Traditionally, process planning has been accomplished by manufacturing engineers who are knowledgeable within the particular processes employed in the factory and are able to read engineering drawings. Supported their knowledge, skill, they develop the processing steps within the most sensible sequence required to create each part. A number of these details are often delegated to specialists, like tool designers. But manufacturing engineering is answerable for them.
Process Planning for Parts
The processes need to manufacture a given part are determined largely by the fabric out of which it’s to be made. The fabric is chosen by the merchandise designer supported functional requirements. Once the fabric has been selected, the selection of possible processes is narrowed considerably.
A typical processing sequence to fabricate a discrete part consists of
- A basic process,
- One or more secondary processes,
- Operations to reinforce physical properties, and
- Finishing operations.
Basic and Secondary Process
Basic and secondary processes are shaping processes that alter the geometry of a piece part. A basic process establishes the initial geometry of the part. Examples include metal casting, forging, and sheet-metal rolling. In most cases, the starting geometry must be refined by a series of secondary processes. These operations transform the essential shape into the final geometry.
There is a correlation between the secondary processes that may be used. And therefore the basic process that gives the initial form. As an example, when a steel plant produces strips or coils of the sheet, the secondary processes are stamping operations like blanking, punching, and bending. When casting or forging are the fundamental processes, machining operations are generally the secondary processes.
The assembly of which consists of casting because the basic process followed by machining because the secondary process. The selection of certain basic processes minimizes the requirement for secondary processes. For instance, if plastic injection molding is that a basic process, secondary operations are usually not required because the molding is capable of providing detailed geometric features with good dimensional accuracy.
Reinforce Physical Properties
Shaping operations are generally followed by operations to reinforce physical properties and/or finish the merchandise. Operations to reinforce properties include heat treating operations on metal components and glassware. In many cases, parts don’t require these property-enhancing steps in their processing sequence. This is often indicated by the alternate arrow path. Finishing operations are the final operations within the sequence; they typically provide a coating on the work part (or assembly) surface. Samples of these processes are electroplating and painting.
In some cases, property-enhancing processes are followed by additional secondary operations before proceeding to finish. An example may be a machined part that’s hardened by heat treatment.
Prior to heat treatment, the part is left slightly oversized to permit distortion. After hardening, it’s reduced to final size and tolerance by finish grinding. Another example, again in metal parts fabrication, is when annealing is employed to revive ductility to the metal after cold working to allow further deformation of the workpiece.
The task of the method planner usually begins after the essential process has provided the initial shape of the part. Machined parts begin as bar stock or castings or forgings, and also the basic processes for these starting shapes are often external to the fabricating plant. Stampings begin as sheet coils or strips purchased from the mill.
These are the raw materials supplied from external suppliers for the secondary processes and subsequent operations to be performed within the factory. Determining the foremost appropriate processes and also the order during which they have to be accomplished relies on the skill, experience, and judgment of the method planner.
The Route Sheet
The process plan is ready on a form called a route sheet. it’s called a route sheet because it specifies the sequence of operations and equipment which will be visited by the part during its production.
The route sheet is to the method planner what the engineering drawing is to the product designer. It’s the official document that specifies the small print of the method plan. The route sheet should include all manufacturing operations to be performed on the work part, listed within the proper order during which they’re to be accomplished.
For each operation, the subsequent should be listed:
- A quick description of the operation indicating the work to be done surfaces to be processed with references to the part drawing, and dimensions (and tolerances, if not specified on part drawing) to be achieved.
- The equipment on which the work is to be performed. and
- Any special tooling required, like dies, molds, cutting tools, jigs or fixtures, and gages. Additionally, some companies include cycle time standards, setup times, and other data on the route sheet.
Sometimes a more detailed operation sheet is additionally prepared for every operation listed within the routing. this is often retained within the particular department where the operation is performed. It indicates the particular details of the operation, like cutting speeds, feeds, and tools, and other instructions useful to the machine operator. Setup sketches are sometimes also included.
Process Planning for Assemblies
For low production, assembly is usually done at individual workstations. A worker or team of workers performs the assembly work elements to complete the merchandise.
In medium and high production, assembly is usually performed on production lines. In either case, there’s a precedence order during which the work must be accomplished.
Process planning for assembly involves the preparation of the assembly instructions that must be performed. It contains an inventory of the assembly steps within the order within which they have to be done.
For line production, process planning consists of allocating work elements to particular stations along the road, a procedure called line balancing. In effect, the mechanical system routes the work units to individual stations. Also, the line balancing solution determines what assembly steps must be performed at each station.