5 computer aided
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computer aided manufacturing pptTRANSCRIPT
Dr Atul Sidola
Computer Assisted Manufacturing Management
System
Dr Atul Sidola
Topics to be covered CAPP
Computer Integrated Production Management System
Inventory Management, MRP, MRP-II
Shop Floor Control, Computer Aided Process Monitoring
Computer Aided Quality Control and Inspection
Dr Atul Sidola
CAPP
Computer Integrated Production Management System
Inventory Management, MRP, MRP-II
Shop Floor Control, Computer Aided Process Monitoring
Computer Aided Quality Control and Inspection
Dr Atul Sidola
Process Planning Process planning is concerned with determining the
sequence of individual manufacturing operationsneeded to produce a given part or product.
In the process geometrical features, dimensional sizes,tolerances, materials, and surface finishes are analyzedand evaluated to determine an appropriate sequenceof processing operations
Dr Atul Sidola
General inputs to process planning
Output of process planning is the process plan
Design data,
Raw material data,
Facilities data (machiningdata, tooling data, fixturedata, etc.),
Quality requirementsdata, and
Production type data.
The process plan is oftendocumented into a specificformat and called : Process plan sheet, Process sheet, Operation sheet, Planning sheet, Route sheet, Route plan, or Part program
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Traditional process planning The process planning process is very much dependent on
experience and judgment of planners.
It is the responsibility of manufacturing engineer or industrial engineer to write the process plan.
Many people participate in planning process, such as manufacturing engineer, planners, part programmers etc.
However, individual engineers each have their own opinion about what constitute the best routing. It create the problem in planning.
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Automated Process Planningor
Computer Aided Process Planning
On the basis of characteristic of given part, the program automatically generates the process plan.
Two approaches of CAPP:
1. Retrieval type CAPP system or variant system
2. Generative CAPP
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Retrieval type CAPP The retrieval approach, which is also called variant
approach, uses a group technology (GT) code to selecta generic process plan from the existing master processplans developed for each part family and then edits tosuit the requirement of the part.
Variant approach is commonly implemented with GTcoding system. Here, the parts are segmented intogroups based on similarity and each group has amaster plan.
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Advantage of retrieval CAPP Once a standard plan has been written, a variety of
components can be planned.
Programming and installation are comparatively simple.
The system is understandable, and the planner has control of the final plan.
It is easy to learn and easy to use.
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Disadvantage of retrieval CAPP The components to be planned are limited to
previously planned similar components.
Experienced process planners are still required to modify the standard plan for the specific component.
Details of the plan cannot be generated.
Variant planning cannot be used in an entirely automated manufacturing system, without additional process planning.
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Generative CAPP In a generative approach, a process plan for each
component is created from scratch without humanintervention. These systems are designed toautomatically synthesize process information todevelop a process plan for a part
Generative CAPP systems contain the logic to usemanufacturing data bases, knowledge bases andsuitable part description schemes to generate a processplan for a particular part.
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Advantages of generative CAPP Consistent process plans can be generated rapidly.
New components can be planned as easily as existing components.
It has potential for integrating with an automated manufacturing facility to provide detailed control information.
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Main steps to CAPPIdentification of part specifications.
Selection of blanks or stock.
Selection of machining operations.
Selection of machine tools.
Selection of cutting tools.
Calculation of cutting parameters.
Generation of setup plans.
Selection of work holding devices (fixtures).
Calculation of times and costs.
Generation of process plans
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Benefits of CAPP
Reduction in process planning time.
Reduction in the required skill of the process planner.
Reduction in costs due to efficient use of resources.
Increased productivity.
Production of accurate and consistent plans.
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Traditional production planning & control Production planning and control : Production (or
manufacturing) planning and control (PPC or MPC)system is concerned with planning and controlling allaspects of manufacturing including materials,scheduling of machines and people, and coordinatingsuppliers and customers.
Traditional PPC functions are given in coming slides .
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1. Forecasting: This is concerned with projecting or predicting the future sales activity.
2. Production planning: It establishes the production levels for product groups over the next coming years. It is based on the sales forecast and used to maintain the desired inventories levels.
3. Process planning : Process planning involves determining the sequence of manufacturing operations required to produce a certain product and\ or its components.
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4. Estimating : It is a process of determining prices,predicting costs, preparing schedules & estimation ofmanufacturing lead time etc.
5. Master scheduling : The production plan must betranslated into a master schedule which specifies howmany units of each product are to be delivered and when.
6. Requirements planning: Based on the master schedule,the individual components and subassemblies that makeup each product must be planned. Raw material andpurchased parts are ordered on the basis of it.
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7. Purchasing : After requirement planning, the “make- or –buy” decision is carried out. For “made in house”, raw material have to be acquired, and other components are purchased.
8. Machine Loading and scheduling: On the basis of requirement planning production scheduling is done.
9. Dispatching : The dispatching function is concerned with issuing the individual orders to the machine operators.
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10. Expediting: In expediting actual progress is compared withproduction schedule. The expediter recommends correctiveaction.
11. Quality control: The quality control department is responsiblefor assuring that the quality of the product and its componentsmeets the standards specified by the designer .
12. Shipping and inventory control: This is final steps in theproduction control cycle involves shipping the product directlyto the customer or stocking the item in inventory. The purposeof inventory control is to ensure that enough products of eachtype available to satisfy customer demand.
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Problems with traditional production planning & control Plant capacity problems
Suboptimal production scheduling
Long manufacturing lead times
Inefficient inventory control
Low work center utilization
Process planning not followed
Errors in engineering and manufacturing records
Quality problem
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CAPP
Computer Integrated Production Management System
Inventory Management, MRP, MRP-II
Shop Floor Control, Computer Aided Process Monitoring
Computer Aided Quality Control and Inspection
Dr Atul Sidola
Dr Atul Sidola
1. Engineering database: The database comprises all theinformation needed to fabricate the components andassemble the products. It includes the BOM, part designdata, process route data sheets etc.
2. Material requirement planning: MRP involvesdetermining when to order raw materials andcomponents for assembled products.
3. Capacity planning: It is concerned with determining thelabor and equipment resources needed to meet theproduction schedule.
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4. Inventory management : It is efficient utilization ofinventory and closely related with MRP.
5. Shop floor control: It refers to a system for monitoringthe status of production activity in the plant andreporting the status t0 management so that effectivecontrol can be exercised.
6. Cost planning and control: The cost planning and controlsystem consists of the data base to determine expectedcosts to manufacture each of the firm’s products.
Dr Atul Sidola
CAPP
Computer Integrated Production Management System
Inventory Management, MRP, MRP-II
Shop Floor Control, Computer Aided Process Monitoring
Computer Aided Quality Control and Inspection
Dr Atul Sidola
Inventory management It deals with flow as well as storage of inventory so that
optimum balance between “cost of inventory and serviceability” could be maintained.
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Types of inventory in manufacturing1. Raw material inventory:
2. Work- in-process inventory
3. Finished product inventory
4. Maintenance, repair and tooling inventories: These include cutting tool, fixtures and repair parts needed to fix the problem.
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Inventory control procedures There are two strategy to control the inventory
1. Order point system: In this system items are restocked when the inventory levels becomes low.
2. Material requirement planning(MRP)
• MRP is suitable control procedure for raw material and work – in –process inventory (type 1 and type 2).
• Order pint system is suitable for finished goods and maintenance, repair, tooling inventories ( type 3 and type 4).
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Material requirement planning Material requirements planning is a computational
technique that converts the master schedule for end products into a detailed schedule for the raw materials and components used in the end products.
The detailed schedule identifies the quantities of each raw material and component item.
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Basic MRP components Independent versus dependent demand
Independent demand indicates that demand for a product which is unrelated to the demand items.(such as end products and spare parts).
Dependent demands indicates the demand for the item which is related directly to the demand for some other product.
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Lumpy demand : Demand is sudden or in large quantity/increments so as to make a certain batch of final product.
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Lead time: Lead time is the time from start to finish of the job. Two kinds of lead time:
Ordering lead time: The time required from initiation of the purchase requisition to receipt of the item from the vendor.
Manufacturing lead time: The time required to process the part through the sequence of machine specified on the route sheet . It includes not only the operation times but also the nonproductive time.
Common use items
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Input to MRP Master production schedule(MPS): It is a list of what
end products are to be produced how many of each product is to be produced.
Boll of material(BOM): It lists component parts & subassemblies that make of each product.
Inventory record file: This file keep record of inventory status. Lead time for the raw material, components and assemblies must be established in the inventory.
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MRP system structure
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MPS Sheet
Week no. 1 2 … … 8 9 10
Product 1 35 45 25
Product 2 30 70 30 60 35
Product 3
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BOMp1
s1
T1 T2 T3
s2
T4 T5
Level 0
Level 1
Level 2
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Inventory record fileperiod 1 2 … … 7 8
Item no. C1
Gross requirement
Scheduled receipts
40
On hand 40 80
Ne t requirement
Planed order release
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Benefits of MRP Reduction in inventory
Improved customer service
Quicker response to changes in demand and in the master schedule
Greater productivity
Reduced setup and product changeover costs
Better machine utilization
Increased sales and reductions in sales price
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MRP II MRP systems that deal with resource capacities are
known as MRP II.
MRP II system consists of the basic MRP modules plus the Capacity Planning, SFC (Shop Floor Control) and financial system modules.
Dr Atul Sidola
CAPP
Computer Integrated Production Management System
Inventory Management, MRP, MRP-II
Shop Floor Control, Computer Aided Process Monitoring
Computer Aided Quality Control and Inspection
Dr Atul Sidola
Function of shop floor control Priority control and assignment of shop orders
Maintain information on work in process for MRP
Monitor shop order status information
Provide production output data for capacity control purposes
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Steps to shop floor control systems Order release
Order scheduling
Order progress
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1. Order release The objective of order release module is to provide the necessary
documentation that accompanies an order as it is processed through the shop.
The documents are collectively called shop packet. Shop packet consists of -
Route sheet(listing of operation sequence) Material requisitions (to draw the raw material from stock) Job cards (to report the labor for each operation on route sheet) Move tickets ( to move the parts between work centers) Parts list(for assembly)
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2. Order scheduling The objective of order scheduling is to make
assignments the various machines in the factory.
Order scheduling is done on the basis of priorities of the orders.
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Priority rules in order scheduling Priority to orders may be given as per following rules
First come first serve
Earlier due date first
Shortest processing time first
Least slack first
Time remaining until due date – processing time
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3. Order progress The objective of order progress is to provide data
relative to work in process, shop order status , and capacity control.
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Computer process monitoring It is a data collection system in which the computer is
connected directly to the workstation and associated equipment for the purpose of observing the operation.
Three computer process monitoring systems are:
Data logging systems
Data acquisition systems
Multilevel scanning
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1.Data logging systems Data logger is used for this purpose.
It is a device that automatically collects and stores the data for off line analysis.
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2.Data acquisition system It is a system that collects data for direct
communication to a central computer.
It is on-line system.
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3. Multilevel scanning If the total number of monitored variable are quite large
then multi level scanning is done.
Two level of scanning: High level
Low level
High level scan uses key variable and status data for monitoring.
In low level scan more complete data logging and analysis is done to ascertain the source of the malfunction .
Dr Atul Sidola
CAPP
Computer Integrated Production Management System
Inventory Management, MRP, MRP-II
Shop Floor Control, Computer Aided Process Monitoring
Computer Aided Quality Control and Inspection
Dr Atul Sidola
Quality What customer requires is quality.
The quality of something can be determined by comparinga set of inherent characteristics with a set of requirements.If those inherent characteristics meet all requirements, highor excellent quality is achieved. If those characteristics do notmeet all requirements, a low or poor level of quality isachieved.
The product should not only conform to specification butalso provide a reliable performance, besides meeting thecost and delivery requirements.
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Quality assurance It is carried before the manufacturing of the product
for maximizing the probability that the component would be manufactured according to the given specifications.
It cover proper selection of work material, equipments, tooling and manufacturing process.
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Quality control Quality control is carried out after QA and it enables
detection of poor quality, suggests corrective action to be taken, the inspection procedures to be followed and specifications of gauges and instruments to be used.
Quality control is a set of activities intended to ensure that quality requirements are actually being met.
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So……………. When these activities are computerized, the procedure becomes
automatic and output documentation is carried out in asystematic manner.
This is an island of automation and it becomes necessary tointegrate it to manufacturing system to save time andmovements.
It leads towards use of non contact sensors. It is helpful in elimination of contact with component, stopping
and need of repositioning of the component. The arrangement also provides feedback, hence leading to near
perfect manufacture of the components.
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Effects of CAQC The inspection and testing will be accomplished on a
100% basis rather than sampling methods.
Inspection during production will be integrated into the manufacturing process rather than requiring that the parts be taken to some inspection area.
The use of non contact devices help in reducing the inspection time.
Manual activity is reduced.
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Types of inspection technology Contact inspection Non contact inspection
Coordinate measuring machine(CMM)
Mechanical probes
Optical techniques Machine vision Scanning beam devices Photogrammetry
Non optical techniques Electrical field techniques
Reluctance Capacitance Inductance
Radiation technique Ultrasonic
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Coordinate measuring machine It consists of a table and movable head which holds a
sensing probe.
The probe can move in 3 directions corresponding to 3 coordinates.
The probe comes in to contact with part surface and provide the information about coordinate positions.
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Machine vision The machine vision system consists of TV camera, a
digital computer .
The system digitize the picture and analyzes the image by comparing it with data stored in memory.
The data are often in the form of models of the object.
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Scanning laser beam devices Laser beam is used for measurement purpose. It measures the time rather than light. A beam of light is made to sweep across the component to
be measured. As the object is scanned the duration of time for which the
lights interrupted is measured. With the help of logic circuitry and program, this is
converted into part dimension and also interfaced to the sorting unit and the handling device.
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Photogrammetry It involves the extraction of three dimensional data
from a pair of photographs taken at different angles.
The twp photograph are read by a device called a monocomparator to establish coordinates and positions of objects.
The data are then computer analyzed to get the desired information.
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Reluctance technique Reluctance transducer are used as proximity
transducer.
It indicates the presence and distance from the probe of a ferromagnetic substance.
The limitation is that object must be electromagnetic.
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Capacitance technique In this technique capacitance is used to measure the
distance of an object from the face of a probe.
The capacitance is inversely proportion to the distance between the probe face and part thus the distance can be calculated.
The material should electrical conductor.
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Inductance technique The inductance system operate by subjecting the object to
an alternative magnetic field by means of an electromagnetic coil.
It results generation of eddy current in the object.
These eddy currents , in turn , create their magnetic field , which interacts with the primary field.
The interaction affects the impedance of the coil, which can be measured and analyzed to determine certain characteristic of the object.
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Computer Aided Testing Computer aided testing is simply the application of the
computer in the testing procedure.
This is used at two levels:1. At the lowest level , the computer is used to monitor
test and analyze the result.
2. Automation at series of testing stations interconnectedby material handling system. This is used whereproduct is complicated such as : automobile engines,aircraft engines, electronic integrated circuit.