Every manufacturing company wants to reduce changeover time. The changeover process may take days or weeks in some industries and only a few minutes in others. In industries where small lots or single pieces are produced, reducing regular changeover times through continuous improvement programs, SMED (Single-Minute Exchange of Die), and standard work can significantly boost efficiency and equipment utilization.
Changeover time is the total time elapsed between the last good part of the previous run and the first good part of the following run. The first piece of the following run must meet quality standards and specifications. “Dial-in” time must also be included in changeover time.
There’s an important distinction between internal and external changeover time. Internal changeover time represents the lapsed time described above. External changeover time is the time spent by operators, technicians, and other staff preparing for the change.
External changeover time variables can affect the total internal changeover time. For example:
Since these variables have an impact on the internal changeover time, they can help to reduce it.
Traditional measurements of changeover time involved pen and paper and the ubiquitous clipboard. Stop and start times were recorded and included in daily production. Many companies took changeover time a step further by requiring task breakdowns within changeover time. These included factors such as:
The problem with these categories is that the more manual the process was, the less accurate the data was; numbers were often excluded, rounded, or omitted. These categories are best recorded and captured when downtime is automated.
Regardless of the method, several factors should be included in downtime calculations:
Lost Labor Cost: Labor is one of the most significant expenditures for any manufacturing company. Lost labor is calculated by the total number of hours lost or expended in the changeover multiplied by the number of workers multiplied by their hourly rate:
(Hours down) x (Number of staff) x (Labor cost per hour)
Product Cost: Changeover time impacts the total production for the week or day counted. Product cost is the unit price multiplied by the total items usually produced during the changeover hours multiplied by the hours down:
(Unit price) x (Standard production rate) x (Number of hours)
Recovery Costs: This includes any maintenance that extends the length of the changeover. It also consists of any maintenance time spent changing gears, pulleys, etc., required for the next run.
Changeovers may be minor (for example, a color or mix change on the fly) or significant (for example, a complete cleaning and resetting of major machine components). The key to measuring changeover time is to include accurate times for all tasks and functions.
The most accurate way to measure change over time is to use a machine data platform. This eliminates data entry errors, enables operators to document changeover procedures quickly, and lets managers focus on reducing times for each category using real-time data.
There are numerous advantages to reducing changeover time in manufacturing, mostly tied to the fact that if changeovers are not occurring, machine can be running. These include:
There are significant distinctions between setup time and changeover time; these differences are best explained by example. Setup time usually indicates a single machine. This may be a single CNC changing from an old die to a new die or replacing machine tools in a carousel for a run using different specifications.
Changeover time applies to a broader system or group of machines. For example, a complete changeover in a CNC machine company may include drilling, milling, cutting, boring, and other value-added tasks on multiple machines or a complete production line to achieve a finished part or product. In this case, all equipment will need new setups to run the batch.
Essentially, setup time may be part of overall changeover time for a large group of machines like a production line, or it may be equal to the changeover time if it affects only one machine.
The advent of lean manufacturing saw many innovations designed to streamline changeover time and standardize the process. One of the most significant innovations heavily used in CNC machining is Single Minute Exchange of Die (SMED).
Shigeo Shingo envisioned the SMED system in the early years of the lean manufacturing movement. The system recognizes internal and external elements of changeovers and focuses on analyzing elements of the changeover reduction process for continuous improvement.
The SMED process uses clear work instructions to formalize the standard work required and reduce changeover time. This process has allowed many companies to reduce downtimes by up to 94%.
Here are the five steps used in the SMED process:
There is another significant piece to this puzzle: accurately tracking changeover times. Attempting to do this manually is likely to lead to delayed, inaccurate data that is difficult to process and analyze. Not to mention the amount of time operators will be required to spend manually documenting everything.
By autonomously tracking production data with a machine data platform like MachineMetrics, continuous improvement managers and engineers can get instant insight into changeover, setup, and other KPIs.
Not only will this help to establish accurate benchmarks as well as set realistic expectations, but it will identify which continuous improvement initiatives to pursue and how effectively they are working.
Minor improvements in changeover time can add several days of capacity to a company’s availability. Huge improvements can add weeks or months to that capacity.
Manufacturers will realize many benefits by focusing on a few methods when conducting a SMED analysis and creating a standard process for changeover times. These best-practice methods include:
MachineMetrics autonomously collects data across all equipment, standardizes the information into a common model, and visualizes the data in production reports and dashboards to enable actionable insights. Further, historical data can be used to accurately assess production performance, such as establishing benchmarks for your most important metrics.
When it comes to increasing efficiencies, such as reducing changeover time, identifying hidden capacity, or responding faster to downtime events, MachineMetrics helps manufacturing leaders identify the most lucrative opportunities so that continuous improvement initiatives can be prioritized correctly.
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