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11.10.2022

What Is Precision Molding?


It’s all about how you build the tool to build the part.’ ~ Alan Lipman, CEO Romar


Precision molding is the process of molding either silicone or plastic in a particular way, with a very high degree of accuracy and tolerance, to ensure repeatability in long machine runs.


As specialists in precision molding, we are able to mould these materials to achieve the required result, using the most cost effective methods.


With over 50 years experience in building precision moulds, we have the technical, engineering and creative expertise required to meet every precise standard. Romar is acknowledged and applauded worldwide for producing injection molded components of the very highest quality and precision.


Our experience in molding has seen products ranging from precision miniature components with micron dimensions to large components weighing in excess of 16kg.


If you're ready to collaborate with a team that understands the precise requirements of precision moulding and micromoulding, let Romar provide you with an innovative, end-to-end design and manufacturing solution. Contact Romar today.


What is metal casting?


Metal casting is the process of making objects by pouring molten metal into an empty shaped space. The metal then cools and hardens into the form given to it by this shaped mold. Casting is often a less expensive way to manufacture a piece compared with machining the part out of a piece of solid metal. There are many metal casting methods to choose from. What type of casting is most efficient depends on the metals used, the size of the run, and the complexity of the casting.


Before starting a production run, it is helpful to know some of the terms and methods from the foundry floor.


Casting terminology


Casting mold


A mold is a cavity in a material that receives liquid metal and produces a cooled object in the shape of that cavity. Molds can be simple. The forms used to create ingots of metal are like loaf pans, with the metal simply poured inside and left to cool. Most molds are for more complex shapes and are based on a pattern. The pattern imprinted into a split mold. Half of the pattern is imprinted on one side of the mold and half on the other, and then the halves are clamped together before the mold is filled. By making the mold in two parts, the pattern can be withdrawn before filling. These molds can be made with a horizontal split


Cope and drag


In horizontal molding, the top half of the mold is called the cope, and the bottom half is called the drag.


Swing and ram


In vertical molding, the leading half of the mold is called the swing, and the back half is called the ram.


Molding cores


If a mold is supposed to have internal spaces or holes, a core is often made. These cores are shaped like the internal space. The cores are usually held in place by extending past the casting and being held in place through core prints, which suspends the core like a bridge between two banks. The empty spaces around the core will fill with metal, and the core will be removed from the final casting, leaving a hole where it once was. If the core is very long, it might be supported by chaplets to prop it up. These are usually made of the same metal as the final casting as they sit in the space that will flood with material and become part of the final casting.


Dimensional tolerance


One of the important factors in choosing a casting method is dimensional tolerance. Dimensional tolerance is the variation acceptable in the size of the final product. Metal shrinks when cooling, and the type of casting influences by how much. If a product needs to be precise, a client may want a casting method that produces near net casting. This means that the product is very close to being the right size when it is shaken out of the mold.


Surface finishing


Another consideration is surface finishing. How granular, bumpy, or rough can the surface of the casting be? What is acceptable for a cast iron pan is not acceptable for a wedding ring. Very smooth metal surfaces are usually created with machining, which is an extra cost: if shiny and smooth is a desired outcome, choosing a casting method with a finer finish may reduce machining costs.


What is injection moulding? – definition, types and materials
Injection moulding is a manufacturing process that allows for parts to be produced in large volumes. It works by injecting molten materials into a mould (or ‘mold’ in the United States). It is typically used as a mass production process to manufacture thousands of identical items. Injection moulding materials include metals, glasses, elastomers and confections, although it is most commonly used with thermoplastic and thermosetting polymers.

How does it Work?


The first stage of injection moulding is to create the mould itself. Most moulds are made from metal, usually aluminium or steel, and precision machined to match the features of the product they are to produce.


Once the mould has been created by the mould-maker, the material for the part is fed into a heated barrel and mixed using a helical shaped screw. Heating bands melt the material in the barrel and the molten metal or molten plastic material is then fed into the mould cavity where it cools and hardens, matching the shape of the mould. The cooling time can be reduced through the use of cooling lines that circulate water or oil from an external temperature controller. Mould tools are mounted on plate moulds (or ‘platens’), which open once the material has solidified so that ejector pins can eject the part from the mould.


Separate materials can be combined in one part in a type of injection moulding called a two-shot mould. This technique can be used to add a soft touch to plastic products, add colours to a part or produce items with different performance characteristics.


Moulds can be made of single or multiple cavities. Multiple cavity moulds can have identical parts in each cavity or can be unique to create parts of different geometries. Aluminium moulds are not best suited to high volume production or parts with narrow dimensional tolerances since they have inferior mechanical properties and can be prone to wear, deformation and damage due to the injection and clamping forces. While steel moulds are more durable they are also more expensive than aluminium moulds.


The injection moulding process requires careful design, including the shape and features of the part, the materials for the part and the mould and the properties of the moulding machine. As a result, there are various considerations that need to be taken into account when injection moulding.


When is Injection Moulding Used?


Injection moulding is used to make a range of widely used products, including common plastic items like bottle tops as well as remote control casings, syringes and more. It is also commonly used for manufacturing larger items such as car body panels.


Injection moulding is mainly used where there is a need to manufacture many thousands or millions of identical parts from a mould.


The main advantage of injection moulding is being able to scale up production to produce a large number of parts. Once the initial costs of the design and the moulds have been covered, the price of manufacturing is very low. The cost of production drops as more parts are produced.


Injection moulding also produces minimal wastage when compared to traditional manufacturing processes like CNC machining, which cuts away excess materials. Despite this, injection moulding does produce some waste, mainly from the sprue, the runners, the gate locations, and any overflow material that leaks out of the part cavity (also called ‘flash’).


The final advantage of injection moulding is that it allows for the production of many identical parts, which allows for part reliability and consistency in high volume production.


While injection moulding has its advantages, there are also a number of disadvantages with the process.


Up-front costs can be high for injection moulding, particularly with regard to tooling. Before you can produce any parts, a prototype part needs to be created. Once this has been completed, a prototype mould tool needs to be created and tested. This all takes time and money to complete and can be a costly process.


Injection moulding is also not ideal for producing large parts as a single piece. This is because of the size limitations of injection mould machines and the mould tools. Items that are too large for an injection moulding machine’s capability need to be created as multiple parts and joined together later.


The final disadvantage is that large undercuts require experienced design to avoid and can add even more expense to your project.

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