International Mold Steel

PX5

PX5 is a modified P20, high performance, high precision, mold steel.

Overview

PX5 is a modified P20, high performance, high precision, mold steel.

Features:

  • Machines 30- to 40 percent faster than P20
  • Pre-hardened to 29-33 HRC
  • Uniform microstructure & hardness with extremely improved machined surface finish
  • Never needs stress relieving
  • Improved weldability and greatly reduced susceptibility to weld cracking
  • Reduced surface-hardened layer in EDM making finishing operations easier

Applications include:

Plastic Molds

Rubber Molds

Press Plates

Dies

Unique Characteristics

  • Exceptionally clean steel with uniform microstructure – no pin holes, inclusions or hard spots.
  • 30-33 HRc hardness.
  • Uniform hardness throughout, even in heavy sections.
  • 75% tougher than typical chrome-moly steels.
  • Patented chemistry suppresses weld cracking and hardness elevation in the heat affected zone, eliminating the need for pre-heating and post-heating in most welding situations.
  • Machines 30-50% faster than any other P20-type steel.
  • Never needs stress relieving, even after heavy machining.
Compare the costs of using PX5 and P20 (or 4140). See how you can save using PX5. Click here.

Welding

Superior mold quality after welding. Low hardness of heat affected zone eases post-weld cutting and grinding operations and minimizes mold distortion, etch unevenness, and differences in luster upon mirror finishing. Unique composition eliminates weld cracking.

Machining

Rough machines up to 50% faster than P20 (30% overall) to a superior surface with negligible dimensional change. Use of PX5 assures the longest cutting tool life of any 30 HRc, P20-type material. Consistent hardness and microstructure allow dependable, unattended machining.

EDM

EDM surface hardness is about 70% of that produced by typical P20-type steels. Post-EDM grinding and polishing operations are simpler and more consistent, and problems

such as surface layer cracking or peeling are reduced.

Stability

Uniform hardness and refined grain structure assure the highest level of dimensional stability (after machining) of any P20-type mold steel.

Surface Enhancements

Can be ion-nitrided to produce a surface hardness over 60 HRc with negligible distortion or dimensional change.

Texturing and Polishing

Uniform microstructure and hardness give PX5 the best surface-finish characteristics of any P20-type material. Low chemical segregation eliminates the occurrence of photo etch unevenness.

Toughness

Exceptional toughness reduces cracking problems in molds.

  • Isotropy and Uniform Strength PX5’s strength is approximately the same at the center and surface of the material, and that isotropy (T/L) is at least 0.05.


Tensile Properties

When designing deep cavities in molds, PX5’s consistent toughness assures the mold center will have sufficient strength, and cracking problems are dramatically reduced.

Toughness

Coefficient of thermal expansion (x10-6/F°)

86-212°F

86-392°F

86-572°F

86-752°F

86-1112°F

PX5

6.6

7.1

7.3

7.5

7.8

Thermal conductivity (btu/ft.·hr.·F°)

68°F

68°F

68°F

572°F

752°F

PX5

24.53

24.48

24.31

22.42

22.42

Specific heat (btu/lb.·F°)

68°F

68°F

68°F

572°F

752°F

PX5

0.027

0.028

0.031

0.032

0.036

Young’s modulus (lbs./in²)

68°F

212°F

392°F

572°F

752°F

PX5

30269

29768

28909

28051

26977

  • Compressive Strength
    Uniform hardness (approximately 32 HRc) from surface to core assures that strength and hardness at the mold center are the same as at the surface. Exceptional toughness reduces cracking problems while increasing flexibility in mold design.

  • Stability PX5 is substantially more stable than common P20-type steels. Since it has a unique heat treating process, it does not have the stresses inherent in typical quenched and tempered steels. PX5 never needs stress relieving, even after heavy machining. It has excellent dimensional stability and consistency during the machining process, and during the heating and cooling cycles of injection or compression molding.

Machining
Use of PX5 assures the longest cutting tool life of any 30 HRc, P20-type material and an overall 20-30% improvement in machining efficiency.

Note: Positive, effective cutting rake angles are recommended, as are inserts with concave faces and chip breaking edges. TiAlN coatings work well.
Machinability
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

P20

PX5

RPM

986

 1600

Feed (in/min)

11.83

27.60

Depth

.120

.120


Program time was reduced from 38 minutes to 15.2 minutes
Tool No. 2
1.000 Diameter Waukesha Ballnose Endmill

P20

PX5

RPM

1600

3000

Feed (in/min)

16.6

33.0

Depth (Contour)

.160-.180

.160-.180


Program time was reduced from 5.7 minutes to 2.85minutes
Tool No. 3
.750 Sandvik Ballnose Endmill

P20

PX5

RPM

2660

3000

Feed (in/min)

 18.2

36.0

Depth (Step Over)

.160

 .160


Program time was reduced from 4.91 minutes to 2.5 minutes
Tool No. 4
(Finish cutter) 1.000 Diameter Iscar Ballnose Endmill

P20

PX5

RPM

2419

3000

Feed (in/min)

19.35

40.00

Depth

.060

.060


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:
EDM
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.
Polishing
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
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.
Welding
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)

Welding method

 MAG

Filler rod

PX5 Weld Rod

Filler rod Diameter

0.047″

Welding Current

280 A

Gas flow rate

25 /min

Pre/post heating

 None

Results

PX5

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
4) Distortion
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.

Test Conditions

Welding method

TIG

Filler rod

PX5 Weld Rod

Filler rod Diameter

0.094″

Welding Current

125 A

Gas flow rate

 7 /min

Pre/post heating

 None

Test Method

Results

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.
Weld Sink

Test Conditions TIG: 160A, no filler Test piece: 10 degree slant

Weld Sink at Heat Affected Zone

PX5

P20

4140

In this section we will feature answers to commonly asked questions. Check back often, as this page is regularly updated.

International Mold Steel specializes in pre-hardened mold and tool steels that are considered to be the finest available in the market place today. Because of their unique and homogenous make-up, deviation in hardness or hard spots is a thing of the past. When machining these materials it will become immediately apparent that much faster metal removal rates can be achieved.

Material Removal Rates
Consider this: material removal rate during this time span in approximately 300 pounds of steel. It showed that we could remove a lot of steel with moderate surface feet but a heavy chip load. Once again, the clean make-up of the material made this possible.

To Calculate Surface Feed
Surface speed is usually given in feet per minute. It is the distance (in feet) that the outermost cutting edge of a rotating tool (circumference) covers in the span of 1-minute.

To understand how this translates into spindle speed, or revolutions per minute (rpm) that the cutting tool is revolving, review this example:

Example:
Surface feet 400 feet per minute Diameter of cutting tool is 4 inches. Revolutions per minute (rpm) if cutting tool is ____

Equation:
C = Surface feet per minute (feet) D = Diameter of cutting tool (inches) R = Revolutions per minute of cutting tool (rpm)

R = (C x 12) = (400 x 12) = 4800 = 382 rpm
        (D x Pi) (4 in. x 3.14) 12.56

If you need to know surface feet per minute and the cutter diameter and spindle speed is known, you will have this equation:

C =

Pi x D x R

__________

12

=

3.14 x 4 x 382

__________

12

= 400 sf. 



To Calculate Chip Load
Chip load is the amount of materials (in .001 inches) that each cutting flute or cutting insert of a rotating tool removes.

Chip load is calculated by dividing the distance of the table travel or feed per minute in inches by the spindle speed of the machine. This will give you the distance the cutter traveled in one revolution. This number is then divided by the number of cutting flutes or inserts.

Example:
Spindle speed is 450 rpm. Table travel or feed rate is 60 inches per minute. Number of flutes or cutting inserts is 6.

Equation:
R = Spindle speed (rpm)
I = Number of cutting flutes or inserts
S = Distance of feed rate or table travel in inches.
C = Chip load


C = 

(

S

___
R

) (

60

____
450

)

=

.13333

 __________

6

= .0222

I



To Calculate Feed Rate
S = C x I x R =
S = .0222 x 6 x 450

To find rpm of spindle or R with chip load and feed rate known:

R =

S

_____

I x C

=

60

__________

6 x .0222

=  450 rpm 

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