Injection Molding
Essay Preview: Injection Molding
Report this essay
Wilbert Plastic Services
Auburndale, FL
202 Progress Road
Auburndale FL 33823
863-967-6604
Fax: 863-967-1254
In the early days manufacturers came to us for a specific thermoformed or injection molded part or parts for a product they were making. Over the years we noticed that, more and more, they were coming to us for entire subassemblies and more complex parts that might incorporate both thermoformed and injection molded parts.
Based on that experience, and our knowledge of the pressures that manufacturers are under to increase efficiency and reduce cost, it became obvious to us that we needed to provide a wider array of services to help our customers increase their efficiencies, reduce their overall costs and maximize their ROI on each project, part or component. This vision has lead us to add assembly, decorating (in and post mold), reusable packaging, RFID and much more to our capabilities.
We believe that Lower Overall Customer Cost comes from an innovative, total solution made up of customer focused, operational excellence. By combining quality production and secondary services with design expertise, supply chain management, and world class logistics WPS has been able to help our customers find new ways to lower their costs and improve profitability.
Injection Molding is the process of forcing melted thermo plastic into a mold cavity. Once the plastic has cooled, the part can be ejected. The first injection molding machines were built in the 1930s.
There are six major steps in the injection molding process:
Clamping
An injection molding machine consists of three basic parts; the mold, the clamping unit, and
the injection unit or units. The clamping unit holds the halves of the mold under pressure during the injection and cooling.
Injection
During the injection phase, plastic material, usually in the form of pellets, are pulled from a hopper on top of the injection unit. The pellets feed into the cylinder where they are heated until they reach molten form. Within the heating cylinder there is a motorized screw that mixes the molten pellets and forces them to the end of the cylinder. Once enough material has accumulated in front of the screw, the injection process begins. The molten plastic is inserted into the mold through a sprue, while the pressure and speed are controlled by the screw or in some cases a ram.
Dwelling
The dwelling phase consists of a pause in the injection process. The molten plastic has been injected into the mold and the pressure is applied to make sure all mold cavities are filled.
Cooling
The plastic cools to its solid form within the mold.
Mold Opening
The clamping unit is released, which separates the halves of the mold.
Ejection
An ejection rod and plate eject the finished part from the mold.
Some Advantages of Injection Molding
High production rates
Repeatable high tolerances
Wide range of materials can be used
Low labor costs
Minimal scrap losses
Little need to finish parts after molding
In-Mold Graphics Molding
In-Mold Painting/Coating
Wilbert Plastic Services has lead the way in the use of In-mold coatings – special paints sprayed onto the mold surfaces – as an alternative to post-mold painting. After application, these paints dry for a brief time so that the injection mixture flows over the semi-dry coating during mold filling. Typically In-Mold painting is used for large, relatively simple parts, without complex details. Other points to consider when selecting an in-mold coating include:
In-Mold spraying is relatively straightforward and less labor intensive than post-painting.
In-Mold coating can reduce and, save the cost of, most secondary finishing steps.
Perfect adhesion between the in-mold coating and the substrate is almost guaranteed.
Because in-mold systems are low in solids they follow the contours of the mold design very well. Therefore, fine details in the mold will be faithfully reproduced.
Mold surfaces must be very high quality, as every detail is reproduced.
In certain instances the presence of an in-mold coating can improve the flow characteristics of the thermoforming material resulting in fewer sub-skin defects.
Paint usage is relatively low compared with post-painting.
In Mold Decorating
Colors, patterns, wood grains, brushed metal, or bright chrome, plastics in a variety of finishes including glossy, matte, or textured are coming out of molds with every kind of finish and feel. The use of formable films is aiding manufacturers seeking lower-cost and environmentally friendly alternatives to paint and other secondary processes. Already well established in auto interior & exterior trim, and hand-held electronics markets, the appeal of In-Mold Decorating is making itself felt in many new areas.
Formable films are an economical, durable, and environmentally friendly means of producing fully decorated parts right out of the mold. In-mold decoration (IMD) with formable film inserts is replacing traditional post-mold painting, printing, hot stamping, and chrome plating. The process achieved its first successes in modestly sized and relatively flat parts for interior and exterior automotive trim and cell phones. Today, IMD technology has progressed to larger 3D parts such as entire instrument panels, bumpers, fascias, roofs, and even hoods for cars and trucks.
IMD also boasts lower scrap rates, ability to mold and decorate in one location, and improved recyclability. IMD can achieve a Class