Manufacturing Cell
Four general categories:
1.
Traditional stand-alone NC machine tool - is characterized as a limited-storage, automatic
tool changer and is traditionally operated on a one-to-one machine to operator ratio.
 In many cased, stand-alone NC machine tools have been grouped together in a conventional
part family manufacturing cell arrangement and operating on a one-to-one or two-to-one or
three-to-one machine to operator ratio.
2. Single NC machine cell or mini-cell - is characterized by an automatic work changer with
permanently assigned work pallets or a conveyor-robot arm system mounted to the front of the
machine, plus the availability of bulk tool storage.
 There are many machines with a variety of options, such as automatic probing, broken tool
detection, and high-pressure coolant control.
 The addition of these and other special option features enables many single NC machine to
operate as a self-contained cell.
 The single NC machine cell is rapidly gaining in popularity, functionality, and affordability,
because it can be purchased for a fraction of the cost of a complete FMS and can be
programmed and loaded with parts to run unattended for several hours.
 This unattended operation can increase spindle utilization and reduced direct labor, while
increasing their knowledge and confidence about unattended machining and manufacturing
capabilities.
3. Integrated multi-machine cell - is made up of a multiplicity of metal-cutting machine tools,
typically all of the same type, which have a queue of parts, either at the entry of the cell or in
front of each machine.
 Multi-machine cells are either serviced by a material-handling robot or parts are palletized
in a two- or three-machine, in-line system for progressive movement from one machining
station to another.
 Typical Multi-machine cells
 The typical application of a multi-machine cell serviced by a robot is high-volume
production of a small, well-defined, design-stable family of part.
 Machine can be different in a cell of this type, and work-pieces can be progressively
moved.
 Palletized in-line cells can also be applied to either high- or low-variety and -volume
production applications.
 Material handling links together a group of flexible general-purpose machine tools
utilizing a common pallet design with pre-fixtured parts on pallets.
4. FMS - sometimes referred to as a flexible manufacturing cell (FMC), is characterized by
multiple machines, automated random movement of palletize parts to and from processing
stations, and central computer control with sophisticated command-driven software.
 The distinguishing characteristics of this cell are the automated flow of raw material to the
cell, complete machining of the part, part washing, drying, and inspection with the cell, and
removal of the finished part.
Selection of FMS and Implementation
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requirements, and unforgiving consequences.
 As a result, many companies, feeling that a single or integrated multi-machine cell is too
little but a full-scale FMS is too much (in terms of cost, technology, and risk), elect to take a
phased approach to system implementation.
 The broader the scope and span of a c
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requirements are the greater the need for a phased
system installation and implementation.
Unattended Machining
 The concept of unattended machining implies running an NC machine tool with no operator in
attendance for extended periods of time, usually eight or more hours. The parts, tools, and NC
programs are considered to be loaded and available at each machine station or are delivered on
an as needed basis to each machine.
 Unattended machining begins by making sure an adequate supply of parts and cutting tools is
available to keep the machine in operation for and extended period.
 Usually the following questions need to be cleared:
1. What type of material to be produced? Steel? Cast iron? Aluminum? or A combination?
2. How long will the machine continue to operate unattended?
3. What provisions are available to keep it running?
4. What assurance is there that the machine will continue to run and not cause damage to itself,
the parts, or the tooling?
5. How many different types of parts can be run unattended on the machine or in the cell?
6. How much extra process preparation work is required ahead of time to process each type of
unattended part (part programs, fixtures, tooling, or material-handling changes)?
 The development of unattended machining
1. Newly purchased single or multi-machine cells should include features such as extended part
queuing and tool-changing capabilities, torque and force sensing of the metal cutting process,
automatic fault detection and probing capabilities.
2. The benefits include increased machine utilization, improved quality through increased
consistency and predictability of operation, reduced floor space because fewer machines are
required to make the same production, and reduced direct labor.
3. Work-in-process inventory, however, will generally not be reduced with the installation of one
unattended machining cell. In fact, a single NC machine cell put in the middle of a batch
manufacturing operation many actually increase WIP depending on how parts are arranged
and scheduled for unattended machining.
 New multi-machine cells should include features such as:
1. extended part queuing and tool-changing capabilities
2. Torque and force sensing of the metal-cutting process
3. Automatic fault detection
4. Probing capabilities - greatly contributes to accuracy, repeatability, and quality of unattended
machine
Example of unattended turning center features and requirements:
1. Part size must be controlled through probe measurement of the part, automated in-process or
postprocessor gauging, and automatic compensation of the machine for changes.
2. Parts must be automatically delivered, loaded, and unloaded, usually by means of an integrated
floor- or machine- mounted robot arm along with part queuing by palletized conveyor.
3. Specific part identification can occur by probing unique dimensions to distinguish random parts
within a given family and calling up the proper NC program as required.
4. Wrecks can be avoided through spindle torque and slide force sensing and shutting the machine
down safely before part, tool, or machine damage occurs (due to exceeded machine horsepower
limits, dull tools, or excess workpiece stock).
5. Chips can be cleared from the chuck by the quick rotation of an empty chuck and applying and
air blast before loading the next part (long unattended applications can create a problem with
disposal of the volume of chips produced).
6. Parts must be easily turned end for end an accurately located for part completion.
7. A fixed probe for automatic tool length setting avoids the time-consuming manual ordeal of tool
setting and for broken tool detection.
Example of unattended machining center features and requirements:
1. Palletized queuing of workpieces by means of a carrousel or in-line part setup arrangement.
2. Detection of missing, miss-aligned, or wrong parts using the probe and part program branching
to bypass the problem area.
3. Determination of excess or insufficient stock with the probe.
4. Detection of broken tools through the use of a fixed probe with a spindle probe to determine
whether the workpiece stock has been removed.
5. Avoiding erroneous probe data, such as touching on a chip with a reasonableness test on the
probe data.
6. Avoid wrecks by spindle torque measurement and predetermined shutdown limits.
7. Clear chips from tools for probing cycles through high-pressure coolant flushing and air blasts.
Cellular versus Flexible Manufacturing
 A FMS is sometimes referred to as a cell - a highly sophisticated and automated one. And, in
some cases, a single NC machine cell or a integrated multi-machine cell is referred to as a
flexible manufacturing system (flexibility is changing to a different part when similar batch
requirements are completed).
 Conventional equipment cannot compete with FMS concepts because of the lack of
management control, and the ever present setup and retooling requirements.
 Both similarities and difference exist between cells and systems. The primary differences
between an automated manufacturing cell and a true flexible manufacturing system are:
1. Cells lack central computer control with real-time routing, load balancing (software), and
production scheduling logic.
2. A FMS, in many cases it is tied directly to the corporate computing system, which may also be
running the material requirements planning (RPM) system, and sometimes the computer-aided
design (CAD) system in design engineering.
3. Cells are typically tool capacity constrained. This limits the part spectrum that could be run
through a cell at given time without stopping the equipment and manually exchanging tools to
accommodate different workpieces.
4. A FMS with automated tool delivery and tool management can automatically transfer,
exchange, and migrate tools through centralized computer control and software independent of
equipment activity.
5. Cells generally have less flexibility than an FMS and are restricted to a relatively tight family
of parts. As long as the part family remains unchanged and design-stable, the automated cell
can operate very efficiently.