DE69032853T2 - INJECTION MOLDING METHOD AND DEVICE - Google Patents

Abstract

This invention concerns an aluminum alloy casting characterized by an iron content of less than about 0.5% by weight, and a gas content of less than or equal to 5 milliliters (STP) per 100 grams of aluminum, said casting having a yield strength in tension (0.2% offset) greater than or equal to 110 MPa and a free bend deformation greater than or equal to 25 min.

Description

The present invention relates to a device for lubrication for casting processes, especially high-pressure die casting processes. The invention finds particular application to that branch of the die casting field where vacuum is used to facilitate the die casting operation and/or to improve the product.

Morgenstern discloses a vacuum die casting apparatus in US-P-2,864,140.

A vacuum die casting apparatus of similar construction to the Morgenstern apparatus is described in US-P-4,476,911, issued to Maschinenfabrik Mueller-Weingarten AG, Weingarten, Germany.

U.S. Patent No. 4,583,5679 to Miki et al. relates to measuring the temperature and calculating the piston-fill chamber clearance (hereinafter referred to as "clearance") of a plunger, plunger chamber and spool sleeve in a die casting machine to control plunger movement and to detect the existence of abnormal operating conditions.

US-P-3,544,355 discloses a method and apparatus for lubricating a shot cylinder in a die casting machine. A spray head device is positioned to spray the lubricant directly into the interior of the shot cylinder.

Notwithstanding the availability of alternative devices for lubricating the piston and loading chamber in high pressure metal die casting processes, there remains a need for a suitable lubricating device for use in processes to reduce the problem of solder formation encountered in castings of low iron non-ferrous metals produced at high gate speeds. One feature that is particularly sought after is load chamber lubrication from the side of the die end, which minimizes solder formation and allows the use of inorganic-based lubricants.

According to the present invention there is provided: an apparatus for lubricating a fill chamber bore 10 of a die casting apparatus which opens into a die 2 at a mold end of the fill chamber, which apparatus comprises: an elongate member 190; means 188 which extends the elongate member 190 into the fill chamber bore 10 from the mold end and then retracts the elongate member 190 through the mold end; and lubricating means 174 carried by said elongate member 190 which sprays the fill chamber bore 10 with a lubricant; which apparatus is characterized by the lubricating means 174 further comprising means 210 for spraying the fill chamber bore with a generally conical spray of a pressurized gas directed against the mold end of the fill chamber bore.

Further according to the present invention there is provided: a method of lubricating a bore of a filling chamber 10 of a die casting apparatus arranged so that the mold end of the filling chamber 10 opens into a die 2, which method comprises: moving a device for lubricating 174 into the bore of the filling chamber 10 from the mold end; actuating the device for lubricating 174 to spray the bore of the filling chamber 10 with a lubricant; and withdrawing the device for lubricating 174 from the bore of the filling chamber through the mold end; which method is characterized by: operating the lubricating device 174 to spray the bore of the filling chamber 10 with a lubricant as the lubricating device 174 is moved into the bore of the filling chamber 10, and to blow a gas peripherally around the bore and radially outward and axially towards the mold end to produce a substantially conical spray of gas which moves vaporized lubricant, together with any loosely adhering metal or flash, out of the mold end of the bore as the lubricating device 174 is moved out of the bore of the filling chamber.

A die casting process incorporating the present invention includes the following points:

Composition of the material for printing Melting operation, including degassing and filtration of the melt Feeding the molten material to the die casting device The filling chamber section Lubricants and coatings for the filling chamber and die casting mold The casting, including its cleaning, heat treatment and properties

The comments on each of these points are following:

1. Composition of the material for die casting

Although the present invention is applicable to die casting of any material, for example magnesium alloys, preferred embodiments are found in connection with certain alloys of aluminium, a particularly advantageous example of which is an aluminum-silicon-magnesium die casting alloy (hereinafter referred to as AlSi10Mg.1 alloy) with the following percentage composition:

Si 9.5 - 10.5

Mg 0.11 - 0.18

Fe 0.4 Maximum

Sr 0.015 - 0.030

Rest Al.

Other elements may be present, some as impurities, some for special purposes. For example, Ti may be present in the range 0.05...0.10%. B may also be present. Reasonable limits for such other elements in an exemplary alloy are not to exceed 0.25% in total. Another choice of limits could be: other ((elements)) 0.05% each max., other ((elements)) total 0.15% max.

Unless otherwise stated, all parts and percentages are by weight.

The functions of the alloy components are generally as follows. Silicon imparts fluidity to the melt to facilitate the operation of casting and to give the casting strength. Strontium rounds off the eutectic silicon particles to improve ductility. Magnesium serves to harden during aging, which is based on Mg2Si precipitation.

An addition of iron suppresses the solder formation of the alloy on the iron mold and on iron pipes or containers on the way to the mold. The solder formation causes the casting to stick to the mold, to the surface roughness of the molds and to the walls of the filling chambers of the die casting device, interrupts the sealing, wears out the pistons of the die casting devices and roughens the surface of the castings that adapt to the surface roughness of the molds.

Solder formation is a particular problem in castings where high gate velocities are encountered relative to other casting methods. Die castings typically have high metal velocities through the gate in the range of about 15 to 70 m/s (50 to 200 ft/s). High gate velocities may be required for a number of reasons. For example, thin gates are advantageous and are sought after in mass production of die castings because the gate material can then be easily and simply broken away from the die casting during trimming. Unfortunately, thin gates (maximum thickness ≤ about 2 millimeters) require high metal flow velocities and higher metal pressures and temperatures therethrough, especially when casting intricately shaped parts, and these conditions have been found to promote solder formation. Another reason for high gate speeds may be the requirement to achieve complete filling of a mold for producing thin-walled die castings, e.g. die castings containing wall thicknesses of ≤ 5 mm.

The commonly used countermeasure against solder formation is an increased iron content up to 1 or even 1.3% iron.

Compared to the iron content typically used in high gating speed die castings, the compositional range for iron is small in compositions preferred in the present invention. This represents an important aspect, i.e. the discovery of ways to die cast lower iron non-ferrous, e.g., light metal or aluminum, die castings at high gating speed. Thus, as far as the iron content present is concerned, it can have an adverse effect on the ductility of the alloy and on the ability of the die castings to pass compression tests. As a general rule of thumb, the lower the iron content can be kept, the better for high elongation and compressive strength. The ability to achieve high gate speed die casting production runs of commercially acceptable duration as provided by the present invention with low iron aluminum casting alloys makes the idea of building vehicles based on aluminum structures even more attractive. For example, the joints of an automotive space frame as disclosed in U.S. Patent No. 4,618,163 may be made from die castings of the present invention.

In contrast, castings with a thick gate and low gate speed can be produced by die casting without much concern about causing solder formation. Of course, the gates then have to be sawn off instead of broken away. In die casting with a low gate speed, iron contents in the range of 0.3 ... 0.4% are used, with iron even being as low as 0.15%.

If one assumes that some iron must be present when, for example, iron molds are used and especially in the case of high speed die casting, it may be advantageous to add to the above composition certain elements which modify the influence of iron on the mechanical properties. For example, an element may be added to modify the morphology of particles comprising platelet iron from a platelet shape to a more spheroidal shape in order to maintain ductility at higher iron contents. Elements which are candidates for modifying the influence of iron are: Ni, Co, Be, B, Mn and Cr in amounts in the range of about 0.05...0.1, 0.2 or even 0.25%.

As stated at the beginning of this chapter, other compositions can be used in connection with the present invention. For example, iron can be varied within a range starting from 0.5% and down, and in some cases iron can be as low as 0.2% and even as low as 0.1%. Silicon can be reduced to around 8%. Magnesium can also be reduced to as low as 0.10%. An alternative composition could therefore be:

Si 7.5 - 8.5

Mg 0.08 - 0.12

Fe 0.15 - 0.25

Sr 0.015 - 0.025

Rest Al.

In certain applications, the present invention may equally well be applied to die casting of the class of aluminum alloys containing 7...11 magnesium.

Products of alloys which can be cast in varying embodiments of the invention are: 356, 357, 369.1, 409.2 and 413.2 as listed in the "Registration Record of Aluminum Association Alloy Designations and Chemical Composition Limits for Aluminum Alloys in the Form of Castings and Ingots" published by the Aluminum Association, Washington, DC.

2. Melting operation, including degassing and filtration of the melt

Material (such as the AlSi10Mg.1 alloy described above) of the correct composition was melted, compositionally adjusted to requirements and then held for feeding to a die casting machine as required.

Composition adjustment involves three parts: removal of dissolved gas, addition of alloy components and removal of solid inclusions.

In the case of an aluminium alloy, for example, it is important that the molten metal be treated to remove dissolved hydrogen for a number of reasons, such as obtaining excellent mechanical properties, avoiding blistering during heat treatment and good welding properties. There are various ways of doing this, such as vacuum melting, reaction with chlorine bubbled into the melt, or physical removal by bubbling an inert gas through the melt, such as argon. Chlorine additionally removes sodium and produces a dry dross of aluminium oxide, the dry being advantageous for good dross removal to avoid solid inclusions in the castings. Dross wetted by molten aluminium is more difficult to remove.

A modifier additive, e.g. strontium, sodium, calcium or antimony, for modifying the shape of the silicon phase can be added, for example in the form of a master alloy wire of composition 3...4% Sr, balance largely aluminum, to a trough where the melt flows from a melting furnace where melting and hydrogen removal are carried out, to a holding furnace where the melt is held in preparation for casting. Since chlorine reacts with Sr, it is useful to add inert gas, such as argon, after the Flux treatment with chlorine bubbles through the melt to remove as much chlorine as possible before Sr addition.

The master alloy wire composition of 3.5% Sr, balance aluminum, has been shown to be more effective for this modification of the silicon in the eutectic mixture than a master alloy wire composition of 9% Sr, balance aluminum.

After the addition of Sr, an incubation period is required. Until the incubation period has elapsed, the modification of the silicon morphology is insufficient. In addition, there is a point in time after the melt becomes stale to the extent that the action of the Sr to modify the silicon shape is no longer effective. When this point is reached, casting is stopped. At a molten metal temperature of 715ºC...760ºC (1,320ºF...1,400ºF), the incubation time can be up to, about 5 minutes for a 3.5% Sr master alloy and about 1 hour for a 9% Sr master alloy. At a holding temperature of 715ºC (1,320ºF), there is a residence time of, say, 6 to 7 hours during which the silicon modification is satisfactory; after such a residence time the melt becomes stale and is no longer effective for silicon modification. The residence time of a satisfactory silicon modification is longer at 732ºC -(1,350ºF) than at 760ºC (1,400ºF).

The strontium content for effective silicon modification is preferably in the range of about 0.01...0.03% in the molten metal and in the casting. Solid inclusions which have not been eliminated by the dross removal in the melting ladle are removed by filtration, for example through ceramic foam or through micro filters. This can be carried out as the melt moves from the trough into the vessel in the holding furnace. In the case of metal, eg aluminium alloy, castings, especially die castings, it is advantageous to reduce the inclusions to about, for example ? one 20-micron inclusions per cubic centimeter of metal in the casting, and preferably ≤ one 15-micron or even ≤ one 10-micron inclusions per cubic centimeter of metal. Pore size or grain size is selected to meet the selected standard. The desired flow rate through the filter is then obtained by appropriate filter area and pressure head. The inclusion content of the metal is determined by metallographic examination of a statistically sufficient sample taken from the area of the holding furnace from which the metal is transferred to the die casting apparatus. The sample is obtained using equipment such as that described by RD Blackburn et al. in papers presented at the Pacific Northwest Metals and Minerals conference on April 27, 1979, and involves drawing a statistically adequate amount of metal through a filter and analyzing the inclusions retained in the filter. In the 20 micron test, for example, the number of inclusions found is divided by the amount of metal drawn through the filter; the presence of inclusions larger than 20 microns will result in the metal failing the test.

3. Feeding the molten material to the die-casting device

The molten material is brought from the holding furnace to the die casting apparatus through an exhaust pipe. The exhaust pipe preferably extends into a region of the holding furnace vessel where the melt pressure head upon removal of the melt for casting causes the melt refill to move through a filter in that region. The exhaust pipe extends from the holding furnace to a filling or charging chamber, also referred to as the shot cylinder, to an opening in the filling chamber referred to as the inlet nozzle.

The exhaust pipe is preferably made of graphite (coated on its outer surface to protect against oxidation) or ceramic to prevent iron contamination of the melt and to facilitate maintenance of the exhaust pipe.

An inlet nozzle insert made of ceramic, e.g. boron nitride, can be used to reduce heat transfer and thus protect against solidification of the metal in the inlet nozzle and reduce erosion at this point. This can be combined with a ceramic insert in the shot cylinder in the area of the inlet nozzle to also prevent erosion. Erosion can be controlled just as well at this point with a steel replacement lining of the H13 type.

An electric heater for the inlet nozzle can also be used to prevent the metal from freezing at the inlet nozzle. This so-called "flat coil" heater works in the manner described below.

A trench may also be used in the outer wall of the fill chamber in the section of the outer wall surrounding the inlet nozzle to reduce heat transfer from that area of the inlet nozzle.

A secondary, compressible, die-cut (by compression of tape) graphite fiber seal may be used on the outside of the inlet nozzle primary seals to protect against air leakage past the primary seals into the melt at the junction between the exhaust pipe and the shot cylinder.

4. The filling chamber section

Several important aspects of the die casting process include the filling or charging, the chamber or the shot cylinder of the die casting device. For example, the filling chamber has a support for a piston or ram, which is preferably made of beryllium copper. The piston serves to convey the melt from the filling chamber to the die or mold. In conjunction with this In the die casting section there are additional devices for applying coatings or lubricants to fill the gaps between the filling chamber and the piston and between the filling chamber and the melt.

a. The piston

Several features of the filling chamber section contribute specifically to the high quality of the die castings. In connection with the piston, an important aspect is the protection against it becoming a source of harmful gases, such as air from the environment, which flow into the molten material held under vacuum in the filling chamber. In order to carry out its various functions, the piston must be able to initially hold the melt and then feed it to the die. It must be both mobile and seal as far as possible against the ingress of contaminants into the melt contained in the filling chamber.

Advantageous features for the piston include: 1) sealing aspects; 2) a connection between the piston and the piston rod; and 3) temperature control measures to stabilize the sliding fit between the fill chamber bore and the exterior of the piston.

According to a preferred form of peripheral sealing of the piston, the seal extends between the filling chamber and the piston rod. This feature ensures sealing for as long as desired during the piston travel.

In a further development of piston sealing, a flexible sleeve between the filling chamber and the piston rod accommodates the different orientations of the piston and rod. This arrangement also prevents damage to sealing gaskets by aluminum solder or casting flash caused by piston movement.

In another embodiment, the piston includes a flexible skirt for adapting to variations in the bore of the filling chamber to maintain the piston/filling chamber bore to better seal against leakage of gas into the melt in the filling chamber.

A hinge or a ball, joint or articulated connection may also be provided between the piston and the piston rod to enable the piston to follow the bore of the filling chamber.

The piston is cooled, which helps, for example, with the solidification of the so-called "casting residue" against which it collides during the final filling of the die-casting mold.

The temperature, and especially temperature differences, between the piston and the fill chamber bore are controlled to prevent contamination of the melt by gas passing through the piston-bore interface. Measures used include directly observing and monitoring the piston temperature, which in turn allows control of the flow of cooling fluid to the piston based on timing or temperature of the cooling fluid.

b. The filling chamber itself

The filling chamber itself, like the die-casting mold, can be made of H13 steel, which is preferably given a nitride coating using the ion nitriding method.

The filling chamber may include a ceramic lining in addition to providing reduced erosion, reduced use of release agent (lubricant) or reduced heat loss. Although the invention as disclosed is presented primarily in the context of so-called "hot chamber" technology, i.e., the machine temperatures are such that the metal from the holding furnace basically loses heat as it moves to the die, the use of "hot chamber" technology where the filling chamber, for example, is at about the same temperature as the molten metal, has an effect of protecting ceramic linings against spalling and other deterioration due to temperature gradients. For example, the lining 20 in Fig. 1 of U.S. Patent No. 2,671,936 to Sundwick may be in ceramic form. together with the replacement of other parts of their molten metal feeder in connection with the objective of creating a hot chamber die casting device that is resistant to attack by the metal being cast, especially aluminum alloy. Ceramic linings provide options for compositions that are not subject to aluminum/iron interaction and can therefore remain smooth longer, which is advantageous for example in preventing wear in the flexible skirt. The filling chamber section additionally includes options for applying and maintaining negative pressure.

Vacuum is achieved by adequate pumping and, more importantly, it is maintained by paying attention to adequate sealing. In general, it is questionable practice to increase pumping and not pay enough attention to sealing. Inadequate sealing means that larger quantities of gas are forced through the evacuated filling chamber with the risk of contamination of the melt. Vacuum quality can be monitored by pressure readings (vacuum levels are maintained at 40...60 mmHg absolute pressure, preferably less than 50 mmHg absolute pressure, down to even less than 25 mmHg absolute pressure) and additionally by means such as gas tracking, for example tracking of argon and/or helium, and gas volume flow measurement either under closed loop control or actuator control.

c. Methods for applying coatings or lubricants

An important aspect of the fill chamber section involves the application of coatings or lubricants. Methods such as ion nitriding are performed once and are used to produce many castings. Other coatings and lubricants are often applied, for example, before each casting is formed.

Coatings and lubricants can be applied by hand using nozzles supplied by opening a valve. Or they can be applied by using so-called "rider tubes" that ride with the piston to lubricate the fill chamber bore. Rider tubes typically involve the use of a non-productive piston stroke between each mold loading stroke to lubricate the fill chamber bore in preparation for the next charge of melt into the fill chamber. Another way to lubricate is the "drip oiler" method, where oil is applied to the sides of the piston when it is exposed for subsequent distribution into the fill chamber bore during the piston stroke.

According to one of the most advantageous embodiments, a fill chamber mold end lubricator is provided. It is referred to as a "mold end" lubricator because it enters the fill chamber bore from the end of the fill chamber near the die when the die halves are opened. With the mold end lubricator, the non-productive stroke is eliminated. Other significant advantages of the mold end lubricator include uniform and thorough application of coatings and lubricants, drying of the water and/or alcohol component of water and/or alcohol based coatings and lubricants, and blowing or evacuating solder or flash and vaporized water and/or alcohol from the feeler chamber bore by compressed gas injection.

5. Lubricants and coatings for the filling chamber and die casting mold

The lubricants and coatings used in the present invention for the filling chamber and die have been found to be particularly advantageous in enabling high pressure casting of low iron content precipitation hardenable aluminum alloy parts. The die castings have a low gas content and can be heat treated to conditions with a combined high yield strength and high compressive strength.

Both the filling chamber bore and the sides of the die receiving the casting metal are preferably nitrided using the ion nitriding method. Ion nitriding, also known as plasma nitriding, is a commonly used surface treatment in die casting. Ion nitriding is mainly used in conventional die casting to reduce die abrasion caused by high-velocity erosion. This surface treatment of the filling chamber bore and the die, preferably in combination with the use of lubricant and especially the halogen salt-containing lubricant, has proven to be particularly effective in inhibiting solder formation in high-pressure casting of low-iron, precipitation-hardenable aluminum alloy.

Lubrication is important for long and successful runs, preventing solder formation, i.e. the attack of the steel filling chamber and the mold casting walls by molten aluminum alloy. Therefore, while die and shot cylinder lubricants for the most part perform very difficult tasks, both lubricants have the common task of reducing the solder formation reaction to a minimum.

In the present invention, a halogenated salt of an alkali metal is added to the die and fill chamber lubricants to achieve a significant reduction in solder buildup, especially in the case of die casting low iron aluminum-silicon alloys. For example, potassium iodide added to the lubricant (2 to 7% in the shot cylinder lubricant and 0.5 to 3% in the die casting lubricant) inhibits the formation of buildup solder and allows a reduction in the lubricant species, such as organic ones, required for performance. The lubricant species in the water-based lubricants to which it is added (emulsion, water-soluble synthetics, dispersion or suspension) serve only to reduce the frictional to provide the necessary reduction in the amount of heat needed to separate the part from the die and to reduce heat transfer in the shot cylinder. An example of lubricant agents is polyethylene glycol at 1% in the water base. Another lubricant agent is graphite, which can be added to facilitate the separation of the castings from the die.

Lubricants containing a halogen salt of an alkali metal provide an overall reduction in the gas content of the die-cast parts.

An important step in reducing the gas content in these die castings was the development of the end-of-mold lubricator described herein for applying lubricant to the fill chamber bore. The device allows the use of water-based and/or alcohol-based bore lubricants. As a result, the end-of-mold lubricator has brought consistency to the lubricant application and offers the possibility of using inorganic materials such as potassium iodide. Importantly, the steam generated by the evaporation of the water is removed from the shot cylinder by the expelling action of the drying air expelled from its nozzle.

6. The casting, including its cleaning, heat treatment and properties

When removing the die castings from the die, the die casting can be cooled to room temperature if desired and subjected to sandblasting to remove surface-entrapped lubricant to reduce the effects of gas during subsequent processing, e.g. reducing blistering during subsequent heat treatment and outgassing during welding. Sandblasting can also remove surface microcracks on the castings, resulting in improved mechanical properties in the castings and especially improved compressive strength.

The heat treatment of die castings made of the aluminum alloy AlSi10Mg.1, for example, is designed to improve both ductility and strength. The heat treatment includes a solution heat treatment and an aging treatment.

Solution treatment is carried out in the range of 482 to 510ºC (900 to 950ºF) for a time sufficient to achieve silicon grain coarsening, resulting in the desired ductility and providing dissolution of the magnesium phase. The lower end of this range has been found to provide the desired results with a much reduced tendency for blistering to occur. Blistering is a function of flow stress, and treating at lower temperatures (which is associated with lower flow stress) therefore helps to prevent blistering. The lower end of this range also provides better control over silicon grain coarsening, with the grain coarsening rate being noticeably lower at the lower temperatures.

Solution heat treatment is followed by aging or precipitation hardening. Ageing is carried out at temperatures lower than those used for solution, precipitating Mg2Si to strengthen the solution. To determine the appropriate combinations of times and temperatures for aging, the concept of the aging integrator as set forth in US-P-3,645,804 can be used. If the casting is later subjected to paint baking at elevated temperature treatments, the aging integrator can be used to determine the effect of these treatments on the strength of the finished part.

It has been shown that this solution plus ageing treatment allows the selection of a combination of high ductility and high strength, with the ductility coming from the solution heat treatment and the strength coming from the ageing treatment, so that a wide range of compressive strength can be achieved, such as in box-shaped die castings.

As stated above, solution heat treatment temperatures at the lower end of the solution heat treatment temperature range are preferably used. The time of solution heat treatment temperature has an influence. The yield strength achievable by aging decreases with increasing time at solution heat treatment temperature. The yield strength achievable decreases more rapidly with solution heat treatment temperature at the higher solution heat treatment temperatures, e.g. 510ºC (950ºF), than is the case at lower solution heat treatment temperatures, e.g. 493ºC (920ºF). The achievable yield strength starts higher in the case of solution heat treatment at 510ºC (950ºF), but falls below that achievable by solution heat treatment at 493ºC (920ºF) as the solution heat treatment time increases.

The properties of die castings after heat treatment of the aforementioned AlSi10Mg.1 alloy are following:

Yield strength under tension (0.2% equivalent yield strength): ≥ 110 MPa

(Typical yield strength: 120 ... 135 MPa)

Elongation ≥ 10% (typically 15 ... 20%)

Deformation in free bending test ≥ 25 mm, even ≥ 30 mm;

Total gas content ≤ 5 ml/100 g metal

Weldability: A or B

Corrosion resistance ≥ EB

Yield strength and elongation were determined according to ASTM-B557.

The deformation in the free bending test was determined using a test setup as shown in Fig. 15. The radii at the heads against which the sample deflects are 1.27 cm (0.5 inches). The sample with a thickness of 2 mm and a length of 7.62 cm (3 inches) and a width of 1.52 cm (0.6 inches) receives a slight Deflection such that the specimen bulges as is evident when the load heads move towards each other. Specimens thicker than 2 mm are ground down to a thickness of 2 mm on one side only and bent so that the outside of the bend is on the unground side. The upper and lower load heads close at a constant controlled stroke rate of 50 mm/min. The "free bend strain" is the number of millimetres of head movement at the onset of specimen rupture. Free bend strain is a measure of compressive strength. Mechanical properties, e.g. yield strength and free bend strength, are determined using specimens cut from the walls of complex die castings as opposed to the practice of direct casting of test specimens which are essentially ready for testing as cast.

The gas content is determined by "melt metal gas analysis" of the whole casting, including mass spectrographic analysis of the constituents. A typical amount of gas is less than 5 ml, at standard temperature and pressure (STP), i.e. 101.325 kPa (1 atm pressure) and 24ºC (75ºF) per 100 g of metal. The practice of melting the whole casting contrasts with the possibility of testing individual sections cut from the casting. Melting the whole casting provides a good measure of the real quality that can be obtained by the melting equipment and melting process.

Weldability is determined by examining the weld molten bubble formation using a rating of A, B, C, where A is associated with no visible gas formation, B with a small amount of outgassing, a slight spraying effect but still weldable, and C with outgassing with large amounts and explosions of hydrogen that render the casting unweldable. On the other hand, the amount of gas is a measure of weldability, with weldability being inversely proportional to the amount of gas.

Corrosion resistance is determined according to the EXCO test, ASTM standard G34-72.

The following results of mechanical testing on castings obtained from two runs are representative of the quality of precipitation hardened high speed die castings made of AlSi10Mg.1 alloy:

Show it:

Fig. 1 is a side view, partly in section, of a die casting apparatus for use in carrying out the invention;

Fig. 2 shows a casting from the mold in Fig. 1;

Fig. 3 is a schematic representation of the melting practice;

Fig. 4 is a detailed elevational view of one of the embodiments of the area around the filling chamber end of the suction tube in Fig. 1;

Fig. 5 is a detailed elevational view of a second embodiment of the area around the filling chamber end of the suction pipe in Fig. 1;

Fig. 5A schematic perspective view of a third embodiment of the area around the filling chamber end of the suction pipe in Fig. 1;

Fig. 6 a detailed view in elevation of a seal for sealing the piston/filling chamber interface;

Fig. 6A and 6B are views of modifications in Fig. 6;

Fig. 7 is an axial cross-section of a second embodiment of a piston;

Fig. 8 is an axial cross-section of a third embodiment of a piston;

Fig. 9 is a schematic cross-sectional view in plan view of a die casting device as described under using a horizontal cutting plane in Fig. 1 which contains the axis of the filling chamber 10;

Fig. 10 is a view similar to Fig. 9 showing more details and a subsequent working stage;

Fig. 11 is a view related to the section plane XI-XI of Fig. 10;

Fig. 12 is a view related to the section plane XII-XII of Fig. 10;

Fig. 13 is a view related to the section plane XIII-XIII of Fig. 10;

Fig. 14 is a view related to the section plane XIV-XIV of Fig. 13;

Fig. 15 is a side elevational view of the test setup for measuring deformation in the free bending test; Fig. 16 is an oblique view of a casting;

Fig. 17A is a schematic cross-sectional view, partially in section, of a piston with internal cooling in a heated filling chamber bore;

Fig. 17B to 17D Control diagrams.

The discussion of the implementation types of the technology is divided into the following chapters:

a. A die casting device in general

b. Melting plant

c. Inlet nozzle

d. Sealing of filling chamber against piston rod

e. Alternative pistons

f. Mold end lubrication device

g. Check the piston filling chamber clearance

h. Example

The following chapters:

a. The die casting device in general

Referring to Fig. 1, in connection with a horizontal, self-loading cold chamber vacuum die casting device, essentially only the area of the fixed clamping plate 1 or clamping plate with the fixedly arranged die casting mold or casting mold, the half 2 and the movable clamping plate 3 or clamping plate with the movable die or casting mold, half 5 of the die casting device together with the piston 4, suction pipe 6 for the supply of molten metal, holding furnace 8 and filling chamber 10.

The vacuum line 11 for removing air and other gases in the direction of the arrow is connected to the die in the area where the die is last filled by the incoming molten metal. Line 11 is opened and closed using valve 12 which can be operated via a control line 13 by a control system (not shown).

Fig. 2 shows an example of a non-deburred die casting, for example in the shape of a hat, with the gate area 14 separating the hat section 15 from the sprue 16 and the casting residue 17. The vacuum connection appears as appendix 18. It is desirable that the gate area 14 be thin, e.g. ≤ about 2 mm thick, so that it can be broken away from the casting. Also, the vacuum appendix is sized for easy removal.

Referring again to Fig. 1, a conical or spherical projection 4a is provided on the front of the piston 4. The rear of the piston is connected to the piston rod 21. The rear area 10a of the filling chamber 10 shows a sealing device 90, which is explained in detail below in the discussion of Fig. 6. The suction pipe 6 is connected to the filling chamber 10 via a clamping device 22. This clamping device 22 has a lower, hook-shaped, forked tongue 24 which extends under the annular flange 25 on the suction pipe 6. From above, a screw 26 is screwed through the clamping device 22. This enables the end of the suction pipe 6 to be clamped to the inlet nozzle of the filling chamber 10.

The mold end lubricator 170 is used to apply lubricant to the bore of the filling chamber 10 from the mold end of the filling chamber when the movable die and platen, plus ejector die (not shown) are removed from the fixed die and clamping plate. For additional information relating to this lubrication device, please refer to Fig. 9.

The operation of the die casting apparatus of Fig. 1 generally includes first and second phases, with a subsequent third phase being included. In phase 1, vacuum is applied to evacuate the die and fill chamber and to draw the metal required for pouring from the holding furnace into the fill chamber. Phase 1 further includes relatively low speed movement of the piston to move the molten charge toward the die cavity of the die. Phase 2, characterized by high speed movement of the piston to inject the molten metal into the die cavity, is initiated at or slightly before the metal reaches the gate, where the metal enters the die cavity and the final part is formed. Phase 3 includes increased piston pressure on the casting residue; piston movement is essentially stopped in phase 3.

Further details of the various aspects of the machine structure shown in Fig. 1 are explained below.

b. Melting plant

Fig. 3 illustrates an example of a melting system used to provide an appropriate supply of molten alloy, e.g. AlSi10Mg.1, for die casting.

Solid metal is melted in the furnace 40 and subjected to a fluxing treatment, for example using a 15 minute flow of argon + 3 volume percent chlorine to the vessels 42 and 44, followed by a 15 minute flow of bare argon. A volume flow rate and gas distribution system appropriate to the volume of molten metal used are used.

If required, for the preparation of the metal to be cast, the metal is led from the melting furnace 40 into the trough 46, where the strontium addition is made from the master alloy wire 48.

The metal flow from the trough is filtered by an inlet filter 50 as it enters the holding furnace 8 and subsequently by an outlet filter 54 before being withdrawn through the exhaust pipe 6. Alternatively, filter 50 can be provided in a separate unit inside the holding furnace 8. The filter pore sizes can be the same or different. For example, the inlet filter 50 can be a coarse-pored ceramic foam filter and the outlet filter 54 a fine-pored ultra-fine filter. Alternatively, both filters can be fine-pored ultra-fine filters. The filter pore sizes are selected so that the metal quality specified above is ensured in relation to the inclusion content in the castings. Filter 54 could be placed on the bottom of tube 6 and sub-compartment 56 eliminated, however the construction shown is advantageous in that it allows the use of a larger extent of fine-pored filter 54, making it easier to ensure an adequate supply of pure molten metal for casting.

c. Inlet nozzle

Fig. 4 shows details of an embodiment of the inlet nozzle 60 in filling chamber 10. Three important aspects of this embodiment protect against 1) solidification of the metal on the walls of the inlet nozzle, 2) erosion of the walls of the inlet nozzle by the flow of molten metal, and 3) loss of vacuum inside the filling chamber.

A boron nitride insert 62 specifically contributes to aspects 1 and 2.

Primary seals 64 and 66 specifically contribute to aspect 3 by sealing the inlet nozzle to the seat ring 68, the connector 70 and the ceramic lining 72.

Heat is supplied to the connecting piece 70 by means of heating coil 71, e.g. an electrical ohmic or inductive heating coil.

A compressible graphite fiber seal 74 is compressed between filling chamber 10 and connector 70 and protects against air leakage at the primary seals.

A flat coil heater 80 is formed by a grooved ring 82. The heater is held on the plane 86 which is a flat surface machined on the outside of the outer surface of the filling chamber. Steel bands 88 encircle the filling chamber to hold the heater in place. Flange 25 is provided to allow the clamping device 22 of Fig. 1 to hold the end of the suction tube tightly sealing against the filling chamber 10.

Fig. 5 shows details of a second embodiment of the inlet nozzle 60 into the filling chamber 10. This embodiment illustrates the use of an air-filled trench 26 surrounding the inlet nozzle. Alternatively, the channel 76 can be filled with an insulating material other than air. The channel mitigates the heat dissipation effect of the walls of the filling chamber and counteracts a tendency of the melt to solidify and block the inlet nozzle.

The embodiment of Fig. 5 also illustrates the idea of a ceramic or replaceable steel lining 78 for the bore of the filling chamber.

The structural details in Fig. 5 which are the same or largely similar to those of the embodiment of Fig. 4 have been given the same numbers as used in Fig. 4.

From the discussions of Figs. 4 and 5, it is clear that a major issue is the maintenance of a sufficiently high temperature at the inlet nozzle. Fig. 5A illustrates an embodiment that satisfies the problem of temperature maintenance in a unique way. According to this embodiment, the suction pipe 6 relatively short compared to its length in the embodiments of Figs. 4 and 5, and the molten metal container 130 is mounted upwardly of the inlet nozzle 60 so that heat transfer from the molten metal into the container keeps the inlet nozzle 60 free of solidified metal. The container is provided in the form of a trough through which the molten metal circulates in a circuit as indicated by the arrows. Pumping and heat preparation are carried out in station 132. All containers may be covered (not shown) and openings provided, e.g. for the access of suction pipe 6. Metal preparation for the circuit comes from the coarse filter 50 of Fig. 3, the fine filter 54 being provided as shown to effect continuous filtering of the circulating metal.

d. Sealing of filling chamber against piston rod

Fig. 6 illustrates several features, one of which is a particularly advantageous seal for sealing the piston/filling chamber interface against outside air and dirt.

In Fig. 6, piston 4 is shown seated in the filling chamber 10 at the end of the filling chamber furthest from the die. In this drawing, the inlet nozzle 60 appears. It will be apparent that the piston shown in Fig. 6 is in the same retracted or rearward position as it is in Fig. 1. Instead of or in addition to the packing seal that could be provided at the interface between chamber 10 and piston 4, the embodiment of Fig. 6 provides a seal 90 extending between the filling chamber 10 and the piston rod 21.

Continuing from the filling chamber, the seal 90 comprises several elements. First, there is a filling chamber connection ring 92 which is screwed to the filling chamber. A flat seal (not shown) fills the space between ring 92 and the filling chamber in order to ensure that the seal does not Surface irregularities between the two ensure gas tightness.

A flexible, airtight casing 94 is hermetically welded between ring 92 and a following connecting ring 93. Ring 93 is in turn also screwed to the piston rod driver 96 in an intermediate position with a flat seal. An airtight packing seal 98 is located between the driver 96 and the rod 21.

Also forming part of the seal 90 are a line 100 from the enclosure 94 to a vacuum source, a line 102 to an argon source and associated valves 104, 106 which are controlled via the lines as shown by means of the programmable controller 103 which are supplied with signals from line 110 indicating the various conditions of the die casting apparatus.

Seal 90 works as follows. The driver 96 "rides" on the rod 21 as the piston performs its movement in the bore of the filling chamber 10 towards the die. Either under influences such as a banana-like curvature of the bore of the filling chamber 10 or as a result of the deflection of the piston rod under the load of its drive (not shown) and even influenced by possible articulated connections of the piston with the piston rod (as provided in the embodiments described below), there may be an inclination of the piston rod with which it tends to rotate about the axes perpendicular to it. Due to the flexible casing, the occurrence of these rotational tendencies is readily permitted without adversely affecting the seal provided by the packing 98. The driver simply moves up and down or in and out as in Fig. 6 to follow the piston rod in whatever way it may deviate from the axes of the piston and the filling chamber bore.

With respect to the regulator 108, it performs the following function. When the piston is in its retracted position as shown, the regulator 108 maintains the valve 104 open and the valve 106 closed. A vacuum is maintained both in the bore of the filling chamber and in the interior of the enclosure 94. The required amount of molten metal enters the bore through the inlet nozzle 60, after which the piston rod 21 is driven to move the piston 4 forwardly towards the die. The supply of molten metal is terminated when the piston moves to the position for closing the inlet nozzle. If the piston is moved further toward the die so that it passes over the inlet nozzle and opens it into the interior of the enclosure 94 while the interior is still under vacuum, molten metal would be drawn through the inlet nozzle into the interior of the enclosure and solidify there and damage the enclosure. The programmable controller prevents this by using the machine state information from line 110 to close valve 104 and open valve 106. The enclosure 94 is filled with argon to remove the vacuum, thus preventing the melt from being drawn through the inlet nozzle 60.

The presence of argon in the system is used to monitor the effectiveness of the seals. Helium is an alternative gas that can be used in this way. For example, the tightness of the sliding fit between the filling chamber bore and the piston can be observed and/or controlled. Helium sensors have been connected to the vacuum lines connected to the die and the filling chamber so that knowledge of where helium has been introduced makes it possible to track and determine the seal of the piston to the filling chamber. Molten metal gas analysis using mass spectrometer technology enables the detection of argon in a Casting, whereby knowing where argon is present during the casting process can provide information about the tightness of the seals in between.

In an alternative embodiment shown in Fig. 6, conduit 102 is replaced or assisted by one or more longitudinal slots 103 on the outside diameter of piston rod 21. An alternative or supplement to the effect of the slots can be achieved by reducing the diameter of the rod. The use of the reduction in diameter is advantageous in comparison to the slot because the edges of the slot, if not rounded, can cut the packing seal. The slots or reduction are arranged in such a way that just as piston 4 clears the inlet nozzle, for example, unmolten metal would be sucked into the casing 94, the slots open a bypass provided in the packing seal 98. The bypass created by the slots 103 opens to the ambient air.

In the alternative of Fig. 6B, the slots 103 open into the interior of 90A which is essentially a duplicate of the components 92, 93, 96, 98 which contain argon substantially at atmospheric pressure based on line 102 and valve 106. Pressures slightly above atmospheric pressure may be used if, for example, argon purge through line 102 as the volume increases due to the access provided by the slots 103 is not rapid enough to otherwise maintain the required pressure drop and maintain the metal level below the inlet nozzle 60. The flexible enclosure 94 of the duplicate and the length of the slots 103 are sufficient so that the argon can be fed into the cylinder 10 directly by the abutment of the piston against the casting residue. The duplicate of 92 is connected to the driver 96 of the construction of Fig. 6. The casing of this duplicate construction is also chosen to be sufficiently long so that the slot 103 the argon chamber (which it supplies) does not open to the outside air when the piston is in its retracted position, that is, in its position shown in Fig. 6B.

Further features of Fig. 6 include an auxiliary seal 112 on the follower 96. The piston presses against the seal 112 when in its retracted position.

Also shown in Fig. 6 are the concentric supply and return lines 114, 116 for cooling fluid (e.g., water and ethylene glycol) to the piston. Thermocouples (not shown) in the fill chamber walls, piston metal contact and bore contact walls (the leads of these thermocouples are returned through the cooling fluid lines) and in the water stream are used to stabilize the sliding fit between the fill chamber bore and piston in open or closed loop control. Other factors, such as the force required to move the piston (which is a measure of the friction between the bore and the piston) or the amount of argon appearing in the vacuum lines connected to the die and the fill chamber, can also be used in monitoring and control systems to stabilize the sliding fit to minimize gas leakage through the piston-bore interface.

Further features are illustrated in Fig. 6. The trailing edge of the piston has been provided with a flash or solder reaction product remover 118. This remover is made of a harder material that retains its sharpness at its edge 120 better than the base material of the piston and is selected based on other design criteria such as high thermal conductivity. During the return stroke of the piston, the function of the remover 118 is to strip or cut off any loose flash or solder left behind during the forward metal feed stroke of the piston. Note that the leading edge 122 is also sharp, with but, as indicated, this is an easier task in the case of the remover 118.

e. Alternative pistons

Fig. 7 shows a second embodiment of a piston. This piston is designated by the number 4 to indicate the intention that it serves as a replacement piston for piston 4 and includes a flexible skirt 140 for adjusting to variations in the bore of the filling chamber. Skirt 140 is made, for example, of the same material as the piston itself. It is flexible in that it is thin compared to the rest of the piston and is long. Its thickness may be, for example, 0.0381 cm (0.015 inches), which in total protrudes beyond the rest of the piston, i.e. the outside diameter of the skirt is, for example, 0.0762 cm (0.030 inches) larger than the outside diameter of the rest of the piston. Preferably, the skirt has an outer diameter about 0.0025 cm (0.001 inch) larger than the inner diameter of the bore of the filling chamber 10, i.e., there is nominally a slight interference fit of the skirt with the bore. The flexibility of the skirt avoids any sticking.

It is understood that skirt 140 is relatively weak in compression. To prevent a build-up of solder or flash from collapsing the skirt on the return stroke of the piston, the skirt includes a skirt 142. The inside diameter of the skirt 142 is smaller than that of an adjacent socket 144 on the piston housing. If the skirts encounter any major resistance on the return stroke of the piston which would otherwise compressively load the skirt, the stop transfers such load to the piston housing and thus protects the skirt from any danger of collapsing.

The threads at points 146 and 148 are used for assembling the piston. The holes 150 are used for using a bolt wrench.

Before assembly, metal turning techniques can be used to prevent bulging of the thin portion of the skirt 140 outward. Metal turning involves rotating the skirt at high speed about its cylindrical axis and placing a forming tool, such as a piece of hard wood, in contact with the inside of the skirt portion 140 to expand the diameter outward. While this helps to increase the nominal dimension with the fill chamber bore, the thin nature of the material prevents the piston from sticking in the bore. This additional bulging increases the sealing effect of the skirt.

Fig. 8 shows a third embodiment of a piston. This piston 4" provides some features in addition to those shown for the piston 4" in Fig. 7. For example, the piston has a ball or hinge joint 160 from piston rod to piston. This includes a spherical segment cap 162 welded to the peripheral joint 164 to provide a containment for cooling fluid.

The stop and seam facing surfaces in Fig. 8 are machined as tapered surfaces to provide improved accommodation when the skirt deflects upwardly by approximately 0.90º as indicated in the drawing by "A".

Assembly of piston 4" is carried out as follows. The ball joint connector is fed to the piston face 266 and piston side wall 268, which are connected by threads 269. Spacers or washers 270 control, by their thickness, the amount by which the threads engage to provide a proper snug fit between the ball and connector. Tightening of the thread engagement is obtained by placing a spanner on the outside diameter of the face portion 66 and a bolt wrench in the slots 272 cut longitudinally in the rear wall 268.

Then the sleeve 274 is screwed onto the outlet end 276 of the ball by using a bolt wrench in the holes 278. The ball is then prevented from rotating relative to the sleeve by inserting the hexagon handle of a wrench for hexagon socket screws into the hole 280, which also has a hexagonal cross-section.

The next step in the assembly is to insert the skirt 282 into threaded engagement with the side wall 268 using the threads 284.

The piston rod 285 with the attached burr removal ring 286 is screwed onto the sleeve 274. An annular recess 288 in the bore of the sleeve ensures that there is a firm engagement between the outlet end 276 and the piston rod 285. O-rings 290 seal against leakage of the cooling fluid.

f. Mold end lubrication device

Fig. 9 shows a general view of the end-of-mold lubricating device 170 of the invention. It is mounted on the fixed clamping plate 31 and can be brought into the working position shown in dashed lines by means of the hydraulic cylinder or pneumatic cylinder 172 when the mold halves are opened. In the working position, a head in the form of nozzle 174 is ready to be inserted into the filling chamber bore to perform its applicator, drying and blowing functions.

In Fig. 10, the end of mold lubricator is shown in more detail. The programmable controller 108 has already received information from the die casting machine via line 110 that the machine is already in an appropriate state (i.e., the mold halves have been opened and the last casting has been ejected) and has interacted with the fluid pressure unit 176 via line 178 to cause the hydraulic cylinder to move the lubricator to its working position.

In addition, the controller has sequentially instructed the servo motor 180 on line 182 to set the timing belt 184 in motion and thereby rotate the pulley 186 and the arm 188 which is connected to the Pulley is firmly connected so that the nozzle 174 moves into the bore of the filling chamber 10.

The connection of nozzle 174 to arm 188 consists, for example, of a length of flexible tube 190 carrying four tubes 192, specifically designated hereinafter as 192a, 192b, 192c and 192d, which serve various purposes to be explained.

Nozzle 174 carries a sleeve 194 made of polytetrafluoroethylene (PTFE) for insertion into the bore of the filling chamber 10. The sleeve typically has a polygonal cross-section, for example a square cross-section as shown in Fig. 11, and contacts the bore only at the polygonal corners, thus leaving gaps 126 for tasks which will become apparent hereinafter.

Fig. 12 shows that the flexible tube 190 is constrained to move in a circular path through the channel 198 containing PTFE rails 200, 201, 202 when driven by the arm 188. Fig. 12 also shows the four tubes which will now be described. Tubes 192a and 192b are supply and return lines for, for example, water-based lubricant or laminate supply to nozzle 174. Tube 192c is the nozzle air supply and tube 192d is a pneumatic supply line for a valve 204 (Fig. 13) in nozzle 174. Tubes 192 extend between nozzle 174, through line 190 and to their starting points at location 206 inwardly toward the hinge point of arm 188. At location 206, flexible hose line (not shown) is connected to tubes 192, the flexible hose line leading to air and lubricant supply vessels (not shown).

Fig. 13 shows in more detail the nozzle 174 of the end-of-form lubricating device. Nozzle head 208, which is circular when viewed in the direction of arrow B, has a sufficient number of spray nozzle openings 210 distributed around its circumference so that a substantially continuous conical shell of a rearwardly directed directed jet. An example of a nozzle head diameter of 5.715 cm (2.25 inches) is 18 evenly spaced nozzle openings, each having a bore diameter of 0.061 cm (0.024 inches). Angle C is preferably about 40º. The objects of the present invention can be achieved by angles in the range of 30...50º and preferably in the range of 35...45º.

For example, the nozzle mixing chamber 212 receives water-based lubricant or laminate from the tube 214 and air from the tube 216 or only air from the tube 216, depending on whether the valve 204 has opened or closed the tube 214 by actuating the pneumatic line 192d.

Nozzle 174 is connected to the flexible hose at junction 218. Line 192c runs directly to tube 216. Lines 192a and 192b are shorted at the junction to prevent continued circulation of lubricant or laminate, which is helpful in preventing settling of suspensions or emulsions. Shorting 220 is shown in Fig. 14. Tube 214 is continuously open to short circuit, but only draws from that point by command of valve 204, at which time controller 108 causes a control valve (not shown) in the return line to close to achieve maximum delivery of lubricant or laminate to the nozzle.

The programmable controller 108 of Fig. 10 interacts with the pneumatic pressure supply for line 192c to send air to open valve 204 so that a lubricant or coating aerosol is sprayed onto the bore of the fill chamber as the nozzle moves toward the die in the bore. The controller does not control the servo motor driving the nozzle far enough to spray lubricant down toward the inlet nozzle 60. The nozzle is stopped short of this point, but with enough aerosol having been sprayed into the area that a portion of the bore at the inlet nozzle has been adequately coated. The controller also provides the option of varying the nozzle speed along the bore in order to supply more coating material to problem areas, if this is desired.

Once the nozzle has advanced as far as it should, just short of the inlet nozzle, it is then retracted. During retraction, the controller causes the pneumatic valve 204 to shut off the supply of lubricant and coating material so that only air from line 192c, tube 216, exits through the nozzles 210. This air dries water from the water-based lubricant coating on the bore and blows it out of the bore in a gaseous state along with any loose solder or flash. When the nozzle has returned to its retracted position, as shown by the dashed line in Fig. 9, the controller 108 actuates the cylinder 172 to swing the lubricating device back out of the way, the mold halves are closed, and the die casting device is ready for the next casting.

The gaps 196 provide space so that the gas flow can exit from the nozzles at the mold end of the filling chamber.

g. Check the piston filling chamber clearance

The present technique departs from the work of Miki et al., described in the aforementioned patent 4,583,579 ('579), by focusing on the piston-fill chamber fit during the metal feed stroke of the piston as a gas source in castings made in vacuum die casting apparatus.

As is apparent from Fig. 5 of the '579 patent and the discussion in the text of that patent, in known practice there has been a significant upward deviation of the temperature of the piston or plunger relative to the temperature of the fill chamber bore, i.e., the shot cylinder, as the piston moves through the metal feed stroke to inject molten metal into the pressure chamber. mold. Referring to Figure 5 of the '579 patent, from a time when the temperatures of the piston and the fill chamber bore are approximately equal, the bore temperature rises to a maximum and then falls while the piston temperature rises to a much higher maximum and then falls with the bore temperature to a point where the temperatures are approximately equal. As pointed out in the '579 patent, the relative rise in temperature of the piston compared to that of the bore can cause both to assume a snug fit, so that retraction of the piston is delayed until cooling releases the snug fit.

The fit between the piston and the bore during the feed stroke of the piston is controlled to resist gas leakage through the piston/bore interface into the metal being forced into the die by the piston while under vacuum. To achieve this control, various measures can be taken. One of the measures is to regulate the cooling of the piston so as to reduce the temperature rise of the piston during the casting cycle. Although a blocked fit cannot thus be accepted, the cooling can be regulated to maintain the piston temperature so that a sliding fit minimizing gas leakage is achieved rather than a looser, gas-permeable fit.

A second measure that can be used in conjunction with the first measure involves creating an interference fit or otherwise tight or sliding fit of the piston in the filling chamber bore at a certain reference temperature, for example room temperature, and heating the filling chamber to make the piston moveable with a tight fit in the filling chamber bore. With the filling chamber heated, the piston temperature will fluctuate less relative to the temperature of the bore. and a gas-resistant fit can be maintained during the metal feeding stroke.

Both measures can be tailored depending on the specific materials of the design, e.g. the thermal expansion coefficients that characterize the materials. The underlying basis for the design is the principle of keeping the clearance between the piston and the filling chamber bore gas-tight during the piston's feed stroke, while balancing the requirements for the force needed to move the piston and control the wear of the piston and the filling chamber bore.

Figs. 17A to 17D illustrate the control of piston to fill chamber clearance. Piston 4 is internally cooled or heated by water or other fluid entering through supply line 114 and returning through line 116. Provision is made for a continuous flow of water through a bypass line 300 containing a manually operated valve 302 and a check valve 304. Controller 306 operates a two-position or sequence control valve 308 (for use in the case of proportional control, proportional-integral control, PID control, etc.) based on its program and information received from thermocouple 310, the leads of which may be led to the controller from lines 114 or 116. In addition, a heater or cooler 312 is provided on the filling chamber 10 and controlled by the controller 306 using the thermocouple 314.

Figures 17B through 17D are examples of different control systems that can be used to control piston temperature. Generally, controlling the piston to fill chamber clearance via piston interactions is preferred because it responds faster than the fill chamber due to its copper material and smaller size.

Referring to Fig. 17B, closed loop control with feedback using the Information on the piston temperature from thermocouple 310 is illustrated. A two-point control with hysteresis is used. The operator selects the set point for the piston temperature, Tsp, and the temperature deviations Δ2 and Δ1, the sum of which determines the differential gap. In a variation of the control shown in Fig. 17B, a closed loop control based on the piston outlet water temperature is used, where there is thus a set point for the water temperature. The feedback signal is the piston outlet water temperature.

Figures 17C and 17D illustrate open loop control with variable pulse width τ1 and τ2 input by the operator. Time 320 is the start of vacuum or phase 2, where phase 2 is the portion of the piston feed stroke for metal where a higher piston travel speed is used once the metal has reached or is about to reach the gate(s) in the portion of the mold cavity where the actual part is formed. Time 322 is the end of vacuum.

h. Example

The following example serves to further illustrate:

Example I

A complex illustrative die casting had the configuration shown in Fig. 16. For naming purposes, it was referred to as the "hat" casting. It consists of a 100 mm section 330 with a wall thickness of 5 mm and a 200 mm section 332 with a wall thickness of 2 mm. The casting has a height 334 and a depth 336, both of which are 120 mm. The main gate 342 has a cross-sectional dimension of 4 mm x 60 mm, while the two side gates 344 each have cross-sections of 2 mm x 10 mm. The casting was made as the 32nd casting of a run of 95 castings in a vacuum die casting apparatus as shown in Fig. 1 using the following parameters: cycle time 0.9 minutes, vacuum during phase 1 about 20 mmHg absolute, piston diameter 70 mm, piston speed in phase 1 about 325 mm/s, piston speed in phase 2 about 1,785 mm/s, metal overpressure in phase 3 868 bar (12,580 psig), 141 ml of 1% KJ lubricant on the outside of the die, 7.6 ml of 5% KJ lubricant on the filling chamber bore and a metal temperature in the holding furnace of 710ºC (1,310ºF). The holding furnace metal analysis was 10.1% Si, 0.3% Fe, 0.13% Mg, 0.03% Sr, 0.052% Ti. The die casting apparatus includes the bellows seal of Fig. 6 and the end of die lubricant apparatus of Figs. 9 through 14. The entire casting, trimmed but cleaned from the overflow 338 and gate to the cast tail section 340, was tested for gas content by melting the entire part and gave the following results in milliliters of gas (standard temperature and pressure) per 100 grams of aluminum alloy: 1.29 hydrogen, 1.66 nitrogen, 0.74 nitrogen, 0.72 other, total 4.4 = 0.5 ml/100 g. The mechanical properties for the run obtained by cutting test specimens from the 2 mm thick wall section of several castings after heat treating the castings for 1 hour at 165ºC (950ºF), quenching to 57ºC (100ºF) in 40% aqueous solution of Ucon-A, a polyglycol product of Union Carbide, followed by 1 hour at 307ºC (400ºF) were:

Claims (7)

1. Apparatus for lubricating a fill chamber bore (10) of a die casting device which opens into a die casting mold (2) at a mold end of the fill chamber, which apparatus comprises: an elongated member (190); device (188) which extends the elongated member (190) into the fill chamber bore (10) from the mold end and then retracts the elongated member (190) through the mold end; and lubricating device (174) carried by this elongated member (190) which sprays the fill chamber bore (10) with a lubricant; which apparatus is characterized by the lubricating device (174) further comprising device (210) for spraying the fill chamber bore with a generally conical spray of a pressurized gas which is directed against the mold end of the fill chamber bore. 2. Method for lubricating a bore of a filling chamber (10) of a die casting device arranged so that the mold end of the filling chamber (10) opens into a die casting mold (2), which method comprises: moving a device for lubricating (174) into the bore of the filling chamber (10) from the mold end; actuating the device for lubricating (174) to spray the bore of the filling chamber (10) with a lubricant; and withdrawing the device for lubricating (174) from the bore of the filling chamber through the mold end; which method is characterized by: actuating the lubricating device (174) to spray the bore of the filling chamber (10) with a lubricant when the lubricating device (174) is moved into the bore of the filling chamber (10) and to blow a gas peripherally around the bore and radially outward and axially towards the mold end to create a substantially conical spray of gas which moves vaporized lubricant together with any loosely adhering metal or mold flash out of the mold end of the bore when the lubricating device (174) is moved out of the bore of the filling chamber. 3. A method according to claim 2 for lubricating the bore of the filling chamber (10) of a die casting device having a the bore; which method is further characterized in that the lubricating device (174) is operated to spray the bore of the filling chamber with lubricant, but not the piston, when the lubricating device (174) is moved into the bore of the filling chamber. 4. Apparatus according to claim 1, further characterized in that the elongate member (190) is flexible and the apparatus includes: means (198) for guiding the flexible elongate member (190) between alignment with the fill chamber bore (10) and a path laterally to the fill chamber bore adjacent the mold end; and means (188) for moving the flexible elongate member (190) back and forth along said path and in and out of the bore of the fill chamber (10). 5. Apparatus according to claim 4, further characterized in that the means (198) for guiding the flexible elongate member (190) comprises a curved channel and the means (188) for moving the flexible elongate member (190) back and forth comprises an arm connected to the flexible elongate member (190) and pivotable for rotation about a center of curvature of the curved channel; and means (180, 184) for rotating the arm. 6. Apparatus according to claim 5, further characterized by fastening means (176) guiding the flexible elongate member (190) adjacent the die (2) for movement between an operative position with the curved channel (198) in alignment with the fill chamber bore for extending the flexible elongate member (190) which holds the device for lubricating (174). 7. Apparatus according to any one of the preceding claims 4 to 6, further characterized in that the device for lubricating (174) comprises a nozzle device with multiple nozzle openings (210) distributed peripherally around this nozzle device and directed obliquely radially outward and axially towards the forming end of the bore of the filling chamber (10) in order to produce a substantially continuous, conical spray jet.