CIM - Computer Integrated Manufacturing

Computer Integrated Manufacturing, known as CIM, is the phrase used to describe the complete automation of a manufacturing plant, with all processes functioning under computer control and the digital information tying them together. It includes CAD/CAM, computer-aided design/computer-aided manufacturing, CAPP, computer-aided process planning, CNC, computer numerical control machine tools, DNC, direct numerical control machine tools, and other integrated systems not discussed in this blog until now: FMS, flexible machining systems, ASRS, automated storage and retrieval systems, AGV, automated guided vehicles, which is the use of robotics and automated conveyance systems, and computerized scheduling and production control. Thus, we have a business system integrated by a common data base.
The heart of computer integrated manufacturing is CAD/CAM. Computer-aided design(CAD) and computer-aided manufacturing(CAM) systems are essential to reducing cycle times in the organization. CAD/CAM is a high technology integrating tool between design and manufacturing. CAD techniques make use of group technology to create similar geometries for quick retrieval. Electronic files replace drawing rooms. CAD/CAM integrated systems provide design/drafting, planning and scheduling, and fabrication capabilities. CAD provides the electronic part images, and CAM provides the facility for toolpath cutters to take on the raw piece.
The computer graphics that CAD provides allows designers to create electronic images which can be portrayed in two dimensions, or as a three dimensional solid component or assembly which can be rotated as it is viewed. Advanced software programs can analyze and test designs before a prototype is made. Finite element analysis programs allow engineers to predict stress points on a part, and the effects of loading.
Once a part has been designed, the graphics can be used to program the tool path to machine the part. When integrated with an NC postprocessor, the NC program that can be used in a CNC machine is produced. The design graphics can also be used to design tools and fixtures, and for inspections by coordinate measuring machines. The more downstream use that is made of CAD, the more time that is saved in the overall process.
Generative process planning is an advanced generation of CAD/CAM. This uses a more powerful software program to develop a process plan based on the part geometry, the number of parts to be made, and information about facilities in the plant. It can select the best tool and fixture, and it can calculate cost and time.
Flexible machining systems (FMS) are extensions of group technology and cellular manufacturing concepts. Using integrated CAD/CAM, parts can be designed and programmed in half the time it would normally take to do the engineering. The part programs can be downloaded to a CNC machining center under the control of an FMS host computer. The FMS host can schedule the CNC and the parts needed to perform the work.
Computer integrated manufacturing can include different combinations of the tools listed above.
Issues
One of the key issues regarding CIM is equipment incompatibility and difficulty of integration of protocols. Integrating different brand equipment controllers with robots, conveyors and supervisory controllers is a time-consuming task with a lot of pitfalls. At times, the large investment and time required for software, hardware, communications, and integration cannot be financially justified or obtained.
Another key issue is data integrity. Machines react in vain to insufficient or bad data, and the costs of data upkeep, as well as general information systems departmental costs, is higher than in a non-CIM facility.
Another issue is the attempt to program extensive logic to produce schedules and optimize part sequence. There is no substitute for the human mind in reacting to a dynamic day-to-day manufacturing schedule and changing priorities.
Computer Integrated Manufacturing is not a cure-all solution. It is an operational tool that, if implemented properly, will provide a new dimension to competing by quickly introducing new customerized high quality products and delivering them with unprecedented lead times, swift decisions, and manufacturing products with increasing velocity.

CAPP - Three Approaches: Variant, Generative, and the Hybrid

Computer Aided Process Planning, (CAPP), is a production orginazation activity that determines how a product is to be manufactured. This is a cornerstone in the manufacturing process. A major part in determining the cost of components and the best combination of manufacturing tools and processes. This directly affects production efficiency, product quality, and company competitiveness. CAPP is a crucial link between design and manufacturing.

Even with today's technology and the everknown importance of process planning, this activity is still very labor intensive. One leans heavily on experinece and intuition that gives the required insight to the different manufacturing processes and possibilities within a company. However, the dependency upon intuition often eliminates a thorough analysis and optimization a process plan. This can result in delays and increased costs. CAPP takes on the role of standardizing processes, reducing generation time, and attempts to ensure consistant quality.

The Variant Approach
The traditional approach to process planning. Here, a part drawing is examined and then similar parts produced in the past are identified. For the previous parts, process plans are examined and then modified to suit the new part at hand. The primise: Similarities between certain producs imply that those parts can be manufactured in more or less the same way. This is the exact route that manual process planning, involving intuition, takes. Computer logrithm strenghtens the identification of 'families' with codes and definitions. Within small corporations, such 'families' of parts are not difficult to identify. The disadvantage of variant planning is that the process plan only caters for a rough outline plan that still needs to be adapted. The main drawback with this approach is that constructing computerized classification systems have yet to be found error free.

Generative Planning
With the generative planning approach, the computer program incorporates metal cutting know-how and the geometric vision of the part. The process plans are generated by making use of algorithms, decision logic, formulas and geometry based data to perform unique processing decisions to take the part from raw material to a finished state. Here there is no referral to previous plans. Part specificatons, as you can guess, are mandatory input. This includes variables such as material for example. After that, the process is fully automatic and it produces plans of consistant quality. However, the systems are complex and difficult to develop. Maintenance is very difficult for there are a large database of rules which have to be consistant in all condidtions. This results in higher probabilities of system failure.

Hybrid Planning
Introduced to limit the drawbacks of both planning approaches, and benefit from there advantages. Generative processes produce consistant results without classification on high levels of complexity. Variant processes are simple and easy to maintain.
The first step in a hybrid program: the workpeice is associated to a family. Associated with these families is a knowledge base that contains all possibilities to manufacture the part. The user again defines mandatory variables; the program attempts to generate an efficient, cost saving plan for the involved processes.

Surface vs. Solid Modeling

Computer Aided Design programs use surface or solid modeling to create geometry. Surface design is the predecessor to solid modeling, but they are derivatives of eachother:
Solids are really just surfaces that follow a set of rules enforced by the modeling software. This includes maintaining 'watertight' sets of surfaces, without gaps or overlaps, and differentiating the inside of the solid from the outside, (assigning a density). The modeling software is doing a lot of automated tasks behind the scenes to make all this happen.

Surface modeling has two principal advantages over solid modeling. The first is in the type of modeling when shapes must be constructed face by face. This is often associated either with complex shapes or with imported models that must be rebuilt or repaired face by face. The second main advantage is defined in terms of efficiency. In the solid modeling world, one often makes use of a solid swept cutting technique. This is a bad habit and is better handled using surfaces to manipulate the solid - hence a hybrid technique. Time is saved by not having to create an inclosed cut profile. From another view, the solid cut profile geometry is not set up to work well with the changes in the model, so they tend to create alot of rebuild errors and extra faces.

A consideration to make when selecting which modeling type, is IGES files, and how often you work with them. IGES files are can be generated by a Coordinate Measuring Machine, (CMM), and are neither solid or surface. Both modeling programs will usually work with the file becuase of their nature: points mathematically defined in a spacial plane. Problems arise in the nature of solid modeling rules. Namely, the 'water-tight' rule. Points will have to be converted into inclosed profiles in 2D planes. Once this is accomplished, a draft or loft technique can be applied to recreate the geometry. This is often a tedious process.

Solids generally take less time to create, but can take more time to regenerate when working with many redundant faces. If you rarely make changes, then maybe modeling efficiency should be your biggest concern.