In the fast-paced world of injection molding production lines, selecting the right automation equipment directly impacts efficiency, costs, and ultimately product quality. When it comes to robotic arms, six-axis articulated robots and Cartesian robots (also called linear robots) often take center stage. Each has distinct advantages—much like choosing between a frying pan and pasta pot for different cooking tasks—and selecting the wrong type can lead to inefficiencies.

Six-Axis Robots: Unlocking Unparalleled Flexibility

Six-axis articulated robots derive their name from their six independent rotating axes, which provide near-human-arm dexterity. These robots can grasp objects at virtually any angle and reach nearly any point within their working envelope. This exceptional versatility enables them to perform diverse operations including loading/unloading, part transfer, decoration, assembly, and inspection. They can even collaborate with Cartesian robots to achieve more complex automation workflows. Multiple mounting options and continually improving speed and programming ease further enhance their adaptability.

The Power Behind Six-Axis Robots

The core strength of six-axis robots lies in their superior flexibility. Their design mimics the human arm, featuring a shoulder-like base rotation, elbow-like bending joints, and a multi-directional "wrist." This structure provides exceptional freedom of movement, enabling precise grasping and placement in various orientations. Consequently, six-axis robots have become one of the most prevalent designs in general industrial applications, widely used for welding, painting, material handling, laser cutting, bonding, assembly, quality inspection, and—critically—part removal in injection molding.

Programming Challenges and Technological Advancements

However, this high degree of flexibility demands equally capable control systems to accommodate diverse applications. Historically, programming six-axis robots for tasks like part removal was more complex than programming Cartesian robots, which typically come with injection-molding-specific control systems offering more intuitive programming. Even simple linear movements with six-axis robots required coordinated motion across multiple joints, leading some molders to believe specialized personnel were needed for programming and maintenance.

This landscape is changing. For instance, Sepro's 6X series articulated robots now use the same Visual control system as their Cartesian counterparts. Through simplified "pick-and-place" programming, users simply identify key points (pickup, quality check, discharge, stacking, etc.) and manually "teach" the robot path. Trajectories (linear or curved) are automatically calculated. As a result, injection molders now find six-axis robots significantly easier to program and operate, enabling them to evaluate Cartesian and articulated configurations purely based on application requirements.

Space Considerations and Mounting Flexibility

Another common concern with six-axis robots is floor space usage. Cartesian robots typically mount above the injection machine's fixed platen, operating primarily above and beside the machine to conserve valuable floor space. Six-axis robots are most commonly floor-mounted beside the machine—an advantage in facilities with height restrictions—but do require more floor area. They typically work from one side (usually the machine rear to avoid interfering with control panels).

However, six-axis robots aren't limited to floor mounting. Depending on application and environment, they can also mount above molds, on fixed platens, nearby walls, or even ceilings. For example, in vertical-clamp insert molding, floor-mounted six-axis robots can effortlessly access multiple stations on rotating tables without vertical-clamp interference.

Additional Key Considerations

• Speed: While six-axis robots have dramatically improved in speed—often matching Cartesian robots in many motions—Cartesian beam-style robots are generally faster when entering/exiting mold spaces for part removal. This explains why most high-speed injection molding applications prefer Cartesian beam robots or dedicated side-entry units.
• Payload Capacity: Sepro's largest beam-style robot handles approximately 90kg (part + EOAT). By comparison, the largest six-axis robot designed for equivalent machine sizes manages 113kg or more, depending on required reach. Maximum payload typically decreases as reach increases.
• Cost: While six-axis robot costs have declined, Cartesian robots with servo-driven wrists typically remain about 30% less expensive than six-axis units.

Collaborative Automation: Combining Strengths

Cartesian and six-axis robots aren't mutually exclusive—they can work together. For example, a machine-mounted beam robot might remove parts before transferring them to a six-axis robot for secondary operations. This combined approach proves ideal when injection cycles are relatively short but downstream processes are numerous, complex, or time-consuming.

The Collaborative Robot (Cobot) Perspective

In plastics, collaborative robots (cobots) largely resemble six-axis articulated robots but incorporate sensors and features to detect human presence and avoid hazardous movements. Proponents highlight cobots' greater flexibility and easier programming compared to standard six-axis robots. However, traditional six-axis robots generally outperform cobots in speed and payload capacity, while cobots' main drawbacks include limited portability and required safeguards.

Sepro Group's partnership with Universal Robots—a cobot market leader—helps injection molders more easily integrate cobots. By equipping leading cobots with Visual control systems, Sepro ensures seamless integration with other Sepro robots and injection machines.

Sepro also developed a hybrid solution—the SeproBot concept—using traditional six-axis or Cartesian robots within physical guards featuring sensor-protected access points. Normally operating at full speed, these systems slow or stop only when humans enter protected areas, resuming full speed after departure. This allows SeproBots to operate two to three times faster than typical cobots while maintaining safe human-robot interaction.

Just as Cartesian and articulated robots can collaborate to integrate machine feeding with downstream operations, cobots with Visual control can enable safe, open multi-robot configurations for diverse processes—including peripheral operations or advanced automation cells.