Molds are the main elements in the conveyor production of metal, plastic and other injection molded products. They determine the shape of the structure of the manufactured objects. The quality of the final product depends on the accuracy of the production of molds.
What is a mold
Press form – a device for the formation of products of various designs from plastics, rubber, metals and other raw materials under the influence of pressure generated on injection molding machines. This is a container that follows the shape of the finished object, into which molten material is poured.
Molds are used during metal and plastic injection molding and investment casting, as well as polymer pressing. Due to the rather high price, they are most often used for mass and serial production.
Molds consist of parts, conventionally divided into two groups. The first is represented technological elements (working). They come into contact with the processed raw materials and are directly involved in shaping the products into the required shape. These include punches, dies, inserts, rings, threaded marks.
The second group includes details of constructive significance. When molding products, they do not come into contact with the material. Designed to ensure the operation of technological elements and are necessary for mutual fixation in a certain position of the mold parts, its closing and opening, as well as communication with the mold clamping unit of the injection equipment. These include clamps, ejectors, column guides, bushings, support bars, heating and cooling system, mold handles.
Classification of types of molds
According to the principle of operation, the molds are divided into:
- Direct pressing … Used to design objects of a simple form. Due to the high cost of production, they are not used for the manufacture of large batches of products. The design of the mold includes a die on which the raw material is laid out, and a punch for compacting it. The material sandwiched between the two elements becomes thinner and fills in all the recesses of the mold.
- Injection molding … The main advantage is the ability to manufacture large batches of products of various configurations and complexity. They are closed before pressing. Raw materials are poured into them using a separate loading chamber (upper or lower).
Molds for the manufacture of objects by casting are classified according to several criteria.
By the nature of use – removable and stationary. Forms of the first type in the process of forming products are not fixed on the plates of injection molding machines and are periodically removed from them in order to extract the finished product. Stationary molds are more common than removable molds. The pouring of material into them, as well as the extraction of manufactured products, is carried out without the need to remove them from the plate of the casting machine.
By the location of the plane of the part – with vertical and horizontal planes. Molds with one vertical surface are equipped with a split into two parts (punch and die) in one plane, which is perpendicular to the horizontal position of the clamping unit force. The containers with two vertical surfaces have a three-piece connector in two planes.
In molds with a pair of horizontal surfaces, a split is formed into three segments in two planes, which are perpendicular to the vertical position of the clamping unit force.
By the number of simultaneously formed objects – single and multi-cavity. In the former, one product is formed in one casting cycle, in the latter, several.
By the method of taking out finished products – with ejector pads or rods, without ejector and with pushing plate. From the molds of the latter type, objects are removed by means of compressed air or manually. The ejection liners, when molded, partially or completely form a certain surface of the product, and during ejection, they press on it until the product falls out of the mold. When extracting an object, the ejection rods press only on its individual areas.
Cold runner and hot runner molds gating system
Gating system – a structural element of the mold from reservoirs and channels through which the liquid material is fed into the casting cavity. When using a cold runner system, the runner does not heat up. When the formed casting cools down, it cools down and then falls out with it during or after the opening of the mold. Products with a cold channel system are distinguished by their reliability, low cost, ease of use and maintenance. But often these advantages are covered by the only drawback – the presence of an unnecessary sprue after the completion of each casting cycle.
When using molds with a hot runner system, the sprue is melted. The system is warmed up before the mold is put into operation, and during the entire production cycle the material in the sprue is maintained in a viscous-flowing state.
Molds with a hot runner system are characterized by high cost and complex design, require high power consumption and intensive cooling, and are difficult to maintain (heater breakdowns occur, impurities sometimes enter the hot channel cavity, non-heat-resistant polymer burns out, etc.). The main advantage is the absence of hardened sprues (although sometimes they are present), which fall out with the finished product during each casting cycle. This allows not only to save raw materials and prevent the formation of production waste, but also to use injection molding machines with a smaller injection volume, as well as to speed up the cooling process of manufactured objects.
Contact the managers of the KLONA company and order the production of samples of molds for casting products from any materials!