Injection molding is a key manufacturing process that is used to make a variety of products like car parts, packaging materials, toys, and many others.
In molding process, usually a liquid thermoplastic in its liquified form, is injected into a mold die to form product or parts. As the material cools down, it hardens and gets the form of the mold, finally coming out as a finished product. This method enables the mass production of the same molded parts by the reusing of the mold many times. Although injection molding is very flexible and the most used process in many industries, not all product designs are perfect for this process. The factors like the material properties, the complexity of shapes, and the features that are to be produced must be carefully examined before the production starts.
This article demonstrates the key factors to consider for designing medical injection molds for fabricating high standard stringent parts for medical use. For example from disposable syringes to housings, and enclosure of medical machines, and components.
6 Considering Factors Designing Molds
Here are crucial considering factors for designing top quality standard medical injection molds. These includes;
1. Drafts Addition Makes Mold Design Easier
While designing a part for injection molding, you should take into account the fact that you should add draft to its faces. The draft is the angling of the sides of the part slightly instead of keeping them straight. This small modification can contribute to a number of advantages.
In mold making process, it’s quite easier to draw out cooled part from the mold. Moreover, it also aids in the avoidance of problems such as deformation. The angle of the draft that is required is determined by the factors like the depth of the cavity and the material that is being used. In general, design engineers applies about 1 degree of draft for every inch cavity depth. Nevertheless, it is a good idea to consult an injection molding expert to figure out the most suitable angle for your part, taking into account the material properties and shrinkage rates.
2. Consider Radii For Optimal Material Flow
The introduction of radii, or rounded edges, in your part design is a good thing when it comes to injection molding. Although some parts may appear to be better for sharp corners, radii can be a good thing for the molding process.
To begin with, the rounded edges facilitate the material to flow through the mold, thereby, making the molding procedure more smooth and efficient. Besides, the removal of sharp corners can be a boost to the part’s durability, thus, lowering the possibility of its breakage when in use. Thus, while not every part may have the rounded edges you would want, taking radii into account in your design will make the injection molded part more efficient and functional.
3. Carving Inside Parts Saves Budget
Coring out, or carving inside of a part, can be a cheap way to do injection molding. On the contrary, designers usually do not create fully solid parts but rather they core out the inside and use walls and ribs in a strategic manner to keep the strength.
Thus, by removing a part, its mass and material usage are decreased, which results in cost savings. Although the hollow interior is present, the walls and ribs designed in a proper way make the part strong and durable.
The main rule that should be followed while designing ribs for a molded part is that the rib-to-wall thickness ratio should be 40 to 60 percent of the part’s surface thickness. In a nutshell, this implies that the ribs should be about half as thick as the solid part of the area that has not been cored out.
Besides the fact that coring out is cheaper and the weight of the parts is reduced, coring out also helps to solve the problems of sink marks and stresses, thus, the injection molded parts will be better.
4. Understand Inside & OuterCut Requirements
Is your injection molded part supposed to have undercuts or not?It is a question that often comes up during the design process. Although easier to mold, simpler designs are not as effective as the complex ones that can improve the performance of the final part.
The undercuts are the areas in a part that are difficult to remove from the mold because of their shape and position. To make the mold for undercuts, the mold may be made of several parts that will enable the side-pull motion. The complexity that is inherent in the design of these cars naturally leads to the increase of the manufacturing costs.
Engineers faced with this decision have two choices: the design should be simplified so that the undercuts are eliminated or the existing design is incorporated while managing the complexities during the molding process.
5. Wall Thickness of Materials Vary From Type To Type
The wall thickness of a part is decided by the factors that include the structural requirements, brittleness, and the most crucial one, the material that is going to be used.
Fortunately, the recommended wall thicknesses for common injection molding materials are available for manufacturers; therefore, they do not have to go through the tedious trial and error process.
6. Batch Volume
The number of parts required is the most important aspect of the mold making. The necessity of increasing the number of molds and their complexity is also a consequence of the fact that they have to be capable of withstanding repeated use over extended periods of time. However, smaller-volume projects might be more suitable for simpler molds, which produce lesser volumes of the product. In most cases, more complicated and stable molds are needed for bigger production runs. Nevertheless, we must keep in mind that lower volumes tend to have a higher cost per part because of the expenses connected with designing and manufacturing complicated molds.
Conclusion
To sum up, injection molding part designing is a multidimensional task that requires a deep knowledge of all the disciplines involved. Skilled mechanical designers may not have the industrial knowledge needed to judge whether or not their designs can be manufactured satisfactorily. Hence, it is strongly advised for designers of parts to work in close partnership with mold makers and molders in the early stage of the design process. The collaboration not only ensures the production of parts that are high quality, functional and cost-effective, but it also reduces the need for revisions.
FAQ’s
Q1. How material impacts in injection molds?
When it comes to appropriate material selection, the design manufacturers must consider the chemical and physical characteristics of intended materials. Because, inefficient material could lead to consequences like; shrinkage, warping, and sinks marks, ghost effects on product being molded.
Q2. What are the basic engineering design considerations for mold designing?
The factors contributes to this includes; part size, volume needed, desired properties, application use, and other crucial factors like; capacity, and material of injection molding mold.
Q3. Which plastics are used in designing injection molding molds?
Well it depends upon intended application of end-use or after market product. In some situations, when lightweight interior or aesthetic parts are required, usually design manufacturers use silicon made molds. Alongside, divers variety of engineered grade plastics are used in mold making process including; abs, polyurethane.