Replacing Obsolete PLCs on Roll Forming Machines — S5, S7-300, MicroLogix and Legacy Platforms

Introduction — Why PLC Obsolescence Is a Major Risk in Roll Forming

Roll forming machines often remain in production for decades. The mechanical components of the machine—such as the forming stands, gearboxes, and frames—can easily last 20 to 40 years. However, the PLC control system rarely lasts that long.

Many older roll forming machines still operate using control platforms such as:

• Siemens S5
• Siemens S7-300
• Allen-Bradley MicroLogix
• Mitsubishi A-Series
• early Omron PLC systems.

These platforms were reliable in their time but are now approaching or have reached end-of-life support.

Operating critical production machinery on obsolete PLC hardware introduces several risks:

• spare parts shortages
• expensive second-hand components
• unexpected machine downtime
• inability to update software
• cybersecurity vulnerabilities.

Replacing obsolete PLC systems safely is therefore an important modernization step for many roll forming manufacturers.

Common Obsolete PLC Platforms in Roll Forming Machines

Several PLC platforms frequently appear in older roll forming equipment.

Siemens S5

The Siemens S5 series was widely used in industrial automation throughout the 1980s and 1990s.

Characteristics:

• rack-based architecture
• limited programming memory
• STEP5 programming software.

These systems are now completely obsolete and spare parts are increasingly difficult to find.

Siemens S7-300

The S7-300 was one of the most widely used PLC platforms for industrial automation.

Characteristics:

• modular rack system
• widely used in forming lines
• STEP7 programming environment.

Although widely supported for many years, the S7-300 platform is now being phased out in favor of newer Siemens PLCs.

Allen-Bradley MicroLogix

MicroLogix PLCs were widely used in smaller machines and auxiliary systems.

Characteristics:

• compact controllers
• ladder logic programming
• RSLogix software.

While many machines still run MicroLogix systems, Rockwell Automation has transitioned toward newer platforms such as CompactLogix.

Mitsubishi A-Series

Older Mitsubishi systems are still present in some Asian-built roll forming machines.

Characteristics:

• large rack systems
• older programming tools.

Most modern Mitsubishi machines now use newer iQ-Series controllers.

Signs That a PLC Platform Needs Replacement

Several warning signs indicate that a PLC system should be replaced.

Common indicators include:

• difficulty sourcing spare parts
• increasing electrical faults
• communication failures with HMIs
• unsupported programming software
• aging hardware components.

When these issues begin affecting production reliability, replacing the PLC becomes necessary.

Risks of Operating Obsolete PLC Systems

Continuing to run production machinery with obsolete PLC systems can lead to serious operational risks.

Spare Parts Availability

Replacement modules may only be available on the second-hand market.

Used parts may have unknown operating history and limited remaining lifespan.

Unexpected Downtime

If a critical PLC component fails, production may stop until a replacement part can be located.

This can lead to expensive downtime.

Software Compatibility Issues

Older programming software may not run on modern operating systems.

Engineers may struggle to connect to the PLC for diagnostics or program updates.

Cybersecurity Vulnerabilities

Legacy systems often lack modern security features.

Machines connected to industrial networks may be vulnerable to cyber threats.

Planning a PLC Replacement Project

Replacing an obsolete PLC should be carefully planned.

A structured approach reduces risk and minimizes production disruption.

The main planning steps include:

1 documenting the existing control system
2 selecting the replacement PLC platform
3 creating a migration strategy
4 testing the new control system.

Each step is essential for a successful upgrade.

Documenting the Existing PLC System

Before removing the old PLC, engineers must document the existing control system.

Important information includes:

• PLC model and hardware configuration
• I/O modules and addresses
• communication interfaces
• wiring diagrams
• HMI connections.

Engineers should also obtain a copy of the existing PLC program.

This information is essential when rebuilding the control logic on the new system.

Extracting the Existing PLC Program

Whenever possible, engineers should upload the current PLC program.

This provides insight into the machine’s control logic.

The program can then be analyzed and translated into the new PLC environment.

If the program is unavailable, engineers must reconstruct the logic manually using electrical drawings and machine observation.

Choosing the Replacement PLC Platform

Selecting the new PLC platform is a critical decision.

Common replacement platforms include:

• Siemens S7-1200 or S7-1500
• Allen-Bradley CompactLogix
• Mitsubishi iQ-F or iQ-R
• Omron NX series.

The choice often depends on:

• regional support availability
• machine complexity
• existing maintenance staff experience.

Choosing a widely supported platform simplifies future maintenance.

Migrating the Control Logic

The old PLC program must be recreated in the new PLC environment.

This process involves:

• converting ladder logic structures
• mapping old I/O addresses to new addresses
• rewriting machine sequences.

Engineers should use structured programming methods to improve clarity and maintainability.

I/O System Migration

Existing field devices must be connected to the new PLC.

Typical devices include:

• proximity sensors
• limit switches
• hydraulic valves
• motor starters.

The new PLC must have enough input and output capacity to support all devices.

During migration, engineers should also inspect field wiring and replace damaged cables.

HMI Integration

The existing HMI may also require replacement.

Older HMIs often use communication protocols that are not compatible with new PLC platforms.

Installing a modern HMI provides improved operator control and diagnostics.

Typical features include:

• touchscreen operation
• alarm history
• recipe management.

Electrical Cabinet Upgrades

Replacing the PLC may require modifications to the electrical control cabinet.

Typical changes include:

• new PLC mounting rails
• updated power supplies
• improved wiring layout.

Proper cabinet design improves cooling and electromagnetic compatibility.

Testing the New PLC System

Once the new system is installed, engineers must perform comprehensive testing.

Typical testing stages include:

1 verifying I/O signals
2 testing manual machine functions
3 validating automatic sequences
4 testing safety circuits.

Testing ensures that the machine behaves exactly as expected.

Commissioning the Upgraded System

After testing, the machine should be run under real production conditions.

Commissioning activities include:

• verifying production speeds
• checking product quality
• adjusting machine timing parameters.

Operators should also be trained on the new system.

Reducing Risk During PLC Replacement

To reduce risk during migration, engineers often use staged upgrade strategies.

Possible strategies include:

• running the old PLC in parallel during testing
• installing the new PLC offline for development
• performing upgrades during planned shutdown periods.

Careful planning prevents unexpected production interruptions.

Benefits of Modern PLC Platforms

Replacing obsolete PLC systems provides several benefits.

These include:

• improved reliability
• easier diagnostics
• better spare parts availability
• improved communication with modern devices.

Modern PLC platforms also support advanced features such as remote monitoring and predictive maintenance.

Extending the Life of Roll Forming Machines

Replacing an obsolete PLC allows older roll forming machines to remain productive for many more years.

Instead of replacing the entire machine, manufacturers can modernize the control system.

This approach reduces capital expenditure while improving operational reliability.

FAQ — PLC Replacement

Why should obsolete PLC systems be replaced?

Older PLC systems may fail unexpectedly and spare parts are often difficult to obtain.

Can the existing PLC program be reused?

In many cases the logic must be rewritten or converted for the new platform.

Will replacing the PLC change how the machine operates?

The goal is to maintain the same machine behavior while improving reliability and diagnostics.

Can the existing sensors and actuators be reused?

Yes. Many field devices can remain in place if they are in good condition.

How long does a PLC replacement project take?

Project duration depends on machine complexity but may range from several days to several weeks.

What is the biggest risk when replacing a PLC?

Insufficient documentation of the original control system can make migration difficult.