Continuous production is one of three production system options, the other two being jobbing and batch production.
Continuous production is distinguished by completing products in one physical location, in a series of continuous operations, using raw materials or subassemblies as inputs.
Depending on whether the continuous process consists of mass, process, or assembly production types, outputs will consist of either one standardized product, different products from different stages of the manufacturing process, or completed products from sub-assemblies.
The key advantages of continuous production systems are increased equipment utilization, reduced labor, material handling and storage costs, consistent quality of output, and minimal work in progress.
Establishing a continuous production system
Feasibility study and conceptual design
The establishment of continuous production facilities requires considerable investment; therefore, diligent up-front planning and analysis will optimize capital spending and ensure evolving product needs and constraints are considered and addressed.
Composed of operations, finance, and engineering personnel, the study team must trade-off four conflicting issues to establish and record the optimal continuous production system for the business.
Feasibility studies are not options studies; they produce in-depth and considered tactical decisions on one option, outputting a comprehensive implementation plan capable of being costed and issued for procurement, engineering, and operations action.
Production methods
Machinery selection and production layouts are strongly influenced by the degree of desired production flexibility. Do you have a single product produced in high numbers or variations on a theme produced to client demand?
It is tempting to build considerable flexibility into the process design at the early planning stages, as predictions of customer demand, product mix, and new technologies are difficult to ascertain.
Yet, flexibility to cope with fluctuating demand adds considerable equipment cost while diluting the gains from standardized systems.
On the other hand, adding flexibility to an already operating system due to unforeseen industry evolution costs considerably more.
Each case differs, driven by industry, product, and risk appetite, underscoring the study team’s need for broad and deep organizational representation. The decision on the production method is fundamental and must precede all others.
Control and monitoring strategies
Whereas job and batch manufacturing provide sufficient breaks in the production process to support off-line monitoring for quality and product conformance, the nature of continuous production demands sophisticated monitoring and control strategies.
Such dynamism demands comprehension beyond the measurement required at each operation, requiring an understanding of the controls demanded by the integrated system.
The following four demands of continuous production systems, with decisions made during the feasibility study, will drive equipment selection decisions, plant layout, and procedural development.
- Raw material or component measurement and control is vital to ensure the production process utilizes conforming products, and where exceedances occur, material traceability must be sufficiently robust to allow timely control and quarantine.
- In-process monitoring and control systems must maintain critical quality attributes or process parameters close to agreed target values in real-time, accommodating and adjusting for transient disturbances arising from normal operations.
- The team must design a system for material diversion and production alerts to accommodate exceedances beyond the upper and lower quality limits, segregating product, creating alerts, and initiating shutdowns where appropriate.
- Investment in an adequate data management system becomes crucial in continuous production, with sensors and networks designed for real-time capture, transfer, processing, and storage of multivariate data.
QA and QC system implementation
Automated continuous manufacturing requires high standards of quality control. With the pharmaceutical industry moving from batch processing to continuous production of drugs, conceptual frameworks are emerging to assist in implementing rigorous and robust QC systems suitable for other continuous production industries.
Beginning with a philosophy of process analytical control (PAT), the focus is on understanding and controlling production processes to achieve quality by design (QbD). QbD requires the formulation and identification of critical quality attributes (CQA) that ensure a conforming product.
Buying decisions, tools, and systems are then enacted to ensure the measurement and strict control of process parameters that achieve the CQA.
Core tactical decisions include whether measurements to guide quality control are taken off-line, at-line, on-line, or in-line.
On-line and in-line require sensors supporting real-time control and possibly automated systems, while off-line and at-line introduce delays in capturing and containing non-conforming products, raising scrap rates, or lowering machine utilization.
Maintenance Management Systems
The team must select and design a maintenance management philosophy providing the lowest cost maintenance interventions while optimizing equipment availability.
This analysis must loop back into the criteria for production equipment selection to ensure the maintainability of the selected equipment supports an optimal asset maintenance program.
It culminates in a customized maintenance management system consisting of preventative and predictive maintenance strategies.
The decisions on strategic control and monitoring and the tactical choices on quality control will dictate the necessary computerized maintenance management system’s (CMMS) comprehensiveness.
Offering an opportunity to capture and aggregate data received from installed equipment sensors, the CMMS can forecast future equipment conditions and schedule maintenance interventions when most cost-effective for production.
Summary
Too often, business owners rush to implement a continuous production line without fully understanding the many complex and interrelated business strategy, procedural, and production design decisions needed. Such haste produces sub-optimal and costly outcomes.
Superior production process control and quality performance demand a notable effort to design an integrated system of process equipment, optimized layout, and effective measurement and control systems.
A structured and diligent feasibility study is a notable effort worthy of a business’s time and investment.
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Article contributed by Bryan Christiansen of Limble CMMS.
