nadca louisville table top paper sept 2013 evaluation of porosity leve

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Evaluation of porosity levels on castings produced by a new concept ofinclined injection system for aluminum die casting

S. Bergeron, M.A.Sc., G. Monette, MBA, C. ThibaultAV&R Die Casting, Saint-Bruno, Quebec, Canada

N. Giguère, Ph.D.Centre de Métallurgie du Québec (CMQ), Trois-Rivières, Québec, Canada

F. Pineau, Ph.D., D. Bouchard, Ph.D.Aluminium Technology Centre, Industrial Material Institute, National Research Concil Canada

ABSTRACT

Considering the increasing number of aluminum applications, the specific demand for this material is expected to grow

continuously in the years to come. According to a NADCA survey carried out in October 2011, porosity reduction is an issue

for 28% of die casters and 11% consider it is a critical issue that should be addressed by new generation machines. There is a

growing demand for aluminum die cast components with low porosity levels that can be welded, heat treated, painted, or

plated with thinner walls or superior metallurgical and structural properties. However, this achievement should not be

accomplished to the detriment of unit cost and production cycle time. This should be achieved by optimizing some of the

major factors influencing air entrapment such as gating design, part geometry, vent position and dimensions, closed loop shot

monitoring of injection profiles and related parameters, etc. Computer simulations play an instrumental role in optimizing

these factors as they allow part designers to test their concepts with virtual casting trials.

The primary objective of this project was to characterize an inclined injection high-speed die casting machine with respect to

the quality of parts produced using shot sizes less than 1 lb and a rate of 5 cycles per minute. Computer simulations were

carried out for various angles and plunger heights and the porosity content was evaluated. The results show that the novel

approach of inclined injection with metal loading at the front consistently produced castings with lower porosity levels than

the horizontal, conventional machines in the thin wall sections of the parts. Metallurgical investigations of cast parts

corroborated the simulation results. This study showed that an approach, based on determination of machine capabilities and

state-of-the-art simulations combined with metallurgical investigations, is successful to minimize porosity.



INTRODUCTION

Since the 1950s, the casting of non-ferrous alloys is carried out using essentially the same technology in cold chamber or hot

chamber with a fixed platen and a movable platen. Recently, the company AV&R Die Casting has developed a new

technology for high pressure die casting under the trademark CADENCE 100T. This new machine is shown in Figure 1.

Figure 1: Inclined Machine CADENCE 100T Figure 2: Integrated feeding system with double

ladles.

The technology was unveiled at the NADCA exhibition in October 2012 in Indianapolis. The machine has several innovative

features such as the patented inclined injection system, integrated feeding system consisting of two ladles (see Figure 2) and a

multiple-slide mold closing system (see Figure 3). The machine is also equipped with a control system called MCS -

Monitoring Control System. This system records all production parameters for each injection and then selects only the parts

produced within a range of predefined operational parameters.

In this article, we summarize the results of the study of the design concept of this die casting machine. We then compare the

performance of this new machine to those obtained with traditional technology. Finally, we perform a metallurgical analysis

of the parts produced from this new technology. This work is the results of the first phase of a research project aimed at

reducing the porosity in castings. Part 1 of the paper is related to the optimization of the injection system and the Part 2 is on

the optimization of the cycle time. A second phase of the project will focus on reducing the amount of air in the die itself and

the results will be published later. The overall goal of these developments is to achieve low porosity levels in castings that

will allow their post-molding treatments like painting & plating, heat treatment or welding.



Figure 3: Multiple-slide closing system

PART 1: OPTIMIZATION OF THE INJECTION SYSTEM

Several technical benefits justify the development of an inclined injection system for high pressure casting at the parting line

of the die. Among these advantages, the volume of metal in the feeding channels is reduced as well as the initial volume of

air contained in the injection chamber. In the first place, the effects of the angle of the injection chamber relative to chasing

out of air pockets in the cast parts and the impact on the quality of parts were investigated.

In high pressure casting machines, the injection speed of the plunger must be increased to minimize the partial solidification

of the metal in the injection sleeve. In conventional horizontal die casting machines, the initial velocity of the plunger must be

carefully controlled to reduce the air entrapment in the feeding system and the die cavities(1,2). However, the problem of

controlling the waves in a horizontal sleeve remains complex. In this study, the work was undertaken with the collaboration

of the Aluminum Technology Centre (ATC) of the National Research Council Canada to analyze the liquid metal flowgenerated by the plunger in the injection system using the commercial software ProCAST. These analyses have shown the

effect of the inclination angle (0°, 30°, 45°, 60° and 90°) of the injection sleeve on the flow and air entrapment at different

injection velocities (1.6, 3.2, 6.4 and 13.1 ft/s - 0.5, 1.0, 2.0 and 4.0 m/s). Since the slow shot phase can generate a partial

solidification of the liquid metal during the injection and also increase the cycle time, the development of a machine concept

without slow phase, i.e. a single stage with rapid acceleration was promoted.

As expected, the amount of entrapped air decreases with the angle of inclination. Calculated results for angles of 0°, 45° and

90° with an injection velocity of 3.2 ft/s (1 m/s) respectively are presented in Figures 4, 5 and 6. The horizontal configuration

where the entrapment of air pockets is most obvious is also the one with a greater plunger stroke for a given volume of

aluminum. This behavior is enhanced with the increase in injection speed. For 45° inclined sleeve/plunger configuration, the

bending of the free surface is greatly reduced. An air pocket is formed almost across the exit of the runner. Note that in this

case and in the case of the 90° position, the molten Aluminum level is set to 0.5 in. (13 mm) from the lower extremity of the

sleeve to prevent overfilling. A very small amount of air is still trapped in the upper region in the sleeve. The injection speed

again had little influence on the shape of the calculated air volume. It is possible to observe that the increase in speed seems

to limit the development of the air pockets in the upper region of the injection sleeve. In this configuration, we also observed

that a large part of the air in front of the free surface is directed into the gating system. In the vertical configuration (see

Figure 6), the air is gradually evacuated in front of the free surface. Due to the development of a parabolic profile in the shot

sleeve, a small amount of air is trapped in an annular portion of the periphery.

These analyses showed that the resulting undesirable effect of the creation of a wave is greatly reduced with the angle of the

injection sleeve and that they disappear completely when the system is vertical. However, the choice of a final configuration



is linked to other design constraints such as the ease of ejecting parts, the height of the machine for maintenance of the die

and the opening angle for pouring the molten metal by gravity from the ladles against the inclination of the sleeve. In

addition, due to the acceleration generated by the hydraulic unit, it takes about a 1 inch (25 mm) plunger stroke to reach its

maximum speed of 19.7 ft/s (6 m/s). For these reasons, the designers of this machine have chosen a 45° inclined injection

system.

a) b)

c) d)

Figure 4: Flow fronts for a horizontal injection system, angle 0°, speed 3.3 ft/s, (1 m/s)

Figure 5: Flow fronts for an inclined injection system, angle 45°, speed 3.3 ft/s (1 m/s)

a) b) c) d)

Figure 6: Flow fronts for a vertical injection system, angle 90°, speed 3.3 ft/s (1 m/s)

a) b) c)



Analyses were performed with two commercial dies used to manufacture electrical lock nuts for the construction industry.

The proportion of initial air in the injection sleeve for horizontal and inclined systems are shown in Figure 8 and Table 1. By

comparison, the volume of initial air in an inclined injection sleeve is significantly lower than that of a conventional

horizontal machine. Typically, a machine with horizontal pressure of 100 tons of clamping force is equipped with a sleeve of

about 11 inches (279 mm) long and requires for injection at least a 35% higher volume of metal to be injected. The lower

volume of air for the CADENCE 100T machine comes from an injection that is in-line with the parting line of the die

combined with a die concept that minimizes flashing. The injection in line with the feeding supply allows for a gating system

with less volume of material and fewer turns. Thus, the flow is less disturbed and pressure losses in the feeding system aremuch lower.

For 1/2'' diameter lock nuts (8 cavities), the volume of metal injected considered for both types of machines are respectively

4.6 in3 (75.3 cm3) for the 100 tons inclined machine and estimated at 6.2 in3 or more (101.6 cm3) for a horizontal machine.

Most importantly, the initial volume of air in the injection system of inclined machine remains constant regardless of the

volume to be injected. Comparing the initial volume of air contained in the injection sleeves of a horizontal machine, 20.2 in3

(331 cm3) with 74.3% air and a 45° inclined machine, 3.4 in3 (55.7 cm3) with 12.5% air, it is clear that there will be less air

injected from the sleeves with different die cavities with the inclined machine. Also, because there is less air, there will be

less restriction during the flow of the molten metal. Given the angle of the sleeve, its effective length restricts the actual

volume required to cast by approximately 40%. Table 1 summarizes the volume differences between the horizontal and the

inclined injection sleeves.

Figure 7: Commercial die for the production of electrical components (lock nut 1/2'' - 8 cavities)

a) b)

Figure 8:- Injection chamber. a) horizontal machine, b) inclined machine CADENCE 100T

Initialvolume of air

Initialvolume of air



Table 1- Initial volume contained in the injection sleeve

Length of sleeve: 11 in (279 mm), Diameter of plunger: 1.772 in (45 mm), volume of sleeve: 27.1 in 3 (444 cm3)

PART

HORIZONTAL MACHINE INCLINED MACHINE

Volume

injected

AIR

volume

AIR

volume

Volume

injected

AIR

volume

AIR

volume

Effective

volume

in3

(cm3)

in3

(cm3)%

in3

(cm3)

in3

(cm3)% %

Lock nut 1/2''

(8 cavities)

6.2

(101.6)

20.9

(342.5)77.1

4.6

(75.3)

3.4

(55.7)12.5 42.5

Lock nut 3/4''

(6 cavities)

7.0

(114.7)

20.2

(331)74.3

5.2

(85.2)

3.4

(55.7)12.5 39.7

To confirm the impact of the air volume in the sleeve on the quality of the parts produced in Aluminum A360 alloy, a

metallographic analysis was carried out by the Centre for Metallurgy Québec (CMQ) on over 400 sections and then compared

with identical sections from parts produced on a horizontal machine. During testing, the casting temperature of the furnace

was set to 1292°F (700°C) and the injection speed in a single phase at 45 in/s (1.1 m/s) as shown on the profile of injection in

Figure 9.

Figure 9: Typical Injection profile generated during tests.

Vel (avg)



Samples taken from die cast 1/2'' and 3/4'' diameter lock nuts were cut, mounted in resin and polished to allow observation

by optical microscopy (as shown in Figure 10). For each part, a thick section, 'Section SB', 0.387 inch (9.8 mm) thick and a

thin section, 'Section SA' of 0.153 inch (3.9 mm) thick were evaluated. Metallographic analyses were performed using the

Clemex VisionTM software on complete sections of each specimen (3). For each of the sections analyzed, the percentage of

porosity as well as some form factors were measured. Identical parts were cast on a classic horizontal machine and on the

inclined machine. The average of all results from the metallographic analysis is presented in Table 2 and typical

metallographic sections are shown in Figure 11. Disregarding casting parameters used for both processes, Table 2 shows that

the porosity in parts produced by the inclined machine is lower, with notably an average rate of 0.6% in the thin wall areas. Itis observed that the dispersion of the porosity is very different from one process to another. For the horizontal machine, the

porosity was uniformly distributed throughout the section while it was more localized towards the center of the part for an

inclined machine. In the latter case, the regions near the surface are practically free of pores.

Figure 10: Position of metallographic sections on the runner of Lock nut 1/2''

a) b)

Figure 11: Typical dispersion of porosity in thin walled sections, (SA) a) horizontal machine, b) inclined machine

SA

SB

1.5 in (38.1mm)



Table 2: Global analysis results of porosity percentage in sections of lock nut.

PART

Thin Sections Thick Sections

inclined

machine

horizontal

machine

inclined

machine

horizontal

machine

Lock nut 1/2'' 0.2 % 2.0 % 1.6 % 4.2 %

Lock nut 3/4'' 1.0 % 1.2 % 1.4 % 1.9 %

AVERAGE 0.6 % 1.6 % 1.5 % 3.1 %

The results of this study showed that, given the small volume of initial air in the injection sleeve and unlike horizontal

conventional machines, the slow injection phase was not necessary for these two geometries to expel the air and avoid the

formation of a wave in the injection chamber. By eliminating the slow phase, we can avoid a partial solidification of the

molten metal and also reduce the cycle time. This is what is shown in Table 3. The porosity level in the 1/2'' diameter lock

nut is about two times lower when only one phase is used in the injection profile.

Table 3: Average rate of porosity according to the injection profiles and wall thickness (Lock nut 1/2'')

1 phase 2 phases

Thin Section Thick Section Thin Section Thick Section

0.2 % 1.6 % 0.5 % 2.5 %

PART 2: OPTIMIZATION OF CYCLE TIME

The CADENCE 100T machine is equipped with a high performance hydraulic system for fast and simultaneous movements

of the various functions. This machine is also equipped with a feeding system with two independent ladles to continuously

provide molten metal to the injection sleeve. However, extracting the heat remains the limiting factor in the speed of the

machine. As mentioned earlier, the objective of this project is to produce low porosity parts without compromising on the

cycle time.

The volume of injected metal for a standard gating system represents about 50-70% loss of total volume injected. The

solidification time of the runner system and the biscuit often impose a limit on the ejection time. In this project, the shape of

the biscuit has been optimized to reduce the solidification time. Different profiles of the extremities of the head of the

injection plunger have been tested in terms of their performance, sealing properties, and their effect on reducing the cycle

time. Profiles of plunger head shown in Figure 12 were evaluated. Figure 13 shows the initial results obtained from thenumerical simulation of heat transfer with the ProCAST software performed by the ATC-NRC. The maximum temperatures

at ejection were 700° F (371° C) for parts and the solidus temperature of 1035° F (557° C) for the biscuit. Subsequently, the

optimization of the shape and cooling system for the components of the gating system has reduced the holding time of the

biscuit in the mold to less than 2.0 seconds. After analyzing the flow, solidification, and the final volume of biscuit,

configuration 2 was chosen.



Figure 12: Profile of the plunger head evaluated in this study

Figure 13: Evaluation of the biscuit solidification time according to a given plunger head

Two of the most important casting parameters to produce high integrity components are the temperature control of the

various machine components and the velocity control of the plunger. Although the volume of the biscuit was decreased to

reduce the solidification time, it still remains the hottest point of the runner system. Perfect control of the heat extraction in

the biscuit area is crucial to achieve short cycle times. To extract the heat provided by the solidification of the biscuit and the

Final biscuit

shape



gating system, the inclined machine is equipped with a collar for oil cooling to regulate the temperature of the injection

sleeve, a water-cooled plunger head and a set of water-cooled runner inserts (Figure 14). A double cooling channel system is

used for the die itself. The repeatability of the thickness of the biscuit is fully controlled with the process control system,

MCS integrated in the software of the machine. Traceability of previous injections and some abnormalities may be

intercepted or anticipated (see Figure 15) to avoid production delays.

Heat transfer accounted by the die lubricant spray is also significant(4.5). It is known that lubrication contributes to more than

15% of heat extraction from the mold. Iterations of comprehensive analysis of heat transfer coupled with the flow were performed with numerical simulations to optimize the production cycle times. The lubrication sequence was modeled by

applying an instantaneous heat flux boundary. In addition to prevent sticking of parts on the dies or cores, numerical

simulation has shown that adequate lubrication time on cores allow for a reduction in the cycle time. Under these conditions,

the gating/runners discussed above were produced at a rate of 5 to 6 cycles per minute (CPM) or 10 to 12 seconds per cycle.

Figure 14: Cooling system of injection and die

Figure 15: Process control system of CADENCE 100T (Monitoring Control System - MCS)

Cooling collar

Oil cooled

Runner Inserts

Water cooled

Head of piston

Water cooled

Die Block

Oil cooled



CONCLUSIONS

The new CADENCE 100T machine reduces cycle time while producing better quality parts with less porosity. The choice of

a 45° inclined angle appears to be a good compromise to reduce waves in the shot sleeve while meeting to various

mechanical and ergonomic constraints of the casting process. The volume of air injected in the injection system is reduced by

65% compared to the horizontal high pressure machines. In most cases, the slow phase of the injection can be eliminated,

which reduces heat loss in the sleeve while reducing cycle time.

The selected shape of the injection plunger reduced the volume of metal injected and the overall cycle time was reduced to 10

seconds by a series of process optimizations. The initial volume of air in the sleeve remains constant regardless of the amount

of liquid metal injected. The first measurements from metallographic sections show a significant decrease in porosity. This

phenomenon is even more pronounced for parts with thin walls. There is also a different dispersion of the porosity compared

to parts cast on a conventional machine.

Further work will be conducted to characterize the overall combined impact of the reduction of air in the die as well as in the

injection system of the machine. The ultimate goal is to reach a level of porosity that is ideal for post-molding operations like

painting/plating, heat treatment or welding.

REFERENCE

1. Barkhudarov, M., “Minimizing Air Entrainment in a Shot Sleeve during Slow-Shot Stage,” pp 34, Die Casting

Engineer , May 2009

2. Yano, A., Hiramitsu, K., Kuriyama, Y., and Nishido S., “Optimum Velocity Control of Die casting Plunger

Accounting for Air Entrapment and Shutting,” Int. J. of Automation Technology , Vol. 2, No. 4, 2008

3. Balasundaram, A., Gokhale, A.M., “Digital image analysis technique for characterization of shrinkage and gas

(air) porosity in cast magnesium alloys,” TMS, Magnesium Technology 2001

4. Graff, J., Kallien, L. H., The Effect of Die lubricant Spray on Thermal Balance of Dies, Chemtrend Technical

Paper, 26 p.

5. Monroe, C., “State of the Art Die Casting Modeling Practices - Spray process,” NADCA Webinar, Oct 2012

nadca louisville table top paper sept 2013 evaluation of porosity leve

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