螺紋水杯的注塑模具設(shè)計(jì)
螺紋水杯的注塑模具設(shè)計(jì),螺紋,羅紋,水杯,注塑,模具設(shè)計(jì)
英文原文
Session VA4
I ntelligent Mold Design Tool For Plastic Injection Molding
Jagannath Yammada, Terrence L. Chambers, Suren N. Dwivedi
Department of Mechanical Engineering
University of Louisiana at Lafayette
Abstract
Plastic Injection molding is one of the most popular manufacturing processes for making thermoplastic products, and mold design is a key aspect of the process. Design of molds requires knowledge, expertise and most importantly experience in the field. When one of these is lacking, selection of an appropriate mold for manufacturing a plastic component is done on a trial-and-error basis. This increases the cost of production and introduces inconsistencies in the design.
This paper describes the development of an intelligent mold design tool. The tool captures knowledge about the mold design process and represents the knowledge in logical fashion. The knowledge acquired will be deterministic and non-deterministic information about the mold design process. Once developed the mold design tool will guide the user in selecting an appropriate mold for his plastic part based on various client specifications.
Introduction
The plastic injection molding process demands knowledge, expertise and, most important, experience for its successful implementation. Often it is the molding parameters that control the efficiency of the process. Effectively controlling and optimizing these parameters during themanufacturing process can achieve consistency, which takes the form of part quality and part cost.
The level of experience of the manufacturer(s) determines how effectively the process parameters are controlled. This sometimes leads to inconsistency introduced by human error. There is also the case where there is inexperience, shortage of time, resources and little scope for innovation. Knowledge-based engineering provides a feasible solution to all these problems by creating what is called an “intelligent model” of the problem.
1 IKEM
Intelligent Knowledge based Engineering modules for the plastic injection molding process (IKEM) is a software technology that is a step ahead of the concurrent engineering and CAD/CAM systems. It integrates current knowledge about the design and manufacturing processes and helps to reduce several man-hours by reducing engineering changes in the design phase of product development by giving users instruction about various design aspects. The system will be used for injection molding design, design iterations, and process integration. The current process consists of many manual computations, CAD graphical constructions, and experience attained from previous projects. Once the engineer completes the design, it will be evaluated for performance. The IKEM project has been divided into three major modules.
1. The cost estimation module
2. The mold design module
3. The Manufacturing module
Input to the IKEM system is of two forms. Input in the form of a CAD model (Pro-E file) and input given at the User Interface form. Figure 1 illustrates the kind of input that goes into each module and the output given to the user.
Figure 1. Organization of the IKEM Project
2 Intelligent Mold Design Tool
The mold design tool in its basic form is a Visual Basic application taking input from a text file that contains information about the part and a User Input form. The text file contains information about the part geometry parsed from a Pro/E information file. The input is used to estimate the dimensions of mold and variousother features.
2.1 Literature Review
Design of molds is another stage of the injection molding process where the experience of an engineer largely helps automate the process and increase its efficiency. The issue that needs attention is the time that goes into designing the molds. Often, design engineers refer to tables and standard handbooks while designing a mold, which consumes lot of time. Also, a great deal of time goes into modeling components of the mold in standard CAD software. Differen
researchers have dealt with the issue of reducing the time it takes to design the mold in different ways. Koelsch and James have employed group technology techniques to reduce the mold design time. A unique coding system that groups a class of injection molded parts, and the tooling required ininjection molding is developed which is general and can be applied to other product lines.
A software system to implement the coding system has also been developed. Attempts were also directed towards the automation of the mold design process by capturing experience and knowledge of engineers in the field. The development of a concurrent mold design system is one such approach that attempts to develop a systematic methodology for injection mold design processes in a concurrent engineering environment. The objective of their research was to develop a mold development process that facilitates concurrent engineering-based practice, and to develop a knowledge-based design aid for injection molding mold design that accommodates manufacturability concerns, as well as product requirements.
Researchers have been trying to automate the mold design process either by capturing only the deterministic information on the mold design process or the non-deterministic information, in various ways. This research uniquely attempts to develop a mold design application that captures information in both forms; deterministic and non-deterministic.
2.2 Approach Adopted
In order to develop an intelligent mold design tool, the conventional method of designing molds is studied. The application developer and the design engineer work together in designing a mold for a particular plastic part. During this time, the approach adopted by the engineer to select the mold base is closely observed and aspects of the selection process that require his knowledge/experience are identified. Also, there will be times when the engineer will refer to tables and handbooks in order to standardize his selection process. This time consuming process is also recorded to incorporate it later in the application.
Formulating the problem for the application in terms of inputs and outputs is the next stage. This involves defining what information about the mold layout is most required for the user and also the minimum number of inputs that can be taken from him to give those outputs.
In injection molding, the polymer melt at high temperature is injected into the mold under high pressure [1]. Thus, the mold material needs to have thermal and mechanical properties capa ble of withstanding the temperatures and pressures of the mold ing cycle. The focus of many studies has been to create the
injection mold directly by a rapid prototyping (RP) process. By eliminating multiple steps, this method of tooling holds the best promise of reducing the time and cost needed to create low-volume quantities of parts in a production material. The potential of integrating injection molding with RP technologies has been demonstrated many times. The properties of RP molds are very different from those of traditional metal molds. The key differ ences are the properties of thermal conductivity and elastic mod ulus (rigidity). For example, the polymers used in RP-fabricated stereolithography (SL) molds have a thermal conductivity that is less than one thousandth that of an aluminum tool. In using RP technologies to create molds, the entire mold design and injection-molding process parameters need to be modi?ed and optimized from traditional methodologies due to the completely different tool material. However, there is still not a fundamen tal understanding of how the modi?cations to the mold tooling method and material impact both the mold design and the injec tion molding process parameters. One cannot obtain reasonable results by simply changing a few material properties in current models. Also, using traditional approaches when making actual parts may be generating sub-optimal results. So there is a dire need to study the interaction between the rapid tooling (RT) pro cess and material and injection molding, so as to establish the mold design criteria and techniques for an RT-oriented injection molding process.
In addition, computer simulation is an effective approach for predicting the quality of molded parts. Commercially available simulation packages of the traditional injection molding process have now become routine tools of the mold designer and pro cess engineer [2]. Unfortunately, current simulation programs for conventional injection molding are no longer applicable to RP molds, because of the dramatically dissimilar tool material. For instance, in using the existing simulation software with alu minum and SL molds and comparing with experimental results, though the simulation values of part distortion are reasonable for the aluminum mold, results are unacceptable, with the error exceeding 50%. The distortion during injection molding is due to shrinkage and warpage of the plastic part, as well as the mold. For ordinarily molds, the main factor is the shrinkage and warpage of the plastic part, which is modeled accurately in cur rent simulations. But for RP molds, the distortion of the mold has potentially more in?uence, which have been neglected in current models. For instance, [3] used a simple three-step simulation process to consider the mold distortion, which had too much deviation.
In this paper, based on the above analysis, a new simula tion system for RP molds is developed. The proposed system focuses on predicting part distortion, which is dominating defect in RP-molded parts. The developed simulation can be applied as an evaluation tool for RP mold design and process opti mization. Our simulation system is veri?ed by an experimental example.
Although many materials are available for use in RP tech nologies, we concentrate on using stereolithography (SL), the original RP technology, to create polymer molds. The SL pro cess uses photopolymer and laser energy to build a part layer by layer. Using SL takes advantage of both the commercial domi nance of SL in the RP industry and the subsequent expertise base that has been developed for creating accurate, high-quality parts. Until recently, SL was primarily used to create physical models for visual inspection and form-?t studies with very limited func tional applications. However, the newer generation stereolitho graphic photopolymers have improved dimensional, mechanical and thermal properties making it possible to use them for actual functional molds.
Based on the information gathered in the mold design exercise, the conventions followed by the engineer are transformed into if-then rules. Decision tables are used to account for all possible cases that arise when dealing with a particular aspect of the mold design process. The rules so framed are then organized into modules interacting with each other, using an application development environment. Finally the application is tested for its validity when it comes to designing molds for plastic parts manufactured in the industry.
2.3 Selection of Appropriate Mold Base
Typically, selection of appropriate mold base for manufacturing a plastic part involves
Estimating the number of cavities
The number of cavities is decided depending on the number of parts required within a given time. There are also other issues like the plasticizing capacity of the machine, reject rate etc that affect the number of cavities to be present in the mold base.
Deciding on the presence of inserts and their dimensions
Inserts facilitate the reusability of the mold base and therefore help in reducing cost of manufacturing. When it comes to selecting the dimensions and the number, a decision is made depending on the reusability of existing old inserts and cost of ordering new ones.
Determining the size and location of runners
The runner size depends on the material being molded. Although there are other considerations material properties determines the channel size required for its flow. Location of runners mainly depends on the topology of runners being used. Though a circular runner system is always preferable, the branched runner system that avoids runner balancing is the one most widely used.
Determining the diameter of sprue
The diameter of the sprue is decided based on the size of the mold, number of cavities, or the amount of plastic that is to be filled within a given time.
Locating gates
Plastic enters the cavity at a point where it can uniformly fill the cavity. A gate can be located at any point on the perimeter of a circular cavity but has to enter at the midsection when it comes to filling rectangular cavities.
Determining the size and location of water lines
Water lines are located at standard distances form each other and from any wall in the mold. The convention is not to locate a waterline within one diameter range on the mold wall.
Deciding mold dimensions based on above conclusions
Based on all the above decisions the approximate mold dimensions can be estimated and rounded off to the nearest catalog number. Considering all the above aspects before even modeling the mold base reduces the cost and time that go into redesigning.
The emergence of mold can be traced back thousands of years ago, pottery and bronze foundry, but the large-scale use is with the rise of modern industry and developed.The 19th century, with the arms industry (gun's shell), watch industry, radio industry, dies are widely used. After World War II, with the rapid development of world economy, it became a mass production of household appliances, automobiles, electronic equipment, cameras, watches and other parts the best way. From a global perspective, when the United States in the forefront of stamping technology - many die of advanced technologies, such as simple mold, high efficiency, mold, die and stamping the high life automation, mostly originated in the United States; and Switzerland, fine blanking, cold in Germany extrusion technology, plastic processing of the Soviet Union are at the world advanced. 0's, mold industry focus is based on subscriber demand, production can meet the product requirements of the mold. Multi-die design rule of thumb, reference has been drawing and perceptual knowledge, on the design of mold parts of a lack of real understanding of function. From 1955 to 1965, is the pressure processing of exploration and development of the times - the main components of the mold and the stress state of the function of a mathematical sub-bridge, and to continue to apply to on-site practical knowledge to make stamping technology in all aspects of a leap in development. The result is summarized mold design principles, and makes the pressure machine, stamping materials, processing methods, plum with a structure, mold materials, mold manufacturing method, the field of automation devices, a new look to the practical direction of advance, so that pressing processing apparatus capable of producing quality products from the first stage.
Into the 70's to high speed, launch technology, precision, security, development of the second stage. Continue to emerge in this process a variety of high efficiency, business life, high-precision multi-functional automatic school to help with. Represented by the number of working places as much as other progressive die and dozens of multi-station transfer station module. On this basis, has developed both a continuous pressing station there are more slide forming station of the press - bending machine. In the meantime, the Japanese stand to the world's largest - the mold into the micron-level precision, die life, alloy tool steel mold has reached tens of millions of times, carbide steel mold to each of hundreds of millions of times p minutes for stamping the number of small presses usually 200 to 300, up to 1200 times to 1500 times. In the meantime, in order to meet product updates quickly, with the short duration (such as cars modified, refurbished toys, etc.) need a variety of economic-type mold, such as zinc alloy die down, polyurethane rubber mold, die steel skin, also has been very great development.
From the mid-70s so far can be said that computer-aided design, supporting the continuous development of manufacturing technology of the times. With the precision and complexity of mold rising, accelerating the production cycle, the mold industry, the quality of equipment and personnel are required to improve. Rely on common processing equipment, their experience and skills can not meet the needs of mold. Since the 90's, mechanical and electronic technologies in close connection with the development of NC machine tools, such as CNC wire cutting machine, CNC EDM, CNC milling, CNC coordinate grinding machine and so on. The use of computer automatic programming, control CNC machine tools to improve the efficiency in the use and scope. In recent years, has developed a computer to time-sharing by the way a group of direct management and control of CNC machine tools NNC system.
With the development of computer technology, computers have gradually into the mold in all areas, including design, manufacturing and management. International Association for the Study of production forecasts to 2000, as a means of links between design and manufacturing drawings will lose its primary role. Automatic Design of die most fundamental point is to establish the mold standard and design standards. To get rid of the people of the past, and practical experience to judge the composition of the design center, we must take past experiences and ways of thinking, for series, numerical value, the number of type-based, as the design criteria to the computer store. Components are dry because of mold constitutes a million other differences, to come up with a can adapt to various parts of the design software almost impossible. But some products do not change the shape of parts, mold structure has certain rules, can be summed up for the automatic design of software. If a Japanese company's CDM system for progressive die design and manufacturing, including the importation of parts of the figure, rough start, strip layout, determine the size and standard templates, assembly drawing and parts, the output NC program (for CNC machining Center and line cutting program), etc., used in 20% of the time by hand, reduce their working hours to 35 hours; from Japan in the early 80s will be three-dimensional cad / cam system for automotive panel die. Currently, the physical parts scanning input, map lines and data input, geometric form, display, graphics, annotations and the data is automatically programmed, resulting in effective control machine tool control system of post-processing documents have reached a high level; computer Simulation (CAE) technology has made some achievements.At high levels, CAD / CAM / CAE integration, that data is integrated, can transmit information directly with each other. Achieve network. Present.Only a few foreign manufacturers can do it.
2.4 Formulation of the Problem
Based on issues that require human knowledge/experience, and aspects of mold design that consume time referring to tables, data sheets etc., the problem for developing the application is defined as shown in Figure 2.
While most of the input, like the number of cavities, cavity image dimensions, cycle time are based on the client specifications, other input like the plasticizing capacity, shots per minute etc., can be obtain
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