In the field of plastic product production, injection molding is one of the most common manufacturing processes. However, if the design process is not well considered, it is very easy to encounter problems such as demolding difficulties and part deformation. These problems will not only seriously affect production efficiency, but also greatly increase production costs. As Elite Mold Tech, which has been deeply involved in the mold manufacturing industry for many years, today we will share with you the top 10 taboos that need to be vigilant in injection molded parts design to help you avoid common traps in the design process.
Taboo 1: Uneven wall thickness
In order to save materials, many designers will design the wall thickness of injection molded parts to be thick and thin. For example, a customer designed a plastic shell with a wall thickness of 3mm in some places and only 1mm in some places. As a result, during injection molding, the thick wall cooled slowly and the thin wall cooled quickly, causing the parts to be severely deformed and unable to be used at all. The correct approach is to keep the wall thickness consistent as much as possible. If it really needs to change, the transition should also be smooth.
Taboo 2: No demolding slope
The demolding slope is like "opening a smooth slide" for the plastic part, allowing it to easily escape from the mold. A customer once designed a mobile phone holder without considering the demoulding slope at all. After production, the part was stuck in the mold and could not be taken out. Forced demoulding also caused scratches and deformation on the surface of the part, and finally had to modify the design. Generally speaking, the minimum demoulding slope should be set between 0.5°-1°.
Taboo 3: Unreasonable undercut design
The undercut structure can realize the snap connection between parts, but improper design will cause big trouble. A customer designed a toy part with too complicated undercut part, which made the mold unable to open and close normally and could not be produced at all. Reasonable undercut design either adopts a detachable slider mold structure or simplifies the undercut shape to ensure that the mold can be demoulded smoothly.
Taboo 4: Improper rib design
The ribs are designed to enhance the strength of the parts, but if they are designed too thin and too dense, the plastic melt will not flow smoothly during injection molding, and short shots are prone to occur. For example, a customer designed an electronic equipment bracket with thin and dense ribs. After injection molding, a large number of cavities appeared inside the bracket, and the strength did not meet the standard at all. The height of the reinforcing rib is generally not more than 3 times the wall thickness, and the thickness is 0.5-0.7 times the wall thickness.
Taboo 5: Missing fillet
Right angles and sharp corners are prone to stress concentration during the injection molding process, causing parts to crack. A customer previously designed a plastic storage box with right angles, which cracked after a short period of use. Adding appropriate fillets during design can not only avoid stress concentration, but also make the plastic melt flow more smoothly and improve product quality.
Taboo 6: Wrong demolding direction
The demolding direction determines whether the part can be smoothly ejected from the mold. A customer once designed a part whose demolding direction was inconsistent with the mold opening direction. As a result, the produced parts could not be demolded at all and had to be redesigned. Before designing, be sure to communicate fully with the mold manufacturing team to determine the correct demolding direction.
Taboo 7: Ignoring shrinkage
Different plastic materials have different shrinkage rates. If this is not considered during design, the size of the produced parts will deviate greatly from the design size. For example, when using polypropylene (PP) material for injection molding, if sufficient shrinkage space is not reserved, the produced parts may be too small and cannot be assembled normally with other parts. Therefore, before designing, you must understand the shrinkage rate of the selected material and compensate for it in the design size.
Taboo 8: Improper gate position
The gate is the entrance for the plastic melt to enter the mold cavity. If the position is not selected well, it will cause defects such as bubbles and weld marks on the parts. A customer designed a large plastic panel with the gate position set in the corner. After injection molding, a large number of bubbles appeared in the middle of the panel and the surface was uneven. A reasonable gate position should ensure that the plastic melt fills the cavity evenly to avoid problems such as trapped air.
Taboo 9: Insufficient exhaust design
During the injection molding process, the air in the mold cavity needs to be discharged in time, otherwise it will cause problems such as burning and lack of material on the parts. A precision plastic part designed by a customer does not have enough exhaust grooves. After injection molding, black burnt marks appear on the surface of the part and it is completely scrapped. Therefore, when designing, it is necessary to reasonably set the exhaust grooves or use breathable steel materials to ensure that the air can be discharged smoothly.
Taboo 10: Ignoring post-processing process requirements
Many people think that there will be no problem after injection molding. In fact, post-processing has a great impact on the performance of parts. For example, some parts with high dimensional accuracy require annealing after injection molding to eliminate internal stress. A customer produced high-precision plastic gears without annealing. After a period of use, the gear size changed, causing equipment operation failure.
Successful case sharing: How professional design helps improve production quality and efficiency
In the field of injection molding design, many companies have successfully avoided common design problems and achieved outstanding results through clever planning and precise execution. As a professional mold manufacturing service provider, Elite Mold Tech has witnessed and participated in many such projects. Here are a few typical cases for you.
Case 1: Optimization design of plastic shells for consumer electronic products
A consumer electronics manufacturer plans to launch a new smart speaker. The design of its plastic shell is directly related to the product's appearance, texture, durability and production cost. In the early stages of design, the manufacturer found us. At first, their design had uneven wall thickness. Some areas had a wall thickness of 4mm, while some thin walls were only 1.2mm. This not only increased the material cost, but also easily caused serious deformation of the product during injection molding due to differences in cooling speed.
After our design team intervened, we communicated closely with the customer and replanned the wall thickness. Through optimized design, the overall wall thickness was controlled at about 2.5mm, and a gradual transition method was used to handle the area with varying wall thickness. At the same time, the reinforcement ribs were reasonably arranged inside the shell, which not only enhanced the strength of the product, but also did not hinder the injection molding process. In terms of the demoulding slope, we designed it to be 1° according to the standard to ensure that the product can be smoothly ejected from the mold.
The final result was satisfactory. The plastic shell of this smart speaker was smoothly demoulded during the production process, with almost no deformation problems. The yield rate increased from the initial estimate of 60% to more than 90%, and the material cost was reduced by about 20%. It successfully helped the customer's product to be quickly launched to the market and won a good reputation.
Case 2: Clever design of undercut structure of automotive parts
The automotive industry has extremely high requirements for the precision and reliability of injection molded parts. An automotive parts supplier needed to design an automotive interior buckle with a complex undercut structure, which not only ensured firm installation, but also ensured smooth molding during mold manufacturing and injection molding production.
Our Elite Mold Tech engineers worked with customers to optimize the undercut structure many times. The original overly complex one-piece undercut design was abandoned, and a split slider mold structure was adopted. The undercut part was split into several relatively simple structures. Through the specially designed slider, the slider can be smoothly pulled out after the injection molding is completed to achieve product demolding. At the same time, we fine-tuned the overall size and shape of the buckle, greatly reducing the difficulty of mold manufacturing while ensuring the function.
The successful implementation of this project not only allowed the automotive interior buckle to be successfully put into mass production, but also increased the mold life from the originally expected 50,000 times to 100,000 times, greatly reducing the customer's mold replacement cost, improving production efficiency, and providing a strong guarantee for automobile manufacturers to supply high-quality parts on time.
Case 3: High-precision design and manufacturing of injection molded parts for medical equipment
Medical equipment has almost stringent requirements on the precision and quality of injection molded parts. A medical equipment company commissioned us to design and produce a precision injection molded part for medical testing equipment. Although the injection molded part is small in size, it has a complex internal structure, contains multiple tiny reinforcing ribs and fine assembly holes, and has extremely high dimensional accuracy requirements, with a tolerance range of ±0.05mm.
In order to meet customer needs, we used advanced simulation analysis software in the design stage to accurately simulate the flow of plastic melt in the mold, the cooling process, and the product shrinkage rate. According to the simulation results, the layout and size of the reinforcing ribs were carefully adjusted to ensure product strength while avoiding injection defects caused by improper rib design. In terms of gate location selection, after multiple simulations and tests, the best location was determined so that the plastic melt can evenly fill the cavity and reduce the generation of bubbles and weld marks.
During the manufacturing process, we rely on high-precision processing equipment and a strict quality control system to ensure that each injection molded part meets the design requirements. The final medical device injection molded parts fully meet customer requirements in terms of dimensional accuracy, complete internal structure, and high surface finish. They are successfully used in medical testing equipment and provide reliable parts support for the medical industry.
These successful cases fully demonstrate the key role of correct injection molded parts design in production. With a professional design team, rich industry experience, and advanced manufacturing technology, Elite Mold Tech is able to provide customers with a full range of high-quality services from design to production. If you have any questions or needs in mold manufacturing and injection molded parts design, please feel free to contact us at contact@elitemoldtech.com! Let us work together to create high-quality molds and plastic products!
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