process_con_over

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Unformatted text preview: MIT OpenCourseWare http://ocw.mit.edu 2.830J / 6.780J / ESD.63J Control of Manufacturing Processes (SMA 6303) Spring 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms . M ANUFACTURING P ROCESSES AND P ROCESS C ONTROL David E. Hardt Laboratory for Manufacturing and Productivity Massachusetts Institute of Technology February , 1996 The following paper outlines a basic modeling paradigm for manufacturing process control. Once the model is defined, three distinctly different modes of process control are described based on this model The model then leads to a control taxonomy for manufacturing processes. Model Definition All manufacturing processes have but two outputs : • Geometry (macroscopic shape of the product) • Properties (all intrinsic material properties) These two outputs completely define the performance of the product, and the design specifications that it must meet. All processes also involve the transformation of material from an initial geometry and set of properties to the final outputs. This transformation is accomplished through the application (or removal) of energy, distributed about the surface or volume of the material. The source of this “directed energy” is the manufacturing machine or equipment. Thus, we can first define a manufacturing process as the interaction of equipment with a material to transform the material to the desired outputs geometry and properties. This model is shown in block diagram form in Fig 1. Outputs Energy Geometry Properties Equipment Material Fig. 1 The Relationship of Equipment and Material in a Manufacturing Process Since all transformations are driven by and governed by the equipment, the only control over the process (other than changing the material itself) is through the equipment. Thus, the control inputs to the process are those equipment inputs that modulate the intensity and distribution of the energy input to the material. In other words, during the operation of the process, the only accessible means of controlled change is the equipment inputs. This leads to the process model shown in Fig. 2 Energy Equipment Material Machine Inputs Outputs Geometry Properties Fig. 2 Process Model with Equipment Inputs Shown To help define internal variables in the process as well as the inputs and outputs, the basic output causality of the process model is shown in Fig. 3 using a simple functional relationship between the process output vector Y and the parameters of the process . Y = ( ) The equipment inputs u are separated as a subset of the parameters that are accessible, certain and “manipulable” in a “reasonable” time frame relative to the basic process execution time....
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This note was uploaded on 09/24/2010 for the course MECHE 2.830J taught by Professor Davidhardt during the Spring '08 term at MIT.

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