Conference PaperPDF Available

Repair of Plastic Injection Moulds

Authors:
  • IDMEC, Instituto Superior Técnico, Universidade de Lisboa

Abstract and Figures

The research reported in this paper aims to contribute to increase the knowledge related with injection moulds repair. The types of moulds repair are identified and characterized in terms of the reasons for repair, the repair’s duration and quality related requirements and the mould’s geometrical and dimensional constraints. The techniques used in injection moulds repair (undercut, inserts and metal deposition by welding processes) are also identified and characterized. A strong emphasis is given to the repair by welding, namely in the comparison of the suitable welding technologies. Furthermore, in order to understand how mould makers and mould users are repairing their moulds, a survey to the industrial companies was conducted and the results are presented and discussed. Taking advantage of the systematization of the moulds repair framework several objective conclusions were withdrawn from the survey, namely as regards the incidence of each type of repair and of each repair technique, the frequency of use of each welding technology and the influence of related technological and business factors. Additionally, a specific analysis of the welding technologies suitable for injection mould repair is presented. They were compared based on eight different repair scenarios character-ized by different factors: mould dimension, repair geometry, repair access point and repair visibility. As main achievement, the paper presents the specific fields of application (repair scenarios) of the analyzed welding technologies.
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1 INTRODUCTION
The repair of plastic injection moulds is a very
important issue during the life cycle of the mould.
The mould repair is usually associated with the re-
building of some mould features eroded or broken
down due to the injection process [Peças et al.
2006]. The high mould cost and the time required to
produce a new mould justify the repair aiming to ex-
tend mould life. Furthermore, the same time and cost
factors justify the need for mould repair in other life
cycle stage – in the mould production phase. In fact,
the repair techniques used to rebuild a mould de-
graded due to its use are the same that are used to
modify a localised region in an already machined
mould cavity during the production phase. The need
of mould repair in the production phase has two
main reasons, one related with human errors and
systems malfunction, and the other related with the
present mould making business characteristics
[Peças & Henriques 2003]. The progressive time-to-
market reduction leads to the dispatching of the
mould production without a complete stabilisation of
the product detail design and determines increas-
ingly the need to reshape already machined zones
[Henriques et al. 2005].
So, the term “mould repair” involves the concepts
of modifying the mould features in order to assure
the intended performance.
The techniques used to repair moulds have ex-
perienced a significant development in the last years,
mainly with the introduction in the market of proc-
esses with the ability to micro-processing [Hollen-
beck 2001, Roy & Francoeur 2002]. It’s possible
nowadays to perform sound repair tasks obtaining a
mould cavity able to accomplish the exigent injec-
tion moulding conditions [Godin & Guadani 2001].
Nevertheless, there is lack of integrated knowledge
as regards the type of mould repairs, the current re-
pair practice at mould makers plants, the type of
technologies used and the application field of the re-
pair processes [Peças et al. 2006].
The aim of this paper is to contribute to a broader
discussion and structured knowledge about mould
repair. The results of the conducted research pre-
sented in the following paper sections foster the use
of the appropriated procedures and techniques, and
contribute to the acceptance of mould repair as a
phase of mould life cycle by the actors of the mould
making sector.
Repair of Plastic Injection Moulds
P. Peças, E. Henriques
IDMEC, Instituto Superior Técnico, TULisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
ppecas@ist.utl.pt; elsa.h@ist.utl.pt
ABSTRACT: The research reported in this paper aims to contribute to increase the knowledge related with
injection moulds repair. The types of moulds repair are identified and characterized in terms of the reasons for
repair, the repair’s duration and quality related requirements and the mould’s geometrical and dimensional
constraints. The techniques used in injection moulds repair (undercut, inserts and metal deposition by welding
processes) are also identified and characterized. A strong emphasis is given to the repair by welding, namely
in the comparison of the suitable welding technologies. Furthermore, in order to understand how mould mak-
ers and mould users are repairing their moulds, a survey to the industrial companies was conducted and the
results are presented and discussed. Taking advantage of the systematization of the moulds repair framework
several objective conclusions were withdrawn from the survey, namely as regards the incidence of each type
of repair and of each repair technique, the frequency of use of each welding technology and the influence of
related technological and business factors. Additionally, a specific analysis of the welding technologies suit-
able for injection mould repair is presented. They were compared based on eight different repair scenarios
characterized by different factors: mould dimension, repair geometry, repair access point and repair visibility.
As main achievement, the paper presents the specific fields of application (repair scenarios) of the analyzed
welding technologies.
P.Peças, E.Henriques. Repair of Plastic Injection Moulds. Em: 3rd International Conference on
Polymers and Moulds Innovations – PMI 2008. Ghent: Univeristy College Ghent, p.118-125 (2008).
2 CATEGORIES AND TECHNIQUES OF
MOULD REPAIR
2.1 Mould Repair Categories
The need to repair a mould is originated by a
cause. Three types of distinct causes that configure
the mould repair categories can be identified. Figure
1 represents the occurrence of each repair category
during the mould life cycle.
One of the categories is the Rebuilding. This
category includes the rebuild of an eroded or worn
localised mould zone due to the polymers abrasive
and/or corrosive actions along the successive injec-
tion cycles.
Other category is determined by the need of
mould Revision. It consists in the modification of
some mould local zone during the mould manufac-
turing process due to a design alteration purposed by
the client. The need for mould design Revision can
also result from an additional feature willing to be
added to the mould. The latter occurs for reasons of
moulding process improvement and/or final part de-
sign revision and updating.
The last category to mention is the Correction re-
pair. It involves the modification of some mould lo-
cal zone during the manufacturing process due to a
mould maker error (in the drawings, programming,
machining, polishing, etc.) or process malfunction
(energy cut-off, tool break, etc.).
Mould
Design
Mould
Manufacturing
Mould
Test
Mould
Use
Mould
End-of-Life
Need of repair due to
eroded or worn features
Mould Rebuilding
Need of repair due to
design changes
Mould Revision
Need of repair due to
production fault
Mould Correction
Figure 1 – The repair categories during the mould life cycle.
A survey was conducted among 40 mould makers
aiming to extract some conclusions related with the
mould repair task. In what regards to the Rebuilding
repair category it was evident that most of this type
of repairs are not done by the company that manu-
factured the mould. Since the time available to re-
pair a mould that is already in its use phase is very
short, the mould owners usually decide on deliver
the mould to a repair shop near the injection facility.
Only special moulds or specific repair tasks demand
for the mould coming back to the mould maker.
Therefore, most of the moulds repair tasks found in
a mould making company are related with Revision
and Correction category. As illustrated in Figure 2,
the amount of moulds per year that require Correc-
tion repair are below 20% but almost 50% of the
moulds are submitted to Revision repair. There is no
visible relation between the mould maker size
(measure in terms of moulds produced per year) and
the need for repair. Nevertheless, it was observed a
significant importance of the type of client the
mould is targeted to. For the moulds to produce
automotive parts the mould makers mentioned that
around 80% of the moulds undergo by a repair proc-
ess (mainly Revision type). On the other hand
moulds to produce electronics or utilities a repair
task is rarely asked.
52%
46%
51%
38%
48%
19%
27%
12%
8%
19%
below 40 40 to 60 60 to 80 upper 80 Global
average
Moulds produced per year
Percentage of moulds repaired
Revision Repair
Correction Repair
Figure 2 – Percentage of moulds submitted to Revision and
Correction repair categories. The number of moulds produced
per year is used as a measure of mould maker company dimen-
sion.
2.2 Mould Repair Techniques
Three distinct techniques used to repair plastic in-
jection moulds can be identified: inserts, weld bead
deposition (welding) and undercutting (of the
moulding and parting surfaces). The interaction of
the repair techniques with the repair categories is
represented in Table 1. The requirements, the final
result and the manufacturing aspects (cost and time)
of each technique are very relevant in the process of
repair technique selection. In fact, the selection de-
pends on the type of repair to perform, but also on
other factors like aesthetic, cost and geometrical
constraints.
The aesthetic factor is one of the most important
ones, mainly when repair is required in the mould
cavity (that represents most of the cases). For repair
tasks in a zone that will be visible in the plastic part
only undercutting and welding techniques are nor-
mally used. The use of inserts will cause the pres-
ence of a visible joint. Regardless the following con-
siderations related with the selection of welding or
undercutting when the aesthetic factor is relevant, it
must be pointed out that the welding technique is
used when it is impossible to apply the undercutting
technique.
The repair category, the repair dimensions and
the confidence in the welding repair technique are
the subsequent factors involved in the repair tech-
nique selection. In Rebuilding category a large re-
pair involving a considerable amount of material
should be done through the undercutting technique.
Undercutting will assure that the wear behaviour and
the shrinkage level will be kept. This can be difficult
to keep if the welding technique is used to deposit
large quantities of material. On the other hand, if
small damaged areas are involved the welding tech-
nique should be used after mould client acceptance
(even in a small and controlled welding there is al-
ways the risk of introducing weld beads in a mould
already submitted to several thermal cycle). It must
be mentioned that there is no need of complicated
calculations to find out that using the undercutting
technique in the repair of small zones is always more
expensive and time consuming than welding – the
undercutting requires the machining of the overall
cavity geometry.
Table 1 – The factors involved in the selection of the type of
repair (U – Undercutting; W – Welding; I – Inserts).
High Importance of
the Aesthetic Factor
Low Importance of
the Aesthetic Factor
Repair Category Repair Category
Welding
Confi-
dence
Repair
Size
Rebui. Rev. Correc. Rebui. Rev. Correc.
Large U W W U W W
High
Small W W W W W W
Large U W U U W U
Low
Small U W U I I I
The last arguments to select welding in detriment
of undercutting are valid for the Revision repair
category. In this category small geometrical modifi-
cations are usually involved, the metallurgical state
of the material is known and the manufacturing time
is narrow.
In the case of the Correction category the tech-
nique selected depends on the confidence in the
welding process and procedures. If it’s possible to
deposit weld beads following the correct welding
procedures, the final result will not affect mould per-
formance during the injection phase.
For repair tasks in which the aesthetic factor is
not relevant, the decision depends on two factors:
repair extension and confidence in the welding proc-
ess. The undercutting is recommended for large re-
pair zones and the welding is recommended for the
rest if there is confidence in the welding process. If
not, the use of inserts avoids the higher costs and
time of undercutting.
3 THE MOULD REPAIR BY WELDING
From the above discussion, the welding technique
has high potential to be further applied in the future
since it is less expensive and less time consuming.
The use of appropriate welding procedures, by well
trained welders and the use of the correct welding
process will avoid problems related with different
metallurgical and wear behaviour, minimising the
fracture risk. Moreover, it can be demonstrated that
welding can be as robust as any other process in the
mould life cycle, as far as it is properly applied
[Baranek 2007, Gervais 2007, Malkasian et al.
2000].
The perception that the use of welding is the most
appropriated solution for most of mould repair situa-
tions is evident in the results of the conducted sur-
vey. In fact, it was concluded that around 80% of the
mould repair is sub-contracted by the mould makers
to welding repair shops in the surroundings. Around
13% of the mould makers mention that they perform
some of mould repair jobs using their own welding
equipment. Nevertheless, as a rule it was mentioned
that for complex repair operations the mould is re-
paired in a dedicated repair shop.
3.1 The welding processes used in mould repair
As stated by other authors the most used welding
processes for mould repair are the TIG and the Laser
welding. The results of the survey confirm this situa-
tion as is presented in Figure 3 and Figure 4. There
is no influence of the mould maker size or of the re-
pair category. In fact, TIG welding is used in 2/3 of
the repair tasks and Laser welding is used in the re-
maining 1/3. The main reason found for the preva-
lence of TIG welding is related with the lower repair
cost and the lower repair time. The lower repair cost
is essentially related with the small investment of the
TIG welding machine (especially when compared to
the Laser welding equipment), causing the lower
cost per hour asked by the repair shop. The lower
repair time is related with three factors. The higher
deposition rate and lower setup time of TIG welding,
and, the most important, the relation of the number
of machines existent in a repair shop. Actually, for
each laser welding machine existent in a repair shop
there is an average of 6 TIG welding machines. This
is a very important factor to select the welding proc-
ess, since usually the repair by TIG welding can start
immediately after the mould arriving at the repair
shop. On the other hand, if Laser welding is se-
lected, it can take some hours or even 1 or two days
to start the repair process. This waiting time is usu-
ally not compatible with the characteristic timeframe
of mould manufacturing.
56%
71%
63%
73%
65%
44%
29%
37%
27%
35%
below 40 40 to 60 60 to 80 upper 80 Global
average
Moulds produced per year
TIG Laser
Figure 3 – Welding process distribution for the Revision repair
category.
61%
72%
57%
73%
65%
39%
28%
43%
27%
35%
below 40 40 to 60 60 to 80 upper 80 Global
average
Moulds produced per year
TIG Laser
Figure 4 – Welding process distribution for the Correction re-
pair category.
From these results it can be concluded that the in-
cidence of each process is very dependent on the
technological configuration of the local repair shops.
In fact, the welding process selection should not be
based only in criterion related with its manufactur-
ing and cost performance. The systematic compari-
son presented in next section helps to define the ap-
plication field of the most appropriated welding
processes to moulds repair.
3.2 The welding process suitable for mould repair
TIG and Laser welding are the processes cur-
rently used to perform most of moulds repair welds.
However one can consider also Plasma welding suit-
able for these operations since it is very similar to
TIG having higher density energy.
TIG welding is characterised by the electric arc
stability and concentration, allowing highly con-
trolled and accurate weld beads in any welding posi-
tion. The TIG equipment is portable, easy to operate
and requires low set-up time. The time required to
begin an operation depends only of the welding op-
erator positioning. There are welding torches of sev-
eral sizes, nevertheless the access to some features
geometries can be impossible. The electric arc melts
the filler material and the base material, producing
final weld beads larger than the filler wire diameter.
It allows good metal deposition rates. On the other
hand the heat input in the base material is high, so it
can be required pre and pos heating in order to avoid
excessive stress concentration. Since it is a manual
process it has a high flexibility, allowing the work
on intricate geometries. Nevertheless it requires a
skilled welding operator.
Plasma welding is very similar to TIG welding.
The main difference is related with a higher concen-
trated welding plume, resulting in higher penetration
and energy density. The heat input to the material is
lower, which is a good characteristic as regards the
affected zone, but the metal melting rate is smaller
than in TIG, which results in a worse productivity.
The Plasma welding equipment is also portable, easy
to operate and set-up.
Laser welding is characterised by its concentrated
density of energy and accuracy allowing narrow
(filler wire diameter), high-quality and deep weld
beads. The heat input to the material is small being a
common practice to perform the welding operation
without pre or pos heat treatment. The metal deposi-
tion rate is lower than in the previous two processes.
Some difficulties can appear when it is required to
fulfil an intricate geometry, since it is a semi-
automatic process, in which the operator controls a
CNC table and visualizes the welding through a
lens. The equipment set-up and control is more
complex and usually the mould/component position
in the welding table can be a time-consuming opera-
tion. In spite of that the welding is less dependent on
the operator skill and experience, since the equip-
ments are often programmed to the most common
welding operations
4 THE APPLICATION FIELD OF THE
WELDING PROCESSES
With the aim to contribute to increase the knowl-
edge about moulds repair by welding, a process clas-
sification/comparison is presented. The comparison
is based on 10 criterion, considered as the most im-
portant as regards to the process, the repair operation
characteristics and impact on the mould:
A. Metal Deposition Rate of the process;
B. Portability of the welding equipment;
C. Flexibility in the Access to complex Ge-
ometries;
D. Welding process flexibility in performing
weld beads with Complex Shapes;
E. Cost per hour of equipment utilisation;
F. Weld bead Appearance and concordance
with the base material;
G. Metallurgical Quality of the welding and its
impact on the base material;
H. Process Capability as a measure of process
reliability and feasibility (operator depend-
ence);
I. Equipment Set-up Time to start the welding
operation;
J. The need of pre and/or pos Heat-Treatment.
Table 3 presents the analysis of the three proc-
esses for each criteria. It must be noticed that these
processes are suitable for most of the welding appli-
cations in mould repair. However a severe classifica-
tion was used in order to emphasise the difference
among the processes. In fact this score amplitude is
commonly used in the decision-making methods. As
an example, for the criteria Deposition Rate, the
three processes have levels of deposition rate com-
patible with the welding operations usually required
in mould repair. Other processes like GTAW or even
SAW have indeed higher deposition rate than TIG,
but are in fact too high to allow a correct control of
the weld bead deposition. Therefore, TIG welding
has the highest score because among the three proc-
esses it has the highest deposition rate. On the other
hand Laser welding has the lowest one so the lowest
score was attributed.
Table 3 – Welding processes classification in each criteria in
injection mould repair.
Criterion TIG Plasma Laser
A Deposition Rate 9 3 1
B Portability 9 9 1
C Access Geometries 9 9 1
D Complex Shapes 9 9 1
E Cost rate 9 3 1
F Appearance 1 3 9
G Metallurgical Quality 1 3 9
H Process Capability 1 3 9
I Set-up time 9 9 1
J Heat-Treatment 1 3 9
9 - Best Performance; 3 - Medium Performance; 1 - Lowest Perform-
ance.
With this process classification it is difficult to
distinguish the processes. The processes characteris-
tics can have different relevance for different appli-
cations. As an example, if the mould repair involves
only the deposition of a very small bead, the criteria
Deposition Rate is of very small importance, yet the
criteria Set-up Time is very important. The opposite
reasoning can be made if a very large zone has to be
repaired.
Having in mind the importance of the specificity
of the repair tasks in the welding process decision,
the comparison methodology presented here is ap-
plication-based. Eight application scenarios,
covering most of the welding repair conditions, were
defined (Figure 5). The three most important factors
that influence the welding process performance in
fluence the welding process performance in mould
repair were used for the scenarios conception. In
addition, the established analysis considers the
mould is repaired in a repair shop, located in the re-
gion of the mould making company. So, there is a
need to transport and move the mould.
Accordingly, one of the most important factors
that influence the welding process performance is
the mould dimension. In this analysis it was consid-
ered that a small mould weights below 2.5 ton.
These moulds can be “easily” transported to the re-
pair shop and moved near to the welding equipment
by a stacker. In contrast, with the mould size in-
creasing it can be recommendable to move the weld-
ing equipment to the place where the gantry placed
the mould. So, for this type of moulds welding
equipment portability is crucial allowing more flexi-
bility to accomplish the repair task.
Scenarios
Scenarios
Small MouldsLarge Moulds
Linear
repair Linear
repair
Area
repair Area
repair
Interior
II
Surface
I
Interior
IV
Surface
III
Interior
VI
Surface
V
Interior
VIII
Surface
VII
Figure 5 – Application scenarios used in the comparative
analysis (8 different application scenarios).
Besides mould dimension, the influence of the
type of geometry to repair was also considered as
crucial. There are two main geometries to repair: the
linear type geometry, related with the rebuilding of
edges; and the area type geometry, related with the
need to fulfil a hole or to rebuild a feature. The dif-
ferences of the welding processes performance in
what concerns to the deposition rate and process ca-
pability will cause different behaviours depending
on the type of geometry to repair.
Finally it was also considered the repair zone as
an important factor in the processes performance.
The zone to be repaired can be placed either in the
mould surface or in an inner part of a depression.
When is required to repair such a zone, the process
versatility in what concerns the capability of access-
ing to complex geometries becomes essential.
The next step required to compare the welding
processes is the attribution of importance weights to
each of the 10 criterion identified for each scenario
(table 4). A classification from 1 to 3 was used,
where 1 means that the criteria has low importance
in that specific scenario, 2 means a medium impor-
tance, and 3 means the criteria is very important in
that scenario for welding process selection.
Table 4 – Importance weight distribution for each scenario
(weightki values, where index k refers to the scenario and i re-
fers to the criteria).
Criterion
Scenarios A B C D E F G H I J
I 3 3 1 1 2 2 3 2 1 3
II 3 3 3 2 2 2 3 2 1 3
III 1 3 1 2 1 3 3 3 2 3
IV 1 3 3 2 1 3 3 3 2 3
V 3 1 1 1 3 2 3 2 1 3
VI 3 1 3 2 3 2 3 2 1 3
VII 1 1 1 2 2 3 3 3 2 3
VIII 1 1 3 2 2 3 3 3 2 3
For each scenario (k) and each process (j), the
weights (weigthki) were multiplied by the criteria
classification (criteriaij) of each process (j), in table
3. The sum of each process parcels is an indicator of
the process performance in each scenario. The final
aim is to compare the processes, so what is impor-
tant is the relative performance among them. Equa-
tion 1 was used to obtain the values present in Table
5:
k
J
Ai kiij
jk formanceMaximumPer
weightcriteria
ePerformanc
(eq.1)
The better process in each scenario has a score of
100%. The difference of the process scores is a
measure of the performance difference in that sce-
nario. Following this approach it is possible to
achieve some degree of quantitative sensibility in
this qualitative comparison.
Table 5 – Relative process performance for each scenario. A
score of 100% represents the best performance in that scenario.
Large Mould Small Mould
TIG Plasma Laser TIG Plasma Laser
Surface 86% 97% 100% 79% 85% 100%Linear
Repair Interior 91% 100% 91% 93% 98% 100%
Surface 100% 91% 93% 100% 84% 100%Area
Repair Interior 100% 93% 76% 100% 87% 81%
From the results presented in Table 5 it is possi-
ble to conclude that the repair application scenario
affects the process performance. To aid the results
interpretation the processes performance is illus-
trated in a graphic mode in Figures 6 and 7.
In Figure 6 the processes performance for differ-
ent mould sizes and repair geometry are compared,
keeping the repair zone at the mould external sur-
face. In this type of repair the process handling ver-
satility has low impact. The access to the geometry
is easy and the welding operator has freedom of
movements.
For surface type repair the Laser welding process
has clearly the best performance when linear type
repair geometries are involved. Its dominance is
higher for small moulds than for large moulds due to
the low portability of the laser welding equipment.
The execution of linear weld beads is in fact more
appropriated to the Laser welding process, since it’s
a semi-automated process and the welding spot is
very small and accurate. It’s also feasible to deposit
linear weld beads using TIG, but a skilled and ex-
perienced welder is required. These facts affect TIG
welding capability and weld bead appearance.
Easy repair location (mould surface)
TIG
Plasma
Laser
Small Moulds
Linear weld
Large Moulds
Linear weld
Small Moulds
A
rea weld
Large Moulds
A
rea weld
Figure 6 – Process performance for the Scenarios I, III, V and
VII, the ones related with repair of zones in the exterior mould
cavity surface.
For repair application involving large moulds and
an area type geometry the TIG welding has the best
performance. The main reason is related with the
higher deposition rate and high portability of the
TIG process.
Plasma welding presents an overall good per-
formance in these 4 scenarios involving repair op-
eration at the mould surface. Although is not the best
choice for any of the scenarios, its performance is
near the other two processes. It must be noticed that
for linear type repair the Plasma welding has a better
performance than the TIG welding, mainly due to its
better accuracy, weld bead appearance and process
capability.
Figure 7 compares the performance of the proc-
esses for the scenarios involving the repair of zones
that are not at the mould surface but in difficult ac-
cess zones. The repair zone is kept as interior and in-
tricate. The processes performances are illustrated
for different mould size and repair geometry.
The repair in interior zones demands for high ver-
satility of welding source handling. It is required to
deposit the weld bead in several positions and the
welder has to access the inner parts of the geometry.
The Laser welding reveals difficulty to fulfil these
requirements since the welding source is fixed and
requires a linear access to the welding zone. In the
case of large moulds the performance of Laser weld-
ing is even more limited. These are the main reasons
for the low performance of Laser welding in these
scenarios as is visible in Figure 7. However, the La-
ser welding accuracy, capability and weld bead ap-
pearance compensate those limitations placing this
process in the selection zone when small moulds and
linear type repair are involved.
Difficult repair location (mould inner zone)
TIG
Plasma
Laser
Small Moulds
Linear weld
Large Moulds
Linear weld
Small Moulds
A
rea weld
Large Moulds
A
rea weld
Figure 7 – Process performance for the Scenarios II, IV, VI
and VIII, the ones related with repair in interior zones of the
mould cavity.
The characteristics of the Plasma welding process
foster for its better performance when the repair in
interior zones is involved. In effect its portability to-
gether with its accuracy and low thermal input con-
tribute to be the selected process when linear type
repair in large moulds are involved.
TIG welding shows an evident supremacy for the
repair applications involving area type geometries in
interior zones. This process is highly versatile in the
welding torch handling and has the highest deposi-
tion rate. This scenario is the one where the Laser
welding reveals its lower performance, mainly when
large moulds are involved.
Accordingly, the comparison methodology used
allows the identification of the application fields of
each welding technology. The key factors that are
the base of processes performance comparison were
identified and the use of different application-base
scenarios allowed the selection of the most appro-
priated process for the type of mould repair to per-
form. For each repair scenario there is a weld technol-
ogy which performance is clearly higher than the
others. So, the three technologies are more than op-
ponents, they are complementary.
Figure 8 and Figure 9 present a simplified view
of the selected process for each type of repair sce-
nario.
Large
Moulds
AreaLine
Laser
Small
Moulds
TIG/
Laser
TIG
Laser
Reparações à Superfície
Easy access welding position
(mould surface)
Large
Moulds
AreaLine
Laser
Small
Moulds
TIG/
Laser
TIG
Laser
Reparações à Superfície
Easy access welding position
(mould surface)
Figure 8 – Processes selected for scenarios related with repair
of zones in the mould cavity external surface.
Large
Moulds
AreaLine
Plasma
Small
Moulds
TIG
TIG
Laser
Reparações no Interior
Difficult access welding
position (mould inner zone)
Large
Moulds
AreaLine
Plasma
Small
Moulds
TIG
TIG
Laser
Reparações no Interior
Difficult access welding
position (mould inner zone)
Figure 7 – Processes selected for scenarios with repair in inte-
rior zones of the mould cavity.
5 CONCLUSIONS
The repair tasks is part of the plastic injection
moulds life cycle. The need for repair has several
causes from the worn mechanisms of the mould dur-
ing the successive injection cycles, to the modifica-
tions introduced in the part design during mould
production phase, and to errors and inaccuracies dur-
ing mould design and production.
This paper presented a definition of three catego-
ries of repair that influence the repair procedures and
the selection of the repair techniques.
The repair techniques were also identified and
characterized in what concerns to their abilities and
limitations, and correlations between the repair cate-
gories and the repair techniques were established.
The use of welding bead deposition is one of the
most flexible and feasible mould repair technique. A
great emphasis was given to the welding processes
with the ability to be applied in moulds repair.
A qualitative comparison of the welding tech-
nologies was presented. Following a comparison
methodology the technologies were compared on a
base of 10 performance criterion. Then 8 applica-
tion-base scenarios were defined in order to identify
the application field of each technology.
From the analysis it can be concluded that each
one of the elected process has special characteristics
that permits its selection, at least, for a mould repair
application scenario.
The Laser welding is best suited for repair sce-
narios involving linear type repair, small moulds and
repair zones located in the mould surface. The
Plasma welding is the process selected only for one
scenario, the one involving large moulds, linear type
repair located in an interior zone of the mould. Fi-
nally, TIG welding is the most suitable process
when large moulds are involved and when deposit
area type weld beads are required.
6 ACKNOWLEGMENTS
The work described in this paper was developed
within the ImpMould Project financially supported
by the Portuguese Science Foundation. The authors
extend their thanks to all who contributed to this re-
search, mainly to the industrial mould-makers and
specialized mould repair companies.
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Article
Several industrial sectors, in which value chains mould making is involved, are actually subjected to a huge demand towards the reduction of their product innovation cycles. This fact induces a strong pressure on mould manufacturing lead times and a clear need to accommodate a growing number of product modifications during mould manufacturing cycle without deteriorate mould final cost and final due date. Implementing management strategies able to cope with a one-of-a-kind production type, with changeable specifications set where delivery date is a critical issue, assuring a continuously improved performance, is the only way to guarantee business excellence and market leadership. In this paper the management strategies and the methodologies to be used on the pathway to fully implement lean manufacturing will be discussed, taking into account mould making companies classical constraints.
Partnering for Success: One Builds, The Other Repairs
  • S L Baranek
Baranek, S.L. 2007. Partnering for Success: One Builds, The Other Repairs. In: www.moldmakingtechnology.com, August.
The Tool of Choice for Mold Repair
  • J E Gervais
Gervais, J.E. 2007. The Tool of Choice for Mold Repair. In: www.moldmakingtechnology.com, February.
Micro welding: Applications beyond mold repair
  • J Hollenbeck
Hollenbeck, J. 2001. Micro welding: Applications beyond mold repair. In: www.moldmakingtechnology.com, October.
Micro-dimensional welding is putting some moldmakers ahead of their competition
  • S Malkasian
Malkasian, S.et all. 2000. Micro-dimensional welding is putting some moldmakers ahead of their competition. In: www.moldmakingtechnology.com, February.
Fostering the Use of Welding Technology in the Mould Repair. Rapid Prototyping Development -RPD
  • P Peças
Peças, P. et all. 2006. Fostering the Use of Welding Technology in the Mould Repair. Rapid Prototyping Development -RPD 2006. Marinha Grande: Centimfe, Cefamol, nº P6031.
Selecting a filler metal for mold repair welding
  • R Godin
  • R Guadani
R. Godin, R. & Guadani, K. 2001. Selecting a filler metal for mold repair welding, In: www.moldmakingtechnology.com., Abril.
Options for restoring molds
  • S Roy
  • M Francoeur
Roy, S. & Francoeur, M. 2002. Options for restoring molds. In: www.moldmakingtechnology.com, September.