When designing a machine or LEAN work cell for automated part handling, it is very common for the engineering team to break a complex assembly process down into the individual elements required to complete the job. These elements or tasks may be manual, automated or a combination of both. They can also be quite different from each other and require unique tooling, feeding systems, processing equipment, orientation mechanisms and holding fixtures. Automated parts handling systems are essential for parts to flow smoothly.
What Are Part Transfer Methods in Automation?
Part transfer methods are systems used to move components between stations in automated manufacturing processes. These methods include conveyors, robotic systems, and precision transfer mechanisms designed to improve efficiency and consistency.
For example, consider this hypothetical assembly and test sequence. A component needs to be automatically picked from a tray, dipped into an adhesive, inserted into a hole in the part, accurately oriented, heated to cure the adhesive, cooled down to room temperature, flipped over, leak tested and labeled. The part is then secure and safe for an operator to visually inspect it and place it into outgoing dunnage for transfer to another part of the plant. It would be impossible or highly inefficient to do all these tasks in a single workstation, so the engineers decide that multiple automated material handling workstations will be utilized to perform this work in the allotted amount of time.
What Are the Most Common Part Transfer Methods?
The following part transfer methods are commonly used in automated manufacturing systems, each suited for different applications and production requirements:
Manual Transfer
Best for simple processes with low production volume.
The most basic and common material handling method is manual transfer, where an operator moves parts between stations. In a LEAN work cell, there may be a designated spot or fixture for the placement of a single workpiece. This system of transfer is known as “one-piece flow” and it keeps WIP, or “work in process,” to an absolute minimum. When it is not safe for a person to manually move parts or when there isn’t time available, other automated means must be utilized.
Gravity Roller Conveyor and Slides
Best for simple, low-cost movement of parts.
Gravity conveyors and slides use inclined surfaces or rollers to move parts without powered systems. They are commonly used to stage or queue parts, though they offer limited control over speed and orientation. The conveyor or slide is angled so that gravity provides the force necessary to move the parts within the confines of the conveyor’s side rails. It is a very common method used in manual work cells when the part has a flat surface and an accommodating center of gravity.
A variant of this method is vibratory rails and tracks. Instead of gravity, vibratory motion is used to move the parts forward. Part orientation can sometimes be maintained utilizing the geometry or unique clocking features of the part. One disadvantage of this method is the potential for part damage due to part-to-part contact, sliding and collisions.
Walking Beams
Best for precise indexing and controlled part movement.
Walking beam systems lift and move parts between stations in a synchronized motion. They are ideal for maintaining consistent spacing and positioning in automated assembly processes.
Beams can be powered by pneumatic cylinders, hydraulic cylinders, servo-driven actuators or cam motion. The parts can be lifted from below by rails or from above with an array of grippers. Another variation of this concept is to slide all the parts utilizing forked tooling that advances and retracts from behind the part. Walking beams can be a very efficient solution to moving a lot of parts with a minimal number of actuators in a small, in-line, footprint.
Rotary Part Handler
Best for compact systems with multiple processing stations.
Rotary transfer systems move parts in a circular motion between stations. These systems are efficient for high-speed operations and allow multiple processes to occur simultaneously within a smaller footprint.
A “cambot” utilizes a smooth, cam actuated, indexing or oscillating motion. Similar to a walking beam, all of the parts are moved from nest to nest simultaneously by an array of grippers, however, the motion is rotary instead of linear. The main advantage of this transfer method over a rotary dial is that the holding fixture at each station can be unique. At times, that is a big advantage for the machine designer.
Robotic, Servo or Pneumatic Pick & Place Transfer
Robotic and pick-and-place systems use programmable motion to move parts between locations. These systems are highly adaptable and ideal for applications requiring precision, repeatability, or frequent changeovers. There are limitless variations of this method of transferring parts. Pick and place mechanisms can only move parts from point A to point B.
The advantage of using a robotic arm or Cartesian robot is that it can be programmed to move parts to multiple points. A robot is commonly used to move parts from an incoming tray, into the process holding fixture for work to occur, and then into a completed part tray or output conveyor. Robot programs can also be easily changed to accommodate future modifications to the workstation.
Precision Link Indexing Chassis
Best for synchronized, high-speed assembly systems.
Precision linkage chassis use mechanically linked carriers to move parts through fixed stations. They provide accurate positioning and repeatability but are typically less flexible for future modifications. When the chassis is signaled by the controller to index, the chain and all the nests attached to it move the parts a precise distance to the next station. After the work is complete, the chassis indexes again. Precision link chassis is available in two configurations, side by side and over-under.
It is also very common to utilize a single cam motion for both the chassis index and to power many of the workstation actuators. These systems are advantageous for high throughput assembly automation that will make a lot of the same part. They are not as easy to reconfigure or change so generally they are used when the assembly will not need frequent modification or design changes.
Indexing and Reciprocating Rotary Dials
Best for high-speed, repeatable indexing applications.
Rotary dial systems move parts through stations using indexed rotation. These systems are commonly used in assembly processes where consistent timing and positioning are critical. In the past, many dial plates were powered by cam actuated indexers with a set number of stops. More recently, servo motors and gear boxes are being utilized. This allows a controls engineer to program the number of stops allowing for future flexibility to add stations or reverse direction. Machine designers utilize this transfer method to assemble many different products.
A disadvantage of this method is that all the nests must be identical. For high force press operations, the dial plate needs to be supported or the part must be lifted out of the nest and supported from below. Dial plates can only be so large, so if the workstations are wide, you may need to add extra blank stations between process stations. Future flexibility, to accommodate product changes, is also somewhat limited with this transfer method. Also, maintenance accessibility can be challenging due to the compact nature of these machines.
Powered Roller & Belt Conveyors
Best for continuous movement in automated production lines.
Powered conveyors use motors to move parts along a production line. They are ideal for transporting parts between stations and can be integrated with sensors and automation systems for improved control. These transfer devices are utilized more often for material handling tasks as opposed to assembly automation but there are exceptions to every rule. Belt conveyors can move parts into an assembly station where they are located with a vision system and picked up with a robot. Conveyors can also have alignment tooling attached directly to the belt which facilitates accurate location of the parts. Powered roller conveyor or mat top roller conveyor can also move parts from station to station in an assembly system although it is more commonly used in a warehouse setting to move pallets or boxes of product that is already assembled and packaged.
Power & Free Overhead Chain
Best for moving parts through complex production paths.
Overhead chain systems allow parts to be transported above the production floor. These systems provide flexibility in routing and are commonly used in large-scale manufacturing environments. These systems often have larger parts hanging from a hook. One common use is for moving parts through automated paint lines or for moving assembled parts long distances from the manufacturing line to a packaging area.
Recirculating Pallet and Puck Conveyors
Best for controlled, repeatable movement with precise positioning.
These systems use pallets or pucks to carry parts through a looped conveyor system. They allow for accurate positioning at each station and are widely used in automated assembly lines. These are often used to transfer parts and assemblies within an integrated assembly system. It is typical to utilize precision tooling to locate the assembly in a known location on pallets. Pucks are often used instead of pallets if the system is handling cylindrical parts. In both cases, pucks and pallets circulate throughout the powered conveyor system from station to station.
Friction and continuously moving belts or side flexing chains are used to transfer power for moving the pucks and pallets through the system.
These systems are asynchronous, so the pallets or pucks can accumulate in queues prior to entering each station. Pneumatically-controlled stops and pre-stops are used to control the flow of pallets and pucks through the system. When precision location is needed at a particular station, a “lift and locate” mechanism is used. There are an endless number of conveyor configurations possible and this is a huge advantage of this type of part transfer system.
Motorized Pallets and Linear Motor Transfer Systems
Best for high-precision, high-speed automation.
Linear motor systems move pallets independently along a track using electromagnetic force. These systems provide exceptional flexibility, speed, and control for advanced manufacturing environments. A motorized pallet system differs from a recirculating pallet system in that the pallets themselves are individually powered. Each pallet carries a small motor that is powered via an electrified rail in the conveyor. Linear motor transfer systems are becoming more mainstream than they were just ten years ago.
Guided Vehicles
Best for flexible material transport across large facilities.
Automated guided vehicles (AGVs) and autonomous mobile robots (AMRs) move parts between areas without fixed pathways. They are ideal for dynamic production environments that require adaptability. These are typically used for material handling as opposed to automation but, with vision and robotics becoming more common, that is changing rapidly in modern factories. Available in many shapes and sizes, AGVs can move trays, bins, boxes or an entire section of an airplane around a factory. These vehicles are controlled by computer and use a series of sensors or on-board cameras to determine their location and speed. They also use cutting edge technology to determine when obstacles or people are blocking their path.
How Do You Choose the Right Part Transfer Method?
- Choosing the right part handling system depends on:
- Production volume and speed requirements
- Part size, weight, and geometry
- Required precision and orientation control
- Level of automation and integration needed
- Flexibility for future product changes
Solve Complex Part Handling Challenges
Keller Technology Corporation has decades of experience selecting the part handling and transfer systems to use in custom engineered industrial automation. Contact Keller Technology to discuss part handling automation and transfer systems for your manufacturing process.