In companies, planning processes can result in increased output, higher precision, and faster turnaround for vital business tasks. A process is described as a set of steps that result in a specific outcome. It converts input into output. Process planning is also called manufacturing planning, material processing, process engineering, and machine routing. It is the act of preparing detailed work instructions to produce a part. It is a complete description of specific stages in the production process. Process planning determines how the product will be produced or service will be provided. Process planning converts design information into the process steps and instructions to powerfully and effectively manufacture products. As the design process is supported by many computer-aided tools, computer-aided process planning (CAPP) has evolved to make simpler and improve process planning and realize more effectual use of manufacturing resources.
It has been documented that process planning is required for new product and services. It is the base for designing factory buildings, facility layout and selecting production equipment. It also affects the job design and quality control.
Objective of Process Planning: The chief of process planning is to augment and modernize the business methods of a company. Process planning is planned to renovate design specification into manufacturing instructions and to make products within the function and quality specification at the least possible costs. This will result in reduced costs, due to fewer staff required to complete the same process, higher competence, by eradicating process steps such as loops and bottlenecks, greater precision, by including checkpoints and success measures to make sure process steps are completed precisely, better understanding by all employees to fulfil their department objectives. Process planning deals with the selection of the processes and the determination of conditions of the processes. The particular operations and conditions have to be realised in order to change raw material into a specified shape. All the specifications and conditions of operations are included in the process plan. The process plan is a certificate such as engineering drawing. Both the engineering drawing and the process plan present the fundamental document for the manufacturing of products. Process planning influences time to market and productions cost. Consequently the planning activities have immense importance for competitive advantage.
Principles of Process Planning
General principles for evaluating or enhancing processes are as follows:
- First define the outputs, and then look toward the inputs needed to achieve those outputs.
- Describe the goals of the process, and assess them frequently to make sure they are still appropriate. This would include specific measures like quality scores and turnaround times.
- When mapped, the process should appear as a logical flow, without loops back to earlier steps or departments.
- Any step executed needs to be included in the documentation. If not, it should be eliminated or documented, depending on whether or not it’s necessary to the process.
- People involved in the process should be consulted, as they often have the most current information.
Process planning includes the activities and functions to develop a comprehensive plans and instructions to produce a part. The planning starts 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 centres, 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 characteristically offer more detailed, step-by-step work instructions including dimensions linked to individual operations, machining parameters, set-up instructions, and quality assurance checkpoints. Process plans results in fabrication and assembly drawings to support manufacture and annual process planning is based on a manufacturing engineer’s experience and knowledge of production facilities, equipment, their capabilities, processes, and tooling. But process planning is very lengthy and the results differ based on the person doing the planning.
Major steps in process planning: Process planning has numerous steps to complete the project that include the definition, documentation, review and improvement of steps in business processes used in a company.
The first step is to describe what the process should accomplish. It includes queries like, what is the output of this process? Who receives the output, and how do they define success?, What are the inputs for the process?, Are there defined success measures in place – such as turnaround time or quality scores? And Are there specific checkpoints in the process that need to be addressed?
Documentation: During the documentation stage, interviews are conducted with company personnel to determine the steps and actions they take as part of a specific business process. The results of these interviews is written down, generally in the form of a flow chart, with copies of any forms used or attached. These flow charts are given to the involved departments to review, to make sure information has been correctly captured in the chart.
Review: Next, the flow charts are reviewed for potential problem areas.
Process planning in manufacturing may include the following activities:
- Selection of raw-stock,
- Determination of machining methods,
- Selection of machine tools,
- Selection of cutting tools,
- Selection or design of fixtures and jigs,
- Determination of set-up,
- Determination of machining sequences,
- Calculations or determination of cutting conditions,
- Calculation and planning of tool paths,
- Processing the process plan
3 Main Types of Process Planning
1. Manual Process Planning:
This type of planning is known as man-variant process planning and is the commonest type of planning used for production today.
Planning the operations to be used to produce a part requires knowledge of two groups of variables:
(i) The part requirements (as indicated by an engineering drawing) and,
(ii) The available machines and processes, and the capabilities of each process.
Given these variables, the planner selects the combination of processes required to produce a finished part. In selecting this combination of processes, a number of criteria are employed. Production cost or time are usually the dominant criteria in process selection; however, machine utilization and routing often affect the plans chosen.
In general, the process planner tries to select the best set of processes and machines to produce a whole family of parts rather than just a single part.
2. Automated Process Planning:
Man-variant process planning (at times) becomes a boring and tedious job. It produces erroneous process plans. This, coupled with the labor intensity of man-variant planning, has led many industries to investigate the automation of process planning.
A completely automated process planning system would eliminate all human effort between the preparation of an engineering drawing and a complete process plan for every manufacturing operation.
The block labeled LOGIC would include the capability to scan and interpret the drawing, to convert this information into process requirements and to select machines, tools and operations to yield an economically acceptable product. Such a system would be truly automated. Self-contained logic would check for contradictory requirements on the engineering drawing.
These requirements would be checked for compatibility with available processes. Selection of the processes (such as turning, milling or stamping) would be based on product requirements, quantities ordered and process capabilities. Whenever contradictory or incompatible requirements were detected, a printed message would indicate the source of the problem and recommend remedial action.
Many developments in computer-aided process planning have focused on eliminating the process planner from the entire planning function. Computer-aided process planning can reduce some of the decision making required during a planning process.
Advantages of computer-aided process planning:
(a) It can reduce the process planning time.
(b) It can reduce the skill required of a planner.
(c) It can create more consistent plans.
(d) It can produce more accurate plans.
(e) It can increase productivity.
(f) It can reduce both process planning and manufacturing costs.
Benefits from computer-aided process planning have been documented by several industries. Such systems can reduce planning time from days to hours or from hours to minutes.
3. Generative Process Planning:
Generative process planning may be defined as a system that synthesizes process information in order to create a process plan for a new component automatically. Process plans are created from information available in a manufacturing database with little or no human intervention.
Upon receiving the design model, the system can generate the required operations sequence for the component. Knowledge of manufacturing must be captured and encoded into efficient software. By applying decision logic, a process planner’s decision-making process can be imitated. Other planning functions, such as machine selection, tool selection, process optimization, and so on, can also be automated using generative planning techniques.
Decisions on process selection, process sequencing, and so on, are all made by the system. However, transforming component data and decision rules into a computer-readable format is still a major obstacle to be overcome before generative planning systems become operational.
Generative method of process planning:
The generative method of process planning essentially consists of four steps:
(1) Describe a part in detail.
(2) Describe a catalog of processes available to produce parts.
(3) Describe the machine tool(s) that can perform these processes.
(4) Create the software to inspect the part, process, and available machinery to determine whether all three are compatible.
(a) It can generate consistent process plans rapidly.
(b) New components can be planned as easily as existing components.
(c) It can potentially be interfaced with an automated manufacturing facility to provide detailed and up-to-date control information.