Description The invention is concerned with a process for commercially manufacturing thin metal foils having a complex, intricate and/or highly toleranced form and precision. The process offers various unique features that are not found with current methods of manufacture. The current area of application is the manufacture of tweeter dome and loudspeaker cone diaphragms.

Principle Features 1. The process allows metal foils to be formed at relatively high speed.

2. The process offers high precision.

3. Intricate detail can be achieved in the foil in a one- stage operation.

4. The process is environmentally friendly.

5. The process allows product engineers to sample multiple forms and a range of materials with a low capital outlay.

Background-Existing Processes Metal foils are commonly formed into shaped parts for their particular application.

1. Cold forming/pressing/drawing using a male/female press and die. These processes allow simple shapes to be formed in certain metals such as Aluminium, Copper, Steel and Titanium.

The inconveniences of these processes are that they are limited to certain malleable metals and only simple forms are possible due to the fact that the process takes place at ambient temperatures where the metals'fatigue limits the complexity of the shape that can be formed without stage heat treatment and processing.

These processes produce deformation where the base metal becomes harder and stronger and a stage is ultimately reached where no more deformation can be produced. Any further increase in applied force will then only lead to fracture. Tensile strength and hardness have reached a maximum and elongation a minimum. The material is said to have work hardened and requires suitable heat treatment before continuation of working.

Furthermore the selection of suitable lubricants to assist processing are very important and it is necessary to such to avoid contamination for subsequent operations such as anodising, painting or plating. Incorrect selection can also damage surface finish of the metal during storage of parts.

It is impossible to form certain metals such as Beryllium, Beryllium alloys and pure Magnesium using these processes.

Tooling is complex and expensive especially where stage working is necessary and in general tooling needs higher tolerances for the same toleranced part making such form limiting.

2. Explosion-Dill Air pressure-Deposition.

By their very nature these methods are very expensive and involved processes that have commercial limitations and are not environmentally friendly.

3. Kiln forming.

In cases such as Beryllium and Beryllium alloy foils it is possible to form using clamp ring and a positive tool as an assembly placed inside a kiln and raised to elevated temperatures where the mass of the tool or controlled mechanical force induces forming of the material.

The inconveniences of this method are that the tooling and foil have to be heated/cooled making the cycle time of the process very lengthy, several hours for each part. Friction between the positive tool and the foil limits the speed at which the metal can be formed. Low precision results due to the nature of the tooling.

Background to the invention Our need was to develop a process that would produce a high precision part to meet the tolerance demand of modern products, e. g. tweeter dome diaphragms, and modern production methods.

There was also a need to reduce production costs of forming high technology foils such as Beryllium whilst allowing the ability to form complicated forms in the foil. An environmentally friendly process which had no need for lubricants was also highly desirable.

Since the currently available method of"matched tool drawing"requires precise set-up in order to ensure that the material is not sheered it was considered that this was a defining limitation of the existing processes which was worth improving.

The process manifest by our invention overcomes this limitation by being simple to set up and requiring no matching parts so that tooling changes in a production environment are rapid.

Essential features of the Invention The invention involves simple tooling consisting of a common and fixed"flat platen"top tool and interchangeable"female profile"bottom tool. The platen tool has a hole (through which gas is introduced) which is able through design to be connected to an external gas supply, commonly, although non-limitive, Nitrogen.

The profile tool has inherent design to both locate and produce specific clamping area. Both parts of the tool are suitably attached to upper and lower heated plates. The upper heater plate is carried on the ram of suitable stroking press and the lower heated plate fixed to press base platform.

Temperature is adjusted and controlled to run at the specific annealing-plastic deformation range of the foil being formed.

The material to be moulded is placed onto the heated lower tool and press operated to bring tools together, which in turn applies clamping force to both hold and seal the material.

Forming is effected by high pressure gas applied through the upper platen tool onto the surface of the material.

The gas pressure follows a predetermined pressure curve calculated to lag behind the critical fracture point of the material. The metal foil is pushed into shape under a constant annealing process. At the end of the cycle gas pressure is increased to ensure that the shape is fully formed and to provide a highly toleranced part.

An unlimitive decision to use N2 for the experiments was made as it is extremely stable and offers no threat to the environment. Air under pressure was also used during the experiments, but reactions between the impurities in

the air mixture and the heated metal surface result in an inconsistent surface colour which is undesirable for aesthetically critical parts.

Introduction to the drawings Figure 1.

The basic concept of the invention uses a lower heater block element 1 onto which is fixed a profiled tool 2a to obtain the shape desired from the metal foil 3. The platen tool 4a is fixed to the upper heater element 5. The platen tool 4a is lowered to clamp the metal foil 3 against the profile tool 2a. Gas pressure is then introduced into the platen tool 4a through the aperture 4b to create the forming pressure on the surface of the heated metal foil 3.

Figure 2.

In a more detailed drawings insulation discs 8 & 9 support machined metal housings 6 & 7 which contain the heater elements 1 & 5. The metal housing 6 provides thermal contact between the lower heater block element 1 and profiled tool 2a. The metal housing 7 provides a thermal contact between the upper heater block element 5 and platen tool 4a.

Gas pressure is introduced into the platen tool 4a through the aperture 4b to create the forming pressure on the surface of the heated metal foil 3. Aperture 2b relieves gas pressure under the metal being formed.

This arrangement was used to form 25micron Beryllium foil to produce 25mm domes of depth 5mm for audio loudspeaker

diaphragms. Example temperature and pressures for this experiment were in the order of 800°C with a variable pressure applied from 0-60psi supplied in the form of Nitrogen gas.

This example is non-limitive and provided for the purpose of exemplifying a typical set of parameters for particular product.

Results of the Invention The developed process allows Beryllium and Beryllium alloy foils to be formed at very low cycle times providing a truly industrial solution. For example, a 25micron foil of 45mm square can be formed into shape in under 1 minute compared to the kiln method that requires several hours.

Aluminium and Magnesium foils in near pure composition, with very low tensile strength, can be adequately formed using this process, something previously not possible with existing techniques.

Aluminium alloys (typically, although non-limatively 1050,1200, 3003,5052 and 5056): complex detail can be readily formed into the foil at high precision, including irregular shapes (non-limitively, conical ellipse, frustrum of pyramid), something not previously possible with existing techniques. The process yielded significant increase in the ratio of material thickness to part size allowing production of lower mass product.

The foil product is greatly improved in terms of the shape of the form and foil desired allowing for greatly widened range of formed foil products.

The resulting part has approximately the same tensile strength and hardness of the original value of the foil since working is being performed at the annealing/stress relieving temperature and the final product is far less liable to inherent fractures of fatigue failure.

No release agents are necessary to aid production. It is an inherently environmentally friendly process with no"oil" wastes to dispose of.

Other areas under investigation Improvement of general technique in order to be able to detail high tolerance regions with a"mechanical"insert to obviate the necessity of high pressure gas application at the end of the cycle. This will further improve production cycle times.

Summary The invention is concerned with a process for the commercial manufacture of thin metal foils having complex and intricate forms. The process offers various unique features which are not found with current methods of manufacture and the current areas of application, although non-limitive, are in the manufacture of tweeter dome diaphragms and loudspeaker cone diaphragms for the use in loudspeakers. Principle features are that thin metal foils can be formed at

relatively high speed, at high precision, whilst allowing intricate detail to be achieved in the foil in a one stage operation which is environmentally friendly.

The process allows product engineers to experiment with sample shapes and materials at low capital outlay.

Viewed from a further aspect, the invention is concerned with a process for commercially manufacturing thin metal foils having a complex, intricate and/or highly toleranced form and precision.

The invention involves simple tooling consisting of a common and fixed"flat platen"top tool and"female profile"bottom tool. The platen tool has a hole which is able through design to be connected to an external gas supply.

The tool is heated. Temperature is adjusted and controlled to run at the specific annealing-plastic deformation range of the foil being formed.

The material to be moulded is placed onto the heated lower tool and press operated to bring tools together, which in turn applies clamping force to both hold and seal the material.

Forming is effected by high pressure gas applied through the upper platen tool onto the surface of the material.

The gas pressure follows a predetermined pressure curve calculated to lag behind the critical fracture point of the material. The metal foil is pushed into shape under a constant annealing process.