Introduction
It's critical for manufacturers to monitor the quality of the products they are producing to reduce waste, prevent rework, and avoid shipping low quality inventory to customers which could result in financial penalties, costly recalls, or loss of reputation and future business.
Customers are also enforcing suppliers to adhere to new initiatives such as "zero defects", as well as reducing the acceptable tolerances on material quality.
Poor quality product eats into profit margins, so it's important manufacturers are able to measure success and failure, as well as perform continuous improvement activities. MES supports this data driven approach.
What is quality in manufacturing?
Manufacturers define quality control plans which document the inspections to perform and when to perform them. Inspections are often valid for multiple materials, but it's common for the specifications to vary by material.
Specifications define the tolerances that are acceptable for a measurement. For example, if the length should be 100mm, then it might be acceptable for the measurement to be between 98mm (lower specification) and 103mm (upper specification). This makes the tolerances 2mm and 3mm respectively.
Inspections consist of variable measurements and attributes, and can be performed on one or more samples taken from the production line.
Variables
Variables can be measured against a unit. For example dimensions, weights, or torque.
Variables can be measured across more than one sample of material, and at multiple positions on the same sample.
If a machine on the shopfloor has multiple output positions then samples can be taken from all of these and tested. An example of this is in injection moulding machines where the tooling produces pieces from multiple cavities at the same time. Tracking the cavity allows quality issues to be tracked against the specific output position, not just against the machine.
Statistical Process Control is a technique used in manufacturing to determine the capability of a manufacturing process through sampling, as opposed to having to perform inspections on everything. This is covered in more detail in a future article.
Defects
A attribute or defect is a way of identifying a non-measurable issue on a product. For example if a dent or scratch is identified on a product this can be logged and counted.
It's possible to define one or more defects on a product, for example on a specific product there are two scratches and one dent. Each of these defect reason can be categorised into:
Minor Defect
Major Defect
Critical Defect
Depending on the severity of the defects, or the number of more minor defects the product is either labelled as good, or defective. For example, if a critical defect is recorded then the product is defective, but if a minor defect is recorded the product is not defective.
When logging defects it's important to specify whether you are counting defects, or counting defective parts. You also need to specify whether you always do the check on the same number of samples each time (fixed sample size), or whether the number of samples you take each time is variable (variable sample size).
This is important as it determines the attribute chart to use when reviewing SPC (statistical process control). This is covered in more detail in a future article, but for now the important thing to know is that there are four attribute charts:
Some more advanced MES systems provide a graphical user interface for the person doing the quality check so that defects can be drawn by the user onto a picture of the product. This means the location of the defect is also logged.
Data Collection
Measurements can be entered manually, but more advanced MES systems allow for automated collection via metrology equipment such as scales and gauges.
Data can also be generated by some equipment and exported to a file. This can then be imported automatically by the MES system to reduce manual input from the operators, and to increase the accuracy of data.
Product removed from the line could be measured and placed back in the production process. In some cases the test damages the sample, this is called a destructive test and contributes to the scrap levels produced by the process, factoring into the OEE calculation for the production line. You can read more about how quality impacts OEE in this article: OEE.
Quality in MES
Quality functionality is heavily tied into a variety of other MES functions, this gives MES a distinct advantage over a selection of disparate systems. It's common for manufacturers to perform quality checks in a number of different scenarios.
Supplier Materials
Quality inspections on supplier materials received into the factory. These could be performed on serialised inventory, or against a batch of material.
A dedicated QMS system doesn't have the context of the inventory in stock without this information being entered manually. When the raw material inventory is subsequently consumed into the process a good MES tracks the quality inspection as part of the traceability record. If issues are found later in the process (or worse found by a customer) the traceability report can look all the way back to the raw materials received by the supplier and the results of any inspections.
Poor quality materials may need to be sent back to the supplier. Alternatively, if the grade of material is still useable, but not within tolerance, or with minor defects this could result in a discount.
In-Line Production
MES knows about the current production order being executed on the production line, and everything about the order such as the material being produced.
When quality inspections are performed MES already has the contextual information available, without the operator having to enter manually each time, speeding up the process, and improving the accuracy of data. In a dedicated QMS system without knowledge of the production run, all data must be entered manually.
Not only that, but a good MES system is able to prompt operators to perform the correct quality checks, using the correct specification, at the right time. This also allows for in-depth compliance reporting to determine the percent of checks completed compared to the quality control plan. MES can adjust the number of checks it asks the operator to perform based on how much downtime has occurred, preventing the operator from being asked to do too many checks based on the run time. This is only possible because MES is a single system which includes both production and quality data.
Lab Checks
Sometimes quality checks are removed from the production line to be tested in a quality lab. This could be an area within the factory with specialised measurement equipment, or it could be sent off-site to a 3rd party.
When samples are taken from the line they need to be labelled and tracked. MES can print a label for the product, which can then be tested in the offline lab.
Automated Inspections
Many manufacturers have equipment which performs inspections on the product, and can export a text file with the measurement results. These files can be imported into MES, where the measurements are compared against the specifications.
It's also common to have visual inspection systems which use AI to review the image and record defects. In many cases, if a defect is found then the product is automatically scrapped by the machine. Again, MES can pick up this information automatically.
Inventory Inspections
MES is responsible for creating inventory on the shopfloor and printing labels. It's possible to record a quality check against a specific piece of inventory for traceability purposes.
This is especially useful when doing visual inspections, because the user logs the defect position visually through the MES (assuming the MES has this capability).
Any quality checks performed on the inventory should form part of the traceability record.
Warehouse Inspections
If semi-finished or finished goods are on stock in the warehouse, it common for quality checks to be performed before putting the inventory away, or before shipping to customers. A quality check may also need to be performed if someone notices an issue with material on the pallet, or package.
Asset Inspections
Some MES systems also allow for inspections to be performed against equipment and assets in the factory, such as machines or tooling.
Quality Functionality
Quality Control Plan
MES defies and manages the control plan,
Quality Control Plans (QCPs) are critical for ensuring product quality and consistency. QCPs define the steps and procedures necessary to ensure that products meet established quality standards. MES systems provide tools for managing and executing QCPs, enabling manufacturers to ensure that quality standards are met at every step of the production process. By monitoring QCP execution, manufacturers can identify potential issues and take corrective action before they impact product quality.
Performing Inspections
Performing inspections is a major component of quality operations. MES systems provide real-time visibility into inspection results, enabling manufacturers to identify and address quality issues as they arise. By tracking inspection results over time, manufacturers can identify trends and patterns in quality issues, enabling them to take proactive measures to prevent future issues. MES systems also provide tools for managing and scheduling inspections, enabling manufacturers to optimize resource allocation and ensure quality standards are met.
It's important that the MES you choose has a great user experience, making it easy and visual for operators to record quality check results.
If the specifications are breached, or critical defects are detected then it's good practice to provide a feedback loop to the operator to inform them of the problem and optionally let them explain the root cause.
Managing Specifications
Out of Spec and Out of Control measurements are important metrics for monitoring and optimising quality processes. Out of Spec (OOS) measurements are measurements that fall outside of established quality specifications. Out of Control (OOC) measurements are measurements that fall outside of established control limits, which are discussed in the SPC article. MES systems provide real-time visibility into Out of Spec and Out of Control measurements, enabling manufacturers to identify and address quality issues as they arise. By analysing these metrics over time, manufacturers can identify trends and patterns in quality issues, enabling them to take proactive measures to prevent future issues.
SPC
Powerful analytical techniques such as Statistical Process Control (SPC) can be utilised to improve product quality. SPC uses statistical analysis to identify the capability of the process. 100% inspection is not possible in most manufacturing processes due to time, costs, and other practicalities. SPC is important because it allows sampling products for quality purposes, reducing the number of quality checks that need to be recorded.
Connection to metrology equipment
Connecting to metrology equipment (gauges and measurement equipment) on the shopfloor is crucial for quality operations. Metrology equipment is used for making precise measurements and ensuring that products meet established quality standards. MES systems provide tools for connecting to metrology equipment, enabling manufacturers to collect measurement data in real-time and monitor product quality at every step of the production process. By integrating MES systems with metrology equipment, manufacturers can streamline quality processes, improve measurement accuracy, and reduce costs associated with manual data collection.
Document Management
Typically document management is considered to be a quality function, but different MES systems handle this in different ways.
Non-Conformance
If issues are detected then MES can raise non-conformances, and track actions against the non-conformance to resolve. Some MES system handle this, and others rely on dedicated 3rd party solutions, or ERP to handle.
The benefit of using MES is that it has the full context of any issues that have been raised and can be tracked as part of the traceability record. This can still be synced with ERP, but often the detail is stored in the MES system.
MES vs QMS
MES replaces the need for an independent Quality Management System (QMS). This comes with several benefits:
One application across operations means super users only need to learn one application, and the business only has to pay for one application. It also means that the communication between departments is simplified, as all departments have visibility of the same data, and quality information is contextualised with other information from other departments.
Summary
Improving quality operations are a big driver for manufacturers, and provide a competitive edge in the market. With the help of MES, manufacturers can gain a deep understanding of their quality operations, make data-driven decisions, and take proactive measures to address issues that arise. By leveraging MES, manufacturers can improve product quality, reduce costs, and increase customer satisfaction. Ultimately, integrating MES systems into quality operations can help manufacturers remain competitive and thrive in an increasingly complex and competitive marketplace.
