Stebro Mold is a Chinese plastic product design company, we mainly do plastic design and manufacturing for consumer products, electronic products, medical devices, housewares, and outdoor power equipment. Differ from other plastic design company or design agency, we not only can help you on new plastic product development, reverse engineering on the existing product, but also can help you to do the rapid prototyping, tool design, mold making, injection molding, and part assembly.
When you do the plastic design, you are faced with many constraints: time-to-market pressure, budget limits, material selection, “moldability”, tooling expense, minimal engineering changes, and tool qualification time. Early stage involvement with the supplier in the plastic development cycles is critical to a successful product launch, and it allows you to concentrate on the user research, user flow, visual design, and UX design while we focus on the designing of plastic products for injection moulding, improving product performance, and reducing time-to-market. Our goal is to help you with the design of plastic components that is to your specifications and also manufacturable.
When we do the plastic component design, the manufacturing process is an important consideration, the goal is to achieve a technically accurate design that functions well and can be cost-effectively manufactured. There are many ways to manufacture the plastic components, casting, compression molding, CNC manufacturing, extrusion, blow molding, thermoforming, rotational molding and injection molding. At Stebro Mold, we use injection molding as the main manufacturing process to bring plastic products to life.
The plastic product design process offers many versatile solutions and unique benefits, but it’s a practice that depends on the strength of its design. The injection molding part design must be developed to maximize the efficiency inherent in high-volume molding. Plastic product and mould design, tool building, plastic material selection, and Injection molding manufacturing process are the four key factors that go into making a high-quality plastic injection molded part. During both the injection and cooling stages of the manufacturing process, below are several factors that may affect the quality of the final product and the repeatability of the manufacturing process.
1, Use uniform wall thickness
Use a uniform wall thickness throughout the part (if possible) is essential to avoid thick sections. Wall thickness between 1.2 mm and 3 mm is a safe value for most materials. The next table summaries specific recommended wall thicknesses for some of the most common Injection Molding materials:
If sections of different thickness are required, make the transition as smooth as possible using a chamfer or fillet. In this way, the material filling will be much better.
The wall thickness specified typically should meet application requirements, moldability, and agency requirements. From a cost standpoint, the thinnest wall utilizes the least material and results in the fastest molding cycle times.
2, Rib Design
Ribs increase the moment of inertia in a design, which in turn will increase the bending stiffness of a part without adding thickness. Ribs should not exceed 70% nor lower 50% of part wall thickness; both scenarios can cause sinking in the surface of your part. We also have to pay attention to the height of the ribs, their location, and their degree of the draft for ease of ejection. Proper rib design involves five main issues: thickness, height, location, quantity, and moldability.
3, Boss design
A boss is included in the part design to accommodate part assembly through screws or pins. Generally, the outside diameter of bosses should remain within 2.0 to 2.4 times the outside diameter of the screw or insert. The thickness should be as same as the ribs. Thicker bosses will create sink defects as the part cools. A boss-rib combination can eliminate sink marks. By using ribs to connect the boss to a side wall, this method of part design will provide the strength necessary to support screws, inserts, etc. Also, adding small radii to break the sharp corners will also greatly reduce stress concentrations. And as with ribs, the boss also needs to have some draft to aid in ejection.
Normally, the boss hole should extend to the base-wall level, even if the full depth is not needed for assembly. If the boss hole is too long, we may have filling problems, knit lies or surface blemishes. If the boss hole is too short, we may have a sink mark on the part surface.
4, Draft Angles
Draft angles must be included in the design. It allows you to remove the part from a mold. The draft needs to be in an offset angle, parallel to the opening and closing of the mold. Surfaces formed by slides may not need draft if the steel separates from the surface before ejection. The mold finish, resin, part geometry, and mold ejection system determine the amount of draft needed. Generally, polished mold surfaces require less draft than surfaces with machined finishes. When you allow for as much draft as possible, you make it easier to release parts from the mold. One or two degrees of drafts, along with 1.5 degrees per .25 millimeters depth of texture should enough.
There are other factors need to be considered when you do the plastics engineered product design for the injection molding such as parting lines, threaded fasteners, snap-fit joints, living Hinges, and undercuts. Avoiding undercuts altogether might be the best option in molding design. Undercuts always add cost, complexity, and maintenance requirements to the mold. A smart redesign can often eliminate undercuts.
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