P&G Explores the Frontiers of Injection Mold-Temperature Control

In the era of “smart machines” and “smart processes,” a number of companies are focusing on one of the last frontiers for getting a firm grip on the injection molding process—mold-temperature control. Two of those companies are Engel Austria and Procter & Gamble (P&G) in Marktheidenfeld, Germany, which has collaborated with Engel since 2007 and became a test customer and development partner in mold-temperature control in 2013.

P&G thus has been one of the first to benefit from the new trend to providing both greater visibility of what’s happening in individual cooling channels inside the mold and direct closed-loop control of cooling at the individual circuit level.

The potential benefits of this trend for injection molders worldwide is enormous. “In injection molding, around 25% of all scrap parts are a result of temperature-control errors,” says Klaus Tänzler, temperature-control product manager at Engel. “This is precisely why Engel’s development team is working intensively on this topic.”

That is also why P&G takes mold-temperature control so seriously. As a healthcare company, P&G has “grayroom” production; all processes are validated, and quality takes top priority in all production areas. Any innovation that enables more consistent processes is generally of great interest to P&G.

OPENING UP THE ‘BLACK BOX’

“Temperature control was a black box for us,” says Andreas Franz, process engineer at P&G’s Marktheidenfeld production plant. For a long time, only the supply temperature was known. To get any more detail on how temperature was distributed over the individual heating/cooling channels during molding, the only option was thermography (an infrared image of the mold or part), a complex process that does not give more than a snapshot.

As part of a reassessment of mold cooling by several industry firms, Engel (U.S. office in York, Pa.) introduced a step forward at K 2010. Its flomo electronic water manifold system replaced the maintenance-intensive cooling-water distributors with a device using vortex flow sensors that have no moving parts. It can individually monitor and document all cooling and temperature-control circuits.

The next-generation e-flomo, which emerged at Fakuma 2014 and NPE2015 goes another step further by actively adjusting valves to control flow rate or temperature difference (ΔT) in all individual circuits.

Three years ago, P&G’s Molding Technology division in Marktheidenfeld started to analyze and optimize its injection mold-temperature control. “Our goal was transparency and with it, increased process reliability,” says Christian Rieb, equipment engineer at P&G.

The Marktheidenfeld plant focuses on oral hygiene and produces Oral B electric toothbrushes. The molding shop has 100 injection machines from 50 to 500 metric tons. One successful application of Engel’s e-flomo was a mold for the housing of the chargers for the hand pieces of electric toothbrushes. This was the first to be investigated by the newly established Temperature Control Project Group at P&G.

The oval base of the ASA housing has a thin dome at top center that holds the hand piece in place when charging. For stabilization, there are small webs on the inside. The fully assembled housing contains all the electronics, including connecting cable, which is embedded in a potting compound. The complex 3D structure of the housing places high demands on precision and process consistency during molding. “Even the tiniest dimensional deviations or incompletely filled areas cause the potting compound to leak out,” explains Andreas Spitznagel, who manages the Process Technology Group for P&G in Marktheidenfeld. “In the past, we frequently experienced warpage due to uneven temperature control. But what exactly was causing the fault was difficult to determine because there was simply too little information.”

This mold, with 56 heating/cooling channels, presents a particular challenge and was well suited to test new temperature-control technology. It’s a stack mold with a total of 32 cavities in two parting lines. Since the melt is routed through the first parting line to the second, a lot of heat is generated in the center mold plate. Before installing e-flomo, 10 temperature-control units (TCUs) were used—eight small ones on the operator side and two large ones on the rear side of the machine.

In collaboration with Engel, a new production cell was planned and the mold design was optimized for the use of e-flomo. All 56 connections are now arranged on one side of the mold, which speeds mold setup, shortens the piping, and makes it easier to inspect. Now nine e-flomo units are mounted near the mold on the  edge of the platens of a tiebarless Engel e-victory 300 press. Each e-flomo supplies several mold circuits.

From dirt, deposits and air bubbles in the mold channels to fluctuations in pump supply pressure, many different factors can disrupt mold-temperature control. If such a condition occurs in the new system, e-flomo detects the irregularity and automatically adjusts the valves to compensate.

All 56 circuits are adjusted at the same time. “Reproducibility has increased enormously,” reports P&G’s Franz. “The blindfolds have gone and we have a genuinely transparent process now.”

Improved reliability opens up massive potential savings, not least because of increased confidence in the mold-temperature control. The new production cell uses just three TCUs instead of the 10 previously. Each mold plate now has its own TCU, and all three units fit under the clamp of the machine, saving space.

The initial temperature of all three TCUs is currently set to 55 C (131 F). Initially, three-quarters of the 200 l/min flow rate available on each TCU was used, as in the past, but P&G found it could cut the flow rate to 40 l/min during the course of system validation—a startling 73% reduction. “This is significantly less than we expected, says Rieb. “At the start of the project, it was not clear to us that we could save so much in addition to the increased transparency and reliability.” Fewer TCUs, and lower flow rates mean lower investment costs, more compact cell layout, and—above all—significant savings in energy consumption.

Similar success was experienced in a second production cell where temperature-control overhead was reduced while also increasing product consistency. Another Engel tiebarless victory 300 machine molds two parts for replacement toothbrush heads. Profile rings of POM (acetal) are produced in a 64-cavity mold, and tube sections of POM are produced in 32 cavities. The flow temperature is 90 C (194 F) in each case. Again, high dimensional accuracy is essential to ensure the functional capability of the toothbrushes.

“Temperature control of the long finger cores forming the tube sections is critical, above all,” says Carmen Stollberger, process engineer in the Temperature Control Technology Team. “If the cores are too hot, distortion can occur. In general, the circuits close to the cavity have a greater influence on the product quality than those farther inside the mold.”

Before optimization, this cell was operated with seven TCUs plus two pressure boosters. Now, with e-flomo, there are only five TCUs, without any pressure boosters. “If everything is functioning optimally and is well monitored, you can venture closer to the limits without needing a safety buffer,” comments Stollberger. Theoretically, even fewer TCUs could be sufficient for this application, but the project team divided the mold into five temperature-control zones, some of which are set to different supply temperatures.

CHECK THE PROCESS, NOT THE PRODUCTS

P&G is training process engineers from other plants to use the new system. “Our goal is to successively retrofit the legacy systems,” says Rieb. After its success with e-flomo, P&G is taking the next step and using Engel’s iQ flow control software to integrate mold-temperature control into the machine controller.

This software was introduced at K 2016 and is seeing its launch in North America at NPE2015 this month. The software networks the TCU, e-flomo, and injection machine to create a single unit, and it controls the TCU pump-motor speed on demand, thus further boosting energy efficiency.

Integration also improves clarity: Engel’s CC300 injection machine controller displays the actual values for all temperature-control circuits in a complete overview. Changes or errors can be detected at a glance.

“We are working on the assumption that we will no longer test the parts in the future, but just the processes.”

A key element of this system is the new e-temp TCU with variable-speed pump, created for Engel by HB-Therm in Switzerland. The first set of e-temp units is being commissioned in production by P&G.

For the connection between e-temp and the CC300, Engel relies on the OPC-UA communication protocol that is becoming increasingly popular in plastics for networking injection machines, sensors, and peripherals, and is an important component of the Engel’s emerging Industry 4.0 platform, which it calls inject 4.0. This platform is designed to help clients pave the way to the “smart factory” with continuously self-optimizing processes aided by smart systems such as iQ flow control.

“We are working on the assumption that we will no longer test the parts in the future, but just the processes,” says P&G’s Spitznagel. “This is our goal: Stable processes that we can rely on 100%.”