Introduction

In recent years, the challenges for plastics molding companies to compete and succeed have increased dramatically. A global economy, price pressures and customer demands have led to the need for molders to operate more efficiently and productively than ever before.

Molding unattended around the clock, or 'lights-out molding', is not a new concept, but it is one that has been adopted by more and more molders in their efforts to increase profitability. The importance of properly managing a molding plant's operations when there are fewer or sometimes, no human operators on the plant floor, cannot be overstated. If a series of protocols and contingencies are not in place, the problems that can occur with operating machinery can lead to disastrous results.

Gammaflux has created the following guidelines after many years of hands-on experience working with customers who run lights-out operations. As a hot runner temperature controller supplier, Gammaflux products include numerous safety features to detect and prevent trouble from occurring in the hot runner system and injection mold. But beyond the mold, there are other procedures that should be followed to ensure the entire molding operation, including the molding machines and auxiliaries, are operating smoothly. The following procedures are strongly recommended to ensure that early detection of problems occurs and the proper corrective actions are in place.

Three-Step Process

There are three main issues to address when planning for lights-out molding:

Identify all key potential problems in the overall molding operation, and plan accordingly. Plan for contingencies to automatically correct problems or if necessary, to safely stop machines.
Identify all parameters that would justify machine shutdown, then program the controller to shut down the machine under appropriate circumstances.
Program hot runner controllers to recognize other damaging conditions. Program controllers to also detect cooling channel blockage, plastic material leakage, heater failure, etc.
We will go through each of these three steps to explain in more detail what needs to be done to prevent problems before they occur.

Step 1: Identify all Potential Problems, Develop a Plan

The first step to responsible lights-out molding is for the molder to closely evaluate their specific operation to determine what problems can occur in the process. This should be evaluating the start-up of the machine right through to the production of parts, to machine shutdown.

This is the time to record the ideal molding conditions and plan for contingencies. For instance, record all of the correct operating temperatures for all zones of the machine and mold; record the ideal mold open/close/eject times, cycle times, and record the correct material handling data for blending, feeding, etc. If the molding cell features robotics and automation, record the pick-and-place sequence data, conveyor speeds, box loading data, etc. All of these values are critical to determining a potential problem in the process.

Once the molder's machines are running and producing parts to specification, and all data has been recorded, it's time to determine the contingency plans. For instance, what do you want to happen if there is a power surge that shuts down the machine? Or if there is a part stuck in the mold? Or if there is a blocked cooling channel in the hot runner system?

If any of these problems or others occur, it's essential that the molder program all machine controllers to recognize the problem, and take appropriate action.

Step 2: Identify Parameters for Machine Shutdown

This step involves determining under what conditions the molder should program his controllers to shutdown the machine if problems occur. In general, the proper rule of thumb to follow is if the machine can't properly recover from a certain problem, the controllers must be programmed to detect the problem and safely shut down the operation completely.

First, a determination should be made as to whether the machine can recover properly from the problem that occurs. For instance, if the mold has a single eject sequence and the machine controller is programmed to sound an alarm indicating a stuck part in the mold, the machine controller needs to be programmed what to do - for example, it could open/close the mold 2-3 times to clear the alarm and if the problem is not solved after this, program the hot runner controller to 'standby' mode to prevent degrading or burning the idle material. Degraded material in the hot runner system can lead to clogged runners or leakage, potentially requiring removal of the hot runner and the difficult, time consuming task of cleaning up of leaked and degraded material from the hot runner and mold.

When running unattended and a problem occurs in the hot runner system, such as heater failure, the machine should stop to prevent excessive pressure in the hot runner manifold or over packing the parts.

The new Gammaflux G24 hot runner temperature controller allows the user to determine which alarms will shut down the machine, and the controller can enable/disable each hot runner zone alarm. Even though it is a hot runner temperature control system, it can be used to shut down the entire machine, not just the hot runner system, if necessary. In addition, the G24 can put all alarms to a single output to the machine ('OK to Run' output). This makes it easy for the molder to program what is 'OK', and what is 'Not OK'.

Besides the hot runner and mold, if there is a problem with another piece of equipment in the molding cell (robot, dryer, material handling, etc.), in each case the molder needs to determine what has to be done. All of this equipment needs to communicate back to the controller and the machine to determine if shutdown is necessary.

Each auxiliary needs to communicate back to the machine and machine control. The Gammaflux G24 can also handle taking the machine out of automatic and into semi-automatic operation. The controller can monitor the machine's performance, and automatically put the hot runner controller and molding machine into standby.

Step 3: Program Hot Runner Controller to Recognize Other Damaging Conditions

The third and final key step for planning for lights-out molding is to program the hot runner controller to recognize whether the mold cooling water is on and working, or not. This is an essential step because if for some reason there is a problem with the water flow and no cooling is taking place, there will potentially be damage to the hot runner seals from overheating, and also the machine will produce poor quality parts. Part shrinkage, finish, dimensional issues, etc. are likely to occur.

There are two methods by which the molder can ensure the controller is measuring the effectiveness of the cooling water:

Flow sensor - monitors water coming out of the tool, relays status to the controller.
Plate temperature monitor - identifies that water channels are blocked or have stopped flowing.
In addition to monitoring the water flow, the controller should also be programmed to determine if there is material leaking out of the hot runner system.

The Gammaflux G24 hot runner temperature controller can be easily programmed to monitor any of these potentially damaging conditions. Regarding cooling water, by monitoring if the water is flowing, the controller can prevent material from burning and monitor heater wattage to determine if there is plastic leakage in the hot runner. A heat sink is created from leaked material in the hot runner system, and the controller applies more power to try to compensate for the problem. A 10% wattage change signals the alarm, upon which the molder can program the controller to shut down machine operation.

Additionally, the controller can monitor individual heater resistance in the hot runner system. A change in resistance can show that heater failure is imminent. A 40% change in resistance signals the alarm; the alarm allows the molder to order the replacement heater and schedule preventative maintenance while optimizing up-time.

Conclusion

Proper planning when undertaking a lights-out molding operation is essential to success. Each molder must carefully examine their specific molding operation, record all parameters affecting their successful molding, and then make use of their controllers by programming them to deal with problems as they occur.

Good controller technology provides excellent features that molders can utilize to ensure the success of their lights-out operation. When in doubt, molders are encouraged to consult with their control suppliers for assistance in programming the equipment for optimal performance. The result of some careful planning can be dramatic increases in overall molding efficiency and profitability.

Contact Gammaflux today for a consultation.