Claims
- 1. A method of forming a contoured surface in a workpiece in the form of a metal mold or die by etching the surface thereof comprising the steps of;
- a. providing a template having a contoured surface which is a negative pattern of the contoured surface to be formed in the workpiece,
- b. applying a meltable coating to the workpiece, the coating being resistant to an etchant and having a melting temperature such that the coating is generally solid after application to the workpiece,
- c. immersing the coated workpiece in an etchant,
- d. heating the template to at least the melting temperature of the coating,
- e. pressing the heated template against the coated workpiece and melting any portions of said coating contacted by the template,
- f. only displacing the melted portions of said coating as the contoured surface of the template moves into contact with the workpiece,
- g. withdrawing the template from the coated workpiece to permit resolidification of any melted coating, while leaving any locations of the workpiece contacted by the contoured surface of the template essentially free of said coatings and exposing portions of the workpiece without withdrawing any coating with the template;
- h. permitting the etchant to etch said portions of the workpiece exposed by displacement of the coating and
- i. repeating steps (e) through (h) until the surface of the workpiece conforms to the contoured surface of the template.
- 2. The method according to claim 1 in which the coating softens before melting, and including the step of heating the workpiece to the softening temperature of the coating before step (e).
- 3. The method according to claim 1 including forming the template by the steps of providing a model for the template, pouring a liquid material over the model which subsequently hardens to form a temporary mold for the template, removing the model from the temporary mold, and casting a hardenable material in the temporary mold to form the template.
- 4. The method according to claim 3 including the step of applying a release agent to the model before applying the liquid material to form the temporary mold.
- 5. The method according to claim 1 including forming the coating by the steps of melting a wax, melting a tar, and mixing the tar into the wax to form a mixture which, when hardened, can be softened before melting.
- 6. A method of forming a contoured surface in a workpiece in the form of a metal mold or die by progressively etching the surface thereof, comprising the steps of;
- a. providing a template having a contoured surface which is a negative pattern of the contoured surface to be formed in the workpiece,
- b. applying a meltable coating to the workpiece, the coating being resistant to an etchant and having a melting temperature such that the coating is generally solid after application to the workpiece, the coating being capable of softening before melting,
- c. immersing the coated workpiece in an etchant,
- d. heating the template to at least the melting temperature of the coating,
- e. heating the workpiece until the coating softens,
- f. pressing the heated template against the coated workpiece and melting any portions of said coating contacted by the template,
- g. only displacing the melted portions of said coating until the contoured surface of the template contacts the workpiece,
- h. withdrawing the template from the coated workpiece to permit solidification of any melted coating while leaving any locations of the workpiece contacted by the contoured surface of the template essentially free of the coating and exposing portions of the workpiece without withdrawing any coating with the template,
- i. permitting the etchant to etch said portions of the workpiece exposed by displacement of the coating, and
- j. repeating steps (e) through (i) until the surface of the workpiece conforms to the contoured surface of the template.
SUMMARY OF THE INVENTION
This application is a continuation of application Ser. No. 850,769, filed Apr. 11, 1986, now abandoned. BACKGROUND OF THE INVENTION
This invention relates to formation of metal dies or molds, and in particular to a method for forming a contoured mold surface by progressively etching the surface of a workpiece until the mold configuration is formed in the workpiece.
Metal molds or dies can be formed in several different manners. The present invention relates to manufacture of molds or dies by etching techniques where an etchant, such as an acidic bath, is used to etch a metal surface progressively in order to form the mold or die. Throughout the remainder of this description, the terms "mold" or "die" will be used interchangeably to mean a tool formed from a workpiece and which has a contoured surface for use in the production in quantity of threedimensional products of metal, plastic or the like.
U.S. Pat. No. 4,325,779, issued on an invention of the same inventor as this application, relates to a method for forming a mold surface by etching techniques. However, in the disclosed method of U.S. Pat. No. 4,325,779, the technique is laborious, requiring removal of portions of a coating covering the mold workpiece surface, application of an etchant to etch any thus exposed metal, removal of the etchant and cleaning of the mold, reapplication of the coating to the entire mold workpiece surface, and then repetition of the procedure until sufficient depth of etching has been effected to form the mold. The method is labor intensive and quite slow due to the necessity for continual cycles of manual application and removal of the coating material and the etchant.
U.S. Pat. No. 3,290,192 discloses a method of continually forming surfaces by etching techniques. An item to be etched is immersed in an etching bath and a heated die is brought into contact with the surface of the item repeatedly in order to etch the surface. The etchant is kept relatively cool to minimize its etching capabilities, while the repeated pulsation of the die is intended to continually replenish fresh etchant between the tool face and the surface being etched. There is no coating to protect the surface being etched, requiring careful control of the temperature of the etchant and of the nature of the etchant to assure that other areas of the surface are not inadvertantly etched where etching is not desired.
The present invention comprises a method of forming a contoured surface in a workpiece in order to form a mold element therein by progessively etching a surface of the workpiece. A template is provided having a contoured surface which is a negative pattern of the contoured surface of a mold to be formed in the workpiece. A meltable, wax-like coating is applied to the workpiece, the coating being resistant to any etchant used and having a melting temperature sufficiently elevated such that the coating, after application to the workpiece, is generally solid. The coated workpiece is then immersed in the etchant, and the template is heated to at least the melting temperature of the coating. The heated template is then pressed against the coated workpiece to melt those selected portions of the coating contacted by the template. The melted portions are displaced by the template as the highest portions of the contoured surface of the template approach and contact the workpiece. After such contact, the warm template is withdrawn from the coated workpiece sufficiently to permit re-solidification of the locally melted coating. The etchant then etches those portions of the workpiece which are exposed by the displacement of the coating. The process is repeated without any extrinsic manipulation of the coating until the surface of the workpiece conforms to the contoured surface of the template.
In accordance to the preferred embodiment of the invention, the coating for the workpiece is a type of material which, when passing from the solid state to the liquid state, softens over a range of temperatures before melting. The workpiece may also be heated to incipient softening temperature of the coating before the heated template is pressed against the coated workpiece.
The coating material preferably has a melting temperature sufficiently elevated that the coating is solid after application to the workpiece at, say, room temperature. The coating may comprise a wax, such as paraffin, which is heated to its melting temperature before application to the workpiece. Depending on the nature of the coating desired, tar is added to the wax, and if desired, rosin is also added. A suitable mixture may be 10 parts wax, 1 part tar and 1 par rosin.
The template is formed from a model of the three-dimensional product which is intended to be produced by the mold formed in the workpiece. A suitable material in liquid form is first poured over the model, with the liquid material subsequently hardening to form a temporary mold for the template. The model is then removed from the temporary mold, and a hardenable material is cast into the temporary mold to form the template. If the material of the temporary mold is susceptible to adhering to the model, a release agent is aplied to the model before the liquid material is poured thereover to form the temporary mold.
The etchant may be an acid of sufficient strength to etch the steel forming the workpiece. Many suitable solutions may be used, such as a mixture of 10 parts urea, 4 parts sulfuric acid, 7 parts nitric acid and one part muriatic acid, all in commercially available concentrations. Suitable etchants are well known in the engraving field.
The template must be formed of a material which flows easily in its liquid state in order to conform to its temporary mold and form a template which is an exact duplicate of the model, but which will not soften or deform in any manner when working temperatures are applied thereto in order to melt the coating as the contoured surface is formed in the workpiece. Preferably, the template is made of epoxy or a similar resin, which may be filled with finely divided aluminum or copper in order to enhance the thermal conductivity of the body of the template for uniformity of temperature. Such metals or powered carbon may also be used to render the template material electrically conductive sufficiently to heat the template by electrical resistance during the progressive formation of the mold surface.
US Referenced Citations (8)
Continuations (1)
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Number |
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850769 |
Apr 1986 |
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Patent Grant
4818336
