Historically, there have been two methods to automate the tending of parts in a CNC machine: part picking robots and pallet picking robots. VersaBuilt’s MultiGrip is a third method for automated tending of a CNC machine. We’ll look at how each technology works, some of the pluses and minuses of each, and how some of the characteristics of your parts and your production may make one technology a better choice than another.
Pallet Loaders
Pallet Loading CNC automation systems shuttle pallets to and from the CNC machine. Each pallet has some sort of fixturing to secure one or more parts to the pallet. Two or more pallets are fed into and out of the CNC machine by the automation system.
A Six-Axis Robot Pallet Loader is shown in this video. Other forms of Pallet Loaders include Horizontal Machining Centers with Pallet Pools.
One of the main advantages of a pallet loading automation system is that they are simple to integrate into the average CNC machine shop. Because the pallet system picks up the same thing every time, a pallet, the automation system doesn’t need to know anything about how to grab the part. Pallet loading automation systems are typically pre-programmed from the factory and only require basic training for the machinists and operators to use effectively. Pallet loading automation systems are generally the most reliable; the automation system itself sees little to no variation regardless of the type of part it is running.
Pallet loading automation systems make it easy for machinists to add parts to the automation system. Traditional CNC fixturing techniques are used and fixtures are easily made in the CNC machine. Another advantage of the pallet loading automation system is the ability to gang multiple parts on a single pallet, increasing CNC processing efficiency.
All of this ease and simplicity does come at a cost. Depending on how the system is configured, pallets and pallet fixturing can be very expensive. Getting long unattended run times requires the ability to load lots of parts into the machine at a time. Running 50 parts at once may require up to 100 fixtures (one for each milling operation), spread across many pallets, all dedicated to a single part. Now imagine fixturing for 100 different part numbers? There are strategies available to reduce the number of unique fixtures and still have long unattended run times. However, each strategy presents its own unique challenges that could make a pallet loading automation system less effective than other automation choices.
Another drawback to a pallet loading automation system is higher operator labor requirements when compared to other automation systems. A pallet loader still requires the operator to fixture every part to the pallet for each milling operation. Pallet loaders typically increase CNC machine efficiency but often require similar amounts of labor when compared to an operator tended CNC. Relying on operators to properly fixture parts increases variability, reducing quality and sometimes resulting in damaged equipment. If a pallet loader is used in a high-mix environment, changing over dozens of fixtures could take hours or even days, sapping operator labor and CNC machine efficiency.
So are pallet loaders always a bad idea? Definitely not, they are much better suited to some applications than others. Although a thorough discussion of where pallet loaders are best suited is beyond the scope of this document, I will throw out where I think they make the most sense.
Part Loaders are Best For:
- Heavy parts that can’t be picked with a traditional gripper
- Parts with geometries that can’t easily be picked by a robot with a gripper – like irregularly shaped castings
- Parts that will be run over a very long time (higher fixturing costs can be amortized)
- Shops that run a limited number of part numbers allowing for a static configuration of the pallet automation system
- Shops that are uncomfortable with new technologies
Part Pickers
Part picking CNC automation systems use a gripper to transfer parts from an infeed to an automatic clamping fixture in the CNC. The robot gripper picks the parts directly, hence the term part picking robot. Picking the part directly represents both a benefit and a challenge.
A Part Picking automation system performing a single milling operation with unique gripper fingers for each operation.
One of the main disadvantages of part pickers is that the automation system needs to understand and adapt to each part added to the system. That means automation system programming and gripper design may be necessary for each part added to the system. Automation system programming and gripper design can be complex and require additional effort or contracting with an expert in robot integration to complete. If you manufacture lots of unique parts, the time cost of integrating each part into the automation system can be significant. Part pickers are generally less reliable than pallet loaders because part pickers must contend with more variability.
For part shapes that start simple, rectangles and squares, and stay simple through the machining process, managing part variability can be relatively easy to manage. Things get more complicated if the part geometry becomes more complex after machining or multiple milling operations are required. If the part geometry changes significantly from raw material to after the first operation, the gripper that loaded the part may not be able to unload the part. In this case, the automation system needs to have two grippers, each with unique gripper fingers, to process the part.
Animation showing some of the challenges in an Op 1 to Op 2 transfer with traditional robot grippers
For many part shapes, a traditional robot gripper is not able to pick a part out of the first operation vise, flip it over, and load it into the second operation vise. Instead, the part must be put down on a custom re-grip fixture so the robot can “re-grip” the part from another angle before loading the part into the second operation fixture.
That’s a lot of disadvantages. So what are the big advantages to part pickers? Lower fixturing costs and less operator labor when compared to pallet loaders. A part picker can process any number of parts with a single set of grippers and CNC fixtures. A part picker does not require the operator to secure each part to a fixture, just to stage the parts in the infeed. Changeover time is typically less with a part picker vs a pallet loader.
Part Pickers are Best For:
- Part shapes that start simple and stay simple
- Single milling operation parts
- High-mix production
- Shops with strong internal technical expertise capable of programming robots
- Shops with labor shortages
MultiGrip: The Best of Both Worlds?
If a pallet loader and a park picker got together and had a baby, it would be MultiGrip. Like a pallet loader, MultiGrip is easier for the average machine shop to add their own parts to the automation system and does not require robot programming. Like a part loader, MultiGrip has much lower fixturing costs and takes less operator labor than a pallet loader. Unlike either a pallet loader or a part picker, MultiGrip can process almost any part shape through multiple operations efficiently and with no extra fixturing or programming.
Video showing job setup and the processing of a two operation part using MultiGrip
MultiGrip is a gripper, vise, and vise jaws that all work together. Like a pallet loader, MultiGrip always picks up and loads the same thing: a set of MultiGrip vise soft jaws. Like a part picker, the MultiGrip gripper can use the MultiGrip vise jaws to pick parts from the infeed. The robot then loads the MultiGrip vise jaws and part into the MultiGrip vise for processing.
Machinists tend to like MultiGrip because it is a familiar form of fixturing and it is simple to make all the fixturing necessary for automation in the CNC. No need to design and make gripper fingers or learn how to program a robot. For the operator, job setup is fast and easy. MultiGrip vise jaws can be exchanged in just a few seconds. MultiGrip has a repeatability of less than 0.0005”, no need to indicate CNC workholding during job changeover. Because MultiGrip is a part picker, there is no need for the operator to spend time individually fixturing each part.
All the advantages of a pallet loading and part picking automation system with none of the disadvantages? Not quite. There are a few trade-offs with MultiGrip too. With MultiGrip, the robot needs to carry around the extra weight of the MultiGrip vise jaws during pick and place. Typical MultiGrip vise jaws weigh around 7 pounds so you’ll need to subtract that from your robot’s available payload. Robot loading and unloading of MultiGrip jaws require more steps than a part picker or a pallet loader; expect a MultiGrip jaw exchange to take 5 to 10 seconds longer per operation than a part picker or a pallet loader. However, MultiGrip’s ability to perform op 1 to op 2 transfers directly will almost always make MultiGrip have higher efficiency overall than pallet loaders or part pickers.
MultiGrip is Best For:
- Simple to complex part shapes
- Parts that require multiple milling operations to complete
- Lighter parts
- High-mix production
- Shops that have many different parts they want to automate
- Shops that don’t have the resources to spend lots of time integrating parts into the automation system
- Shops with labor shortages
Which Automation Strategy is Best for CNC Milling?
If you have a limited number of part numbers that run in sets, a statically configured pallet loader can be a really good choice. Parts that can’t easily be located in an infeed for robot pickup are another good choice for pallet loaders, so are parts that are too heavy for part pickers.
High-volume, low-mix production is most commonly implemented with part pickers. The additional programming and engineering costs can be offset by the the “chip-to-chip” efficiency of a highly optimized part picking automation system.
For almost everything else, MultiGrip is probably your best choice. MultiGrip excels in high-mix environments, is easy to integrate with your existing staff, minimizes operator labor, and has multi-operation processing built-in.
We invite you to reach out to VersaBuilt to discuss your automation challenges. We will take the time to understand your operation and your needs and make a recommendation for what we believe is the best solution for your challenges; even if that means pointing you to one of our competitors. Call us at 208-906-0814 or send us an email at sales@versabuilt.com.
