Process Planning

Process Planning (definition)Process planning maybe defined as the determination of the processes and the sequence of operations required to make the product. It consists of devising, selecting and specifying processes, machine tools and other equipment to transform the raw material into finished product as per the specifications.

Purpose of Process PlanningThe purpose of process planning is to determine and describe the best process for each job so that:Specific requirements are established for which machines, tools and other equipment can be designed or purchased.The efforts of all engaged in manufacturing are co-ordinated. A guide is furnished to show the best way to use the existing or proposed facilities.

Procedure of Process PlanningTo achieve the main economic manufacture of the product, process planning is done as follows: The finished product is broken into components of the product which forms a basis for purchase of raw materials.Prepare a bill of materials for all components of the product which forms a basis for purchase of raw materials. Decide which parts are to be manufactured in the plant and which parts are to be purchased from the market depending upon the facilities available in the plan.

Procedure for Process Planning(cont.)Choose the appropriate blank size and select most economical process for manufacture components of the product. Decide the sequence of operations to be performed on each componentDepending upon accuracies called for by the drawings, determine the machine tools to do the operations. Determine need for special equipment like jigs, fixtures, etc Estimate standard time for performing job. Determine the type of labour(skilled, semi-skilled or unskilled) required for the job.

Steps involved in process planningRequirements and conditions of the process Improvements of the Specifications List of basic operationsDetermination of the most practical and economical manufacturing methodSelection of equipment Combine the operations and put them in proper sequence

1. Requirements and conditions of the processBefore any problem can be solved, its requirements and conditions must be defined. In process planning, these things includeThe specifications of the finished product.The size, shape and other properties of the raw material.The quantity or number of pieces of the product to be made and date of delivery

2. Improvements of the SpecificationsAll specifications must be clear and explicit. Faulty specifications include: Overlapping dimensionsOmitted tolerancesIndefinite notations for surface finish quality The process engineer consults with the product designer to clarify all points which are not explicit.

3. List of basic operationsUnder this step, the basic operations required to satisfy the specific surface relationships are listed. This listing is in no particular sequence and is merely the recognition of the basic operations required to manufacture the product.

4. Determine the most practical and economical manufacturing methodIn this, step 3 is examined to determine the most practical and economical methods to manufacture the product. The best selected method is one which can produce the part at the lowest overall cost.

5. Selection of EquipmentSelection of equipment is closely related to the selection of process of manufacture. They usually represent long term capital commitment. The following factors are considered while selecting the right equipment:-Size and shape of the workpieceThe work materialThe accuracy and surface quality required.The quality of parts and the sizes of lots requiredPersonal preferences.

6. Combine the operations and put them in proper sequenceThe purpose of this step is to combine the basic operations which have been already determined and put them in the best sequence. Operations can be combined by,SimulationIntegration

Simulation Two or more elements of an operation or two or more operations are performed at the same time. For example, drilling a series of holes simultaneously using a multiple spindle drill head. IntegrationSeveral individual elements of an operation or group of operations are combined in succession but not simultaneously, the performance is said to be integrated. For example, hole must be drilled before it is tapped.

Advantages of Combining operations are:- Improved accuracy Reduced labor costLess tooling requiredLess handling requiredFewer set upsLess scrapFewer inspection points required

Disadvantages of combining operations:-Maintaining tool accuracyPossible higher tool costMore costly set ups

Process Planning SheetThe whole information determined by the process planning is recorded in a tabular form in a sheet called the process planning sheet. Process planning sheet is also called as route sheet.

Process planning sheet consists of the following data about the components of the product: Name and part number of the main product. Name, part number, drawing number of the component and number off per product. Info. concering blank (material used, size and weight of stock).Operations listed in proper sequence alongwith the shops in which these operations will be performed.

Info. regarding machines used for each operation. Data on jigs, fixtures and other special tools used.Inspection devices needed for inspection. Cutting data(speeds and feeds of each operation)Setup time, handling time and machining time for job.

Uses of Process SheetIt helps in advance planning and for purchase of raw materials, design and manufacture of special tools, jigs, fixtures and inspection devices. It helps in estimating the cost of the product before it is actually manufactured. It helps in planning for man power required for doing the job.

CAPP

Computer Aided Process Planning (CAPP)Computer-aided process planning (CAPP) is the use of computer technology to aid in the process planning of a part or product, in manufacturing. CAPP is the link between CAD and CAM in that it provides for the planning of the process to be used in producing a designed part.

Methods of Computer Aided Process PlanningThe ultimate goal of an automated process planning system is to integrate design and production data into the system that generates useable process plans. There are two approaches:-Variant Process planningGenerative ApproachSemi Generative Approach

Variant Process Planning A Variant process planning system uses the similarity among components to retrieve the existing process plans. The variant process planning system has two operational stagesA preparatory stage A production stage

During the Preparatory stage, existing components are coded, classified, and subsequently grouped into families. During the Operation stage, the code is input to a part family search routine to find the family to which the component belongs, The family number is then used to retrieve a standard plan.

Sequences of Variable Process Planning SystemThe following is the sequence of Variable process planning system, Family FormationDataBase Structure DesignSearch Algorithm development and implementationPlan Editing Process parameter selection/updating

Family FormationPart family classification and coding is based on manufacturing features of the partComponents requiring similar processes are grouped into the same familyAll parts in a part family must be related

Database Structure Design The database contains all the necessary information for an application and can be accessed by several programs for specific application.

Plan Editing and Parameter Selection Plan editing involves some modification that is to be made to the standard plan before it can issued to the shop. A Process plan also includes process parameters The parameter file can be integrated with the variant planning to select process parameters automatically

Generative Process PlanningProcess plans are created from information available in manufacturing data base without human intervention. Upon receiving the design model, the system can generate the required operations and operation sequences for the component. Decision logic is employed to produce the process plan.Machine selection, tool selection, process optimization, etc are automated using generative planning techniques

StartNew/OldComponent representation moduleCode GenerationPart geometry creation (Design and manufacturing attributes)

Forward and Backward PlanningIn generative process planning, when plans are generated, the system must define an initial state in order to reach the final state (goal)If the initial state is the raw material and the final state is the finished product, and the planning is done from bottom-up, it is called forward planningIf it is done from top-down, it is called backward planning( i.e. assuming the finished component and going back to the unmachined workpiece.)

Advantages of Generative Process PlanningComponent representation moduleFeature extraction moduleFeature process correlation moduleOperation selection and sequencing moduleMachine tool selection moduleStandard time/cost computation moduleReport generation module

Semi-Generative Process planningThe semi- generative approach is defined as a combination of the generative and the variant, where a pre-process plan is developed and modified before the plan itself is used in a real production environment. This is similar to the generative approach, expect that the final process plan and intermittent stages of the generative process plan is modified, or supplemented by a process planner Modifying and process planner intervention is small compared to the variant approach.

Manufacturing Processes

Manufacturing processManufacturing processes are the steps through which raw materials are transformed into a product. The manufacturing processes can be broadly classified into three categories viz. ShapingJoiningFinishing

Shaping ProcessThe shaping processes are referred to those that use a certain raw material and shape it to a final part.Typical examples include, CastingFormingMachining

Casting In this process, metal is first heated in a furnace until it melts and then the molten metal is poured into a mold so that the liquid metal takes the shape of the mold cavity, which is the final shape of the part. Once the liquid metal in the mold cavity solidifies, the mold is broken or opened to take the final part out of the mold cavity. The metal casting process involves three sequential steps:- liquefying of metallic material by properly heating it in a suitable furnace, pouring of hot molten metal into a previously made colder mould cavity, extraction of the solidified cast from the mould cavity

Forming This involves use of mechanical forces like compression, tension, shear or combined forces to produce plastic deformation to produce the required shapesIt is broadly classified into two types:-Hot Working Involves deformation above recrystalization temperatureCold Working Involves deformation below recrystalization temperature Examples include, forging, extrusion, sheet metal forming and wire drawing.

MachiningMachining is a manufacturing process that involves removal of the material from the workpiece by means of appropriate machine tools to obtain the required shape. It is carried out on an already cast or formed workpiece. Examples include, turning, drilling, milling and shaping.

JoiningIt is concerned with the physical joining of two pre-shaped parts to form a fully functional product.It is broadly classified into two types:-Permanent jointNon-permanent jointPermanent jointAs the name suggests, this type of joint cannot be removed or modified. Eg. Arc welding, riveting, etc. Non Permanent jointThese joints are not permanent and can be removed or replaced at any time. Eg. Screw and nut, turnbuckles, etc.

FinishingThese processes are concerned with post-processing activities like polishing, electro-plating, heat treatment, printing, enameling, etc

They are done to improve the surface or physical properties(hardness, corrosion resistance, etc) of the finished product.

Selection of primary manufacturing process (rough rules)The following design factors have a bearing on the choice of a manufacturing process:QualityComplexity of formNature of materialSize of partSection thicknessDimensional accuracyCost of raw material, possibility of defects and scrap rateSubsequent processes

A general rule to follow while manufacturing products may be ranked in order of economic consideration as follows: High quantity ( 2000 or more): Forming from solid by deformation Forming from liquid casting, molding Forming from joining parts Forming from solid by material removel Forming by assembly

Low quantity (upto 50):Forming from solid by material removalForming by joining partsForming from solid by deformationForming by assemblyForming by material increase

Medium quantities should be analyzed separately in each case . For a simple part, the lower quantity should be increased to 150 pieces and the higher quantity should be reduced to 1000 pieces. For complex parts, the higher quantity may be reduced to 1500 pieces.A more specific primary process selection is the refined rules for manufacturing process selection

Selecting primary manufacturing process ( Refined rules)The quantity of parts is divided into low and high numbers. The quantity values are a function of the shape complexity. A code of the basic forming technique is given below, Code A = forming from liquid (casting , molding)Code B = forming the solid from deformationCode C = forming from solid by material removalCode D = forming from joining partsCode E = forming by assemblyCode F = forming by material increase

Mono Open Complex Very Complex Quantity Quantity Quantity Quantity 1000 200015001000DBCBCAEBEEDAD BDDBDBDBCCECCECEDAAAAFEFEBA--A-A-FF

Selecting among forming from liquid processesThe commonly used liquid forming processes are:-Sand castingPermanent castingDie castingInvestment castingEach molding method has certain inherent advantages and limitations. Select a molding method based on the following parameters:- Part materialSize of PartSection thicknessDimensional accuracyCost of raw material, possibility of defects and scrap rate

Sand Permanent Die InvestmentMaterialAllAlmost all Light materialsCertain alloysSize or WeightAny sizeUpto 25 kgUpto 10 kgUpto 40 kgSection thickness3 5 mm minimum2.5 mm minimum0.6 mm minimum0.75 mm minimumAccuracy+ - 1.5 mm+ - 0.4 mm+ - 0.05 mm + - 0.12 mmSurface finish (um)6.25 252.5 6.251 2.50.25 - 2Tool costsLow MediumHigh High

Selecting forming from solid by deformation processThe commonly used forming processes are:-G 11 Rolling G 12 ExtrusionG 13 SwagingG 14 forgingG 21 spinningG 22 deep drawingG 23 Bending (brake press)G 24 Press work (power press, with progressive die)

Selecting of machining process, tools and cutting parametersThis is closely linked with the geometry of the finished product and quantity of parts required. To illustrate this, let us take the following example:

The initial job is produced by means of sand castingThe initial job gives the approximate dimensions that have been specified. Machining operations are carried out to achieve the final tolerances and accuracies. One should be able, by use of logical decisions, to determine the sequence of machining operations required to obtain the final part.

Sequencing of operations according to precedence relationship (anteriorities)The operations defined above have to put in a certain order according to precedence relationships or anterioritiesThe different categories of anteriorities are can be classified as,Dimensions with a datum as anteriorityGeometric tolerances with data references as anterioritesTechnological constraints in order to execute the sequences of operations properlyEconomic constraints which reduce production costs and wear or breakage of costly tools, etc

Anteriorities for the given part

Examples of Process sheet

Drawing of the component 1.CNC TURNING OF GEAR BLANK

Blank

Process Sheet for first operation

Process sheet for second operation

2. CNC turning of a casting

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