Since the type and characteristics of the injection molding machine can affect the project outcome, you might think that the equipment selection is best left to the injection molding machine.
There is no doubt that the input of the mold maker is the key to adjusting the project and the injection molding machine. However, familiarity with machine basics will help you make better design choices, more accurately predict project costs and production times, and even guide you to the injection molding partner that best meets your needs.
Types of Injection Molding Machine
There are three types of injection molding machines, categorized by drive/motor type – hydraulic, electric or hybrid.
Hydraulic Injection Molding Machine
Hydraulic injection molding machine is a large injection molding machine. The action of the hydraulic injection molding machine is to control each action of the injection molding machine by controlling the flow, pressure and direction of the hydraulic power source.
The full hydraulic injection molding machine uses a hydraulic valve to control the flow direction or flow of the high-pressure hydraulic oil extracted from the hydraulic pump to drive the piston rod or hydraulic motor of the hydraulic cylinder to complete linear reciprocating or rotary motion, but if the synchronization of each axis of the full hydraulic machine is to be realized action, an additional hydraulic accumulator must also be configured.
Hydraulic injection molding machines can use accumulators to achieve high-speed injection molding, and can also achieve special injection molding such as micro-foaming. The maximum clamping force of the hydraulic injection molding machine can reach 80,000kn, which can process larger injection parts.
Fully hydraulic injection molding machines use valves and oil motors to complete and control the injection movement. There are various types of actuators to choose from, and the clamping mechanism can adopt various clamping forms, which can better meet the processing requirements of various plastic products.
For more information, you can read this article: What is a Hydraulic Injection Molding Machine
Servo Injection Molding Machine
In a servo injection molding machine, a servo motor is used instead of an ordinary AC motor. Servo motors can be used for all drives of the machine, such as pump motors and injection drives.
In the application of the injection molding machine, the servo system receives the command signal from the computer to change the speed and torque of the servo motor to achieve precise speed and pressure control. During the execution process, the servo system detects the feedback through the rotary variable pressure encoder and pressure sensor. Correction and compensation are carried out, which means closed-loop control of speed and pressure, so that the injection molding machine runs stably and has a high product qualification rate.
Electric injection molding machine
All-electric injection molding machines use electric motors and screws to achieve their injection molding. The development of the actuator is restricted by the research and development level of the drive servo motor, so that the form of the actuator is less. In order to generate a larger clamping force for the servo motor, a toggle mechanism with a relatively small expansion force/large stroke is often used. Form of clamping mechanism. The limitation of the servo motor is in the clamping force. For example, the maximum clamping force of an all-electric injection molding machine is 10,000kN, which is more suitable for making small plastic products.
Weighing tonnage
Each of the injection molding machines mentioned above are still in use today. Although each iteration introduces certain technical advantages, tonnage (a measure of the force required to keep the tool closed during injection) remains a major factor in determining the size of the injection molding machine needed to produce a part.
Sizes can range from under 5 tons to over 4,000 tons. Considering such a wide range of possibilities, tonnage calculation is a necessary and critical step. Finding the right tonnage range takes into account the area of the part, the type and viscosity of the plastic, and the "clamp factor". Some molders do this by using industry-accepted estimating equations.
Influence of injection molding machine tonnage on injection molding
Injection molding is a complex dynamic system with multiple interacting factors - all of which affect performance, cost and quality. One of these factors is the injection molding machine tonnage calculation, also known as clamping force.
"Tonnage" is a measure of the force required to keep the tool closed during the injection process. This force is a major factor in determining the size of the injection molding machine required to produce the part. This may seem simple, but a lot depends on accurately determining the tonnage, which is why working with an experienced injection molding machine is crucial for producing complex plastic parts.
Effects of Improper Tonnage
Too low clamping force can lead to inconsistent results or defects including variable size and weight, flash, short shots, wall thickness variations and irregular surface finishes. Excessive clamping force increases unnecessary wear, which shortens tool life and ultimately increases production costs to rebuild tools more frequently.
Machines that offer high clamping force are more expensive than those that offer low clamping force, and inexperienced or commodity molders may not have the right machine for your project. Plastic engineers on custom injection molding machines can accurately calculate tonnage, ensuring the correct machine is used and eliminating the risk of over-clamping.
Cost reduction through tonnage calculation
Tonnage calculations are usually expressed as a range (for example, from 550 to 750 tons for single-cavity tools). An injection molding machine can certainly save money by buying a smaller machine that offers the lowest clamping force in the range and claims it will do the job well. However, if the optimal tonnage calculation is actually in the upper middle part of the range, this increases your (the manufacturer's) risk of flashing of plastic parts. Flashing is when the tool opens slightly during the injection process because the machine lacks sufficient clamping force to produce flash-free parts.
Instead of using an injection molding machine tonnage calculator, many molders typically estimate tonnage using a "rule of thumb" formula involving part area, plastic type, viscosity, and a "clamping factor" ranging from 2 to 8. Depending on the part and Material type, some molders simply use an "average" clamp factor of 5 to calculate tonnage.
This approach can result in inaccurate tonnage calculations that are too small (resulting in quality issues and delays) or too large (resulting in increased tooling costs and premature failure).
A more accurate way to determine an injection molding machine tonnage calculation is through a mold fill analysis, which takes most of the guesswork out of the calculation. In our experience, using a die fill analysis to determine the tonnage factor, then adding a "safety factor" of approximately 15%, results in highly accurate clamping forces and flash-free parts.
There are many variables when calculating accurate tonnage that can significantly affect the quality and profitability of plastic parts. Having the right injection molding partner is key to ensuring that these calculations are properly measured for your project's long-term success.
Knowledge of injection molding machines
For OEMs looking to manufacture these parts, finding the right mix of injection molding specialists under one roof is important to a successful production job. In order to efficiently produce the desired plastic parts, plastic manufacturers must know a lot because every injection molded part is different and each part has its own variables. Plastic manufacturers must understand these variables.
When evaluating who to work with, you should be proficient in three areas of expertise in injection molding machines:
Material selection
The choice of resin—in fact, there are thousands—must be determined by evaluating the conditions to which the finished product will be exposed and the physical requirements that the product must meet. The quality of electrical insulation may be paramount, and close dimensional tolerances may be critical. When choosing an injection molding company as a supplier of plastic parts, the company must have the expertise to meet the specific needs of the product in the end application. In all too many cases, many molding companies limit their recommendations on which raw materials to use—not for what is best, but to accommodate their machine limitations, or their limited knowledge of molding techniques for different resins.
Tooling Design
Selection of mold design and correctness are equally important in selecting an injection molding partner, a mold design expert who has the knowledge to ensure that the finished molded product meets all required specifications. Material flow, mold clamping force, pour length and shape, cavity size and machine capacity are all factors that affect final product performance. The number of cavities in the tool depends on the production scale and is proportional to the cost. Molding experts will calculate a mold flow study for each resin to ensure the molded part is optimal and imparts its unique properties.
Surface treatment of moulded parts
As more plastic injections are used to replace traditional materials such as metal castings and forgings, the need to make them look like metal has become an important requirement. The phone and camera come standard with a shiny metallic finish or a matte black enamel finish. Injection molding machines must account for the different molding techniques required for these finish variations.
Log Machine has many types of injection molding machines, focusing on the development of injection molding solutions. We have the ability to provide the solution you are looking for and the design, engineering, production knowledge and processes you need to make your project a success.
Log Machine keeps pace with the latest injection molding machine technology, so our customers have the most efficient and suitable option. It's a value-added service that enhances our customer relationships and helps guide pre-production decisions, just like the information you'll find in "The Process of Scientifically Identifying Tools". This easy-to-reference infographic delves into tool performance and how it affects projects in the short and long term.
Read More:
How to select a Plastic Injection Molding Machine
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