation of the surface roughnessith different blanking velocities is shown in Fig. 13. The results

ndicate that the surface quality can be improved significantly byncreasing the blanking velocity. The surface roughness Ra can

Fig. 14. Micro-holes punched in brass foil:

Fig. 13. Effects of blanking velocity on the surface roughness of the cross-section ofa micro-hole.

reach the nano-scale when the blanking velocity is more than10 mm/s. Therefore, higher blanking velocities should be utilizedin micro-blanking. Since the strain rate during micro blanking isrelated with foil thickness, shear velocity (ratio of blanking velocityto thickness) is adopted for the choice of blanking velocity.

3.3. Micro-punching tests of micro-hole arrays with an automaticfeeding apparatus

The micro-punching processes were carried out with a relativeblanking clearance of 5% and shear velocity of 100 s−1. The micro-holes of 600 �m, 300 �m and 150 �m in diameter was piercedwith a good profile and high dimensional accuracy, as shown inFig. 14, which indicate that the micro-forming system can satisfythe accuracy requirements of micro-scale parts.

In order to verify the performance of mass production of micro-forming system, micro-punching processes of micro-hole arrays ina 50 × 4 matrix and 0.6 mm in diameter were investigated with theautomatic feeding apparatus guided by a microscopic visualizationsystem for assisted localization. The micro-hole arrays were man-ufactured with good profile accuracy on the conditions of 50 mm/s

and feeding velocity of 10 mm/s as shown in Fig. 15.

Fig. 16 shows manufacturing efficiency of micro-array holeswith different punching velocity. The results show that the man-ufacturing time of one array of 50 × 4 micro holes is less than

(a) 600 �m; (b) 300 �m; (c) 150 �m.

J. Xu et al. / Journal of Materials Processing Technology 212 (2012) 2238– 2246 2245

Fig. 15. Photograph of the micro-hole arrays.

0

50

100

150

200

250

300

350

400

Array hole: 50x4

Line space: 1.0mm

Colu mn: 1.0mm

Micro-h ole diameter: 600μm

Blankin g cle arance: 5%

Feeding speed : 10mm /s

Punching stroke: 7mm

80 1005020

Man

ufa

ctu

rin

g t

ime

of

pu

nch

ing

arr

ay h

ole

s (s

)

10

Punching ve locit y (mm /s)

1mpt

dTrT(Tha

F

Table 5Measurement results of the micro-array holes.

Parameters Micro-holediameter/d (�m)

Line space/�x(�m)

Columnspace/�y (�m)

Design values 600 1000 1000

Fig. 16. Manufacture efficiency analysis of micro-array holes.

20 seconds with the micro punching velocity of 50 mm/s. Theanufacturing efficiency of micro single hole can be arrived at 6000

er hour, which indicates that the micro-forming system can meethe requirement of mass production of micro-array holes.

The dimensional accuracy of the micro-hole arrays was con-ucted with laser focal microscopy (OSL3000) as shown in Fig. 17.he standard deviation was used to evaluate the dimensional accu-acy of micro-hole array with 30 test points for each parameter.he measurement results of micro-hole diameter (d), line space�x) and column space (�y) were obtained as shown in Table 5.

he results show that the dimensional accuracies of the micro-ole diameter, line space and column space were 1.0 �m, 2.4 �mnd 1.8 �m, respectively, which indicate that the automatic feeding

ig. 17. Dimensional accuracy measurement of micro-hole arrays with OLS-3000.

Measurement results 601.4 1001.5 1001.7Accuracy 1.0 2.4 1.8

apparatus with microscopic visualization is suitable for micro-punching of micro-hole arrays.

4. Conclusions

In this paper, a micro-forming system with high speed and highprecision was developed, and micro-punching processes of micro-hole arrays were conducted with an automatic feeding apparatus.The main summary points are listed below:

(1) A micro-forming drive mechanism was designed with sym-metric distributed double linear motors, which not onlyeffectively counteract the attraction force between the primaryand secondary sections but also achieve large accelerations.The micro-forming system was developed and equipped withmicro-punching tools and automatic feeding apparatus formetal foil.

(2) The servo control of the micro-forming system was performedwith the SIMOTION D445. Parallel control method with a singlemotor module was adopted to solve the synchronous controlproblem of the double linear motors. The maximum veloc-ity, the maximum acceleration, the position resolution andthe positioning repeatability were 1.1 m/s, 5 g, 0.12 �m and0.25 �m, respectively, which can satisfy the high speed and highprecision requirements for the micro-forming system.

(3) The optimum parameters of blanking clearance and blankingvelocity were obtained. The minimum micro-hole of 150 �min diameter was punched with the micro-forming system.Micro-hole arrays of 50 × 4 matrix and 0.6 mm in diameterwere manufactured using the automatic feeding apparatus withmicroscopic visualization. The results indicate that the micro-forming system can satisfy the accuracy and mass productionrequirements of micro-scale parts.

Acknowledgements

The authors would like to acknowledge the financial sup-port from the National Basic Research Program of China (GrantNo. 2012CB934100), the National Natural Science Foundation ofChina (Grant No. 50835002 and 51105102), the High TechnologyResearch and Development Program of China (2006AA04Z331) andthe Scientific Research Foundation of Harbin Institute of Technol-ogy (Grant No. HIT.2011.513).

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