2. Mould Steels
Costs of mould making
The toolmaker's task is to make a mould of the
right shape and quality in the most economical
way. Total cost in mould making split into each
cost factor is of interest.
The manufacturing costs for plastic moulds vary
with the shape of the mould, surface finish and
choice of material. The following table shows a
typical distribution of costs for manufacture of a
mould.
3. Mould Steels
% of total cost
Material cost 10
Chip-forming machining 30
Heat treatment 10
Grinding 15
Polishing 30
Assembly 5
100
4. Mould Steels
Toolmakers' demands on mould steel
From the standpoint of the toolmaker, the most
important demands on the mould steel
concern:
1. Machinability
2. Polishability
3. Surface execution and stock standard sizes
4. Heat-treatment properties
5. Surface-treatment properties
5. Mould Steels
Machinability
The economic importance of
machinability is very great indeed
Roughly 30 % of the total cost of
a mould is accounted for by the
machining costs.
6. Mould Steels
Polishability
Polishing is a time-consuming and costly
process. The result of polishing will depend
in the first instance on the polishing
technique used. The polishability of a steel
depends on the homogeneity of the steel
and on the type, distribution and size of
slag inclusions
7. Mould Steels
Hard, large slag particles are particularly
troublesome. Polishability is also highly
dependent on the hardness level and heat
treatment of the material.
To receive the highest purity, the steel should be
vacuum degassed or electro-slag-remelted.
It is well known that electro-slag remelting (ESR)
improves homogeneity and freedom from slag in
comparison with conventional processes.
8. Mould Steels
Surface execution and stock
standard sizes
Even when the bar material arrives at the
tool-maker's shop there are differences in
surface execution machining allowance and
actual size, depending on the supplier.
By selecting rough-machined
(premachined) material, the customer gains
the following benefits:
9. Mould Steels
— less material needs to be bought for a
mould (the scrap remains in the
steelworks).
— lower machining costs for removal of
oxidized and decarburized surface layer.
Less machine capacity is tied up.
—faster output time. One or more operation
stages are avoided, more reliable
calculations in respect of finished products
10. Mould Steels
Heat-treatment properties
To reduce dimensional changes in hardening, the
tools should be stress-relieved after rough
machining so as to relieve the stresses formed in
course of chip-forming machining .A small change
in hardening is unavoidable. It is nevertheless
possible to limit the changes (warpage) through
slow and even heating to the hardening
temperature and by choosing a low hardening
temperature and a suitable quenching medium.
13. Mould steel-420
CHEMICAL COMPOSITION (average %)
C Si Mn Cr
0.35 0.40 0.30 13.00
STANDARDS
EN / DIN AISI BS UNI
~1.4028
~X30Cr13
420 ~420S45
~X30Cr13
~X31Cr13KU
UNE AFNOR JIS GOST
~F5262
~F3403
~Z30C13 SUS420J2 ~30Ch13
14. Mould steel-420
PROPERTIES
Advanced martensitic stainless chromium
steel for grass moulding, particularly for
TV glass moulding.Vacuum remelting,
special hot forming and heat treatment
and optimized chemical composition yield
the following advantages:
- Highest polishability
- Good corrosion resistance
- Good photoetching properties
- Good machinability
15. APPLICATION
Due to the excellent polishability of M330 it
is particularly suited to the moulding of TV
glass.
Additional applications include moulding of
lenses for spectacles and camera parts,
moulds for chemical aggressive plastics
and moulding for plastics containing
abrasive fillers
Mould steel-
420
19. Pre-hardened tool steel
P20 is a vacuum degassed
Chromium-Nickel-Molybdenum-
alloyed steel which is supplied in
the hardened and tempered
condition, offering the following
benefits:
20. Pre-hardened tool steel
•No hardening risks
•No hardening costs
•Time saving, - no waiting for heat treatment
•Lower tool cost -no distortion to rectify, only one
polishing sequence
•Modifications easily carried out
•Can be subsequently nitrided to increase surface
wear resistance or locally flame-hardened to reduce
surface damage
21. Pre-hardened tool steel
Property
• Good machinability
• High purity and good homogeneity
• Good polishing properties
• Uniform hardness in all dimensions
22. Pre-hardened tool steel
Heavier sections are supplied pre-machined which offers the
following advantages compared to un-machined material:
• Saving of weight
• Non-decarburized surface
• Exact nominal measure (plus tolerance)
• Less machining
• Absence of scale minimizes machine and tool wear
23. Pre-hardened tool steel
Applications
•Tools for injection moulding of plastics
•Tools for transfer and compression moulding of
•plastics (in the nitrided condition)
•Tools for die-casting of tin, lead and zinc alloys
•High-strength bolsters, backing plates
•Structural components, shafts
•Forming tools, press-brake dies (possibly flame-
hardened or nitrided)
24. CHEMICAL COMPOSITION (average %)
C Si Mn Cr Mo S
0.40 0.40 1.50 1.90 0.20 0.07
STANDARDS
EN / DIN AISI
<1.2312>
40CrMnNiMoS8-6
~ P20
Pre-hardened tool steel
