Plastic and nonmetallic article shaping or treating: processes – With step of making mold or mold shaping – per se – Utilizing surface to be reproduced as an impression pattern
Reexamination Certificate
2000-07-24
2003-12-16
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With step of making mold or mold shaping, per se
Utilizing surface to be reproduced as an impression pattern
C249S134000, C264S220000, C264S328100
Reexamination Certificate
active
06663812
ABSTRACT:
The present invention relates to component design and, in particular, to a method and system for producing verified component designs and to assist in tool design to near-production specification in the materials of choice, via production processes and in considerably shorter time scales than has previously been possible.
Traditionally, pattern makers and tool makers have undertaken key roles in bringing new component designs through design evaluation, development and modification to production standards. Until comparatively recently, such work was labour-intensive, time consuming and, as a result, costly. More recently, computer aided design has enabled some of the early evaluation steps to be carried out before a new design is reduced to a 3-D prototype. Nevertheless, a point is inevitably reached during design evaluation when a 3-D prototype of the new design is required.
So-called “rapid prototyping” techniques have been developed which enable designs to be produced in 3-D form using a variety of techniques now well established in the art. Such rapid prototyping methods allow compression of timescale in the production of a component master pattern.
The drawback of current rapid prototyping methods is that the 3-D representation which results is not necessarily made from the production material of choice and, in any case, is not made via a production process. For example, one known rapid prototyping method is so-called “laminated object manufacturing” in which the computer design is recreated in 3-D form as a multiplicity of laminated layers. A component master pattern is produced in a material, such as paper, which is easily laid down as thin layers bonded together. However, some form of tool then needs to be made to produce a mould for replicating the design in the correct material using a production process. The rapidly-produced prototype or simulant material part is only of limited use in the evaluation process because the material from which it has been produced and/or the method by which it has been produced are not the same as the material and/or method that will be used in full scale production.
Despite its limitations, if evaluation of the rapidly-produced prototype is favourable, the conventional methods of producing a mould tool, using traditional tool room methods or, alternatively, using sintered or resin based materials, must then be employed to take the verification process forward. As discussed above, these known methods are costly and time-consuming to implement, and have their own particular limitations regarding parameters such as temperature, geometry, pressure and surface finish.
It is also true that the time and cost penalties of changing component design and hence tooling when modifications are required will influence the majority of designers to follow a well-defined, minimal risk path based on their experience. This means that they tend to be inhibited about deviating from conventional techniques.
What is therefore needed is an intermediate verification step which enables a quickly-produced component to be obtained from a master pattern, in the material of the designer's choice and using a production process. Preferably, this design verification step should be carried out as early as possible during the design process, for example at the concept stage or as soon as a master pattern can be made.
It is therefore an object of the present invention to provide a method of producing designs in the material of choice with relative ease, relatively quickly and cost effectively compared to conventional methods. It is another object of the invention to provide a method of producing designs via a production process. It is a further object of the invention to enable verification of component design to be carried out prior to commitment to high cost tooling upon finalisation of a design. It is a still further object of the invention to provide a process which enables design iteration to be carried out relatively easily and cheaply, thereby giving both engineers and designers greater design freedom before commitment and with a hitherto unattainable degree of confidence that the resulting production parts will satisfy the design criteria.
The invention is a method of producing an article in a mould cavity formed by casting around a pattern of the article to be produced, the method comprising:
(a) pouring a mould matrix material around said pattern in a mould bounded by solid retaining means;
(b) causing said mould matrix material to harden to produce a flexible moulding medium having the following physical properties:
flexural strength in the range 20-300 MPa;
flexural modulus in the range 700-10,000 MPa;
tensile strength in the range 16-200 MPa;
tensile modulus in the range 850-10,000 MPa;
compressive strength in the range 24-500 MPa;
compressive modulus in the range 400-10,000 MPa;
hardness in the range 5-100 Vickers; and
relative density in the range 1-10
(c) removing the pattern from the flexible moulding medium to leave a mould cavity conforming to the profile of the pattern;
(d) forming or moulding an article in the mould cavity under production-representative conditions of temperature and pressure, and
(e) removing the article from the mould cavity.
Advantageously the flexible moulding medium has a flexural strength in the range 30 to 100 MPa and preferably around 40 MPa.
Advantageously, the flexible moulding medium has a flexural modulus in the range 1000 to 4000 MPa and preferably around 1500 MPa.
Advantageously, the flexible moulding medium has a tensile strength in the range 20 to 70 MPa and preferably around 22 MPa.
Advantageously, the flexible moulding medium has a tensile modulus in the range 1000 to 4000 MPa and preferably around 1300 MPa.
Advantageously, the flexible moulding medium has a compressive strength in the range 30 to 120 MPa and preferably around 40 MPa.
Advantageously, the flexible moulding medium has a compressive modulus in the range 600 to 2000 MPa and preferably around 1000 MPa.
Advantageously, the flexible moulding medium has a hardness in the range 7 to 80 Vickers and preferably around 9.5 Vickers.
Advantageously, the flexible moulding medium has a density in the range 1.2 to 5 and preferably around 1.3.
Preferably, the pourable material is a curable resin such as a urethane polymer cured by incubation for a short spell (about one hour) at room temperature in the presence of an isocyanate cross-linking agent. Most preferably, the pourable material is a polyester-based polyurethane.
The pourable material may be loaded with a variety of fillers to regulate the properties of the hardened material which forms the flexible mould. For example, the pourable material may include suspended particulate metal to improve the heat transfer characteristics of the cured mould. Alternatively, a material, such as glass or ceramic beads, could be added to impart better insulation capacity. Similarly, additives can be incorporated to influence hardness, rigidity, toughness, operating temperature range and such like in the cured mould.
The exact nature of the physical additives will vary according to the particular additive material in question. For example, in the case of particulate metal additives, the buoyancy of the additive particles relative to the matrix material must be taken into consideration. A buoyancy approaching neutrality is best, otherwise there may occur marked settlement of the added particulate material during hardening or cure of the matrix material. A certain degree of settlement is permissible and may even be desirable, for example in the preparation of a mould which needs to have its thermal conductivity boosted for moulding hot materials. If metal particles gravitate towards the split line during mould cure, thermal conductivity enhancement is greatest in the portion of the mould immediately surrounding the mould cavity. This makes the mould more tolerant of hot moulded product.
Generally, the fillers or additives are included in an amount ranging from 30 to 70% in proportions by volume measured relative to the total vo
Cesari and McKenna LLP
Kuhns Allan R.
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