Written by Seppo Pyykkö
A traditional challenge in manufacturing small batches has been the time (and money) consuming machine tool setup change between the batches. Setup change has required the machine to be stopped and the operator intervention in order to change or rebuild the fixture, tooling or otherwise change the setup for the next part to be produced. In this blog series I will introduce three technical approaches on how to make small series production more economical – starting with the part fixturing to machines.
1. Load workpieces faster
The first step of cutting the setup-time of machining centers is to have the machine equipped with an automatic pallet changer (APC). With the changer the setup-time can at least partially be carried out on the APC side of the machine as the previous workpiece is being machined in the spindle side. The next step is to have the pallets buffered in a pallet pool or flexible manufacturing system. Neither of these systems however offers automatic part loading / unloading, so in order to decrease the need of human intervention, also the material handling should be automated.
2. Automate the setup changes
Luckily fixture suppliers have introduced products with which the setup changes can be automated and thus done during the fully automated period.
Naturally the fully automatic setup change causes certain limitations to the manufactured products. If machined parts can be limited to some geometrical similarity (like cubic part in some limited part size range), the solution can be a standard and thus cost efficient long stroke screw vise, which can be opened and closed with a servo motor. Such a servo system is available as a product for example from the company Allmatic. If the vises are equipped with interchangeably formed jaws, the part variety can be increased even further. We at Fastems promoted a similar system, but with a hydraulic fixture in EMO 2017 together with clamping solutions company Polund (watch a video here).
3. Combine pallet and part automation
If the part variety cannot be simplified but there’s no constant need of introducing new part variants to the production either, the exchange of the part fixture can be automated with the same robot that handles the part loading and unloading. This is a valid option if the weight of the empty pallet can be held under approximately 500 kilograms. This allows combining the best of the traditional FMS system by changing the machine fixture setup quickly, with the benefits of a conventional part loading / unloading robot cell. Loading of the part can either take place outside of the machine, or into the machine, depending on the machine type and charachteristics of the production.
Of course, the time used for the setup change will lower the machine utilization rate – but on the other hand the system is able to produce the parts which can be immediately delivered and thus generate instant turnover instead of increasing stock value. In comparison to traditional FMS operation, using direct part loading / unloading not only saves the operator time to more productive tasks than part loading, but can also lower the needed fixture investment – as the fixtures do not necessarily have to be designed to hold as many as parts as possible to keep the number of fixtures low but still to be able to produce greater variety parts.
Direct part loading / unloading not only saves the operator time to more productive tasks, but can also lower the needed fixture investment.
All the solutions mentioned in this post are applicable only in machining centers. If you happen to need turned parts, the fixturing solutions are somewhat different. Luckily all major chuck manufacturers have already introduced jaw systems for a quick manual jaw change, and most of them already offer a variant of the same system which is meant to be changed with a robot. If the part diameter and thus the required spindle RPM varies a lot, even the chuck can be automatically changed to allow different spindle speeds.
This is about fixturing – in the next post I focus on how the production of smaller batches can become more economical with robotics.