DE102005045699A1 - Die casting method employs mold with areas of different thermal conductivity, setting up different rates of heat dissipation from casting - Google Patents

Abstract

Heat is dissipated from the die casting into the mold. In one section of the mold, the rate of heat dissipation in this manner, differs from that in another, adjacent section of the mold. The die casting equipment (1) includes a molding cavity (4), in which one section of the working area of the mold has a coating (9). The thermal conductivity of this coating differs from that of the die plates (3a, 3b) or mold carriers (2a, 2b). The coating bond is formed by a diffusion layer of both materials. The coating laser-applied, using a powdered coating material. An independent claim is included for corresponding equipment.

Description

The The invention relates to a method and an apparatus for the production of workpieces in diecast.

Die casting is a casting process in which liquid metal (eg zinc, aluminum, magnesium or copper alloys) is pressed under relatively high pressure by a casting drive into a multi-part closed for casting permanent metal mold (hot work tool steel). The mold filling process is based on the reaction of the pressure energy acting on the liquid metal through the casting piston into kinetic energy. The locking force of the permanent mold through the machine must counteract the explosive force of the casting process. The explosive force F _s results from the casting pressure p _g , which is reached during the mold filling and the explosive surface A _{s of} the component (the formula for the calculation is: (1) F _s = A _s □ p _g ).

authoritative for the casting pressure is the pressure with which the die casting device the casting piston drives. From the pressure on the part of the device and the Gießkolbenfläche results the effective casting pressure, which over the liquid Metal transfer (Explosive area of the component As) tries to force the mold. With this pressure must the die-casting machine (with a security surcharge of approx. 10-25%) the permanent form at least Squeeze. This fact results in different sizes of die casting machines (Classification according to closing force) on which only components of the respective size, i. the required closing force produced can be.

The competitive advantage of die casting over other existing casting methods is the ability to produce thin-walled, dimensionally accurate castings of high surface quality. However, because the solidification time of the cast metal correlates with the square of the wall thickness and the high heat output of the cast metal to the casting mold, mold filling times in the range of up to under 10 ms are necessary for the casting of thin-walled components. The formula for calculating the solidification time according to B. Nogowizon is

• • Es ist ein hoher Gießdruck und somit hohe Zuhaltekräfte der Druckgießmaschine erforderlich.
• • Die erosive Beanspruchung der Form (Auswaschungen) ist hoch.
• • Es tritt ein Strahlzerfall des Gießstrahles auf, d.h. Luft und Gase werden von der Schmelze eingeschlossen. Es ist ein hoher Nachdruck (durch Multiplikator) zum Komprimieren erforderlich.

As a result, flow velocities of up to 100 m / s are required in order to ensure complete mold filling within the casting time (time until the first casting defect occurs in the form of pre-solidified material). These high flow velocities have the following disadvantages for the casting process:

• • It is a high casting pressure and thus high clamping forces of the die casting machine required.
• • The erosive stress of the form (washout) is high.
• • There is a jet disintegration of the pouring stream, ie air and gases are trapped by the melt. It requires a high reprint (by multiplier) to compress.

One Another problem area in the production of die-cast parts is the porosity; she is one of the most common Committee causes. In addition to possible Leaks in demanded pressure tightness, the impairment the surface quality and their adverse influences on the quality of castings cause gas pores as well as internal shrinkage cavities such as micro-slots, voids and shrinkage cracks worsening the mechanical-technological properties of cast materials.

• • Porosität durch Schwindung (flüssig-fest), also Unvermögen des angewendeten Prozesses die Volumenschwindung während der Erstarrung durch Speisung auszugleichen.
• • Porosität durch Luft-/Gaseinschlüsse, hervorgerufen durch die beim Gießvorgang eingeschlossenen Gase.

Pores in a die casting result from two problems:

• • Porosity due to shrinkage (liquid-solid), ie inability of the applied process to compensate for the volume shrinkage during solidification by feeding.
• • Porosity due to air / gas inclusions caused by the gases trapped during the casting process.

The porosity is is a clear quality feature, which limits the application areas of die-cast workpieces. To the porosity preferably To keep it low, several methods have been developed but due to economic or casting aspects only partially or have not enforced, these are the vacuum die-casting, low pressure die casting, the Acurad process, the Porefree process and the Sachs-Poral method.

Therefore The object of the invention is to use common die casting so on to develop that the aforementioned disadvantages at least can be partially reduced.

The Task is accomplished by a process for the production of workpieces in Die casting according to the features of claim 1 solved; a new device for carrying out of the method disclosed in claim 2. Embodiments are the subject of the dependent claims.

Around the mold filling or to influence the solidification, according to the invention only a few millimeters of mold steel / mold plates by another thermally conductive Material replaced, at least in some areas of the contact surfaces. Around to withstand the thermal stresses of die casting, is also in new type of bond between the base material of the mold plates and the coating materials by forming a diffusion layer made between the two. In one embodiment, the relevant Coating material in powder form by means of a laser on the Base material welded.

Differently thermally conductive Materials in a die to combine different applications and improvements over common Die casting.

• • Weniger Verwirbelung der Luft in der Form, somit weniger Gaseinschlüsse und höhere qualitative Eigenschaften des Bauteils.
• • Geringerer Gießdruck. Das gleiche Bauteil ist somit auf einer kleineren Maschine zu produzieren und somit kostengünstiger.
• • Wandstärken und Fließlängen die bis jetzt im Druckguss nicht möglich waren, sind möglich.

According to a first embodiment is extended by a complete coating of the effective surface of a die with a material having a lower thermal conductivity than the standard hot-work steel, the casting and solidification time of the casting metal according to the alternative metal. As a result, lower flow velocities of the casting metal are necessary for filling the mold. The extended casting time in a new way results in the following positive effects:

• • Less turbulence in the air in the mold, thus less gas bubbles and higher quality properties of the component.
• • Lower casting pressure. The same component is thus to produce on a smaller machine and thus cheaper.
• • Wall thicknesses and flow lengths that were previously not possible in die casting are possible.

The Feasibility could be achieved by means of a thin - walled specimen in Try to be proven.

To another embodiment become the active surfaces the form plates of a form set only partially with a Material of different thermal conductivity coated. This is especially true when casting die castings Areas of different wall thickness expedient. Since thicker walled areas longer solidification times have (Formula 1), arise there, due to the "liquid-solid volume shrinkage," voids.

These Pointy cavities have a devastating effect on the strength properties of the workpiece. In a normal die would In the thickest wall area of the workpiece cavities are created.

at this further embodiment is now in another special design, the die - their Molded plates - with coated to the gate towards lower and lower heat-conductive materials or the solidification time is regulated by the thickness of the coating. This can also be the base material (usually a hot-work tool steel 2343) be used. The materials just have to interact Be agreed that at the thickest wall the material with highest and the thinnest Place (usually the bleed) the material with the lowest heat conduction is arranged. With the solidification of the bleed last a make-up to the complete Solidification of the component ensured become. The component is then free of voids and clearly shows better strength properties.

A further embodiment is the combination of the two aforementioned applications.

The The invention will be described with reference to schematic shown in the drawings Representations closer explained. Show it:

The 1a to 1c in sketches, the die casting method according to the prior art with a hot chamber,

2a to 2c in sketches, the die casting method according to the prior art with a cold chamber,

3 schematically a sectional view of a portion of a die casting device with new mold and

4 a further embodiment of the new mold in a schematic sectional view.

In the 1a to 2c is sketchy respectively the basic structure of a die casting device according to the prior art for die casting according to the hot chamber method ( 1a to 1c ) and for die casting by the cold chamber method ( 2a to 2c ).

Of course, belong to the shown Druckgießvorrichtungen also drive means for the movement of the movable mold carrier and the casting piston as well as control and / or regulating technology, not shown here are. The variants of the new die casting apparatus described below are preferably in the aforementioned Druckgießverfahren used.

A variant of the die casting apparatus according to the present invention is shown in FIG 3 shown. The representation in 3 shows a section of a new die casting 1 , To form the mold cavity 4 is the one in a movable mold carrier 2 B held mold plate 3b to the fixed mold plate 3a introduced, wherein the end faces of both mold plates 3a and 3b be pressed against each other by means of a predetermined closing force. In this illustration, there is a casting chamber in the lower area 6 that with liquid casting metal 7 is filled. The connection between this casting chamber 6 and the mold cavity 4 is through a channel 5 produced. By movement of the casting piston 8th in the direction of the arrow 10 becomes cast metal 7 over the canal 5 into the mold cavity 4 pressed; also called mold filling process. The respectively on the active surfaces of the mold plates 3a and 3b According to the invention provided coating 9 causes - in comparison to known devices and methods - in the outer regions of the workpiece to be produced by casting (molding), the heat dissipation is carried out at a lower speed, so that, as mentioned earlier, air pockets etc. are avoided. The thickness of the coating as well as its thermal conductivity depends, inter alia, on the shape of the workpiece to be produced and on the composition of the cast metal.

So z. B. the representation in 4 a further embodiment of the new die casting. The surfaces of the mold plates 3a and 3b , which specify the shape of the outer surfaces of the workpiece to be produced, are provided in this embodiment with a coating which has sections at least each have a different thermal conductivity. In the upper part of the illustrated mold cavity 4 is in a predetermined portion of the effective area (pressing surface) of the mold plate 3a and the movable mold plate 3b a coating 91 and 92 , Although the same thermal conductivity, but each have a different thickness.

The additional coatings provided in sections in this embodiment 94 . 95 and 96 as well as the sections without coating 93 on the fixed mold plate 3a and the movable mold plate 3b Show that in addition to the attachment of sections of coating with different thermal conductivities also by the different thickness (thickness) of the intended sections coatings the speed of heat dissipation is affected. Also in this embodiment is by movement of the casting piston 8th in the direction of the arrow 10 in the casting room 6 found casting metal 7 into the mold cavity 4 pushed. By the variant of the attachment of the coating shown here 9 , in the form of section-wise coating 91 . 92 . 94 . 95 and 96 ensures that the mold cavity 4 finished molding (workpiece) at its so-called gate (channel 5) last solidifies.

All mentioned in the above description as well as alone Removable from the drawings features are additional components the invention even if not particularly highlighted and in the claims mentioned are. The invention is not limited to the embodiment but in the Revelation often variable.

1

die casting

2a

fixed mold carrier

2 B

Portable mold carrier

3a

mold plate

3b

portable mold plate

4

mold cavity

5

channel

6

Casting / casting container

7

casting metal

8th

casting plunger

9

coating

91 92, 94, 95, 96

sections the coating with different thermal conductivities

93

section without coating

10

Direction of movement of pos. 8th (To water)

Claims (4)

Process for the production of metal workpieces in diecasting, in which metal or metal alloy heated for castability is pressed into a mold cavity of a multi-part casting mold of a die casting apparatus, characterized in that the dissipation of the heat from the casting into the casting mold is at least partially opposite that of the casting each adjacent section is at a different speed. die casting, at least comprising a fixed and a movable mold carrier, the each holding a mold plate, wherein the mold plates each other are facing and each having a recess which when closed Condition of die casting device, so form a mold cavity in adjoining mold plates, into the flowable material by means of a casting piston via a feed channel depressed can be, for use in a die-casting machine, characterized that at least a portion of the active surfaces of the mold cavity a Coating which is opposite to the Material of the mold cavity forming mold plates and / or the the mold plates holding mold carrier a different thermal conductivity having. Device according to claim 2, characterized in that that the bond between the base material and the coating the mold plates by a diffusion of both materials diffusion layer is made. Device according to claim 3, characterized in that that the coating on in powder form by means of a laser the base material is applied coating material.