Index:

• The Assembly Systems;
• Fixed Position;
• Assembly Shop & Cell;
• Assembly Line;

The ASSEMBLY SYSTEMs:

-> DEF: system which join together components in order to obtain finished products;

• Composed by workstations and handling systems for parts and WIP;

MANUAL ASSEMBLY SYSTEM: system composed by a several stations in which one or more workers executes assembly activities.

• Stations are linked through a handling system (or transfer system);
• Main resource is the workforce;
• ✔ Dipend on operators activities (flexible for the versatility of the workers);
• ❌Variability of the manual assembly time (depending on operators)

Type of Assembly System:

-> FIXED POSITION ASSEMBLY: product don’t move while beingh assembled, required components are brought to the working station.

• All activities are executed in only one workstation;
• Tipical of heavy and bulky products;

-> ASSEMBLY SHOP & CELL: the product move through different manual assembly workstations.

• No rigid transport system (every product has its specific flow)
• Transfer could be manual or using AGV.

-> ASSEMBLY LINE:  workers are stationary in the workstations and a transfer system moves the semi-finished assembly through the workstations where the parts/ components are added in sequence until the final assembly is realized.

• Workstations are assigned a subset of the operations of the assembly process.
• The transfer can be:
  • synchronous (absence of buffers between workstations),
  • asynchronous (buffers between workstations) or
  • continuous (operators move together with the assembly and at the same time they work on it or, similarly, the assembly is moving along the station and the operators are concurrently carrying out the assigned operations).

Other definitions:

Variety: Variety of the assemblies (product types, variants within families) and, as induced effects, of assembly operations executed inside the work-stations of assembly systems.

Repetitiveness: Repetitiveness of the assembly operations executed by / tasks assigned to the operators inside the work-stations of the assembly systems (as opposite to the variety).

Flexibility: the ability to change or react with little penalty in time, effort, cost or performance (e.g. quality).

• The ability of the assembly system to adapt, with low costs and times and penalties, to changes in the external or external context; Cost, times… etc. are both due to the assembly process as well as to the material feeding.

Volume: the ability of the assembly system to assemble a given range of volumes of assemblies (as opposite to flexibility …)

General Features of the Assembly Systems:

-> CHAR:

• We don’t manage machines but humans (they’re more flexibility).
• TECHNOLOGY:
  • Components assembly to make groups, sub-groups and FP;
  • Operations are reversible;
  • Free technolgoy route, degress of freedom;
  • Low relevance of process technology parametersM
  • Process flow is synthetic;
• COST STRUCTURE:
  • Low relevance of fixed assets (depend on utilization and customization of machinery);
  • Workforce utilization caused by lot of manual operations;
• Assembly tasks usually not require a specific tools;
• Need of correctly “feeding” the workstations:
  • Small buffer each WS;
  • User overhead conveyors to move components;
  • Use assembly kit: set of assembly and components;

Classification:

-> Three indipendent axes for classification:

• Layout configuration
• Production mix management
• Task organization
• Reciprocal movement of assembly, operator & components

-> According to…

• …LAYOUT configuration:

• …PRODUCTION MIX management

-> SINGLE-MODEL:

• Establish one assembly line for each product;
• CHAR: high volumes and stability of demand;
• PRO: low management issues;
• CONS: low flexibility;

-> ASSEMBLY SYSTEM:

• DEF: more products are assembled in the same line:

-> Respecting multi-model the production batch size is equal to one;

-> Implementen with continuous and upaced lines (often asynchronous);

• Set up time relevant;
• CT and # workstations depend on the product to be assembled;
• Need good balancing and scheduling of all the products to be assembled on the same line (trade off);
• High inventory of finished product (demand not precisely satisfied).
• PRO: opportunity to follow the demand;
• CONS:

-> need compulsory to reduce set up time;

-> properly schedule to be assembled;

-> difficult management component flows and parallel workstations.

📌Ford symbol of the industryal assembly systems;

• …RECIPROCAL MOVEMENT:

-> Operator-Assembly

• Operator à Assembly
• Assembly à Operator

-> Assembly-Components

• Assembly à Components
• Components à Assembly

📌“à” = towards

-> Befor design ass. line we should know  Demand and type product and the specific activity that should be needed,

• Type of product;
• How produce it;
• Number of product;
• Time (design variable)!

-> Average assembly time Mk for each operation k and associated standard deviation Sk can be defined using the following methods:

1. Work sampling;
2. Standard times;
3. MTM method (Motion Time Measurament);

-> These methods calculate the duration of each assembly operation by composition of elementary operations given:

1. Value of each elementary operation:

mi: mean

si: standard deviation

2. Duration of the resulting assembly operation and his standard deviation:

-> HP: statistical independence among various elementary operations of which k is made;

-> LEARNING CURVE: affects the work time due operator’s learning effect.

• It decrease if with # of repetitions of the activity itself.

Methods to Calculate Assembly Times:

-> Ways:

• Work sampling;
• MTM method;

Work Sampling:

-> DEF: observation of specific assembly operations and calculation of the average duration and standard deviation (Mk, Sk) of each operation using the standard statistical approaches.

-> REQUIRES:

• Create a sample of each operation’s duration by registering the assembly time;
• Meaningful sample size: to provide reliable data;
• Drawback of the method: to monitor and collect the data;

-> STEPS:

1. Chose and identify the assembly operation to monitor;
2. Inform the operator of the work sampling study;
3. Divide operation in smaller components (max 5-30 secs each);
4. Calculate the required number of repetitions (accuracy);
5. Measure the elapse time for each work component (precise timing) and store captured data;
6. Calculate the average assembly time and its standard deviation.

MTM, Motion Time Measurament:

-> HP: achieve of elementary operation data (duration and standard deviation are assigned)to compose any complex operation and calculate its average duration and standard deviation;

-> CHAR:

• Is the most commonly method used;
• Database is used to calculate the average time and standard deviation;
• Based on basic human movements;

-> CALCULATING:

1. Tables of human movememnt times under different circumstances;
2. Times are expressed in “TUMs” – Time Measurement Units (1 TMU = 0.00001 hr = 0.036 secs);
3. Add the times of the different elementary movements necessary to compose the needed operation and convert to seconds or minutes.

-> ADVANTAGES:

• Quicker and cheaper than time study (work sampling)
• Reliable (based on large number of studies)
• Planning and estimating new jobs
• Useful for short runs
• Rating already incorporate

-> EX: How calculate TMU of a reach activity

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Fixed Position:

-> DEF: the product is assembled in a single stite, rather than being moved through a set of assembly stations.

• Materials, equipement and tools are brought to the site.

-> DESCRIPTION:

• Every workstation could be modeled as a unique block and correspond to a single site.
• Input = components to be assembled;
• Output = finished product;
• Every WS assembly a different types of product;
• Mix flexibility: is reached thanks to the parallel station prepared for different products type;

-> CHAR:

• Complex flow: all components must flow to single site depending on schedule;
• Work force assignment depends on one or more operator (require multi-skilled workers)

-> CHAR of PRODUCT assembled:

• Heavy and bulky machines:
  • Big amounts of parts;
  • Small quantities;
  • Big size (physical volume/dimension) and heaviness (weight);
• Simple Production/Objects:
  • Medium quantities;
  • Few parts requiring to be assembled;
  • The limited range of necessary components doesn’t justify the splitting of the workload in more workstations, while the moderate volumes required doesn’t justify the building of an assembly line;
• Fragile products, difficulto to hadle because movements could create scraps;

Physical structure and organization of the single site:

• Components are stocked around the site (challenge: need for room/space to place components);
• Assembly equipment and tools are placed around the working position where the product to be assembled is;
• Product is placed in the central area of the workstation (working position).
  • Keavy and bulky located on ground / floor in a delimited zone;
  • Small products  placed on a worktable / assembly work bench.
• The operator works on the product while standing and moving in the surrounding area.

📌NOTE: the space required depends on the kind of product to be assembled, the number of parts to be assembled and their characteristics (amount and size), the number of tools/equipment ….

-> ERGONOMIC PRINCIPLES:

• Locate materials and components in way that ease operator movements so to be efficient and to be safe;
• Provide the equipment onto adjustable bases to adapt their height to workers characteristics;
•  etc. …

The Strengths …

• HIGH FLEXIBILITY:

-> MIX FLEXIBILITY: (short period) assemble different types of product in the same time;

• Meeting a specifical and periodically changing demand requirements (independence and decoupling of the WS)

-> PRODUCT FLEXIBILITY: new product -> need to be trained to acquire the new required skills for new types of product;

-> EXPANSION FLEXIBILITY: (long period) not difficult add new WS thanks to their independence/decoupling (constraint = room/space);

• LOW INVESTMENT:

-> Doesn’t require particular structure;

-> Investment may increasing if some necessary equipement are expensive;

-> Is advisable to buy a limited number of equipment;

• JOB ENLARGEMENT, ENRICHMENT and rotation for the employee:

-> Every operator execute the entire process or significant part of it;

-> high number of different operations/tasks => low repetitiveness => more gratification;

-> Job Enlargement.

… and Weaknesses:

• Potentials for interviewing of material flows:
  • Every material/component has to be brought to every workstation + every FP has to be handled;
  • Material flow is extremely rationale;
  • Different I/O points; different requirements;
• High WIP:
  • One or more pallets of components are kept for a long time as WIP;
  • FP are not delivered immediately;
  • Buffers;
• Large space requirement: room to place FP and additional between different WS to allow a safe material handling;
• Labor training might be difficult and time-consuming: employee need time to learn and be trained.
• High cost of workforce: related to the difficult and time consuming labour.

Rough Deisgn of a Fixed Position Assembly:

-> DEF: determining the necessary number of single sites/manual stations.

-> Number of single sites/stations:

Where:

• PCj: requested production capacity for product-type j [pieces/h];

-> Consider the value of the waste which could be produced;

• -> Not high otherwise wouldn’t be correct to build up a fixed position assembly.
• Tj: time required in order to complete the assembly process on a piece of product-type j [j/piece];

📌The system layout is defined by the market;

-> If Nj increase => the “interwining of material flows issue” becomes excessively relevant.

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Assembly Shop:

-> DEF: series of stations and each station is assigned a phase of the assembly process of a product type.

• Both manual and automated.
• A mix of different product types can be produced within the assembly shop and its stations.

📌Handling:

-> Can be:

• Manual;
• Automated (AGV):

-> Computer already knows where the vehicle has to go.

-> A supervisor is present as a computer that assign the traveling mission.

• Semi-automated (Hand cart): the operators have to move pieces from stations to stations and have to make the L/U;

✔Strength…:

• The stations (phases) are decoupled by buffer (the cycle time is not a constraint & operators are not forced to finish the cycle);
• The flexibility is high in terms of mix, product, expansion and flexibility

… & ❌Weaknesses:

• Investment depends on the level of automation of the system
• It might be difficult to manage the flows of products and components
• The complexity of production planning and control can cause bottlenecks and idle-times

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Assembly Cell:

-> DEF: suitable solution for the assembly of a medium range of medium volume products;

• The product moves during assembly through a number of stations with some flexibility in its trajectory (slightly different flows for different products);
• The organization of work is based on team-work following similar rules and organizational solutions adopted for manufacturing cells;
• Normally the operator follows the product being assembled, its mean that the complete assembly process can be made by the operator together with product testing and quality assurance;
• Operators can be given production responsibilities regarding the cell
• It is easy to allocate to cell the testing and adjusting (and repairing) of assembled product.

-> Example: Cell assembly of electro-mechanical products in medium volumes.

-> Main features of the solution:

• Assembly workbench for 2 operators
• First operator executes product assembly
• Second operator executes the testing and adjusting of the product.

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Assembly Line:

-> DEF: series of stations where the product is progressively assembled.

• Lines can be modeled as a series of workstations linked by the rigid transfer system;

• The handling system is integrated (installed on the roof or on the floor)
• Every line could be involved in the assembly of different types of product, and could be manage as:
  • single-model line (only one product type);
  • multi-model line;
  • mixed-model line (more flexible solution, even if it is always a line).
• Logic of allocation is dictated by certain constraints and/or the optimization of certain objective functions.

-> CHAR of PRODUCT:

• High demand;
• Some product variety;

-> SYSTEM CHAR and CRITICS:

• Workforce assignment: one or more operators could work on same WS;
• CT: fundamental parameter for this kind of systems. CTs are short: aech operator executes small part of the product assembly cycle.

Physical Structure:

-> Each station is dedicated ot a few tasks and is equipped with specific tools;

-> Necessary components are brought to their corresponding stations.

-> Flows are more rationsal.

Types:

1.Multi-Model Lines:

-> DEF: line can assemble more than one product type.

• Products managed in batches;
• It’s impossible to have two different product assembled in the same time.

-> CHAR:

• Products are made in batches;
• Model variations can be wide;

-> PROBLEM:

• High inventory;
• Determining the CT and the # of stations related to each model;
• Determining the batch size and sequence in shich different models have to be launched onto the line,

 Balancing:

1. Calculate the minimum number of stations of the line

 where:

• Qj = quantity of model j (yearly demand)
• Sj = set of tasks related to model j
• T_ij = mean time of task i of model j
• H = number of available hours (available time)
• α = maximum value of the utilization rate (0 < a £ 1)

2. Calculate the cycle time for each model j

3. Balance the line for each model j and determine the number of stations Kj**
4. Adjust the line balancing if needed (e.g. keeping the same number of stations for all models)
5. Verify the feasibility of the solution:

Where:

• SUT_j = setup time related to model j
• NB_j = number of batches of model j

-> Remark: the verification also regards transient periods when models are changed (dependent on production equencing)

2.Mixed-Model Lines:

-> DEF: the line can assemble  more than one product type and there’s no need to manage products in batches thanks to the strong reduction in setup times.

• Possible realize sequences of different type products.

General Features:

• Different models can be assembled simultaneously without batching
• Production rates of different models can be adjusted as product demand changes
• Problems
  • Reducing / eliminating setup
  • Getting the right components to each station for the model currently there
  • Determining the sequence in which different models have to be launched onto the line
  • Managing flows when parallel stations are used

Objectives:

• Minimizing the probability of no completion:

• Keeping a constant rate of usage of all components used by the line;
• Minimizing the number of stations, given the cycle time (line balancing)
• Minimizing the probability of no completion (station balancing)

 Balancing:

1. Calculate the balancing Index within the stations (station balancing)

   

Technical Obljectives:

• Lower BI;
• Vetter balance within each line station;

2. Calculate the balancing Index within the stations (station balancing)

Where:

Technical objectives: lower the BI better the balance along the line.

✔Stengths…

-> Solution for 🔺 volume, featuring efficient and limited cost of operations;

• Rationalization of material flows:
  • Ragionable because each WS is fed with just its pertinent components;
  • Product assembled is moved along the line and the finished product is taken from just one specific point.
• Low WIP:
  • Components are stocked in correspondence of the afferent stations;
  • Product assemble remains at the stations just for the duration of a short CT, when it exit is soon delivered.
• Limited space requirement:
  • Directly related to low WIP;
  • Related to the compact and rationable transfer system;
• Labour training might be easy (🔺 repetitiveness, 🔻 tasks/operations);
• Low cost for workforce (not require high skills).

UNPACED LINE (non continua): no maximum limit imposed on the processing time available to the operator or machine.

PACED LINE (continua): there is a fixed time for items to move through the process;

… and ❌Weaknesses:

• LOW FLEXIBILITY:

-> Rigid system linking workstations together design for a specific characteristics of the product;

-> To introduce nwe products or to modify the existing line.;

-> Mix flexibility can be managed at some extent

• Long time required to start new productions (🔗low flexibility);
• Repetitive work;
• Line balancing might be difficult:
  • Design pahse (define # stations and allocate tasks) & Managmenet phase (rebalance the line or change on times);

-> The modification of thecnological process is changing this points.

Peaced and Un-Peaced:

Paced line

-> DEF: system in which a common cycle time is given which restricts process times at all stations.

• Constrained; always synchronous.

INTERMITTENT TRANSPORT:is a conveyor belt that….

• keeps up the pace,
• The pieces comes to a full stop at every station,
• Transfer the pieces automatically (as soon as the time span elapsed);
• Forces the operators to finish their operations before the workpiece has reached the end of the respective station.

-> CHAR:

• Workstations are not separated by buffers;
• Material handling/transfer system is generally a conveyor which moves the pallet/base where the parts are placed and assembled.
• Material handling/transfer system generates an intermittent movement:
  • During “transfer” phase, conveyor moves simultaneously every base/pallet from a station to the following one, then
  • Stops for a period which lasts the CT of the line (allowing an operator to work on the job);

-> CRITICALITY:

• Each station/operations cycle there is the risk/possibility of failing to complete the assigned tasks within the CT.
• To avoid incompletion:
  • Increase the CT;
  • Increase the # of stations;

Machines-Paced Lines:

-> The movement of pieces is paced by a timer and given by the cycle time of the line:

✔Strength: Cycle time and production capacity are perfectly controlled;

❌Weakness: Probability of no completion (at the line stations) and problems of unfinished pieces.

Operator-Paced Lines:

-> The movement of pieces is paced by the operators: the material handling system moves only after all operators have given their approval

 ✔Strength: No problem of unfinished pieces

 ❌Weakness: Cycle time is variable and it is determined by the slowest operator 

-> The risk of giving approval too late compared to the theoretical cycle time:

• 🔺 as 🔺 operator utilization level (i.e. when the sum of durations of the assembly tasks allocated to a station is close to the theoretical cycle time, risk is higher);
• 🔺 as 🔺 number of stations (because having more stations increases the probability of one station leads to a delay).

-> Ideal solution: operators help each other to minimize the delay generated with respect to the CT. Requires some conditions:

• Mutli tasking/ multi skilled;
• Close stations;
• CT should be sufficiently long
• Assembled pieces not too small.

Continuous flow paced lines:

-> DEF: The system moves at a constant speed and operators follow the piece on which they have to perform the assembly tasks (or they move with it on a platform);

• Conveyor moves at costant and low speed;
• Every station is coincident with physical portion of the line;
• Velocity is choose considering maximum space available, physical interface and allow the execution.CT = D/v_c, where D: distabce between two consecutive pieces; v_c: velocity conveyor.

-> TYPE:

• Operator can’t stop the line;

✔ CT and production capacity are perfectly controlled;

❌ Probability of no completion and problems of unfinished pieces.

• Operator can stop the line.

✔ No problem of unfinished pieces;

❌ CT and production capacity are not perfectly controlled.

Unpaced Lines:

-> DEF:  workpieces are transferred whenever the required operations are completed, rather than being bound to a given time span.

• WS are separated by buffers.
• The buffers should be opportunely sized.
• Workpieces simultaneously (synchronous) or whether each station decides on transference individually (asynchronous).
• Non-constrained
• ⚠Operastors can’t systematically exceed the CT;

-> PROBLEMS:

• Problem of blocking: an upstream station can’t drop the piece if the buffer is full;
• Problem of starvation: a downstream station can’t take a new piece if buffer is empity.

-> FREQUENCY depends on:

• Sizing buffers;
• Balancing the line.

✔Strengths:

• No unfinished pieces;
• CT can be exceeded (only occasionally);

❌Weaknesses:

• CT and production capacity are not perfectly controlled.

Design of a Manual Assembly Line:

-> OBJ: determining the number of stations.

-> The design consists of Assembly Line Balancing (ALB):

1. Identify the production mix;
2. Definition of the balancing constraints;
3. Evaluation of the time of each assembly operation
4. Calculation of the cycle time

Balancing:

Balancing Constraints:

• Cycle time;
• Precedence relationships among operations;
• Incompatibility between operations that cannot be assigned to the same station (negative zoning):
  • to safety problems; it is better to split into more stations operations requiring consecutive tasks (that are) dangerous because of non compatible characteristics,

-> e.g. cleaning using a flammable solvent is not compatible with welding. 

• to logistics problems due to the size of the components/tools involved by the assembly operations; for instance operations which require different and bulky tools should be split into more stations in order to avoid creating stations exceeding some “standard”/reference dimensions.

• Opportunity or necessity to assign some operations to the same station:
  • Operations which share the same used tools / equipment (especially when they are particularly expensive -> no duplication);
  • Operations which share the same required positioning of a bulky / heavy product; operations should be grouped to avoid excessive handling for re-positioning (i.e. operations in the bottom part of a machine -> using a lift”).
• Constraints related to space;
• Constraints related to workers;
• Constraints related to the material feeding;

Balancing Objectives

Technical objectives:

• Minimizing the number of stations, given the cycle time;
• Minimizing the cycle time, given the number of stations;
• Minimizing the total idle time:

where:

    n = number of stations

    CT = cycle time

    N = number of assembly operations

 t_i= time to perform operation i (i.e. unit working time)

• Minimizing the probability of no completion
  •  in a machine-paced line, or
  •  in a continuous flow line, in case the operator can’t stop the line
• Minimizing the probability that the times of operations in one or more stations exceeds CT
  • in an operator-paced line, or
  • in a continuous flow line, in case the operator can stop the line

Economical objectives:

Minimizing the total expected cost (TEC)

   TEC = LC + E_CUT

    LC = line cost (equipment cost + operators cost)

    E_CUT = expected cost of unfinished operations (i.e. tasks)

E_CUT = ∑_k (P_k * C_k)

• Ck is the cost associated with the completion of the operations not completed in a station
• Pk: probability of the each k operations of no completion

Buffer Size:

-> Buffers between stations:

• Are inter-operational, with the function to decouple the operations in the stations;
• Provide space to hold a certain number of pieces;
• Correspond to portion of the material handling system.
• Decoupling function: allow operators to occasionally exceed the CT;

-> PROBLEMS since buffer have finite capacity:

• Blocking: when a buffer is full the upstream station can’t drop the piece;
• Starvation: when a buffer is empty the downstream station can’t take pieces.

-> It’s possible to identify a typical behaviour of the production capacity of a line as a function of:

• Buffer size;
• Coefficient of variation (CV= standard deviation of times required for the assembly tasks)

1. Production Capacity 🔺 <=> 🔺 buffer size. OSS: it became less and less relevant;

-> There is a trade-off between:

• Increasing production capacity;
• Increasing occupied space;

1. For a given buffer size, PC rises with the decrease of the coefficient of variation.

-> Buffer size may have important influence:

• buffers enable to limit the reduction of production capacity of the line, due to assembly time variability;
• importance of buffers increases with the amount of assembly time variability.

-> Buffers lead to higher investment / space requirement; therefore, it is crucial to find the optimal buffer size.

-> The optimal buffer size is influenced by the goodness of assembly line balancing.

Station Length:

-> OBJ: allows to insert a time buffer to protect the line against assembly time variability (limiting the problems of unfinished pieces).

-> CHAR:

• Conveyor moves at costant and low speed;
• When L > D => L > CT * V => The conveyor acts as a time buffer: operator has extra time to finish his activities.

-> Given the Flow Time is possible to determine the station length:

-> Longer is the station, the more an operator has time buffer to complete tasks.

• High station lengths has high investment costs and space occupancy costs.
• High WIP (many products being assembled along the line);
• Defining Station Length = Defining Buffer Size: Buffers enable to limit the problems of unfinished pieces, reducing the impact on the PC of the line.

• Distance between two consecutive assemblies is related to CT and PC.
• Station Length is not related to PC but affects probability of no completion and WIP products.

-> Techniquest tto make buffer sizing similar in case of unpaced lines:

• Analytical approach: based on queuing theory;
• Simulation which allows to use various probability distributions.

Open Stations:

-> In continuous flow lines, stations can be all open or closed.

-> DEF OPEN STATIONS: stations don’t have defined boundaries that separate each other.

• Operators can easily cross over them (anticipate or postpone the operations).

-> Type Adiacent Stations:

• UPSTREAM ZONE: the operator of the station k shares with the operator of stations k-1;
• DOWNSTREAM ZONE: the operator of the station k shares with the operator of the station k+1.

Automated Assembly Lines:

Index:

• General Features;
• Examples;
• Automated Assembly Cells.

General Features:

-> DEF: assembly lines performed by using assemly lines, assembly robotized WS and assembly cells.

• Each assembly line consists of a series of stations where the product is progressively assembled.

-> CHAR:

• HIGH SPEED;
• LOW FLEXIBILITY:
  • Stations rigidly connected to each other;
  • Sequence of WS closely linked to the sequence of assembly activities;
  • Automated are less flexible than manual.
• LOW VARIETY & HIGH REPETITIVENESS;
• HIGH VOLUME.
• DETERMINISM OF TIME: operations have extreme uniformity and really constant conditions &  absence of uncertainty.
• MACHINES STOPPAGES (sensor detecting problems).

Examples:

• Components (refrigerators) -> thermocouple
  • high volume (part common to many finished product types);
  • high standardization;
  • few components to be assembled.
• Feeding system for automated assembly lines -> vibratory bowl feeders
  • Vibratory bowl feeders are the most common device used to feed components in Industrial Assembly Automation Applications:
  • Vibratory feeders are self-contained systems, comprising of a specially tooled bowl feeder that orients the components, a vibrating drive unit upon which the bowl feeder is mounted, and a variable-amplitude control box.
• Configuration of this case may be: Paced line or Un-paced line

Automade Assembly Cells:

-> Flexible assembly systems vased on the concept of the automated assembly of a family of similar products, takin into account the possibility to perform the same types of operations and to use the same types of fixtures, tools and components.

• Similarity of products must be high so to be possible to realize the cost effective assembly cells.

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Models for Line Balancing:

-> For steps 1,2 look ato Transfer Lines.

1. Linear Programming (optimal)
2. Maximum fixed utilization rate (heuristic)
   1. Simple method, without priority rules (i.e. the first available operation is assigned)
   2. With local priority rules for assigning priorities, such as:
      1. MaxDur (longest processing time)
      2. MaxNFol (largest number of immediately following tasks/operations)
   3. With global priority rules, such as:
      1. MaxFol (largest number of following tasks/operations) et similia
      2. Ranked Positional Weighting
3. Probability of no completion

Line Balancing – Probability of no-competition:

-> For each task the following constraint has to be satisfied:

where:

    P_k = probability of no-completion of task k

    P* = maximum probability of no-completion

-> In fixing the value of P*, it must be considered that:

• Fixing a value too low implies:
  • High number of stations or, in other words, high line cost (LC);
  • Low expected cost of unfinished operations  (E_CUT)
• Fixing a value too high implies:
  • Low line cost (LC)
  • High expected cost of unfinished operations (E_CUT)

Steps:

1. Calculate the remaining time (RT) related to task k:

-> Is the mean remaining time after the operation k is assigned.

where:

• CT = cycle time
• ti = mean time of task i (time required to perform task i)
• S = set of tasks assigned to the operator (task k included)

2. Calculate the variable associated to the remaining time:

  where:

    σi = standard deviation of the time required to perform task i

3. Φ(Zk) is the probability of completion

-> P(∑_iєs T_i ≤ CT) -> probability of completion

1. Therefore the probability of no-completion is: