In my last post about pre-requisites for CNC automation, I talked about high mix, low volume vs. high volume low mix production. Those two extremes could not be farther away from each other. For the latter, I absolutely cannot think about any solution without thinking about a fully automated line. I will concentrate on the first variant in this post. High Mix. Low Volume. Especially as I believe that this is the regime in which small medium sized companies are typically operating.
But what exactly is high mix low volume production? You can most likely find yourself positioned comfortably in this area if you are for example operating a job shop. Meaning you are producing small to medium sized series of parts for a variety of customers. But also companies specialised in producing prototypes or pre-series parts and mould makers are normally producing a high variety of parts in rather small numbers.
Let me define it simple: let’s assume you are not running machines for a specific contract. Then flexibility is your cup of tea. If you don’t know exactly where to start, this post is for your.
First things first: you need to make an important decision before placing finally a robot in front of your machine! What do you want to handle?
Part or Pallet?
That’s the main question. Which way of CNC automation fits your parts portfolio better? Maybe you even need both variants.
Parts handling is the one you have first in mind when talking about producing series of parts with 200.. 20,000 or more parts in one shot. Then you are changing tooling and start producing the next series. The larger the series, the more you can invest in efficiency like e.g. offline programming and simulation, specialised fixtures, optimised grippers, camera system for bin picking operations and so on. For producing series, handling the parts directly is typically the right choice.
On the other side you may produce single parts. Either unique parts only, or small series from which your customer only needs sporadically a few pieces. In that case, it makes absolutely no sense to handle the parts directly. The effort for setting up the process would be too high, also the effort for changing processes in the machine. Such parts cry for indirect handling methods. They get mounted to a pallet, either directly with special bolts fitting to a zero lamping system or with the help of fixtures – in the easiest case just vices mounted to the pallet.
For the production of special parts, there is also highly flexible systems available, which allow you to build up a modular fixture for a dedicated part in no time.
Logistics: Conveyor, Box or FMS?
If you handle parts directly, they must somehow get into your robot cell. In a connected process you may use conveyors – or for a more agile way AGVs. Another typical way of loading/unloading cells is with the help of logistics boxes or pallets.
In the last years, small and transportable cells have been established for a parts weight of typically up to 20 kg. They are highly standardised and the whole robot cell is built around a frame which can be moved by forklift truck. They come with an integrated parts buffer and are set-up for the next round of parts within a matter of minutes.
Transportable Robot Cells for CNC Automation
Big advantage: they can be used “part time” in front of your machine (for example in order to gain an additional unmanned night shift), or they can be used flexible for different machines. Imagine the possibilities: your highly skilled worker is setting the cell up in front of the milling machine where it produces a series of parts in the morning while he is working on a prototype part on another machine tool for which he is required to frequently measure the quality manually.
If you are handling pallets, you might be already familiar with the good old FMS – Flexible Manufacturing System. In the earlier days they made use of heavy AGVs which relied even on tracks or at least on some other guides which had to be mounted to the floor.
Flexible Manufacturing System – Flexibility is Key
Today, you can put even a heavy-payload 6-axis robot on an additional linear track which allows a maximum of dynamics and which gives you the flexibility to integrate more than one machine tool into one line. If you are using vertical machine tools, you equip them with a zero clamping system.
If you are making use of horizontal machine tools you can exchange the whole machine pallet. You can also integrate a CMM and have – typically on the opposite site of the machine tools – enough storage room for pallets with both, raw and finished parts. For maximum flexibility you can design such systems so that you can run different pallet sizes as well.
Mobile Robots Make CNC Automation Agile
If you are handling smaller parts like mould inserts, there is also the possibility, to use a mobile robot. This solution gives you the highest flexibility, as you can combine different machine tools which don’t need to be perfectly aligned on your shop floor. A mobile robot also allows you to not only load parts but also tools into your machine tool. Also, you can integrate existing storages and other equipment, even without building a fence around the whole line – as there will be no line. The mobile robot becomes more like a robot colleague mingling with your staff.
Takeaway
There is no best universal robot cell available when it comes to CNC automation. There is only the best possible fit between your individual product mix and the CNC automation of your choice.
Hence it is worth it to have a look at different ways to automating your shop floor and before doing so, you need to take some time to develop the right concept for the mix you are typically running through your production – either on your own or with some external help.
Let me know about your experience in the comments below – or drop me a note if you need some help finding the right automation concept for your shop floor.