Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2002-01-24
2004-03-02
Picard, Leo (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S197000, C345S420000, C264S401000
Reexamination Certificate
active
06701200
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the field of mold making, and particularly to the manufacture of molds, such as for use with injection molding presses, from blocks of metal. More specifically, the present invention relates to software supported methods, systems and tools used in the design and fabrication of molds for custom plastic parts.
Injection molding, among other types of molding techniques, is commonly utilized to produce plastic parts from molds. Companies and individuals engaged in fabricating molds arc commonly referred to as “moldmakers.” In many cases (referred to as “straight pull” injection molding), the mold consists of two metal blocks, one top and one bottom. Most commonly, the metal blocks are high quality machine steel, so the mold will have an acceptably long life. Opposed surfaces of each mold block are machined to jointly produce the required cavity in the shape of the desired part, as well as “shut-off” surfaces sealing the cavity when the mold blocks are pressed together. The line on which shut-off surfaces intersect with the surface of the cavity is called the parting line. The corresponding line on the surface of the part formed by the parting line is called the witness mark. After the mold assembly is set up in an injection molding press, parts are made by filling the cavity with molten plastic. The mold blocks are separated from each other after solidification of the molten plastic. The plastic part, normally sticking after separation to the bottom block, is then ejected by means of ejectors.
The moldmaking art has a long history of fairly gradual innovation and advancement. Molds are designed pursuant to a specification of the part geometry provided by a customer; in many cases, functional aspects of the plastic part also need to be taken into account. Historically, moldmaking involves at least one face-to-face meeting between the moldmaker and the customer, in which the customer submits detailed part geometry, usually with the aid of drawings, to the moldmaker and outlines the function of the part. Armed with knowledge of injection molding technology, the moldmaker designs the mold corresponding to the drawings of the part. In particular, the moldmaker orients the part to enable a straight pull mold separation, splits its surface into two areas separated by a suitable parting line, and replicates these areas in the top and bottom blocks. The moldmaker determines the location and shape of the shut-off surfaces and enlarges the dimensions of the cavity relative to the desired part as necessary to account for shrinkage of the plastic material. The moldmaker determines the size and position of one or more gates and runners to provide an adequate flow path for the molten plastic shot into the cavity. Sizes and locations of openings for ejection pins are also selected by the moldmaker. The machining operations to be performed to fabricate the designed mold are determined by the moldmaker. The moldmaker then runs various cutting tools, such as endmills, drills and reams, to machine the basic cavity, shut-off surfaces, runners, gates and ejector pin openings in blocks of metal. To produce certain hard-to-mill features in the mold, the moldmaker may also design and machine electrodes, and then perform electro-discharge machining (“EDM”) of the mold blocks. The moldmaker then outfits the mold blocks with ejection pins and prepares the mold assembly for use in the injection molding press. Throughout all of this design and fabrication, the moldmaker makes numerous design choices pertaining to the geometric details of the cavities to be machined as well as to the tools to be used for machining.
All these steps involve a high degree of skill and experience on the part of the moldmaker. Experienced moldmakers, after having considered the design submitted by the customer, may sometimes suggest changes to the part geometry so that the part is more manufacturable and less costly. Highly experienced, gifted moldmakers can charge a premium for their services, both in return for the acuity of their experience and perception in knowing what will and will not work in the mold, and in return for their skill, speed and craftsmanship in machining the mold.
Because of the large number of technical decisions involved and considerable time spent by highly skilled moldmakers in analyzing in detail the part geometry by visual inspection, obtaining a desired injection mold has generally been quite expensive and involved a significant time delay. A single mold may cost tens or hundreds of thousands of dollars, and delivery times of eight to twelve weeks or more are common.
As in many other areas of industry, various computer advances have been applied to the moldmaking art. Today, most of customer's drawings are not prepared by hand, but rather through commercially available programs referred to as CAD (Computer-Aided Design) software. To produce drawings of the molds based on the drawings of custom parts, moldmakers also use CAD software, including packages developed specifically for this task. Also, in most moldmaking companies machining operations are not manually controlled. Instead, CNC (Computer Numerical Control) machines such as vertical mills are used to manufacture molds and, if needed, EDM electrodes in accordance with a set of CNC instructions. To compute detailed toolpaths for the tools assigned by the moldmaker and to produce long sequences of such instructions for CNC mills, computers running CAM (Computer-Aided Manufacturing) software (again, including packages developed specifically for the moldmaking industry) are used by most moldmakers. CAD/CAM software packages are built around geometry kernels—computationally intensive software implementing numerical algorithms to solve a broad set of mathematical problems associated with analysis of geometrical and topological properties of three-dimensional (3D) objects, such as faces and edges of 3D bodies, as well as with generation of new, derivative 3D objects. At present, a number of mature and powerful geometry kernels are commercially available.
While existing CAD/CAM software packages allow designers and CNC machinists to work with geometrically complex parts, they are still far from completely automating the designer's work. Rather, these packages provide an assortment of software-supported operations that automate many partial tasks but still require that numerous decisions be made by the user to create the design and generate machining instructions. CAD/CAM packages usually facilitate such decisions by means of interactive visualization of the design geometry and machining tools. This makes software applicable to a wide variety of tasks involving mechanical design and machining operations. The downside of such versatility, when applied to moldmaking, is that it results in long and labor intensive working sessions to produce mold designs and CNC machining instructions for many custom parts, including parts lending themselves to straight pull molding.
Visualization allows the moldmaker to evaluate whether the mold and injection molded parts can be made sufficiently close to the design using available tools. The fidelity with which plastic parts can be manufactured is limited by the finite precision of mills and cutting tools used to machine the mold, and by shrinkage of plastic materials (slightly changing the shape and dimensions of the injection molded parts as they cool down and undergo stress relaxation in a way that is largely but not entirely predictable). These rather generic factors establish the level of dimensional tolerances for injection-molded parts, the level that is generally known and in most cases acceptable to the customers.
Oftentimes, however, additional factors come into play that can result in more significant deviations of injection molded plastic parts from the submitted design geometry. These factors are usually associated with certain features that are hard to machine in the mold using vertical mills. For example very thin ribs in the part can be m
Dreizin Yuri Arnoldovich
Gilbert John Mark
Lukis Lawrence Joseph
Bahta Kidest
Picard Leo
Shechuk Jeffrey D.
Shewchuk IP Services
The Protomold Company, Inc.
LandOfFree
Automated custom mold manufacture does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Automated custom mold manufacture, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Automated custom mold manufacture will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3289416