In-mold manufacturing appliances and key related trends

TRW Advanced Plastics is involved in engineered fasteners and components. It produces several different industrial products. The reduction in assembly effort with in-mold assembly is particularly apparent with the production of industrial cold storage refrigerator air diffusers for Whirlpool, Electrolux, and Lucky Goldstar.

TRW's in-mold assembly product used for the air diffuser reduces independent parts by more than 50% with concurrent increased precision of the finished assembly.

Injection molded IMA appliance parts
(Source: TRW Advanced Plastics )

The company uses TRW Advanced Plastics Technologies' specialized injection molding knowledge. It helps to create perfect-fit components for most industrial sectors. For example, a crankshaft smaller than 1 cm with a flexible connecting rod. This was developed by TRW for use in an electric toothbrush appliance by one of the leading manufacturers, Oral-B. It was also developed as an oven control housing for use by Miele and KitchenAid.

Using a 2x2-cavity tool, two materials are molded into two parts of a housing for an oven control. It is produced as a 2-piece assembly consisting of a tubular housing with a freely rotating shaft inside. Until TRW redesigned it for in-mold assembly, the component consisted of 3 molded pieces and 2 metal screws. This required the following:

• 3 molds,
• 3 machines,
• purchased screws,
• incoming and intermediate part warehousing,
• an assembly operation, and
• intraplant movement of parts

Now, this is all accomplished inside the mold, allowing the separate assembly process to be eliminated for different end products. TRW says the overall accuracy of the finished assemblies is very high. Select 62,600+ injection molded polymers available in our database.

Appliance oven control receptacle
(Source: TRW Advanced Plastics)

Injection molding machine and mold makers say multi-material molding demand in North America is still less than 10% of their sales. Multi-material molding in North America lags significantly behind that in Europe. However, the technology is attracting increasing attention in North America, driven by growing Asian competition.

Injection molders are recognizing that the elimination of capital and operating costs for downstream equipment, made possible by producing a finished part in the mold. This can result in significant savings. With less part handling, manufacturing cycle time may be reduced by as much as 20%, and total assembly costs may also be reduced by 15% or more. Additionally, capital investment for a job may be cut by up to 25% as a result of using just one machine and mold instead of two.

Milacron states that in the U.S., multi-molding machine quotes have increased to 15% of the total for their injection molding machines. Whereas over 20% of the company's sales in Germany are for multi-material units. Arburg also sees growing interest. Other companies in the U.S. are also noting growing interest in multi-material molding.

MGS Manufacturing Group needed more space to meet the growing demand for multi-material molding equipment produced by its Universal Multishot Systems division. The Universal Multishot business, which makes portable, bolt-on injection units, rotary indexing plates, rotating platens, and other multi-material molding equipment, has moved to a dedicated, 12,000 sq. ft. structure to keep pace here.

Multi-material molding is evolving in new directions. Recent developments include larger machines with more cavities, combinations of materials, and larger parts. Some presses are being equipped with 4-6 injection units, or for thermoplastic/thermoset combinations.

Sophisticated rotating tools allow for in-mold assembly and finishing. Other multifaceted tools produce parts with combinations of multiple materials. They use water injection technology or gas assist. Novel uses for coinjection go beyond embedding recycled plastic material within a plastic part.

Large stack turning 32-cavity mold, for 3-component deodorant roller
(Source: Foboha GmbH)

The injection molding machine's role in production has been expanded. There is an addition of various secondary processes into the mold to become a manufacturing cell. Traditionally, the injection molding machine was a single cog in a value-added process, responsible only for molding. 

The machine is transformed from a segregated operation into the hub of an integrated processing system. This produces value-added sub-assemblies or finished products rather than a range of individual parts requiring secondary assembly.

This can be incorporated into one machine. Thus, reducing the machines, operators, auxiliary, and assembly equipment required. It is increasingly common for multi-component molding, in-mold assembly, and/or other operations. This ability to incorporate secondary operations into the molding machine, through the use of innovative tool designs, offers benefits like:

• reduction in manufacturing costs,
• improvement in quality, and
• creation of new opportunities for molders

The technology also allows molders to maximize production with existing equipment. It also adds flexibility from interchangeable mold cavities, allowing molders to add printing, welding, painting, assembly, or other secondary processes in the tool. The expanded role of the injection molding machine is finding applications in various markets. This includes appliances, medical, personal care, packaging, large parts of automotive areas, etc.