The improper design for the structure of plastic parts, the incorrect setting of injection molding technical condition, inappropriate design of mold feed system, temperature control system as well as ejector unit etc altogether result in overlarge remnant internal stress inside the products, and accompanied with insufficient rigidity of product structure and delayed treatment for the removal of stress, the final shape of products after ejection shall be inconsistent with mold cavity, manifesting such change of shape as warping, bending as well as distortion.Solutions:
1 Avoid excessive injection of melt.
2 Reduce injection rate, optimize design of feed system, and realize sound mold filling.
3 Reduce injection pressure and dwell pressure, shorten dwell time.
4 Properly improve mold temperature, reduce cooling speed, prolong cooling time in the mold,
optimize the relation between mold temperature control system and structure of products and try to achieve uniform cooling of products in the mold.
5 While ensuring proper retaining mode of plastic parts in the mold, increase draft and reduce ejection resistance.
6 According to the structural features of plastic parts, carefully analyze the ejection resistance and its distribution, use suitable ejection mode, properly arrange position of ejector pin, and try to achieve balanced ejection; increase number of ejector pins at places with large ejection resistance, and meanwhile expand section dimension of ejector pin, reduce ejection stress at contact area of product and ejector pin, whereby the deformation of products can be avoided during ejection.
7 Increase smoothness for the surface of cavity, and at the final stage of polishing for molding parts, the work should be done along the ejection direction of plastic parts to reduce ejection resistance.
8 Structurally try to avoid or reduce such cases as uneven wall thickness; sometimes due to the overlarge structure of products or the particularity in structure, such as the front and rear protecting casing or some inner decorative articles of cars, the deformation tendency shortly after ejection shall unavoidably exist, and therefore timely restriction measures should be made after ejection by employing steel stand, appliance or draw hook withal.
9 For important plastic parts, timely post-treatment can be made after ejection to reduce the influence of remnant internal stress on the precision of products’ shape and dimension.
10 When large deformation occurs to the products, major causes for such deformation should be analyzed. Usually optimization for the process of dwell pressure, i.e. through sectional and hierarchical dwell, can greatly relieve the degree of such deformation as warping.
Injection molding is a process that is comprised of injecting material into a mould. The material used can vary such as metals for die casting, thermoplastic, glass, thermosetting polymers and elastomers (a polymer with viscoelasticity).
The proposed material are then placed into a heated container, stirred well and then poured into the appropriate mold. The mixture is then allowed to cool so that it can harden within the cavity of the mold.
Typically, the product is designed by an engineer or industrial designer. It is then sent to a toolmaker or moldmaker. Depending on the design and project, a moldmaker uses a certain metal such as steel and aluminum. Precision machinery is used to form the structures of a certain part anywhere from tiny to massive sizes.
Importance of Accurate Designs
When it comes to injection molding, parts must be carefully designed so that the molding process is simplified. Otherwise, costs can be phenomenal. This includes the type of materials needed, special features of the parts, preferred shape and the capacity of the molding machine.
Regardless of the design precision, there will always be flawed parts when producing injection molding. And as for troubleshooting, faulty parts are carefully examined for specific defects. However, trials for finding potential defects are often done prior to completing the full production.
Plastic Deformations and Defects
Since the process of injection moulding is very complicated, there is always the chance of production issues. The problems can be caused from molding process or defects in the mold. Some of the deformation is caused by:
Deformations produced by inadequate cooling time
Residual stress that is caused in injection molding
Long-lasting stress during the process of demolding
Lingering stress from product thickness or in the forming shrinkage rates
Deformation Basics
Basically, molding deformation is in reference to bending, cracking and warping of the item. It can also be tiny wrinkles which can cause issues. The deformation is the residual stress of the product. As for designing and production, residual stress can be reduced by using the proper molding conditions. For instance, the cylinder and mould temperature can be increased. Also, when the material has a good flow, the injection pressure should never be too high. Generally, heat distortion temperature is below 10℃ (50 F°). It is also heated for about two hours so that internal stress is removed. Unfortunately, this method is not used often because of the high cost.
Also, the cooling water hole cannot be too shallow. Other solutions include:
Immediate – amply solidify and cool the product in the injection mold, increase barrel temperature, reduce injection pressure.
Short-term – injection mould needs uniform cooling.
Long-term – keep an even thickness in product design, use more large R curves (straight lines tend to warp), increase the stripping slope or raise the number of the ejection lever.
To avoid plastic components deformation issues during the injection molding process, the following measures can be taken:
1. Reasonable selection of plastic materials: According to the requirements of the product, plastic injection moulding manufacturer should choose suitable plastic materials to ensure that the melt fluidity and thermal expansion and contraction performance of the material meet the requirements.
2. Design a reasonable mold: During the mold design process, injection mould manufacturer has to consider the shape and size requirements of the plastic molding parts, design the mold structure reasonably, ensure uniform wall thickness and simple structure, and reduce the possibility of deformation.
3. Injection molding manufacturer should professionally control the heating and cooling process: The heating and cooling process should be uniform and stable, avoiding excessive temperature gradients to reduce deformation caused by uneven thermal expansion and contraction.
4. Control injection pressure and speed: Based on the characteristics of plastic materials and product requirements, plastic injection molding manufacturers should reasonably control injection pressure and speed to ensure uniform filling and filling, and reduce the possibility of injection molded plastic parts deformation.
Plastic injection molded parts deformation is caused by various reasons, including the properties of the material itself and problems during operation. Understanding these reasons and taking corresponding measures can effectively avoid plastic molding articles deformation problems, improve product quality, and reduce production costs. By continuously improving and optimizing the molding process, the quality and competitiveness of plastic products can be further improved.
Injection molding is one of the most essential technologies in modern manufacturing. This process enables the creation of products with complex shapes and high dimensional accuracy. However, without proper control, defects can occur easily, leading to losses in both time and material. Molding defects not only affect the product’s appearance but also compromise its mechanical integrity. In fact, the three most frequent issues found in plastic molding are shrinkage and warpage, air bubbles or voids, and weld lines. These problems often arise during the injection phase and can seriously impact the performance and durability of the final product.
Deformation is usually caused by uneven shrinking of the plastic parts, exclusive of the deformation due to demold. The common deformation of plastic parts starts with the use of glass-reinforced plastic molding, large-area parts or very slender products. These have the highest likelihood of this problem forming.
1. Improper cooling
Plastic parts are easily deformed due to improper cooling during the forming process. The structural design of plastic parts and the section thickness of all parts should be as consistent as possible. Enough cooling time must be maintained for the plastic parts in the mold. For the design of mold cooling system, attention should be paid to setting the cooling pipe at the place where the temperature rises and the heat is concentrated. For those parts that are difficult to cool, the cooling should be slowed down as much as possible so as to make the cooling of all of the plastic parts balanced.
2. Incorrectly designed mold pouring system
When determining the position of the gate, the melt should not directly impact the core and the force on both sides of the core should be as even as possible. For rectangular or flat plastic parts with large surface area, using molecular orientation, or plastic material that tends to shrink a lot, use of a film gate or multi-point gate should be adopted while side-gates should be avoided. For ring-shaped plastic parts, a disc gate or spokes gate should be used and side gate or spot-gate should be avoided. For shell parts, direct gate should be used instead of side gate.
3. Mold Release and Exhaust System Design
In terms of mold design, it is necessary to design the draft angle, position, and quantity of the ejection rod reasonably to improve the strength and positioning accuracy of the mold. For medium and small molds, the reverse deformation mold can be designed and manufactured according to the deformation rule. In mold operation, the ejection speed or ejection stroke should be slowed down appropriately.
4. Process setting is improper
The corresponding process parameters should be adjusted according to the specific situation.
the non-uniform orientation of the filler is often the main cause of product deformation. People usually adopt measures such as changing the gate position and adjusting the injection speed. It can be seen that there are five major factors that affect the deformation of injection products, mixing the three-color injection molding machine, in order to improve or eliminate the resulting product deformation. The influence of forming raw materials on product deformation mainly refers to the molecular structure of the resin in the raw materials and the types of fillers. At present, the forming methods are: forming raw materials, forming methods, product design, mold design, and injection molding process conditions. Gradually transition to the production of complex products in the home appliances, audio, automotive, office supplies and toys industries. On the basis of traditional injection molding, various molding methods such as ultra-high-speed injection molding and gas-assisted molding have been developed. Gas-assisted molding has made breakthroughs. This overcomes the technical limitations of traditional injection molding. In particular, the application of gas-assisted molding has changed from simple products such as handles and handrails to more and more types of products produced by gas-assisted molding. It not only saves plastic raw materials, eliminates surface sink marks, shortens the molding cycle, The advantages of simplifying product design, reducing mold costs, etc., are becoming more and more complex. The hybrid three-color injection molding machine, thereby reducing internal stress and product deformation, is an innovation to traditional injection molding technology. After gas-assisted molding is used, the overall part does not deform. Therefore, the pressure difference in the mold is reduced. At the same time, the injection pressure can be reduced. The influence of the wall thickness of the product on the deformation is usually different depending on the type of plastic, and it is an irregular S-shape. The surface of the thin plate is a smooth arc. At the same time, increasing the wall thickness appropriately also increases the rigidity of the product to some extent. The surface deformation of the thin plate is serious when the automobile parts bumper is formed by traditional injection molding. For amorphous plastics, the measures to reduce deformation during design are often to reduce wall thickness and improve the uniformity of wall thickness. Product design The influence of product design on deformation is mainly concentrated on product wall thickness, uniformity of wall thickness, and product shape. In terms of structural rigidity and other aspects, reducing wall thickness can reduce the volume shrinkage of the product. The purpose is to reduce the adverse effects of molecular orientation.
Injection moulding is a process that is comprised of injecting material into a mould. The material used can vary such as metals for die casting, thermoplastic, glass, thermosetting polymers and elastomers (a polymer with viscoelasticity).
The proposed material are then placed into a heated container, stirred well and then poured into the appropriate mould. The mixture is then allowed to cool so that it can harden within the cavity of the mould.
Typically, the product is designed by an engineer or industrial designer. It is then sent to a toolmaker or mouldmaker. Depending on the design and project, a mouldmaker uses a certain metal such as steel and aluminum. Precision machinery is used to form the structures of a certain part anywhere from tiny to massive sizes.
Importance of Accurate Designs
When it comes to injection moulding, parts must be carefully designed so that the moulding process is simplified. Otherwise, costs can be phenomenal. This includes the type of materials needed, special features of the parts, preferred shape and the capacity of the moulding machine.
Regardless of the design precision, there will always be flawed parts when producing injection moulding. And as for troubleshooting, faulty parts are carefully examined for specific defects. However, trials for finding potential defects are often done prior to completing the full production.
Plastic Deformations and Defects
Since the process of injection moulding is very complicated, there is always the chance of production issues. The problems can be caused from moulding process or defects in the mould. Some of the deformation is caused by:
Deformations produced by inadequate cooling time
Residual stress that is caused in injection moulding
Long-lasting stress during the process of demoulding
Lingering stress from product thickness or in the forming shrinkage rates
Deformation Basics
Basically, moulding deformation is in reference to bending, cracking and warping of the item. It can also be tiny wrinkles which can cause issues. The deformation is the residual stress of the product. As for designing and production, residual stress can be reduced by using the proper moulding conditions. For instance, the cylinder and mould temperature can be increased. Also, when the material has a good flow, the injection pressure should never be too high. Generally, heat distortion temperature is below 10℃ (50 F°). It is also heated for about two hours so that internal stress is removed. Unfortunately, this method is not used often because of the high cost.
Also, the cooling water hole cannot be too shallow. Other solutions include:
Immediate – amply solidify and cool the product in the injection mould, increase barrel temperature, reduce injection pressure.
Short-term – injection mould needs uniform cooling.
Long-term – keep an even thickness in product design, use more large R curves (straight lines tend to warp), increase the stripping slope or raise the number of the ejection lever.
thanks very much for sharing your experience on the issue of injection molding