Post Molding Injection Processes

Machining to Finished Dimensions

Many value added services like printing and hot stamping are generally done in the Post Injection Molding Process. These additional operations are only done after the molding process because they cannot be done during the molding process or at the molding machine. This is often because the post injection molding process is for example, placing the part into a CNC machining center after "aging" the part. Aging the part is used for the purpose of allowing the part to reach its maximum shrink properties so that in the machining process dimensions will not continue to move thereby rendering the part a reject after the machining process. A very expensive reject, I might add.

Our ISO 9001 certified company has all the process information documented so that you can find any location in the process that is or would be at fault for causing the final machining process to make an out of tolerance part other than the machining process itself.

Tampo Pad Printing

The printing of finished custom plastic injection molded parts is a very popular way of increasing the visual aesthetics of the part for a relatively low cost. At PMC, pad printing is just another way to carry out printing of a wide variety of inks onto plastic parts.

Pad printing is a cost effective way to print parts yet is also a highly reliable process and can produce parts to a very high standard. The most crucial part to the pad printing process is the plate on which the graphic is etched and this is called the clishe. The etching of the graphics onto this plate is very important, as it will determine the quality of the final graphics once printed onto the component. Once this cliché is placed in its fitting in the machine the "cup", containing the ink for the printing, is positioned on top of it so that while the pad is printing the component, the cup will distribute ink into the etch on the cliché. As the arm, controlling the pad, slides back the ink cup moves with it and slides away from the etch. This means that the only ink on the plate will be retained in the etched area and so can be picked up by the pad.

The pad is then lowered onto the designed graphic, formed by the etching and picks up the ink that is transferred to the next injection molded part. This is the printing process. The pad is made from silicon as this means it can pick up the inked pattern without the ink permanently becoming attached to the silicon pad. The hardness of the pad will depend upon the texture of the plastic injection molded surface that is to be printed. For example for a rough surface more pressure will be required to apply the ink on the surface, so a harder pad is required. The opposite is true for surfaces that have a smooth finish. The consistency of the ink is also very important.

Printing using a state of the art CNC machine ensures that graphics are printed to the highest possible standard. Six pads, using 5 colors, can be programmed using a touch screen panel interface so that the sequence of printing can be optimized. CNC pad printing also means that each part to be printed is lined up using lasers to insure that it is in exactly the right position under the pads. This ensures that even when the machine is loaded with a number of moldings at the same time, each one will be printed to the same standards. CNC pad printing also benefits from having a 3-axis servo motor driven robot-printing arm. This means that it is possible to print very large parts or even parts that have an uneven surface to them, since injection molded parts are rarely perfectly flat this is a major benefit as it means any graphic can be printed onto the surface of the molding with little difficulty.

Hot Stamping

Hot stamping is defined as a dry printing process, which uses controlled heat, pressure, and precision timing to transfer a color pigment from foil to surfaces of varied shapes and materials. This process forms a permanent bond between custom plastic injection molded part and the foil, and creates a dry print.

The advantages of hot stamping include increased productivity, multiple colors in one step, and a variety of available materials and finishes.

Important Notes:
The image you decide to use during hot stamping must fit within an area of the plastic part the lends itself to the die size to fit the part printing area. You may send art larger than these sizes and it can be reduced to meet the size constraints. Remember, when art is photographically reduced line weights decrease at the same rate as the reduction.

Large solid areas do not receive hot stamping well because air is trapped during the stamping process. Areas of detail that are too small may fill in, and bridging of lines can occur particularly when a very fine line is created by space between two dark areas. Very fine lines in conjunction with large solid areas also can produce "cut-through" from uneven distribution of stamping pressure.

Specialty foils (i.e.. Holograms, fractures and patterns) are less likely to hold hot stamping of very fine lines, type & detail.

The die making process requires black on white (CAMERA READY) art. Please send us clean, originals. We accept e-mail submissions but occasionally experience transfer problems and software conflicts. If you choose electronic submission please be prepared to send hard copy if necessary. Native files can be sent for the following software: PC versions- Adobe Illustrator v10 or earlier, Adobe Photoshop v6 or earlier, Corel Draw & Corel Photopaint v11 or earlier and Freehand v10 or earlier.

Generic file formats that have worked well for us are: .eps, .tif, .jpg & .bmp. The formats .tif, .jpg & .bmp can create difficulties when not set to 300 d.p.i. resolution or higher.

We will be happy to review a fax of your art and give you our advice on any changes that may help to prevent technical difficulties.

Plastic Molded Concepts Inc. provides custom plastic injection molding from start to finish. Our post molding processes come with years of experience in areas like hot stamping and printing. Contact us today for questions about our post molding services.