Cost Saving Automation in Injection Molding

TAGS:  Machinery    Part Design & Manufacturing    Cost Efficiency    

This article was first published in 2009 and is revised in 2021.

Historically, plastic material in a melted form during processing has different properties. There are many ways to control processes as detailed factual predictions of final output are difficult to arrive at prior to prototyping, fabricating, or having prior experience.

Research and hands-on operation have been directed mainly at explaining the behavior of melted plastics as with other materials (steel, glass, and so on). Modern equipment and process controls are overcoming some of this unpredictability. Ideally, processes and equipment should be designed to take advantage of the novel properties of plastics rather than to overcome them.

Injection molding sensor controls are not something to be toyed with, as they demand a high level of expertise from the processor. There are those that:

1. Provide closed-loop control of temperature, pressure, thickness, and so on
2. Maintain preset parameters
3. Monitor and/or correct equipment operations
4. Constantly fine-tune equipment
5. Provide consistency and repeatability in the operations, and
6. Provide self-optimization of the process

Most processes operate more efficiently when machine sensor functions must occur in the desired time sequence or at prescribed intervals of time. In the past, mechanical timers and logic relays were used. Now, fully electronic logic and timing devices are used based on computer software programmable logic controllers.

Let’s take a historical look at Kistler Instrument and Dynisco mold control advances as our starting point.

Mold Control Advances

Modern injection molding technology involves a growing number of increasingly complex injection molding processes. For many applications, process consistency and part quality optimization can only be ensured for extended periods by using measuring systems focused on mold cavity pressure.

Process conditions within the mold largely determine the quality of the injection molded parts. As the molding process cannot be viewed directly, attempts have been made to use machine parameters to describe molding conditions with limited success, mainly because these parameters cannot account for the effects of sprue solidification or melt compressibility.

Continuous monitoring of the mold cavity pressure profile has been found to be the only reliable method of describing process conditions occurring during the injection, compression, and holding pressure phases of injection molding. This is also the only molding parameter to correlate with quality-related part properties such as part weight, part reproduction accuracy, shrinkage/warpage, flash, sink marks, and voids.

Equipped with high-performance control systems based on mold cavity pressure measurement, injection molding machines are able to produce high-quality parts. These systems can automatically monitor, optimize and control injection molding processes, increase productivity and reduce costs. Mold cavity pressure measurement and systems using cavity pressure for monitoring and controlling injection molding processes offer:

• Reduced installation and setup time
• Reduced labor reduced rejects
• Cycle time optimization
• Improved material use
• Reduced energy costs, and
• Mold protection

Plastics Quality Control via Injection Molding/Extrusion – Watch Online Tutorial

Injection Molding Process Optimization Software

A new version of DataFlow process analysis software, type 2805A, for optimizing, monitoring, and documenting injection molding operations has been commercialized by Kistler Instrument. Like injection molding machines, the user management feature of this version, Dataflow v2.3, allows split operation permitting the set-up level to be separate from the production level.

New data compression technology significantly facilitates data processing, and the product’s floating tolerance band can accommodate intermittent disruptions such as delayed start-up of the injection phase. New filter features facilitate off-line data analysis while off-line graphics display data for the analysis of mold sampling (valuable in long-run set-ups) or large-scale production processes.

The new features enhance the series of process visualization tools used for process set-up and optimization, including monitoring, cavity pressure, contact temperature, and robotic reject gate for bad part separation. A network-capable statistical analysis tool documents:

• Production parameters for yield improvement measures, and
• Quality certifications for customer verification requirements

Additionally, a new signal conditioner (T2865B) is available with USB connectivity replacing the two cables previously used for connecting to a PC when operating Kistler’s DataFlow system.

Simplified Mold Sensor Connections

New multi-channel cable technology from Kistler Instrument Corporation greatly simplifies connections, particularly when used in multi-cavity molds. Between one and four, or one and eight sensors can be connected with a single multi-channel cable running from the mold to the monitoring system. Based on its single wire technology, the different wire strands are combined into one cable.

Historically, the connection of the mold to the monitoring device required up to eight cables and connectors, where now, one single multi-channel cable and multi-channel connector are sufficient. The single connector uses:

• Less space within the mold cavity
• Minimizes the cost of mold cable connections, and
• Cuts set-up time to a fraction of the time previously required

Additionally, the multi-channel cable technology is safer, as it minimizes the risk of errors when connecting sensors. Multi-channel cable is available with UniSens technology for UniSens single wire sensors designed for uniform sensitivity, which greatly simplifies the configuration of the monitoring systems. Various adapter cables are available to make certain that the new connection technology is compatible with existing analysis systems such as Kistler’s DataFlow.

DeviceNet Digital Polymer Melt Pressure Transmitters

DeviceNet transmitters are Dynisco LLC's addition to their line of digital pressure transmitters. The company is a worldwide leader in pressure/temperature sensors and instruments for plastics processing and other industrial applications.

The DeviceNet transmitters provide for high-level bus-enabled communication technology that opens new cost-saving opportunities for users. Looking to reduce total operating costs, processors are increasingly adopting control strategies that incorporate smart, bus-enabled devices. This simplifies wiring to reduce installation costs, and through the diagnostic information available, also reduces maintenance costs.


DeviceNet Pressure Transmitters
Source: Dynisco LLC
The innovative DeviceNet digital pressure transmitters make use of the latest embedded microprocessor technology, in which the pressure sensing element, the low-level analog signal, is converted to a digital value at a conversion rate of 20 milliseconds, which meets the requirements of most melt pressure and industrial applications. The digital pressure signal is made continuously available to the master control system via the DeviceNet bus.

In combination with CANbus circuitry, the microprocessor automatically monitors the condition of the sensor electronics and reports fault conditions over the bus. The capabilities designed into the DeviceNet structure and the communication protocol used also provide other features such as:

• Automated transducer calibration
• Limit-setting, and
• Error analysis

Also available with the ‘Melt Monitor’ is an optional built-in temperature measurement sensor. This feature allows the melt monitor’s LED display to show temperature and pressure readings simultaneously.

Suitable Grades that Undergo Injection Molding

Autodesk's Moldflow® – Cost Saving Automation in Injection Molding

Discover more about Autodesk's Moldflow®, a complete suite of manufacturing software simulation solutions for the automation, control, and monitoring of the injection molding process.