Production System Design

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Resources

• Script Part 3: Production Systems Design
• Exercise Questions 1, Exercise Questions 2

Note on this Note

I did not take lecture notes on Production Management. Below is an AI-generated summary of this chapter, and you’ll want to check out the resources above.

Design of Production Systems

1. Infrastructure of a Production System

• Work system: The smallest organizational unit of the production system.
• Production is the transformation of work pieces, using operators and machines.
• Data flow: Master data and transaction data flow into the work system, and feedback flows out.

2. Layout Types of Production Systems

Production systems are categorized based on their physical arrangement and the mode of interaction between various work units. The layout types depend on Product variety and Production volume (workload fluctuation).

1. Job Shop (Functional layout)

   • Suitable for one-of-a-kind and small series applications.
   • Spatial concentration of similar work systems.
   • Characteristics: Low production volume, high demand fluctuation, various product types, manual production processes.
   • Pros: High flexibility, low monotony of work, lower initial investment in automation.
   • Cons: High transportation costs, complex material flow, long throughput times, high work-in-process (WIP), high space requirement, complex production control.

2. Flow Shop (Object layout)

   • Suitable for large series and mass production applications.
   • Arrangement of work systems according to the uniform material flow.
   • Characteristics: High production volume, low demand fluctuation, few product types, automated production processes.
   • Pros: Low transportation costs, streamlined material flow, short throughput times, low WIP, lower space requirement, simple production control, good visibility.
   • Cons: Low flexibility, high monotony of work, high investment (automation).

3. Cellular Manufacturing

   • Object layout with production-dependent material flow.
   • Assignment of product families to machine groups.
   • Characteristics: Medium production volume and demand fluctuation, moderate number of product types.

3. Factory Layout Planning

Determines the spatial arrangement of objects (facilities, machines) on a defined floor space.

• Simplifying assumptions:
  • Entire floor space is divided into equally-sized grid squares.
  • Each object occupies exactly one grid square.
  • Distance measures: Usually rectangular distance along traffic lanes.
    $d_{ij}^r=|x_i-x_j|+|y_i-y_j|$
  • Objective: Minimize the entire proxy criterion (product of transport quantity and distance summed over all goods).

Greedy Method (Construction Heuristic)

1. Determine the object $i^{\ast }$ with the most intensive transport relations to/from all other objects.
2. Assign $i^{\ast }$ to a grid square at the center of the floor space.
3. Determine a yet unassigned object $i^{\ast \ast }$ which shows the strongest transport relations to/from the already assigned objects.
4. Assign $i^{\ast \ast }$ to a grid square closest to the already assigned objects so that the proxy criterion between $i^{\ast \ast }$ and the assigned objects is minimized.
5. If all objects are assigned, stop; otherwise, repeat step 3.

Improvement Procedure

1. For each pair $(i,j)$ of objects, determine the change of costs resulting from swapping their locations.
2. Find the pair $(i^{\ast },j^{\ast })$ that achieves the largest cost reduction.
3. If no cost reduction is achieved, stop. Otherwise, swap the locations and repeat step 1.

4. Flow Shop Production

Types of line production:

• Paced lines vs Unpaced lines
• Discrete material flow vs Continuous material flow (open or closed stations).
• Geometrical line layout: Cyclic, U-line, Straight line, Serpentine.

Assembly Line Balancing (Paced Lines)

Given a required cycle time based on desired production volume, the objective is to minimize the number of work stations.

• Cycle Time ($C$):
  $C=\frac{T}{X}$
  Where $T$ is the effective operation time and $X$ is the production volume.
• Theoretical Minimal Number of Work Stations ($M$):
  $M=\lceil \frac{\tau }{C}\rceil$
  Where $\tau$ is the total assembly time (sum of all task times).
• Line Utilization ($\rho$):
  $\rho =\frac{\tau }{M\cdot C}$

Priority Rule-Based Heuristic (Ranked Positional Weight)

Successive assignment of feasible tasks to stations based on a priority rule (e.g., maximum standard time, max number of successors, or positional weight).

• Positional weight ($p_i$): Sum of task times of the task itself and all direct and indirect successors.
  $p_i=t_i+{\sum }_{k\in N(i)}{t}_k$
  Where $N(i)$ are the successors of task $i$.

Mixed Model Assembly Line

Used when different product variants are manufactured on the same line without changeovers.

• The process requires generating a “hybrid” precedence graph.
• Task times for the hybrid are calculated using the demand ratios of the variants as weighting factors.

5. Cellular Manufacturing

Established through the spatial consolidation of a limited number of working systems/machines into Manufacturing cells.

• Product families are generated based on the similarity of machine requirements.
• Machine groups are defined for specific product families.
• Based on the Machine-product incidence matrix.

Binary Sorting Method

Aims to generate a block-diagonal structure to form cells.

1. Sort rows (machines) to group similarities.
2. Sort columns (products/components).
3. Identify cells. If perfect block-diagonalization isn’t possible, material flows between cells (inter-cell transfers) occur, or machines must be duplicated to eliminate inter-cell transfers (evaluating the trade-off between machine investment costs and transportation costs).