There are basically three types of inspections: first-article, in-process, and pre-shipment. First-article inspections are conducted with the onset of initial production. An in-process inspection takes place on the assembly line, or during the manufacturing process and determines whether the appropriate tests and checks are taking place and whether the quality checks are consistent with the customer’s requirements. A final inspection is a final sampling of finished product to check that conformance is acceptable prior to shipment. Based on the outcome of a final inspection, a lot can be accepted, rejected, or placed on hold.
Pro QC recommends ANSI Z1.4 2003 sampling tables to determine the number of units that will be randomly selected for evaluation. Based on the lot or batch size, code letters are assigned that cross-reference to the sample size required depending on which plan is being employed. Single and double normal sampling plans are the most commonly used.
If you do not have existing sampling requirements, Pro QC will assist you in determining which plan works best for your specific needs.
Samples are checked against a detailed inspection plan for appearance, applicable functionality, packaging integrity, workmanship, etc. If you currently do not have an inspection plan, Pro QC can assist.
Defects noted are classified as major, minor, or critical depending on inspection plans. The acceptable quality level (AQL) is determined by totaling the defects and using the corresponding accept/reject criteria within the sampling plan.
An AQL, or Acceptable Quality Limit, is a probability limit chosen for a given product or process characteristic. There are normally three limits chosen, one for critical, major and minor. Usually, each of these three limits is different for each category. A typical sampling plan would be as follows:
|General Level II||0.01||1.5||4.0|
The lower the number, the fewer defects can be accepted in the sample of product. When choosing AQLs, it is important that one understands the balance between setting them too low, and rejecting many shipments, and setting them too high and releasing unacceptable product.
A lot is rejected when there is a clear non-conformance with the inspection plan. A “hold shipment” normally occurs when the problem is subjective against the inspection plan definition of non-conformance.
The AQL sets a numerical limit for the acceptance of non- conformances in the sampled lot based on critical, major and minor problems. Each of these “criteria” is a description of a problem based on the effect it has. These descriptions are critical to performing an inspection, as they describe what is important to the appearance, the shape and/or the function of the product. International standards, industry standards, the quality engineer’s experience and/or the buyer can determine inspection criteria.
Pro QC offers secure online reporting and scheduling. Reports and other relevant information, such as digital photos, are uploaded to an online database where clients are provided confidential access.
Audits identify problems or shortcomings in the management system that could allow poor quality product to be produced and brings it to the attention of management so they can correct the problem. Audits are often preventive actions in that they identify problems before they have produced poor quality product. This is why audits are often used as part of the basis for selecting suppliers.
First article inspections immediately identify conformance issues with new product as it is initially produced. In-process inspections identify problems as they develop on the production line and save time in making corrections and reduce costs of reworking completed product. Pre-shipment inspections identify non-conformances prior to shipment, reducing the risks to the buyer of receiving defective product along with the associated delays in receiving replacement products.