#coggingforce

Iron-Core Linear Motor Applications in Laser Welding Machines Laser Processing Automation | Linear Motion Components

Direct-Drive Motion on the Weld Axis

An iron-core linear motor moves a mover directly along a magnetic track. The mover carries iron laminations wound with copper coils. In turn, these coils interact with a magnet track fixed to the base rail. This magnetic interaction produces thrust without gears, screws, or belts. As a result, a laser welding machine gains direct-drive motion with zero mechanical backlash. In fact, every millimeter of travel comes straight from the electromagnetic field. No transmission link sits between the motor and the welding head. This direct coupling also cuts maintenance points across the whole gantry. Laser welding machines must track a seam path at a fixed torch angle and a steady speed. Any wobble along the path throws off the focus spot on the workpiece. An iron-core linear motor holds the welding head on this path with a stiff magnetic coupling. Therefore, the head follows straight lines and tight corners without lag. At the same time, the motor keeps constant velocity through the whole weld pass. Consequently, the heat input into the seam stays even from start to finish. In this case, uneven speed never shows up as a weak spot in the joint. For example, seam tracking accuracy stays tight even at high traverse speed.

Why Iron Core Linear Motor Raises Thrust

Iron laminations inside the mover raise the magnetic flux between the coil and the magnet track. This raised flux delivers much higher thrust for the same mover size. In fact, an iron-core design pushes force density up to double an ironless motor's rating. However, iron also pulls the mover toward the magnet track with strong attraction force. This attraction force can run five to thirteen times the rated thrust of the motor. So the bearing and rail system must handle this pull without flexing. In turn, TallMan Robotics pairs the iron-core mover with heavy-duty linear guides rated for this load.

Cogging and Thermal Behavior

Iron-core motors also produce a small cogging force as the laminations cross each magnet pole. This cogging force can ripple the velocity of the moving head. However, modern servo drives compensate for cogging through current feedback and motion profiling. As a result, a well-tuned iron-core axis still delivers smooth weld speed control. Meanwhile, the same iron core gives the motor strong thermal performance under continuous duty. This thermal strength supports long welding cycles without a drop in thrust.

Iron Core Linear Motor vs. Ironless Linear Motor

Function

Iron Core Linear Motor

Ironless Linear Motor

Thrust output High force density, up to double an ironless motor Lower force density for the same frame size Attraction force Five to thirteen times rated thrust, pulls mover to track None; no magnetic pull between mover and track Cogging effect Present, offset by servo current compensation Absent; naturally smooth force delivery Thermal performance Strong heat dissipation through the iron core Lower heat dissipation than iron-core designs Bearing and rail demand Heavy-duty guides needed for the attraction load Lighter guides sufficient without magnetic pull Best fit High-thrust laser welding and cutting gantries Ultra-smooth scanning and light-payload positioning Table 1. Functional comparison for engineers selecting a linear motor axis on a laser welding gantry.

Case Study Figures

Field data confirms this performance profile. One linear motor gantry built for flat sheet processing reaches a positioning speed of 2 meters per second. This gantry holds repeatability to 0.005 millimeters across the travel range. In similar fashion, gantry stages built specifically for laser welding duty pair iron-core linear motors with recirculating ball guides and absolute linear encoders. This pairing keeps the welding head locked to programmed coordinates through the full weld cycle. These figures show why iron-core linear motors dominate high-thrust laser processing gantries today. Consequently, system integrators specify this motor type for continuous multi-shift welding lines.

Selecting an Iron-Core Linear Motor for a Laser Welding Line

Engineers choose an iron-core linear motor for a laser welding line by weighing four factors. First, the rated thrust must clear the mass of the welding head, cable carrier, and any wobble optics. Second, the attraction force rating sets the bearing and rail specification for the whole axis. Third, the cogging force spec sets how much velocity ripple the seam can tolerate at weld speed. Finally, the cooling method sets the duty cycle the motor can sustain.

Technical Parameters at a Glance

Parameter

Typical Range

Function in Laser Welding

Positioning speed Up to 2 m/s (gantry-class stage) Sets weld traverse speed on flat-sheet seams Repeatability ± 0.005 mm (gantry-class stage) Keeps the focus spot locked to the seam path Attraction force 5 to 13 × rated thrust Sets the bearing and rail specification Force density Up to 2 × an ironless motor Delivers high thrust in a compact mover Guide type Recirculating ball guide Carries the attraction load without deflection Feedback device Absolute linear encoder Holds position through power cycles, no homing needed Table 2. Representative iron-core linear motor parameters relevant to laser welding gantries.

Conclusion