The structure of an injection mold depends on the injection molding machine type and plastic part structure. Due to the different use requirements, there are a wide variety of designs for the plastic injection molding part. And then, types of injection molds are various. While analyzing them, we find that each injection mold consists of many functional parts. Also, each mold component plays an important role. According to the different functions, an injection mold can be divided into these parts as follow.
1. Injection mold components
Forming mold parts
They are the parts that give the molding plastic material shape and size, that is, parts that make up the mold cavity. Generally, they include core, cavity, threaded core or ring, and embedded lump. After heating treatment in the injection unit, the molten plastic material is poured in there. When the material has filled the cavity, it requires an appropriate clamping force to keep mold close. To prevent mold swelling and ensure the smooth injection, we should choose a plastic injection molding machine with a large enough clamping force.
Runner system
It is the connection and transition channel between the nozzle of the plastic injection molding machine and the mold cavity. This system consists of the main runner, branch runner, gate and cold slug well. Before injecting the plastic material into the cavity, we need the help of a reciprocating screw machine, the most common injection unit. Unlike the traditional machine, it uses the same barrel to melt and inject. After heating, the molten plastic material enters the runner system through the nozzle of a reciprocating screw machine. It goes through the sprue bushing, then to individual runners.
To make sure the plastic keep molten state, there is hot runner to heat it. It is generally not necessary to open the flow passage to take out the condensate after the shutdown. Just heat the runner to the required temperature when starting up again. So, the hot runner system can save raw material and reduce the cost.
Guide parts
It is to ensure the accurate positioning of the movable and fixed molds during the mold close period. Sometimes, it can also keep the demolding mechanism flexible and stable. It generally consists of a guide post and a guide sleeve.
Ejecting System
This is a device for demolding custom injection molding plastics parts. There are many structural forms; the most commonly used are demolding structures such as ejector pin, spinal canal and push plate. As we all know, plastic molds are divided into upper and lower molds. The parting line is between them and on the product. To make the plastic part beautiful, we design the parting line to avoid the appearance surface as far as possible.
Parting and core pulling mechanism
For plastic parts with side holes and side protrusions, the mold must first be pulled out or parted laterally. This process is before the plastic part is pushed out, and it’s to ensure the smooth going of demolding. Broadly speaking, it is also a device for demolding the plastic part.
Temperature regulation system
In order to meet the mold temperature requirements in the injection molding process, we need it to adjust the mold temperature. The injection molding cycle times consist of clamping time, filling time, holding pressure time, cooling time and demolding time. Among them, the cooling time accounts for the largest proportion, about 70% to 80%. To reduce the cycle times and increase production efficiency, we need to control the cooling time. And an important factor is the wall thickness of plastic parts, which is usually between 1.2mm-3mm. For example, if we reduce the wall thickness from 3mm to 2mm, the cycle time can be decreased by 50% to 75%. Other factors also include mold material, cooling method, coolant flow, plastic material and so on.
Exhaust system
To exhaust the gas in the cavity, we usually set an exhausted groove on the mold’s parting surface. For small plastic parts with low exhaust volume, the parting surface can be used to exhaust directly. The matching gap between the ejector pin (or the core) and mold plate can play the exhausting role. And there is no need to set up an additional exhaust groove.
Other parts
Including support, fixed parts, positioning and limit parts, etc.
The injection molding process has many advantages. It can make complex parts, has excellent surface smoothness, high accuracy and low labor cost. If we design one mold with several holes, it has high volume machining capabilities and production efficiency. However, as we all know, the key tool for custom injection molding is the mold. So it’s not suitable for rapid prototyping. It may have a long production time from mold design, custom manufacture, and trial. CNC machining services, CNC turning and milling, grinding, EDM, and so on. Solutions from design, rapid prototyping, and high production runs can be provided.
2. Injection mold parts machining requirements
At first, all plastic mold components should meet the needs of the relating drawings. They include terms of material, processing accuracy, and heat treatment quality. Secondly, parts that make up the mold base should meet the specified machining requirements. The assembled mold base should be free to move and meet the specified parallelism and perpendicularity. Thirdly, of course, mold functions should meet the design requirements.
To identify the quality of plastic mold components, we should test the assembled mold under production conditions. Also, precision components company propose the solution according to the problems during trimming. This process continues until we make qualified injection mold parts.
3. Plastic injection mold manufacturing process
When receiving the mold making job, the first thing to do is analyze and understand the mold drawing. Suppliers learn mold structure features and operation principles. Also, the technical machining services requirements of injection mold parts and the relationship between the mold and the use are essential. Then, make some preparation according to the required materials in injection mold components drawing. For example, prepare blanks, necessary special tools, and prototypes. Next, custom manufacture the mold cavity and core. We can choose CNC machining, EDM, electroforming and cold extrusion for them based on different equipment.
After making them, it’s time for injection mold components suppliers to produce other parts. All parts should meet the dimensional accuracy and surface roughness required by the drawing and we will check it. Then, the fitter performs the necessary grinding, polishing and grinding. Next, assemble all plastic mold components according to the general assembly drawing. After trial and adjustment, we deliver it to use.
4. Injection mold parts producing features and attentions
4.1 Runner system
In general, manufacturers first make the runner system of the injection mold according to the drawing. But then they will also amend its size on the basis of molding situation of trial mold during the manufacturing process. After passing it, they continue the surface finishing services including quenching, polishing and shaping.
4.2 Demolding mechanism
In each working cycle, custom injection molding suppliers must take out the plastic part. Generally, forming mold is to make the part adhere to the movable mold. Then, we can take out the injection molding plastics through the machine tool’s mold opening action and using the ejector pin. Usually, the ejector mechanism should be reliable and flexible. And manufacturers trim the demolding agent in the trial mold. We won’t stop until the plastic part is not deformed and the appearance is not damaged after demolding. After trimming, it’s time to make the surface finishing for injection mold parts. The ejector pin, reverse push rod, and pull rod should all be head quenched. And after assembling the ejector pin, its end surface should be 0.05-1mm higher than the mold cavity plane or insert.
4.3 Cooling and heating device
Processing the position and size of the water hole according to the mold design. But during machining services, be sure not to damage the cavity. When the water hole passes through the insert, it should be sealed. The water hole pipe should be unobstructed during the mold trial. And when designing a mold with a heating device, pay attention to the heating rod’s insulation during custom manufacture. It’s to prevent the unsafe situation of electricity leakage.
4.4 Forming device
The cavity, core, and insert of the injection mold make up forming parts. During the manufacturing process, injection mold components suppliers make them according to drawings. First of all, producing the core, and then making the cavity according to it. In the processing, we try to match them at the same time. Until they are suitable, we begin surface finishing services including quenching, polishing or electroplating. Besides, there are also some other requirements. For example, the draft angle should be processed during CNC machining. Then, strictly prevent the injection molding parts from scratches, cracks, and bumps. And the surface roughness is below Ra0.20. When using inserts, the connection between them and the mold cavity must be close to prevent large gaps and cracks. Lastly, the injection molding components should meet the hardness requirements after quenching.
4.5 Guiding device
Machining guide parts according to the drawing requirements to ensure their matching accuracy and coaxiality. And the guide sleeve should be vertical to the supporting plane of the mold plate.