WO2005109984A2

WO2005109984A2 - A process for the manufacture of a hybrid element comprising a metal skin

Info

Publication number: WO2005109984A2
Application number: PCT/DK2005/000331
Authority: WO
Inventors: Jesper Abell; Klaus Mortensen
Original assignee: Bang & Olufsen A/S
Priority date: 2004-05-18
Filing date: 2005-05-18
Publication date: 2005-11-24
Also published as: WO2005109984A3

Abstract

Hybrid metal-plastics elements are habitually manufactured by casting/moulding the resin into the rear side of a pressed metal shell. According to the invention, the hybrid element comprising an outer metal skin is manufactured in one step consisting of injection moulding, using the molten injection moulding material as the hydraulic fluid for hydroforming the shell.

Description

A process for the manufacture of a hybrid element comprising a metal skin.

The invention relates to the manufacture of a hybrid element comprising a metal skin, i.e. an element that has at least one outer surface made in a metal. The other part of the element may be made in a polymer or plastic, or it may be the same or a different metal. The metal and the other element are tightly bonded to each other. The metal skin is intended to be a visible outside part of the element.

Field of the Invention

Aluminium and other metal sheets may be given a particular shape in many different ways like stamping, deep drawing, or explosive forming. It is also known that inserts in metals can be fixed in injection moulded plastics parts, for instance using a mechanical fixation caused by a deformation of the metal part outer surface. Melting the plastics material using an oven, a heat mandrel, or ultrasonic welding could also provide the fixation. In these techniques there are no chemical bonds between the metal and plastics and the bond line consists more or less of friction between metal and plastics and/or a mechanical interlock. This technique is already well established in the plastics injection moulding industry.

Also in extrusion processes the combination of metal sheets and plastics is known. In this case the plasticized thermoplastics material is extruded between two continuous sheets of metal in a roller press. Due to the compression in the roller press the plastics material and the metal sheets are in very close contact. The adhesion between metal sheets and plastics is in this case mainly chemical due to a tie layer or chemicals previously applied to the facing surfaces of the metal sheets.

The hydro-forming process has been used in many industries to shape aluminium pipes to a certain shape defined by a mould cavity by injecting water at 200-400 MPa in the pipe once the two ends are sealed properly. During the injecting process the aluminium starts to flow and the material is displaced in one or more steps till it finally has the shape of the mould cavity.

Background of the Invention

Injection moulding of plastics and aluminium as well as the hydro-forming process for aluminium pipe being well known, the present invention intends to combine injection moulding of plastics or aluminium with hydro-forming of thin metal shells and achieve adhesion between the two layers. In the process the specimens achieve their final shape and surface texture from the mould, while the metal surface material starts to flow in the mould cavity and take up any shape and texture from the surface of the tool. Once the shell material and the back filling have obtained their final shape the back filling material goes from a liquid state to a rigid state and from that moment keeps the shell fully supported and unchanged over time. The adhesion is due to a tie layer and/or chemical pre-treatment of the metal surface. The technique is especially useful for many kinds of 3-D multi-shape composite structures. Products that may be produced in this process are various multi-shaped 2- or 3 dimensional parts having a metal decorative outer surface like:

* Household equipment

* Lamps

* Furniture

* Lids and cabinets * Radio and TV-cabinets

* Loudspeaker cabinets

* Remote controls

* Car parts, such as handles, coverings, dashboard, control panels, door steps, push buttons, and wheels * Decorative panels for construction use

* LCD monitors for computers

* Control buttons for all kinds of household equipment, lighting, electronics ->

Description of the Invention

In this new process injection moulding, tie layers, chemical pre-treatment of metals, and the hydro-forming process are combined to a unique process where the final shape of the specimen, the shape of the back filling material, the surface texture, and the adhesion between two or more layers is obtained in one single step.

The intention is to produce sheets or pipes from aluminium or other metals to a given shape in an injection moulding process using thermoplastics, thermosetting plastics, or aluminium or similarly performing metals as the hydrostatic compound that enables all kinds of shapes to be produced. The plastic material could be a rigid material, an elastomer or cellular plastics material in its final or cured state. The cellular material could be an expanding material as well. The displacement and shaping of the metal sheet or pipe in the mould cavity is performed by the injection pressure applied to one side of the sheet or pipe interior. In the same process the two materials (plastics/metal or aluminium/metal) are bonded to each other using a tie layer and/or a chemical surface preparation of the metal sheet or pipe. In the case of aluminium-to-aluminium bonding a pre-treatment of the sheet material or pipe will be necessary and/or the injection in the cavity should occur in an inert atmosphere to prevent the metal surface from oxidation. After the processing the metal sheet or pipe 1) has the final shape from the mould and 2) has the surface texture from the mould and 3) adheres to the plastics materials or the metal back filling. Using an injection pressure of hundreds of MPa the surface texture of the metal surface is easily generated by the surface of the mould cavity. After the injection process the parts have to be cooled to a temperature below the melting point. Once the moulding process is finished the specimens in the case of aluminium, magnesium, and titanium sheets or pipes may.be anodized due to the chemical resistance of the bond line between skin material and back filling. Using high quality aluminium sheets on top of an aluminium cast material it will be possible to obtain surfaces without imperfections, which is not possible with a full cast aluminium material.

Using a special mould construction it will be possible to clamp two metal plates in the mould. With a distance between the plates > 1 mm it will be possible to inject the plastics or metal between the two layers and obtain a flat sandwich structure or a 3-D structure with metal skin on two sides.

Definition of the invention

In order to obtain the desired improvement over prior approaches to obtain a hybrid component of the type here presented, the invention is particular in that the sheet or pipe of metal or the pipe is clamped in the cavity of an injection moulding mould, whereupon a liquid material that is solid subsequent to manufacture is injected with sufficient pressure on only one side of the sheet or inside the pipe to make the metal sheet or pipe conform to the inner surface of at least one part of the mould, whereupon the element cools until it is solid.

An advantageous procedure is particular in that the liquid material is a plastics material in its molten state, which means that well-known equipment may be used.

A further advantageous procedure is particular in that the plastics material is a mix of polymers with an adhesive component. In this manner the properties of the plastics material may be precisely tailored to the double task it has to perform.

An advantageous procedure uses a thermoplastic material.

An further advantageous procedure uses a thermosetting material. This provides a higher temperature tolerance of the finished hybrid product.

A further procedure according to the invention is particular in that the plate or pipe of metal is provided with a tie layer as a pre-treatment step before the injection moulding of the plastics material in its molten state. This enables an improved bonding between the materials, and a silane surface treatment on the surface facing the liquid material may be used or the surface facing the liquid material may be etched. A further advantageous procedure is particular in that the liquid material is a metal that will wet and adhere to the metal plate or pipe. Hereby a solid metal object is obtained, with the desired surface quality, in a single operation.

In a further advantageous procedure the metals for the sheet or pipe and the metal for the liquid material are chosen from the group consisting of aluminium, titanium, or magnesium. These are all materials that behave well in their molten state, in particular when their surfaces are protected against oxidation.

A procedure is particular in that the sheet or pipe is provided as a fine-grained material. This ensures ductility when the metal sheet material shall conform to a heavily profiled surface.

A further advantageous procedure is particular in that subsequent to cooling the hybrid element is given a surface treatment by anodizing. This step, known in itself, enhances the quality of the surface obtained by the combined hydroforming and the bonded support material.

A mould part for a procedure according to the invention is particular in that it is constituted of a standard injection moulding part with reinforcement to withstand the hydrostatic pressure required for hydro-forming. Also, special clamping features may be available, or the parallel parts of the mould part or tool may be made to clamp the metal sheet, thereby creating the combined function of a gasket function and the ability to withstand the stresses of forming the sheet metal. The excess metal sheet may then be trimmed off subsequent to the forming.

A product of the manufacture according to the invention is particular in that it consists of a plastics material, a chemical bonding layer, and an outer metal layer with a pre-determined surface texture.

A product according to the invention particular in that the plastics material functions as a clamping means for further mechanical or chemical treatment of the metal layer. This ensures a very solid attachment of the hybrid element to the work holder of a processing machine. An advantageous product according to the invention is particular in that the plastics material holds mechanical interface means for fastening the hybrid element in a fixed relationship to a mechanical assembly. Fasteners and other inserts may much easier be fitted into the plastics material to ensure a firm hold than in known solutions, where elements with a metal outer surface are held by clips.

Detailled description of the invention

The invention will be described in greater detail with reference to the drawing, in which

Fig. 1 shows a mould holding a product manufactured according to the process,

Fig. 2 shows a different mould before injection/forming, and

Fig. 3 shows the same mould after injection/forming.

The process flow is as follows:

Process flow (metal to plastics)

1. The surface of the metal has to be pre-treated in one or a combination of the following ways:

A a tie layer is applied to the surface of the metal using a heat-stamp, heat-roll process, or spray application B the surface of the metal is etched with diluted hydrochloric acid or similar

C the surface is chemically pre-treated by bonding a reactive chemical in the surface of the metal

D in case a special plastics material containing an adhesive component is intended the surface is only cleaned. In the case of a tubular material the pre-treatment can only be applied as a chemical pre-treatment.

2. The sheet of metal or pipe is clamped in the injection-moulding tool with a certain clamping force and clamping frame. The prepared side is facing the gate in the mould, see Fig. 1

3. The plastics material is injected in the cavity at specified pressure, temperatures, and time in such a manner that the plastics material is confined to one side of the metal sheet

4. The metal sheet or pipe is displaced and formed to the cavity and the surface texture is established due to the high pressure at one side of the aluminium sheet, see Fig. 2

5. The adhesion between plastics and metal is built up due to temperature and pressure and a chemical reaction at the surfaces

6. The plastics material is reacting and/or solidifies. The final shape is kept by the combined stiffness from the metal shell and the plastics part.

7. The part is ejected from the moulding tool

8. Optionally, the excess metal sheet that was clamped in the tool may be trimmed off.

9. The part can be finalized by abrasion, milling, turning, polishing and/or anodizing to achieve a smooth and resistant surface on top of the metal surface. If the deformation of the skin material is very limited the sheet or pipe can be pre- anodized.

Process flow (metal to aluminium) 1. The oxide layer on top of the metal sheet is removed from one or both sides of the plate. Using a pipe material the surface could be etched instead.

2. A tie layer and/or chemical pre-treatment is applied to the sheet of metal on the adherent face of the metal. The application can be performed in a heat-roll or spray application. In the case of pipe materials only chemical pre-treatment of the interior of the pipe can be performed.

3. The sheet of metal or pipe is clamped in the injection moulding tool with a certain clamping force and clamping frame. The prepared side of the sheet is facing the injection gate of the mould.

4. Either the metal surfaces are protected from oxidation due to the pre-treatment, or an inert atmosphere is established at the prepared surface, in that the whole moulding tool is encapsulated and filled with inert gas.

5. The cast aluminium material is injected in the cavity at specified pressure, temperatures, time and injection speed or injection profile.

6. The metal skin is displaced and formed to the cavity and the surface texture is established due to the high pressure at one side of the skin material.

7. The adhesion between metal skin and cast aluminium is built up due to temperature, pressure and surface reactions.

8. The cast aluminium is tempered below the melting point.

9. The part is ejected from the moulding tool once the temperatures are low enough to keep the shape stable.

10. The part can be finalized by trimming, abrasion, milling, turning, polishing and/or anodizing to achieve a smooth and resistant surface on top of the aluminium, titanium or magnesium surface. If the deformation of the skin material is very limited the sheet or pipe can be pre-anodized. Pre-anodizing can also be used to protect the skin material from scratches during processing.

The thickness of the metal plates for the skin depends on the construction and the shape. Since the idea is to reduce the amount of high quality materials in the surface skin layers of 0.3 to 3 mm would be appropriate but other thicknesses are possible. If the skin metal can harden by deformation and/or if the displacement of the material is very high, it might be necessary to warm the material in one or more steps to remove the hardening from the material.

The pre-treatment of metal skin materials can be performed in different ways. As an example, metal sheets can have a tie layer applied like the PLAT AMID HX2519 from Atofina. Another chemical pre-treatment could be application of a silane to the surface. Silanes like Dynasylan HS 2909 from Degussa or Oxilan 705 from Chemetall will perform well with many plastics materials and metal combinations. The silanes could also protect many metals from oxidation between processing steps.

Example

The process parameters must be adjusted in each individual case according to the desired geometry, the choice of materials, and the process equipment available. In the present case it is desired to manufacture a component consisting of an aluminium shell with a polyurethane core of the general shape shown in the drawings. It is a spherical cap with a diameter of 60mm. It is important that the aluminium shell is not stretched beyond its yield stress.

Materials:

the shell: one aluminium plate 100 x 100 x 1 mm Peraluman 708

the polymer: thermoplastic polyurethane Estane 58887, Natural 038 (Noveon)

the tie layer material: a silane, type Dynasylan HS 2909 (Degussa) The process equipment:

an injection molding machine Allrounder 1600-625, 470C (Arburg) with a mould according to Fig. 2 and a direct supply gate as shown.

Pre-treatment of the plate:

In order to obtain the desired adhesion between polymer and aluminium the aluminium surface is given a silane coat in the following way: The aluminium plates to be used are hung on anodizing clips in titanium at two of the cut edges. The plates are anodized in sulphuric acid with a decorative oxide layer of 17 μ . Immediately subsequent to the sealing and drying a thin layer of Dynasylan HS 2909 is sprayed on, and excess silane is blown off with dry and clean high pressure air. The silane- coated plates are dried for at least 48 hours at 20°C and 50% RH. After the silane treatment the plate must not be contaminated.

Pre-treatment of the plastic:

The granulate must be pre-dried at 70 °C for at least 3 hours to obtain a maximum water content of 0.2 % w/w.

The injection moulding machine is adjusted as follows:

closing force 1600 kN melting temperature 200 °C injection pressure 80 MPa for 12 seconds cooling time 2 minutes

Preparation of the mould:

the mould is connected to a Boeterm heat exchanger type TP 140 and the mould temperature is adjusted to 30 °C. Performance of the procedure:

Taking care not to contaminate the components subsequent to the pre-treatment, the process is as follows:

1. The mould parts are fitted to the fastening planes and centered with respect to the inlet.

2. The mould cooling system is connected and the mould is pre-heated to 30°C.

3. A silane-treated aluminium plate is fitted in the mould and centred with respect to the inlet. 4. The mould is closed.

5. The moulding cycle is initiated. Then 0.019 kg polymer is injected into the mould cavity maintaining the parameters specified above, whereby the aluminium plate assumes the shape and surface texture of the cavity. 6. The injection pressure is maintained for 12 s while the part cools down.

7. The plastic is left to cool for 120 s.

8. The mould is opened.

9. The plastic part is removed, while the aluminium shell and plastic are now joined and have obtained the desired geometry and surface texture. 10. The part is cooled to room temperature.

The part is now ready for further processing, such as machining and/or anodizing.

It should be mentioned that plastics as a back filling material may cause a drastic noise reduction in the structure of a component. Sound and noise reduction in aluminium or other metal parts is therefore possible.

Since the back filling material adheres very well to the metal shell it is possible to transmit mechanical forces from the shell to the back filling and vice versa. This may be used in different ways:

* It is possible to use the back filling as a handle while the metal part is being machined, polished, surface treated, and so on. * It is possible to fixate the part during later assembly using the back filling as a fixation

* Mechanical fixation with fasteners, screws, bolts, and snap fasteners in the back filling will also fixate the shell material, which makes assembly very easy

* The connecting parts may be hidden, since the fastening elements may be hidden between the shell and back filling.

* It is possible to use the back filling as a platform for other components like printed circuit boards, electric motors, displays, and mechanical components.

Claims

PATENT CLAIMS

1. A procedure for the manufacture of a hybrid element comprising a metal skin, consisting of at least one sheet of metal or a pipe, characterized in that the sheet or pipe of metal is clamped firmly in the cavity of an injection moulding mould, whereupon a liquid material that is solid subsequent to manufacture is injected with sufficient pressure on one side of the sheet or inside the pipe to make the metal sheet or pipe conform to the inner surface of at least one part of the mould, whereupon the element cools until it is solid.

2. A procedure according to claim 1, characterized in that the liquid material is a plastics material in its molten state.

3. A procedure according to claim 2, characterized in that the plastics material is a mix of polymers with an adhesive component.

4. A procedure according to claim 2, characterized in that the plastics material is a thermoplastic material.

5. A procedure according to claim 2, characterized i n that the plastics material is a thermosetting material.

6. A procedure according to claim 2, characterized in that the plate or pipe of metal is provided with a tie layer as a pre-treatment step before the injection moulding of the plastics material in its molten state.

7. A procedure according to claim 2, characterized in that the sheet or pipe of metal is provided with a silane surface treatment on the surface facing the liquid material.

8. A procedure according to claim 2, characterized in that the sheet or pipe of metal is etched on the surface facing the liquid material.

9. A procedure according to claim 1, characterized in that the liquid material is a metal that will wet and adhere to the metal plate or pipe.

10. A procedure according to claim 9, characterized in that the metals for the sheet or pipe and the metal for the liquid material are chosen from the group consisting of aluminium, titanium, or magnesium.

11. A procedure according to claim 9, characterized in that the sheet or pipe is provided as a fine-grained material.

12. A procedure according to claim any of the above claims, characterized in that subsequent to cooling the hybrid element is given a surface treatment by anodizing.

13. A mould part for a procedure according to any of the claims 1-11, characterized in that it is constituted of a standard injection moulding part with reinforcement to withstand the hydrostatic pressure required for hydro-forming.

14. A product of the manufacture according to claim 6, characterized in that it consists of a plastics material, a chemical bonding layer, and an outer metal layer with a pre-determined surface texture.

15. A product according to claim 14, characterized in that the plastics material functions as a clamping means for further mechanical or chemical treatment of the metal layer.

16. A product according to claim 14, characterized in that the plastics material holds mechanical interface means for fastening the hybrid element in a fixed relationship to a mechanical assembly.