AUTOMATED AND COMPUTER INTEGRATED MANUFACTURING

UNIT -4

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https://www.youtube.com/watch?v=viUNH5iGIBA

PROCESS PLANNING


INTRODUCTION TO PROCESS PLANNING

In manufacturing, the goal is to produce components that meet the design specifications. The design specification ensures the functionality aspect. Next step to follow is to assemble these components into final product.  Process planning acts as a bridge

between design and manufacturing by translating design specification into manufacturing process detail. 

make fig 9.1 of the given pdf given below

APPROACHES TO PROCESS PLANNING

There are basically two approaches to process planning which are as follows :

(i) Manual experience-based process planning

(ii) Computer-aided process planning method. 

(i) Manual experience-based process planning: It is time consuming and over a period of time, plan developed are not consistent.  Feasibility of process planning is dependent on many upstream factors (design and availability of machine tools). Downstream manufacturing activities such as scheduling and machine tool allocation are also influenced by such process plan

(ii)Computer-Aided Process Planning:Computer-aided process planning (CAPP) helps determine the processing steps required to make a part after CAP has been used to define what is to be made. CAPP programs develop a process plan or route sheet by following either a variant or a generative approach. The variant approach uses a file of standard process plans to retrieve the best plan in the file after reviewing the design. The plan can then be revised manually if it is not totally appropriate. The generative approach to CAPP starts with the product design specifications and can generate a detailed process plan complete with machine settings. CAPP systems use design algorithms, a file of machine characteristics, and decision logic to build the plans. Expert systems are based on decision rules and have been used in some generative CAPP systems

make fig 9.3 in given  pdf  below

Steps Involved in CAPP

(i) Design input

(ii) Material selection

(iii) Process selection

(iv) Process sequencing

(v) Machine and tool selection

(vi) Intermediate surface determination

(vii) Fixture selection

(viii) Machining parameter selection

(ix) Cost/time estimation

(x) Plan preparation

(xi) Mc tape image generation

APPROACHES TO COMPUTER-AIDED PROCESS PLANNING

These systems can broadly be clarified into two categories :

(i) Variant computer aided process planning method.

(ii) Generative computer aided process planning method.

(i)Variant Process Planning-Variant process planning approach is sometimes referred as a data retrieval method. In this approach, process plan for a new part is generated by recalling, identifying and retrieving an existing plan for a similar part and making necessary modifications for new part. As name suggests a set of standard plans is established and maintained for each part family in a preparatory stage. Such parts are called master part. The similarity in design attributes and manufacturing methods are exploited for the purpose of formation of part families. Using coding and classification schemes of group technology (GT), a number of methods such as coefficient based algorithm and mathematical programming models have been developed for part family formation and plan retrieval. After identifying a new part with a family, the task of developing process plan is simple. It involves retrieving and modifying the process plan of master part of the family.  

fig 9.4 in given pdf below

(ii)In generative process planning-process plans are generated by means of decision logic, formulas, technology algorithms, and geometry based data to perform uniquely processing decisions. Main aim is to convert a part form raw material to finished state. Hence, generative process plan may be defined as a system that synthesizes process information in order to create a process plan for a new component automatically.

Generative process plan mainly consists of two major components :

(i) Geometry based coding scheme.

(ii) Proportional knowledge in the form of decision logic and data.

Geometry-based Coding Scheme -All the geometric features for all process such as related surfaces, feature dimension, locations, on the features are defined by geometry based coding scheme. The level of detail is much greater in generative system than a variant system. For example, various details such as rough and finished state of the part are provided to transform into desired state

Proportional Knowledge in the Form of Decision Logic and Data : Process knowledge in the form of decision logic and data are used for matching of part geometry requirement with the manufacturing capabilities. All the methods mentioned above is performed automatically. Operation instruction sets are automatically generated to help the operators to run the machines in case of manual operation. NC codes are automatically generated, when numerically controlled machines are used.

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