Production Control
Chapter 21
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Competencies
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Describe the difference between Jigs and Fixtures
Describe the difference between CAD/CAM
Define computer integrated manufacturing
List essential components of robotics and describe
their function
Describe the disadvantage of Just-in-time scheduling
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CHARACTERISTICS OF
DIFFERENT TYPES OF FACILITIES
The most important factor in manufacturing is the rate of
production, because it determines which manufacturing
processes will be the most efficient for any given
product. This system is driven by the customers’
demand (Pull system)
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Characteristics Of
Different Types Of Facilities
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Piecework Production
Small Batch Production (1-20 Parts/Hr.)
Large Batch Or Continuous Processes (20-200
Parts/Hr.)
Mass Production (Over 200 Parts/Hr)
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Piecework Production
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Defined as the fabrication of one complete unit at a
time.
Utilization of equipment is not a great concern since
the equipment is not usually shared or tied up
continuously for the production run.
Piecework facilities are often batch processes in
which products are made individually.
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Piecework Production
1.
Jigs and Fixtures
a)
A fixture is a device that is individually designed to hold a
specific workpiece in place. Its specific job is to facilitate
setup or to make holding easier.
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b)
A jig is a fixture that establishes certain critical location
dimensions on the workpiece.
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c)
Ex. - Use a fixture to hold a particular plug at an angle for
easier soldering.
Ex. – Using a jig for the holding and drilling precise holes
(into a casting) for the shafts of a three dimensional
mechanism.
Work holder is the general term for either a jig or a
fixture. A miter box or a bench vise might be a workholder.
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Piecework Production
2.
Inspection is the act of determining whether or not
the size, shape, and location of all features of the
workpiece are consistent with the drawings or
other specifications. Inspections are performed by
machinists or operators.
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Small Batch Production
(1-20 Parts/Hr.)
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At this rate of production, completed parts begin to
take up a significant amount of space before they
can be shipped and raw materials are needed at a
faster rate than they are with piecework.
Boredom becomes a concern and not only affects
the quality of the product, but safety is also
affected.
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Small Batch Production
(1-20 Parts/Hr.)
Numerical Control is a way of controlling the action of
machines by giving them a set of instructions in
numerical form.
Computerized Numerical Control
• Can be programmed to control several production
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machines
Can store programs and data that would allow it to
track the wear of the cutting tools and automatically
compensate for that wear.
Machines were designed with a tool carrier so that
tools could be changed by computer control.
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Small Batch Production
(1-20 Parts/Hr.)
Some Problems of CNC
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New machines are very expensive and only 5% of
the part’s total manufacturing time is it actually on
the machine.
Only profitable if it frees up time to supervise more
machines or to spend time with the human activities
that computers cannot do well
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Large Batch Or Continuous Processes
(20-200 parts/hr.)
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No longer does one person see the part from start
to finish.
Scheduling is an important part of this type of
manufacturing.
Inspect the parts frequently to detect trends in
parts not meeting standards and take corrective
action before the parts are so far from the
specifications that they are scrap.
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Large Batch Or Continuous Processes
(20-200 parts/hr.)
3.
Computer-Aided Drafting/ Computer-Automated
Manufacturing
a) Computer-Aided Drafting is a method of drafting that uses
a computer to draw on the screen as instructed by an operator.
The computer acts only as an “electronic drafting board”; it does
not do anything on its own.
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Large Batch Or Continuous Processes
(20-200 parts/hr.)
b) Computer Automated Engineering (CAE) is a system
that uses a computer to make design drawings, but additionally is
capable of doing engineering analysis of the designed object.
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Determine the volume and weight of the part and locate its
center of mass.
Do a complete structural analysis of the product.
Determine clearances and allowances between matching
parts.
Devise the optimum steps for the manufacture of the product.
Create the commands for the computer controlled machines
that make the product.
Keep the inventory records and other documentation for the
product
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Large Batch Or Continuous Processes
(20-200 parts/hr.)
c) Computer-Automated Manufacturing is an approach
to organizing a manufacturing plant so that all possible
analyses, decisions, and actions are assigned to a master
computer.
d) Typical Computer Operations in CAM
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Control the inventory.
Direct the transportation of raw materials, completed
products, and parts at different stages during
manufacture.
Create machine maintenance schedules.
Control the automatic inspection
Maintain documentation
Control the actions of robots.
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Large Batch Or Continuous Processes
(20-200 parts/hr.)
Robotics
Robots have five essential components:
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5)
Manipulator - the part of the machine that actually
handles the tool, material, or part.
Actuators - respond to the signals from the controller,
causing the manipulator to perform its assigned function.
Sensors - detect the positions of the various components
of the arm and hand and feed data back to the controller.
Controllers - computers that send control signals to the
manipulators and respond to the data fed back to them by
the sensors.
Power supplies - provide the energy that drives the
controllers, sensors, manipulators, and actuators.
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Large Batch Or Continuous Processes
(20-200 parts/hr.)
Use of Robots
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Manipulators
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The robot manipulator must duplicate essentially every
movement of the human arm and hand.
Actuators
The “muscles” of the robot mechanism. These may be
powered by air, hydraulic fluid, electricity, magnetism, or a
vacuum.
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Large Batch Or Continuous Processes
(20-200 parts/hr.)
• Air-operated and vacuum-operated (pneumatic)
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mechanisms are usually small and limited by the amount
of force they can exert, but they are inexpensive to
construct and operate.
Hydraulic mechanisms are capable of exerting large
forces, are high powered, and are amazingly quick for
their size. They do tend to be messy due to the
inevitable leakage of hydraulic fluid.
Electrically driven mechanisms are appropriate for light
duty. They are very accurate, precise, and clean.
Magnetically driven actuators such as solenoids are very
quick but are limited by the amount of force they can
exert on the workpiece.
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Large Batch Or Continuous Processes
(20-200 parts/hr.)
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Computer Functions
The “brain” of the robot is the computer that controls the
robot.
Control System Functions
If the computer is the ‘brain” of the robotics system, then
the control system is its “nervous system.”
Robot Functions
Through its end-of-arm device (“hand”), the robot either
picks up the workpiece or does something with it.
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Quality Assurance Through
Automated Inspection
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Quality Control (QC)
Concerned with ensuring that the products meet their
design standards
Causes of Product Variation
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Inherent Variation is the unavoidable variation in the
dimensions of a part due to such causes as flexure of the
cutting tool, etc.
Assignable Cause is an act or activity that can be identified
as the reason why a workpiece deviates.
A manufacturing process is said to be “in control” when the
assignable causes have been detected and corrected so that
only the inherent variation is left.
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Quality Assurance Through
Automated Inspection
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Statistical Quality Control
• the control of the quality of the parts produced by an
analysis of the numerical data derived from
measurements taken on those parts.
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Meeting Drawing Tolerances
• If the designer asks for tolerances that are smaller
than can be achieved with a machine, then either the
tolerances need to be “loosened” or else the process
needs to be done on a different machine.
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Just-in-Time Scheduling
A type of production organization in which the material for
a part or assembly is delivered just in time to be
used.
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Shifts responsibility for quality to the suppliers
Reduce production costs by 20% to 40%.
The drawback to JIT is that the production line is shut
down if even one part does not come in “just in time.”
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Mass Production (over 200 parts/hr)
Constantly focused on reducing fractional costs.
(Saving $.20/pc @ 300 pcs./hr. = $600,000/yr.
1.
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Adaptive Control
A type of feedback control that senses changes outside of
the feedback loop (temperature, pressure, vibration, etc.)
and changes the instructions (to the actuators) so that the
desired result is still accomplished in spite of the exterior
change.
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Mass Production (over 200 parts/hr)
2.
Cellular Organization
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3.
is a way of organizing a manufacturing facility so that
most of the processes are carried out by a small group of
machines (the “cell”). Ex. – Combining turning, milling,
and drilling operations in a machining center.
Flexible Manufacturing Systems (FMS)
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same concept as that of the machining cell except that
the elements of the FMS are machining cells rather than
machining centers. Fig. 21-34
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Mass Production (over 200 parts/hr)
4.
Computer-Integrated Manufacturing
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CIM is a methodology and a goal; it is not a collection of
equipment and software.
Its method is to integrate all aspects of design, planning,
manufacturing, distribution, and management.
Its goal is to transform product designs and materials into
saleable goods at a minimum cost in the shortest possible
time.
CIM treats manufacturing processes and plant operations
and their management as a single system, not a
sequential activity.
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