【導(dǎo)讀】Keywords:Die,Mold,Manufacturing.Engel-LFTErlangen,Prof.Weinert-ISFDortmund,□r.Leopold-GFEChemnitz,Mr.Reznick-ExtrudeHoneCorp.,Prof.Gunasekera-OhioUniversity,Prof.Bramley-UniversityofBath,Prof.Bueno-FundacionTekniker,Prof.

　　

【正文】 model of the mold insert, with runner geometry attached. This mold insert is filled with silicone, which is allowed to cure. The silicone positive is then used to cast an epoxy tool, which can typically withstand several hundred injectionmolding cycles. Because epoxy molds are limited in the number of parts they can deliver, there is much interest in industry in finding other techniques to cast tools around masters derived from RP methods. A method was developed by a car manufacturer to spray molten tool steel onto ceramic molds, which are produced from RP models. To date this method is used to produce relatively small (600 mm χ 600 mm) tool sets. However, work is in progress to scale up the technique to produce sheet metal dies for auto body panels [17], Another related method is called Rapid Solidification. It involves spraying a molten metal, in this case H13 tool steel, against a ceramic master. The developers of the method claim that the resulting tool steel shell shows superior strength, hardness, and surface finish. The first tool produced by this process is due to go online in July of 2021 [19], Several other techniques use socalled indirect methods to produce tool sets in metals. These methods have almost all been applied to injection molds, due to the relatively benign production environment. Ainsley and Gong report on a method to slip cast stainless steel molds using RP masters of the mold [20], Weaver et al. report on a method to produce the model of the tool set. Silicone is used as the intermediate material, and slurry of metal powder and polymer is then cast around the silicone. After curing, the tool is debound and sintered, which produces a tool set with properties approaching hardened tool steel [21], A similar process has been in use for several years. It uses one of three proprietary metal posites, which is cast around a silicone master. Details on this tec hnique are available in [22], Direct Methods These processes all use RP technologies to make a die or mold directly from the CAD model, without using additional pattern transfer techniques. The most mon method for direct tooling involves a green part that is created either by selective laser sintering (SLS) or threedimensional printing (3DP) methods. SLS [23] deposits a layer of polymer coated metal powder, which is then selectively sintered using a laser. With the 3D Printing process a layer of powder is first deposited, and then an adhesive binder selectively applied. The major advantage of the powderbased systems is that the powder that is not used to form the part provides support for overhanging structures. In this way, conformal cooling channels and undercuts can be created without need of additional support material. An excellent overview of recent work in various direct tooling methods is given in [24], In an overview of recent developments in direct tool fabrication using the SLS process, Klocke notes that precision on the order of hundredths of a millimeter is now possible, with attainable surface finishes (after some postprocessing) of Rz= 15 μιτι or better. Rather plex parts can be made with these tools [25], Considerable work has gone into developing Selective Laser Sintering (SLS) as a process for building dies and molds directly from the CAD model. Details are available for sheet forming dies [26], DTM rapid steel process [27] and the rapid mold process [28], In addition Ramp。D is in progress for further improving the SLS process itself, specifically on powder deposition [29] and on the effects of laser power and traverse speed upon microstructure and porosity of deposited surface [30], An overall practical review of rapid prototyping and rapid tooling is given in a recent publication [14], 4 CAVITY AND PUNCH/CORE MACHINING The steps involved in manufacturing a typical mold for injection molding is seen in Figure 8 [31], The cost ponents of an example injection molded part are given in Figure 9. This example illustrates that considerable cost reduction potential exists in rough and finish machining of dies and molds. Tool Path Generation and Optimization Today nearly all die and mold makers use High Speed Cutting or Machining (HSC or HSM) in cavity and punch manufacturing. HSM requires not only specific machine tools (rigid, high spindle RPM, high feed rate, software with look ahead capabilities, high acceleration and deceleration) and cutting tools (ultra fine carbide with various and multiple coatings, optimized tool edge geometry, high performance cutting tool materials, . PCBN and ceramics) but also special CNC tool path programming strategies. This is now being recognized not only by research institutions but also by various CAM system vendors. ■ Design (plastic part geometry) by OEM or Injection Molder ■ Process Simulation (mold design) by Injection Molder or Mold Maker ■ First Rough Machining of the Mold Steel Block, by Steel Supplier ■ Rough Machining of Cavity (milling, drilling) by Mold Maker ■ SemiFinish and Finish Machining (milling, EDM) by Mold Maker ■ Polishing and Assembly, by Mold Maker ■ Mold Tryout and Finish, by Mold Maker ■ PreProduction Qualification, by Mold Maker, Injection Molder and OEM Figure 8: Operations involved in making a typical mold [31], Figure 9: Cost Components (in %) in Manufacturing of an Example Automotive Part by Injection Molding (assuming 250,000 parts were produced in one steel mold) [31], Constant Chip Load and Cutting Speed Early studies on this topic concentrated on the optimization of the tool paths for 3D milling of sculptured surfaces with ball end mills. The basic approach was to maintain the cutting speed and the chip load approximately constant by controlling the spindle speed and the feed rate. Computer codes were developed, based on this principle and allowed the reduction of milling time 20 to 30%,