Fast product delivery and on-budget production are two crucial elements of manufacturing. Manufacturers and injection molders agree that the design for the manufacturing phase has the most impact on production results. Mold flow analysis and prototype development, part of the part design process for plastic injection molding, can lead to high cost and time efficiencies.
It involves several considerations to ensure that plastic parts are manufacturable from the outset, which can significantly impact critical variables. It’s critical to collaborate with your molder this early on to uncover design changes to improve the efficiency of part production and performance. Although some manufacturers don’t account for design changes in their timelines, early collaboration may reveal design changes that can be implemented to improve efficiency. A few common design-for-manufacturing elements include:
| Materials | Manufacturers often select a standard grade of plastic for a similar application or based on supplier recommendations. However, these resins may not be optimal. In plastic selection, there are many factors to consider, including: Heat: The stress created by normal and extreme conditions of use and during the assembly, finishing, and shipping processes. Chemical resistance is a property affecting part performance when solids, liquids, or gases are in contact. Agency approvals: Standards developed by the government or the private sector for properties like heat resistance, flammability, and mechanical and electrical performance. Assemblage: During the assembly process, the plastic is bonded, mechanically fastened, and welded. Finish: Ability of the material to come out of the mold with the desired appearance values, such as gloss and smoothness. Price: The price of resin, costs of manufacturing, maintenance, assembly, disassembly, and other costs to reduce labor, finishing, and tools. Access: The availability of resin from the point of view of the amount required for production. |
| Draft | A draft angle makes it easier to remove a cooled, finished part from a mold when it is cooled. Draft angles are an essential component of injection molding. Minimizing friction during the part release process can achieve a uniform surface finish and reduced wear and tear on the mold. An angle of the draft is measured according to the direction of pull. Draft angles of at least 0.5° for the cavity and 1.0° for the core are suggested by most design engineers for parts with sufficient draft. The tool must also be designed with more draft if a textured surface is desired and steel shut-off surfaces. |
| Wall Thickness | The wall thickness of injection molded parts is also an important consideration. An injection molded part with a proper and uniform wall thickness is less prone to structural and cosmetic problems. Most resins have a typical wall thickness ranging from .04 – .150. Yet, it is recommended that you obtain thickness specifications for your material(s) of choice by consulting with an injection molder/design engineer. Wall thickness should be analyzed during the design process to ensure that parts don’t sink, warp, or become non-functional. |
| Ribs | As ribs are used to reinforce the walls of your injection molded parts without increasing their thickness, they are a valuable component in injection molded parts. Rib design should reduce mold flow length when designing complex parts and ensure that the ribs are appropriately connected to increase the part’s strength. Ribs should not exceed 2/3 of the wall thickness, depending on the material used. WIDE ribs may create sinking and design problems. It is typical for a design engineer to core out some fabric to reduce shrinkage and keep the strength. If the height of the ribs exceeds 3 times the wall thickness, this could result in the part being short/unable to be filled. Rib placement, thickness, and length are critical factors in determining the viability of a part in its early design phases. |
| Gate | In a mold part, a gate is a point at which liquid plastic flows into it. Injection molded parts have at least one gate, but they are often produced with multiple gates. Runner and gate locations influence polymer molecules’ orientation and how the part shrinks during cooling. As a result, gate location affects your part’s design and functionality. Part. Injection Molding Runner and Gate. The gate should be placed at the end of a long and narrow part if it must be straight. It is recommended to have a gate positioned in the centre of parts that must be perfectly round. With the input of your injection molding engineering team, you will be able to make optimal decisions regarding gate placement and injection points. |
| Ejector Pin | Mold ejector pins (located on the B-side/core of the mold) are used to release plastic parts from a mold after being molded. The design and positioning of ejector pins should be considered as early in the process as possible. This is even though they are usually a relatively minor concern in the early design phases. Indentations and marks can result from improperly placed ejector pins, so proper placement should be considered in the early phases. Ejector pins are typically located at the bottom of side walls, depending on the draft, texture, depth, and type of material. You might be able to confirm that your initial ejector pin placement was correct by reviewing the design. In addition, you may be able to make further changes to improve production outcomes. |
| Sink | Sink marks can appear on the injection molded plastic part during injection moulding when the material shrinks more in thicker areas such as ribs and bosses. In this case, the sink mark is caused by thicker areas cooling slower than thin ones, and the different cooling rates lead to a depression on the adjoining wall. Sink marks are formed due to several factors including the processing method, the geometry of the part, the material selection, and the tooling design. The geometry and material selection of the part may not be able to be adjusted based on its specifications, but there are several options to eliminate sink areas. Sinking can be influenced by tooling design (e.g., cooling channel design, gate type and gate size), depending on the part and its application. The manipulation of process conditions (for example, packing pressure, time, phase of packing, and conditions) can also reduce sink. Further, minor tool modifications (e.g., foaming or gas assist) can reduce sink. It is best to consult your injection molder regarding the most effective method to minimize sink in injection-molded parts. |
| Parting Lines | For more complex parts and/or complex shapes, it is important to note where the parting line is located. Having your design shared with your injection molder can greatly influence your finished product’s production and functionality since designers and molders tend to evaluate parts differently. The challenge of parting lines can be addressed in several ways. It’s important to be aware of the importance of the parting line when designing your initial concept, but you are not limited to that. You may be able to locate other possible locations using CAD software and mold flow analysis. When you work with an injection molder, they keep your part end use in mind and help you determine where the parting lines should be placed. |
| Special Features | It is essential to design plastic parts so that mold tools can open them and eject them without difficulty. Injection molds release parts by separating the two sides in opposite directions. A side action may be necessary in some instances, where special features such as holes, undercuts, or shoulders prevent the release from occurring. Coring is pulled in a direction opposite that of mold separation as a side action. In some cases, costs may increase due to this flexibility in part design. When designing and developing a product, you were having the right injection molder, and engineer on your side is essential. You can avoid many issues by working with them. In integrating these elements into your product design process and working with a plastics engineer who has experience with these materials, your goal will be to get your product to market as quickly and cost-effectively as possible. |