CAPP is the acronym in English for "computer-aided process planning". CAPP is a highly effective technology when used by manufacturing organizations with a large number of products and process steps. Its objective is the automation of planning through the use of digital tools. CAPP is an alternative to the traditional way of process planning. Figure 1 shows the framework for the implementation of a CAPP system.
Figure 1. Framework for the implementation of a CAPP system.
Process planning involves the activities and functions necessary to prepare a set of procedures and instructions required for the production of a part. The process starts with engineering drawings, specifications, bill of materials and a projection of the quantity of parts to be produced. The result of process planning are the routing sheets with the necessary operations and their sequence, the machinery to be used, the standard operating times and the necessary tooling.
Production planning and control can be performed on the basis of routings by different methods: manual or computer-assisted. Another product of process planning is detailed work instructions, fabrication drawings and assembly diagrams to assist in the manufacture of parts. This should happen regardless of whether it is done by manual or computer-assisted methods or a mixture of the two. Process planning is then concerned with selecting production methods, sequences of operations, machines and tools. This set of elements must be calculated in detail by the process planners before starting any production task.
When planning is done manually, it requires a large number of man-hours of highly experienced personnel. Using the computer-aided methodology, generating roadmaps means managing the information, storing it and relating it to the relevant part in some way. Sometimes, this relationship is carried out by means of barcodes attached to the part.
In addition to the advantage of CAPP, for the reduction of time spent in manual process planning, these systems perform their function considering the operation as a total system, so that all operations required by a part are coordinated with each other and performed efficiently.
Despite the high technical requirements of this type of systems (software, coordination with other manufacturing platforms, among others.), it is unquestionable that they are of great help for the efficient planning and scheduling of highly complex manufacturing operations, proving to be a very useful tool when working with a large number of different parts and having a low demand for them.
Imagine the following situation, which is real in many machined parts manufacturing industries with low production volume and large variety of models. The plant has more than 100 machine tools capable of performing multiple processes, such as turning, grooving, drilling, gear generation, flat surface grinding, cylindrical surface grinding, internal threading, external threading, mechanical cutting, plasma cutting, plate bending, among others.
On the other hand, there are more than five thousand parts in the company's manufacturing catalog, of which there are usually five hundred types of parts that are manufactured in the same period of time. Every week 100 completed orders are delivered to customers and an average of 100 new orders are received. But that's not all, each piece in the production catalog has an average of fifteen different processes that normally must be performed on different machines.
Now you have been tasked with planning the optimal sequence of processing for each part and next week's production of the plant. Achieving optimal process and production scheduling in the plant using conventional tools is virtually impossible. This is where the CAPP system comes in, which must be compatible (communicate) with the plant's computer-aided production planning system.
The previous scenario is also present in the electronic card manufacturing industry with SMD (Surface Mounting Devices) components, only the processes and the type of machinery change, but the complexity scenario is the same as the one described above.
Now imagine a company like the ones described above that doesn't use computer-aided planning systems competing against one that does. The disadvantage in terms of total plant efficiency and therefore in terms of manufacturing cost is obvious. Such a company, without the information that computer-aided systems can generate, will not even be able to determine its operating efficiency. From the above you can identify the importance of these systems in a company where the complexity of the manufacturing system is present.
Classification of CAPP systems
CAPP systems are classified into two large groups: in variant (derivative) systems or in generative systems. Similarly, if we consider the complexity of the tasks that these can perform, the variant type systems are the least complicated.
Variant or derivative type systems basically work from a collection or database of standard processes for the parts to be manufactured, i.e., they are based on knowledge already existing within the manufacturing operation in which this type of system is installed. On the other hand, generative systems automatically build process plans from logical procedures, as a human programmer would do, i.e., they incorporate in their software the knowledge of traditional programmers about the manufacturing system they are working on. They are considered expert systems (Groover, 2018).
The future of CAPP systems
With the rise of artificial intelligence and machine learning, the capabilities of generative systems have reached a new level. However, an exclusively generative type of system that can develop a complete process plan from the classification of parts and other design data is a developing goal. These new systems that have made inroads with the instruction of these new tools have been given the name automatic computer-aided process planning (ACAPP) (Al-wswasi, Ivanov, and Makatsoris, 2018).
Evolution of process planning systems
Click on each section for more information.
Prior to CAPP systems, manual scheduling problems were addressed by using a basic classification of parts into families and developing standard process plans for the part families. When new parts were introduced, the process plan of the family to which it belonged was manually retrieved, identified and reissued. Productivity in process planning improved a little, but there were still many points to be resolved.
CAPP systems started as tools to store process plans in a computer's memory, retrieve them, modify them and publish them again. Some other tools of standardization of calculations existed in this approach. For example: the use of standardized computerized formats for the creation of the processes themselves, but without greater intelligence, only performing basic mathematical operations, text editing and data storage.
CAPP systems variants use a methodology similar to the manual approach. If it is needed, they develop a process plan for a new part, they identify an existing plan of a similar part and work on it to include the required modifications. The greatest innovation in these systems is based on the use of computing tools to manage, classify, and code the family of parts. It is an efficient system that simplifies the planning process by using part variants from preexisting families.
The next development was generative systems, in which decision rules are introduced for process planning. These rules are based on group technology or feature coding technology to produce a process plan that needs very little modification or manual intervention.
In recent years, new tools have been introduced in the design of CAPP systems. Among the most outstanding are artificial neural networks, genetic algorithms, fuzzy logic or Petri nets. The core of ACAPPs lies in automatic feature recognition (AFR), which has been greatly simplified with image recognition and computer vision techniques. At present, there are several companies such as Siemens or Dassault Systèmes betting heavily on this type of initiative, so it is practically a fact that we will have them actively in the market in a few years (Al-wswasi, Ivanov and Makatsoris, 2018).
3.1 Selection criteria for CAPP systems
The only CAPP systems that are commercially active are the variant system and the generative system, let's take a little more detailed look at the way both work and their prerequisites:
The sequence necessary for the installation of a variant system planning system is relatively simple, it is a matter of relating a code to a pre-established process plan stored in the system's memory. The initial difficulty lies in the development of the group technology classification and code structure for the families of parts and in the manual development of a standard basis of processes for each family of parts.
For the implementation of a generative system, the first key step is the development of appropriate decision rules for the items to be processed. Such decision rules are specified using decision trees and programming languages. According to the complexity of the parts, the number and level of decision rules required for generative planning.
The second key step, for generative planning systems, is the information available on the part that will be the center or core of the planning. Some generative planning systems can be implemented using group technology codes, the type of feature classification technology without numerical code can also be used to implement this system. This approach requires the user to answer a series of questions about the part, which ultimately capture the same information as the group technology or manufacturing technology codes (Groover, 2018).
The advantages of the CAPP variant system are as follows:
One of the main disadvantages of the CAPP variant system is that the quality of process planning still depends on the knowledge of the human process planner; and the computer is only a tool to assist in manual process planning activities.
The advantage of generative CAPP systems, due to their operating architecture, is their ability to generate process planning by requiring only the input data and eliminating the need for decision making by human process planners and their ability to handle more complex parts than variant systems. The advantages of the variant CAPP system are the disadvantages of the generative CAPP system.
In summary, depending on the degree of complexity that an organization is willing to handle, the type of CAPP system to be implemented will depend on the type of system chosen.
3.2 Access to process planning
The concept of access to process planning can be based on the following definition:
Access to find information is a process that usually comprises six types of activities:
Hence, the search for information is defined as the process through which the user and information seeker intentionally deals with modifying their state of knowledge. It is a higher-level cognitive process that forms an integral part of general learning, learning to learn, learning to solve problems and, processes involved in knowledge construction (Harman, 2019).
Access to process planning refers to the way in which the different types of process planning (the manual, variant CAPP and generative CAPP) retrieve and process the necessary information. The manual process planning method does a manual search, retrieval and processing of relevant information that has been stored, either physically or electronically, for the manual planning of the next process.
The variant CAPP system searches and retrieves relevant information electronically for the planning of the next process, however, the planning itself still needs decision making by a human planner; the generative CAPP system searches, retrieves and processes relevant information electronically for the planning of the next process, with no human intervention other than feeding the necessary data about the product whose process is planned.
Look at the following image:
All the parts shown in the image need several mechanical processes before they look as shown. In addition, each piece has particular design and production characteristics. The processes involved in the different parts can be cutting, turning, milling, grinding, drilling, tapping, forming, bending, finishing, just to name a few.
To perform process planning for a given part, the following steps are required, regardless of the method used for that purpose (Figure 2):
Figure 2. General stages of manufacturing process planning.
3.3 Manual, variant and generative access
Manual planning access: all steps and decisions are made by human planners. The information in point two may be stored in a computer. Steps three through four are decided and ordered by a human planner (Figure 3).
Figure 3. Representation of access to manual planning.
CAPP variant access: The first steps are ordered by the human planner. Steps three and four are performed by the variant CAPP, but human intervention may be required in making certain decisions. As a final step, the CAPP system communicates with the company's production planning system (Figure 4).
Figure 4. Representation of the variant CAPP access.
Generative CAPP access: all steps are performed without human intervention. The information required for step zero is taken from the part drawings, by computerized visual inspection. The system can iterate between points two and five to comprehensively optimize the planning of the production process (Figure 5).
Figure 5. Representation of generative CAPP access.
To learn about the features of a modern manufacturing process planning tool (Siemens Easy Plan 6.0), you can watch the following video:
Siemens Software. (2021, December 9). Manufacturing Process Planning with Easy Plan 6.0 [Video file]. Retrieved from https://www.youtube.com/watch?v=1G1Bi32FfCs
The following link do not belong to Tecmilenio University,
when accessing to them, you must accept their terms and conditions.
Process planning is the activities that determine the sequence of manufacturing processes that will be used to convert raw material or parts from an original state to a final state. Attached to the process sequence is a description of the procedures, process parameters, equipment to be used and equipment tooling. The planned processes must be optimal, ensuring that the production is carried out within the deadlines required by the client and at the lowest production cost.
This implies the need for computerized systems that allow the process planning function to be performed fully or partially digitally and consistently produce optimized process plans consistently fast. The planning of processes by computer requires certain information regarding the product, the processes needed for its production and the machinery available to carry it out.
Commercially available CAPP computer-based process planning methods are the variant or derivative type and the generative type. The variant CAPP is the simpler of the two and is basically considered to be a systematization of the work and information used by a human programmer and requires the skills and decision making of the human programmer.
The generative CAPP belongs to the category of expert systems, since, based on product, process and machinery information, it is able to make decisions regarding its process planning task. Either way, the knowledge and experience of a human process programmer is incorporated into your system at the time of installation. Therefore, the generative CAPP is the more complex of the two systems and attempts to automate decision making and has higher hardware and hardware and software compared to the variant system.
The advantages of computer-based process planning include reduced clerical work, fewer calculations, fewer forgotten details and immediate access to up-to-date information, consistent information at all times, rapid response to engineering and production changes, assurance that the latest revision of information is available, more detailed uniform planning, and more efficient use of resources.
Once you have studied the topic of computer-aided process planning, I invite you to continue with the review of computer-aided process control, which is the next topic.
Make sure that you:
The following links do not belong to Tecmilenio University, when accessing to them, you must accept their terms and conditions.
To learn about cost-saving manufacturing, check out the following video:
To learn about selecting a CAPP system, check out the following video:
To learn more about automatic process planning, we recommend reading:
To learn more about CAPP system, we recommend reading:
From the analysis of a case, the student will identify the type of CAPP system that would be appropriate to implement in a company.
Objective:
To identify a CAPP system and its applications in a company.
Requirements:
Read the explanation of topic 3 and review the resources of topic 3.
Instructions:
A Mexican company is incorporating the manufacture of computer cabinets into its product portfolio. After conducting a market analysis, the marketing team determined that the two most profitable audiences are video game players and the professional sector, so it has suggested to the design team the development of three models for each of these audiences. The company's machines perform the processes of cutting, drilling, threading and bending sheet metal. Due to the variability in demand, the company has decided to implement a CAPP system to guarantee the production process from the beginning of its operations.
Evaluation criteria:
Description:
Through research, the student will identify at least three commercial CAPP system software variants and generative systems, including the following points: manufacturer or designer of the software, type of market targeted, and advantages of the software.
Instructions: