First published in the August 1997 issue of Cutting Tool
Engineering magazine.
Eliminate Bottlenecks and Waste
A bottleneck keeps a person (or department) from completing their assigned
tasks - and all shops have them. Workpieces are not reaching assemble at the
appropriate time. Tooling is not ready for the setup person when a setup is
started. The CNC program isn’t finished when the setup is completed. The
operator can’t find the program in your distributive numerical control
(DNC) system. New programs take too long to verify. The machine sits idle while
the first workpiece is being inspected. Replacement tools are not readily
available as tools dull during the production run. The list of potential
bottlenecks goes on and on. Here we offer a few suggestions about approaching
and eliminating bottlenecks in the CNC environment.
Identify the bottleneck - With most bottlenecks, identifying
bottlenecks is easy. If a person or department is kept from completing their
tasks in a timely manner, production will suffer. In a company that runs small
lots, for example, the excessive time it takes to make setups is commonly
identified as a serious bottleneck.
Evaluate current methods - While identifying a bottleneck supplies
you with a problem to solve, you must become much familiar with the problem/s
before you can target areas for improvement. A company complaining about
lengthy setups, for example, should begin by studying how setups are currently
made. One common practice for getting material to evaluate is to video-tape
tasks related to the bottleneck. This will provide information that can be
studied by everyone in the CNC environment.
Formulate suggestions for improvement - Once you have information to
study (the results of studying the problem), invite everyone involved with the
problem to suggest and evaluate potential improvements that can be made. This
can be treated as a brain-storming session, in which everyone has an
opportunity to make their ideas known. In the setup time reduction example,
possibly the setup person is taking quite a long time to find hand tools and
gages needed to complete the setup. It is suggested that if each setup person
has their own set of tools, this wasted time can be eliminated.
Prioritize based upon benefit and feasibility - With a variety of
viable solutions to analyze, you’ll need to pick the one that best suits
your company’s corporate goals. Every potential improvement must be
justified. Most justifications are cost-based. Additional hand tools and gages
in the setup time reduction example will likely be easily justified based on
the machine cost (its shop rate) during the time wasted while searching for
tools. This gained time (money) can easily pay for the additional hand tools in
a very short period of time.
Note that not all justifications are cost based. Some must be based upon the
company’s corporate goals and philosophies. If, for example, your company
places a high emphasis on just-in-time, workpieces must reach the next step in
the manufacturing process at the appropriate time. If they do not, the next
step (possibly assembly) will be halted. In this scenario, the cost of
eliminating a bottleneck may be less related to the single CNC machine causing
the bottleneck than it is to the bigger picture of getting a product shipped.
Don’t take "no" for an answer - Even given limited
resources, there is very little that is impossible with CNC machine tools.
Given your new-found aggressive awareness, ingenuity, and determination, you
should be able to eliminate any bottleneck.
Organization and preparation versus waste
As you begin evaluating the bottleneck (especially if you have never applied
these principles before), you will likely find a great deal of waste. Wasted
time, wasted (duplicated) effort, and wasted money. As you begin to study a
setup to be improved, for example, you set up the video camera to tape the
setup and get everything ready. The setup person says "go" and you
press the record button. The setup person looks around for a few moments, then
disappears from view. Ten minutes later he comes back (breathing hard) and gets
started with the setup. After two more minutes, he disappears again. This
continues throughout the setup. When finished, you take note of the fact that
the setup person was only at the machine for a very small percentage of the
time it took to complete the setup.
As you begin evaluating the video tape, the operator explains that each time
he disappeared from view it was to find something. "I had to get hand
tools." "I had to get cutting tool components from the tool
crib." "I had to find my fixture." I had to find the gages
needed to check the part." It is obvious that the setup person (probably
through no fault of his own) was not very prepared to make the setup in the
first place. It is not uncommon for a company’s people to be spending a
great percentage of their time performing tasks that can be classified as
wasteful.
