Key Manufacturing Points for High Quality Molded Plastic Components

Table of Contents

I. Introduction

A. A brief description of plastic injection molding

The manufacture of plastic products is generally carried out by molding methods which have many types such as injection molding, blow molding, thermoforming, 3D printing and so on. Among these methods, Injection molding is selected as the most versatile process for manufacturing repeatable plastic products of various shapes, sizes, and dimensions. The basic operations of injection molding are plastic heating, pressurized injection of molten plastic, cooling or compaction and dispensing of plastic products.

Key Points for High Quality Mold
Figure 1 Injection Molding Diagram Schematic

The plastic injection molding process starts with loading a certain amount of plastic pellets from the feed hopper into the cylinder. Next the plastic pellets are moved forward by rotating a tapered screw called a spreader. The spreader not only transfers but also heats the material by the friction created between each pellet and in contact with the heated cylinder walls. As a result, the plastic pellets melt to form a viscous molten plastic. Then a ram behind the spreader pushes the molten plastic at a constant pressure, causing it to flow through the nozzle into the closed mold cavity. After the molten plastic is solidified due to a cooling system that fits into the mold, the mold cavity is opened and the plastic product is ejected by a set of ejector pins. Finally the mold is closed again and the cycle is repeated.

 B. The importance of high quality molded plastic parts in various industries

High quality molded plastic parts play an important role in various industries to ensure products perform well, last long and reliably. For example, in the automotive industry, high quality molded plastic parts such as dashboards, steering wheels and door handles contribute to fuel efficiency due to their light yet strong nature.

High-quality plastic products can also lead to business cost-effectiveness because fewer defective products are associated with product failures and customer complaints. The fewer customer complaints, the higher the business profit. Safety aspects will also occur when a plastic product has high quality, guarantees safety aspects to the end user, which will then lead to market trust and satisfaction. So, it is very important to prioritize the quality of molded plastic parts if the manufacturer wants to have a profitable and sustainable business.

II.  Understanding Quality in Molded Plastic Components

A. The definition of quality in the context of printed plastic parts

The definition of quality of molding plastics refers to the standards and requirements established for their use. Its quality can be seen from the following aspects:

  1. Dimensions, dimensions of plastic parts must meet the specified structure and tolerances.
  2. Strength and toughness. Plastic parts must have the strength and toughness according to standards
  3. Interface and appearance. The surface of the plastic parts cannot win defects such as scratches, stains or deformation. The good appearance of the finished product is important, especially the part that is seen by consumers
  4. Chemical safety and stability. Plastic materials must be safe to use and must not contain hazardous materials that can contaminate the product. In addition, plastic must be chemically stable so that it does not experience a significant loss of quality over time
  5. Color matching. If a plastic product has a certain color, the quality value will also affect it

B. Factors contributing to the quality of molded plastic parts

Factors that affect the quality of printed plastic include parameter settings during the production process. The parameters that affect the plastic production process with the injection molding method are:

  1. Melting temperature

The temperature limit at which plastic materials or plastic pellets begin to melt through the application of heat energy.

  1. Pressure limit

There is a limit to the required air pressure. Given to actuate the piston during use. Press the melted plastic material. If the pressure is too low, the material won’t come out, injected into the mould. But if air pressure too high cause the plastic to explode. From within the type, this leads to the fact that the production process does not start efficient.

  1. Hold time

Taking into account the time measured from reaching the predetermined melting temperature until all the plastic pellets contained in the heating tube are confirmed to have completely melted as a whole, because it takes time for the heat to spread to all the desired parts. hot. If the holding time is too fast, some of the plastic pellets in the heating tube have not completely melted, making the process of running the plastic pellets difficult.

  1. Press time

The length of time required to produce a compressive force against the piston which pushes the melted plastic. Setting the pressing time aims to ensure that the plastic material or plastic pellets have actually spread into the mold cavity. The dimensions of the mold greatly affect the pressing time, the larger the size of the mold, the longer the pressing time will be.

  1. Mold temperature

The initial temperature of the mold before the plastic material melts

  1. Injection speed

The speed of movement of plastic pellets that have been melted out of the nozzle to fill the cavity in the mold.

  1. Mold wall thickness

Depends on the whole mold design. The thicker the walls of the mold, the greater the probability of shrinkage defects 

 III. Key Manufacturing Points for High Quality Molded Plastic Components

A.  Precise mold design and maintenance

Mold design also affects product quality, if the mold design is too detailed and complicated then the process of spreading the heated plastic pellets will also take a long time to spread. The basic material structure of the mold is composed of hardened steel, pre-hardened steel, aluminum and beryllium copper alloy. However there are usually economic considerations to consider when choosing a mold material given the life of the mold.

In general, mold components can be described as follows:

Key Points for High Quality Mold

The print design also requires sufficient ventilation to remove air and gas, if the ventilation in the print design is lacking, it can interfere with the printing process so that the product becomes defective. In the printing process, the printed design also requires cooling to cool the printed material quickly and evenlyto reduce cycle time and avoid deformation. At the cooling stage of the plastic material product, the next process is the product material to be ejected, with ejection in this mold design a proper ejection design is needed to ensure that the plastic material product is easily removed and when the product is released it does not damage or cause damage. with disabilities.

Mold maintenance is also necessary to maintain the quality of plastic products, starting from daily or monthly maintenance.

  1. Daily maintenance
  • Periodic checks before starting production
  • maintenance of cooling water channels that function as cooling water channels
  • maintenance on the mold, check whether the mold has corrosion or not, so as to prevent the mold passage from being blocked
  • maintenance of the axle under normal conditions and lubrication of all parts of the shaft serves as a lubricant to prevent corrosion and blockage of the shaft due to corrosion
  1. Monthly maintenance
  • Polishing of mattresses that have been torn due to frequent pounding, this is done so that the condition of the mattress remains in good condition so that production results can be up to standard.
  • Replacing cooling water and checking pumps, to ensure water conditions remain normal and no pumps are clogged due to dirt in the water

B. Selection of the appropriate plastic material

In addition to the manufacturing process factors that affect the quality of molded plastic products, the selection of plastic materials also has an effect on avoiding shrinkage defects.

Table 1. Percentage of shrinkage defects in various plastic materials

Key Points for High Quality Mold

C. Precision in the injection molding process


The precision of the enjcetion setting also affects the process of making plastic products.

Many important factors in the injection process, including:

  1. Pre – Heating in Hopper and barrel temperature

For certain materials, sometimes these materials must be heated in the hopper to reduce their water content.

You can see the settings for each different material in the table below

Key Points for High Quality Mold

At the ideal barrel temperature setting, the temperature rises gradually from low at the rear to high at the front, especially at the nozzle. In this vat mixed dyes and polymeric materials. If the temperature setting is too hot, it will cause the silver or the product to become too shiny.

  1. Mold temperature

This greatly affects the production process, product yield and speed in the production process. Various temperatures in the mold greatly affect the surface quality of the product. Therefore the cooling process has a big role in the mould.

Many molds use water cooling, but sometimes molds are heated using MTC (Mould Temperature Control), especially for products intended to illuminate or hide weld lines.

The ideal mold temperature is around 25-30 Celsius. Cooling is used for products that require stable sizes and faster cycle times.

  1. Screw Turn

Screw rotation also affects machine filling time and product yield, especially for colored products. If it’s too fast it can cause overheating and the material will change color and if it’s too slow it will slow down the Cycle Time.

  1. Metering Stroke / Short size

Determine the amount of material to be dispensed into the mould. To determine the metering stroke / short size, use the formula

SM = Bx100/3.14xD^2xBj/4

B = Weight of product + Runner

D = screw diameter

Bj=Plastic specific gravity

Each material has different specific gravity variations, for example in the table below:

Key Points for High Quality Mold

To find out whether the material setting matches the size of the printout, you can check it by moving the bolt forward, you can see the bolt position on the display

  1. Suck back

This happens after the filling process, to avoid drooling in the nozzle orifice. Sucking on the back for too long will result in a silver strike. Ideally 3-8% of metering step although in some cases the value may not be valid.

  1. Bearing

material residue at the end of the screw when the screw is in the forward position. always position the Cushion 6.35 to 12.7mm so that the threaded end does not come out and cause defects

  1. Speed ​​Injection

forward movement of the crew during the injection of material into the mould. This also affects the product yield, if it is too fast it will cause flashing or flow marks and if it is too low it will cause the shot to be short/not full.

  1. Pressure Injection

Adjust the pressure at each injection resistance. The first pressure should not be too large, the amount ranges from 30-100 bar depending on the tonnage of the machine used. The second injection pressure is between 40-60% of the first pressure. If the pressure is too high, the mold will be damaged and if the pressure is too low, the product will not be finished perfectly

  1. Withstand Pressure

Is the pressure that is held so that the material that has been injected into the mold does not change shape. The holding press setting for the initial stage is recommended to be 50% of the injection press. At this stage product quality is also very influential

D. Quality control and testing

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  1. Display Check

This check is done manually to check the appearance and similarity of the types of plastic products. The tester checks the printed parts to ensure that there are no inappropriate or defective colors, shapes or textures

  1. Dimension Check

This measurement is carried out on the product, measured by a measuring instrument that has a high level of accuracy. It is intended that the product meets the specified standard size specifications

  1. Endurance Testing

This can be done by applying a load to the molded part, testing the extent to which the part can withstand compressive forces and wear during actual use.

To reduce testing costs, testing can be done by taking samples of several plastics. With this test the plastic parts are extracted to evaluate the quality of the plastic parts. Compared with the full inspection sample inspection, it tests a small number of plastic parts, low testing costs, testing speed. Examination Sampling and batch size of the number of samples, volume, number of samples, small amount, less, sampling, as long as the number of samples according to the test results has a high aura.

 IV. Addressing Common Challenges in Producing High Quality Molded Plastics

 A. Handle defects such as warping, sink marks, flash, etc.

In the manufacture of quality molded plastic, of course, there are several challenges, both from poor technology, malfunctions, untimely timing, and an imbalance between cost and quality. Therefore optimizing the machine and human resources is the main thing. In dealing with warping, sink marks, and flash defects, the most important things to consider are the correct temperature as well as sufficient pack and hold pressure.

B. Ensuring consistency in mass production

The production process to produce quality plastic molds is highly dependent on optimal machining so that in mass production there will be consistency between the plastic products produced, this must be balanced with qualified human resources.

C. Balancing cost-effectiveness with quality

The mass production of high quality plastic molding products also requires a lot of money, therefore balancing costs with quality and quantity is also one of the things that must be considered. Again, this will lead to how to deal with defects like warping and sink marks

 V. The Role of Technology in Producing High Quality Molded Plastic Components

 A. Advanced printing presses and their impact on quality

In the production of high-quality printed plastic, good technology and machinery are the main points in its manufacture. In response to this, the hot runner system can be a good alternative for the plastic injection molding manufacturing process where this system offers better control over the temperature of the plastic melt so as to prevent various defects in plastic products. This is the answer to the problem of defects and will have a positive impact on the quality of the plastic produced

B. The role of software in monitoring and controlling mold parameters

With the addition of a hot runner system or combined with well-integrated software, the plastic molding process will be more efficient, monitoring temperature, time, and also health parameters will be truly accurate without having to think about it, this of course happens. returning that there is software or a system integrated with the machine is helpful and an important aspect of creating high quality plastic molds

C. The impact of 3D printing and other innovative technologies

Additive manufacturing (AM), also known as 3D printing, is one of the fastest growing manufacturing technologies in the world. It is a layer-by-layer process of depositing material to produce parts from a 3D model, especially plastic models. 3D printing technology can produce lighter components, shorter lead times and lower costs. This is all thanks to its main feature: greatly enhanced design freedom, which allows the design of parts with highly customizable and unusual geometries. Nearly all of the benefits of 3D printing stem from this and lead to many features such as rapid prototyping

VI. Case study

A. Example of successful manufacturing of high quality molded plastic parts in the industry

We can find the manufacture or production of high-quality plastic in factories or industries engaged in the manufacture of plastic injection or molding production. An example is Limaputra Contrindo which is a manufacturing company engaged in plastic injection molding, mold and jig manufacturing. Limaputra Contrindo’s success in producing high-quality plastic is proven by the many companies that have used its services for the manufacture of injection plastics, as well as jigs and molds. This is due to good facilities and qualified human resources so that the quality of the plastic produced is truly standardized.

B. Innovative solutions to quality control challenges

To overcome a problem, especially regarding quality, good supervision and control is needed, but negligent supervision often occurs and goods are passed that are not according to standards, an alternative is needed that can monitor and inspect and control the quality of the plastic produced. An innovation with integrated technology is an alternative for this, with an integrated system that has received orders and good standard references, the plastic produced can be directly monitored and checked for quality without hesitation and also more accurately. However, this must also be balanced with skilled human resources

 VII. Conclusion

 A. Recap of key points

Plastic injection molding as a versatile method for manufacturing plastic parts with various shapes and sizes requires high quality which is defined by dimensions, strength, and appearance. Melting temperature, pressure, hold time, mold temperature, injection speed, wall thickness, mold design, material selection and maintenance are the the factors that contributing the quality of molded plastic parts. Typically challenges in injection molding process are warping, sink marks and flash which can be prevented by optimizing machine parameter.

B. Final Thoughts On The Importance of Focusing On Quality In The Manufacturing of Molded Plastic Parts

Focusing quality of molded plastic parts can lead to customer satisfaction, reputation, cost-effectiveness, safety and reliability, sustainable business.


Gary Liao

Gary Liao

Gary Liao is the Engineering Manager of TDL Company and has more than 20 years of mold design experience.

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