AUTOMATION INSIGHTS – Leverage your automation tools and automate the process – not the parts
June 15, 2009 by Chris Stergiou
High mix, low volume manufacturing is everywhere and build-to-order requirements may sometimes look impossible to automate economically. However, that’s not the case. A useful approach is to identify “common” process requirements for many or all part numbers of a product family and to automate using quick-change tooling and re-configurable parameters to handle the parts range. Your first thought might be that it can’t be done because of size or other variations and overcoming your hesitation is as much faith as it is expertise.
This approach leverages in-house product knowledge along with automation tools, which are integrated. Creativity can take any operation to a higher level of automation if you use process knowledge to “see” what the manufacturing floor might look like with a particular step or operation automated.
In a job shop environment, investment in automated parts handling/feeding is not easily justified. Instead, we focus on automating the process itself in order to reduce cycle time by making the operator the load-unload function and designing our system to perform the operation with hands-off automation. A familiar example of this is the manual loading of stock into a CNC machine, which executes a preprogrammed sequence including tool changes and machining without operator intervention. We can extend this to our secondary assembly operations by developing custom tools that work in the same way.
To accomplish this, the first step is to design a “universal” fixture that can present the part/assembly for as many operations as possible in a single set-up. Secondly, the process sequence is automated using a PLC, reducing operator skill level and variation. Custom tooling is required and an initial set-up for a specific part number should take some small multiple of process cycle time. By way of manual set-up or automation of the set-up itself, set-up time should require approximately 10-20 times the cycle time. So if we have a 10 second cycle time, a 100-200 second set-up time should be acceptable, but the lower the better.
The physical form factor often looks like a simple tabletop fixture with quick-change tooling or set-up parameters. The operator is positioned in front of the universal fixture and has an input of raw parts and an output for completed assemblies. Inputs can vary from a single piece or several unique parts, which are presented to this single set-up for assembly or other operations. Operations can include press assembly, dispensing, leak testing and automated fastening, among others.
In developing a universal process automation tool, first a matrix of mechanical or other common attributes in the product’s intrinsic design must be developed. Sorting this matrix will produce at least one common parameter to all products in that family. This may be a common centreline, bolt pattern, dimension or other feature. If a common parameter isn’t found, then the family of products will have some scaleable attribute/parameter that will become the common parameter with adjustment.
The design engineering group can often assist in identifying this parameter. In either case, this common parameter or “handle” will “hold” all products in the universal fixture. You know you’ve found a good “handle” when it is simple and applies to the full target family of products. The 80/20 or Pareto Rule is relevant here, meaning that some of the products in the family fall outside the economic justification because in order to accommodate them, more money would need to be spent to automate them. Actually, by automating as few as 20 per cent of the part numbers, 80 per cent of the volume is effectively automated.
The next step is to identify all operations required for the product at this stage and to sequence those operations so that as many/all operations on this single set-up are covered. Often operations can be pulled downstream into this set-up or pushed upstream.
The goal is to perform as many operations and bury as many cycle times as possible into this universal setup and maximize value. At a minimum, other setups are eliminated and in most cases the total cumulative operation cycle time is reduced. The result is almost always a net gain in cycle time and usually quality improvement as multiple handling/variation is reduced.
In summary, the automation of high mix, low volume operations can be achieved by rejecting the notion that it can’t be justified. It’s possible to meet the challenge with creative process automation that addresses the full range of the target product family and seeks to eliminate direct labour while maintaining or improving quality as standard tools that remove operator skill and variation from the target operation are introduced. By leveraging the knowledge of automation tools and framing this challenge as a goal that is achievable, it becomes a question of how, rather than if.
Chris Stergiou (firstname.lastname@example.org) is a manufacturing consultant with 25 years of experience. He provides custom automation and consulting services to clients, many of them Fortune 500 companies.
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