The basics of troubleshooting in plastics processing pdf

Check the flow rate if its sufficient for cooling the hopper locking device, adjust the flow rate if necessary. Reduce the cycle time to increase plastic that is passed by the cylinder device. Using the incorrect screw surface speed and back pressure, causing the molten plastic over cut. Use minimum back pressure and the correct use of the screw surface speed 6. Use a correct type of screw design in the process of plastic. Use a lower rate of a extrusion screw. Mold 1. Grease or oil occur within the mold.

Mold and nozzle should be removed and thoroughly cleaned. Gate is too small. Increase the gate size. Wall injection molded too thin, so that plastic flow is not sufficient to pass through, so it causes no degradation.

Check the correctness and consistency of wall thickness, if necessary, will be modified. Hot runner mold produces impurities. The hot runner mold aggregates tube completely remove and clean.

Plastic 1. PVC or other heat-sensitive plastic appear impurities. Check the source of impurities, especially with PVC manufacturing and conveying plastic pipe part. Excessive heating of the back using the previous materials. Strict inspection after the separation of impurities in materials. Due to the lack of room cleaning or plastic dry cause plastic blended with burnt particles.

Dry cleaning and reuse of some materials. Poor plastic flow characteristics caused by Insufficient lubrication of plastic. Adda certain amount of external lubricant such asZeng0. How to recruit Mold and Process Technicians?

You are not alone with your difficulty finding talented injection molding technicians. With the industry down turn cycles and mass closing of many injection molding companies most of the junior The benefits of building tools and mold parts in China I have lived and worked in China for many years and I have seen the Good, Bad and Ugly as it pertains to tool makers and molders. Most of the horror stories I have heard about Chinese Toolmakers How to define the viscosity curve of injection molding?

This means only injection no holding. Language English Chinese Menu. Posted on: Nov. The article aims to plastic injection molding problems and solutions, mainly as follows: Analyze the causes of these problems generated from raw materials, plastic parts or mold design, molding processes, etc.

Short Shots Short shots are a phenomenon in which the mold cavity cannot be completely filled. Causes: 1 Die temperature, material temperature or injection pressure and speed are too low 2 Uneven plasticization of raw materials 3 Poor exhaust 4 Insufficient liquidity of raw materials 5 The part is too thin or the gate size is too small 6 Polymer melt is prematurely cured due to unreasonable structural design Remedies: Material: Use more fluid materialsMold design: 1 Fill the thick wall before filling the thin wall to avoid the retention phenomenon.

Process: 1 Increase injection pressure and injection speed to enhance shear heat 2 Increase the amount of injection 3 Increase material cylinder temperature and mold temperature 2. Air Traps Air traps is that air is trapped in the cavity to create bubbles in the part. Remedies: Structural design: Reduce thickness inconsistency and try to ensure uniform wall thickness Mold design: 1 Add a vent at the last filled place 2 Redesign the gate and runner system Process: 1 Reduce the injection speed of the last stage 2 Increase the mold temperature 3.

Brittleness Brittleness is that the plastic part is easily cracked or broken in some place Causes: 1 Dry conditions are not suitable; use excessive recycled materials 2 Injection temperature setting is wrong 3 The gate and runner system settings are not appropriate 4 The melting mark strength is not high Remedies: Material: 1 Set appropriate drying conditions before injection molding 2 Reduce the use of recycled materials and increase the proportion of raw materials. Mold design: Increase the size of the main runner, branch runner, and gate Machine: Choose a well-designed screw to make the temperature distribution more uniform during plasticization Process: 1 Reduce the temperature of the material cylinder and nozzle 2 Reduce back pressure, screw speed and injection speed 3 Increase the material temperature and injection pressure, improve the melting strength 4.

Burn Marks The burn marks are that the gas in the cavity cannot be removed in time, resulting in blackening at the end of the flow. Flash It means that excess plastic is present on the mold parting or ejector part. Causes: 1 Insufficient clamping force 2 The mold has defects 3 The molding conditions are unreasonable 4 Improper design of the exhaust system Remedies: Mold design: 1 Reasonably design the mold to ensure that the mold can be closed when the mold is closed 2 Check the size of the exhaust port 3 Cleaning the mold surface Machine: Set the machine of the appropriate size process: 1 Increase the injection time and reduce the injection speed 2 reduce the barrel temperature and nozzle temperature 3 Reduce the injection pressure and pressure 6.

Delamination It refers to the surface of the part that can be peeled off layer by layer. Causes: 1 Mixing other incompatible polymers 2 Excessive release agent used during molding 3 resin temperature is inconsistent 4 Excessive moisture 5 The gate and the flow path have sharp angles Remedies: Material: Avoid incompatible impurities or contaminated recycled materials mixed into the raw materials Mold design: Chamfer all runners or gates with sharp angles Process: 1 Increase the barrel and mold temperature 2 Appropriate drying of the material before molding 3 Avoid using too much release agent 7.

Jetting A spray trace caused by the melt flowing too fast, generally serpentine. Causes: 1 The gate size is too small, and it is facing the product surface with a large cross-sectional area 2 Filling speed is too fast Remedies: Mold design: 1 Increase the gate size 2 Change the side gate to the lap gate 3 Increase the stop pin in front of the gate 8.

Flow Lines Flow lines are molding defects that are wavy on the surface of the product known as a kind of frog jump caused by the slow flow of the melt. Fog A cloud-like discoloration occurs near the gate. The reason is the melt fracture. Streaks Streaks are those in which water, air, or char is distributed in the direction of flow along the surface of the part. Causes: 1 The moisture content in the raw materials is too high 2 Air is trapped in the raw material 3 Polymer degradation: the material is contaminated, barrel temperature is too high; insufficient injection volume Remedies: Mold design: Check if the exhaust position is sufficient Process: 1 Choose the right injection molding machine and mold 2 When switching materials, clean the old materials completely from the barrel 3 Improve the exhaust system 4 Reduce melt temperature, injection pressure or injection speed Sink Marks It is a phenomenon in which the surface of the part is concave at the wall thickness.

Causes: 1 Injection pressure or holding pressure is too low 2 The holding time or cooling time is too short 3 Melt temperature or mold temperature is too high 4 Improper design of the structure of the parts Remedies: Design: 1 Corrugated surface on the surface where dents are easy to occur 2 Reduce the thick wall size of the workpiece, minimize the aspect ratio, and the adjacent wall thickness ratio should be controlled at 1.

Process: 1 Increase the injection pressure and pressure 2 Increase the gate size or change the gate position Weld Lines The weld lines refer to the surface defect caused by the two streams being welded together.

Remedies: Material: Increase the fluidity of plastic melt Mold Design: 1 Change the position of the gate 2 Add a venting slot Process: 1 Increase the melt temperature 2 Reduce the amount of release agent It works with other approaches for design optimization like designing for functionality, assembly and sustainability, each of which is discussed further, below.

Design for Manufacturing DFM describes the process of designing or engineering a product to reduce its manufacturing costs, allowing potential problems to be fixed in the design phase which is the least expensive place to address them.

Depending on various types of manufacturing processes there are set guidelines for DFM practices that precisely define various tolerances, rules and common manufacturing checks related to DFM. Design for assembly DFA is a process by which products are designed with ease of assembly in mind with the ultimate goal of reducing assembly time and costs. The reduction of the number of parts in an assembly s usually where the major cost benefits of DFA occurs.

Design for sustainability focuses on designing parts with print measurement intent in mind - sustaining tolerances with proper measurement on an ongoing basis. The sheer number of types of plastics and their associated properties makes discussions between material providers, injection molders and product manufacturers critically important, as addressing specific needs early in the design process is key to avoiding costly changes later.

Materials selection affects strength and flexibility, temperature resistance, durability, appearance, toughness, life-span, and of course production cost. Other needs can include:. When it comes to selecting the right material, it takes experience, expertise and discussion to balance all of these factors prior to building a mold and tooling. Manufacturers use a wide variety of plastics to mold parts incorporated into products and have increasingly begun to replace other materials like bronze, stainless steel, aluminum, and ceramics.

Some of the most popular reasons for using or switching to plastic include longer overall lifespan of the part, reduced wear on other components of a product, faster production line speeds, corrosion resistance and weight reduction. In addition, companies report an average percent cost savings when parts are converted to plastic which oftentimes exhibit superior performance attributes.

Material selection plays a critical role in the strength and flexibility of your molded part. Addressing specific needs early in the design process can help you avoid costly changes later. Balancing characteristics like stiffness, durability, toughness, and others are key in achieving optimal part functionality.

ABS acrylonitrile butadiene styrene is a common injection molding material that can be sourced and molded relatively easily, at an accessible price point. Polycarbonates are a high-grade class of thermoplastics that are easily molded and often increases shatter resistance.

Naturally transparent, polycarbonate is ideal for high-strength glass-like applications safety goggles, medical lab applications and more.

Glass-filled nylon is a reinforced thermoplastic, where the base nylon resin has glass fibers added to it for extra strength and heat resistance. This resin is also more nonconductive to electricity than many others, but despite of its high melting point, it is more susceptible to burning than other materials. Polypropylene is a flexible thermoplastic that is suitable for industrial and consumer applications. Polypropylene also offers resistance to solvents, chemicals and UV rays.

Acetal is known to provide great friction resistance and is a highly rigid material. It can be easily colored and dyed in the molding process; however, does not offer superior heat resistance.

One of the most vital steps when preparing for injection molding resin selection is to create a comprehensive material selection list of requirements for the product. The list should most certainly include price target and resin availability — as resin availability can be a risk and backup resin choices should be considered. It's also important to consider that some characteristics of high heat and exotic resins are unique and may perform differently from one application to another.

Design for Manufacturing a plastic part or product, prior to building a mold or tooling, must involve discussions and decisions about surface finishing. Conversations about desired aesthetic and performance characteristics of the finish will impact type of material selected, additives required, and other parameters such as fill rate, pressure and temperature tolerances. In the design stage, the plastic injection molding partner, OEM and customer should be discussing desired outcomes for the part or product, such as needs for:.

Source: K. In recent years, plastic injection molders have turned to the principles and technologies associated with scientific molding. The goal of scientific molding is to 1 save developmental costs and time by eliminating trial and error in the design process, 2 create dependable, defect-free tooling that eliminates costly mold rework, improves part quality, and accelerates time to market, and 3 create a repeatable and easily auditable manufacturing process.

To complete the technology picture, plastic injection molders should be using state of the art Enterprise Resource Planning ERP software like IQMS that provides complete, centralized financial and operational management. Using and integrating technologies supporting the plastic injection molding DFM process is challenging.

It involves communication and collaboration between molder, OEM and customer, across many different disciplines. It simulates how melted plastic flows during the injection molding process to predict manufacturing-related defects so you can quickly evaluate part manufacturability while you design. Plastics manufacturing is a highly competitive, global industry where businesses are presented with both time and cost challenges. Avoiding delays and reducing risks for costly design changes can mean that your product gets to market faster than your competitors.

The sharp line that was once drawn between development and production is now, oftentimes, blurred with manufacturers leaning on industry design experts to become involved in the design for manufacturability process.