Rubber Mold Steels
A recent machining test was performed on PX5 material at a mold base
manufacturer. Listed below are the tool settings for P20 and the results
achieved with PX5.
Tool No. 1
1.250 Diameter DIJET Ballnose Endmill
Program time was reduced from 38 minutes to 15.2 minutes
Tool No. 2
1.000 Diameter Waukesha Ballnose Endmill
Program time was reduced from 5.7 minutes to 2.85minutes
Tool No. 3
.750 Sandvik Ballnose Endmill
|Depth (Step Over)
Program time was reduced from 4.91 minutes to 2.5 minutes
Tool No. 4
(Finish cutter) 1.000 Diameter Iscar Ballnose Endmill
Program time was reduced from 10 minutes to 4.85 minutes
Note: There was no noticeable wear in any of the cutting tools using PX5.
- Manufacturing Process
A 40" x 41" x 87" block of PX5 was forged and heat treated. The piece was
cut through 61" into the 87" length. The following hardness readings were
taken across the face of the test piece.
- Inspection Result
Sectional Hardness Rockwell C Scale:
The recast layer from EDM for PX5 is soft, approximately 70% of that
produced with typical chrome-moly steels. Because the EDM white layer must
be removed, the subsequent stoning or grinding of PX5 is much easier than
with other steels. There is also a significant reduction in the incidence of
problems involving the hardened layer, such as surface layer cracking or
peeling. Consequently, no post EDM stress relieving is needed.
Hardness of EDM Affected Area
PX5's exceptional cleanliness, uniform microstructure, and uniform through
hardness facilitate excellent and consistent surface finishing
characteristics. PX5 polishes faster and easier to a superior mirror finish
than common P20-type steels. PX5 will polish to a 6000-7000 grit finish,
while P20 polishes to only a 5000 grit finish.
- Photo Etchability
PX5 is an excellent steel for photo etching. Low chemical segregation of the
alloying elements results in a clean, homogenous steel. Absolutely no etch
unevenness will occur due to chemical segregation. PX5's uniform hardness
and refined grain structure also provide a consistent surface condition for
texturing. A reduction in work time and cost can be anticipated due to the
elimination of etch unevenness problems.
Ion-nitriding increases wear resistance and creates a hard surface ideal for
slides or molds which will be molding abrasive or mineral-filled
thermoplastics. PX5 can be ion-nitrided to produce a surface hardness over
60 HRc without distortion or dimensional changes. This ion-nitrided surface
also improves part release and corrosion resistance.
It is essential that no rod other than PX5 should be used in all welding
situations. All other rods are incompatible with the base metal chemistry of
PX5 and will produce unacceptable results.
In most cases, PX5 can be welded with no pre- or post-heating procedures.
However, this is not true in all situations. We suggest that in the event a
polished surface must be welded (such as a lens or chrome-plated parts),
pre-heat the block to between 650-900°F. Weld with PX5 rod, then post-heat to
between 1040-1050°F. Final draw temperature for PX5 mold steel is 1117°F.
DO NOT, under any circumstances, exceed final draw temperature.
On a textured surface, the need to pre- and post-heat is determined by the
etching method used by the grain source. If the selected grainer uses the
immersion process with a nitric acid-based solution, then there is generally
no need for pre- or post-heating procedures. If the grainer uses a ferric
chloride flow technique, it is recommended that a full pre- and post-heating
procedure be performed prior to texturing as outlined above.
We recognize that many mold welders apply heat locally with torches as a means
of pre-heating the welded area. While this is a commonly used procedure, and
generally produces acceptable results on non-polished surfaces, it is not
recommended for post-heating welded blocks. The result of localized heat of
this type is an actual flame-hardening of the weld that will produce an
inconsistent increase in hardness by as much as 10-12 points (Rockwell C).
1) Weld Cracking Sensitivity
The compositional balance of PX5 was designed to suppress crack sensitivity.
The weld will not shrink and crack at the marriage line, even without pre- and
post-heating, as long as basic welding conditions are observed.
Y-Split Cracking Test
(determines cracking susceptibility)
|PX5 Weld Rod
|Filler rod Diameter
|Gas flow rate
PX5 exhibits no cracking in either the weld surface or interior.
Weld cracking will not occur as long as basic welding conditions and
procedures are observed.
2) Weld Hardness
PX5 has the lowest level of hardness in the heat-affected zone of any P20-type
mold steel. This relatively low increase in hardness reduces post-weld cutting
and grinding times (i.e., high-speed steel end mills can be used).
Hardness Distribution Around Weld
3) Photo Etchability
After weld repair, typical P20 will have etch unevenness due to its increased
hardness. This requires many hours to correct. PX5's relatively small increase
in hardness in the heat affected zone reduces the incidence of etch unevenness
and requires minimal correction work.
Photo Etch Quality Around Weld
Post-weld distortion is the lowest for any P20-type material, due to the
relatively small increase in hardness in the weld area. Post-repair
dimensional correction work is simplified.
|PX5 Weld Rod
|Filler rod diameter
|Gas flow rate
5) Undercut Characteristics
While undercutting or "sink" surrounding the weld will always occur to some
degree, PX5 has only a small degree of undercutting, dramatically reducing the
amount of repair time.
TIG: 160A, no filler
Test piece: 10 degree slant
Weld Sink at Heat Affected Zone
All technical and engineering data and suggested procedures,
specifications and applications contained in this publication are for general
information only. Daido Steel, International Mold Steel and/or their
distributors disclaim any and all express or implied warranties of
merchantability, suitability for any particular purpose or use, or freedom from
infringement of any patent, trademark or copyright. PX5® is a registered
trademark of International Mold Steel, Inc. and Daido Steel Limited.