Value Stream Mapping and Production Layouts
Value Stream Mapping (VSM)
Value Stream Mapping (VSM) is a flowcharting tool used to develop lean processes. This technique visualizes product flows through various processing steps. It also illustrates information flows resulting from the process, as well as information used to control flow. The aim is to provide a brief introduction to VSM and illustrate its use with an example.
To create a lean process, one needs a full understanding of the business, including production processes, material flows, and information flows. This discussion focuses on a production process where a product is being made. However, VSM is not limited to this context and can be readily applied to service, logistics, distribution, or virtually any type of process.
In a manufacturing plant, VSM is used to identify all value-adding and non-value-adding processes that materials undergo, from raw material intake to delivery to the customer. Material is deposited in a raw material inventory, indicated by a triangle. The average level for this inventory is 2,500 units. This material is run through a five-step process: machining, drilling, cleaning, inspection, and packaging.
The machining, drilling, inspection, and packaging processes each use a single operator. Under each process symbol is the activity cycle time (CT), change-over time (C/O time, to switch from one item type to another), lot size, available seconds per day, and percentage of uptime. The cleaning activity is a multi-step process where items are handled on a first-come, first-served basis. The customer provides monthly forecasts and places orders weekly.
VSM symbols are somewhat standardized, but many variations exist. Value Stream Mapping is a two-part process: first depicting the “current state” of the process and second, a possible “future state.” Instead of “pushing” material through the system based on weekly schedules, the entire process is converted to a pull system, operating directly in response to customer demand. The lead time in the new system is only 5 days, compared to the 34-day lead time with the old system. VSM is a great visual way to analyze an existing system.
Operations and Supply Chain Management
Operations and Supply Chain Management (OSCM) is defined as the design, operation, and improvement of the systems that create and deliver a firm’s primary products and services. Like marketing and finance, OSCM is a functional field of business with clear line management responsibilities. OSCM is concerned with the management of the entire system that produces a product or delivers a service. Producing an item, such as the Men’s Nylon Supplex Parka, or providing a service, such as a cell phone account, involves a complex series of transformation processes.
Machine Classification
Real Machines (where mechanical work prevails):
- Power Machines: Transform any form of energy (electric, thermal) into mechanical work (e.g., thermal engines, electricity).
- Generating Machines (Generators): Perform the reverse operation of motors; mechanical work is transformed into another form of energy, such as electricity.
- Operator Machines: Use mechanical work provided by a power machine to carry out operations required by industrial activities (most common in industry). They produce a final artifact.
- Transmitting or Processing Machines: Include machines inserted between two different types, such as speed gearboxes.
Appliances: All other machines (stoves, welding machines, computers).
Production Tool Classification
- Generic: Perform different, but not too dissimilar, operations on various pieces differing in shape, size, and function. They require skilled labor and offer lower performance than special machines (due to unproductive time). They have high operating costs and are used by industries operating on a project or model basis with intermittent projects. They are less expensive than special machines.
- Special: Built for a specific purpose and can only perform one operation. They are very complex and produced after an order. They have high purchasing costs but lower operating costs (used by non-skilled labor). Used by industries that work in series.
Machinery Choice Factors
The choice of machinery depends on:
- Purchasing and installation cost
- Time for machine installation and startup
- Production quality
- Hourly output (fixed or variable)
- Type of warranty and assistance provided
- Consumption
- Flexibility
- Type of labor required
Production Layouts
Depending on the production process, layouts can be classified as:
Product Layout (Line or Assembly Line)
- Applied in continuous or repetitive processes.
- Linear arrangement of machines (fixed trajectory of the product). Stations are in series, following the processing order.
- Continuous transport between stations (e.g., conveyor belts).
- Rigid layout using special machines with a high degree of automation.
Advantages:
- Low material transportation costs
- Short total production time per unit
- Reduced processing stocks
- Simplified production controls
- High automation
- High productivity
Disadvantages:
- Low flexibility (can be improved with adaptable machines)
- Need for adequate line balancing
Line Balancing Problem:
Ensuring equal production capacity across stations. Tasks must be designed so that the working time required by each station is equal across the entire line. Two extreme situations:
- High automation line without human intervention (time imposed by the machine, balancing already established at project…).
- Line influenced by human labor (more flexible, you can act by redistributing the workforce).
Process Layout (Functional or Workcenter)
- Applied in intermittent processes (on order).
- No prior standard disposition, as work changes.
- Machines with homogeneous functions are grouped in specialized areas (e.g., lathes) along with operators.
Advantages:
- High flexibility
- Specialization of leaders and effective controls
- Possibility of applying individual incentive methods
- Good chance to avoid failures
Disadvantages:
- Increased internal transportation costs
- Increased stocks, detention times, and need for careful programming and control
Process Layout Problem:
- Reduce transports between workcenters and associated costs. The total process cost depends heavily on transport.
- The cost of internal transport depends on the total distance traveled (product quantity, distances between workcenters, and transport frequency).
- Workcenters with higher transport frequencies are placed closer together.
- Network diagrams are created, where nodes represent departments and meshes represent material flow lines. The network diagram replaces the scale-block scheme, accounting for machinery size.
Fixed-Point Layout (Project Layout)
- Applied in shipyards (naval or construction).
- All inputs converge on a fixed working point.
Mixed-Type Layout
- Islands Layout (Group Technology or Manufacturing Cell): A hybrid of in-line and departmental layouts. Machines with different functions are grouped and arranged according to the production cycle’s operation sequence. Within each group, machines are arranged in line to perform elementary operations for that phase.
- In-Line Workcenter Layout: Workcenters of similar machines (e.g., lathes) are placed in succession according to the production cycle phases. Advantages include better stream programming, as semi-finished products from different cycles can be compacted.
Study of Methods
- Individual steps through which the process is carried out.
- All operations of the process are split into elementary phases until they reach the movements of individual people (where human work is relevant).
- Once the elementary phases are obtained, they are divided according to the classification (processing, movement, waiting, storage, control) and the flow diagrams are compiled (the number and the nature of the operations and the times of each one as well as the distances traveled).