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Materials Engineering, Vol. 16, 2009, No. 1
26
THE WEAR OF INJECTION MOULD FUNCTIONAL PARTS
IN CONTACT WITH POLYMER COMPOSITES
Janette Brezinová, Anna Guzanová
Received 27th January 2009; accepted in revised form 28th February 2009
Abstract
The paper deals with the evaluation of material wear of injection moulds made of aluminium alloy Alumec
89 and copper alloy Moldmax HH in friction couples with plastomer materials with various filler contents. The
friction relations in injection moulding were simulated in an adhesion dry wear test using an Amsler machine,
with an area contact of the friction couple materials. The wear intensity was evaluated by determination of
friction coefficient and relative wearing by the mass loss. Surface morphology changes of evaluated alloys after
wear and the thermal conditions in particular friction couples were analysed simultaneously.
Keywords: Adhesive wear; Friction coefficient; Mass loss
1. Introduction
Injection moulding is one of the most
widespread polymer processing technologies. It
allows producing moulds of both simple and complex
form. Products made by injection moulding are
characterized by a very good dimensional and shape
accuracy and high reproducibility of mechanical and
physical properties. An advantage of injection
moulding is high efficiency of processed material,
which ranks it among closed-cycle technologies.
The quality of moulded parts depends above all on
the quality of the production tool, i.e. injection mould.
The main function of an injection mould is to
give a processed polymer the required shape and cool
it to the temperature that allows removing the
moulded part without any deformation. The shaped
cavity is the most important for injection mould
function. Its shape corresponds with the shape of the
desired product; the dimensions differ only by the
shrinkage value. Injection moulds must conform to
the technical requirements, which guarantee their
correct function for the required number, quality and
precision of mouldings together with the economic
requirements characterized by low acquisition price,
easy and fast production and also high utilization
efficiency of processed plastomers. Operation
conditions of injection moulds loading are as follows:
injection pressure, tension, and wear intensity as well
as higher temperatures of processed plastics including
their chemical effects on functional surfaces [1, 2].
The lifespan of an injection mould is
determined by its engineering design, mould inserts
used, dimensioning, maintenance and storage.
A mould dissipates heat from the processed polymer
and even cooling – a homogeneous temperature field
in the injection mould – is required for the properties
of a moulding. The usage of suitable mould inserts for
extremely stressed mould parts can extend the
operating life of the moulds. Mould inserts made of
highly thermally conductive materials inserted near
the shaped mould cavity increase the heat removal,
especially under low annealing temperatures. The aim
is to provide a balanced thermal load of both the tool
and the moulded piece in the whole volume while
increasing productivity. Utilization of mutual
relations between the active (water circulating in
annealing channels) and the passive annealing
medium (mould inserts made of highly thermally
conductive material) results in: the thermal balance in
the whole volume of the moulded piece at the same
time, minimization of the thermal difference in the
injection mould, and increasing the crystalline phase
J. Brezinová, doc. Ing. PhD.; A. Guzanová, Ing. PhD. – Department of Technologies and Materials, Faculty
of Mechanical Engineering, Technical university of Košice, Mäsiarska 74, 040 01 Košice, Slovak Republic.
*Corresponding author, e-mail address: [email protected]
Materials Engineering, Vol. 16, 2009, No. 1
27
ratio by optimal crystallization process in injection
moulding of semi crystalline polymers. Other
advantages of annealing are: easier processing of
products with complicated shape without any creation
of cold weld lines, shortening of the moulding cycle
time, increasing the moulded piece surface quality by
suitable technological timing, and higher functional
safety (smoother surfaces, more suitable friction
properties). High requirements are imposed to surface
quality of shape parts of injection moulds. Great
attention is paid to high wear resistance of functional
parts, mainly when polymers reinforced with abrasive
fillers are processed. [3-6] Wear intensity is affected
predominantly by the kind of processed polymer,
moulding shape and dimensional complexity, its
segmentation and required precision, and the
temperature and pressure of the injected polymer [7,8].
In processing filled polymers there occur
various fibre orientation patterns in the melt. There
are a number of distinct layers within the moulding
with different fibre alignments. [9] In the skin layer,
the fibre orientation is predominantly parallel to the
flow direction due to the elongation forces developed
during fountain flow at the melt front as well as due to
the shear flow after the front has passed. In contrast, a
random-in-plane alignment of fibres is observed in the
core layer due to slower cooling rate and lower
shearing. Just this mutual relative motion of self
orienting filler and mould wall causes adhesive-
abrasive wear of injection moulds, which leads to
necessary renovation or moulds replacement. [10-13]
The aim of the experiment was to carry out
complex analysis of the wear resistance of selected
aluminium and copper alloys, designed for the
production of shape mould parts, in interaction with
glass fibre reinforced plastomers in adhesive wear
conditions.
2. Experimental methods
The material wear resistance of mould shaping
parts was determined by adhesive dry wear test.
Material and test specimen
Aluminium alloy Alumec 89 (marked A)
was used as a sample of mould shaping part material
for adhesive dry wear test. Alumec 89 is a high
strength and high stability aluminium alloy. It is of
low specific weight, which makes opening and
closing the moulds easier. The alloy is characterized
by high thermal conductivity, good thermal stability,
and it can be covered with hard layers to increase its
wear and corrosion resistance. Another tested material
was copper alloy Moldmax HH (marked M). It is
a high strength material used especially for polymer
processing moulds. As a mould insert in steel moulds,
it effectively cools hot spots and reduces the need for
annealing channels. The chemical composition of the
evaluated alloys is shown in Tab.1, 2 and their
selected mechanical properties are shown in Tab. 3.
Tab. 1
Chemical composition of Alumec 89 [%]
Si Fe Cu Mn Mg Cr Ni Zn Ti Zr Al
0.1
2
0.1
5
2.0
0.1
0
2.6
0.0
5
0.0
5
6.7
0.0
6
0.1
6
89
Tab. 2
Chemical composition of Moldmax HH [%]
Be Co+Ni Cu
1.9 0.25 98
Friction mates for the adhesive dry wear test were
made of the following polymers:
1 Durethan PA 66 GF30 (polyamide 66 reinforced
with 30 % of glass fibres); Shore D - 85
2 Slovamid 66 GF25 (polyamide 66 reinforced
with 25 % of glass fibres); Shore D - 86
3 Slovamid 6 GF30 (polyamide 6 reinforced with
30 % of glass fibres); Shore D - 83
4 Slovaster B1 GF10 (polybutyleneterephtalate
reinforced with 10 % of glass fibres); Shore D - 78
Tab. 3
Mechanical properties of the evaluated alloys
Mechanical properties
Alumec 89 Moldmax HH
Rm 650 – 720 [MPa] 1280 [MPa]
Rp0.2 600 – 650 [MPa] 1070 [MPa]
A5 8 – 11 [%] 6 [%]
Hardness 199 HV30 400 HV30
Adhesive dry wear test
Adhesive dry wear test was carried out using
the Amsler machine with a surface contact between
the test samples. In a friction couple the disk was
made of selected alloys (diameter φ 35 mm, width 10
mm, prepared by turning) and friction mates made of
particular plastomers (20x15x8 mm, prepared by
milling). Friction couple materials were held together
by a spring of normal force Fn = 500 N, the disk
speed n was 200 min-1
. The adhesive wear was
evaluated by the direct method based on mass loss Wh
of the alloy disks. The duration of the friction test was
15 minutes, and the friction moment M was observed
Materials Engineering, Vol. 16, 2009, No. 1
28
simultaneously. All test samples were degreased
before the adhesion wear test. The arrangement of the
friction couple are shown in Fig. 1.
The equipment includes a dynamometer, which
continuously measured the friction moment M. The
friction moment M is given by equation (1):
M = Ft . r [N.mm], (1)
where Ft – friction force [N]
r – disk radius [mm]
The friction force Ft is determined from the friction
moment M according to equation (2)
t
MF
r= [N] (2)
The friction coefficient µ is determined as a ratio of
friction force and normal force (3)
t
n
F
Fµ = [-] (3)
Surface morphology evaluation
The surface morphology of alloy disks was
evaluated by roughness measurement using a stylus
profilometer Surftest SJ 301 according to ISO 4287
before and after wear. The following parameters were
monitored: Ra – arithmetical mean deviation of the
profile, Rz – maximum height of the profile. The
surface roughness was measured in parallel with the
disk axis. The measuring and recording conditions
were as follows: evaluation length - 4 mm, sampling
length – 0.8 mm, number of sampling lengths - 5,
measured system – mean line R, Gauss filter,
horizontal record magnification 50x, vertical record
magnification 1000x.
The adhesive worn surfaces were also
displayed in 3D view using Matlab software.
Thermal conditions during wear test
During the adhesive dry wear test the surface
temperature of alloy disks was also monitored in
order to study the friction thermal aspects. The
temperature of alloy disks was monitored on the area
of 1mm2 by a contactless pyrometer TESTO 845 with
two laser-aiming points. The distance between the
thermometer and the scanned disk was 70 mm. Time
of temperature scanning: 15 min during friction, next
10min in free cooling phase after wear finishing.
3. Results
The initial course of friction coefficients for all
friction couples corresponded to the running-in phase
of contact materials and gradually became stabilized,
see Fig.2. The characteristic surface macro and micro
relief resulting from the production process influences
the initial phases of the adhesive wear. The surface
micro-relief is closely related to the structural
properties of the surface layers of frictional materials
and it changes after mutual running-in of the friction
couple. The highest values of the friction coefficient
were observed in friction couples A-2 and M-2 – both
evaluated alloys in friction couples with Slovamid 66
GF 25. There was increased resistance against mutual
relative motion of evaluated materials. Other friction
couples showed lower friction coefficients. Wear
intensity of Alumec after friction with all used
plastomers was relatively high in regard to its
relatively low hardness, see Fig.3. The highest weight
loss Wh was observed after wear in plastomer No.2,
which is in accordance with observed values of
friction coefficient. In the course of contact friction of
particular plastomers with Moldmax the observed
weight loss was lower due to its higher hardness. The
ighest weight loss was observed again in friction
couple M-2, which is in accordance with the observed
values of friction coefficients. Besides the volume of
the dispersed compound and its arrangement in the
matrix, the wear course is significantly influenced by
the plastomer matrix hardness and the extent of the
interfacial matrix – filler adhesion.
The adhesive friction thermal conditions
recorded by a contactless pyrometer for particular
friction couples are shown in Fig.4 and Fig.5. The
highest temperature was observed for friction couple
A-2 and M-2, which is again in accordance with the
observed values of friction coefficients for both
alloys. Maximum achieved temperatures for particular
friction couples were in direct proportion to the
hardness of the tested plastomers.
Fig. 1. View on friction couple
Materials Engineering, Vol. 16, 2009, No. 1
29
0
0,02
0,04
0,06
0,08
0,1
0,12
0,14
0,16
A - 1 A - 2 A - 3 A - 4
Wh
[g
]
a) Alumec 89
0
0,02
0,04
0,06
0,08
0,1
0,12
0,14
0,16
M - 1 M - 2 M - 3 M - 4
Wh
[g
]
b) Moldmax HH
Fig. 3. Time dependence of alloy mass loss
Three stages can be observed on the thermal
curves: the first phase (I) corresponds to the
temperature increase up to the maximum depending
on friction process conditions and material characte-
Fig. 4. Thermal conditions during friction with Alumec
Fig. 5. Thermal conditions during friction
with Moldmax
ristics of friction couples. At the same time it also
corresponds to contact materials running-in and the
initial change of surface micro-relief. The second
phase (II) is characterized by stabilised thermal
relations depending on friction conditions and by the
balance between the heat development in the contact
area and the heat removal into the material and
friction system environment. The third phase (III) is
characterized by a rapid temperature decrease and
corresponds to free cooling phase to room
temperature. This phase corresponds to the ending of
the wear process.
Fig. 6 shows profilographs of Alumec surfaces
before wear and after the contact friction with
particular plastomers. Fig.8a shows initial oriented
surface corresponding to the production genesis –
turning. Fig.8b-e shows profilographs of Alumec
surfaces worn by particular polymer composite friction
mates. After the contact friction Alumec surfaces are
considerably rougher depending on the matrix type
and the filler content in the polymer composite
friction mate. The profilographs record both Alumec
0
0,1
0,2
0,3
0,4
0,5
0,6
0 100 200 300 400 500 600 700 800 900
time [s]
fric
tion c
oeffic
ient [-
]
A - 1 A - 2 A - 3 A - 4
a) Alumec 89
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0 100 200 300 400 500 600 700 800 900
time [s]
fric
tion c
oeffic
ient [-
]
M - 1 M - 2 M - 3 M - 4
b) Moldmax HH
Fig. 2. Time dependence of friction coefficient
Materials Engineering, Vol. 16, 2009, No. 1
30
surfaces and polymer surfaces for each particular
friction couple. On the surface boundaries of two
contacting materials of a friction couple micro-welds
occurred. In dry friction of contact surfaces the
attractive forces between friction materials were
sufficient to create strong joints. Adhesive micro-
welds occur on the whole area of real contact. The
transmission of Alumec alloy particles to polymer
composites surface was caused by adhesive-abrasive
effect of the filler in polymer composites. The surface
of plastomers after wear test was covered in grey
aluminium oxides with low adhesion to surface,
arising as a result of temperature increase during
friction. In the first phase of friction, real contact area
of friction couple was considerably smaller, because
the contact of material surfaces of defined roughness
occurred only on roughness peaks. The specific
pressure on this area was high and the applied loading
deformed the material surface, therefore the contact
area of the friction couple was enlarged. Alumec
surface peaks were elastically deformed and
consequently there arose a new plastically deformed
surface. The grooving intensity of Alumec surface
was intensified by the presence of a dispersed phase
in plastomers – glass fibres. Due to wide differences
in the hardness values of structural compounds at the
beginning there occurred an intensive wear of
polymer matrix, thus increasing the stress on the
peaks of the hard compound. The hard abrasive
particles – glass fibres consequently stamped into the
Alumec surface and caused micro-cutting of the alloy.
Simultaneously there was local displacement of
material volume on the surface. In the course of
friction with polymer composite Slovamid 66GF25
the filler consecutively dislodged from the soft
matrix, consequently acting as an abrasive and
causing grooving of Alumec surface, see Fig.8a.
Fig. 7a shows a profilograph and the view of
the initial surface of copper alloy Moldmax. Figs. 7 b-e
show changes of the profile image after wear. In
friction couples M-1, M-2 and M-3 there occurred
smoothing of the initial turned surface, the surface of
Moldmax alloy after contact with composite 4
remained significantly unchanged owing to the low
hardness of polymer friction mate 4. In this case the
oriented surface of Moldmax alloy was replicated on
the surface of polymer 4, see Fig. 7e. A view of
friction couples surfaces shows the transmission of
Moldmax alloy particles to polymer composites
surface. The cohesive strength in the surface layers of
Moldmax alloy was lower than the adhesive strength
Fig. 6. Profilographs of A alloy and surfaces of friction couples (surfaces, mag. 100x)
Materials Engineering, Vol. 16, 2009, No. 1
31
of the micro-welds. The arrow in Fig.8b is pointing to
a detail of dislodged glass fibres and their orientation
in the direction of the friction force.
Fig. 9a shows a 3D view of oriented alloy
surface before wear. Characteristic surface changes
are visible in 3D views, see Fig.9b & c. The 3D views
show the wear mechanisms of particular alloys, i.e.
formation of grooving and pitting, as analysed above.
The observed roughness characteristics of the
evaluated alloys after wear showed some specifics
resulting from material properties of particular alloy
groups. In case of Alumec alloy there occurred an
increase of the roughness value in comparison with
the initial state. The most intensive change was
observed for friction couple A-2. This tendency is
similar for each evaluated roughness parameter, see
Fig.10a. Due to higher hardness of Moldmax alloy no
grooving by composite friction mate, i.e. by glass
fibres contained in the matrix, occurred during
friction. On the contrary, smoothing of Moldmax
surface was observed almost in all friction couples,
which resulted in roughness parameters decrease.
Fig. 7. Profilographs of M alloy and surfaces of friction couples (surfaces, mag. 100x)
a) b)
Fig. 8. Transmitted particles detail of alloy a) Alumec
b) Moldmax on surface of polymer composite Slovamid 66 GF25, mag. 100x
Materials Engineering, Vol. 16, 2009, No. 1
32
In friction couple M-4 the primary
oriented surface was even replicated into the
surface of the friction mate –polymer 4. An exception
was friction couple M-2, where the roughness
parameters of Moldmax surface increased, see
Fig.10b. We assume that this fact was caused by the
reduced adhesion at the boundary interface between
the matrix and the dispersed phase.
4. Conclusion
The paper deals with the study of aluminium
alloy Alumec 89 and copper alloy Moldmax HH
resistance against adhesive wear in interaction with
polymer composites reinforced with glass fibres. The
wear intensity was evaluated by friction coefficient,
mass loss of evaluated alloys, and by monitoring
the thermal conditions during friction. Roughness and
morphology changes of evaluated alloys were
evaluated simultaneously.
After the initial running-in and consequent
stabilization of friction couples the highest value of
friction coefficient was observed in both evaluated
alloys in friction couples with polymer composite
Slovamid 66 GF25, which indicates the highest wear
intensity. This was also confirmed by the evaluation
of mass loss. The surface roughness of Alumec 89
increased after wear in each friction couple, especially
after friction with composite Slovamid 66 GF25. The
a) b) c)
Fig. 9. 3D views of a) oriented alloy surface, b) Alumec worn surface, c) Moldmax worn surface
0 1 2 3 4
initial value
A-2
A-4
Ra [µµµµm]
Ra [µµµµm]
0 0,5 1
initial value
M-1
M-2
M-3
M-4
0 5 10 15 20
initial value
A-1
A-2
A-3
A-4
Rz [µµµµm]
Rz [µµµµm]
0 2 4 6
initial value
M-1
M-2
M-3
M-4
a) b)
Fig. 10. Roughness parameters before and after wear of a) Alumec alloy, b) Moldmax alloy
Materials Engineering, Vol. 16, 2009, No. 1
33
roughness of Moldmax HH alloy decreased after wear
with all polymer composites, the copper alloy surface
was smoothed by polymer composite friction mates.
In some cases there occurred a temperature increase
and material transmission within the friction couples.
Surface visualization before and after the wear
confirmed the wear mechanism for aluminium alloy
to be the grooving and pitting formation caused by the
abrasive effects of the dispersed filler, and for copper
alloy the surface smoothing effect.
The experimental works show that polymer
composite No.1 – Slovamid 66 GF25 reinforced with
25% of glass fibres caused the most intensive wear of
both evaluated alloys. The wear of Alumec 89 alloy
was more intensive than the wear of Moldmax HH.
Despite its higher thermal conductivity, Alumec 89 is
not suitable for mould inserts production designed for
injection moulding of reinforced polymer composites,
due to its hardness.
Acknowledgements
This work was done within the scientific project
VEGA No. 1/4166/07.
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