Dr Angel Lopez, Director of Business Development, micrometal GmbH
The automotive industry is a driving force when it comes to innovation and development of micro-systems, with demand for high volume production, unlike the more niche applications in the aerospace sector. It is likely that the automotive industry — along with the medical device sector — will be a major stimulus behind the growth in the micro manufacturing space in the short to medium term. As such, the automotive industry is an early adopter of photo-chemical etching (PCE), which today is the go-to technology for the production of ultra-precise metal parts and components at volume and repeatably.
The automotive sector is characterized by demand for cars that emit less in the way of pollutants, and run economically and efficiently. This has a knock-on effect to manufacturers that find themselves forced to design more and more sophisticated engines, which demand more and more accurate components made out 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 sector.
Micro manufacturing is helping to address these dual needs — increased sophistication and efficiency while also reducing weight — through miniaturisation. The ability to manufacture micro-sensors, for example, not only saves on weight when compared to traditionally-sized sensors, but also means that more can be used to monitor vehicle performance parameters in greater depth and detail.
QUALITY & PARTNER SELECTION
One key and relatively recent change in the automotive sector that makes partner choice a key concern in the design to manufacturing cycle is the ever-increasing pressure in the area of quality control. Quality control and exacting quality requirements have been a characteristic of the aerospace sector and the medical sector for a long time, but are more of a recent pressure in the automotive sector. This is a direct consequence of the fact that many micro manufactured components in cars are now performing critical functions, and so failure rates — even in high volume mass manufacture — must be zero. This not only requires painstaking attention to manufacturing process control, but also demands that focus is maintained on quality control 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. As well as assessing the nature of the equipment that a micro manufacturing partner has in-house (this including not just processing equipment but handling, assembly, and inspection equipment as well), of paramount importance is the location of a supplier with an intimate knowledge of the automotive sector.
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, and backs this sensitivity to the automotive sector with expertise in the PCE process is vital for success.
WHAT IS PHOTOCHEMICAL ETCHING
Photochemical etching employs chemical etching through a photo-resist stencil as a method of material removal over selected areas. The use of photo-resists allows for the manufacture of high-resolution parts with complex geometries or with large arrays of variable aperture profiles in thin, flat metal sheet.
Commonly misrepresented as merely a prototyping technology, photo-chemical etching is in fact a versatile and increasingly sophisticated metal machining technology, with an ability to mass manufacture complex and feature-rich metal parts and components. The process is characterised by retention of material properties, burr-free and stress-free parts with clean profiles, and no heat-affected zones.
As a machining technology, PCE has been around for over fifty 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, which due to its versatility is stimulating innovation and is allowing the manufacture of previously “impossible to make” parts.
Tooling is a key area where PCE has the edge! As a process it uses easily re-iterated and low-cost digital or glass tooling, which makes it cost-effective when compared to many traditional machining technologies such as metal stamping, pressing, CNC punching, and laser and water-jet cutting.
Traditional machining technologies often produce undesirable effects in metal at the cut line, often deforming the material being worked, and leaving burrs, heat-affected zones, 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 industry sectors (especially the medical device sector) require. There are instances — typically when an application requires multiple millions of parts and absolute precision is not a priority — when these traditional processes may be the most cost-effective. 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 processes tend to struggle when applied to the working of thin metals, stamping and punching being inappropriate in many instances, and laser and water 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 micron foil.
It is in the manufacture of intensely complex and feature-rich precision parts that PCE really finds its perfect application, as it can be applied to any shape and configuration of product, however complicated or unusual. The nature of the process means that feature complexity is not an issue, and in many instances, PCE is the only manufacturing process that can accommodate certain part geometries.
PCE & AUTOMOTIVE APPLICATIONS
Electronics & Safety Critical Applications. It is fair to say that as cars have become more and more technical, there has been an explosion in the demand from automotive OEMs for intricate electronic components. In general in the automotive sector, there is an increasing need for higher and higher levels of precision and tighter tolerances in order to improve operational efficiency, and an exponential growth in electronics in control engineering. PCE comes from the PCB industry, so it is rooted in electronics, and is frequently the “go-to” technology 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 packaging are made by placing the silicon chip on a lead frame, then 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, RFI shielding, components for engine management systems, sensors, and conductive springs are in many instances safety critical, and require absolute precision and zero failure rates, which makes the choice of an appropriate manufacturing process 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.
ABS/GDi Flat Springs. Another area where etching has been embraced by automotive manufacturers is in the manufacture of ABS/GDi flat springs. Today, most fuel injectors and braking systems feature chemically etched flat springs, and they are produced in their millions — dispelling the commonly held myth that the sweet spot for PCE is in prototyping and short runs.
In general, there is a significant upturn in demand for flat springs as a result 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 methods have their limitations. Blanking 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. Both of these manufacturing techniques generate burrs that need to be removed by tumbling, a process that can in itself compromise the material surface finish and add additional process cost.
PCE overcomes all these potential problems, producing perfectly flat springs and imposes no stress on the material. The burr-free parts have an exceptional edge finish with no lips, pits, or surface imperfections that could become initiation points for fatigue fracture.
Flat springs are expected to flex millions of times over many years and with market-led process innovations, competent PCE partners can help spring manufacturers achieve that objective.
Fuel Cells. For sure, the use of fuel cells will turn the conventional view of powering cars on its head in the relatively near future. Huge resources are focussed on this area in the automotive industry. PCE can be used to manufacture plates and meshes for fuel cells from stainless steels, aluminium, nickel, titanium, copper, and a range of exotic alloys for various industry sectors. In general, manufacturing fuel cell plates and meshes from metal increases durability, conductivity, can shorten stacks, and facilitates better cooling due to its excellent thermal conductivity.
As a manufacturing process for plates and meshes, PCE has proved to be more economical than other metal machining processes. Plates are profiled and channels generated simultaneously in a single etch process, and as discussed previously, unlike alternative manufacturing processes, PCE imparts no mechanical or thermal stresses on the metal being worked, which when looking at fuel cell plates can compromise flatness. In addition, extremely accurate channels can be produced on both sides of a plate in a single operation, and interlaced for more efficient use of space and optimum cooling performance.
High-End Automotive Interiors. In the realms of more decorative automotive applications, PCE has pretty much cornered the market where high-end automotive OEMs are looking for complex, highly decorative designs. Applied to high-end inlays, tread plates, trims, and speaker grilles, PCE allows automotive manufacturers to differentiate their vehicles with unique and attractive design touches which would be impossible or entirely uneconomic to make with standard pre-perforated meshes.
Complex designs, mesh patterns, logos, and high-definition surface engravings can all be made at the same time with micron precision and with sharp aperture edge definition.
Specifically applied to the manufacture of speaker grilles, PCE has stimulated an explosion of new designs due to its precision and versatility, replacing as it does traditional metal “hard” grilles that 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 possible to apply a wide variety of finishes to fit precise customer requirements.
QUALITY CONTROL & QUALITY MANAGEMENT
In the safety critical automotive applications detailed above, the ability to verify total accuracy and precision necessitates that your chosen PCE partner is not just expert in etching per se, but also has a forensic focus on quality control. Speedy time-to-market and absolute precision needs to be delivered with 100% verification and zero failure rates.
A partner should be selected that continually invests in a variety of measurement technologies which assist in such verification, and which ensure competitive and cost-effective part manufacture, while at the same time reducing cycle times.
In today’s world, improved productivity is every manufacturer’s goal. The use of innovative measurement technologies provides the opportunity for achievement and maintenance of unparalleled quality and productivity for automotive customers.
It is also extremely important to ensure that your chosen PCE partner has a certified quality management system in place according to IATF 16949 or equivalent. This will ensure compliance with the stringent demands of the automotive sector.
CONCLUSION
PCE is a versatile and cost-effective mass manufacturing technology that can be applied to numerous different applications in the automotive sector. Automotive manufacturers and tier 1 and tier 2 suppliers demand the highest levels of quality and also require outstanding repeatability, and PCE achieves these goals. Partnering with a competent PCE specialist allows automotive OEMs to benefit not just from process engineering expertise, but also from stringent quality systems that ensure the attainment of continually high standards.
