Mold halves with metal-matrix composite at feature areas

Abstract

A mold half, especially for blow molding of thermoplastic articles, has a mold body defined at least in part by a single piece of aluminum or aluminum alloy mold material having a cavity and a pinch-off or other feature area and further having a metal-matrix composite (MMC) layer formed integrally in the mold body at the pinch-off or other feature area. A mold is fabricated from two mated mold halves. A process of producing a mold half involves machining a single piece of mold material to provide a mold body having a cavity and a pinch-off or other feature area, the pinch-off or other feature area being of smaller dimension than required for the mold half, integrally forming a metal-matrix composite layer in the pinch-off or other feature area to build up the pinch-off or other feature area to at least a dimension required for the mold half. The metal-matrix composite comprises an aluminum-nickel alloy matrix (e.g. AI-12Si alloy alloyed with Ni) having WC particles embedded therein or a aluminum matrix (e.g. AI-12Si alloy) having TiC particles embedded therein and has greater wear resistance, greater strength, greater toughness or any combination thereof than the mold material.

Claims

1. A mold half comprising a mold body defined at least in part by a single piece of aluminum or aluminum alloy mold material, the single piece defining a mold cavity by a cavity surface having a shape for imparting to a part of a molded article, the cavity surface including a feature area comprising a layer of a metal-matrix composite (MMC) formed integrally therein, the MMC comprising an aluminum-nickel alloy matrix having WC particles embedded therein or an aluminum matrix having TiC particles embedded therein, and the cavity surface defined by the aluminum or aluminum alloy away from the feature area.

2. The mold half according to claim 1, wherein the WC or TiC particles are distributed in the matrix in an amount in a range of from 5 wt % to 50 wt %, based on the weight of the composite.

3. The mold half according to claim 1, wherein the WC or TiC particles are distributed in the matrix in an amount in a range of from 20 wt % to 35 wt %, based on the weight of the composite.

4. The mold half according to claim 1, wherein the MMC is formed by cladding a powder mixture onto the cavity surface at the feature area, the powder mixture comprising an Al-12Si alloy.

5. The mold half according to claim 1, wherein the MMC comprises the aluminum-nickel alloy matrix having embedded WC particles.

6. The mold half according to claim 5, wherein the WC particles are distributed in the aluminum-nickel alloy matrix in an amount of about 27 wt %, based on the weight of the composite.

7. The mold half according to claim 1, wherein the MMC comprises the aluminum alloy matrix having embedded TiC particles.

8. The mold half according to claim 7, wherein the TiC particles are distributed in the aluminum matrix in an amount of about 30 wt %, based on the weight of the composite.

9. The mold half according to claim 5, wherein the MMC comprises 1.5-5.4 wt % Ni, based on weight of the composite.

10. The mold half according to claim 1, wherein the aluminum or aluminum alloy away from the feature area comprises an Al alloy of any one of Al 7075-T6 through T7351.

11. The mold half according to claim 1, wherein the MMC is formed integrally with the mold cavity, and comprises a metallurgical bond between the metal-matrix composite and the aluminum or aluminum alloy.

12. The mold half according to claim 1, wherein the feature area comprises a pinch-off area.

13. The mold half according to claim 1, wherein the aluminum or aluminum alloy away from the feature area is a single piece of aluminum or aluminum alloy mold material.

14. A mold comprising two mold halves as defined in claim 1 mated to receive a molding substance.

15. The mold according to claim 14, wherein the cavity is shaped for molding a container.

16. The mold according to claim 14 which is a blow mold.

17. A process of producing a mold half comprising: machining a single piece of aluminum or aluminum alloy mold material to provide a mold body comprising a mold cavity defined by a cavity surface having a shape for imparting to a part of a molded article, except at a feature area, the feature area being of smaller dimension than required for the mold half; and integrally forming a layer of a metal-matrix composite (MMC) in the feature area to build up the feature area to at least a dimension required for the mold half, the MMC comprising an aluminum-nickel alloy matrix having WC particles embedded therein or an aluminum matrix having TiC particles embedded therein.

18. The process according to claim 17, wherein the MMC layer is formed by first engineering the mold body in which the feature area is machined to an undersized dimension, and then adding MMC material to the feature area to build up the feature to final dimension.

19. The process according to claim 17, wherein the feature area is built up with MMC material beyond final dimension and then machined down to final dimension.

20. The process according to claim 17, wherein the MMC layer is formed by laser cladding.

21. The process according to claim 17, wherein integrally forming comprises forming a metallurgical bond between the metal-matrix composite and the mold material.

22. The process according to claim 19, wherein machining the mold material comprises rough machining an area of the mold material adjacent the feature area, which is also of smaller dimension than required, and both the feature area and the adjacency are machined down to the final dimension which is the shape for imparting to a part of a molded article.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order that the invention may be more clearly understood, embodiments thereof will now be described in detail by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic drawing of a traditional blow mold half with insert segments;

(3) FIG. 2 is a schematic drawing of a one-piece blow mold half in accordance with U.S. Pat. No. 7,531,124;

(4) FIG. 3 is a schematic drawing of one embodiment of a one-piece blow mold half pre-machined to an undersized shape at the pinch-off and other feature areas;

(5) FIG. 4 is a schematic drawing of one embodiment of a metal-matrix composite (MMC) layer integrated on to the mold half of FIG. 3 at the pinch-off area, where FIG. 4A shows the MMC layer with an initial excess of MMC material and FIG. 4B shows the MMC layer after being machined to final dimension;

(6) FIG. 5 is a schematic drawing of a one-piece blow mold half of the present invention having a metal-matrix composite layer integrated at the pinch-off and other feature areas;

(7) FIG. 6A depicts microstructure of a cross-section of a Al 7075-T651 substrate clad with a Al 4047+30% (90% WC+10% Ni) metal-matrix composite layer;

(8) FIG. 6B depicts microstructure of a cross-section of a Al 7075-T651 substrate clad with a Al 4047+30% (TiC) metal-matrix composite layer;

(9) FIG. 7 depicts a graph showing hardness depth profile of Al 4047+30% (90% WC+10% Ni) metal-matrix composite layer clad on Al 7075-T651 substrate;

(10) FIG. 8 depicts a graph comparing Vickers hardness of Al 4047+30% (90% WC+10% Ni) metal-matrix composite layer to that of Al 7075-T651, A2 steel, BeCu alloy and Stainless Steel Stavex ESR; and,

(11) FIG. 9 depicts a graph comparing wear loss of Al 4047+30% (90% WC+10% Ni) and Al 4047+30% (TiC) metal-matrix composite layer to that of Al 7075-T651, A2 steel, BeCu alloy and Stainless Steel Stavex ESR.

DESCRIPTION OF PREFERRED EMBODIMENTS

(12) FIG. 1 depicts a traditional blow mold half for a bottle blow mold in which insert segments are used in the pinch-off and other feature areas. Thus, mold half 10 comprises mold body 11 having cavity 12. Pinch-off insert segment 14 comprising raised pinch-off area 15 is inserted into pinch-off insert area 13 of the mold body and secured to the mold body by bolts. Bottle top thread insert 17 comprising raised thread feature 18 and bottle top insert 19 comprising raised bottle top feature 20 are inserted into bottle top feature insert area 16 of the mold body and secured to the mold body by bolts. Bottle shoulder insert 22 comprising raised shoulder feature 23 is inserted into shoulder insert area 29 of the mold body and secured to the mold body by bolts.

(13) FIG. 2 depicts a one-piece blow mold half for a bottle blow mold in accordance with U.S. Pat. No. 7,531,124. Mold half 30 comprises mold body 31 having cavity 32, raised pinch-off area 35, raised thread feature 38, raised bottle top feature 40 and raised shoulder feature 43. The mold body, pinch-off area and all three features comprise the same mold material.

(14) FIGS. 3-5 depict one embodiment of a one-piece blow mold half for a bottle blow mold in accordance with the present invention at various stages of fabrication. Referring to FIG. 3, one-piece blow mold half 50 comprising aluminum alloy mold body 51 and cavity 52 is pre-machined to an undersized shape at pinch-off area 53, thread feature area 56, bottle top feature area 57 and shoulder feature area 59. Referring to FIG. 4A, in order to complete the mold half, a layer of MMC material is laser clad at pinch-off area 53 (and the other feature areas not shown in FIG. 4) to provide raised layer 70 of the cladding material having excess portion 71. In order to avoid undercut and/or mismatch, mold body 51 at each side of raised layer 70 is rough machined prior to the laser cladding step to leave spare layer 72 of mold material at each side of raised layer 70. After the cladding step, spare layer 72 is machined off along with excess portion 71 of the cladding material to bring mold body 51 and raised layer 70 to final dimension (FIG. 4B). For certain processes, the spare layer may not be necessary provided no undercut and/or mismatch between the MMC material and the mold body occurs. Referring to FIG. 5, after cladding, one-piece blow mold half 50, having mold body 51 and cavity 52, comprises clad pinch-off area 55 and clad other feature areas 58, 60 and 63 in which an MMC layer is integrally formed.

Example 1

Laser Cladding of Al 7075-T651 Substrate with Al 4047+WC/Ni

(15) Laser cladding was performed by using a focused Nd:YAG laser beam with a 115-mm focal length lens. A powder feeder was used to simultaneously deliver Al 4047 and WC/Ni powder mixture through a feed nozzle into the melt pool at a rate of about 2 g/min. The laser beam and powder feeding nozzle were kept stationary, while the Al-7075-T561 substrate was moved under the beam by a CNC motion system. The cladding was conducted with an average laser power up to 500 W with a beam diameter of about 1 mm. A laser pulse duration of 10 ms and a frequency of 10 Hz were used for the processing. An overlap ratio of 30% was used between passes to produce multi-passes to cover the required area, while a z movement of about 130 m was used to deposit multi-layers to reach the required height.

Example 2

Laser Cladding of Al 7075-T651 Substrate with Al 4047+TiC

(16) Laser cladding was performed by using a focused Nd:YAG laser beam with a 115-mm focal length lens. A powder feeder was used to simultaneously deliver Al 4047 and TiC powder mixture through a feed nozzle into the melt pool at a rate of about 2 g/min. The laser beam and powder feeding nozzle were kept stationary, while the Al-7075-T561 substrate was moved under the beam by a CNC motion system. The cladding was conducted with an average laser power up to 500 W with a beam diameter of about 1 mm. A laser pulse duration of 10 ms and a frequency of 10 Hz were used for the processing. An overlap ratio of 30% was used between passes to produce multi passes to cover the required area, while a z movement of about 200 m was used to deposit multi-layers to reach the required height.

Example 3

Microstructure Analysis of Clad Substrates

(17) In a preliminary experiment, a layer of Al 4047 (which is the matrix material of the metal-matrix composite) was laser clad on to Al 7075-T651 substrate by a modification of the procedure of Example 1 in order to examine the microstructure of the clad specimen. This was compared to a similar specimen in which a layer of Al 7075 was clad on to Al 7075-T651 substrate. Examination by optical microscopy of a cross-section of the specimens showed that cladding with Al 7075 showed a tendency for cracking while cladding with Al 4047 produce a good metallurgical bond without inducing cracks or pores in the clad layer. Further, the laser clad Al 4047 layer showed good machinability, a smooth transition of hardness from the substrate to the clad layer, and a generally uniform hardness through the layer. Finally, a polishing test showed that the laser clad Al 4047 layer is superior to the Al 7075-T651 substrate in polishing.

(18) With reference to FIG. 6A, microstructure analysis was extended to a metal-matrix composite (MMC) in which Al 4047+30% (90% WC+10% Ni) MMC layer 100 was laser clad on to Al 7075-T651 substrate 101 in accordance with the process in Example 1. The MMC comprises WC particles embedded in an Al 4047/Ni matrix formed using 30 wt % WC/Ni material. The WC/Ni material consists of 90 wt % WC (tungsten carbide) and 10 wt % Ni (nickel). Thus, the amount of WC in the MMC layer is about 27 wt % and the amount of nickel alloyed with the Al 4047 is about 3 wt %, based on the weight of the MMC. A good metallurgical bond was formed with no formation of cracks or pores in the MMC layer. Further, in the MMC layer, WC hard particles 102 were evenly distributed in Al 4047/Ni matrix 103, while the Ni from the WC/Ni material dissolved in the Al 4047 to form intermetallics that further increase matrix hardness. Similar experiments were performed with other metal-matrix composites, i.e. Al 4047+Al.sub.2O.sub.3 and Al 4047+WC/Co. In the case of Al 4047+Al.sub.2O.sub.3, laser cladding did not generate hardening, probably due to the decomposition of Al.sub.2O.sub.3 during the cladding process. In the case of Al 4047+WC/Co, the clad layer had improved wear resistance but showed a tendency to crack.

(19) With reference to FIG. 6B, microstructure analysis was extended to a metal-matrix composite (MMC) in which Al 4047+30% (TiC) MMC layer 200 was laser clad on to Al 7075-T651 substrate 201 in accordance with the process in Example 2. The MMC comprises TiC particles embedded in an Al 4047 matrix formed using 30 wt % TiC material. A good metallurgical bond was formed with no formation of cracks or pores in the MMC layer. Further, in the MMC layer, TiC hard particles 202 were evenly distributed in Al 4047 matrix 203.

Example 4

Microhardness Analysis of Clad Substrates

(20) A Vickers hardness test (ASTM E384-10e2) was conducted on the laser clad products of Examples 1 and 2 using a load of 500 g for 15 s at evenly distributed points spaced by 0.2 mm. FIG. 7 depicts hardness depth profile of the Al 4047+30% (90% WC+10% Ni) MMC layer clad on the Al 7075-T651 substrate. It is evident from FIG. 7 that the Al 4047+30% (90% WC+10% Ni) is harder than the Al 7075-T651 substrate. The substrate near the clad layer has a softening zone with a Vickers hardness (Hv0.5) of around 140, perhaps due to annealing induced by laser cladding. There was a larger deviation in the hardness of laser clad (Al 4047+30% (90% WC+10% Ni)) layer due to heterogeneous features in the MMC.

(21) Further, with reference to FIG. 8, Vickers hardness of the Al 4047+30% (90% WC+10% Ni) MMC layer was compared to that of the Al 7075-T651 and other typical mold insert materials (i.e. A2 steel, BeCu alloy and Stainless Steel Stavex ESR). Table 1 summarizes the results and includes the hardness of the Al 4047+30% (TiC) MMC layer. Table 1 and FIG. 8 demonstrate that the Al 4047+30% (90% WC+10% Ni) layer is harder than Al 7075-T651 and approaches that of the steels. Table 1 demonstrates that the Al 4047+30% (TiC) layer is somewhat softer than Al 7075-T651.

(22) TABLE-US-00001 TABLE 1 Vickers Hardness Material Vickers Hardness (Hv0.5) A2 steel 222 BeCu alloy 384 Stainless Steel Stavex ESR 231 Al 4047 + 30% (90% WC + 10% Ni) 198 Al 4047 + 30% (TiC) 141 Al 7075-T651 177

Example 5

Wear Resistance Analysis of Clad Substrates

(23) Wear resistance was performed with pin-on-disc testing as per ASTM G99-05 (2010) to evaluate sliding wear resistance of a laser-clad specimen of the present invention (Al 4047+30% (90% WC+10% Ni) on Al 7075-T651; Al 4047+30% (TiC) on Al 7075-T651) in comparison to Al 7075-T651, A2 steel, BeCu and Stainless Steel Stavex ESR. The test was performed with a Falex Pin-on-Disc Tester with a dry slide to determine volume wear loss. All sample surfaces were fine ground and cleaned before testing. The testing was done with a normal load of 3.5 N, at a linear slide speed of 300 mm/s over a total slide distance of 1500 m using a tungsten carbide (WC) ball.

(24) Wear loss results from the pin-on-disc testing are shown in FIG. 9 and summarized in Table 2. Using wear of Al 7075-T651 substrate as a reference, relative wear resistance (R) was calculated by dividing volume wear loss of Al 7075-T651 by volume wear loss of the other materials. Wear resistances of the clad Al 4047+30% (90% WC+10% Ni) and Al 4047+30% (TiC) in accordance with the present invention are significantly better (5.28 and 4.99 times, respectively) than that of the Al-7075-T651 substrate. The wear resistances of the Al 4047+30% (90% WC+10% Ni) and Al 4047+30% (TiC) layers are similar to that of Stavex Stainless Steel. The wear resistances of the Al 4047+30% (90% WC+10% Ni) and Al 4047+30% (TiC) layers are close to but still relatively inferior to that of BeCu.

(25) TABLE-US-00002 TABLE 2 Wear Loss Volume Wear Loss Relative Wear Material (10.sup.3 mm.sup.3/m) Resistance (R) A2 steel 0.085 17.1 BeCu alloy 0.157 9.27 Stainless Steel Stavex ESR 0.251 5.80 Al 4047 + 30% (90% WC + 0.276 5.28 10% Ni) Al 4047 + 30% (TiC) 0.292 4.99 Al 7075-T651 1.456 1

(26) Cladding of an aluminum or aluminum alloy substrate with a Al 4047+30% (90% WC+10% Ni) or Al 4047+30% (TiC) metal-matrix composite provides an excellent balance of properties for molding, especially blow molding, applications. The clad metal-matrix composite layer forms a good metallurgical bond with the substrate with no formation of cracks or pores. Excellent hardness and wear resistance for Al 4047+30% (90% WC+10% Ni), approaching that of materials used in the prior art, and excellent wear resistance for Al 4047+30% (TiC) leads to extended life at feature areas of the mold, while good thermal compatibility between the substrate and metal-matrix composite layer makes the MMC layer less prone to cracking further extending the life of the mold. Good machinability provides for ease of manufacturing.

(27) In contrast, Al 7075-T651 itself is soft and easily worn, therefore its use at feature areas in one-piece molds results in reduced service life of the molds. Use of typical hard, wear resistant materials such as steels and BeCu alloy at feature areas extends working life of aluminum or aluminum alloy molds, but is still unsatisfactory since thermal incompatibility leads to cracking which prevents a full realization of the benefits of the harder material. Further, such hard, wear resistant materials are difficult to machine, which makes manufacturing more difficult.

REFERENCES

(28) The contents of the entirety of each of which are incorporated by this reference.

(29) Dickinson A, et al. (1991) Process for forming an extrusion-blow molded ultrathin container using a heat generating pinch off arrangement. U.S. Pat. No. 5,021,209 issued Jun. 4, 1991.

(30) Kobayashi S. (1996) Blow molding die and method of manufacturing same. European Patent Publication 742,094 published Nov. 13, 1996.

(31) Lee N. (2007) Understanding blow molding. Hanser Publications, p. 61-70.

(32) Paget T. (2009) One-piece blow mold halves for molding a container. U.S. Pat. No. 7,531,124 issued May 12, 2009.

(33) Other advantages that are inherent to the structure are obvious to one skilled in the art. The embodiments are described herein illustratively and are not meant to limit the scope of the invention as claimed. Variations of the foregoing embodiments will be evident to a person of ordinary skill and are intended by the inventor to be encompassed by the following claims.