EP1615767A1

EP1615767A1 - Rapid prototyping process

Info

Publication number: EP1615767A1
Application number: EP04727650A
Authority: EP
Inventors: Hartmut Sauer
Original assignee: AHC Oberflaechenechnik GmbH
Current assignee: Aalberts Surface Technologies GmbH Kerpen
Priority date: 2003-04-16
Filing date: 2004-04-15
Publication date: 2006-01-18
Also published as: CA2522504A1; US20060188650A1; WO2004091907A1; JP2006523769A

Abstract

A method for producing injection-moulding, shaping, cutting and/or casting tools, as well as prototypes, starting from models, is characterised by the following steps: i. the model surface is roughened without a preliminary chemical treatment of the model surface; ii. an intermediate copper or nickel layer is applied to the surface of the model, the intermediate metallic layer not being applied by thermal spraying, CVD, PVD or laser treatment; iii. a metallic or ceramic coating is applied to the intermediate layer by thermal spraying; and iv. the model is removed from the intermediate layer.

Description

Rapid prototyping process

The present invention relates to a method for producing injection molding, forming, stamping and casting tools.

The conventional way of producing investment casting models, injection, forming and punching tools as well as prototypes is to manufacture the prototypes or the tools and models according to drawings on cutting and / or eroding machines.

Newer methods for the production of models / prototypes are the rapid prototyping

Processes, including stereolithography, the method of laminated object production, fixed deposition modeling and laser sintering.

A common feature of these processes is that a 3D CAD model is first created. The 3D CAD constructions are converted into volume data in the CAD system.

The 3D volume model for rapid prototyping is then divided into cross sections on the PC. These cross sections have a layer thickness of approximately 0.1 to 0.2 millimeters. After the data has been transferred to a rapid prototyping machine, the original shape is created layer by layer from polymer plastics, paper, powdered metal or similar.

The prototypes produced in this way can often only be used to assess functionality and design.

For product development and optimization, it is usually necessary to examine material properties and behavior as closely as possible to the original. This requires the parts made of the materials that will later be used in series production. In order to be able to manufacture the tools for production as well as small series, cast shells, plastic injection, aluminum injection and forming and stamping tools have to be manufactured by mechanical processing.

The rapid prototyping processes can be used in part for the processes for producing the tools.

One of the older ways of making cast trays for investment casting is one

To slip and sand over the wax model several times until there is a thick one Layer around the model. The wax is then melted out and the mold is fired. Only then can you pour the desired part.

For the sand casting, negative wooden models are made, which are then mounted on plates and pressed into the upper and lower boxes with so-called molding machines. The resulting cavities are filled with cast aluminum or steel after the top and bottom boxes have been joined together.

In another method, the prototype / model is poured out in a mold with a clay or ceramic mass. The resulting negative impressions are dried in ovens. Liquid metal is then introduced into the dried mold.

The prototypes produced in this way must be further processed using mechanical working methods such as grinding and polishing. These older methods, such as making wooden models, are time-consuming and can take a few weeks for complex parts.

In addition to these conventional methods, more modern and faster working methods are also used (rapid tooling). Rapid prototyping technology is applied to the manufacture of tools.

One of these newer methods is laser sintering. Here, a laser melts a ceramic powder, for example zirconium silicate, in layers around the model into a casting mold.

Methods such as laser sintering are fast, but they require relatively expensive machine equipment.

Another method of producing molding, injection and pressing tools is to measure the prototype on a measuring machine and to pass the data on to a CNC machine. Alternatively, CAD data can also be used. Due to the tool and scanning head geometry, it is often not possible to produce an exact tool. A tool manufactured in this way has to be manufactured for use by extensive post-processing.

When producing large tools, the more modern methods, such as stereolithography or laser sintering, also require the model or prototypes to be divided into segments that are later combined to form the tool. be set because the machines do not exceed a certain size (approx. 400 mm x 600 mm).

From US Pat. No. 6,305,459 it is known to mold plastic cores, the interior of which is cooled, with a metallic layer on the outside by thermal spraying. A disadvantage of this method is that only simple, rotationally symmetrical objects can be covered with a corresponding layer. Flat structures that do not have an axis of rotation cannot be metallized with this method, since so-called hot spols, i.e. local overheating, and the plastic substrate melts due to the thermal energy used.

Furthermore, US Pat. No. 6,257,309 B1 describes a method for producing an injection mold which can be produced by thermal spraying. A disadvantage of this method is that the positive impression of the model must be made of a material whose melting or softening temperature is above the temperature of the material applied by thermal spraying. This means that a mold made of tool steel can only be produced in accordance with the methods presented in US Pat. No. 6,257,309 B1 if the models used have a melting or softening temperature of more than 1600 ° C. In this case, only ceramic models can be used. The production of such ceramic models is, however, very complex. Therefore, this method is hardly suitable for the production of models with small tolerances.

From GB 2 367 073 a method is known in which a mold is produced by thermal spraying using a model which is produced by milling a soft metal block. After milling, i.e. before thermal spraying, a copper layer is applied to the soft metal. The disadvantage of this method is the very complex production of the model. Due to the necessity of the machining manufacturing process, it is not possible to produce models with fine surface contours or corresponding molded parts. In addition, the production of larger models requires a considerable amount of time, which could be a reason why this method has not yet been used economically.

Furthermore, EP 0 781 625 A1 discloses a method for producing mold tools for the automotive industry, in which a negative model is first generated by stereolithography. A ceramic impression is then made from this negative model. print manufactured. In order to comply with the tolerances necessary for the automotive industry, this molding process is very complex. The molds must first be frozen and then fired ceramic. The sintered ceramic mold is then coated with tool steel by thermal spraying. In addition to the very complex manufacturing process, the fact that no larger molds can be produced with this process is part of the problem with this process, since such larger molds would have flaking or cracks in the ceramic model due to the high thermal energy. For this reason, the production of larger forming tools, such as those used in the automotive industry for the production of engine hoods, is only possible by producing several small molds, which are then assembled into one large mold. However, this creates problems with regard to the dimensional accuracy of the forming tools.

The invention is therefore based on the object of providing a method with which casting, injection, shaping and stamping tools can be produced quickly and precisely. The tools produced should be suitable for small series as well as for production.

This object is achieved according to the invention by a process for the production of injection, forming, stamping and / or casting tools and prototypes, starting from

Models characterized by the steps: i. Roughen the surface of the model without chemical pretreatment

Surface of the model; ii. Applying an intermediate layer of copper or nickel to the surface of the model, the metallic intermediate layer not being applied by thermal spraying, CVD, PVD or laser treatment; iii. Applying a metallic or ceramic coating to the intermediate layer by thermal spraying; and iv. Remove the model from the intermediate layer.

In contrast to the known methods of the prior art, no negative impression of the model, for example made of ceramic or metal, is used in the method of the present invention. In this way it is possible to work with greater precision and to avoid the time-consuming and technically demanding preparation of such a negative impression.

The injection, forming, standing and casting tools produced in this way can be carried out in a further step after step iii. or step iv. be backfilled. In this case, is on a corresponding mass is applied to the covering in order to ensure the rigidity of the mold, to ensure absorption into the press and, on the other hand, to evenly dissipate the energy generated during the pressing or forming. The backfill can either be made of the same material as is applied by thermal spraying. But it is also possible to use other materials, if necessary

Metal particles or fiber reinforced epoxy resins to use.

In a further embodiment according to the invention, it is also possible, after step iii. or iv. to remove the intermediate layer. Before that, of course, the model has to be detached from the manufactured shape. This process variant should be selected if the applied intermediate layer made of copper or nickel would behave disadvantageously when using the corresponding tools.

With regard to the possible backfilling of the coating of the casting tool produced by the method according to the invention, the thickness of the coating does not play a decisive role. With regard to the highest possible dimensional accuracy, however, it is advantageous if the covering has an average thickness of at least 4 mm.

As already mentioned above, the method according to the invention makes it possible for the first time to easily produce dimensionally accurate casting tools from tool steel. According to a preferred embodiment, the covering has a hardness of at least 35 HRC, in particular 50 HRC.

Due to the high hardness, high wear resistance is achieved. The model can be made from all common materials.

In particular, it can be made from a plastic, preferably from CKF, polyamide, polymer resin, polyethylene, polypropylene, PMMA, GFK, polyvinyl chloride, polystyrene, epoxy resin, polyether ether ketone, polyether imide, polycarbonate, polyphenyl sulfone, polyurethane, NBR, SBR, polytetrafluoroethylene and phenolic resin , This plastic model can preferably be laminated by stereolithography

Object Manufacturing (LOM) or by laser sintering. In this way, it is particularly easy to produce accurate models in a very short time. But it is also possible to make the model out of wood or paper. Here, too, a preferred manufacturing process is laminated object manufacturing (LOM).

According to the invention, it is very particularly preferably a method in which the roughening of the surface of the model is carried out using an abrasive, preferably using silicon arbide with the P80 grit. The surface pretreatment can be carried out, for example, with a modified pressure jet system. The blasting system is operated at a pressure of 4 bar. For example, a boron carbide nozzle with a diameter of 8 mm can be used as the jet nozzle. The average beam duration is 4.6 s. However, it can also be between 1 s and 15 s. SiC with a grain size of P80 with an average grain diameter of 200 to 300 μm is preferably used as the abrasive. Other blasting media that can be used are glass balls, broken glass, ceramics, high-grade corundum, mixed corundum, normal corundum, cast steel, wire grit, chilled cast iron, Alusat, shell granulate or dry-strip. In order to adapt the blasting system specifically to the requirements of the plastic modification to be treated with regard to reproducible surface topographies, two pressure circuits can be installed, one each for the transport of the blasting medium and the actual acceleration process. This modification results in a very constant volume flow and a large pressure range. A stream of compressed air transports the abrasive to the lowest possible pressure

Jet. The flow conditions ensure, caused by a high volume flow of the blasting medium and a low proportion of compressed air, a low wear of the system and the blasting medium. The cross section is only reduced at the end of the transport hose in front of the mixing nozzle in order to set the desired volume flow. In the case of plastic pretreatments, a constant volume flow of 1 l / min is preferably specified. However, volume flows between 0.1 l / min and 3 l / min can also be selected. In the second part of the system, compressed air (volume flow 1) flows up to the nozzle, which can be continuously adjusted within a pressure range of 0.2-7 bar. The blasting medium, which is conveyed into the mixing nozzle at a very low flow rate, is then accelerated by the high flow rate of the compressed air flow.

In a further, likewise particularly preferred embodiment, the intermediate layer is coated with copper or nickel using an external currentless chemical process.

As the process designation already says, in the case of metal deposition without external current, no electrical energy is supplied from the outside during the coating process, but the metal layer is only deposited by a chemical reaction. The metallization of non-conductive plastics in a chemically reductive metal salt solution requires a catalyst on the surface in order to disrupt the metastable balance of the metal reduction bath and to deposit metal on the surface of the catalyst. This catalyst consists of precious metal nuclei such as palladium, silver, gold and occasionally copper, which are based on the art Fabric surface from an activator bath are deposited. It is preferred, based on process engineering, however, activation with palladium seeds. Essentially, the substrate surface is activated in two steps. In a first step, the component is immersed in a colloidal solution (active bath). The palladium nuclei that are necessary for metallization and are already present in the activator solution are adsorbed on the plastic surface. After germination, the tin-II or tin-IV oxide hydrate additionally formed when immersed in the colloidal solution is dissolved by rinsing in an alkaline, aqueous solution (conditioning) and the palladium seed is thereby exposed. After rinsing, chemical reduction baths can be used to nickel or copper.

This is done in a bath kept in a metastable equilibrium by a stabilizer, which contains both the metal salt and the reducing agent. The baths for the nickel or copper deposition have the property of reducing the metal ions dissolved in them at the nuclei and of depositing elementary nickel or copper. In the coating bath, the two reactants have to approach the noble metal nuclei on the plastic surface. The resulting redox reaction creates the conductive layer, the noble metal nuclei taking up the electrons of the reducing agent and releasing them again when a metal ion approaches. This reaction releases hydrogen. After the palladium nuclei have been coated with nickel or copper, the applied layer takes on the catalytic effect.

This means that the layer grows together from the palladium seeds until it is completely closed.

The deposition of nickel is dealt with here as an example. When coating with nickel, the germinated and conditioned plastic surface is immersed in a nickel metal salt bath, which allows a chemical reaction in a temperature range between 82 ° C and 94 ° C. The electrolyte is generally a weak acid with a pH between 4.4 and 4.9.

However, in a further, likewise preferred embodiment, it is also possible to apply one or more metallic layers to the intermediate layer applied without external current, in particular by electrolytic processes. The thin copper or nickel coatings applied without external current can be reinforced with an electrolytically deposited metal layer. Coating components with layer thicknesses> 25 μm is not economical due to the low deposition rate of chemical coating processes. Furthermore, only a few coating materials can be deposited with the chemical coating processes, so that it is advantageous to use electrolytic processes for other technically important coating materials. Another important point is the Different properties of chemically and electrolytically deposited layers with layer thicknesses> 25 μm, for example leveling, hardness and gloss. The basics of electrolytic metal deposition can be found in B. Gaida, "Introduction to Electroplating", EG Leuze-Verlag, Saulgau, 1988 or in H. Simon, M. Thoma, "Applied Surface Technology for Metallic Materials", C. Hanser- Verlag, Munich (1985).

Plastic parts that have an electrically conductive layer due to an electroless coating process differ only slightly from those of the metals with regard to electrolytic metallization. Nevertheless, some points should not be neglected in the electrolytic metallization of metallized plastics. Due to the mostly low conductive layer thickness, the current density must be reduced at the beginning of the electrolytic deposition. If this point is not observed, the conductive layer may peel off and burn. Furthermore, care should be taken to ensure that annoying tarnish layers are removed with specially suitable decapitation baths. Furthermore, residual stresses can destroy the layer. When nickel layers are deposited from an ammoniacal bath, tensile stresses of the order of 400 to 500 MPa, for example, can occur. Additives such as saccharin and butynediol can change the structure of the nickel coatings in the form of a changed grain size and form microdeformations to promote the reduction of internal stresses, which can have a positive effect on a possible premature coating failure.

Examples of metal layers applied without external current are described in detail in the manual of the company AHC Oberflächentechnik ("The AHC surface", manual for construction and manufacture, 4th edition, 1999).

In a further embodiment of the present invention, a layer made of aluminum, titanium or their alloys is applied to the metallic layer of the molding tool or prototype produced using the method according to the invention, the surface of which is anodically oxidized or ceramized.

Such anodically oxidized or ceramicized layers of aluminum, titanium or their alloys are known on metallic objects and are sold for example under the name Hart-Coat ^® or Kepla-Coat ^® by the company AHC Oberflächentechnik GmbH & Co. OHG. These layers are characterized by a particularly high hardness and a high operating resistance and by mechanical stress. One or more further metallic layers can be arranged between the metallic layer deposited without external current and the layer of aluminum, titanium or their alloys.

The further metallic layers arranged between the electrolessly deposited layer and the aluminum layer are selected depending on the intended use. The choice of such intermediate layers is well known to the person skilled in the art and is described, for example, in the book "The AHC Surface - Manual for Construction and Manufacturing", 4th extended edition 1999.

It is also possible for the surface of such an object to pass through

Foreign ion storage is black colored, ceramic oxide layer made of aluminum, titanium or their alloys.

The ceramic oxide layer made of aluminum, titanium or their alloys, colored black by foreign ions, is of particular interest for high-quality optical elements, especially in the aerospace industry.

The production of ceramic oxide layers colored black by foreign ion incorporation is described, for example, in US-A-5035781 or US-A-5075178. The production of oxide ceramic layers on aluminum or titanium is described, for example, in EP 0 545 230 B1. The production of anodically produced oxide layers on aluminum is described, for example, in EP 0 112 439 B1.

In a further embodiment of the method according to the invention, the model provided with the intermediate layer can be positioned and fixed in a frame.

This variant should be selected if the external dimensions of the part to be manufactured are to be specified. This reduces mechanical rework.

The covering can be filled in or backfilled within this frame. Thermal spraying or pouring out with an epoxy resin which may contain metal particles or with aluminum-containing foams are particularly suitable.

According to a particularly preferred embodiment of the present invention, the coating applied by thermal spraying is an alloyed tool steel. This makes it easy to make high-strength and extremely wear-resistant

Manufacture tools in less time. One possibility for producing such coverings is thermal spraying using a wettable powder, which preferably consists of 30-50% by weight of molybdenum powder and 70-50% by weight of steel powder. It is particularly preferably such a powder which consists of 50% by weight of molybdenum powder and 50% by weight of steel powder. The tools produced in this way are suitable for normal use in production, ie their resilience is in no way inferior to that of a tool manufactured in a conventional manner from the same material. This makes it possible for the first time to produce a production-ready tool in a very short time, which also has significant advantages in terms of dimensional accuracy.

Claims

Patent claims

1.) Process for the production of injection, forming, stamping and / or casting tools and prototypes, based on models, characterized by the steps: i. Roughening the surface of the model without chemical pretreatment of the surface of the model; ii. Applying an intermediate layer of copper or nickel to the surface of the model, the metallic intermediate layer not being applied by thermal spraying, CVD, PVD or laser treatment; iii. Applying a metallic or ceramic coating to the intermediate layer by thermal spraying; and iv. Remove the model from the intermediate layer.

2.) Method according to claim 1, characterized in that after step iii. or iv. the surface is backfilled.

3.) Method according to one of claims 1 or 2, characterized in that after step iii. or iv. the intermediate layer is removed.

4.) Method according to one of the preceding claims, characterized in that the covering has an average thickness of at least 4 mm.

5.) Method according to one of the preceding claims, characterized in that the covering has a hardness of at least 35 HRC, in particular of more than 50 HRC.

6.) Method according to one of the preceding claims, characterized in that the model made of plastic, preferably of CKF, polyamide, polymer resin, polyethylene, polypropylene, PMMA, GFK, polyvinyl chloride, polystyrene, epoxy resin, polyether ether ketone, polyetherimide, polycarbonate , Polyphenyl sulfone, polyphenylene sulfide, polyarylamide, polyurea, NBR, SBR, polytetrafluoroethylene or phenolic resin.

7.) Method according to one of claims 1 to 5, characterized in that the model is made of plastic, preferably by stereolithography, laminated object manufacturing (LOM) or laser sintering.

8.) Method according to one of claims 1 to 5, characterized in that the model is made of wood or paper.

9.) Method according to one of the preceding claims, characterized in that the roughening of the surface of the model is carried out with an abrasive, preferably with silicon carbide with the grain size P80.

10.) Method according to one of the preceding claims, characterized in that the intermediate layer is coated with copper or nickel by means of an electroless chemical process.

11.) Method according to claim 10, characterized in that a further metallic layer, in particular by an electrolytic method, is applied to the intermediate layer applied without external current.

12.) Method according to one of the preceding claims, characterized in that a layer of aluminum, titanium or their alloys is applied to the metallic layer deposited without external current, the surface of which is anodically oxidized or ceramicized.

13.) Method according to claim 12, characterized in that one or more metallic layers are arranged between the metal layer deposited without external current and the layer of aluminum, titanium or their alloys.

14.) Method according to claim 12 or 13, characterized in that the surface of the object is a ceramic oxide layer made of aluminum, titanium or their alloys, which is colored black by the inclusion of foreign ions.

15.) Method according to one of the preceding claims, characterized in that the model provided with the intermediate layer is positioned and fixed in a frame.

16.) Method according to claim 15, characterized in that the covering is filled or backfilled within the frame, in particular by thermal spraying or pouring with an epoxy resin which may contain metal particles or with aluminum-containing foams.

17.) Method according to one of the preceding claims, characterized in that an alloyed tool steel is applied by thermal spraying.

18.) The method according to any one of the preceding claims, characterized in that by thermal spraying a wettable powder, which preferably from 30-50 wt .-% molybdenum powder and 70-50 wt .-% steel powder, in particular from 50 wt .-% molybdenum powder and 50 wt .-% steel powder, is applied.