When it comes to quality manufacturing, “Does this look good to you?” is the one question that most managers hate to hear, yet is one of the most common questions asked by quality inspectors, line personnel and sometimes even suppliers and customers.
What it really means is “we don’t know what our visual quality criteria are for this part”. In too many cases, the appearance of manufactured parts is left to subjective judgement and can easily change from inspector to inspector, and from day to day depending on light, awareness, and differences in understanding. I have even heard quality managers say, “this is a gray area, today it might be ok and tomorrow it might be rejected”. This undefined gray area leaves everyone concerned in a foggy haze, from suppliers through inspectors all the way to customers.
Is there an answer? I believe there is and in my previous career where the visual criteria of a part were of primary importance, we developed a system that cleared the fog of uncertainty and eliminated 99% of the questions about visual quality.
My previous career involved injection molding and imprinting, which is what I will discuss here, but the same system could be used for any manufactured item no matter the process used.
We started with the guidelines established by the Society of Plastic Engineers (download the SPE Guidelines free). These guidelines give a detailed description of the flaws and defects found in a molded part. Not all the problems outlined were of concern to our customers, so we picked the critical components of the listed criteria and re-wrote them to fit our customer’s needs. We also added visual aids in the way of drawings to illustrate each defect. THIS WAS A CRITICAL STEP. The diagrams gave all the stakeholders involved a clear definition of what we considered acceptable and what we considered a reject.
As an example, we could not accept a knit line longer than .125 inches in length on any portion of the part. This was diagramed in a two-inch square, showing a knit line less than .125 inches long and one square showing a knit line longer than .125 inches both coming off a feature that created the knit line.
We also described heat blush around the gate, splay, scratches, pits and warp in the same manner. For imprinting, we described color registration, line clarity, and scratches, pits and all other print defects we encountered. Each defect was again illustrated with a two-inch square (or larger if necessary) box with both acceptable and unacceptable criteria shown.
During this compilation, we didn’t find any criteria that couldn’t be measured, described and visually reproduced so that everyone understood acceptable and unacceptable visual defects.
It was also important to outline the method of inspection. We chose that method directly from the SPE guidelines, including viewing distance, time and angle.
For our purposes, all parts were inspected to the same criteria. All customers received that same level of quality, the bar was set to satisfy the most stringent requirements. I realize this might not be possible for all parts nor all clients. If exceptional finishes are demanded, those usually require special processes or additional manufacturing operations. It would be equitable for all concerned to consider those exceptional parts as unique part numbers with an additional cost applied. If those parts exist, then the visual criteria must also be described in your handbook.
Once your handbook has been developed through an internal team approach, the next critical step is obtaining approval from your suppliers and your customers. Make sure your supply chain can produce the parts based on your quality standards. Are there any modifications or changes that must be made to maintain pricing consistency and/or delivery cycles?
Likewise, let your customers know that you have developed a set of visual quality standards that will be measured and used on their finished parts. Again, any modifications or changes should be made as needed after a review of the documents by their quality and purchasing departments. Obtain their approval in writing and make sure they are supplied with an updated copy of the criteria for their incoming inspection.
This is not an easy process and will result in some lengthy and potentially divisive discussions that must be brought to a consensual conclusion; but it is worth the time and effort. When consciously and consistently applied, it will result in the elimination of questions internally; and when strictly followed it will eliminate customer generated returns for quality issues related to visual criteria.
If thoughtfully prepared, there isn’t a visual quality issue that can’t be quantifiably described and measured and pictured. Once everyone is on board, you will wonder why you didn’t create these guidelines before. The silence will be deafening.
If you would like a free copy of the SPE guidelines, please click here.
If you have any questions on developing your own standards, please contact Steve Gauer. Comments, questions and thoughts are gladly accepted.