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Injection molding machine controls vanquish variabilities

Articles

Mikell Knights, senior correspondent at Plastics Machinery Magazine

New control options for injection molding machines automatically make adjustments to enhance productivity or bring new life to old equipment. Achieving optimal processing conditions minimizes scrap, saves energy and yields better parts. Two companies provide insight into their machine control enhancements for original equipment and retrofits.

One control serves all Van Dorn models
The Van Dorn Universal (VDU) retrofit machine control system offered by Sumitomo (SHI) Demag Plastics Machinery North America Inc., Strongsville, Ohio, has more programmable options and can be installed more quickly since becoming commercially available in 2008, says after-sales director Steven Ross.

Sumitomo (SHI) Demag offers a Van Dorn Universal retrofit machine control system that provides more programmable options.

Sumitomo (SHI) Demag represents an amalgamation of three companies that support five product brands, says Ross. The after-sales division supports: new equipment made by Sumitomo Demag in Japan; equipment that Sumitomo sold independently in the U.S. for years; equipment sold in the U.S. years ago by an independent Demag; the fleet of Van Dorn machines manufactured in the U.S. up until 2008; and the Newbury fleet of vertical injection presses, says Ross.

Production of the Van Dorn machines ended in 2007, and in 2008 the after-sales division introduced the VDU to serve the entire fleet of Van Dorn machines, which range from 50 to 4,400 tons. The Van Dorn hydraulic toggle (HT) series, ranging from 85 to 650 tons, was manufactured from 1989 to 2007 and represents the most popular of the fleet's models. Sumitomo Demag developed the base programming and design of the VDU so that it can be retrofitted to any Van Dorn machine. "Based on parts activity and service activity, there remains an installed base of approximately 13,000 units today, even though we have not manufactured a Van Dorn machine in seven years," says Ross.

The robustness and structural longevity of Van Dorn machines were not equaled by the machine control system that was originally used with them. The machine control system uses an obsolete programming language and components. Initially, Sumitomo Demag created the retrofit package with 40 basic functional modules. "We started with standard operations such as core pull, air blow, robot interface, melt-temperature
control and mold-temperature control," says Ross. The VDU system today has more than 140 programmable options.

Users now have the option to integrate a hot-runner temperature control or connect to an add-on or second injection unit. The VDU retrofit machine control can be integrated with the eDART process/production monitoring and control system from RJG Inc., Traverse City, Mich., or with open-platform communication software, says Ross.

Sumitomo also developed a new 15-inch operator panel where half the panel is touch-screen control and the other has keys. The graphical analysis of cycle time and closed-loop control tuning have been improved. "We've conducted a radical reprogramming of the unit ... which overall delivers finer control over closed-loop processing," Ross says, "Users have an increased ability to iron out any small processing detail that will improve their molding precision. The software developments can boost aspects of the process like pack and hold, and the software can process information much faster than it could with the prior controls."

The VDU controls are created at Sumitomo Demag's manufacturing sites in Wiehe and Schwaig, Germany, where controls for the other machines in the company's product line are made. All of the final assembly occurs at the company's Strongsville facility. There, the VDU operator panel is pre-wired, requested modules are installed in the cabinet and the power supply is added.

"The modules required to run their options, the terminal strip and the wiring are all added in Strongsville, and the unit is ready to ship," says Ross. It previously took five and half days to supply the unit from order to delivery, but manufacturing efficiencies have trimmed the time to three days.

Sumitomo Demag also offers a machine control for its line of all-electric machines that reduces part defects and trims cycle times. Its Z-molding machine control incorporates the company's Flow Front Control (FFC) software, which controls the movement and position of the screw during injection and helps to execute mold filling at lower injection pressures. This is combined with its Minimum Clamping Molding (MCM) system that determines, then applies, the lowest clamping force for the application. A Simple Process Setting (SPS) feature in the control allows for the input of select mold settings on a single screen.

KraussMaffei’s patented Adaptive Process Control provides valuable support for the mold setter. Germany’s KH Foliotec GmbH uses a KraussMaffei machine to mold a two-component radio dial panel.

Zero-defect production
KraussMaffei Technologies GmbH, Munich, has developed a new machine control program that minimizes part rejects, trims scrap production, reduces machine start-up times and maintains part quality by compensating for fluctuations that occur during molding.

KraussMaffei developed and patented its Adaptive Process Control (APC) as a tool that measures machine parameters in real time and then adjusts the changeover point from injection to holding pressure in each cycle in order to achieve a consistent part quality. It is an add-on software upload available for use on all of its injection molding machine models.

"Component quality serves as the definitive control variable. Utilizing online measurement of the melt viscosity and current melt flow resistance in the mold allows the APC to automatically maintain the shot weight specified by the molder even as factors external to the process vary," says Dr. Reinhard Schiffers, head of machine technology.

External factors that influence process conditions include the plant's temperature and humidity; fluctuations in the tooling components, from the hot runner to mold cooling and heating, to variances in the operation of the shut-off nozzle or nonreturn valve; material changes due to fluctuations in batch quality, contamination or additives; and human error.

The APC does not require the installation of additional sensors on the machine and looks at data that is already collected and available through KraussMaffei's MC6 machine control system. The APC requires a reference value, or baseline value, in order to operate. The molder selects the APC function on the display screen of the machine control, at which point the program analyzes numerous parameters related to the molding of the part over two or three cycles. For proprietary reasons, Schiffers can only provide a general overview of the parameters analyzed by the APC.

The reference value is determined from two separate process/production values. It is critical to determine the specific position when the nonreturn valve is closed. One of the integral values measures the pressure curve from the machine at the beginning of injection.

The pressure curve profile and the nonreturn valve position are used to determine what KraussMaffei calls the fill integral. A second integral or value involves the measurement of the viscosity of the melt. "It is important to measure viscosity in an area where you have constant flow with no compression of the material. This value forms the second condition or integral value, which we call the viscosity index," says Schiffers.

Together, the filling integral and the viscosity index create a value KraussMaffei calls mold part volume (MPV). The MPV value tells the APC the amount of material pushed into the mold. The APC uses the value as a reference. When activated, the APC can adjust the switchover point from injection to holding by comparing real-time conditions of the melt in the machine to the reference value.

The two-component radio dial panel.

The APC performs its calculations within 1 millisecond and is able to set the new switchover position just as quickly. The actual switchover position time may vary by hundredths of a second and the positional difference from shot to shot may be as little as 0.10mm, says Schiffers.

"When APC is on, the operator is unable to change certain relevant parameters such as screw speed, temperature profile or injection speeds, as they will have a direct effect on viscosity. APC will correct for the changes," he says.

KraussMaffei's MC6 control and machine technology provide molding consistency, even when the APC is not used. But users looking for even greater precision in part weight can achieve it with the advanced control. KraussMaffei conducted a test of the APC on a CXZ 500-2000/750 KM machine at KH Foliotec GmbH, a Sparneck, Germany, manufacturer of automotive surface components. Foliotec molded a two-component radio dial panel in a 1 + 1 injection mold featuring a decorative foil that is back-molded with PC, then over-molded with PC/ABS blend. The company produced the parts over a 24-hour period with and without the use of the APC. Standard weight deviation dropped from 0.16 grams to 0.03 grams with the APC enabled.

KraussMaffei's MC6 control can store and retrieve the APC reference value. Molders can activate the APC at startup and the machine will compensate for fluctuations from the first shot, minimizing scrap generation during startup.

The APC is also a useful tool if a machine operator is running an unfamiliar project. Instead of the operator making adjustments to bring the process into a steady state in which acceptable parts are made, the APC achieves it automatically.

When the APC is activated, it is no longer necessary to tweak temperature, pressure and time settings, or to overcompensate for unknown variables. This allows molders to save energy and time while producing high-quality parts. Also, the APC allows the molder to better mold parts containing recyclate while keeping scrap generation low.

Schiffers says the APC has been installed in approximately 500 machines since its commercial introduction last year at Fakuma.

 

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