Full PLC Retrofit Guide for a Used Roll Former — Scope, Hardware Selection & Bill of Materials

Introduction — Why PLC Retrofits Are Common in Roll Forming Machines

Many roll forming machines operate for decades. Mechanically, these machines can remain productive for 20–40 years, but the control systems often become obsolete much sooner.

Older roll forming machines frequently use:

• outdated PLC platforms
• relay-based control systems
• unsupported drive technology
• obsolete HMIs.

When spare parts become difficult to obtain or control reliability decreases, a PLC retrofit becomes the best solution.

A well-planned retrofit can transform an old roll forming machine into a modern production system with:

• improved reliability
• modern diagnostics
• better safety integration
• remote support capability.

This guide explains how to plan and execute a complete PLC retrofit for a used roll former.

What Is a PLC Retrofit

A PLC retrofit replaces the existing machine control system with a modern automation platform.

Typical components replaced include:

• PLC CPU and I/O modules
• HMI operator interface
• electrical control panels
• communication networks
• drive control systems.

The retrofit preserves the mechanical structure of the machine while modernizing the control electronics.

When a Roll Former Needs a PLC Retrofit

Several signs indicate that a retrofit may be required.

Common indicators include:

• frequent electrical faults
• obsolete PLC hardware
• unavailable spare parts
• unreliable machine operation
• limited diagnostics.

Older relay-based systems may also lack modern safety features.

Upgrading the control system improves both reliability and safety.

Defining the Retrofit Scope

The first step in any retrofit project is defining the scope of work.

Scope planning determines which components will be replaced and which will remain.

Typical retrofit scope elements include:

• PLC replacement
• new HMI system
• drive interface upgrades
• electrical cabinet redesign
• wiring upgrades.

Clearly defining the scope prevents project delays and cost overruns.

Evaluating the Existing Machine

Before designing the new control system, engineers must evaluate the existing machine.

Important information includes:

• machine functions
• sensor types
• actuator systems
• existing wiring layout.

Technicians should document the current control system thoroughly.

Photographs and wiring diagrams are valuable during this stage.

Identifying Machine Functions

A roll forming machine contains multiple automation functions.

Typical functions include:

• uncoiler control
• pinch roll operation
• roll forming drive control
• punching or notching systems
• shear cutting systems
• stacker control.

Each function must be mapped to the new PLC control architecture.

Creating an I/O List

An I/O list identifies all sensors and actuators connected to the control system.

Typical inputs include:

• proximity sensors
• limit switches
• pressure switches
• encoder signals.

Typical outputs include:

• hydraulic solenoid valves
• motor contactors
• stacker actuators
• alarm signals.

Creating a complete I/O list ensures the new PLC has sufficient input and output capacity.

Selecting the PLC Platform

Choosing the correct PLC platform is critical for a successful retrofit.

Common PLC platforms used in roll forming machines include:

• Siemens S7 series
• Allen-Bradley CompactLogix
• Mitsubishi FX series
• Omron NX series
• Delta PLC systems.

The choice depends on factors such as:

• local support availability
• machine complexity
• budget.

Selecting a platform with strong regional support simplifies maintenance.

HMI System Selection

Modern roll forming machines typically include touchscreen HMI interfaces.

The HMI allows operators to:

• start and stop the machine
• load product recipes
• monitor alarms
• view diagnostics.

Popular HMI platforms include:

• Siemens Comfort panels
• Allen-Bradley PanelView
• Weintek industrial HMIs.

The HMI should provide clear operator controls and diagnostic screens.

Drive System Integration

Most roll forming machines include motor drives.

Typical drive types include:

• VFD drives for line speed control
• servo drives for positioning systems.

The retrofit design must ensure proper communication between the PLC and drives.

Communication methods may include:

• PROFINET
• EtherNet/IP
• Modbus.

Proper drive integration improves machine performance.

Safety System Upgrade

Older machines may lack modern safety systems.

A retrofit project often includes upgrading safety components such as:

• safety relays
• guard switches
• emergency stop circuits
• safety light curtains.

These upgrades help meet current safety standards.

Electrical Cabinet Redesign

Many retrofits involve redesigning the electrical control cabinet.

New cabinets may include:

• PLC hardware
• power supplies
• communication modules
• safety relays.

Proper cabinet layout improves cooling and reduces electrical noise.

Wiring Upgrades

Older wiring systems may degrade over time.

Retrofitting often includes replacing:

• control wiring
• communication cables
• sensor wiring.

Modern wiring practices improve reliability and maintainability.

Example PLC Retrofit Bill of Materials (BOM)

A typical PLC retrofit BOM may include the following components.

PLC Hardware

• PLC CPU module
• digital input modules
• digital output modules
• analog input modules
• communication modules.

HMI System

• industrial touchscreen HMI
• mounting hardware.

Electrical Components

• industrial power supplies
• safety relays
• terminal blocks
• circuit breakers.

Network Equipment

• industrial Ethernet switch
• shielded Ethernet cables.

Miscellaneous Components

• wiring ducts
• cable glands
• cabinet cooling fans.

The exact BOM depends on machine complexity.

Software Development

PLC retrofit projects require new control software.

Typical software tasks include:

• PLC program development
• HMI interface design
• communication configuration
• safety logic implementation.

Engineers must replicate the original machine functionality while improving diagnostics and reliability.

Testing the New Control System

After installation, the new control system must be tested thoroughly.

Testing phases may include:

• input/output verification
• manual function testing
• automatic sequence testing
• safety system validation.

Testing ensures that all machine functions operate correctly.

Factory Acceptance Testing (FAT)

Factory Acceptance Testing verifies the control system before full production use.

Typical FAT procedures include:

1 verifying sensor inputs
2 testing actuator outputs
3 validating machine sequences
4 checking alarm handling.

Successful FAT ensures the system is ready for production.

Site Acceptance Testing (SAT)

Site Acceptance Testing confirms machine performance under real production conditions.

Typical SAT activities include:

• running test material
• verifying product quality
• testing maximum line speed.

SAT confirms the retrofit meets production requirements.

Benefits of PLC Retrofits

A well-executed retrofit offers many advantages.

These include:

• improved reliability
• modern diagnostics
• easier spare parts availability
• improved operator interface.

Retrofitting often extends the life of the machine by many years.

Production Impact of PLC Upgrades

Upgrading control systems improves production stability.

Benefits may include:

• reduced downtime
• faster troubleshooting
• improved machine control accuracy.

For roll forming companies, this can significantly increase productivity.

Preventing Future Obsolescence

When designing a retrofit, engineers should consider long-term support.

Important factors include:

• selecting widely supported PLC platforms
• documenting the control system
• maintaining software backups.

These practices ensure future maintenance is easier.

FAQ — PLC Retrofit Projects

Why retrofit a roll forming machine instead of buying a new one?

Retrofits are often more cost-effective when the machine structure is still mechanically sound.

What components are replaced during a PLC retrofit?

Typical replacements include the PLC, HMI, electrical wiring, and control cabinet components.

How long does a PLC retrofit take?

Depending on machine complexity, retrofits may take several days to several weeks.

Can modern safety systems be added during a retrofit?

Yes. Safety upgrades are often included during PLC retrofit projects.

Will the machine operate faster after a retrofit?

In many cases, improved control systems allow better speed control and reliability.

What is the most important step in a PLC retrofit?

Careful planning and accurate documentation of the existing machine systems.