Automated handling systems can streamline the production process and cut inefficient non value-added time without compromising quality.
Regardless of the application or a component’s complexity, production costs can be broken down into value and non-value added time. But in some cases the percentage of non-value added time is as high as 95 per cent of the total production time, meaning value is only being added for five per cent of the time — when it is being machined.
Naturally the aim is to reduce the non-value added time by cutting inefficiency without compromising quality. This means taking a good look at such issues as material handling, set-up time, tool changes, spindle acceleration/deceleration, and traverse times. It’s a daunting task, but don’t despair — there are faster routes to the same ends.
One key solution is to increase spindle utilisation by repeatedly and rapidly providing the right component to the machining centre. Because if work handling isn’t efficient it will take up too much of the total cycle time and lower productivity.
If, for example, a loading time of five seconds accounts for 40 per cent of the cycle time, handling has to become the focus of any future productivity gains.
Machining flexibility is another important concern. This allows a wide range of jobs to be performed, fast reconfiguration and the freedom to carry out different operations with a given tool or machine so that set-ups, work handling and/or tool inventory can be reduced. Naturally this level of flexibility has its own penalty in the form of reduced raw machining speed.
Another approach that helps reduce costs is the use of palletised work handling systems. An automated pallet changer allows an operator to load/unload a machine in progress, thus increasing throughput by more or less eliminating job changeover time.
When set-up and work handling are factored into the processing time for a given component, a good production rate for a standalone machine with a dual-pallet shuttle is around 40 per cent, nearly double the efficiency of a typical manually loaded machining centre.
A multi-pallet machine with a shuttle of six or eight stations can average around the 60 per cent mark. Even better is a machining centre with a rail-guided vehicle and sequencing logic in its controller, which in-cut time moves into the 90 per cent range.
That’s the direction shopfloor production is moving, according to Cincinnati Machine, which suggests that workshop size is no longer a determining factor for efficiency. The company supports the argument that increasing the time a spindle spends cutting is the key to increased efficiency.
Even higher production and throughput efficiencies than pallet changing systems is offered by flexible, cellular manufacturing — considered by some experts as the successor to a Flexible Manufacturing System (FMS), at a fraction of the cost.
A ‘cell’ can be a single machining centre with an automated work handling system, or a close group of machines connected by an automated handling system. In effect, a cell becomes a manufacturing solution configured with the type and quantity of equipment needed to meet specific production requirements.
The primary advantage of cellular manufacturing is that automated pallet delivery keeps the spindle in the cut. In most cell applications, spindle use averages 90 per cent and can be as high as 98 per cent.
Since processing is not sequential, components can be routed to any available machine in the cell, which can also be set up so that all machining operations can be performed on one machine. Additionally, cellular, process-oriented manufacturing is less labour intensive than operation-oriented manufacturing — so even more savings can be made.
So do you need to invest in the ‘cell’ philosophy?
You must first satisfy yourself that your production requirements change faster than your workshop can react.
Other questions include: Do you purchase multiple machines to produce the same part or part families because set-up time limits machining time and throughput? Are you plagued by customer design changes? Are your tooling costs excessively high?
If the answer is yes to any of these, then a cell will certainly improve matters. Just as with palletised workholding systems, small to medium-sized prismatic parts are prime candidates.
Again, the need for more flexibility is a factor. Repeated design changes often wreak havoc with sequential process control strategies. Most strategies aim at ‘process equilibrium’, where each operation takes around the same time. A single change can upset this by increasing or decreasing the cycle time.
This often complicates matters by causing a bottleneck further down the production process. In an effort to alleviate this, many workshops find themselves producing overruns to help speed delivery response on repeating orders. This in itself is a risky business, as a further design change can render an entire inventory scrap.
This is true to a certain extent, but equally valid is the high-volume repetitive end, since a cell can be reconfigured relatively easily, compared to a dedicated line.
According to Cincinnati Machine, cellular manufacturing fosters a team spirit which means employees are more likely to take a holistic approach to refining production processes and improving efficiency.
Finally, like most of the newer production set-ups, cells also optimise information retrieval through relational databases. Remote access through various interface options allows managers to call up status displays, generate reports, import/export NC programs, review tool data, workloads and routes, and exchange messages with operators from a remote PC.
So it’s clear that any machine shop that is considering increasing its capacity should investigate pallet changing systems and machining cells. A careful analysis of set-up and queue times, capital utilisation, direct labour rates and work-in-progress inventory could be the justification you need.