3D printing masks for metallization processes of plastic

Metallization in the automotive industry

Cars, trucks, buses, and bikes all have in common parts that are metallized, i.e., they have been coated with a thin layer of metal. Examples of metallization include components such as logos, lights, interiors, optics, and touch screens, which serve both to protect the components, especially if they are external and exposed to the weather (thus increasing durability and lower maintenance), but also to make them more aesthetically pleasing.

What is the metallization process?

A lot of metallized parts, when touched, will turn out to be made of plastic that has been metallized. Metallization is a process which gives plastics properties which they don’t innately possess, such as electrical conductivity and abrasion resistance: the coatings can be made of aluminium, zinc, or a combination of various metals depending on the substrate.

There are various types of metallization processes that can be adopted:

• cold spraying;
• vacuum metallization;
• thermal spraying.

The basic process first involves the elimination of defects and imperfections from the surface of the component, then the metal coating is applied using one of the techniques listed above, and finally the component is cleaned and polished to eliminate any unwanted residuals and to achieve the desired look.

Masking to metalize plastic

One very important aspect of metallization of plastic materials, like with other coating techniques, is the covering of areas where the metal must not be deposited. Masks are not used all the time but there are various reasons for their use, from aesthetic purposes, to increasing the abrasion resistance of a specific area, to the creation of a reflective surface. When used in high volume production lines, the main purpose of masks is to standardise the metallization process so that it is consistent and can be automated.

Masks are manufactured with a variety of materials, from fibre glass filled plastics to aluminium. The process of mask manufacturing goes hand in hand with that of the component because the mask is designed to fit on it and must respect tight tolerances to prevent the metal from seeping in between the mask and the component.

As the masks are used, they become covered in layers of deposited metal therefore they need to be cleaned every so often. This is done with a variety of techniques depending on the metal deposited and the substrate. Even with washing, after some time the surface quality of the masks becomes too low to be useable, therefore they need to be changed with new ones.

The issue with traditional mask manufacturing

Unlike the masked components, which are often mass-produced with techniques like injection moulding so the cost per part is low, the number of masks required is relatively limited, thus automatically raising the cost per mask, which can range from a few hundred dollars up to a thousand or more.

On top of that they are often made from stock material and CNC machined, a long and laborious process that can take several days if not weeks, depending on the complexity of the mask. This slows down the entire manufacturing process since metallization cannot take place without masks.

The result is that often companies must work around the complexity and cost of mask production more than the components themselves. This not only slows down the manufacturing process but can also lead to sub-par component production and potentially lower customer satisfaction, resulting in a loss of business opportunities.

The Roboze solution: 3D printing in metallization processes

Using a combination of advanced 3D printing materials, the most accurate and repeatable printers on the market, and by leveraging the design freedom inherent in additive manufacturing, Roboze has developed a suite of solutions for the manufacturing of masks for coating processes.

High-performance polymers are a class of plastics that offer higher mechanical, thermal, and chemical properties than consumer or engineering plastics and these are what Roboze specialises in. ULTEM™ AM9085F is part of this family of polymers and possesses outstanding properties that include exceptional thermal resistance (heat deflection temperature of 175°C at 1.82 MPa), a very wide chemical compatibility, resistance to radiation, and low outgassing (releasing of trapped air particles when exposed to very low pressures).

The ARGO 500 is a top-of-the-line FFF 3D printer for industrial manufacturing boasting the greatest accuracy and repeatability in the world. It comes with a dual extruder system, where the main material and support material are printed with two different extruders, both mounted on the same head. Roboze has developed a breakaway material for ULTEM™ AM9085F that greatly reduces the time for support removal.

Application example: a 3D printed mask for car lights covering

In this application it was necessary to metallize the cover of the rear lights of a car. The mask was used to cover the external areas and allow the metal to deposit only inside the headlight cover.

The mask, shown below, was originally made using 2-part epoxy shaped with casting and then refined with CNC machining. The masks had to be chemically resistant to the metal being deposited and to the cleaning process, which involved corrosive chemicals. Since the metallization process used involved a vacuum, the mask material also needed to have low outgassing.

Production volumes were low, a couple of hundreds for an entire production run of lightweight enclosures that could last up to 5 years, and two external companies had to be contacted, one to design the mask and the other to manufacture it.

The mask manufacturing process involved casting so it was necessary to make moulds for the masks, which greatly increased the cost. Of the few hundreds of masks ordered only about 80% were used, the rest were stored as spares for up to 15 years, taking up space in warehouse storage and further adding to the cost.

The Roboze solution was to print the mask with ULTEM™ AM9085F and breakaway supports using an ARGO 500. This has several advantages over traditional manufacturing:

• ULTEM™ AM9085F is one of the most chemically resistant materials in the Roboze portfolio so can survive the cleaning process;
• It also has low outgassing properties (it is qualified for use in the spacecraft), meaning it is appropriate for use in vacuum metallization;
• Using a dual extruder printer and breakaway supports adds to the design freedom and greatly reduces the need for post-processing, just some sanding to smooth the contact areas between the mask and the component;
• The creation of a digital model allows the manufacturing of masks on-demand and just-in-time, eliminating the need for mould manufacturing, and greatly reducing the lead time.