STEELS FOR MOLDS - Villares Metals

STEELS FOR
MOLDS

Aspects related to Mold
Manufacturing
The machining and polishing processes can take up to 80% of the total resources needed for the
manufacturing of molds and dies. And, for those molds that have long usage times and seldom get to
the end of their life cycle, the main items associated with the fi nal mold cost can be considered.
Amongst the conventional machining processes of a metal cavity, milling is the one responsible for
the manufacturing of the complex surfaces. Several aspects must be taken into consideration, such
as: cutting parameters, the material to be machined, the cutting tool, the cutting strategy and the
technological resources provided by the machine/tooling.
Another fundamental point in the manufacturing of molds are the fi nishing processes, especially
polishing and texturizing. The following document refers to some basic considerations so as to facilitate
the manufacturing operations of metal cavities.

Milling
In the milling process, the knowledge of techniques is necessary in order to minimize fl ank wear and to control vibrations, so as to avoid damages.
The cutting direction can be carried out both in concordance or in opposition. In the concordance mode milling, the cutting and travel forward
movements have the same direction, while in the opposition mode they have different directions (see Figure on the right).
The cutting parameters exert the following influences:
Concordance mode milling
Opposition mode milling
• Cutting speed (Vc) – it infl uences the cutting tool wear, as it amplifi es the friction conditions, thus increasing the temperature at the cutting zone, resulting from diffusion related phenomena to problems associated
with thermal and/or mechanical origin shocks.
• Travel forward per tooth (fZ) – with the increase in travel forward per tooth, greater mechanical strains occur, increasing the tool defl ection. With low travel forward there happens an increase of the machined path
by the cutting edge, causing a high fl ank wear. One aims here at an intermediate condition.
• Axial depth of cut (ap) – it is the direct factor responsible for the increase in cutting power, thus limiting the roughing process.
• Radial depth of cut (ae) – large radial increments(>50% of the tool diameter) increase the machined path for each cutting edge. However, they do improve the impact characteristic, directing the stress towards the
tool inner part. The opposite case occurs for small engagement conditions (

Table 1- Summary of the applications as a function of the tool pitch.
Type of Milling Cutter
Coarse Pitch – few teeth.
Fine Pitch – greater number of teeth and spaces between
small teeth.
Extra Fine Pitch – many teeth and bags for storage of very
small chips.
Application
Roughing and semi-finishing of steel or where there is a
vibration trend.
Cast iron cutting, light roughing and steel finishing.
Interrupted cutting of cast iron and titanium alloys steel
finishing.
Some Additional Practical Recommendations
• Roughen as much as possible with tools with large sharp corner radius.
• A surface must be fi nished with the largest tool possible.
• Machining should have a continuous contact of the milling cutter with concordance cutting and with a minimum of travel variation
in relation to the milling line.
• It is recommended to use smooth approximation movements and always towards one cutting direction in hard-to-machine
materials.
• It is important to make the tool stay in contact with the work as long as possible (in order to increase the useful life).
Parameter Calculation
Cutting speed
(in/min)
v c
d n
1000
Travel Forward
Speed (mm/
min)
v
f
Chip Removal
Rate (mm/min)
= z ⋅ f ⋅ n Q = ae
⋅ a
p
⋅ v
f
Where d = tool diameter (mm); rotation (rpm); z = number of teeth of the tool; fz =
travel forward per tooth (mm/tooth); ae = working penetration (mm); ap = depth or
width of the machining (mm)
z
• During fi nishing or super-fi nishing, it is recommended to use small cutting depths. The ratio axial depth of cut (ap) and radial depth
of cut (ae) must be equal to or less than 0.2 (ap/ae < 0.2).
• Quite often it is advantageous to use the travel forward per tooth (fz) equal to the radial depth of cut (ae), with advantages in terms
of machining time and lesser roughness (better fi nish).
• Invest time in the interpolation method to be applied, so as to reduce the machining time and improve the fi nishing conditions of
the machined surface.
Example of Cutting Parameters
Recommended cutting speeds for milling facing with coated hard metal.
Material VP20ISO VP20ISOF VP20ISOFS VH13IM VP420IM N2711M VP50IM
Condition Machined Machined Machined Annealed Annealed Machined Machined
Hardness 32 HRC 32 HRC 32 HRC 200 HB 200 HB 40 HRC 40 HRC
Roughing* 120 to 150 120 to 150 170 to 190 180 to 260 180 to 260 80 to 110 100 to 150
Finishing** 220 to 240 220 to 240 260 to 280 220 to 300 260 to 300 100 to 150 110 to 160
* fz = 0.15 to 0.3 mm/tooth and ap = 2 to 4 mm Class : P25 – P35
** fz = 0.05 to 0.2 mm/tooth and ap = 0.5 to 1 mm Class P10 – P20

STEELS FOR MOLDS USED IN THE PLASTIC
VILLARES METALS VP20ISO VP20ISOFS VP50IM VP100 N2711M
SIMILAR ALLOYS Wnr 1.2738 Wnr 1.2312 NO SIMILAR STEEL NO SIMILAR STEEL Wnr 1.2711 MOD.
CHEMICAL COMPOSITION (%)
C 0.36 – Mn 1.60 - Cr 1.80 –
Mo 0.20 – Ni 0.70
C 0.36 – Mn 1.60 – Cr 1.80 –
Mo 0.20 S 0.06
C 0.15 - Cu 1.00 – Ni 3.00 – Mo 0.30 –
Al 1.00 – S 0.10
Cr-Ni-Mn
C 0.56 – Mn 0.70 – Cr 0.70 –
Mo 0.30 Ni 1.65 V 0.075
CHARACTERISTICS
Steel supplied as machined. It has good
polishability and response on texturization.
It has improved machinability through
special melt shop treatment. For improvement
of the wear resistance it can be nitrided or
cemented.
Steel supplied as machined. Excellent
machinability. Good response to nitriding.
Not recommended for parts that require
texturization processing, chromium plat ing
and higher polishability.
Tool steel for molds especially developed
to be hardened via ageing heat treatment,
with resistance higher than the VP20. It has
excellent polishing and texturizing properties.
It has an excellent weldability.
Steel made under vacuum degassing,
having an improved machinability through
Calcium inclusion treatment. The main
benefits are: high uniformity in hardness
with a less than 2 HRC variation along
the whole part’s cross section. Excellent
weldability. High polishability (except
mirror finish) and high reproducibility of
performance and manufacturing.
Steel supplied as machined. It has
good polishability and response on
texturization. For improvement of the
wear resistance it can be nitrided or
cemented. Due to the as supplied high
hardness, special care in machining is
necessary, particularly boring.
SUPPLYING STATE
Hardened and tempered
(30 - 34 HRC)
Hardened and Tempered (30-34 HRC)
Solubilized and aged (40-42 HRC) or
Solubilized (330 HB max)
Supplied as machined (285 to 321 HB)
Hardened and Tempered (38-42HRC)
RECOMMENDED HEAT
TREATMENT
- -
Ageing (in case it is supplied in the
solubilized state)
- -
MOLD HARDNESS TYPICAL
RANGE
28 - 37 HRC 28-37 HRC 38-42 HRC 30-34 HRC 38 - 42 HRC
POLISHABILITY Medium to High Low High High Medium to High
CORROSION RESISTANCE Low Low Low to Medium Low Low
RESPONSE TO NITRIDING Medium Medium High Medium Medium
RESPONSE ON TEXTURIZATION Medium to High Low High Medium to High Medium to High
WELDABILITY Medium Medium High High Medium
WEAR RESISTANCE Low to Medium Low to Medium Medium Low to Medium Medium to High
STEEL IDENTIFICATION COLOR Lavender – Black – Lavender Green-Brown- Green Lavender-Gold-Lavender Red-Blue-Red Green-Yellow
APPLICATIONS
Molds for injection and extrusion of
non-chlorinated thermo-plastics and little
abrasive. Large dimension molds.
Molds for injection and extrusion of
non-chlorinated and little abrasive
thermo-plastics that have low polishability
requirements. Bases and structures for
plastic molds. Cores for injection molds.
Molds for injection and extrusion of
non-chlorinated thermo-plastics. Molds
for load reinforced thermo-plastics.
Mold carriers, molds for non-chlorinated
plastic injection, dies for non-chlorinated
plastic extrusion, molds for blowing,
hot chambers, when a high corrosion
resistance is not necessary and several
applications in molds for plastics. Not
recommended for applications in which
toughness and mirror finish are design
requirements.
Molds for injection of non-chlorinated
thermo-plastics. Molds for blowing.
Extrusion dies for non-chlorinated
thermo-plastics.
The classification Low, Low to Medium, Medium to High and High are for guidance, and serve as a comparative guide just for this group of steels.
* Due to the need to break the passive layer (stainless steels), it is recommended to use the ion plasma nitriding process.

AND GLASS INDUSTRY
VP ATLAS VH13IM VP420IM V630 VIMCOR
- AISI H13 Wnr 1.2344
AISI 420
Wnr 1.2083
AISI 630
Wnr 1.4548
NO SIMILAR STEEL
Cr – Mo – Mn
C 0.40 – Si 1.00 – Cr 5.20 – Mo 1.50 – V
0.90 – P 0.015 max - S 0.003 max
C 0.40 – Si 0.80 – Cr 13.5 – V 0.25
C 0.035 – Cr 15.40 – Ni 4.40 –
Cu 3.50 – Nb+Ta 0.25
C 0.05 – Mn 2.5 Cr 12 –
Si 0.40 – S 0.1
Steel supplied as machined. It has good
polishability and response on texturization.
For improvement of the wear resistance it
can be nitrided or cemented. Due to the
as supplied high hardness, special care in
machining is necessary, particularly boring.
However, it has machinability advantages
when compared to the DIN 1.2711.
Tool steel used for applications in molds
when hardness higher than VP20 and VP50
hardnesses are desired. It has an excellent
polishing capacity.
Stainless steel after hardening and
tempering. It has as its main advantage
an elevated corrosion resistance, which
allows working in humid environments..
Precipitation hardening stainless
steel. It has the following excellent
properties:
- Dimensional and shape stability
- Weldability
- Corrosion resistance
- Polishability and response on texturization
Resulfurized stainless steel, supplied
as machined. It has an excellent
performance in machinability, mainly
in deep boring. Properties:
- Excellent machinability
- Excellent weldability
- Good corrosion resistance
- Hardness homogeneity
Quenched and Tempered (38 – 42 HRC)
Annealed (235 HB max)
Annealed (200 HB max) or hardened
and tempered (30 – 34 HRC)
Solubilized (38 HRC max) or solubilized
and aged (40 HRC max)
Machined (290 – 330 HB)
- Hardening and Tempering
Hardening and Tempering
(for the annealed material)
Ageing (in case it is supplied in the
solubilized state)
-
38-42 HRC 42 - 52 HRC 48-54 HRC 24-40 HRC 29-34 HRC
Medium to High High High High Low
Low Low to Medium High High High
High High High * High* High*
Medium to High High High High Low
Medium to High Low to Medium Low to Medium High High
Medium to High Medium to High Medium to High Medium Low to Medium
Blue - White Green – Silver – Green Blue-Brown Silver-Red Black – White
Cr-Mo-Mn alloyed steel, with micro-additions,
and already supplied in the machined
state. Due t o its balanced chemical
composition, this material has good
machinability, weldability, polishability,
good response on texturization and good
response to nitriding. It is indicated for
molds for injection of non-chlorinated
plastics, especially for applications that
need higher mechanical resistance and
higher wear resistance than AISI P20 or
DIN 1.2738 steels; dies for extrusion of
non-chlorinated thermoplastics. Several
applications in molds for plastic.
Molds for injection of non-chlorinated
thermo-plastics for which a higher
resistance to wear is required, coupled to
good polishability. Molds for glass.
Molds for injection of chlorinated
thermo-plastics. Processing or storage in
humid environment. Glass industry.
Tools for thermoplastic forming, including
corrosive processing (chlorinated polymer
forming). It can be worked and stored in
humid places.
Hot chambers, Cooling Plates, Mold
Carriers. It can be worked and stored
in humid atmosphere.

Mold Polishing
Polishing is used in molds to meet various requirements of the injected part:
• Aesthetic requirements: gloss and transparency.
• Mechanical: to avoid nicks and breaks by fatigue or overload.
• Functional: ex.: optical devices (lenses).
Polishing is a stage that takes up time and resources. The average time spent in the manual polishing of large size molds is
around 300 to 400 hours per mold. Two observations are important in the evaluation of the mold surface quality. First, the surface
must have the correct geometrical form, without any waving. These are derived from recent machining operations. Second, the
evaluation of the mirror polished condition of the metallic mold is often carried out by visual comparison of the mold or of the
surface of the injected part, based upon the operator’s experience.
The fi nal quality of the polished surface of a steel depends on factors such as: the polishing technique, the type of tool steel and
the heat treatment applied to the material. In general, one can say that the polishing technique is the most important factor. A
typical example is shown on the graph below, the excessive polishing known as over polishing, caused by a mechanical cold work
of very fi ne layers on the mold surface. In over polishing, roughness increases with the increase in polishing time. The problem
is only solved with the removal of part of the surface (tenths of mm) through machining and the application of a new polishing.
Visually, the phenomenon appears as “orange peel”.
Roughness Rugosidade RA (mm) RA (mm)
50
45
40
35
30
25
20
15
10
5
0
Overpolishing
VA2 - 60 HRC
P20 - 32 HRC
0 5 10 15 20 25
Roughness Tempo RA (min) (mm)
Graph showing the effect of excessive polishing (over polishing) for two steels with different
hardness levels.

For a good polishing, the mold surface must be free from scratches, pores, orange peel effect, pitting and pinholes. In Brazil, the problem of pitting and pinholes are commonly called “porosity”. Although visually correct,
the term porosity is erroneously applied here, as it should be used only for pre-existing voids in the material. In the case of pinholes or pitting observed after polishing, the problem is normally caused by a process not
well carried out (for a given steel and hardness), using steels with an inadequate level of nonmetallic inclusions or even by the combination of these two factors. Other possible sources of problems are surfaces with
electro-erosion defects or excessive machining cold work.
As to the inclusions, they can be mechanically understood as particles on the steel surface with hardness and ductility rather different from the metal. All steels have inclusions. However, the quantity and distribution
depend on the manufacturing process. For high polishing applications, therefore, remelting via ESR is recommended (ISOMAX® process). As shown in the scheme below, there is a signifi cant reduction of the level of
inclusions.
a) Conventional ASTM G 2.0
b) ISOMAX, ASTM 1.0 F
Type D inclusions
a) Level 2.0 acceptable for Conventional materials
b) Level 1.0, Typical of material made via ESR (Source: ASTM E 45)

Texturization
The response on texturization measures how easy it is to apply a texture to the tool steel used in the mold. The texturizing treatment is normally carried out by photo-etching differentially applied on the mold surface,
thus generating the “negative” of the fi nal desired aspect of the injected part.
The process control, in terms of the acid medium used and of the applied procedure, is essential for a good texturization result. As to the quality of the steel, similar polishing requirements are necessary: homogeneity
of microstructure and hardness, besides a high level of cleanliness as to nonmetallic inclusions.
4 mm
2 mm
4 mm
2 mm
Several examples of texturized surfaces in VP 100 steel, observed in stereoscope.

Junho/2012
0800 19 0577
0800 707 0577
55 19 3303.8160
arnaldo.zangueri@villaresmetals.com.br
www.villaresmetals.com.br
Rua Alfredo Dumont Villares, 155
Jardim Santa Carolina - Sumaré / SP
CEP 13178-902