Sensor detects visual color discrepancies in injection molded plastic components
Industrial processes for the production of high-quality injection molded plastic components don’t only demand just-in-time delivery throughout the supply chain. The harmonious matching of color, surface texture and gloss level are also important quality features. Even before the complete end product is delivered, it is essential to ensure that the various components do not show any visually distinguishable differences. But who is responsible for this process? The visual appearance of a product made up of various components, such as a car dashboard, is achieved with the aid of elaborate molds, by experts in the injection molding manufacturing process. Despite the use of sophisticated equipment, there can be color discrepancies in the finished end product. The reasons for this often include component wear in the injection mold or non-compliance with process parameters.
“In order to prevent such problems and to avoid any subsequent expensive and time-consuming complaints, the finished product must always be checked with a reliable color meter. We have developed such a device in the form of the Datacolor 45G spectrophotometer, which measures color, surface and gloss level and reliably draws attention to any discrepancies from standard, in terms of color and texture, as well as possible wear in the molds,” explains Walter Franz, Datacolor’s Sales Director EMA and Global Key Accounts.
Coloration and surface finishing by means of injection molding machines
Various factors are specified in advance of the injection molding process, defining standards and tolerances for the product in question. Each manufacturer of injection molded parts receives the color concentrates for the actual production process from various manufacturers as prepared mixtures of the required color. The concentrate is mixed with a polymer in the extruder and then fed into the injection mold under high pressure. This creates not only the shape, but also the surface of the product. However, even though the injection molding company is supplied with prepared basic materials and uses highly modern and expensive machinery, there may in the end still be color and surface discrepancies. How can these inconsistencies be explained? “As a result of the frequent replication of products which are produced in the machine, the molds are subject to wear. This shows up in surface changes in the end product,” acknowledges Franz.
The solution to prevent these visually unacceptable differences is now offered by metering devices – known as spectrophotometers – which compare the surface and color quality of a product with reference values, and display any discrepancies. They also function as a monitoring tool for injection molding processes, since the discrepancies indicate possible incorrect adjustments of traces of wear in the molds. This enables the user to carry out appropriate corrections in advance.
Measuring Color and Gloss by Means of Sensors
For this inspection method, Datacolor has developed the Datacolor 45G, a highly accurate, portable spectrophotometer with integrated gloss metering, which measures the visual impression of the color, the gloss level and the influence of the surface texture of a finished injection molded part. The technology works as follows: The sample is concentrically illuminated at an angle of 45 degrees by means of the 45G. The measured area is exactly eleven millimeters in diameter. A sensor looks vertically down on the sample and records how much light is reflected by the sample. This quantity of light is passed onto a monochromator, which analyzes the light and creates a reflection curve. This is comprised of measured values between 400 and 700 nanometers, the range in which the human eye is sensitive to light. “We produce what is known as a color fingerprint, which is very precise, so we have an actual image of the sample,” explains Walter Franz. The level of gloss is also measured at the same time. For that purpose, light is emitted onto the sample at an angle of 60 degrees. Positioned on the opposite side of the sample, also at an angle of 60 degrees from the vertical, a light receptor in the 45G measures how much light is detected there. The more light the receptor detects, the higher the gloss level of the product. Should the level of gloss have reduced in comparison with the index value, this is an indication of wear and the mold must be reconditioned.
Documentation of the Quality of the Injection Molding Process
Any color discrepancies resulting from fluctuations in industrial production processes are thus detected in good time. By measuring the level of gloss, it is also possible to detect mold wear at an early stage before it results in any significantly recognizable deviation from the specified tolerances. Therefore, the employee can recondition his/her machine at regular intervals.
The 45G is already being utilized within the automotive supply chain. The surface quality of the finished injection mold components, such as dashboards, glove compartment covers and door and side trim panels, is checked by the quality controllers at suppliers, using the 45G, before being dispatched to the automotive manufacturer.