Molding techniques are diverse as different products require different types of molding techniques and equipment. For example, blow molds and rotary molds are suitable for making hollow plastic products such as bottles and cups, while rolling a product surface gives an attractive shine. When choosing a molding process, it is important to take into account the capabilities of the technique in relation to the desired final product. In addition, molding methods vary in terms of production time. Rotomolding typically processes slow-curing plastics, while the method itself is much slower than the immediacy of molding. The initial costs of injection molding can be high, considering the cost of the machines and molds themselves. Subscribe to America`s largest dictionary and get thousands of additional definitions and advanced search – ad-free! The molding machine must be able to hold the mold surfaces together with sufficient pressure to overcome the actual pressure in the projected area of the cavity perpendicular to the separation line. For example, if the projected surface of the cavity and wheel system was 10 square inches and the actual cavity pressure was 4000 psi, there would be a separation force at the demarcation line of 40,000 lbs or 20 tons. The clamping force of the machine must exceed this separation force, otherwise the mold will open, the separation line will be damaged, and the part will flash. As soon as the flashing occurs, it worsens and the damage to the demarcation line increases. Thermoforming is a thin or thermoplastic thermosetting plastic sheet that is pressed into the mold using a vacuum.
Plastic molding machines that perform thermoforming usually move a plastic plate onto a mold so that the plastic seals tightly with the pattern. The plastic is heated until it is malleable. Then a vacuum is applied, which sucks the plastic into the mold. Cutting devices prune excess plastic around the edges of the mold and the plastic is removed from the mold. The molded plastic is distributed on the line when a fresh plastic plate gets into position. An injection molding machine or (BrE injection molding machine), also known as an injection molding press, is a machine for the production of plastic products by injection molding. It consists of two main parts, an injection unit and a clamping unit. Type of defect (failure of a machine, injection mold or other equipment in a production line), Figure 4.36. Schematic representation of the cycle of the compression machine. (Image courtesy of Sacmi).
A precisely measured drop of resin, cut from a continuous extruded current, is placed in a transmission wheel. The same wheel also takes finished caps from the main wheel. In position (1), the distribution wheel is positioned above an empty cavity of the main wheel and lets the plastic fall into it. At position (2), the cavity rises vertically into the core and actual shaping takes place. In position (3), the plastic now spreads between the core and the cavity and climbs on the side walls of the cap under relatively low pressure. Therefore, there is no sprue point, which can be a great advantage if the surface of the cap needs to be decorated. During position (4), the fully formed cap now cools. In position (5), the cavity moves downwards, leaving the cap on the core. In position (6), a stripping ring presses the finished cap onto the timing wheel.
An additional transfer wheel then places the finished caps on a conveyor belt (Fig. 4.37). Punching presses are used. The plastic used can be TS sheet casting compounds (SMC) and punch-reinforced thermoplastic sheets (STX) (STX is a registered trade name; Azdel Inc., Shelby, North Carolina). It usually consists of a thermoplastic fiberglass RTP (Chapter 15). A frequently used classification method is the differentiation of machines according to the principle of compression of the molding material with additional subdivision by single-step compaction processes (e.g., compression molding) and two-step compaction processes (e.g., blowing, drive, vacuum, and airflow compression). Intermediate compaction process As experience shows, bentonite-bound molding sand has a higher post-compression strength (= dimensional strength) on the side on which the crushing force was exerted than on the opposite side. The measured tool thicknesses are proportional to the forces acting at each point. The diagram in Fig. 1 (Künkel Wagner Germany GmbH) illustrates this effect. The figure shows a mold that was first pre-compacted and then subjected to final mechanical compaction.
The measured resistance values decrease as you get closer to the sample plate. The reason for this is that the frictional forces on the pattern surface and piston wall reduce the force as the power transmission path increases in length. This gradual reduction in resistance is caused by the conduction of force through the molding sand at the resting angle of the mold sand. A finite component of this force is redirected to the surfaces bordering the sides of the molding sand, i.e. the piston wall and the contours of the pattern. This causes the gradual decrease in force on the transmission path (Fig. 2 Künkel Wagner Germany GmbH). This variation in dimensional force, that is, a higher dimensional force on the back and a weaker dimensional force on the side of the pattern, is a disadvantage.