Die Materials

DIE MATERIALS& TECHNOLOGIES

2009

Turn Research into ActionBusiness Solutions Based on NADCA Research

NORTH AMERICAN DIE CASTING ASSOCIATION

Project Objectives: High productivity is the ultimate driver for most process improvements. In die casting, in-creasing productivity is to a large extent determined by the cycle time. In turn, the cycle time depends on the ability of the cooling system to extract the heat from the dies. Ideally, this function is performed by optimized de-sign of the internal cooling lines and use of high thermal conductivity die materials for rapid heat extraction from the casting. This project was designed as an in-plant ex-perimental program to determine the potential for cycle time reduction by aggressive placement of cooling lines and use of high thermal conductivity cores.

Approach: Traditional design of the cooling lines is an iterative process that targets a balance between the heat input from the molten metal and the heat extracted by the coolant. At the end of this process, the designer will have a schematic of the die with the required water or oil line sizes and routing. The heat input is determined mainly by the weight and the total surface of the casting, the cycle time, and the alloy cast. This heat must be extracted by locating appropriate cooling lines in proximity to the cavity. It is common practice to divide the casting into segments, and calculate the heat balance individually for each seg-ment. The length of the cooling line is determined based on heat transfer calculations. In general, cooling lines located closer to the surface of the cavity are more ef-fective in removing heat. However, the industry has ad-opted thumb rules relative to the depth of the cooling lines that provide a safeguard from catastrophic cracking of the die. These thumb rules suggest a minimum distance of 0.75” between the water cooling lines and the surface of the cavity. This distance can be reduced to 0.5” in the case of oil lines. According to these thumb rules, drilling cooling lines closer to the surface increases the risk of gross cracking, i.e., catastrophic cracking due to exces-sive thermal stresses. The financial liability associated with cracking a die is significant. Consequently, designers have been taking a conservative approach by following these guidelines. However, anecdotal evidence sug-gests that cooling lines can be placed closer to the sur-face. Considering modern advances in steel quality and heat treat specifications, this option should be explored, especially when the die develops hot spots that result in soldering and downtime. The main reason to experi-ment with more efficient internal cooling is the potential for shorter cycle time. The end result of shorter cycle time is a more productive die casting operation.

Results: The project was conducted in collaboration with St. Clair Die Casting, St. Claire, MO. A four cavity die mak-ing aluminum heat sinks, about 4.5”x2.5”x1.15” weighing 1.1 pounds each, was built for this study. A superior tool

HIGH PRODUCTION RATE TOOLINGD. Schwam, Case Western Reserve University

steel with higher toughness of over 20 ft-lbs, compared to 10-12 ft-lbs typical in Premium Grade H13 was used. The higher toughness minimizes the risk of gross cracking due to increased thermal gradients when cooling lines are closer to the surface. The cast parts are chunky and have a larger weight to volume ratio than typical die castings. This means a relatively large amount of heat needs to be extracted after each shot in order to bring the die back to the required temperature before the next shot can be made. The potential for faster extraction of the heat by improved cooling line design is high. Another advantage of this die set is the existing base-line of operating condi-tions and performance from a previous study. An identical die has been in use for the last four years. The die was re-designed by bringing the cooling lines closer to the sur-face. The H13 core pins were substituted with Anviloy to further enhance heat extraction during solidification. Sub-sequently it was operated with progressively shorter cycle times while monitoring the die temperature. A long term goal is to determine potential changes in die life.

The first step in the project was to re-design the size and location of the cooling lines. The distance of the cooling lines from the surface of the die has been reduced from 0.87” to 0.5”. A detailed flow and solidification computer simulation was conducted to determine the effect of the changes in the cooling line configuration. The simula-tion is used to verify the design of the gating and cooling system in regard to the cooling line size and location; it will indicate any hot spots in the die or areas where the molten metal becomes too cold to fill the mold. In such cases, the cooling line design is modified and the simulation is repeated until a satisfactory temperature distribution is obtained. This procedure is also effective in preventing shrinkage porosity associated with undesirable hot spots in the casting. The simulation predicted a cycle time shorter by 20% relative to the original cooling line design.

To confirm the results of the simulation, the cycle time feasible with the re-designed cooling system was mea-sured in production runs. Embedding thermocouples in the inserts and attaching them to a data acquisition sys-tem was used to monitor the temperature. A high tem-perature flow meter was installed to measure the flow of the cooling medium in the inserts. The cycle for die casting the tank thread heat sinks could be shortened by 13% by improved heat extraction into water cooling lines drilled closer to the surface.

A set of inserts was fabricated out of a tool steel with su-perior toughness of over 20 ft-lbs, compared to 10-12 ft-lbs typical in Premium Grade H13. The higher toughness minimizes the risk of gross cracking due to increased

Turn Research into Action Business Solutions Based on NADCA Research

thermal gradients when cooling lines are closer to the surface. Production runs with the improved dies have demonstrated a reduction of 13% in cycle time. Further reductions in cycle time are anticipated by replacing the oil with water-cooling.

Implementation Strategy: Die steels with superior toughness as compared to Premium Grade H13 are now available. These die materials offer the die caster with an opportunity to move cooling lines closer to the cavity surface for faster heat removal and lower cycle times. The die caster should consider using new materials and placing cooling lines closer to the cavity surface. Con-sult with the researcher and die material suppliers to ob-tain guidance for placing cooling lines at a safe distance from the cavity surface. ■

Monitoring Task Force: Die Materials CommitteeSponsored by: DoD-ARDEC, Picatinny, NJ and Benet Laboratories,

Watervliet, NY and NADCA

For further information, contact:North American Die Casting Association847.279.0001 – phone847.279.0002 – faxwww.diecasting.org/[email protected]

NORTH AMERICAN DIE CASTING ASSOCIATION241 Holbrook Dr. Wheeling, IL 60090

Email: [email protected]/research


Figure 1. Oil (V04) vs. Water (V05) comparison when moving lines closer to the cavity surface. Computer simulation predicted a 20-40% cycle time reduction. Measured reduction was 13% when oil was used in the lines.

INTEGRATION OF RSP TOOLING WITH RP FOR DIE CASTING APPLICATIONSJ. Folkestad, Colorado State University; J. Knirsch, RSP Tooling, LLC; K. McHugh, Idaho National Engineering and Environmental Laboratory


Project Objectives: The objective of this project is to de-velop and utilize RSP Tooling within the die casting industry by introducing a new tooling technology that will reduce lead times, extend die life, and reduce energy consumption.

Approach: The Rapid Solidification Process (RSP™) was developed at INEEL under grants from the DOE. The initial patent for the process was written in 1990 and had as its basis the invention or discovery that a liquid could be broken down into small droplets by use of the shearing effect of a flowing gas. There are a large num-ber of possible applications of this invention.

An early application of the process was the production of low-carbon steel strip, the industry’s highest volume com-modity. There are many advantages to producing strip us-ing RSP, but the most significant to DOE was a significant reduction in energy use. Work on the process resulted in another patent in 1995 which introduced the use of the pres-surized injection of liquid into a Ventura tube, thereby im-proving the operational flexibility of the device while produc-ing a more uniform droplet size distribution. An additional benefit was the ability to control and increase the cooling rate of the droplets, which results in microstructure and ma-terial property improvements in the deposited metal.

Since the grain structure of the spray deposited metal was good, as was the ability of the spray deposited metal to replicate complex surface shapes, the idea of using the process to manufacture tools was developed. This resulted in two things: a new patent in 1997, and the terminology of RSP™ Tooling. Additional patent applica-tions have been submitted, which refine the actual pro-cess to produce tooling.

RSP™ Tooling is a spray forming technology tailored for producing molds and dies. The process allows the die caster to build production tooling in the time it usually takes

to make prototype tooling. This means that the prototypes can be made from the actual production process and the time normally needed to produce the production tooling disappears. Furthermore, very little is sacrificed by using the RSP process and there is strong evidence that this rapid tooling approach may increase tool life compared to conventional tooling made from the same alloy.

Results: Although the RSP™ Tooling process can manu-facture tooling for any forming process from virtually any tooling material, it is of significant benefit to die casting. This is true because of the added benefits that develop when spray forming H-13 and because of the nature and expense of die cast tooling. The speed of the process allows the die caster to compete with standard prototype sources for producing prototypes in the required timing. This benefits the customer by receiving a prototype made from the production process instead of an alternative pro-cess providing different properties. Another benefit is that the time while the prototype is being tested can be used to develop the die cast process. In normal practice, the prototype testing period is idle time to the die caster. With this tooling, the high quality production process can be de-veloped during the prototype period without the pressure of meeting production delivery times.

The benefits to the die caster don’t stop at die build. There is strong evidence developed from actual produc-tion testing that the RSP tool is more resistant to wear, heat checking and soldering than the standard heat-treated steel insert. This reduces the ongoing high cost of die maintenance and replacement tooling. When the tool does need to be replaced, the amount of time needed to build the replacement component is cut substantially, further reducing the need for large tooling inventories.

The benefits of the RSP™ Tooling process can be sum-marized as:

• Reduces tooling lead time. • Reduces tooling cost, especially for replacement

tooling.• Can be artificially aged and does not need to be

heat treated.• Increased tool life. • The process can use standard H-13 in place of pre-

mium grade H-13 and can probably use recycled materials.

• The process eliminates the need to build prototype tooling.

• The process can replicate details smaller than what can normally be machined.

Figure 1. Process Sketch





Implementation Strategy: Die casters should evaluate the potential of RSP™ Tooling to reduce the cost of die cast tooling. Especially die casters who utilize small dies may be able to substantially reduce the cost and lead time for dies.

RSP™ Tooling, LLC, was formed in January 2002 to design, build, use and sell machines that manufacture tooling using this process. A production machine is in operation which can produce a 50-pound steel insert (6”x6”x4”) every two hours. Die inserts are being pro-duced for various processes, including die casting.

The RSP technology has the potential to eliminate a sub-stantial bottleneck for die casters, tooling lead time, while potentially providing longer lasting tooling as well. ■

Figure 2. Machine Process

Figure 3. RapidSolidification in Action

Monitoring Task Force: Die Materials CommitteeSponsored by: U.S. Department of Energy and NADCA

This research is featured in more detail in the following transactions:T02-051 and T05-053

RAPID TOOLING FOR LOW VOLUME DIE CASTINGJ. Wallace and D. Schwam, Case Western Reserve University


Project Objectives: Rapid prototyping casting methods are often employed when a small number of cast parts are needed. The casting method of choice is dictated by the dimensional accuracy, mechanical properties and surface finish required of the parts. Sometimes the de-sirable casting method for rapid prototyping is a metal mold technique such as die casting, squeeze casting or permanent mold casting. In all of these cases, a metal mold needs to be fabricated first.

In the military, rapid tooling is needed when a product is un-der development or when relatively few parts are required to replace components in legacy weapon systems. It would strengthen and speed the supply chain to develop rapid, low-cost means of producing dies suitable for a limited number of die castings such as 5,000 pieces before serious thermal fatigue or other cracking occurred in the tooling.

The objective of this project was to evaluate methods and materials that can potentially shorten the lead time and/or reduce the cost of rapid tooling used in die cast-ing, squeeze casting and permanent mold casting. The dimensional characteristics and durability of the resulting tooling were also addressed.

Approach: With few exceptions, most metal molds are fab-ricated from ferrous alloys. Tool steels in general and hot tool steels in particular are the most frequently used die materi-als for production die casting and squeeze casting inserts. Permanent molds are often cast in gray or ductile iron.

The types of steels of interest in this study were H-13, H-11, or modified H-11, as well as some lower alloy, more economical, steels such as 4140, P20, and, for

very short runs, 1040, or high strength gray and ductile iron. The study evaluated and compared the following methods of rapid tooling fabrication:

1. Casting ductile iron rapid tooling in no-bake sand molds from oversized patterns produced from 3D CAD programs.

2. Investment casting rapid tooling in H-13 die steel from prototype wax patterns produced from a 3D CAD model.

3. Machining rapid tooling from a forged block that had been tempered to a lower hardness of 40-42 HRC. This method utilized Numerical Control (NC) machining from 3D CAD computer models of the tooling for rough and finish machining.

The evaluation of the potential materials and fabrication processes included dimensional accuracy, surface condi-tion and performance of the tooling. A key issue in select-ing the material for rapid tooling is to ensure it will last long enough to make the required number of parts yet last no longer than necessary. To test the performance of candidate materials, the Thermal Fatigue Immersion test at CWRU was used to simulate the casting environ-ment. This test has become a preferred and widely ac-cepted method of screening die and mold materials. The standard procedure is to operate the test for 5,000 immer-sion cycles, measure the cracking pattern and follow this method for 10,000 and 15,000 total cycles. A more severe crack pattern indicates a lower thermal fatigue resistance of the tested material. The results of this test have corre-lated closely with the behavior of dies in industry.

Results: Rapid tooling for permanent mold casting was made by casting ductile iron in no-bake molds with sat-isfactory results. While some machining was required to bring the critical dimensions of the cavity into the speci-fied tolerance window, the lead time was still relatively short. When die casting inserts were investment cast from H-13 tool steel, the flatness and dimensional accu-racy were not acceptable. While machining of the cast inserts is an option, it would offset some of the advan-tages of net shape casting, especially the lead time.

While machined rapid tooling can be made in very large sizes, cast rapid tooling is normally limited to smaller sizes. Complex rapid tooling can often be cast in a more cost effective way and with shorter lead times. However, the accuracy and surface finish of cast rapid tooling is not as good as machined rapid tooling.

Fabrication of rapid tooling of tool steels by NC machining, directly from a CAD model provides the best combination

Figure 1. Direct Metal Deposition Process





of lead time, performance and cost. Careful selection and heat treating of the insert material is essential. Recent advances in cutting tool technology allow high speed machining of quenched and tempered steels up to 42-43 HRC hardness. Furthermore, Electro-Discharge Ma-chining (EDM) can be performed on rapid tooling inserts of any hardness. These developments narrow the gap between rapid and production tooling. It is possible, as demonstrated by this study, to utilize modified H-11 steels in a pre-hardened condition, to fabricate rapid tooling that can last long enough to be used for production of large numbers of die castings, well beyond short runs. At the same time, if only a small number of castings are required, further savings in cost can be achieved by utilizing lower alloy, softer steels. In every case, the size and configu-ration of the part and the die design have to be carefully considered to avoid premature failure of the tooling.

Figure 2. P20 inserts produced in less than three weeks from a CAD model by Rapid Machining

Implementation Strategy: This project demonstrated that there are techniques which can be used to quickly provide tooling for prototype castings or even small production runs. These techniques open new opportunities for cast-ing producers to enter new markets, where the long lead times required for conventional tooling prohibited their par-ticipation. In addition, these techniques offer the potential to reduce the lead time and cost of even conventional die casting, squeeze casting, or permanent mold tooling. ■

Monitoring Task Force: Die Materials Task ForceSponsored by: U.S. Department of Defense and NADCA

This research is featured in more detail in the following transaction:T07-061

EFFECT OF DIE DESIGN ON THERMAL FATIGUE CRACKING OF DIESJ. Wallace & D. Schwam, Case Western Reserve University


Project Objectives: The thermal fatigue of steel die cast-ing dies becomes more severe at higher operating service temperatures, reducing die life significantly. Consequently, to extend die life, die design has to address efficient cooling methods. A key issue in this respect is the size and loca-tion of cooling lines relative to the surface of the die. This subject was studied in detail, to determine the effect of die temperature on thermal fatigue cracking of H13 dies.

Approach: This investigation correlates the thermal fa-tigue cracking of die steel in an immersion test specimen with the die temperature attained near the surface and the corresponding softening of the steel. The effect of cooling line location versus the surface temperature and the resulting cracking pattern were determined for vari-ous immersion times and different sizes of cooling lines.

The experiments involved testing three specimens for which the immersion time in the molten metal was the only variable. The maximum and minimum temperatures reached at the corner of the specimen and the temperature distribution inside the specimen (toward the cooling line) varied as a function of the time spent in the molten metal bath. The thermal fatigue behavior of the three specimens was compared with the reference specimen which had 9 seconds of immersion time. There is a clear trend for the thermal fatigue cracking parameters to increase with im-mersion time. Since the thermal fatigue test at CWRU has previously provided a remarkably accurate prediction of the relative thermal fatigue cracking, these results should have good applicability in die casting operations.

Results: Higher die temperatures induce faster and deeper softening of the steel leading to more thermal fatigue damage. Die designs with cooling lines close to the die surface can reduce this damage significantly.

The results demonstrate that the higher the temperature, the more thermal fatigue damage will occur. Initially, the surface strain is within the elastic capabilities of the die steel. The surface of the specimen has irregularities in the form of corrosion pits or surface scratches.

These sites serve as stress concentrations. Plastic de-formation can therefore occur at stresses well below the yield strength of the parent material (it must be noted that the strength of the material drops at high tempera-ture) and initiate fatigue cracks. In addition to the stress concentrations caused by surface imperfections, tem-pering weakens the surface material. A cumulative fa-tigue process occurs in the material, since plastic strain gradually increases during the test as a result of the low-er yield strength of the material. The compressive stress

will eventually exceed the elastic limit of the steel and plastic deformation will take place after the initial elastic strain has occurred. Under these conditions, it is there-fore necessary for the material to drop below a certain strength level characterized by a lower hardness value in order for the crack to initiate.

It has been experimentally demonstrated that if the strength properties of the material are reclaimed before the cracks are initiated; the thermal fatigue behavior can be markedly improved. This experiment consisted of cy-cling an H13 steel specimen for 2,500 cycles and then re-heat treating it to the original hardness value. It is clearly shown that re-heat treating the specimen to 51 HRC after every 2,500 cycles exhibits better resistance against heat checking. The cyclic heat treatment re-claimed the strength of the material and its resistance against cracking, impeding crack initiation, as well as the propagation of the existent cracks.

The following three conclusions were drawn from the project:

1. For a configuration without severe stress concentra-tors, the softening of the steel is the most important factor for the crack initiation. Less thermal fatigue damage has been observed when the conditions promoted lower temperature at the surface, which preserved the hardness and hence the strength. A high value of yield strength means higher material resistance to plastic deformation. At the same time, elevated temperature at the surface will induce a deeper softening. It appears that a condition for the extension of the thermal fatigue cracking damage is the decrease in strength ahead of the crack front.

2. In die casting applications, the highest maximum temperature will occur in the thin sections where

Figure 1. The Effect of Cooling Line Diameter on Average Maximum Crack Length





the material’s capacity to absorb and transfer the heat from the surface is very different. From another point of view, high temperature – long resident time conditions are important, because of the similarity with die casting of large components, when the die is subjected to elevated tempera-ture for longer periods of time. The experimental results have shown an important decrease of the cracking when the cooling line is positioned closer to the surface. Moreover, the experimental data indicates the existence of a temperature thresh-old, below which the thermal fatigue damage is minimal. A cooling line closer to the surface will shift the maximum temperature towards lower values, and at the same time, keep the stresses at a relative constant value. However, decreasing the maximum temperature at the surface by plac-ing the cooling lines too close to the surface may be limited by the high level of hoop stresses that could be created at the cooling line.

3. The presence of strong carbide-former elements like chromium, molybdenum, and vanadium will reduce the softening by preserving a fine distribution of carbides. These elements inhibit the coarsening of cementite in the range of 400-700°C. At the same time, these elements form fine carbides that are ther-modynamically more stable than cementite. Among the three elements, chromium-rich carbide is the most susceptible to growth, but the presence of molybde-num and vanadium inhibits it to a certain extent.

Figure 2. Total Crack Area vs. Maximum Temperature at the Corner of 2x2x7 H13 Specimen for Different Immersion Times

Implementation Strategy: This project showed that soft-ening of the steel by excessive die steel temperature is the most important factor for the initiation of cracks in the die surface. Both the use of larger cooling lines and mov-ing the cooling line closer to the die surface are effective in reducing the maximum die surface temperature. Where possible, die casters can minimize heat checking of dies by managing the maximum die temperature. In addition, the presence of molybdenum and vanadium in the die steel allow cooling lines to be closer to the die surface. ■

Monitoring Task Force: Die Material Task ForceSponsored by: U. S. Department of Energy and NADCA

This research is featured in more detail in the following transaction:T07-053

RAPID TOOLING FOR FUNCTIONAL PROTOTYPING OF METAL MOLD PROCESSESL. Ouimet, G. Ward, GM


Project Objectives: The goal of this project was to build, run and validate a mid-size transmission case die to prove out the Rapid Tooling-Rapid Machining technology and provide a new benchmark (16 weeks from design release) for prototyping medium to large die castings. Standard timing for a production die of this size is 46 to 52 weeks from release of data base to parts. Comparable timing for prototype sand castings was benchmarked at 12 weeks.

Approach: “Fast to Market” is a major initiative for the Automotive Industry. GM Powertrain’s Transmission Engineering developed a master timing plan and deter-mined that the transmission case castings were among the critical long lead time items which drove the current product lead time. Dissecting the problem further, the die casting die for the transmission case castings was one of the key drivers of lead time.

A USCAR project “Rapid Tooling for Prototyping Metal Mold Processes” took on the problem of long die cast tooling lead time. The project investigated many technologies for gener-ating the insert steel quickly and developed a generic holder block for large sized die castings. Utilizing rapid machining of prehardened H-13 steel technology and generic holder blocks, tooling lead time was cut by more than 50%.

The part design was completed using Unigraphics ver-sion 11. A fully filleted 3D solid model was completed by a very experienced designer. Process simulation soft-ware was used to design the cooling system and met-al injection system for the die. The die was built in 15 weeks from release of part data utilizing a generic holder block and rapid processed and machined pre-hardened tool steel inserts. Three thousand parts were made in six days with only minor process modifications.

Results: To achieve “fast” die cast prototypes, coor-dination of the following areas must be controlled by a cross-functional team: product design/analysis, tool de-sign/analysis/build, process design/analysis, and a ca-pable die casting manufacturer. Each of these areas is discussed in more detail below.

Product Design. The product design time was not in-cluded in the project timing but it is the key enabler to fast lead-times. Many projects have been stalled or stopped with a poorly designed casting. Good design guidelines for die cast products and an experienced product designer with excellent CAD skills are a must for setting up a successful rapid tooling project. Poor designs can cause high scrap rates and major process startup/debug problems. Poor CAD model construction can cause delays in tool programming. Filleting has long

been a major time element in the design. New CAD soft-ware revisions have eliminated many of these problems and have cut at least 4 weeks off the design process. A fully filleted 3D part solid model is needed.

The product must be designed for both tool build and die casting. Early involvement of all parties allows part design consideration to be incorporated that will have a positive effect on project timing and casting quality for both prototype development as well as production.

Tool Design. The design of the die was based around an existing generic holder block. The generic holder block is a common frame in which the part specific inserts are located and secured. This particular generic holder block was converted from a 3-slide to a 4-slide die configuration. The holder block is termed “generic” because it is designed with flexibility in mind. Regular production holder blocks are built to be robust while being economical so they tend to be specific for each part. Utilizing a generic holder block reduces tooling lead time by 16-20 weeks over a conven-tional die build. With this generic holder block as a base, in-serts were designed to produce the mid-size transmission case. Locator positions, gating position, and casting critical areas were all considered in the initial casting orientation along with whatever die set limitations there are.

The part was fully defined using Unigraphics parametric solids. This allowed rapid definition of die inserts. Tooling models were developed for CAM programming. Program-ming was done as the die design was completed. Assem-bly prints were produced, rather than individual detail draw-ings, to speed up the total design time frame. This reduced the design time by 75% over standard design time. The lead tool maker was allowed flexibility in the tool build, with the major criteria being die functioning rather than long run capability or replaceability as would be required in full pro-duction tooling. Three thousand castings was the criteria.

Tool Build. The material was purchased, and immediately heat treated to 36-38 Rc. The normal procedure would be to rough machine, heat treat, and then finish machine. This alone saved about 4 to 6 weeks versus conventional pro-duction die procedures. Only the casting areas of the inserts were benched where necessary for part removal. Normally the entire insert surface is polished. Some EDM areas were not polished to eliminate the “white layer” which is inherent in the EDM process. This saved approximately 2 weeks. Final stress relief was not incorporated. This would normally take 3-4 days. Since the holder block was available from the start, inserts were fit as operations were finished, assur-ing proper sizing, water line locations, screw locations and ejector pin locations, minimizing last minute problems.





Process Design. This added step in the project stands out as being the most different from a standard die build. This activity was done concurrently with initial tool design so no additional project time was taken. Generally the die builder designs the die registration system, cooling sys-tems, and metal injection system with help from the die caster, but with little or no knowledge of the parts func-tional requirements. The die caster sets the die up in a die cast machine with locking force and parameter capa-bilities based on past experience. The thrust of this proj-ect was to design the process based on knowledge of the functional requirements using process analysis software and NADCA process design equations. This added step saved 2 to 6 weeks in process set-up and debug.

Capable Manufacturing. Even with all of the preparation for this project, attention to every manufacturing detail had to be met. For this reason, an experienced trans-mission case die caster was selected to make the parts. The die was set and initial samples were made. On one of the initial shots the bottom slide stuck. Clearance was added and the slide re-assembled. When restarted the casting stuck in the die. Some radii were increased in non-functional areas to strengthen the part. Once the radii were added the die began to run well. The parts looked good except for one area of poor fill. The analy-sis work was reviewed and confirmed this area to be the last to fill. Based on direction from the analysis, gates were opened, vents were added, and water was turned off. This initial development work took less than 2 full days. After these changes, the castings looked better and the decision was made to accept and continue to run. From that point the die ran consistently without in-terruption for the entire 3000 piece run. ■

Monitoring Task Force: NADCA Staff and Eppich TechnologiesSponsored by: USAMP

This research is featured in more detail in the following transaction.T99-121

Business Benefit: This project provides the die caster withinformation on extending die life and reducing thermal fatiguecracking.

Project Objectives: The primary objectivewas to determine how the heat-treating ofH13 die steel can optimize its useful life.

Approach: Thermal fatigue test bars werecooled at various rates from the austenitizingtemperature. These test bars were thencycled repeatedly into molten aluminum andthen sprayed with die lubricant.

Results: The extensive studies conductedon the heat treating behavior of premiumgrade H13 steel have shown that the heattreating process is at least as important asthe selection of the proper die steel in deter-mining die life. The thermal fatigue crackingis sharply reduced by using an austenitizingtemperature that will place the maximumamount of carbide forming alloys in solutionin the austenite without reducing the toughness significantly.

This quenching temperature for H13 is 1,900ºF, although itmay be 1,875ºF for other die steels. Then, the die casting dieshould be cooled as rapidly as possible from the austenitizingtemperature to help retain as many of these alloying elementsin solution as feasible to reduce their tempering or softeningtendency at the die surface. The die life can be extended bykeeping the die surface as hard as possible in service.

The influence of the high rate of cooling on the die life isshown in Figure 1. In this figure, the effect of the cooling ratefrom the austenitizing temperature on the total area of thermalfatigue cracks obtained for the immersion thermal fatigue testis shown. Although the thermal fatigue test is small and sim-ple in design, compared to die casting dies, some of theadvantages of the rapid cool from the austenitizing tempera-ture can be obtained with dies by using an interrupted oilquenching treatment on the die.


Figure 1. Effect of Cooling Rate on Total Crack Area(Premium Grade H13 heat treated to 46-47 HRC).

The use of such a treatment is shown in Figure 2. In this case,a die insert of 14.6 by 7.9 by 7.75 inches was quenched fromabout 1,900ºF in oil for 9 minutes, pulled out into air to allow itto equalize in temperature and then reinserted in oil for cool-ing to 200ºF. This die was not cracked; it had a maximumamount of distortion of 0.030 inches. The cooling rate for thecritical temperature required was 177ºF/min. This is fastenough to provide high resistance to thermal fatigue cracking.

Figure 2. Interrupted Quench

EXTENDING H13 DIE LIFE THROUGH HEAT TREAT OPTIMIZATIONJohn Wallace and David Schwam, Case Western Reserve University

50000 10000 15000

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Heat Treatment on Die LifeThe Effect of Cooling Rate on Total Crack Area ( H13 — 46-47 HRC)

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(Die 14.6”x 7.9”x 7.75”) -- Interrupted Oil Quench @ EHT

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Cooling Rate Measured by the Surface (1/8”) Thermocouple at the Center of the Largest Face between 1750 F to 615 F is 177 F/minooo

Implementation Strategy: The implementation plan shouldbe to follow the NADCA Recommended Procedure for H13Tool Steel, Item #229. This document specifies the heat treatment cycle including austenitizing temperature, minimumquench rate, and tempering temperatures, as well as materialand heat treatment acceptance criteria. �


North American Die Casting Association

241 Holbrook Drive Wheeling, IL 60090Email: [email protected]

www.diecasting.org/research

For further information, contact:


847.279.0001 – phone847.279.0002 – facsimile

www.diecasting.org/[email protected]


Additional resources: NADCA Transaction T99-102. Also, the resultsof this project have been incorporated in the NADCA RecommendedProcedure for H13 Tool Steel, Publication Item #229 and the NADCACare and Maintenance of Die Casting Dies Manual & Checklist,Publication Item #501.

Business Benefit: This project provides the die caster withinformation on the benefits of rapid quenching to improvehardness on the die surface.

Project Objectives: The primary objective was to determinewhat can be done to minimize the effects of high compressionstresses that occur at the heated die surface in die casting.

Approach: Thermal fatigue immersion tests were conductedto determine how the austenitizing temperature and the coolingrate from that temperature contribute to die steel life.

Results: The thermal fatigue cracking of the die surface hasbeen shown to be caused by upsetting of the die produced by the high compression stresses that occur at the heated die surface. This high temperature can produce a softening of the die surface from both the temperature and the highcompressive stresses. The studies conducted on this projecthave shown how a rapid quench from the austenitizingtemperature and tempering to a high hardness can reduce thesoftening that occurs. The plot of the decrease in hardness atthe corners of the thermal fatigue immersion test conductedby this project shows how the decrease in hardness is sub-stantially less for the test pieces cooled from the austenitizingtemperature at 340ºF/minute in oil compared to the slowercool at 160ºF/min for the 5 bar nitrogen quench. The decreasein hardness is much greater for the slowly cooled specimen at50ºF/minute in a one bar nitrogen quench. These results showwhy the rapid cooling from the austenitizing temperatureincreases the die life.


The residual stress on the surface of the die is usually compressive and additive to the applied thermal stress. Whencracking occurs, the residual stress is relieved. The work conducted with applied known residual compressive and tensile stresses at the surface show somewhat reducedthermal fatigue cracking with residual tensile stress. �


RESIDUAL STRESS AND SOFTENING EFFECTSON DIE LIFEJohn Wallace and David Schwam, Case Western Reserve University






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Cooling Rate50 F/mino



1 Bar Nitrogen1875 F/49Rco

5 Bar Nitrogen1875 F/44Rco

Oil Quench1875 F/49Rco

Softening of H13 Thermal Fatigue Samples After 15,000 Cycles

Business Benefit: This project confirms the value of followingthe NADCA Recommended Procedures for H13 Tool Steel,eliminating the need for more costly testing.

Project Objectives: The primary objective was to establishthird-party industry specifications for the acceptance of premium quality H13 heat treated tool steel. The NADCARecommended Procedures for H13 Tool Steel (NADCAPublication #207) has improved the quality of die cast toolingby providing the die casting industry with premium quality H13 steel acceptance criteria, a vacuum heat treatment procedures and proper welding procedures. The documentonly provides specific acceptance criteria for the starting,annealed H13 premium steel. The acceptance criteria for vacuum heat treatment have not been established for this procedure. Several individual die casting companies haveestablished their own internal specifications for heat treatmentacceptance, but it has been the goal of the NADCA DieMaterials Committee to establish a third party industry specification for the acceptance of premium quality H13heat treatment.

Approach: This ambitious project was initiated to examine theeffects of steel quality, heat treatment quench rate and Charpyv-notch impact test temperature on the microstructure andtoughness of premium quality H13 tool steel. The project wasbased upon an experimental matrix consisting of four steelquality levels with three heats of steel for each quality level.Five quench rates were evaluated to examine the effects ofheat treatment variables and the resulting heat-treated steelwas subjected to Charpy v-notch impact testing at fourdifferent temperatures. Representative samples from eachsteel quality/heat treatment quench rate combination weresubjected to microstructural evaluation.

The die steel was supplied to the project as "in-kind" contribu-tions from steel company members of the NADCA DieMaterials Committee. Criteria for the steel to be included in thestudy was that the parent block be between 10 inches and 14inches in thickness by at least 16 inches in width to providematerial representative of the larger cross-sections utilized inthe die cast tool building industry. Twenty coupons measuringapproximately 1/2 inch by 2-3/16 inches by 4 inches were prepared from each block of steel. The coupons were cut fromthe center portion of the parent steel blocks where the 2-3/16inch dimension of each coupon represented the short-trans-verse orientation.

Commercial vacuum heat-treating members of the NADCA


Die Materials Committee provided heat treatment processingas "in-kind" contributions to the project. The test procedureconsisted of tack welding four coupons of each steel qualitycapability level onto a master block measuring approximately12 inches by 12 inches by 24 inches. Thus, a total of 40 couponswere attached to the master block prior to commercial heattreatment. The coupons were randomly tack-welded to themaster block such that there were 10 coupons attached toeach of the four 12 inch by 24 inch sides. This entire procedurewas conducted four separate times, using different heattreaters to produce heat-treated coupons representing thefour targeted cooling rates. The selected rates consisted of aslow air cool (<15ºF/minute), 50ºF/minute, 80ºF/minute and120ºF/minute. Thermocouples were imbedded into the masterblock at various locations to measure the actual cooling rateduring the vacuum quenching process.

Each master block/coupon set was heat treated per therequirements of the current NADCA 207 recommended procedure with the exception of the cooling rate. The vacuumheat treatment furnaces were operated to produce the fourtargeted cooling rates. Following the controlled quenchingprocess, the coupons were triple-tempered to produce a finalhardness of 44/46 HRC and were submitted for Charpy v-notchimpact testing. To investigate the possibility of increasing theability of the test method to separate high toughness from lowtoughness material, the CVN testing of each combination ofsteel and heat treatment cooling rate was done at four testtemperatures; room temperature, 200ºF, 350ºF and 500ºF.

Results: The scope of this project resulted in a significantamount of data in the form of CVN impact toughness valuesand microstructures as a function of steel quality and heattreatment quench rate. There were more than 600 individualCVN specimens tested and 250 microstructure photos produced. Several conclusions can be drawn from the resultsof the project:

1. Conducting the CVN impact toughness tests at elevatedtemperatures did increase the measured toughness values.However, it did not significantly improve the ability of the testto separate high-toughness and low-toughness steels. The elevated temperature impact testing did not help to differ-entiate between heat treatment quench rates. The additionalvariables and costs associated with the elevated temperatureimpact test were determined to be undesirable as a standardNADCA test protocol. 2. A Charpy test methodology based upon testing five individ-ual specimens and reporting the average results of threespecimens after dropping the high and low values was found

IMPACT ROUND ROBIN TESTING FOR H13 DIE STEELG. Brada, Bodycote Taussig, Inc.

to significantly reduce the average standard deviation of CVN data. 3. The CVN impact toughness of premium quality H13 wasfound to increase with increasing quench rates. However,based upon the limited data resulting from this investigation,there is no clear justification for altering the current NADCAminimum recommended quench rate of 50ºF/minute. 4. The degree of intergranular carbide precipitation did notcorrelate with the impact toughness of commercially heat-treated steel in the range of 50ºF/minute to 120ºF/minutequench rates.


Implementation Strategy: The results of this project confirmthe value of following the NADCA Recommended Proceduresfor H13 Tool Steel, including the Charpy v-notch testing of H13 steel used for die casting dies and inserts. Even morecostly testing of die steel samples was only marginally able todiscriminate better than the current NADCA procedure. All diecasters should adopt the NADCA procedure and monitor revisions to the procedure as they are published. �

Monitoring Task Force: Die Materials Task ForceSponsored by: NADCA






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Business Benefit: This project provides the die caster withinformation on the use of die steels with improved thermalfatigue resistance, such as Dievar and QRO-90 that couldimprove cycle rates compared with H13 die steel.

Project Objectives: A significant amount of testing has beenconducted to determine the best composition and processingtechniques for H13 steel used for die casting dies. Throughthese efforts, significant improvement has been made in thefunctional life of die casting dies. The purpose of this projectwas to study whether other types of die materials, such asnickel-based alloys and refractory metals, might provideincreased resistance to failure by thermal fatigue cracking,which would permit them to be used in demanding applica-tions or which would allow faster cycle rates than permitted byconventional H13 die steel.

Approach: Tests were conducted on two types of candidatedie materials. These included: new types of H13 and H11 diesteels, and non-ferrous materials, including metal matrixcomposite and high-thermal conductivity alloys.

The H13 and H11 samples were tested by immersion inmolten aluminum at 1350ºF to determine the total crack areaand the average maximum thermal fatigue crack length. Theresults showed that some of the materials behaved somewhatbetter than the control premium grade H13 processed by afast quench and double temper. In addition, some of the morerecently developed steels showed considerable improvementin thermal fatigue cracking and have changed the crackingmode from "corner cracks" to a "surface crack" behavior.Examples of this are QRO 90 and Dievar, which show mostlysurface cracks. The surface cracking has very limited depthand does not appear to produce thermal fatigue cracking thatsubjects the metal to significant thermal fatigue damage.

In an effort to determine the reasons for the improved behaviorof these steels, additional experimental procedures were conducted. These procedures included:

• Determining the carbide count in the as-oil quenchedcondition with the MSQ Image Analysis System. • Determining the softening at the thermal fatigue sample corner by microhardness testing after 5,000; 10,000; and15,000 cycles. • Computing the total corner crack area and the maximumcrack length utilizing the MSQ Image Analysis System.

The results of these tests showed that carbides are not ascommon in as-quenched Dievar, QRO-90 and TQ1 steels.


Steels with lower carbide content resist thermal fatigue crack-ing better. Steels that exhibit the best tempering resistancealso exhibit the best resistance to cracking. The cracks in theH13 specimen cut through the corners of the specimen,whereas, the cracks in the Dievar and QRO-90 tests werevery shallow and were only on one side of the corners withconsiderable improvement in thermal fatigue resistance.

Testing of non-ferrous candidate materials included somerefractory metals, nickel-rich and copper-rich materials, andmetal matrix composite materials. The testing showed that allof these materials are more resistant to thermal cracking thanH13. However, when the average maximum crack length isconsidered, some of these materials, such as the Nybrilcompositions, can be subject to an occasional long crackforming from the corners.

While many of the copper and nickel alloys exhibit better thermal fatigue behavior than H13, these alloys can be subjectto damage on the corners of the specimen. This damageoccurs because of the high solubility of copper and nickel inthe molten aluminum and can cause difficulty in their use asdie materials. It should be noted that none of the refractorymetals which were produced from tungsten or molybdenumshow any tendency to thermal fatigue crack.

A metal matrix composite made from Ti-6Al-4V with titaniumcarbide particles was tested as a die material. This metal wasinferior to H13 in thermal fatigue resistance. It is considered asa good shot sleeve material for aluminum because of its goodresistance to soldering and its low thermal conductivity.

Some of the high thermal conductivity materials, such asBrush Alloy 3, have been used in shot blocks. The rate of cool-ing of the biscuit in this shotblock is substantially faster for thiscopper material than for conventional steels. High thermalconductivity materials including the refractory metals can beconsidered for the shotblock or other inserts in the die wherefaster cooling is desirable.

Results: The results of this project indicate that some of themore recently developed steels exhibit better thermal fatigueresistance than H13, even when that steel is produced to premium grade specifications. The copper and nickel alloysare also more resistant to thermal fatigue cracking but aresubject to solution of the sharp corners into the molten aluminum alloy. The refractory metals from tungsten ormolybdenum are not subject to thermal fatigue cracking andoffer the possibility of being inserted into the die at hot spot

DIE MATERIALS FOR CRITICAL APPLICATIONS AND INCREASED PRODUCTION RATESJ. Wallace, D. Schwam and Q. Zhou, Case Western Reserve University

areas. Refractory metals do not undergo any visible type ofthermal fatigue cracking or other problems, except for theirhigh cost and susceptibility to cracking under the wrong circumstances. The use of high thermal conductivity diematerials at critical locations is an excellent way to avoiddifficulty at these locations.

Implementation Strategy: Die casters should consider theuse of die steels with improved thermal fatigue resistance,


such as Dievar and QRO-90. Refractory base molybdenumand tungsten alloys have excellent thermal fatigue resistanceand should be considered for use in areas with high thermalstress. High conductivity materials such as Brush Alloy 3 facil-itate rapid solidification of the surrounding metal and shouldbe used to increase the production rate of die castings. �

Monitoring Task Force: Die Materials Task ForceSponsored by: U.S. Department of Energy and NADCA






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Business Benefit: This project provides the die caster withinformation on how to optimize the material properties of diesteel by specifying more rapid cooling rates from the austeni-tizing temperature.

Project Objectives: The main mechanism of die failure isthermal fatigue cracking. It has been shown in previous inves-tigations that the thermal fatigue behavior depends on the initialmechanical properties of the material and their behavior withtemperature. The ability of die steels to resist thermal fatiguecracking depends upon both their resistance to temperatureand their ability to deform without cracking. These are themain properties that control the resistance to elastic and plasticstrain. The microstructure that is obtained during austenitizationand quenching of the die steel is the primary feature thatdetermines the behavior and the cracking of the steel. For thisreason, the cooling rate from the austenitizing temperaturehas an important effect on the cracking resistance of the diesteels. The objective of this project was to quantify the effectof the cooling rate from the austenitizing temperature on thethermal fatigue cracking, microstructure and impact resistanceof premium grade H13 die steel.

Approach: A block of Premium Grade H13 was cut into eightthermal fatigue test specimens and 16 Charpy V-notch pieces.These specimens were then quenched at controlled coolingrates: about 14ºF/min, 100ºF/min, 200ºF/min, and 7,250ºF/minfor the rapidly oil quenched material. The temperature rangeof 1,880 to 1,000ºF was used for the controlling cooling rates.A test specimen with thermocouples embedded at 3 inchesfrom the top and 0.05 inches from the corner was used to con-trol the cooling rates. After testing for the thermal fatiguebehavior in the regular immersion thermal fatigue test, thecrack propensity of the material was determined. The finaloperation on these specimens consisted of metallographicmeasurements of the steels at the critical edges of the speci-mens. The impact bars were fractured at room temperature.

Results: The cracking susceptibility of this material was wellrelated to the rate of cooling. The most rapid cooling presentedthe best results followed by the rates of cooling at 200, 100and 14ºF/min. The metallographic tests clearly showed theeffects of the rates of cooling on the transformation structuresof the thermal fatigue specimens. The microstructure of thesematerials reflects the rate of cooling, with the final structureillustrating the advantages of rapid cooling from the austeni-tizing temperature. The impact results varied from an averageof 6 ft.lb. at the slowest rate, 12.75 ft.lb. at 100ºF/min, 18 ft.lb.for the 200ºF/min and 23.75 ft.lb. for the rapidly quenchedspecimen.


The results can be summarized as follows:

1. The rate of cooling from the austenitizing temperature of1,880ºF is a very important factor in providing the structureand properties needed to attain dies with an excellent resist-ance to thermal fatigue cracking. In this investigation, therapid cooling rate from oil quenching provided the best prop-erties, followed by the cooling rates of 200ºF/min and 100ºF/min. Excessively slow cooling resulted in the lowest resist-ance to thermal fatigue cracking.

2. The structure from the rapid cooling resulted in a fine distri-bution of alloy carbides in the steel. The size of these carbidesincreases somewhat with the cooling rates of 200 – 100ºF/min.At the slowest cooling rate, a large number of carbides werepresent, particularly at the grain boundaries.

3. The results of the Charpy V-notch tests are related to thegross cracking behavior of the die steels. In this instance, forPremium Grade H13, the most rapid cooling rate provided thehighest values (23.75 ft.lb. average). Intermediate impactresults were obtained with cooling rates of 200 and 100ºF/min(18 and 12.75 ft.lb. average, respectively). The lowest impactresults (6 ft.lb. average) were obtained for the slowest coolingrate, as shown in Table 1.

TABLE 1. Charpy-V notch Results – Average of 4 Bars

Specimen Cooling Rate [ºF/min] Charpy-V notch Energy [ft.lb.]

Oil 7250 23.75

10 bar 200 18

1 bar 100 12.75

Insulated 14 6

Implementation Strategy: The die casting industry shouldoptimize the material properties of die steel by specifyingmore rapid cooling rates from the austenitizing temperature.While consideration must be given to cracking and distortionduring faster cooling of larger pieces of steel, all specimens ofH13 have greater resistance to failure during service with theuse of more rapid cooling rates. �

Monitoring Task Force: Die Materials Task ForceSponsored by: NADCA R&D Funds

THE EFFECT OF COOLING RATE ON THERMAL FATIGUE CRACKINGAND IMPACT RESISTANCE OF PG H13 DIE MATERIALJ. Wallace, D. Schwam and S. Birceanu, Case Western Reserve University







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Business Benefit: This project provides designers and diecasters with information to effectively use rapid tooling methodsto generate new business opportunities for parts that might nototherwise be suitable for die casting due to short productionruns or long lead times.

Project Objectives: Rapid prototyping casting methods areoften employed when a small number of cast parts are needed.The casting method of choice is dictated by the dimensionalaccuracy, mechanical properties and surface finish required ofthe parts. Sometimes the desirable casting method for rapidprototyping is a metal mold technique such as die casting,squeeze casting or permanent mold casting. In all of thesecases, a metal mold needs to be fabricated first.

In the military, rapid tooling is needed when a product is underdevelopment or when relatively few parts are required toreplace components in legacy weapon systems. It wouldstrengthen and speed the supply chain to develop rapid, low-cost means of producing dies suitable for a limitednumber of die castings such as 5,000 pieces before seriousthermal fatigue or other cracking occurred in the tooling.

The objective of this project was to evaluate methods andmaterials that can potentially shorten the lead time and/orreduce the cost of rapid tooling used in die casting, squeezecasting and permanent mold casting. The dimensional char-acteristics and durability of the resulting tooling were alsoaddressed.

Approach: With few exceptions, most metal molds are fabri-cated from ferrous alloys. Tool steels in general and hot toolsteels in particular are the most frequently used die materialsfor production die casting and squeeze casting inserts.Permanent molds are often cast in gray or ductile iron.

The types of steels of interest in this study were H-13, H-11,or modified H-11. In addition, the study evaluated some loweralloy, more economical steels such as 4140, P20, and, forvery short runs, 1040, or high strength gray and ductile iron.The study evaluated and compared the following methods ofrapid tooling fabrication:

1. Casting ductile iron rapid tooling in no-bake sand moldsfrom oversized patterns produced from 3D CAD programs.

2. Investment casting rapid tooling in H-13 die steel fromprototype wax patterns produced from a 3D CAD model.

3. Machining rapid tooling from a forged block that had beentempered to a lower hardness of 40-42 HRC. This method


utilized Numerical Control (NC) machining from 3D CADcomputer models of the tooling for rough and finish machining.

The evaluation of the potential materials and fabricationprocesses included dimensional accuracy, surface conditionand performance of the tooling. A key issue in selecting thematerial for rapid tooling is ensuring it will last long enough tomake the required number of parts, yet last no longer thannecessary. To test the performance of candidate materials, theThermal Fatigue Immersion test at CWRU was used to simulatethe casting environment. This test has become a preferredand widely accepted method of screening die and mold mate-rials. The standard procedure is to operate the test for 5,000immersion cycles, measure the cracking pattern and followthis method for 10,000 and 15,000 total cycles. A more severecrack pattern indicates a lower thermal fatigue resistance ofthe tested material. The results of this test have correlatedclosely with the behavior of dies in industry.

Results: Rapid tooling for permanent mold casting was madeby casting ductile iron in no-bake molds with satisfactory results.While some machining was required to bring the criticaldimensions of the cavity into the specified tolerance window,the lead time was still relatively short. When die casting insertswere investment cast from H-13 tool steel, the flatness anddimensional accuracy were not acceptable. While machiningof the cast inserts is an option, it would offset some of theadvantages of net shape casting, especially the lead time.

While machined rapid tooling can be made in very large sizes,cast rapid tooling is normally limited to smaller sizes. Complexrapid tooling can often be cast in a more cost effective wayand with shorter lead times. However, the accuracy and sur-face finish of cast rapid tooling is not as good as machinedrapid tooling.

Fabrication of rapid tooling of tool steels by NC machining,directly from a CAD model provides the best combination oflead time, performance and cost. Careful selection and heattreating of the insert material is essential. Recent advances incutting tool technology allow high speed machining ofquenched and tempered steels up to 42-43 HRC hardness.Furthermore, Electro-Discharge Machining (EDM) can be performed on rapid tooling inserts of any hardness. Thesedevelopments narrow the gap between rapid and productiontooling. It is possible, as demonstrated by this study, to utilizemodified H-11 steels in a pre-hardened condition, to fabricaterapid tooling that can last long enough to be used for productionof large numbers of die castings, well beyond short runs. At

RAPID TOOLING FOR LOW VOLUME DIE CASTINGJ. Wallace and D. Schwam, Case Western Reserve University

the same time, if only a small number of castings are required,further savings in cost can be achieved by utilizing lower alloy,softer steels. In every case, the size and configuration of thepart and the die design have to be carefully considered toavoid premature failure of the tooling.

Implementation Strategy: This project demonstrated thatthere are techniques which can be used to quickly providetooling for prototype castings or even small production runs.


These techniques open new opportunities for casting producersto enter new markets, where the long lead times required forconventional tooling prohibited their participation. In addition,these techniques offer the potential to reduce the lead timeand cost of even conventional die casting, squeeze casting, orpermanent mold tooling. �

Monitoring Task Force: Die Materials Task ForceSponsored by: U.S. Department of Defense and NADCA






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Business Benefit: This project provides the die caster withinformation on the use of coatings and other techniques toimprove the operation of shot sleeves. These improvementscould result in potential cost savings of up to 20% throughimproved quality, less downtime and reduced energyconsumption.

Project Objectives: The use of shot sleeves has been a con-siderable problem in die casting operations. This item has ahistory of warping and bending in the operation of the process.In addition, the shot sleeve experiences a serious probleminvolving the build up of sintered material and rapid erosion ofthe material under the pour hole. These problems can requirethe replacement of the shot sleeve entirely too frequently. Theobjective of this project was to study the build up and erosionof shot sleeves in an attempt to end the problem as it exists inthe industry today.

Approach: After a long period of time and considerable effort,a method was developed that offered the opportunity ofsolving the problem for better life in shot sleeves. This methodof testing the shot sleeve and its operation consists of a 1,500psi maximum pressure hydraulic cylinder, actuated by a 30HPelectric motor, which moves a plunger rod and plunger tip in ashot sleeve. The components are mounted on two U-beamsassembled on a 300 gallon hydraulic fluid tank by means ofshock absorbers. The automated ladle takes aluminum alloyfrom the furnace and pours it through a funnel into the shotsleeve. The plunger tip pushes the molten metal out of theshot sleeve at a rate of 6 inches per second. The metal isdirected back to the furnace by means of an insulated launder.This procedure is repeated numerous times, with 36 secondsrequired for each cycle.

The aluminum alloy used in this project was A356 with regularcomposition of: 7% Si, 0.3% Mg and 0.2% Fe. During theoperation of this equipment, the automatic ladle picks up theA356 molten aluminum alloy at a temperature of 1,250-1,350 ºFand pours it into the shot sleeve through the funnel. The plungertip employed initially was water-cooled nitrided H13. The moltenmetal was applied at a rate of about 7 pounds per ladle.

The initial testing was performed with a nitrided H13 shotsleeve. The thickness of the shot sleeve was first held to 0.5inches to accelerate the failure of the shot sleeve. After 2500cycles, the original nitrided H13 sleeve was replaced and sec-tioned longitudinally. This sectioning showed the adherence ofaluminum on the nitrided shot sleeve after it had worn throughthe nitrided layer. Further testing was conducted using other


shot sleeves with an increased sleeve thickness of 0.75 inches.Other shot sleeves with H13 base material were also testedwhich had either a TiAlN PVD coating, an addition of Stellite#6 because of its known wear resistance, or a molybdenumcoating applied throughout the sleeve.

Results: The results of the various tests conducted duringthis project can be summarized as follows:

• It is evident that penetration of the sleeve material involvedwashout by dissolution of aluminum intermetallic material at thealuminum and steel interface and the diffusion of aluminumand iron across the interface. The damage that occurred to theoriginal 0.5 inch thick nitrided H13 sleeve indicated that sol-dered aluminum alloy had adhered to the original steel inter-face. The depth of the damage to the coating was 0.17 inches.

• The PVD coating of TiAlN on the inside surface of a nitridedH13 sleeve had a thickness of about 10 microns and was placeddirectly on the surface that was damaged, by a commercialcoating supplier. This material was excellent until it worethrough the 10 micron thickness. After that, the materialbehavior was similar to the nitrided H13.

• The Stellite #6 alloy was tested as a welded insert. Some difficulty developed welding directly on the surface of thesleeve and that forced the use of a separate plug on the sur-face. The welded insert was placed into a hole that was cutinto the bottom of the shot sleeve directly below the pour hole.The composition of the Stellite #6 was: Cr 28.5%, W 4.5%, Co60%, Fe 2%, Ni 2%, C 1%, Si 1%. It performed very poorlybecause of the solubility of the cobalt in the liquid aluminum.

• The molybdenum coating was applied over the entire surfaceof the shot sleeve, which was near the pour hole, to a depth of250 microns or 0.01 inches. The plunger tip used for thisexperiment was made from Be-Cu alloy instead of nitridedH13 and was cooled by water. The reason for the use of a Be-Cu plunger tip is that the molybdenum coating is softerthan nitrided H13 and a softer plunger tip is designed to avoidadditional damage. This material held up the best of any material, and finally wore off in sections as the bond started to fail. With more experience, it is evident that molybdenumcoatings could be a very good addition.

Implementation Strategy: Based upon the results of thisproject, the following conclusions and recommendations aremade:

• The molybdenum coating was the very best material foravoiding damage to the shot sleeve steel. The molybdenumheld up longer than any other material. With an improved

IMPROVED DESIGN, OPERATION AND DURABILITYOF SHOT SLEEVESJ. Wallace, D. Schwam and S. Birceanu, Case Western Reserve University

bond, the molybdenum coating would have lasted for a longerperiod of time. Additional experience with the application anduse of molybdenum coatings in shot sleeves could providesignificant improvement in shot sleeve performance.

• The nitrided coating of the H13 sleeve material providedsome assistance to withstanding the wearing and solderingeffect.

• The hard coating (TiAlN PVD) performed in an excellentmanner as long as the coating was maintained. However, itsthickness was limited to about 10 microns. After this coatingwore off, the behavior was similar to that of the nitrided H13.

• The Stellite #6 material showed considerable wear under theaction of the molten aluminum alloy with cracking occurring in





the weldment. This wear is the result of the solubility of cobaltin the molten aluminum and shot sleeves are not an appropri-ate application for this material.

The improved operation of shot sleeves will save a lot of energy and reduce downtime in the die casting operation. Byreducing the lost energy and producing better die castings, thecost and energy consumed during die casting will be greatlyreduced. It is estimated that the improvement in shot sleevedesign and operation could reduce the energy required for diecasting by 20%. �

Monitoring Task Force: Die Materials Task ForceSponsored by: U.S. Department of Energy and NADCA



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Location of Cut-Out Under Pour Hole Where theStellite Insert was Welded







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Die Materials

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