UNIT-III

Concurrent engineering
Concurrent engineering is a work methodology based on the parallelization of tasks (i.e.
performing tasks concurrently). It refers to an approach used in product development in which functions
of design engineering, manufacturing engineering and other functions are integrated to reduce the elapsed
time required to bring a new product to the market.

Introduction

 The concurrent engineering method is still a relatively new design management system, but has
had the opportunity to mature in recent years to become a well-defined systems approach towards
optimizing engineering design cycles. Because of this, concurrent engineering has gathered much
attention from industry and has been implemented in a multitude of companies, organizations and
universities, most notably in the aerospace industry.
 The basic premise for concurrent engineering revolves around two concepts. The first is the idea
that all elements of a product’s life-cycle, from functionality, producibility, assembly, testability,
maintenance issues, environmental impact and finally disposal and recycling, should be taken
into careful consideration in the early design phases.
 The second concept is that the preceding design activities should all be occurring at the same
time, or concurrently. The overall goal being that the concurrent nature of these processes
significantly increases productivity and product quality, aspects that are obviously important in
today's fast-paced market.This philosophy is key to the success of concurrent engineering because
it allows for errors and redesigns to be discovered early in the design process when the project is
still in a more abstract and possibly digital realm. By locating and fixing these issues early, the
design team can avoid what often become costly errors as the project moves to more complicated
computational models and eventually into the physical realm.
 As mentioned above, part of the design process is to ensure that the entire product's life cycle is
taken into consideration. This includes establishing user requirements, propagating early
conceptual designs, running computational models, creating physical prototypes and eventually
manufacturing the product. Included in the process is taking into full account funding, work force
capability and time, subject areas that are extremely important factors in the success of a
concurrent engineering system.
 As before, the extensive use of forward planning allows for unforeseen design problems to be
caught early so that the basic conceptual design can be altered before actual physical production
commences. The amount of money that can be saved by doing this correctly has proven to be
significant and is generally the deciding factor for companies moving to a concurrent design
framework.
 One of the most important reasons for the huge success of concurrent engineering is that by
definition it redefines the basic design process structure that was common place for decades. This
was a structure based on a sequential design flow, sometimes called the ‘Waterfall
Model’.Concurrent engineering significantly modifies this outdated method and instead opts to
use what has been termed an iterative or integrated development method.The difference between
these two methods is that the ‘Waterfall’ method moves in a completely linear fashion by starting
 with user requirements and sequentially moving forward to design, implementation and
additional steps until you have a finished product. The problem here is that the design system
does not look backwards or forwards from the step it is on to fix possible problems. In the case
that something does go wrong, the design usually must be scrapped or heavily altered. On the
other hand, the iterative design process is more cyclic in that, as mentioned before, all aspects of
the life cycle of the product are taken into account, allowing for a more evolutionary approach to
design.The difference between the two design processes can be seen graphically in Figure 1.

 A significant part of this new method is that the individual engineer is given much more say in
the overall design process due to the collaborative nature of concurrent engineering. Giving the
designer ownership plays a large role in the productivity of the employee and quality of the
product that is being produced. This stems from the fact that people given a sense of gratification
and ownership over their work tend to work harder and design a more robust product, as opposed
to an employee that is assigned a task with little say in the general process.
 By making this sweeping change, many organizational and managerial challenges arise that must
be taken into special consideration when companies and organizations move towards such a
system. From this standpoint, issues such as the implementation of early design reviews, enabling
communication between engineers, software compatibility and opening the design process up to
allow for concurrency creates problems of its own .Similarly, there must be a strong basis for
teamwork since the overall success of the method relies on the ability of engineers to effectively
work together. Often this can be a difficult obstacle, but is something that must be tackled early to
avoid later problems.
 Similarly, now more than ever, software is playing a huge role in the engineering design process.
Be it from CAD packages to finite element analysis tools, the ability to quickly and easily modify
digital models to predict future design problems is hugely important no matter what design
process you are using. However, in concurrent engineering software’s role becomes much more
significant as the collaborative nature must take into the account that each engineer's design
models must be able to ‘talk’ to each other in order to successfully utilize the concepts of
concurrent engineering.
Concurrent engineering elements

Cross-functional teams

Include members from various disciplines involved in the process, including manufacturing, hardware
and software design, marketing, and so forth

Concurrent product realization

Process activities are at the heart of concurrent engineering. Doing several things at once, such as
designing various subsystems simultaneously, is critical to reducing design time

Incremental information sharing

It helps minimize the chance that concurrent product realization will lead to surprises. As soon as new
information becomes available, it is shared and integrated into the design. Cross functional teams are
important to the effective sharing of information in a timely fashion

Integrated project management

It ensures that someone is responsible for the entire project, and that responsibility is not abdicated once
one aspect of the work is done.

Definition for concurrent engineering

Several definitions of concurrent engineering are in use.

The first one is used by the Concurrent Design Facility (ESA):

Concurrent Engineering (CE) is a systematic approach to integrated product development that

emphasizes the response to customer expectations. It embodies team values of co-operation, trust and
sharing in such a manner that decision making is by consensus, involving all perspectives in parallel,
from the beginning of the product life cycle

The second one is by Pennell and Winner, 1989:

Concurrent Engineering is a systematic approach to the integrated, concurrent design of products and
their related processes, including, manufacturing and support. This approach is intended to cause the
developers from the very outset to consider all elements of the product life cycle, from conception to
disposal, including cost, schedule, quality and user requirements.
What is concurrent engineering?

 The definition of Concurrent Engineering that we have adopted for the Concurrent Design
Facility is: "Concurrent Engineering (CE) is a systematic approach to integrated product
development that emphasizes the response to customer expectations. It embodies team values of
co-operation, trust and sharing in such a manner that decision making is by consensus, involving
all perspectives in parallel, from the beginning of the product life-cycle."
 Essentially, CE provides a collaborative, co-operative, collective and simultaneous engineering
working environment.

The concurrent engineering approach is based on five key elements:

 a process
 a multidisciplinary team
 an integrated design model
 a facility
 a software infrastructure

The spacecraft design is based on mathematical models, which make use of custom software and
linked spreadsheets. By this means, a consistent set of design parameters can be defined and
exchanged throughout the study, and any changes which may have an impact on other disciplines can
immediately be identified and collectively assessed. In this way, a number of design iterations can be
performed, and different design options can easily be analyzed and compared.

CDF activities are conducted in sessions: plenary meetings in which representatives of all space
engineering domains participate, from the early phases (requirement analysis) to the end of the design
(costing). Even those disciplines that were traditionally involved at a later stage of the process are given
the opportunity to participate from the beginning and to identify trends that might later invalidate the
design.

Simultaneous engineering approach to an integrated design and process planning:

To support integration of design and process planning, a reference model has been developed.
This reference model represents the basis for a new methodology for integrated design and process
planning which enables a Simultaneous Engineering approach in the early stages of product development.
The reference model consists of four partial models. These are the activity model, the information model,
the technical system model and the model of integrating methods. Using these models, the methodology
enables a concurrent processing of design and process planning activities with regard to different
components of a product. Furthermore, the methodology covers planning methods as well as execution
methods, to support early transmission of information to downstream activities and a feedback of
information to upstream activities within the process chain of design and process planning.
 Simultaneous engineering is a procedure in the technical development. With this procedure
it is possible to reduce the development costs and time to market of the new product.
The main idea of this procedure is the time effective overlapping of following procedures
which are made simultaneous / parallel instead of behind each other. Once there is enough
information within the workflow, the next procedure can be started parallel. This can cause
more work seeing that the latest information is not always present and then can change the
procedure while working on it. Therefore mistakes can be seen earlier and one can correct
them before they cost more money in a later phase of development (see picture).

Simultaneous Engineering is very effective in the steps between Product development and
production tool planning. Traditionally the product development and the production tool
planning were two different steps following each other. At first the new product is being
constructed and completely planned (see also construction process). After that the planning of
the production facilities starts.

When using Simultaneous Engineering the production planning starts earlier. As soon as parts of
the new product have been developed or plans for it have been finalized the planning of the production is
started. The further development of the parts is driven forward in parallel sections.

While both departments are working on their specific solutions, there is a continuous information flow
between them. Changes in the construction of the product must be involved in the planning of the
production tolls and process. In the contrary there is the possibility that within the optimizing process of
the production planning there are changes to be made in the construction.

The main profit of working in this method is the time saving seeing that production tools are already
planned. Another important aspect , is the early knowledge of constructive production problems. This
means the earlier construction changes can be made the less money is spent. Worst case scenario as in the
past a product was finished in construction of tools and it did not work, so everything had to be done
again.

Simultaneous Engineering helps to achieve the important knowledge in an earlier stage.

Design for assembly

o Design for assembly (DFA) is a process by which products are designed with ease of
assembly in mind. If a product contains fewer parts it will take less time to assemble,
thereby reducing assembly costs. In addition, if the parts are provided with features
which make it easier to grasp, move, orient and insert them, this will also reduce
assembly time and assembly costs. The reduction of the number of parts in an assembly
has the added benefit of generally reducing the total cost of parts in the assembly. This is
usually where the major cost benefits of the application of design for assembly occur
DESIGN FOR MANUFACTURABILITY / ASSEMBLY

1. Simplify the design and reduce the number of parts because for each part, there is an opportunity for a
defective part and an assembly error. The probability of a perfect product goes down exponentially as the
number of parts increases. As the number of parts goes up, the total cost of fabricating and assembling the
product goes up. Automation becomes more difficult and more expensive when more parts are handled
and processed. Costs related to purchasing, stocking, and servicing also go down as the number of parts
are reduced. Inventory and work-in-process levels will go down with fewer parts.

As the product structure and required operations are simplified, fewer fabrication and assembly steps are
required, manufacturing processes can be integrated and lead times further reduced. The designer should
go through the assembly part by part and evaluate whether the part can be eliminated, combined with
another part, or the function can be performed in another way. To determine the theoretical minimum
number of parts, ask the following: Does the part move relative to all other moving parts? Must the part
absolutely be of a different material from the other parts? Must the part be different to allow possible
disassembly?

2. Standardize and use common parts and materials to facilitate design activities, to minimize the amount
of inventory in the system, and to standardize handling and assembly operations. Common parts will
result in lower inventories, reduced costs and higher quality. Operator learning is simplified and there is a
greater opportunity for automation as the result of higher production volumes and operation
standardization. Limit exotic or unique components because suppliers are less likely to compete on
quality or cost for these components. The classification and retrieval capabilities of product data
management (PDM) systems and component supplier management (CSM) systems can be utilized by
designers to facilitate retrieval of similar designs and material catalogs or approved parts lists can serve as
references for common purchased and stocked parts.

3. Design for ease of fabrication. Select processes compatible with the materials and production volumes.
Select materials compatible with production processes and that minimize processing time while meeting
functional requirements. Avoid unnecessary part features because they involve extra processing effort
and/or more complex tooling. Apply specific guidelines appropriate for the fabrication process such as the
following guidelines for machinability:

 For higher volume parts, consider castings or stampings to reduce machining

 Use near net shapes for molded and forged parts to minimize machining and processing effort.
 Design for ease of fixturing by providing large solid mounting surface & parallel clamping
surfaces
 Avoid designs requiring sharp corners or points in cutting tools - they break easier
 Avoid thin walls, thin webs, deep pockets or deep holes to withstand clamping & machining
without distortion
 Avoid tapers & contours as much as possible in favor of rectangular shapes
 Avoid undercuts which require special operations & tools
 Avoid hardened or difficult machined materials unless essential to requirements
 Put machined surfaces on same plane or with same diameter to minimize number of operations
  Design workpieces to use standard cutters, drill bit sizes or other tools
 Avoid small holes (drill bit breakage greater) & length to diameter ratio > 3 (chip clearance &
straightness deviation)

Example of DFM guidelines for sheet metal

4. Design within process capabilities and avoid unneeded surface finish requirements. Know the
production process capabilities of equipment and establish controlled processes. Avoid unnecessarily
tight tolerances that are beyond the natural capability of the manufacturing processes. Otherwise, this will
require that parts be inspected or screened for acceptability. Determine when new production process
capabilities are needed early to allow sufficient time to determine optimal process parameters and
establish a controlled process. Also, avoid tight tolerances on multiple, connected parts. Tolerances on
connected parts will "stack-up" making maintenance of overall product tolerance difficult. Design in the
center of a component's parameter range to improve reliability and limit the range of variance around the
parameter objective. Surface finish requirements likewise may be established based on standard practices
and may be applied to interior surfaces resulting in additional costs where these requirements may not be
needed.

5. Mistake-proof product design and assembly (poka-yoke) so that the assembly process is unambiguous.
Components should be designed so that they can only be assembled in one way; they cannot be reversed.
Notches, asymmetrical holes and stops can be used to mistake-proof the assembly process. Design
verifiability into the product and its components. For mechanical products, verifiability can be achieved
with simple go/no-go tools in the form of notches or natural stopping points. Products should be designed
to avoid or simplify adjustments. Electronic products can be designed to contain self-test and/or
diagnostic capabilities. Of course, the additional cost of building in diagnostics must be weighed against
the advantages.

6. Design for parts orientation and handling to minimize non-value-added manual effort and ambiguity in
orienting and merging parts. Basic principles to facilitate parts handling and orienting are:

 Parts must be designed to consistently orient themselves when fed into a process.
 Product design must avoid parts which can become tangled, wedged or disoriented. Avoid holes
and tabs and designed "closed" parts. This type of design will allow the use of automation in parts
handling and assembly such as vibratory bowls, tubes, magazines, etc.
 Part design should incorporate symmetry around both axes of insertion wherever possible. Where
parts cannot be symmetrical, the asymmetry should be emphasized to assure correct insertion or
easily identifiable feature should be provided.
 With hidden features that require a particular orientation, provide an external feature or guide
surface to correctly orient the part.
 Guide surfaces should be provided to facilitate insertion.
  Parts should be designed with surfaces so that they can be easily grasped, placed and fixtured.
Ideally this means flat, parallel surfaces that would allow a part to picked-up by a person or a
gripper with a pick and place robot and then easily fixtured.
 Minimize thin, flat parts that are more difficult to pick up. Avoid very small parts that are
difficult to pick-up or require a tool such as a tweezers to pick-up. This will increase handling and
orientation time.
 Avoid parts with sharp edges, burrs or points. These parts can injure workers or customers, they
require more careful handling, they can damage product finishes, and they may be more
susceptible to damage themselves if the sharp edge is an intended feature.
 Avoid parts that can be easily damaged or broken.
 Avoid parts that are sticky or slippery (thin oily plates, oily parts, adhesive backed parts, small
plastic parts with smooth surfaces, etc.).
 Avoid heavy parts that will increase worker fatigue, increase risk of worker injury, and slow the
assembly process.
 Design the work station area to minimize the distance to access and move a part.
 When purchasing components, consider acquiring materials already oriented in magazines, bands,
tape, or strips.

7. Minimize flexible parts and interconnections. Avoid flexible and flimsy parts such as belts, gaskets,
tubing, cables and wire harnesses. Their flexibility makes material handling and assembly more difficult
and these parts are more susceptible to damage. Use plug-in boards and backplanes to minimize wire
harnesses. Where harnesses are used, consider foolproofing electrical connectors by using unique
connectors to avoid connectors being mis-connected. Interconnections such as wire harnesses, hydraulic
lines, piping, etc. are expensive to fabricate, assemble and service. Partition the product to minimize
interconnections between modules and co-locate related modules to minimize routing of interconnections.

8. Design for ease of assembly by utilizing simple patterns of movement and minimizing the axes of
assembly. Complex orientation and assembly movements in various directions should be avoided. Part
features should be provided such as chamfers and tapers. The product's design should enable assembly to
begin with a base component with a large relative mass and a low center of gravity upon which other
parts are added. Assembly should proceed vertically with other parts added on top and positioned with the
aid of gravity. This will minimize the need to re-orient the assembly and reduce the need for temporary
fastening and more complex fixturing. A product that is easy to assemble manually will be easily
assembled with automation. Assembly that is automated will be more uniform, more reliable, and of a
higher quality.

9. Design for efficient joining and fastening. Threaded fasteners (screws, bolts, nuts and washers) are
time-consuming to assemble and difficult to automate. Where they must be used, standardize to minimize
variety and use fasteners such as self threading screws and captured washers. Consider the use of integral
attachment methods (snap-fit). Evaluate other bonding techniques with adhesives. Match fastening
techniques to materials, product functional requirements, and disassembly/servicing requirements.
10. Design modular products to facilitate assembly with building block components and subassemblies.
This modular or building block design should minimize the number of part or assembly variants early in
the manufacturing process while allowing for greater product variation late in the process during final
assembly. This approach minimizes the total number of items to be manufactured, thereby reducing
inventory and improving quality. Modules can be manufactured and tested before final assembly. The
short final assembly leadtime can result in a wide variety of products being made to a customer's order in
a short period of time without having to stock a significant level of inventory. Production of standard
modules can be leveled and repetitive schedules established.

11. Design for automated production. Automated production involves less flexibility than manual
production. The product must be designed in a way that can be more handled with automation. There are
two automation approaches: flexible robotic assembly and high speed automated assembly.
Considerations with flexible robotic assembly are: design parts to utilize standard gripper and avoid
gripper / tool change, use self-locating parts, use simple parts presentation devices, and avoid the need to
secure or clamp parts. Considerations with high speed automated assembly are: use a minimum of parts or
standard parts for minimum of feeding bowls, etc., use closed parts (no projections, holes or slots) to
avoid tangling, consider the potential for multi-axis assembly to speed the assembly cycle time, and use
pre-oriented parts.

12. Design printed circuit boards for assembly. With printed circuit boards (PCB's), guidelines include:
minimizing component variety, standardizing component packaging, using auto-insertable or placeable
components, using a common component orientation and component placement to minimize soldering
"shadows", selecting component and trace width that is within the process capability, using appropriate
pad and trace configuration and spacing to assure good solder joints and avoid bridging, using standard
board and panel sizes, using tooling holes, establishing minimum borders, and avoiding or minimizing
adjustments.

Design for manufacturability(DFM)

Design for manufacturability (also sometimes known as design for manufacturing)- (DFM) is the general
engineering art of designing products in such a way that they are easy to manufacture. The basic idea
exists in almost all engineering disciplines, but of course the details differ widely depending on the
manufacturing technology. This design practice not only focuses on the design aspect of a part but also on
the producibility. In simple language it means relative ease to manufacture a product, part or assembly.

The design stage is very important in product design. Most of the product lifecycle costs are committed at
design stage. The product design is not just based on good design but it should be possible to produce by
manufacturing as well. Often an otherwise good design is difficult or impossible to produce. Typically a
design engineer will create a model or design and send it to manufacturing for review and invite
feedback. This process is called as design review. If this process is not followed diligently, the product
may fail at manufacturing stage.

If these DFM guidelines are not followed, it will result in iterative design, loss of manufacturing time and
overall resulting in longer time to market. Hence many organizations have adopted concept of Design for
Manufacturing.
Depending on various types of manufacturing processes there are set guidelines for DFM practices. These
DFM guidelines help to precisely define various tolerances, rules and common manufacturing checks
related to DFM.

While DFM is applicable to day to day design process, a similar concept called DFSS (Design for Six
Sigma) is also practiced in many organizations.

ADVANCED PLANNING AND SCHEDULING

Advanced planning and scheduling (also referred to as APS and advanced manufacturing) refers to a
manufacturing management process by which raw materials and production capacity are optimally
allocated to meet demand. APS is especially well-suited to environments where simpler planning methods
cannot adequately address complex trade-offs between competing priorities.

Traditional planning and scheduling systems (such as Manufacturing resource planning) utilize a stepwise
procedure to allocate material and production capacity. This approach is simple but cumbersome, and
does not readily adapt to changes in demand, resource capacity or material availability. Materials and
capacity are planned separately, and many systems do not consider limited material availability or
capacity constraints. Thus, this approach often results in plans that cannot be executed. However, despite
attempts to shift to the new system, attempts have not always been successful, which has called for the
combination of management philosophy with manufacturing.

Unlike previous systems, APS simultaneously plans and schedules production based on available
materials, labor and plant capacity.

APS has commonly been applied where one or more of the following conditions are present:

1. Make-To-Order (as distinct from make-to-stock) manufacturing

2. capital-intensive production processes, where plant capacity is constrained
3. products 'competing' for plant capacity: where many different products are produced in each
facility
4. products that require a large number of components or manufacturing tasks
5. production necessitates frequent schedule changes which cannot be predicted before the event

Advanced Planning & Scheduling software enables manufacturing scheduling and advanced scheduling
optimization within these environments.

REVERSE ENGINEERING

Reverse engineering is a methodology for constructing CAD models of physical parts whose drawings are
not available by digitizing an existing prototype, creating a computer model and then using it to
manufacture the component.The techniques available for reverse engineering, with particular emphasis on
the three-dimensional model generation.

The different steps involved in the process are described, and then a number of techniques available for
the model generation from the point data are illustrated. These are then compared with regards to speed,
accuracy and domain of problems solved.

Creation of new products from existing solutions (product re-design) shortens new product introduction
phases and reduces costs. The product re-engineering process is a new approach to the realisation of
substitute components without the benefit of original design process documentation or any other
documentation relating to the component.

Re-engineering comprises stages which are potentially applicable to many industries. This research
applies an enterprise modelling architecture to modelling the re-engineering process, producing
descriptions of the process from several different descriptive views, namely function, information,
resource and organisation.

This results in a more complete description of the process, in which the model itself may be used as a
reference for the implementation of a re-design process in a particular company. This research also shows
how the information modelling constructs of CIMOSA can be used to meet the particular unique
requirements of the process of re-design.

Computer-aided process planning (CAPP)

Computer-aided process planning (CAPP) is the use of computer technology to aid in the process
planning of a part or product, in manufacturing. CAPP is the link between CAD and CAM in that it
provides for the planning of the process to be used in producing a designed part.

Process planning is concerned with determining the sequence of individual manufacturing operations
needed to produce a given part or product. The resulting operation sequence is documented on a form
typically referred to as a route sheet containing a listing of the production operations and associated
machine tools for a workpart or assembly. Process planning in manufacturing also refers to the planning
of use of blanks, spare parts, packaging material, user instructions (manuals) etc.

The term "Computer-Aided Production Planning" is used in different context on different parts of the
production process; to some extent CAPP overlaps with the term "PIC" (Production and Inventory
Control).

Process planning translates design information into the process steps and instructions to efficiently and
effectively manufacture products. As the design process is supported by many computer-aided tools,
computer-aided process planning (CAPP) has evolved to simplify and improve process planning and
achieve more effective use of manufacturing resources.
Process planning encompasses the activities and functions to prepare a detailed set of plans and
instructions to produce a part. The planning begins with engineering drawings, specifications, parts or
material lists and a forecast of demand. The results of the planning are:

 Routings which specify operations, operation sequences, work centers, standards, tooling and
fixtures. This routing becomes a major input to the manufacturing resource planning system to
define operations for production activity control purposes and define required resources for
capacity requirements planning purposes.

 Process plans which typically provide more detailed, step-by-step work instructions including
dimensions related to individual operations, machining parameters, set-up instructions, and
quality assurance checkpoints.

 Fabrication and assembly drawings to support manufacture (as opposed to engineering drawings
to define the part).

Keneth Crow stated that "Manual process planning is based on a manufacturing engineer's experience and
knowledge of production facilities, equipment, their capabilities, processes, and tooling. Process planning
is very time-consuming and the results vary based on the person doing the planning".

According to Engelke, the need for CAPP is greater with an increased number of different types of parts
being manufactured, and with a more complex manufacturing process.

Computer-aided process planning initially evolved as a means to electronically store a process plan once
it was created, retrieve it, modify it for a new part and print the plan. Other capabilities were table-driven
cost and standard estimating systems, for sales representatives to create customer quotations and estimate
delivery time.

INTRODUCTION TO CAPP

Process planning translates design information into the process steps and instructions to efficiently and
effectively manufacture products. As the design process is supported by many computer-aided tools,
computer-aided process planning (CAPP) has evolved to simplify and improve process planning and
achieve more effective use of manufacturing resources.

PROCESS PLANNING

Process planning encompasses the activities and functions to prepare a detailed set of plans and
instructions to produce a part. The planning begins with engineering drawings, specifications, parts or
material lists and a forecast of demand. The results of the planning are:

 Routings which specify operations, operation sequences, work centers, standards, tooling and
fixtures.This routing becomes a major input to the manufacturing resource planning system to
define operations for production activity control purposes and define required resources for
capacity requirements planning purposes.
  Process plans which typically provide more detailed,step-by-step work instructions including
dimensions related to individual operations, machining parameters, set-up instructions, and
quality assurance checkpoints.
 Fabrication and assembly drawings to support manufacture (as opposed to engineering drawings
to define the part).

Manual process planning is based on a manufacturing engineer's experience and knowledge of production
facilities,equipment, their capabilities, processes, and tooling. Process planning is very time-consuming
and the results vary based on the person doing the planning.

COMPUTER-AIDED PROCESS PLANNING

Manufacturers have been pursuing an evolutionary path to improve and computerize process planning in
the following five stages:

Stage I - Manual classification; standardized process plans

Stage II - Computer maintained process plans
Stage III - Variant CAPP
Stage IV - Generative CAPP
Stage V - Dynamic, generative CAPP

Prior to CAPP, manufacturers attempted to overcome the problems of manual process planning by basic
classification of parts into families and developing somewhat standardized process plans for parts families
(Stage I). When a new part was introduced, the process plan for that family would be manually retrieved,
marked-up and retyped. While this improved productivity, it did not improve the quality of the planning
of processes and it did not easily take into account the differences between parts in a family nor
improvements in production processes.

Computer-aided process planning initially evolved as a means to electronically store a process plan once
it was created, retrieve it, modify it for a new part and print the plan (Stage II). Other capabilities of this
stage are table-driven cost and standard estimating systems.

This initial computer-aided approach evolved into what is now known as "variant" CAPP. However,
variant CAPP is based on a Group Technology (GT) coding and classification approach to identify a
larger number of part attributes or parameters. These attributes allow the system to select a baseline
process plan for the part family and accomplish about ninety percent of the planning work. The planner
will add the remaining ten percent of the effort modifying or fine-tuning the process plan. The baseline
process plans stored in the computer are manually entered using a super planner concept,that is,
developing standardized plans based on the accumulated experience and knowledge of multiple planners
and manufacturing engineers (Stage III).

The next stage of evolution is toward generative CAPP (Stage IV). At this stage, process planning
decision rules are built into the system. These decision rules will operate based on a part's group
technology or features technology coding to produce a process plan that will require minimal manual
interaction and modification (e.g., entry of dimensions).

While CAPP systems are moving more and more towards being generative, a pure generative system that
can produce a complete process plan from part classification and other design data is a goal of the future.
This type of purely generative system (in Stage V) will involve the use of artificial intelligence type
capabilities to produce process plans as well as be fully integrated in a CIM environment. A further step
in this stage is dynamic, generative CAPP which would consider plant and machine capacities, tooling
availability, work center and equipment loads, and equipment status (e.g., maintenance downtime) in
developing process plans.

The process plan developed with a CAPP system at Stage V would vary over time depending on the
resources and workload in the factory. For example, if a primary work center for an operation(s) was
overloaded, the generative planning process would evaluate work to be released involving that work
center,alternate processes and the related routings. The decision rules would result in process plans that
would reduce the overloading on the primary work center by using an alternate routing that would have
the least cost impact. Since finite scheduling systems are still in their infancy, this additional dimension to
production scheduling is still a long way off.

Dynamic, generative CAPP also implies the need for online display of the process plan on a workorder
oriented basis to insure that the appropriate process plan was provided to the floor. Tight integration with
a manufacturing resource planning system is needed to track shop floor status and load data and assess
alternate routings vis-a-vis the schedule.Finally, this stage of CAPP would directly feed shop floor
equipment controllers or, in a less automated environment,display assembly drawings online in
conjunction with process plans.

CAPP PLANNING PROCESS

The system logic involved in establishing a variant process planning system is relatively straight forward
- it is one of matching a code with a pre-established process plan maintained in the system. The initial
challenge is in developing the GT classification and coding structure for the part families and in manually
developing a standard baseline process plan for each part family.

The first key to implementing a generative system is the development of decision rules appropriate for the
items to be processed. These decision rules are specified using decision trees, computer languages
involving logical "if-then" type statements, or artificial intelligence approaches with object-oriented
programming.

The nature of the parts will affect the complexity of the decision rules for generative planning and
ultimately the degree of success in implementing the generative CAPP system.The majority of generative
CAPP systems implemented to date have focused on process planning for fabrication of sheet metal parts
and less complex machined parts. In addition, there has been significant recent effort with generative
process planning for assembly operations, including PCB assembly.
A second key to generative process planning is the available data related to the part to drive the planning.
Simple forms of generative planning systems may be driven by GT codes. Group technology or features
technology (FT) type classification without a numeric code may be used to drive CAPP. This approach
would involve a user responding to a series of questions about a part that in essence capture the same
information as in a GT or FT code. Eventually when features-oriented data is captured in a CAD system
during the design process, this data can directly drive CAPP.

CAD/CAM INTEGRATION AND CAPP FEATURES

 A frequently overlooked step in the integration of CAD/CAM is the process planning that must
occur. CAD systems generate graphically oriented data and may go so far as graphically
identifying metal, etc. to be removed during processing. In order to produce such things as NC
instructions for CAM equipment, basic decisions regarding equipment to be used, tooling and
operation sequence need to be made. This is the function of CAPP. Without some element of
CAPP, there would not be such a thing as CAD/CAM integration. Thus CAD/CAM systems that
generate tool paths and NC programs include limited CAPP capabilities or imply a certain
approach to processing.

CAD systems also provide graphically-oriented data to CAPP systems to use to produce assembly
drawings, etc. Further, this graphically-oriented data can then be provided to manufacturing in the
form of hardcopy drawings or work instruction displays. This type of system uses work
instruction displays at factory workstations to display process plans graphically and guide
employees through assembly step by step. The assembly is shown on the screen and as a
employee steps through the assembly process with a footswitch, the components to be inserted or
assembled are shown on the CRT graphically along with text instructions and warnings for each
step.

If NC machining processes are involved, CAPP software exists which will select tools, feeds, and
speeds, and prepares NC programs.

CAPP BENEFITS

Significant benefits can result from the implementation of CAPP. In a detailed survey of twenty-two large
and small companies using generative-type CAPP systems, the following estimated cost savings were
achieved:
  58% reduction in process planning effort
 10% saving in direct labor
 4% saving in material
 10% saving in scrap
 12% saving in tooling
 6% reduction in work-in-process

In addition, there are intangible benefits as follows:

 Reduced process planning and production lead-time; faster response to engineering changes
 Greater process plan consistency; access to up-to-date information in a central database
 Improved cost estimating procedures and fewer calculation errors
 More complete and detailed process plans
 Improved production scheduling and capacity utilization
 Improved ability to introduce new manufacturing technology and rapidly update process plans to
utilize the improved technology.