Automation Industry Association

Delphi Automotive customizes its Injection Molding with Support from System Integrators.

Benefits: Advanced Diagnostics, Better Quality, Low Cost

When Delphi Automotive Products, Michigan, needed closed loop process control for its full-sized pickup truck line presses, it decided to combine a low-cost process control hardware platform with a high-end graphical user interface. Could this be done with standard products from automation vendors? This is where innovative thinking came in.

A low cost Injection Molding Control hardware platform was available, but it did not have a high-end Human-Machine Interface. Delphi wanted to modify the system to utilize a PC-based operator interface and alongwith the automation vendor, organized a cross-functional team that got the job done.

A Systems Integrator in Grandville, Michigan, delivered machine-specific customization and installation services while the hardware vendor provided system training. A software Partner did Visual Basic customer training and worked with Delphi to develop a VB-based program for displaying injection molding parameters.

Delphi makes automotive components, systems, and modules in about 200 factories all over the world. The firm's 10 injection molding plants are equipped with 590 large presses that consume about 180 million pounds (81 million kilograms) of resin each year.

The Adrian facility makes interior components for General Motors. Some of these parts are exceedingly complex, like instrument panels and dashboards.

Any Way You Want:

There were "months of investigation" while Delphi looked at all the options. Then they specified a PLC based Injection Molding Machine Control System adapted for the plastics industry. It provides complete control capabilities for injection molding machine injection, clamp, and ejection. Its standard HMI is used to enter and display speed and pressure set points, temperatures, and other molding parameters.

This packaged product is an "awesome" machine, and comes with open architecture so it can be customized easily. But as one cannot anticipate every possible customer need, it is engineered to let customers make parts any way they want to and not be restricted by the control algorithms.

However, Delphi needed an HMI that showed quality parameters that were to be rapidly processed and displayed. They wanted to read five sensors with a rate of 20 Hz, which amounts to about 5K for each 50 second molding cycle. Dedicated hardware-based solutions typically use high-speed analog to digital converter cards to buffer this data. The challenge was how to handle this on a conventional PC running Windows NT®?

Working together, Delphi and the Software Partner blocked off a 5K memory area in the PLC to collect data during the cycle. At the end of each cycle, a Visual Basic program running on the PC reads the data without requiring any proprietary hardware. This program uses a variety of ActiveX controls as Dynamic Data Exchange (DDE) clients, to read the PLC data.

A key advantage of the new software, named Injection Profiler, is that it can be configured easily because it is software rather than hardware based. The user can click a button to change from monitoring hydraulic pressure, cavity pressure, or screw velocity. Development costs were low because the program was based on off-the-shelf products.

Having established the design criteria for Injection Profiler, the System Integrator developed the PLC programming to do the necessary data gathering and wrote the other VB-based applications that were needed to round out the operator interface. The overall application can track all operator initiated changes to the process.

Going the Extra Mile:

The Injection Molding Control system automatically tunes the hydraulic system of an injection molding machine to eliminate error. "The screen shows what pressures should be through a cycle," says the System Integrator. "If the pressures are OK, the part is OK and there's no inspection sampling. If the pressures are wrong in some way, you get a bad part," he continues. "The part is rejected and then you figure out what happened. One possibility is plant temperature or humidity-an outside variable that can influence the way an injection molding machine functions. If there's a problem with the injection molding process, you know about it in real time. The control system compensates automatically to get the process back on track. If the problem is too large for it to handle, you get an alarm. Probably it's a mechanical or hydraulic problem, so the machine shuts down."

Modern PLC architecture provides excellent value in process control and can be extremely flexible. Its design allowed Delphi's modification to go smoothly. The leadership of the Systems Integrator and his close association with the Software Partner were crucial to the project's success.

- Debasish Ghosh