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material is plastic deformation resistance of small after annealing; large and complex molds requires that
material has good welding process in order to be able to easily repair local damage and so on. The cost of
plastic mold is high, generally is about 75% of the total cost, while the cost of materials and heat
treatment is about 10% each. Thus, the more important plastic molds, under the premise of good
performance should choose easily manufacturing materials, and the price factor is of secondary fact.
5 The choice of plastic mold materials
5.1 Cold forming plastic mold material selection
For this type of mold we usually select low carbon steel (carburizing steel) and strive to choice low-
carbon or very low carbon steel such as DTl, 20,20 Cr, 12 Cr Ni3 A, 40Cr and so on.
For the injection, extrusion forming molds that have high wear-resistant surface and heart department
toughness good and less complex in shape ,we can use carburizing steel to cold forming mold. we also
use 10,20,12 CrNi3A, 20Cr,20CrMhmo and 20Cr2Ni4A,etc.
5.2 Cutting molding plastic mold material selection Mailly use quenched and tempered steel after quenching and tempering treatment processing.
1)Small production, or small molds can use quenched and tempered carbon steel, such as 40,50,55, etc.
2)large quantities or large, complex molds can use alloy quenched and tempered steel, such as 3Cr2Mo,
4Cr3MoSiV, 5CrNiMo, 5CrMnMo, 4Cr5MoSiV, 4Cr5MoSiVl ,etc.
3)High-precision,large quantities injection molding, we choice pre-hardened steel ,such as
4Cr5W2SiVl, 8Cr2MnWMoV. Pre-hardened hardness is about 42～48HRC. Sometimes we choice pre-
hardened cutting steel.
Working conditions Recommended steel
small plastic mold with small production and less
precision products
45、55 or 10 Carburizing steels、20 Carburizing
steels
withstand a larger dynamic load, producing larger
quantities, more serious wear
12CrNi3A、20Cr、20CrMnMo、20Cr2Ni4A
Carburizing steels
Large, complex, large volume, injection molding or
extrusion dies
3Cr2MO、 4Cr3M03SiV、 5CrNiMO、
5CrMnMO、 4Cr5MoSiV、4Cr5MOSiVl
Thermoset molding requiring high wear, high
strength
9Mn2V、7CrMn2WMO、CrWMn、MnCrWV、
GCrl5、5Cr2MnWMOVS、Cr2Mn2SiWMoV、
Cr6WY、Crl2MOV、Crl2
Corrosion resistance and high-precision plastic
mold
4Crl3、9Crl8、Crl8MoV、Crl4Mo、Crl4M04V
Complex, sophisticated, high wear-resistant plastic
mold
25CrNi3MoAl“Ni(250)、18Ni(300)、18Ni(350)`
6 Plastic mold heat treatment
Plastic mold should have a moderate hardness and good toughness, different types of mold requires
different hardness, several types of plastic mold steel and hardness of the requirements are show below.
As thermosetting plastic mold is heated and works under pressure in a long time, through heat treatment,
has a high enough resistance to pile collapse capacity.
The work hardness of different types of plastic mold
Mould type Die steel Work hardness Description
plastic with a simple
shape and inorganic filler
Crl2Mo or 5CrW2Si
Carburizing steels
56～60HRC Requirs wearability under
high pressure
small plastic mold with a
simple shape and a long
life
alloy tool steel such
as 9Mn2V、Cr12 etc
54～58HRC high wearability and good
strength and toughness
high precise plastic mold
with a complex shape
and a micro-deformation
quenching
T7A、T10A 45～50HRC Parts for easily broken (eg,
core)
Soft injection plastic
mold
Carbon tool steel、
3Cr2Mo