plastic mould and custom injection moulding tips

Undercuts Modern molding practice dictates certain principles of design which should be observed if molded articles are to be produced successfully. Most elementary is the fact that the piece must be easily removed from the mold after it has been formed. https://res.cloudinary.com/dl8a9jvpa/video/upload/v1515562261/Undercuts_ni5xth.mp4   This point is frequently overlooked, and many products are designed with undercuts which make it impossible to eject them directly from the mold cavity. If undercuts are essential, then split molds or removable mold sections are required, and these increase the cost of molds and of the molded articles. Undercuts should always be avoided unless mechanical construction or the function of the piece make such a design an absolute necessity. External Undercuts When undercuts are located in the outside contours of the piece, they are called external undercuts. It would be impossible to withdraw a piece of such a shape from a one-piece mold cavity. While m

Flash Lines Flash is defined as that portion of the material which flows from or is extruded from the mold during the molding. The designer must design specifically for molding. For example, it is impracticable to duplicate, by molding, the appearance of a handle which has been fabricated from wood or metal by machining. To design a molded piece of good appearance calls for a knowledge of the molding technique and of mold-construction. In compression molds, the closing or telescoping of the two parts of the mold results in flow of material into the clearance between these parts. This material is known as flash and occurs at the parting line of the molds. The removal of flash from the article leaves a flash line, which is unavoidable and generally unsightly. The problem of flash lines is one that requires careful consideration by the designer, as the attractiveness of the product may depend to a large degree on a careful location of the flash line where it will not be seen. When a pie

Scope There is no easy solution to the problems encountered in designing molded articles of plastics. The design will often hinge on what is the best process of molding for the piece in question. The selection of the molding process is, in turn, determined by the choice of the molding material best suited to provide the desired physical properties in the finished molded piece. Often the necessity for certain elements in the design, such as thin sections or long delicate inserts, or requirements of exact concentricity or of accuracy of dimensions and working tolerances, make it desirable to use one technique of molding rather than another. The problem is complicated by the facts that there are two types of molding materials in general use, i.e., the thermosetting and the thermoplastic, and three basic methods of molding commonly used, i.e., compression, transfer and injection molding Frequently in the problem of design it is necessary to put the cart before the horse; we must k

Heating   The correct heating of hot runner manifold systems is very important and is crucial to the success of the tool in production. There must be good heat transfer between the heater and the surface being heated or the heater will fail prematurely. Heater channels in the manifold should be smooth in order to achieve this and must not be left rough machined. There are six types of heating systems that are commonly used in hot runner tooling: Band heaters Coil heaters Cartridge heaters Tubular heaters Integral heaters Hybrid heater/heat pipe systems Band Heaters This is the most common method of heating external cylindrical surfaces such as barrels, nozzles and tubular manifolds. Band heaters give good uniform heating right across their width and are available in a wide range of wattages and sizes. Mica and ceramic insulation are usually used. Mains voltage operation is most common, although low-voltage systems are available at higher cost. Sizes up to 100 mm diam

opportunities for the production design engineer Production design work in both the areas of product and process design will provide a rewarding lifetime job. The engineer knows that his work will make possible better products for more people at less cost. He will have rewarding personal contacts with the shop, sales, and service forces, and with his fellow engineers, research workers, designers, shop supervisors, and managers. The field of production design has come to offer some of the best opportunities afforded in industry. It may involve just a routine operation wherein apparatus is designed or modified to suit customer requirements, or it may be a comprehensive program including —in addition to design —sales analysis, research, invention, experimentation, and field tests which result in the development of a product. It may include the development of special equipment for the manufacturer of a product; the training of operators, construction and service men, and salesmen; and co-

systematic procedure design for plastic molding The road taken by the creative thinker in developing new injection molded parts  is long, expensive, and difficult, beset with many detours and byways. A systematic procedure for the development of a product will reduce the time and effort of the engineer, who promotes the development from its early stages to completion. He sees it through design; selection of materials; setting up of operations and processes; selection of equipment; design of tools ; formulation of specifications, operation sheets, and sales data; use of standards; adoption of ideas; obtaining of patents; and many other functions. All of these items are governed by economic or cost requirements and are developed by a systematic procedure. The systematic procedure that will give results through creative thinking begins with the establishment of the problem area. Being able to accurately and completely define the problem area is a long step toward problem solution. Certain

Thermoplastic Sheet Forming Method Cold bending . Simple circular or cylindrical Vacuum forming or blow molding in female mold shapes. The thicker the sheet, the larger the bend diameter must be to prevent high stress concentrations. Ex: consumer packages. Hot line bending . Two-dimensional shapes with arc, angle or channel cross section. Gradual to sharp bends, depending on heating procedure. Ex: safety guards. Stretch forming (hot draping, yoke forming) . Two-dimensional or slightly compound shapes, especially large shapes. Subject to surface distortion. Not suitable for reproduction of fine details. Yoke forming provides more uniform thinning out and is suitable for longer runs than manual stretch forming. Ex: aircraft canopies. Plug and ring forming . Shallow to deep drawn shapes with gradual to sharp angles and curves. Not suitable for highly accurate contours or fine mold details. Considerable surface distortion, especially at inside comers一unsuitable where optical properties ar

Design rules Designing molded reinforced plastics parts is difficult because of the large number of variables encountered in the material and the process, and the difficulty of controlling some of them. These variables include: composition of the resin, including fillers, catalysts and gardening agents, geometry of the reinforcing material, resin-reinforcement ratio, degree of saturation of reinforcement by resin, and temperature and time of cure. The cardinal design rule , which cannot be overemphasized, is: consult the custom mold maker in the primary design stages. In addition, follow these general design rules:    Integrate parts.     Make prototypes .    Mold to dimensions; parts cannot be “sprung” after they are molded.    Use stress formulas valid for fiber-reinforced plastics.    Know the conditions of use.    Consider effects of the molding procedure.    Use sandwich construction for maximum strength-to-weight ratios.    To increase rig

Reinforced Plastics Molding The term “ reinforced plastics moldings ,” as used here and in the plastics industry, refers to parts produced by impregnating a reinforcing material, in the form of cloth or mat, with a liquid thermosetting or thermoplastic resin, laminating the material into multiple layers, and curing with heat and pressure to form a dense, hard solid. It does not include materials discussed later as “high pressure laminates, which are available from stock as flat sheet, rod or tube. Materials . Resins used for reinforced plastics moldings include polyesters, phenolics, epoxies, melamines and silicons. Reinforcements include cloth or mat made from cotton, glass, asbestos and nylon. Glass reinforcements are most commonly used. Recently, there has been much interest in reinforcing thermoplastic resins, such as vinyls and acrylics, with cloth or mat made from thermoplastic synthetic fibers such as nylon. However, the bulk of reinforced plastics moldings today utilizes thermo

The plastic molding process cycle We are ready to study the actual plastic molding process cycle in the press room inasmuch as we have become familiar with not only the component parts of the mold itself but also the materials which are placed in them. The method of loading the cavities varies in accordance with the design and size of the part to be molded, the capacity of the die, and the style of mold. Preforms or powder can be used and sometimes both, but wherever possible it is more economical to load with preforms. In using compressed pellets special loading racks are usually constructed in order to bring the bench operator’s time down to a minimum. This rack or loader is made in such a manner as to permit the preforms to fit into proper sized receptacles and contains the number of impressions to correspond with those of the mold. The operator loads the rack during the time that the previous heat is being cured and is thence ready to place the entire load into the lower section o

casting Materials . Any resin available in liquid form can be cast . Castable resins include phenolics, polyesters, epoxies, silicones and acrylics. Types of molds. The type of mold used depends on the plastic, the size and shape of the part, and other design considerations. Draw mold 一No undercut is possible. Flutes and scallops must run in the direction of removal. Taper must be provided to break the vacuum and reduce friction. Castings are removed by force, and minimum wall thickness is critical, running from 1/8 in. on tiny parts to 3/16 in. on parts the size of radio cabinets. Split mold ~Undercuts may be provided if they do not prevent release from the separate parts of the mold. Minimum wall thickness is 3/16 in., and parts less than 0.1 lb are not commonly produced economically. Cored mold ~This type allows complexity of design, but is not usually feasible from a cost standpoint for parts less than 4 x 4 x 4 in. Molds require no taper. Minimum wall thickness is 3/16 in. Mold sh

Advantages and Disadvantages of Plastics The growth of the polymer industry in  the  latter half of the 20th century has been phenomenal and shows no signs of decreasing. If the advantages of synthetic polymers over competing materials such as metals and ceramics are considered, it is reasonable to predict that polymers will take an even greater share of the total materials market in the future. Some of these advantages and disadvantages will now be discussed. Strength and stiffness  in plastics should be discussed in terms of strength/weight or strength/cost ratios to be significant. unfilled plastics cannot approach structural metals in absolute values of strength or stiffness (where stiffness is proportional to modulus of elasticity). It also shows that plastics tend to be inferior to metals and to wood in stiffness/weight ratio (E/S g ). Only costly polymer composites (fiber reinforced plastics) approach alloy steels or hardened aluminum in strength/weight ratio (a/Sg). Increasing

plastic molding term Heat-distortion temperature (°F) at fiber stress of 264 psi (ASTM D 648) is a statement of the temperature required to permit an arbitrary standard amount of deflection by a standard load, in a test in which the specimen is subjected to a gradually increasing temperature. It is thus an indication of the ability of a material to retain its stiffness, or resistance to deformation, against the weakening influence of high temperature. A similar test，under the lower load of 66 psi (ASTM D 648), in which, of course, a higher temperature is recorded, has similar significance for material subjected to lighter load. Values determined by this second test are shown, for some materials, in the 6th column of the table. A large difference between heat-distortion temperatures in these two tests gives warning of the need to pay particular attention to designing so as to minimize the stress in service of articles subjected to heat. Impact strength , Izod {ft-lb per iti. of notch&