Dr Angel Lopez, director of business development, micrometal
The automotive industry is a driving force when it comes to innovation and development of microsystems, with demand for high-volume production, unlike the more niche applications in the aerospace industry. It is likely that the automotive industry, along with the medical device industry, will be a major stimulus behind the growth in the micromanufacturing space in the short to medium term. As such, the automotive industry is an early adopter of photochemical etching (PCE), which today is a go-to process for the production of ultra-precise metal parts and components at volume and repeatably.
The automotive industry is characterised by demand for cars that emit less in the way of pollutants and run economically and efficiently. This has a knock-on effect on manufacturers, which find themselves forced to design more and more sophisticated engines demanding more and more accurate components made of increasingly innovative materials. Weight, while not an issue at the level of importance it is in aerospace, is also a major factor in the automotive industry.
Micromanufacturing is helping to address these dual needs—increased sophistication and efficiency while also reducing weight—through miniaturisation. The ability to manufacture microsensors, for example, not only saves on weight when compared with traditional-sized sensors but also means that more can be used to monitor vehicle performance parameters in greater depth and detail.
Quality and partner selection
One key and relatively recent change in the automotive industry that makes partner choice a primary concern in the design to manufacturing cycle is the ever-increasing pressure in quality control (QC). QC and exacting quality requirements have been a characteristic of the aerospace and medical industries for a long time but are more of a recent pressure in the automotive industry. This is a direct consequence of the fact that many micromanufactured components in cars are now performing critical functions, and so failure rates, even in high-volume mass manufacture, must be zero. This demands that painstaking attention is not only paid to manufacturing process control but also QC procedures and validation.
For automotive OEMs seeking to take advantage of the possibilities that exist today for the manufacture of precision parts, partner selection is vital. Of paramount importance is a prospective partner’s in-house equipment (this includes not just processing equipment but also handling, assembly and inspection equipment), their location and if they have an intimate knowledge of the automotive industry.
Creating desirable features in vehicles gives a competitive edge. These features might be in navigation, heating/cooling, sensing, entertainment, safety, comfort, handling or fuel efficiency. A PCE partner that understands this is vital for success.
An overview of PCE
PCE employs chemical etching through a photoresist stencil, allowing for the removal of material over selected areas. The use of photoresists allows for the manufacture of high-resolution parts that have complex geometries or large arrays of variable aperture profiles in thin, flat metal sheets.
PCE is commonly misrepresented as merely a prototyping process, but it is, in fact, a versatile and increasingly sophisticated metal machining process that can be used to mass manufacture complex and feature-rich metal parts and components. Advantages of the process include retention of material properties, burr- and stress-free parts with clean profiles and no heat-affected zones (HAZs).
PCE has been around for more than 50 years, but it is still a relatively low-profile process in industry. In recent years, however, with the explosion in demand for more and more precise, smaller and complex metal parts, automotive OEMs are increasingly turning to PCE.
Tooling is a key area where PCE has the edge over many traditional machining processes. It uses easily re-iterated and low-cost digital or glass tooling, which makes it cost-effective when compared with processes such as metal stamping, pressing, CNC punching and laser and waterjet cutting.
Traditional machining processes can produce undesirable effects in metal at the cut line, often deforming the material being worked and leaving burrs, HAZs and recast layers. In addition, these processes struggle to meet the detail resolution required in the ever smaller, more complex and more precise metal parts that many industries (especially the medical device industry) require.
There are instances when traditional machining processes may be the most cost-effective, typically when an application requires multiple millions of parts and absolute precision is not a priority. However, if manufacturers require runs up to a few million and precision is key, then PCE, with its lower tooling costs, is often by far the most economic and accurate process available.
Another factor to consider in process selection is the thickness of the material to be worked. Traditional machining processes tend to struggle when applied to the working of thin metals, stamping and punching being inappropriate in many instances, and laser and waterjet cutting causing disproportionate and unacceptable degrees of heat distortion and material shredding, respectively. While PCE can be used on a variety of metal thicknesses, one key attribute is that it can also work on ultra-thin sheet metal, even as low as 10 μm foil.
It is the manufacture of intensely complex and feature-rich precision parts that PCE is perfectly suited to, as it can be applied to any shape and configuration of product, however complicated or unusual. The nature of the PCE process means that feature complexity is not an issue, and in many instances, it is the only manufacturing process that can accommodate certain part geometries.
Photochemically etched parts delivered on reels to enable a highly efficient, ongoing automatised production process.
PCE and automotive applications
Electronics and safety critical applications
It is fair to say that as cars have become more technical, there has been an explosion in demand from automotive OEMs for intricate electronic components. In the automotive industry in general, there is an increasing need for higher levels of precision and tighter tolerances to improve operational efficiency, and an exponential growth in electronics in control engineering. PCE comes from the printed circuit board (PCB) field, so it is rooted in electronics and is frequently the go-to process for the manufacture of numerous electronic and high-load lead frame applications.
Lead frames are used in almost all semiconductor packages used in automotive manufacturing. Most kinds of integrated circuit (IC) packaging are made by placing the silicon chip on a lead frame, wire bonding the chip to the metal leads of that lead frame and then covering the chip with plastic.
In lead frame design, one size does not always fit all, and very often demand is for customised specifications and features, designs that enhance electrical and thermal properties, and specific cycle time requirements, i.e., thinning of material areas without stress generating punching.
Applications such as high-load lead frames, precision connectors, contacts, radio frequency identification (RFI) shielding, engine management system components, sensors and conductive springs are, in many instances, safety critical and require absolute precision and zero failure rates, meaning the choice of an appropriate manufacturing process is absolutely vital. It is the ability of PCE to manufacture such components while retaining the integrity of the metal being worked that makes it the chosen technology in so many critical automotive applications.
In addition, the complexity of such parts often requires tweaking of tools. When cut from steel, such tooling iterations to perfect the precise nature of intricate metal parts are expensive and time consuming. PCE’s use of inexpensive digital and/or glass tooling allows for cost-effective, speedy and efficient tooling alterations.
Antilock braking system (ABS)/gasoline direct injection (GDI) flat springs
Another area where etching has been embraced by automotive manufacturers is in the manufacture of ABS/GDI flat springs. Today, most braking systems and fuel injectors feature chemically etched flat springs, and they are produced in their millions, dispelling the commonly held myth that the sweet spots for PCE are prototyping and short runs.
In general, there is a significant upturn in demand for flat springs because of the increasing popularity of specialist martensitic stainless chrome steels, such as Sandvik 7c27mo2 and 1.4028Mo, for this application. As the fatigue properties of flapper valve steels continue to improve, focus is turning to the method of spring manufacture. Flatness, recoil and fatigue strength are enormously important in this stringent application, material properties that must not be compromised during spring production.
Conventionally, flat springs have been stamped or laser cut, but both processes have their limitations. Stamping creates deformation, stressing the material and compromising flatness. Laser cutting is a thermal process that causes heat stress and leaves rough edges that could be initiation points for fatigue fracture if not removed completely. Furthermore, both of these processes generate burrs that need to be removed by tumbling, a process that can, in itself, compromise the material surface finish and add to the cost.
PCE overcomes the aforementioned problems, producing perfectly flat springs that have no burrs, lips, pits or other surface imperfections that could become initiation points for fatigue fracture.
Flat springs are expected to flex millions of times over many years and competent PCE partners can help spring manufacturers achieve this objective.
Fuel cells
The use of fuel cells will turn the conventional view of powering cars on its head in the near future. Huge resources are focussed on this area in the automotive industry. PCE can be used to manufacture fuel cell plates and meshes for various industries from aluminium, copper, nickel, stainless steel, titanium and a range of exotic alloys. In general, manufacturing fuel cell plates and meshes in metal increases conductivity and durability, can shorten stacks, and facilitates better cooling due to its excellent thermal conductivity.
PCE has proved to be more economical for fuel cell plates and meshes than other metal machining processes for the following reasons. Firstly, fuel cell plates can be profiled and their channels generated simultaneously in a single etch process. Secondly, and as discussed previously, unlike alternative machining processes, PCE imparts no mechanical or thermal stresses on the metal being worked, which when looking at fuel cell plates, can compromise flatness. Lastly, extremely accurate channels can be produced on both sides of a plate in a single operation, and these can be interlaced for more efficient use of space and optimum cooling performance.
High-end automotive interiors
PCE has pretty much cornered the market where high-end automotive OEMs are looking for complex, highly decorative applications. It can be applied to high-end inlays, tread plates, trims and speaker grilles, allowing automotive manufacturers to differentiate their vehicles with attractive and unique design touches, which would be impossible or entirely uneconomical to produce with standard pre-perforated meshes. Complex designs, mesh patterns and logos, and high-definition surface engravings can all be produced at the same time with micron precision and sharp aperture edge definition.
PCE has stimulated an explosion of new generation speaker grilles due to its precision and versatility. These are replacing the traditional hard grilles, which are produced from woven wire. Photochemically etched grilles are both functionally and aesthetically superior and provide greater rigidity for better protection, higher durability for longevity, greater open area for finer apertures if required, the ability to incorporate logos and legends, and the ability to vary aperture size, shape and position with tight tolerances. It is also possible to apply a wide variety of finishes to fit precise customer requirements.
A photochemically etched bipolar plate featuring exceptionally thin channel structures.
Quality control and quality management
In the safety critical automotive applications detailed above, the ability to verify total accuracy and precision necessitates that a chosen PCE partner is not just expert in etching but also in QC. Speedy time-to-market and absolute precision needs to be delivered with 100 percent verification and zero failure rates.
A partner should continually invest in a variety of measurement processes that assist in such verification as well as ensure competitive and cost-effective part manufacture and minimum cycle times. In today’s world, improved productivity is every manufacturer’s goal. The use of innovative measurement processes provides the opportunity for achievement and maintenance of exceptional quality and productivity for automotive customers.
It is also extremely important to ensure that a PCE partner has a certified quality management system (QMS) according to IATF 16949 or equivalent in place. This will ensure compliance with the stringent demands of the automotive industry.
Conclusion
PCE is a versatile and cost-effective mass manufacturing process that can be applied to numerous, different applications in the automotive industry. Automotive manufacturers and tier 1 and tier 2 suppliers demand outstanding levels of quality and repeatability, and PCE achieves these goals. A competent PCE partner allows automotive OEMs to benefit not just from process engineering expertise but also stringent quality management that ensures the attainment of continually high standards.