In this part of the basics of mold design, we will cover the following:
Before learning how the tool design works, here is a basic overview of how the entire plastic production process works.
It is important to note that a single company need not necessarily do all the steps mentioned here. Some processes can be done by partner companies or even outsourced.
1. Sales Team: The sales team takes the product from the original equipment manufacturers (OEMs) or product design department and quote an amount for the mold. They handle everything right from purchasing and selling the mold to the delivery time and more. As soon as the customer is satisfied with the price and confirms the purchase, the order is placed.
2. DFM: Next, the CAD model goes to the Design for Manufacturing (DFM) team. This department checks the feasibility of making the bold based on the CAD diagram.
The product design team may not be aware of the problems that might occur in mold manufacturing. So, the DFM department enlightens the customer about the potential issues during production.
3. Mold Flow: The purpose of the mold flow department is to identify the right inlet points for the molten material. The team will specify the location of the gate.
The mold flow department will analyze how the flow of material will take place by using simulation software tools. They also do cooling and warpage analysis (a defect in plastic components).
4. Tool Design: The tool design team gets the gate point location as input from the mold flow team. This department decides the cooling channel location, location of ejector pins, core cavity separation, parting lines, and more.
5. CAM Programming: The computer-aided manufacturing (CAM) programming team writes the programs for the tool.
6. The materials for the tools are ordered as per the specifications given by the tool design team.
7. Once that is done, the actual manufacturing of the tool starts using machines like CNC.
8. Inspections include checking if the right dimensions have been achieved or not and whether the dimensions are within the tolerance levels.
9. All the parts of the mold, like the core cavity, guide pillar, and everything else is assembled.
10. The entire tool is then assembled into the molding machine.
11. The production of plastic parts begins.
12. The manufactured parts are then checked using tools like Coordinate Measuring Machine (CMM), which reviews the dimensional accuracy of the component.
13. Finally, the parts can be shipped after they pass the quality checks.
The basics of mold design are incomplete without learning about the components of the mold itself. Below is a picture that gives an idea of the working of the injection molding process using a two-plate mold.
1. Cavity Plate and Cavity Back Plate: On the right-hand side, you can see the cavity plate and the cavity backplate. In a two-plate mold, the cavity plate is fixed. Hence, only the core side (the left side) of the system moves.
2. Guide Pillars and Guide Bush: On top of the cavity, the plate is the guide pillars. They are used in aligning the core and the cavity. Guide pillars will always be present on the cavity side of the mold, whereas the guide bush will be present on the core side. The length of the guide pillar should always be more than the core length so that it aligns before the core and the cavity align.
3. Sprue and Sprue Bush: On the right side, you can also see the sprue and the sprue bush. The sprue is a channel with a large diameter through which the material enters the mold.
The sprue is tapered outwards to facilitate the easy removal of the part from the mold. The molten material flows from the sprue to the cavity, leaving behind solidified material in the sprue region. If the sprue were straight, it would scrape the surface of the sprue bush, making it more difficult to remove. For the same reason, the components are given drafts.
You might also notice a separate sprue bush around the sprue. This is because the material injected from the nozzle to the sprue is quite hot, and the material of the sprue bush is specifically pre-hardened to handle the heat.
4. Register Rings: The register rings are provided for the alignment of the entire tool with the molding machine.
5. Core Plate and Core Backplate: On the left of the cavity plate, you can see the core plate and the core backplate. These move to the right and get attached to the cavity plate.
The material is injected into the region between the core and the cavity. The injected material is allowed to cool for a while. When the part solidifies, the core retracts.
6. Ejector Pins: The ejector pics come into play after the core retreats. They are used to eject the molded part.
You now understand how the new product development process works, along with the different departments in the molding industry and important mold components.
In the next part of the basics of mold design, we will take a look at:
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