PLC Retrofit for a Used Roll Former — Scope, BOM, FAT/SAT & Commissioning

Introduction — Why PLC Retrofits Are Common in Used Roll Forming Machines

Many roll forming machines remain mechanically capable of production long after their original control systems become obsolete. Older machines often contain outdated PLC systems, aging electrical components, and unsupported automation hardware.

A PLC retrofit replaces or upgrades the machine control system while keeping the mechanical equipment intact.

Retrofits are commonly performed when machines experience problems such as:

• obsolete PLC hardware
• unreliable control electronics
• lack of spare parts availability
• poor operator interfaces
• limited automation capability

Instead of replacing the entire machine, upgrading the control system allows manufacturers to modernize the equipment at a significantly lower cost.

A well-planned PLC retrofit improves:

• machine reliability
• diagnostics and troubleshooting
• operator usability
• production efficiency

This guide explains how PLC retrofits are planned and executed for roll forming machines.

What Is a PLC Retrofit?

A PLC retrofit involves replacing or upgrading the machine control system while keeping the mechanical equipment in place.

Typical retrofit elements include:

• PLC controller replacement
• new I/O modules
• modern HMI interface
• updated servo or VFD drives
• safety system upgrades
• new electrical cabinet components

The retrofit modernizes the automation system while preserving the machine structure.

Determining the Scope of a Retrofit

The first step in a PLC retrofit project is defining the project scope.

This determines which components will be replaced and which can remain in service.

Common retrofit scope elements include:

• replacing the PLC processor
• upgrading operator interface systems
• replacing obsolete communication networks
• updating safety circuits
• upgrading motor drives

Some retrofits replace only the PLC controller, while others include a complete electrical redesign.

The scope depends on factors such as machine age, condition, and production requirements.

Machine Assessment Before Retrofit

Before designing the retrofit system, the machine must be inspected thoroughly.

The assessment should evaluate:

• mechanical condition
• electrical wiring condition
• sensor types and locations
• drive systems
• hydraulic components

Documentation should also be collected.

Important documents include:

• electrical schematics
• PLC programs
• drive configuration files
• machine manuals

Understanding the existing system helps engineers design an effective retrofit solution.

Selecting the New PLC Platform

Choosing the correct PLC platform is critical.

The PLC should be selected based on:

• machine complexity
• required I/O capacity
• communication requirements
• motion control needs

Common PLC platforms used in roll forming retrofits include:

• Siemens S7 systems
• Rockwell ControlLogix or CompactLogix
• Beckhoff control systems

The selected platform should provide long-term support and availability.

Developing the Bill of Materials (BOM)

The Bill of Materials defines all components required for the retrofit.

Typical BOM items include:

• PLC CPU
• digital input modules
• digital output modules
• analog input modules
• analog output modules
• HMI operator panel
• industrial network switches
• safety relays or safety PLC

Additional components may include:

• power supplies
• terminal blocks
• relays and contactors
• communication cables

A detailed BOM ensures that all necessary components are available during installation.

Electrical Panel Design

Many PLC retrofit projects involve redesigning the electrical control cabinet.

Panel design considerations include:

• component layout
• power distribution
• cable routing
• cooling and ventilation
• grounding systems

Proper cabinet design improves reliability and simplifies maintenance.

PLC Program Development

The PLC program must be developed or adapted for the new control system.

Typical PLC program sections include:

• machine start/stop logic
• safety interlocks
• drive control
• encoder length measurement
• shear control sequences
• alarm handling

The program should be modular and well documented to simplify future maintenance.

HMI Interface Design

The HMI provides the operator interface for the machine.

Typical HMI functions include:

• machine status display
• alarm notifications
• production counters
• recipe selection

Modern HMIs provide graphical interfaces that make machines easier to operate and diagnose.

Factory Acceptance Testing (FAT)

Before the retrofit system is installed on the machine, it should undergo Factory Acceptance Testing.

FAT verifies that the control system operates correctly before shipment.

Typical FAT tests include:

• PLC program verification
• I/O signal simulation
• HMI functionality testing
• safety circuit verification
• communication network testing

FAT helps identify problems before installation.

Installation of Retrofit System

Installation involves removing the old control system and installing the new hardware.

Typical installation tasks include:

• removing obsolete PLC hardware
• installing new control cabinet components
• rewiring sensors and actuators
• connecting communication networks

Careful wiring and labeling are essential for reliable operation.

Site Acceptance Testing (SAT)

After installation, the system undergoes Site Acceptance Testing.

SAT verifies that the retrofit system operates correctly with the machine.

Typical SAT procedures include:

• verifying sensor signals
• testing output devices
• confirming drive operation
• validating safety systems

SAT ensures that the machine is ready for commissioning.

Commissioning the Retrofit System

Commissioning brings the machine into production using the new control system.

Typical commissioning steps include:

1. verify PLC communication with all devices
2. test I/O signals
3. configure drive parameters
4. verify encoder measurements
5. test machine motion at low speed

Production testing should begin slowly to identify any remaining issues.

Verifying Machine Performance

Once commissioning is complete, the machine must be tested under production conditions.

Verification includes:

• measuring panel lengths
• checking punch accuracy
• verifying machine speed capability

Adjustments may be required to optimize performance.

Benefits of PLC Retrofits

PLC retrofits offer several advantages for roll forming manufacturers.

These include:

• extended machine lifespan
• improved reliability
• easier troubleshooting
• modern operator interfaces
• improved production efficiency

A well-designed retrofit can significantly improve machine performance.

FAQ — PLC Retrofits for Roll Forming Machines

Why retrofit the PLC on a roll forming machine?

PLC retrofits replace outdated control systems, improving reliability, diagnostics, and compatibility with modern automation technologies.

What components are typically replaced during a retrofit?

Common replacements include the PLC controller, HMI interface, I/O modules, communication networks, and sometimes motor drives.

What is FAT in a PLC retrofit project?

Factory Acceptance Testing verifies the control system functionality before installation at the customer site.

What is SAT in a retrofit project?

Site Acceptance Testing confirms that the system operates correctly once installed on the machine.

How long does a PLC retrofit typically take?

Retrofit projects can take several weeks depending on the complexity of the machine and the scope of upgrades.

Does a PLC retrofit improve machine performance?

Yes. Modern control systems provide faster processing, improved diagnostics, and better automation capabilities.