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Additive/Subtractive Rapid Pattern Manufacturing for Casting Patterns and Injection Mold Tooling
| Content Provider | Semantic Scholar |
|---|---|
| Author | Frank, Matthew C. Peters, Frank E. Karthikeyan, Rajesh Kumar |
| Copyright Year | 2010 |
| Abstract | This paper presents a Rapid Pattern Manufacturing system that involves both additive and subtractive techniques whereby slabs are sequentially bonded and milled using layered toolpaths. Patterns are grown in a bottom-up fashion, both eliminating the need for multi-axis operations and allowing small features in deep cavities. Similar approaches exist in the literature; however, this system is able to provide a larger range of both materials and sizes, from smaller conventional injection mold tooling to very large wood or urethane sand casting patterns. This method introduces a novel sacrificial support structure approach by integrating a flask into the pattern build process. The system has been implemented in an automated machine capable of producing patterns in excess of several thousand pounds in a build envelope over 1m. In this current research, a new layer bonding method using friction stir welding of aluminum plates is presented. In this manner, one can create seam-free laminated aluminum injection mold tooling using a unique combination of industrial adhesives and friction stir spot welding to secure the slab initially, then continuous friction stir welding of layer perimeters that are subsequently machined in a layer-wise process. Introduction Although most rapid prototyping systems are appropriate for testing form, fit and function, they usually require a long processing time; which is reasonable if only one or a few parts are required. When there is a need to make tens, hundreds or thousands of parts, RP systems are not always the best choice because of the cost and processing time for each part. The availability of rapid prototyping systems for the areas of mass production is limited, but is just starting to see some successes. One of the most commonly chosen manufacturing methods for the mass production of plastic parts is the injection molding process. A wide range of products that vary in their size, shape and complexity can be easily manufactured using injection molding. However, the process of manufacturing an injection mold tool is a complex and highly skilled task that is very costly. Once the design is confirmed it usually takes several weeks or months to actually manufacture and market the product. This is mainly due to the complexity involved in creating the mold tooling. There is a strong motivation to implement rapid manufacturing technology for the manufacture of plastic injection molds to reduce the product development time and reduce the cost of manufacturing. Related Work Different types of rapid prototyping and manufacturing methodologies have been developed in the past few decades. Some of the noteworthy methods are Stereolithography (SLA), Fused Deposition Modeling (FDM), Laminated Object Manufacturing (LOM), Selective Laser Sintering (SLS), Electron Beam Melting and other direct metal method, and 3-D Printing. These RP systems are excellent for testing the form, fit and sometimes function of a new design; however most are limited in terms of part accuracy, size and choice of materials. Hybrid RP process combines the advantage of conventional CNC machining process and a layered manufacturing process to find the solution to these problems [3]. Shape Deposition Manufacturing (SDM) was a hybrid process developed at Carnegie Mellon University that employed an additive process to deposit the part or support material using micro-casting process. The material is then machined to achieve the desired accuracy and finish [4]. Solvent welding freeform fabrication technique (SWIFT) creates short run tooling based on solvent welding and CNC machining [5]. For each layer a thin film of high-density polyethylene (HDPE) is printed through a laser printer. HDPE is the solvent mask that prevents unwanted bonding wherever it is applied. After masking, acetone solvent is applied to the bottom side of the sheet and then stacked to the previous layers and bonded under force. A three axis CNC machine is used to mill down the current sheet to the shape. Computer-aided manufacture (CAM) of laminated engineering materials (LEMs) is another hybrid RP process for fabricating laminated engineering components directly from sheet metal. A laser was used to cut the part slices from the stock of materials such as metals and ceramics. These slices are then assembled together using a selective area gripper [6]. However the part accuracy of this system was low due to unpredictable shrinkage which can be as high as 12 – 18 percent [7]. Rapid Tooling is an extension of rapid prototyping which is used to prototype mold tooling that can be used for early production. Rapid tooling (RT), allows manufacturing of production tools such as molds and dies rather than the final part itself which can reduce the lead time for the product to reach the market [2]. Rapid laminated tooling is similar to laminated object manufacturing (LOM), In the LOM process, each layer of the part is formed from an adhesive coated sheet of paper which were subsequently cut with a laser [10]. Instead of paper, other forms of laminated tooling used sheets of metals. These sheets of metals could be joined together by bolts, welding or brazing. Extensive research has been conducted on creating tooling for plastic and metal forming processes. Laminated tooling is not a new concept, where research and development in this field has been conducted since early researchers like Nakagawa back in 1980, who were creating blanking dies for sheet metal components by using bainite steel sheets for the tool face and cheaper steel as backing plates. The steel sheets were cut using a laser, stacked horizontally and joined together by using mechanical fasteners [11]. Most of these laminated tool manufacturing processes follow a build sequence of cut, stack and bond. First, the plates are cut to the required cross section using a laser or EDM process and then these laminates are cleaned and stacked in either horizontal or vertical orientation. Finally, the stacked plates are bonded together. Many researchers used different bonding methods, such as mechanical fasteners, laser welding, diffusion bonding and bonding by adhesives. The more popular joining method being the use of mechanical fasteners such as bolts and rivets to join the laminates together [11-14]. However, most of these processes do not provide a complete automated process planning solution. In addition, selecting the thickness of the laminates has always been an issue, where selecting thin laminate thickness of 0.5 and 2mm increased both the complexity and time in creating the tooling The proposed process, Rapid Manufacturing of Plastic Injection Mold (RMPIM) uses a build sequence of stacking-bonding-cutting of aluminum plates as opposed to cutting-stacking-bonding cited in most of the literature. This approach should more readily enable completely automated process planning for creating injection mold tooling. The proposed process uses a new layer bonding method; a unique combination of industrial adhesives and friction stir welding. A hybrid Rapid Pattern Manufacturing system (RPM), previously developed by the authors, can create large wooden casting patterns [8-9]. The process combines depositing a thick slab of Medium-density fiberboard (MDF) and a three axis CNC machine to cut the board to a defined layer thickness and to create part geometry on the layer. The advantage of this system is that the patterns are built in the bottom-up fashion so a small tool can be used to mill deep cavities without the use of multi-axis (beyond three-axis) CNC machines. Friction stir welding (FSW) is a solid-state joining process. A non-consumable rotating tool with a specially designed pin and shoulder is inserted into the abutting edges of sheets or plates to be joined and traversed along the line of joint. Frictional heating is produced from rubbing of the rotating shoulder with the work pieces, while the rotating pin causes plastic deformation of work piece. The heating is accomplished by friction between the tool and the work piece and plastic deformation of work piece. The localized heating softens the material around the pin and the combination of tool rotation and translation leads to movement of material from the front of the pin to the back of the pin where it is forged into a joint [15-16]. |
| Starting Page | 242 |
| Ending Page | 255 |
| Page Count | 14 |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://sffsymposium.engr.utexas.edu/Manuscripts/2010/2010-22-Frank.pdf |
| Alternate Webpage(s) | https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1069&context=imse_conf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
